Interim ReportWireless Repeater, Pico-BTS, WLAN

and W-PBX

Ian F. AkyildizBroadband and Wireless Networking LaboratorySchool of Electrical and Computer Engineering

Georgia Institute of TechnologyAtlanta, GA 30332

Email: ian@ee.gatech.eduTel: (404) 894-5141; Fax: (404) 894-7883

Executive Summary

Wireless technology is the solution to fulfill people’s desire to communicate from anywhere and at anytime. Compared to wire-line schemes, they have many advantages such tether-less communication, easy deployment, and low cost. The existing schemes of wireless local area communication can provide wireless services to end users to some extent of satisfaction. However, considering the ever-increasing demands for high speed, QoS, and global mobility of multimedia services, a new approach to wireless area communication is needed.

In order to succeed in the fierce competition of the Wireless market, it is imperative for a leader like KTICOM to adapt the recent most technologies in this area. The report concerns KTICOM and its attempts to develop a new approach to the next generation wireless communication in local areas. Typical existing local area wireless communication alternatives such as repeater, pico-BTS, WLAN, and WPABX are investigated individually. Such investigation mainly consists of technology analysis, target market forecast, technology development prospect analysis, network integration, service analysis, network design plan, network deployment scenarios, and network costs analysis.

The typical alternatives of wireless local area communications are also compared from the perspectives such as services, technical characteristics, costs, market, and network deployment scenarios.

To meet the goal of high speed, QoS guarantees, and global mobility of the next generation wireless communication networks, launching a project to develop new products for wireless local area communication is highly motivated. Such a project can be accomplished with solutions that have great potentials of market penetration capability.

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CONTENTS

EXECUTIVE SUMMARY 1

INTRODUCTION 7

1. WIRELESS REPEATER 8

1.1. OVERVIEW.....................................................................................................................................81.2. TECHNOLOGY, STANDARDIZATION, PRESENT CONDITIONS OF REPEATERS................................10

1.2.1. The Repeater Technology and Standards...............................................................................101.2.2. Current Use of Repeaters and Industry Practices..................................................................131.2.3. Detailed System Analysis of the Repeater Technology...........................................................161.2.4. Interference to Repeaters.......................................................................................................171.2.5. Environmental Issues..............................................................................................................181.2.6. Major Suppliers of the Repeater Products.............................................................................19

1.3. REPEATER TYPES AND THEIR CHARACTERISTICS.......................................................................191.4. MAIN TARGET MARKET FORECAST.............................................................................................21

1.4.1. Current Market Segments and Their Penetration..................................................................221.4.2. A Forecast of the Target Markets and Estimated Market Size...............................................22

1.5. TECHNOLOGY DEVELOPMENT PROSPECT ANALYSIS...................................................................231.6. SERVICE ANALYSIS......................................................................................................................241.7. NETWORK DESIGN PLAN ANALYSIS............................................................................................241.8. IN-BUILDING NETWORK DESIGN ALTERNATIVES USING THE REPEATER TECHNOLOGY............25

1.8.1. Coverage and Capacity Analysis as Part of the Network Design Process............................271.9. NETWORK DEPLOYMENT TECHNOLOGY AND PREMISE NETWORK SECURITY PLAN..................281.10. NETWORK DEPLOYMENT SCENARIOS..........................................................................................281.11. NETWORK COST ANALYSIS..........................................................................................................291.12. CONCLUSIONS..............................................................................................................................31

2. PICO-BTS 32

2.1. OVERVIEW...................................................................................................................................322.2. TECHNOLOGY AND STANDARDIZATION OF PICO-BTS.................................................................32

2.2.1. Characteristics and Advantages.............................................................................................322.2.2. Components and functionality................................................................................................332.2.3. Current Progress of Pico-BTS................................................................................................342.2.4. Standardization.......................................................................................................................352.2.5. Frequency Allocation.............................................................................................................352.2.6. Power Management................................................................................................................362.2.7. Interference.............................................................................................................................362.2.8. Environmental Conditions......................................................................................................382.2.9. Major Suppliers and Products................................................................................................38

2.3. TYPES OF PICO-BTS....................................................................................................................392.4. MAIN TARGET MARKET FORECAST.............................................................................................39

2.4.1. Discussion of the Current Market Segments..........................................................................402.4.2. A Forecast of the Target Markets and Estimated Market Size...............................................40

2.5. HEALTH AND SAFETY..................................................................................................................402.6. TECHNOLOGY DEVELOPMENT PROSPECT ANALYSIS...................................................................412.7. SERVICE ANALYSIS......................................................................................................................43

2.7.1. Current Services (2.5G/3G)....................................................................................................442.7.2. Future Services.......................................................................................................................44

2.8. NETWORK DESIGN PLAN ANALYSIS............................................................................................452.8.1. Distributed Antenna Approach...............................................................................................452.8.2. Distributed BTS Approach.....................................................................................................47

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2.9. NETWORK SECURITY PLAN.........................................................................................................482.10. NETWORK DEPLOYMENT SCENARIOS AND ANALYSIS................................................................482.11. NETWORK COST ANALYSIS.........................................................................................................492.12. CONCLUSIONS..............................................................................................................................50

3. WIRELESS LAN51

3.1. OVERVIEW...................................................................................................................................513.2. TECHNOLOGY, STANDARDIZATION, PRESENT CONDITIONS OF WLAN......................................52

3.2.1. The WLAN Technology and Standards...................................................................................523.2.2. Current Use of WLAN and Industry Practices.......................................................................623.2.3. Working Frequency, Typical Bandwidth, and Propagation Footprints of WLAN.................633.2.4. Interference to WLANs...........................................................................................................643.2.5. Environmental Issues..............................................................................................................663.2.6. Major Suppliers of the WLAN Products.................................................................................67

3.3. WLAN TYPES AND THEIR CHARACTERISTICS............................................................................693.4. MAIN TARGET MARKET FORECAST.............................................................................................72

3.4.1. Current Market Segments and Their Market Penetration......................................................723.4.2. A Forecast of the Target Markets and Estimated Market Size...............................................74

3.5. TECHNOLOGY DEVELOPMENT PROSPECT ANALYSIS...................................................................743.6. INTERWORKING/INTEGRATION WITH IMT-2000..........................................................................753.7. SERVICE ANALYSIS......................................................................................................................773.8. NETWORK DESIGN PLAN ANALYSIS............................................................................................77

3.8.1. Description of Possible In-Building Network Design Alternatives using the WLAN Technology and possible external interference/interoperability..........................................................813.8.2. Coverage and Capacity Analysis as a part of Network Design Process................................81

3.9. NETWORK DEPLOYMENT TECHNOLOGY AND PREMISE NETWORK SECURITY PLAN..................813.10. NETWORK DEPLOYMENT SCENARIOS..........................................................................................833.11. NETWORK COST ANALYSIS.........................................................................................................84

3.11.1. Identification of the cost of various components involved in Wireless LAN setup............843.11.2. Analysis of the total Economics Involved in Deploying and Running such WLANs.........85

3.12. CONCLUSIONS..............................................................................................................................85

4. WIRELESS PBX86

4.1. OVERVIEW...................................................................................................................................864.2. TECHNOLOGY ANALYSIS.............................................................................................................86

4.2.1. Current Technology of WPBX................................................................................................864.2.2. The Frequency Bands.............................................................................................................884.2.3. Products by Leading Vendors................................................................................................88

4.3. CHARACTERISTIC ANALYSIS........................................................................................................894.4. MAIN TARGET MARKET DEDUCTION..........................................................................................90

4.4.1. Current Wireless PBX Market Segments................................................................................904.4.2. Market Forecast.....................................................................................................................90

4.5. TECHNOLOGY DEVELOPMENT PROSPECT ANALYSIS...................................................................914.6. INTERWORKING / INTEGRATION TECHNOLOGY ANALYSIS WITH IMT-2000...............................924.7. SERVICE ANALYSIS......................................................................................................................934.8. NETWORK DESIGN PLAN ANALYSIS............................................................................................94

4.8.1. Wireless Telephone Solution for Mobile Communication in the Workplace.........................954.8.2. Wireless Voice and Data Solutions Over Local Area Networks............................................97

4.9. SECURITY.....................................................................................................................................994.10. NETWORK DEPLOYMENT SCENARIOS..........................................................................................994.11. NETWORK COST ANALYSIS.......................................................................................................100

5. COMPARISON OF WIRELESS REPEATER AND PICO-BTS 102

5.1. COMPARATIVE SERVICE ANALYSIS...........................................................................................1025.2. TECHNICAL CHARACTERISTIC COMPARISON AND ANALYSIS....................................................103

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5.2.1. Cost Comparison and Analysis............................................................................................1045.2.2. Comparison and Analysis of Main Markets and Network Deployment...............................105

6. COMPARISON OF WLAN AND WPBX 107

6.1. COMPARATIVE SERVICE ANALYSIS............................................................................................1076.2. TECHNICAL CHARACTERISTIC (CAPACITY AND COVERAGE) COMPARISON AND ANALYSIS.......1086.3. COST COMPARISON....................................................................................................................1096.4. MARKETS AND NETWORK DEPLOYMENT COMPARISON............................................................109

7. COMPARISON OF PICO-BTS AND WLAN/WPBX 111

7.1. COMPARATIVE SERVICE ANALYSIS...........................................................................................1117.2. TECHNICAL CHARACTERISTICS COMPARISON AND ANALYSIS..................................................1137.3. COST COMPARISON AND ANALYSIS..........................................................................................1147.4. COMPARISONS AND ANALYSIS OF MAIN TARGET MARKETS AND NETWORK DEPLOYMENTS. 115

8. IN-BUILDING DEPLOYMENT 118

8.1. TAKING ADVANTAGE OF TECHNOLOGICAL EVOLUTION AND MEETING CUSTOMER DEMANDS. .1188.2. NETWORK DEPLOYMENT SCENARIO (TECHNOLOGY, MARKET, ARCHITECTURE, IMPLEMENTATION PHASES, SCHEDULE, RESOURCE ESTIMATES).............................................................120

8.2.1. Wireless PBX System deployment for corporate..................................................................1208.2.2. WLAN internetworking with Wired Network........................................................................1218.2.3. Unified 3G Wireless Network...............................................................................................1228.2.4. Complementary Technologies of cdma2000 and 802.11.....................................................1238.2.5. VPN security for Wireless Communication..........................................................................1248.2.6. HiperLAN/2 deployment for Corporate LAN.......................................................................125

9. CONCLUSION 127

10. REFERENCES 128

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LIST OF FIGURES

FIGURE 1. WIRELESS REPEATER.....................................................................................................................11

FIGURE 2. MULTIPLE TRANSMITTER NETWORKS............................................................................................12FIGURE 3. MULTIPLE REPEATER NETWORKS...................................................................................................12FIGURE 4. WIRELESS NETWORK WITHIN A SINGLE CELL................................................................................26FIGURE 5. WIRELESS NETWORK USING REPEATERS.......................................................................................26FIGURE 6. WIRELESS REPEATER......................................................................................................................30FIGURE 7. MAJOR COMPONENTS OF A PICO-BTS...........................................................................................33FIGURE 8. IP RADIO ACCESS WIRELESS NETWORK..........................................................................................43FIGURE 9. IN-BUILDING NETWORK..................................................................................................................45FIGURE 10. DISTRIBUTED ANTENNA...............................................................................................................46FIGURE 11. DISTRIBUTED BTS.......................................................................................................................47FIGURE 12. ALTERNATIVE DEPLOYMENT WITH PICO-BTSS............................................................................49FIGURE 13. PROTOCOL ARCHITECTURE OF IEEE 802.11................................................................................53FIGURE 14. MAIN OPERATION PROCEDURES OF THE IEEE 802.11 MAC PROTOCOL.....................................53FIGURE 15. SCATTER AD-HOC NETWORK OF BLUETOOTH..............................................................................55FIGURE 16. HOME NETWORKING BASED ON HOMERF...................................................................................56FIGURE 17. THE FRAME STRUCTURE OF SWAP..............................................................................................57FIGURE 18. THE FRAME STRUCTURE OF HIPERLAN/2...................................................................................59FIGURE 19. WLAN MARKET SHARE OF DIFFERENT SEGMENTS......................................................................73FIGURE 20. INTEROPERATION BETWEEN WLAN AND 3G..............................................................................76FIGURE 21. INTER-SYSTEM MOVEMENT BETWEEN WLAN AND 3G...............................................................76FIGURE 22. AD-HOC WLAN...........................................................................................................................78FIGURE 23. CLIENT-SERVER BASED WLAN...................................................................................................79FIGURE 24. WPBX INTER-OPERATION WITH 3G SYSTEMS.............................................................................93FIGURE 25. LINK WIRELESS TELEPHONE SYSTEM ARCHITECTURE..................................................................96FIGURE 26. NETLINK WIRELESS TELEPHONE SYSTEM ARCHITECTURE...........................................................98FIGURE 27. A WIRELESS PBX SYSTEM FOR SMALL SIZE CORPORATE..........................................................121FIGURE 28. WLAN 11MBPS SYSTEM ARCHITECTURE..................................................................................122FIGURE 29. UNIFIED 3G WIRELESS NETWORK..............................................................................................123FIGURE 30. VPN (IPSEC) PROVIDES WIRELESS NETWORK SECURITY...........................................................125Figure 31. HiperLAN/2 used in a corporate network...................................................................................126

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LIST OF TABLES

TABLE I. BANDWIDTH AND RANGE OF REPEATER FROM DIFFERENT SUPPLIERS.............................................17

TABLE II. COMPARISON OF PRODUCTS OF MAJOR SUPPLIERS.........................................................................19TABLE III. CAPITAL COST OF ITEMS IN BASE STATIONS AND REPEATERS......................................................31TABLE IV. COMPARISON OF CDMA PICO-BTS PRODUCTS............................................................................34TABLE V. FREQUENCY BANDS FOR GSM BASE STATION SYSTEMS................................................................35TABLE VI. PICO-BTS POWER CLASSES...........................................................................................................36TABLE VII. COMPARISON BETWEEN 802.11 AND HIPERLAN/2.....................................................................60TABLE VIII. DIFFERENT PHYSICAL LAYERS SPECIFIED BY IEEE 802.11.......................................................63TABLE IX. COMPARISON OF ACCESS POINT PRODUCTS OF MAJOR SUPPLIERS................................................68TABLE X. COMPARISON OF LAN ADAPTER PRODUCTS OF MAJOR SUPPLIERS................................................68TABLE XI. COMPARISON OF LAN BRIDGE PRODUCTS OF MAJOR SUPPLIERS.................................................69TABLE XII. SYSTEM PARAMETERS..................................................................................................................70TABLE XIII. RANGES POSSIBLE FOR DIFFERENT DATA RATES........................................................................78TABLE XIV. PRICE COMPARISON OF DIFFERENT COMPONENTS OF WLAN PROVIDED BY MAJOR SUPPLIERS85TABLE XV. SYSTEM CAPACITY AND AREA COVERAGE..................................................................................96TABLE XVI. COST COMPARISON OF WLAN AND WPBX (UNIT: $)............................................................109TABLE XVII. COMPARISON OF THE FEATURES AND SERVICES OF PICO-BTS AND WLAN..........................112TABLE XVIII. COMPARISON OF THE COSTS OF PICO-BTS, WLAN, AND WPBX........................................115Table XIX. Comparison of the markets of pico-BTS, WLAN, and WPBX................................................116

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Introduction

Wireless technology is the solution to fulfill people’s desire to communicate from anywhere and at anytime. In order to succeed in the fierce competition of the wireless market, it is imperative for a company like KTICOM to adapt the recent most technologies in this area.

In this report, we have given detailed description about various alternative wireless technologies for KTICOM to keep its leading position in the future competitive wireless market. We introduce, analyze and compare each technology with respect to its technical advantages, forecasted markets, costs, and service capabilities.

In Chapter 1, we talk about Wireless Repeaters. Repeater is a bi-directional RF amplifier used to extend the reach of a base station. The standards and present use of Wireless Repeater are discussed in first section. Then, different types of wireless repeaters, market forecast, service analysis, network design, deployment scenarios, and network cost analysis are given detailed discussion in later sections.

Pico-BTS technology is investigated in Chapter 2. Pico-cellular solutions can offer higher capacity and better service quality inside buildings. Pico-cell base station systems are also suitable for shadowed areas and over-populated subscriber regions.

Section 1 and 2 discuss about technology and standards of Pico-BTS, followed by characteristics, advantages of different types of Pico-BTS. The subsequent sections present a detailed analysis of environmental effect, safety, expected market, network design and deployment of this technology.

Great details about Wireless LAN technologies are provided in Chapter 3. We start with an overview of various standards and types of Wireless LAN. Products from major suppliers are compared from different prospective. The issue of internetworking/integration of WLAN with IMT-2000 is presented too. The last few sections focus on various network deployments scenarios, network security plans and network cost analysis.

Chapter 4 is about Wireless PBX technology. A Private Automatic Branch eXchange (PABX or PBX) is a private telephone system within an enterprise that switches calls between the enterprise users on local lines automatically. Technology analysis, products from different vendors, main target market deduction, technology development prospect, internetworking with IMT-2000 and network design issues are all presented here.

Chapter 5 gives a detailed comparison of Wireless Repeater and Pico-BTS. WLAN and WPBX are compared in Chapter 6. Then, Chapter 7 compares Pico-BTS and WLAN/WPBX.

Chapter 9 presents different alternatives using the technologies mentioned above for in-building network design and deployment, followed by the final Conclusion.

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1. Wireless Repeater

1.1. Overview

In a wireless communication system, a repeater consists of a radio receiver, an amplifier, a transmitter, an isolator, and two antennas [1]. The transmitter produces a signal on a frequency that differs from the received signal. This so-called frequency offset is necessary to prevent the strong transmitted signal from disabling the receiver. The isolator provides additional protection in this respect. A repeater, when strategically located on top of a high building or a mountain, can greatly enhance the performance of a wireless network by allowing communications over distances much greater than would be possible without it.

Traditionally, repeaters have simply been bi-directional RF amplifiers used to extend the reach of rural base stations, or to allow in-town base stations to cover areas shadowed by hills, valleys or buildings. Currently, a repeater is no longer just antennas, amplifiers and connecting cables [2]. The technology between the base station communication end of the system and the remote transmitters/receivers has evolved to a new, more capable level. For example, fiber optic inter-connection and adaptive interference cancellation (AIC) could be two additional features of wireless repeaters [2], [3], [4], [5]. The low loss characteristics of fiber allow a carrier to centralize base station radios and distribute radio signals to desired coverage areas where the size or cost of deploying additional base stations is not feasible. These repeaters are designed to enhance coverage and capacity in airports, malls, offices, campuses, industrial facilities, dense metropolitan areas, tunnels and highways. With the advantages of AIC, repeaters can have higher power, because AIC achieves much greater input/output isolation by canceling out the repeaters' own transmissions. Self-interference, which formerly limited the power and range of a repeater, is reduced by 30 dB or more [2].

Various standards, e.g., [6], [7], [8], [9], have been proposed for wireless repeaters in different application environments such as GSM, 3G systems, and wireless local area networks (WLAN). The objective of these standards is to make wireless repeaters fully compatible with CDMA, TDMA/IS-136 and PCS1900/GSM, and also forward-compatible with 3G/cdmaOne and W-CDMA.

Compared to base stations, wireless repeaters have many advantages:

Extended transmission distance and increased coverage of wireless networks. This is the basic function of repeaters. By using wireless repeaters, the wireless signal can reach a longer distance. Some places such as hilly and shadowed areas, tunnel, in-building areas, and mine fields can be easily covered by repeaters.

Reduced initial cost of wireless networks. Using repeaters instead of base stations can greatly reduce the cost. In some areas such as tunnel, shadowed areas, and highways, it is not necessary to deploy base stations because the overall traffic is not very high. Using repeaters, the backhaul traffic can also be more concentrated so that less backhaul links such as T1/E1 are needed [4].

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Easy deployment. Since repeaters are much simpler than base stations, they can be deployed easily and can be mounted anywhere. Moreover, when repeaters mounted on top of a tower, which is infeasible for base stations, can greatly improve the link budget [3].

Improved capacity of existing wireless networks. Besides extending the coverage, repeaters can also improve capacity of wireless networks [2]. This feature is not obvious since no more base stations are added to the system. However, repeaters allow each base station to operate closer to its capacity by filling the "blind spots" in the coverage. By eliminating unusable capacity, more locations are served by the same number of base stations.

Some issues exist in wireless repeaters. One typical problem is the interference. For example, other radio communication devices in the same area can degrade the performance of wireless repeaters. Thus, certain rules must be used to provide reasonable protection against interference. Another typical issue is that harmful radiation of wireless repeaters must be avoided since repeaters are much closer to human beings in order to extend the coverage of base stations. Again, regulations of operating radio devices must be followed when manufacturing and using wireless repeaters. Moreover, deploying many towers and equipment of wireless repeaters around residential and in-building areas cannot always get user acceptance.

However, due to their advantages, wireless repeaters are being widely deployed. Companies such as Repeater Technologies have achieved great experience in developing and deploying wireless repeaters. Considering the quick evolution of wireless networks, new technologies still need to be developed in order to satisfy future requirements of wireless networks. First of all, the existing issues of wireless repeaters need to be resolved. Moreover, support of high speed and multimedia traffic is one of the challenging demands on future wireless repeaters. Also, a future wireless repeater must have the capability of being both backward-compatible with 2G and 3G wireless systems and forward-compatible with next generation wireless systems.

Wireless repeater is one of the key technologies for wireless communications. They will continue to be important components of wireless networks.

In this report, we give a comprehensive investigation of wireless repeater technologies. In Section 1.2, we first describe the functions, techniques, and standards of wireless repeaters. Then, current applications of repeaters, interference, and environmental issues are investigated. In the final part of this section, major suppliers of wireless repeaters are presented. In Section 1.3, repeater types are categorized. Characteristics of different types of repeaters are also addressed in this section. The target market forecast and technology development prospect are reported in Sections 1.4 and 1.5, respectively. Services provided by repeater technologies are presented in Section 1.6. Network design plan and network deployment technology based on wireless repeaters are analyzed in Sections 1.7 and 1.8, respectively. In Sections 1.9 and 1.10, the network deployment scenarios and cost analysis are presented.

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1.2. Technology, Standardization, Present Conditions of Repeaters

1.2.1. The Repeater Technology and StandardsWhen the target receiver is beyond the range of the wireless transmitter, and is therefore incapable to receive transmissions directly, we need repeater links. On the other hand, deployment of repeaters can allow bases stations to support traffic in high usage areas, thus achieving a flexible capacity.

A repeater is a network device that repeats a signal from one port onto the other ports to which it is connected. Repeaters are low-level devices that amplify or regenerate weak signals, i.e., it merely passes along bits of data, even if a data frame is corrupt. A repeater does not filter or interpret anything; instead, it merely repeats a signal, passing all network traffic in all directions.

Wireless repeater, or wireless relay station, can extend the coverage/range of a base station, without the need to install additional wired base stations. It does not need an Ethernet connection. In instead, as shown in Figure 1, wireless repeater establishes a wireless communication link to one or more access points that are connected to an Ethernet LAN, while concurrently supporting wireless communications with stations within its local coverage area.

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Figure 1. Wireless Repeater

A wireless repeater consists of a radio receiver, an amplifier, a transmitter, an isolator, and two antennas. Each repeater has a transmitting and receiving range of between 100 to 1500 feet (30 to 450 m) depending on different terrains and different manufactures. We call such range as Line of Sight.

Typically, there are three different cases to use repeater:

Single Repeater. This is the simplest way to use a single wireless repeater to extend the radio coverage.

Multiple transmitter networks. In this case, we set one repeater to listen to up to a number (example: 8) transmitters directly, and then re-transmit those signals to their respective receivers, as shown in Figure 2.

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Figure 2. Multiple transmitter networks

Multi repeater networks. In case of the distance between the transmitter and the target receiver is too large to be covered with a single repeater, we should use several auxiliary repeaters together along the communication path. Each auxiliary repeater retransmits data received from another repeater. Another condition is to improve signal reception in hilly, heavily-wooded or urban areas. In this way, we create a multiple repeaters network, as shown in Figure 2.

A Repeater Network extends range in layers and such layers may overlap. However, we cannot go beyond 4 layers of range. Another fact is that data travels along a single path to the receiving transceiver.

The network is self-configuring, i.e., it periodically discovers the devices to which they can connect. It is also self-correcting: when one path between the transceiver and a remote target is unavailable, the network will choose another path automatically.

Figure 3. Multiple repeater networks

Depending on the working area, different standards should be applied to wireless repeaters [8]. In a wireless LAN environment, IEEE 802.11 wireless LAN is a typical standard. In such a standard, an access point is specified. It can be switched into repeater state depending on the necessity. Thus, the functions and requirements of wireless LAN repeaters are implicitly specified in IEEE 802.11. In larger wireless environment such as fixed wireless communication areas, IEEE 802.16 standard draft specifies an optional

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configuration for IEEE 802.16 networks. In one of the three interface specifications of IEEE 802.16 [10], a wireless repeater is used to bypass obstacles and extend cell coverage.

For wireless cellular systems, many standards are available for repeaters. These standards can be categorized according to the evolving phase of the wireless cellular networks. For example, for GSM network Release 1999, the standard is GSM 11.26 v.8.0.2 [1]. In each release of GSM network, there is a standard for repeater. Although there are some differences between these releases, most of the contents are similar. In the 3G networks such as UMTS, repeaters are specified in standards 3GPP TR 25.106 v.4.0.0 [7] and 3GPP 25.956 v.4.0.0 [8]. Similarly, both standards have multiple releases.

1.2.2. Current Use of Repeaters and Industry PracticesRepeater technology offers operators a chance to optimize network capacity and coverage, cut operating costs, speed up network roll-out, and reduce capital expenditure. Traditionally, repeaters have been used to improve RF coverage so as to improve voice quality and reduce the dropped call rate. However, the largest benefit is the reduction in cost per coverage area. Repeaters are small and light which makes site acquisition easier and less expensive. Operators' licensed spectrum for repeaters eliminates the need for microwave links and other transmission equipment. The following are the typical areas where wireless repeaters are extensively used:

Problematic environments. In problematic environments, there is often a pressing need for reliable radio coverage. Wireless repeaters can be used to solve the problem in these environments without increasing too much cost.

Highways and small villages. The coverage of highways and small villages along the road is an important task but often associated with very high initial costs. Wireless repeaters present a cost-effective solution to this problem. For example, when using frequency-shifting repeaters in combination with base stations to cover highways, roll-out cost savings can be up to 40% [11].

Coverage gaps. It is annoying that customers' calls are dropped because of coverage holes in the mobile network. Coverage has become an important competitive issue for the operators. However, covering a limited area with a complete new base station is often unnecessarily expensive. In such situations, a repeater is a cost effective alternative.

In-building areas. For in-building coverage, using repeater is essential in many old buildings. Installation costs, generally the most expensive part of an in-building coverage project, can be kept to a minimum when using repeaters. Also, deploying base stations inside a building is not always practical.

Currently, many companies are manufacturing wireless repeaters. Their practices have shown the benefits of using repeaters:

Repeater Technologies. This company proposed a repeater hybrid network (RHN) for CDMA carriers [3]. To date, more than a dozen CDMA carriers have designed or turned up networks that are utilizing RHN architecture. Compared to all base station approach, an RHN can save up to 30--60% cost in low traffic areas. Several key

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technologies have driven the promising development of repeaters in this company. First, the repeaters are taken to new heights. The towers can be as high as 300 feet, and repeaters are mounted on top of towers. In such a way, 3 dB link budget can be gained, which translates into additional 30% of coverage [3]. Second, high performance donor antenna is used to pick up the base station donor signals from farther distances without isolation problems. Such a high performance donor antenna is achieved by suppressing E field, increasing antenna gain, and using narrow beam-width. There are two configurations of RHN: cascaded and parallel [5]. In cascaded configuration, the base station signal is passed down the line from repeater to repeater, up to a maximum of two repeaters in a given chain. A cascaded repeater will project 75% of its power forward down the chain and 25% of it back through a back-beam antenna that fills in the weaker, fading portion of the donor signal. Cascaded repeaters are particularly useful for covering hilly and curvy terrain where line of sight (LOS) is difficult. In parallel configuration, towers are placed further from the BTS and are equipped with two repeaters --- along with a larger, more sensitive receiving antenna to receive more distant BTS signal. One repeater transceives back toward the BTS, the other away from it --- both at 100% power. The parallel setup is ideal for straighter, flatter terrain. It also provides a greater degree of network reliability because only one segment will lose coverage in the event of an equipment failure. The repeaters from this company have been applied to different environments such as huge mall, highways, world cup skiing field, mountain areas, low population density but large coverage areas like Australia [3].

Allgon Inc. Allgon's repeater system equipment provides cost-effective solutions for creating clear and reliable signal coverage, with minimal dropped call rates, in all of the traditional problem areas of cellular mobile systems, such as tunnels, shopping centers or mountain valleys. Simply by extending the coverage of base stations, they reduce infrastructure costs as well as improving a system's overall trunking efficiency by reducing the number of base stations that need to be backhauled to the switch.

Avitec Inc. Avitec designs and manufacturers repeaters for both mobile telephone and trunk radio networks. Repeaters provide new and experienced network operators with choices. Increasing the network coverage can be achieved with varying combinations of both base stations and strategically placed repeaters. The alternatives in expansion methods allow the network operator flexibility in reducing the overall cost.

DECT Repeater Manufactures. The technology of DECT repeaters is reasonably straightforward but sales volumes are small compared to the mass markets for cordless telephones. Thus, at the start of 1999, these products are primarily being supplied by small players rather than by the major players.

o Dancall. Cordless repeater equipped with a special directional aerial. The repeater relays signals between the handset and the base station and can double the range of the system.

o Kirk Telecom. Kirk Telecom is one of the few manufacturers to be actively promoting a range extender product. The repeater is generic access profile (GAP) compliant and thus can be used with any manufacturers' DECT GAP telephones. The product is specifically

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applicable to use in a business multicell environment, where it can provide improved coverage in black spots as well as flexing traffic capacity in high usage hot spots.

o RTX Telecom. Early products from this company followed the ETSI wireless relay station specification ETS 300, 700, GAP (TBR22), and CTR6, and thus, were suitable for operation with a range of manufacturers' DECT phones. The newer product features an exclusive design that fits into almost all DECT product programs, yet is small enough in size to be able to integrate discretely into any user environment. It includes a built-in directional antenna and improved range and contains clever software that allows plug-and-play installation for the end user, using a new matchless automatic registration method. With this feature, the repeater automatically assigns itself to the most powerful DECT GAP base station. For the end user this means that the repeater installation has been reduced to plug-and-play.

o Smart Telecom Solutions. Digital personal repeater (DPR) in this company is available as a module. The DPR is suitable for low data rate point-to-point connections. By implementing the GAP protocol, the DPR can operate with existing DECT installations, using the existing DECT infrastructure.

QUALCOMM and Ortel. QUALCOMM and Ortel Corporation worked together to develop and optimize the required technology for a receiver diversity option in CDMA repeaters. They successfully demonstrated measurable performance improvements through the use of diversity. On the one hand, repeaters are a proven, cost-effective technology for enhancing coverage and expanding cell site footprints in CDMA networks. On the other hand, the use of receive diversity in a CDMA repeater has been shown to reduce mobile transmitter power and signal to interference ratio (SIR), resulting in an increased range for the repeater and cell site, improved battery life for the mobile, and improved capacity for the cell site associated with the repeater. CDMA operators have experienced the benefits of using repeaters as strategic network elements to serve cover difficult coverage areas and expand roll-out. Ortel's wireless repeater product has been proven to provide both indoor and outdoor coverage in commercial CDMA networks, reduce infrastructure cost, and expedites roll-out of wireless networks.

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Manufactures Repeater Technologies[20]

Avitec[101 ]

Allgon[102]

Qualcomm/Ortel [103]

Network AMPS/TDMA/CDMA

GSM mobile phone and trunk radio networks

GSM, AMPS, TDMA, WCDMA

CDMA

Featured Techniques

High tower and high performance donor antenna

Fiber optic distributed repeater

Channel/band/segment selective repeaters, 3-G repeaters, minimized dropped-call rates.

Receiver diversity

Coverage 60% additional coverage extension from a BS.

Connected to up to 2~4 carriers.

78% extension of coverage.

NA

In the future, capacity of a wireless repeater will become higher and higher in order to satisfy the multimedia and high speed applications. Due to the increased data capacity, several problems will arise and need to have solutions.

1. New digital signal processing (DSP) techniques. A certain Signal-to-interference ratio (SIR) is required for a certain data throughput in a repeater. When the throughput is higher, the SIR needs to be increased. In order to achieve a good SIR, new DSP schemes need to be proposed.

2. New antenna and diversity techniques. In order to increase SIR, antenna and diversity can also be used to achieve such an objective.

3. Optical repeaters. Optical transmission in a wireless repeater cannot only achieve high SIR, but also delivers high speed traffic rate.

4. New network design. With the same type of repeaters, different type of netwotk design could result in different network performance. The network design needs to answer the following questions:

a) what kind of architectures must be used: cascaded or parallel, or hybrid?b) How to connect repeaters to base stations?c) How to optimize the number of repeaters?

5. New management tools. In order to optimize the network configuration and performance of high speed wireless repeaters, management tools need to be developed. The tools should have easy-to-use interface to network operators.

1.2.3. Detailed System Analysis of the Repeater TechnologyThe function of a repeater is to increase the signal strength/power. Conceptually, it can be viewed as a simple amplifier which amplifies the received signal and then retransmit the

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amplified signal. The transmitted signal frequency differs from that of the received one. This frequency offset is necessary to prevent the strong transmitter signal from disabling the received signal.

To accomplish its function, a repeater consists of a radio receiver, an amplifier, a transmitter, an isolator, and two antennas (one for reception and another for transmission). The radio receiver receives the incoming signal, the amplifier amplifies the received signal and the transmitter transmits the amplified signal. The isolator isolates the low-power received signal and the high-power transmitted signal from each other, hence gives protection to the received signal from the transmitted one. The receiving and transmitting antennas are either directional or omni-directional depending on application and network configuration. When the network is such that the repeater is designed to amplify the signal coming from only one direction and then transmit that in another direction, the antennas used are directional. On the other hand, when the repeater is designed to receive and send signal in all directions the antennas are omni-directional. It can also be possible that one antenna (either receiving or the transmitting) is directional and the other one is omni-directional, depending on the application scenario.

Repeater can be AC powered, solar powered, battery powered, partly solar and partly battery powered etc. The power supply mode depends on its use to a great extent. For example, when a repeater is used in WLAN network usually it is battery powered. One used for recording weather condition is usually solar powered along with a battery which gets charged during day time to be the power source during night. When the position of a repeater is fixed (as in case of a repeater used to cover the shadowed regions of cellular network), usually it is AC powered.

Repeater Technology use lower frequency band, in most cases the ISM band (in US prospective bandwidth of 26MHz, 83.5 MHz and 125MHz around 915MHz, 2.4GHz and 5.8GHz respectively). Hence FCC license (in US prospective) is not required. Typical frequencies used by repeater from leading Wireless repeater providers are in the in the range: 300MHz- 6 GHz.

Table I gives information about the bandwidth and range of repeater from suppliers: (a detailed description of repeater products is provided in Section 1.2.6).

Table I. Bandwidth and range of repeater from different suppliers

Supplier Typical bandwidth (MHz) Range (m)The solutions Group 10 8000

Allen Telecom 5-18 54

1.2.4. Interference to RepeatersWhen a repeater is in operation, interference is an important factor that needs to be considered. For example, a 2.4 GHz repeater in can be virtually unusable because of the very high noise caused by Part 15 license-free devices [12].

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The interference to repeaters mainly comes from two sources:

Equipment working in the same frequency band. Although certain rules on interference are supposed to be followed if devices work in the same frequency band, interference still exist due to open air of wireless links.

Repeaters working in the same system. In such a scenario, multiple repeaters are in the same system. Since these repeaters work in the same frequency band, one repeater experiences interference from other repeaters.

In order to reduce interference experienced by a repeater, several ways can be used:

When a repeater works in a license-free band, it must experience interference from different devices working in the same frequency band. One way to reduce interference is to make the surrounding environments of the repeater be clear enough so that the interference level is not so high. The other way is to use DSP techniques in the repeater so that interference can be suppressed.

If a repeater works in a licensed band, its experienced interference must be low. In the case that other devices generate interference at an unacceptable level to the repeater, these devices need to be removed, changed, or modified. In such a situation, DSP techniques used in repeaters also help to reduce interference.

Since repeaters of the same system may interference with each other, the deployment of repeaters is very important in order to reduce interference. The neighboring repeaters can be cond so that they are working in a different time duration, such as the parallel configuration of repeaters in Repeaters Technologies. The repeaters also need to be deployed with enough distance in-between of them. Moreover, the transmitting power and antenna sensitivity are also parameters that can be used to reduce interference.

1.2.5. Environmental IssuesCompared to base stations, repeaters have some advantages in terms of environmental issues. For example, it is more acceptable to deploy repeaters inside a building because repeaters have simpler architecture, low cost, smaller effect to human health. However, because repeaters are more likely to be deployed to the environments that are close to human beings, its effects to human beings need to be paid attention to:

Radiation of magnetic waves. It is proved that electro-magnetic waves have harmful effects on human health. There are several national and international safety guidelines for exposure of the public to the RF radiation produced by the antennas of any device, and hence for repeaters. The most widely used standards are those developed by the ANSI/IEEE and the International Commission on Non-Ionizing Radiation Protection (ICNIRP), and the National Council on Radiation Protection and Measurements (NCRP).These standard bodies have defined their guidelines both with respect to frequency of radiation and its power level. For wireless repeaters, even though different companies have different frequency of operation which varies from around 300MHz up to around 6GHz, still this is much below the one specified by the above standard. Hence, repeater technology does not pose as a threat to the user and people

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around. Thus, all the suppliers of repeaters should strictly follow the above safety requirements with quite a reasonable margin. In such a way repeaters are safe to use.

Appearance of repeaters. When many repeaters are deployed in a building, along streets and highways, and on a scenery mountain, it is generally not acceptable that many towers are there just for deploying repeaters. Thus, some repeaters vendors manufacture some tree-like towers for repeaters along street and highways. Inside a building, the repeaters are built into a smaller size and can be attached on the ceiling or wall so that repeaters are relatively far from the crowd. Since normally a building has been wired with cables, thus wiring between repeaters and BTS are not a significant issue of user acceptance.

1.2.6. Major Suppliers of the Repeater ProductsAs the market for repeater is growing, the number of products is also increasing. Different products are suitable for different applications, hence have different range, bandwidth, power consumption. Table II gives a brief comparison of repeaters from different suppliers.

Table II. Comparison of products of major suppliers

Major Suppliers

Freq of operation

(MHz)

| Bandwidth (MHz)

LOS range (m)

Power supply

Power consumption

(W)Davis 916.5,

868.35-- 122 AC, Solar 0.5

Visonic 315, 404, 433.9

-- 300 AC, DC 0.3

Cylux Technologies

1860-1870 9.4 -- AC --

Repeater Technologies

870-880 12.5 -- AC,DC --

Allen telecom

824-849 5-18 54 AC --

The repeater of Repeater Technologies is designed for long range, and also has high output power/carrier. Hence its power consumption is much higher compared to others.

1.3. Repeater Types and Their Characteristics

There exist various ways to classify Repeater types. One such way is according to theTechnology/Frequency used. The major types of repeaters now being used for extension of cellular network coverage to blind spots, are:

Fiber-Optic Repeater: Fiber-Optic repeater receives, amplifies, and then retransmits signals over the fiber cable between the base station and remote antenna. It addresses the need to extend the mobile cellular network to locations that were previously blind

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spots. Fiber-Optics technique is selected as one of the solutions because of flexibility in cable laying design, lower cost of installation, broader service area. The fiber network is extended from the outside cellular network to the blind spots through repeaters, which takes care of signal distortion, interference , and propagation loss.

There exists various products from different vendors, some of them are ORS-800/1800 Optical Repeater System (operating frequency 800 MHz (CDMA), 1800/1900 MHZ (CDMA PCS) ), DRAN (Digital Radio Access Network) Optical Repeaters designed for W-CDMA from Airvana, Mikon’s MOR701B Power Remote which functions as band selective or channel selective optical repeater for GSM, CDMA, and TDMA.

RF Repeater: RF repeater is a band selective repeater which amplifies signals between mobile stations and a base station. It is employed to extend the cellular network coverage to blind spots. These repeaters are nowadays being widely used in all cellular systems. For example MR701B Power from Mikon. This is a band selective RF repeater for GSM, CDMA and TDMA and a channel selective repeater for CDMA and TDMA. This repeater amplifies signal in both directions, between multiple mobiles and a single base station in the PCS 1900 MHz band. MR301B from the same vendor operates at 900 MHz with similar functionalities.

Microwave Repeater: Microwave repeater first converts the base station signal to broadband M/W signal, then amplifies and transmits it to a remote point. Upon reception the signal is converted back to RF signal and then transmitted via antenna. There are products from different vendors: MMC CDMA cellular/PCS microwave repeater from C&S Microwave, MRS-800/1800 CDMA Cellular/PCS frequency band repeater (operating frequency of 800 MHz (CDMA), 1800/1900 MHz ( CDMA PCS), with microwave module operating at 18GHz).

Frequency Shift Repeater: Frequency shift repeater consists of a donor unit located near BTS and a remote unit located in shadow area. These two units are linked by converted frequency, which is operators non-used band. They are used for extension of network to outdoors shadow area such as highways, resorts, valleys, road-cuts etc. Examples of few products: FRS-B (CDMA frequency shift repeater), MGFS-900 of Mobilink.

There are two main types of repeater systems in use according to public/private operations:

UHF CB or public frequency repeaters. UFH (ultra high frequency) is the region of the radio spectrum between 300 and 1000 MHz.

Private Repeaters for commercial operations.

According to repeater's functionalities, there are following types of repeaters:

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Over-the-air repeater (off-air repeater). It is the most common type of repeater. Over-the-air repeaters use a frequency translation scheme. It operates entirely on one pair of frequencies which are used by the donor BTS. While working similar to a mobile terminal and repeating the signal at the same frequency into the desired coverage, Over-the-Air Network Repeaters offer the lowest cost alternative. Many manufacturers provide over-the-air repeaters for AMPS, TDMA and CDMA networks.

RepeaterHybrid network repeater (RHN). RHNs were first introduced by Repeater Technologies in 1997 for CDMA networks. They can be implemented in non-contiguous suburban, rural and rural highways where RF coverage is the primary consideration other than capacity. If base stations and repeaters are combined to use, the base station count can be dropped greatly compared to traditional all base station deployment.

Hole fill-in repeater. Tunnels, large buildings and hilly terrain often result in wireless coverage gaps. In this case, the system has already had the required capacity installed. Then repeaters can be used to fill-in the gaps and thus will save a lot compared to use base station.

In-building repeater. In some situations, it will be very expensive to install a dedicated radio base station when for in-building service such as sports arenas, convention centers, transportation terminals and office buildings. So we use In-building repeater to achieve the same purpose with a minimal cost while having a high reliability is high.

Linked repeater. Sometimes, we can not use the Over-the-Air Network Repeaters because of interference limitations. Linked repeaters can provide us an alternative to bypass such limitations. Since linked repeaters are linked to the donor base station via a fiber optic cable, they can be utilized in virtually any environment and extend the same benefits as Over-the-Air Network Repeaters. However, relevant products are not available for all frequency bands.

ETSI have standards for two types of DECT repeater:

The REP - Repeater Part. It requires a change in the frame structure in the base station. It results in minimum audio delay but degrades overall system capacity.

The CRFP - Cordless Radio Fixed Part. With this implementation the frame structure in the handset and base station remain unchanged. It results in additional audio delay and requires special handling of encryption, but has good system traffic capacity.

1.4. Main Target Market Forecast

The future of the wireless repeater market is forecast to be huge and its utility is going to be widespread starting from small and individual domain to large and public domain.

1.4.1. Current Market Segments and Their PenetrationAt present the repeater market consists of segments some of which are the existing since long time for example:

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Ham-radio network

Cable-TV network

Fiber optics network

Telephone network (PSTN)

Apart from the above listed traditional uses, repeater technology has captured several new market segments in last few years, these segments are (to name a few):

Improvement of signal power inside a car in a cellular environment

Coverage of shadowed regions in cellular environment. There are often gaps in wireless coverage due to shadowed areas from the base station caused by hilly terrain, large buildings and tunnels. Since the required capacity is already installed, repeaters become the ideal solution to fill-in the gap because a repeater will cost 75network setup in mines.

Transfer of weather information from the location under study to the weather Laboratory

1.4.2. A Forecast of the Target Markets and Estimated Market SizeEven though the present use of repeaters is not wide spread, this technology is foreseen to be widely used. Considering its advantages market experts have envisioned a big success for this technology in the near future. Repeater technology is targeting the following market segments in the near future:

Setting up Wireless home

Setting up WLAN for offices, shopping malls, educational institutes, factories, mines

Quick network deployment in a area affected by natural calamities like earthquake, flood, cyclone etc

Out of all the different types of uses give listed above, the second one seems to be the most promising (considering revenue and wide use). This is expected to have wide acceptance because of following advantages:

Quick network setup. As infrastructure requirement is much less in case of WLAN using repeaters, the network setup time of this type of network is much less compared to the one using base-stations, where the infrastructure requirement is much more.

Low cost. WLAN using repeaters network involve low cost compared to base station based WLAN environment.

Convenience in network setup. It is very convenient to set up a WLAN using repeaters compared to the one using only base stations (it is not easy or convenient to put base stations inside building or factory).

Ease of relocation. Relocation of a repeater network is easy compared to other types of networks.

It has been envisioned that, the existing niche market for second generation mobile telecommunication repeaters will continue to exist, as existing second generation

22

mobile telecommunications will continue to spread into remote, mountainous and secluded regions. Repeater Technology is also going to get more attention and wide spread use in the upcoming third generation communication technologies. The market for Repeaters is estimated to be around 100 billion dollars by 2003 [22], [23].

1.5. Technology Development Prospect Analysis

As wireless communication networking evolves quickly, the repeater techniques also need to be updated to catch up the pace of the evolution of wireless networks. Generally, it is expected that the repeater technology will have the following advances:

Repeaters will support high speed of multimedia traffic. In the next generation networks, traffic will be in a multimedia format. Moreover, in the local area networks, the applications of end users need more and more bandwidth to transmit high speed traffic. Thus, repeaters in the future must support high speed multimedia traffic rate, which in turn requires advanced techniques in antennas, modulation schemes, and DSP algorithms.

Capacity of a repeater will be increased. As the capacity of a base station will be greatly increased in the next generation wireless networks, the capacity of a repeater also needs to be significantly increased. As an example, repeaters of IEEE 802.11 are able to support traffic rate of 11 Mbps. This number is going to be significantly increased by advanced techniques in the physical layer of repeaters. For example, wideband CDMA and OFDM techniques will enhance the capacity of repeaters as that used in 3G wireless communications systems and wireless networks.

The size, weight, and transmitting power of a repeater will be decreased. In the future, more repeaters are going to be used to extend the coverage of wireless networks. In order to guarantee user acceptance, the repeaters will have much lower size and weight. In such a way, repeaters can be easily installed in different places without much difficulty. The power consumption of a repeater also needs to be low so that the cost of repeater is low and its effect to human health is reduced. However, it is obvious that reducing transmitting power of a repeater requires advanced radio and modulation techniques.

Repeater networks should be self-configuring and self-healing to accommodate radios being moved, added or deleted from the wireless system. This feature will enhance the fault-tolerance of repeater networks. Also, the services in such networks are guaranteed to be seamlessly continuous. This feature requires that additional functions of both physical layer and higher layers need to be developed.

1.6. Service Analysis

Different service types can be provided by repeater technology. Depending on different scenarios where repeaters are used, services are also different, which is described as follows:

Traditional services such as voice and medium rate data service such as those in GPRS system. When a 2.5G cellular network uses a repeater to extend the coverage of

23

highways, mountains, tunnels, the services provided by 2.5G have to be supported by the repeater.

Multimedia services such as those in 3G wireless communication systems. In the 3G system, multimedia traffic is supported. In such a system, the repeater must be able to deliver different traffic types. Basically, the repeater does not need to differentiate the traffic types, and it just receives and retransmits signals to the destination. However, because of the more complicated resource allocation at the base station when multimedia traffic exists, the synchronization of receiving and transmitting signals between repeaters and base stations must be a very important and difficult issue. Moreover, the SINR's (???) of signal of different traffic types need to be controlled so that the BER is satisfied and power allocation is optimized.

Broadcast service. In both terrestrial and satellite networks, repeaters can be used to extend the coverage of broadcast services such as TV, radio, and other applications.

High speed data service. In wireless LAN environments, an access point can be switched into the repeater mode. Thus, in such a situation, a repeater is able to deliver high speed date traffic, which could be up to 11 Mbps as in IEEE 802.11b wireless LAN. As the traffic rate becomes higher and higher, the repeaters in a wireless LAN will also be able to deliver very high traffic rate.

QoS guarantees. Although repeaters do not have higher layer functions such as routing and MAC, QoS guarantee also needs to be considered by them. For example, if the repeater is based on CDMA technique, BER should be satisfied when signals pass through repeaters and are received by users or base stations.

1.7. Network Design Plan Analysis

There exist both wired and wireless networks using repeaters. The wired network using repeaters have existed for long time. The most common example is the use of repeaters in Cable-TV network. Similarly, Ham-Radio network is the most common and ancient use of repeaters in wireless scenario.

The following part of this section focus on design of Wireless Network in LAN or cellular environment. While designing such wireless networks using repeaters, the possible topology can be one of the following two types:

Use of one central access point and repeaters

Use of optimum combination of base stations and repeaters

Both the above options are good and are suitable to different applications. For example when the number of users in the network is less and also user mobility is confined to a small region (for example in a wireless home), the first option is good enough. Whereas, when number of users is more and/or the area of coverage is large, as in case of wireless factory/wireless office/wireless educational network, network management load is much more. And use of single base station will make it more complex and expensive. In such cases it is wise to use an optimum combination of repeaters and base stations. This type of network is also known RepeaterHybrid Networks (RHN) [20].

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The use of RHN is emerging as a promising solution because of its following advantages:

Full coverage of cellular environment. It extends the network coverage to the shadowed region of cellular environment.

Reduction in number of base-stations. The number of base stations is reduced to 50 network setup.

Minimization of network operational cost. The operational cost of the RHN network is around 50consisting of only base stations.

1.8. In-Building Network Design Alternatives Using the Repeater Technology

Repeater technology gives a practical solution to extend the cellular wireless communication technology to each and every corner of the indoor space e.g. deep corners of buildings, ramps of parking space, and corners of shopping malls, which usually fall into shadowed region of the base station antennas. Here the idea is, by using repeaters it will be possible to establish a connection between the mobile and the base station (even when the mobile is in shadowed region of the base station), and thereby maintaining the communication without call drop. Here, repeater functions as an intermediate bridge between the base station and the mobile.

An in-building network design using repeaters is quite similar to the in-building cellular network setup with certain differences. To start with the network can consist of few transceivers (as few as two) [24]. One of these will function as central transceiver (known Central Access Point, CAP), and the other one will get connected to this using a wireless link. When more subscribers need to be added to this network one of the following situation will arise,

The new subscriber is within the LOS of the CAP, or

The new subscriber is outside the LOS of the CAP

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Figure 4. Wireless network within a single cell

In the first case, (as shown in Figure 4) the new subscriber gets connected to the network through one wireless link between the new subscriber and the CAP. Here the network expansion and configuration is exactly the same as that of the cellular network. In Figure 4, '1' represents the CAP and '2' the initial subscriber. Then subscribers '3' to '8' are added afterwards. All these subscribers are with in the LOS of CAP.

Figure 5. Wireless Network using repeaters

In the second case, when the new subscriber is outside the LOS of the CAP (subscriber '9' as shown in Figure 5), a cellular network would require a new base station

26

at the center of a new cell to cover the new subscriber, and a backbone connection between the two base stations. But in case of network using repeaters, what need to be done is to find an already existing subscriber which happens to be within the LOS of the new subscriber (e.g. subscriber '2' as shown in Figure 5). Then a wireless link is set up between this subscriber and the new subscriber. This already existing subscriber works as a repeater. The new subscriber gets connected to the CAP through this repeater. A situation might arise when there is no existing subscriber which is with the LOS of the new subscriber. In such a case we can set up one or more new repeaters to add the new subscriber to the network. Here we have seen that just by using repeaters, we get rid of the new base station requirement in case of a cellular network.

As the network grows, any of the already existing subscribers (also known as network node) can be promoted to become a repeater by setting a wireless link between this and the newly added node. Hence, the only requirement for a new node to get attached is to have a wireless (in most cases RF) link to any one of the already existing network node. This type of network topology is known as "anypoint-to-multipoint", since any node already in the network can become the center of a point-to-multipoint branch. As more and more nodes are deployed, the range and coverage of the network grows. This way the locations like deep corners in a house, shop, office or ramps in parking lot, which fall into the shadowed region of cellular environment, can be covered by the network.

We can keep on increasing the range and capacity of our network in the above mentioned way so long as, the network load is within the capacity of the CAP. Once the network load becomes more than the CAP capacity, the need for an additional base station arises. And the network can be increased around the second base-station, with a backbone network between two base stations. This is how a RHN, is setup in an indoor environment.

1.8.1. Coverage and Capacity Analysis as Part of the Network Design Process

As we have seen in the above section, once the network grows beyond the LOS of the (CAP), there arise a need for a repeater. And by using this repeater the coverage of the network is increased. The coverage radius around each repeater and hence the CAP depends on the range of the antenna used by the CAP and the repeaters. In present market, repeaters are available with ranges as small as 50m to that of 8000m. Hence appropriate repeaters can be used depending upon the network coverage requirement.

Capacity of the network is going to decide how many base stations we need and this number can be dependent on the type of the base station used for the network design. If the available base station can handle large network load and has more range, the network can be designed with fewer base stations. Whereas if the load-handing capacity of the base station is low and also it's range is small, then more number of base stations are used to get the same network capacity and coverage.

From the above discussion, it is clear that depending upon network specifications like required coverage, required capacity, and also type of repeater and base station available for the network design, the optimum number of repeaters and base stations

27

required for the network design can be calculated. This is very critical to ensure the QoS for the network users.

1.9. Network Deployment Technology and Premise Network Security Plan

In order to implement the most common over-the-air repeater network, we should deploy with donor antenna technology effectively. First, we should optimize the repeaters and donor antenna design for satisfactory performance. We also need network management (operation and maintenance) software for the repeater site elements. These requirements are especially important to achieve a robust RHN (repeater hybrid networks).

Many companies use repeater technologies combined with satellite communications to build up their broadcast network. They will create up to 100 channels with digital-quality. In this way, repeaters network will augment the satellite system by re-transmitting its signals in dense urban areas where the satellites' signals may be shadowed by tall buildings and other obstructions. Technology will include the use of COFDM (Code Orthogonal Frequency Division Multiplex), which is a superior modulation technique for the delivery of high quality audio, video and data. This modulation technique allows a moving vehicle to receive quality service at highway speeds.

To protect network security and to reduce fraud, each receiver will contain a security circuit with an electronically encoded identification number. Only if the verification of receiver is correctly passed, the repeater network will transmit a digital signal to activate the receiver's capability.

1.10. Network Deployment Scenarios

In a wireless network, repeaters can be deployed in several ways:

Single repeater. In this scenario, one repeater is only used between a transmitter and one or multiple receivers.

Daisy-chain installation [13]. In this scenario, multiple repeaters are installed in a succession to extend the distances between a single transmitter and one or more receivers.

Network Installation [13]. In this scenario, multiple repeater/transmitter ID DIP switches are in a single repeater, which can be turned ON/OFF depending on necessity. This scenario can have three possible configurations:

o Single repeater and multiple transmitters and receivers.

o Multiple repeaters and one transmitter and one receiver.

o Multiple repeaters and multiple transmitters and receivers. In this case, repeaters are deployed in a succession mode. How, each repeater is able to receive signals from transmitters or transmit signals to receivers.

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Specifically, the deployment scenarios are different depending on environments. Typical ones are analyzed as follows:

A building or a cluster of buildings such as a mall. In such a case, normally one base station is installed on top of a building, repeaters are installed on different places of the building so that wireless services can be covered at all corners of the building. In such an environment, all the above-mentioned deployment alternatives can be applied.

Highways. In order to extend the coverage of wireless services on highways and reduce the cost, repeaters are deployed like a daisy-chain configurations. Along a highway, there are multiple repeaters installed in a succession and then connected to a base station.

Mountains. In a mountain area such as a snow skiing field, normally, a base station is installed at the lower part of the mountain so that higher traffic rate in this area can be satisfied. Due to lack of LOS on top of a mountain, a repeater can be used to provide the coverage of wireless services. This environment belongs to the single repeater deployment scenario.

Tunnels. In such a scenario, a single repeater can be applied on the ceiling if a tunnel is not long. When it is very long, multiple repeaters are required. Thus, the daisy-chain installation is more applicable to this scenario.

Stadium. Because of bursty traffic rate depending on the sport events, using repeaters in such an environment can greatly reduce the cost of providing good quality of wireless services. In a stadium, the most appropriate way is that multiple repeaters together with multiple base stations are deployed according to the network installation alternative. A repeater can communicate with multiple transmitters and receivers, multiple transmitters and receivers can communicate with one repeater, or multiple repeaters communicate with multiple receivers and transmitters.

1.11. Network cost analysis

Many people know the advantage of repeater cost savings, and regard it a strong economic motivation to deploy repeater other than base station and microcell. Repeater cost savings can be achieved via 2 respects: capital saving and operating saving.

If BTS or microcell is replaced with a repeater, lots of capital savings can be gained. The reduction of relevant hardware and software required by BTS or microcell will save much cost.

By using wireless repeaters, we do not need E1/T1 backhaul and their corresponding maintenance time and utility costs. Thus, we gain many operating savings. We can also save the downstream capital costs associated with BTS or microcell use, including port cards, per-BTS operating software, maintenance fee, leased fee, and per-BTS feature software.

There are many cases in which network coverage is the first consideration rather than network capacity. Users use a repeater-augmented solution to extend the coverage of each cell with over-the-air repeaters. By this means they can cut costs by up to 45%.

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For RHN applications, we combine base stations and repeaters rather than use the all-base station solution while providing the required coverage. In an RHN implementation, the base station count can be saved by 50% for suburban/rural, coverage and by 67% for rural highways compared to the traditional all-base station solution. The RHN design can extend the BTS's coverage to a greater area.

An example is explained as follows [25]. In a typical suburban area with 1.2 million POPS, the total coverage area would be about 2,600 square km. For 90% coverage quality, each CDMA PCS cell would be 30.1 square km, requiring 87 cells at $400,000 each, or $34.8 million. Assuming an aggressive 3% penetration rate and usage of 0.03 Erlangs/subscriber, this CDMA build out would leave you with 80% wasted capacity.

If you modified the cells to consist of a base station and three over-the-air repeaters, you would increase cell coverage to 52.8 square km shown in Figure 6. With this build out structure, it would only take 50 repeater-augmented cells at $490,000 each, or just $24.5 million in capital. Your savings would be 30% and your underutilized capacity would be virtually eliminated. Moreover, you would have 37 fewer cells for your switch and BSC to handle, further reducing your costs. In addition, by deploying twice as many radiating elements, you improve network coverage and minimize the number of holes.

Figure 6. Wireless repeater

By adding three Over-The-Air repeaters to the base station, the cell coverage footprint can be enlarged to 53 squire km, at an added cost of only $90,000. In capital, the savings would be 30% and the underutilized capacity would be virtually eliminated.Here are some comparisons of capital cost of items used in Base Station and Repeater [26]. The cost of items of repeater is much lower than those of base stations.

Table III. Capital Cost of items in base stations and repeaters

ITEM BASE STATION REPEATERREAL ESTATE LEASE $1,000 $500

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ELECTRICITY ($0.10/KWH)

$430 $20

HARDWARE MAINTENANCE

$150 $50

SOFTWARE MAINTENANCE

$20 $5

T1 BACKHAUL (75 MI) $2,000 $25DIVERSITY BACKHAUL $2,000 NOT REQ'D

TOTAL $5,600 $600NPV 1 YEAR $65,066 $6,971

5 YEARS (PCS CDMA ESTIMATES ONLY)

$289,663 $31,035

1.12. Conclusions

In this report, wireless repeater technologies were comprehensively investigated. The advantages and issues of wireless repeaters were also pointed out. Other issues related to the market of wireless repeaters were also analyzed. Due to their advantages, it is believed that wireless repeaters continue to be promising equipment of wireless networks.

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2. Pico-BTS

2.1. Overview

Large scale multi-sector base stations have been the main stream in the current mobile telecommunication systems. However, there is an explosive growth in demand for indoor cellular coverage with higher capacity. Traditional macro- and micro-cellular networks require real estate lease and have higher power consumption. Hence, it is not easy to satisfy the growing demands for indoor mobile applications with low cost, high bandwidth, and great flexibility through traditional cellular networks. Pico-cellular solutions can offer higher capacity and better service quality inside buildings such as corporate premises, congress centers, hotels, and lounges. This requires a base transceiver station (BTS) that is compact, and capable of providing at least the same service quality as the outdoor networks. Pico-cell base station systems are also suitable for shadowed areas and over-populated subscriber regions.

In this chapter, we analyze the technology of pico-cell BTSs, their characteristics and deployment.

2.2. Technology and Standardization of pico-BTS

2.2.1. Characteristics and AdvantagesCurrently, pico-cells are the smallest radio cells defined in mobile networks. They often extend to only a few hundred meters in diameter. Pico-BTSs are used to create pico- or in-building cells. These cells have the following characteristics:

Very low delay

Low speed mobile subscribers

Small size

Usually deployed at hot spot traffic areas like convention centers, shopping malls, and train stations to provide high capacity.

The advantages of pico-BTS can be summarized as follows:

Cost efficient manufacturing:

Pico-BTSs are of small size and modular design. They can be manufactured in high volumes. Therefore, the manufacturing cost is reduced.

Easy and flexible installation:

The antennas of macro-cell base stations are usually mounted above the rooftop level of surrounding buildings. However, pico-BTSs can flexibly be installed on the wall, utility poles, and many other places.

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Cost savings associated with network design and operation:

Compared with macro-cellular networks, the pico-cellular solutions do not require towers or shelter to protect the equipment. This feature helps to reduce the cost associated with the deployment of the infrastructure.

Reduction in site construction and field maintenance:

Since pico-cells have small sizes, and pico-BTSs are usually installed in-doors, field maintenance cost for pico-BTSs is reduced.

Time-saving implementation:

The design does not include the time-consuming procedure of applying approval from local city zoning committees for the construction of towers and outdoor shelters used to house cellular antennas. It is easier for the pico-BTS to get approval because of its small size.

2.2.2. Components and functionalityThe purpose of pico-BTS is to modulate, amplify, filter, and transmit signals. It can also relieve capacity in hot spot areas. The major components of a pico-BTS are shown in Figure 7.

Figure 7. Major components of a pico-BTS

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Controller

RFFront-end

Transceiver

.

.

.

IF/BBInterface

Modem

.

.

.

DC Power, Time-frequency

BackhaulInterface

Transceiver

Modem

BSC

The key functionality of pico-BTS includes:

RF transmission and reception,

Frequency up and down conversion,

Modulation / Demodulation,

Interface to BSC,

Call processing and management.

2.2.3. Current Progress of Pico-BTSThe latest trend in pico-BTS has the following focuses:

Compact, low cost, quick installation, and less maintenance,

Smart antenna to help to increase capacity,

Software defined radio:

o One platform for multiple protocols,

o Flexible upgrades, longer life cycle, and quick to the market with new services.

Table IV gives a summary of the latest CDMA pico-BTS products. It shows a comparison of the features for each pico-BTS, which including dimension, weight, capacity, RF output power, and antenna configuration.

Table IV. Comparison of CDMA pico-BTS products

SCTM 601

by Motorola

Pico-BTSTM

by Samsung

Flexcent

by Lucent

Qcell 500

by Qualcomm

Dimension (inch)

34x28x12 RMU 18x20x10

PRU15x12.5x6

34.6x18.25x12 26x15x8

Weight (lb) 210 RMU 80

PRU 45

110 75

Capacity (channel elements)

16 64 40 64

RF Output Power (W)

5 5/10 10 10

Configuration Omni Omni, 3 sector, 6sector

Omni Omni

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2.2.4. StandardizationThe European Telecommunications Standards Institute (ETSI) developed several standards and technical specifications on Base Station Systems (BSS) for GSM and third generation wireless systems [27], [28], [29], [30]. In [27], the requirements for the transceiver of the digital cellular telecommunications systems GSM are presented. This standard defines Radio Frequency (RF) characteristics for the Mobile Station (MS) and BSS. The BSS contains either a normal BTS or BTSs at micro-cells and pico-cells (micro-BTS, pico-BTS). In [28], the RF test methods and conformance requirements for GSM 900 and DCS 1800, PCS 1900, GSM 850, MXM 850 and MXM 1900 BSSs are specified. These specifications are derived from the core GSM specifications. This document is applicable to BSSs meeting the requirements of both GSM Phase 2 and GSM Phase 2+. In [29], the requirements for transceivers (BTS, micro-BTS, and pico-BTS) in a 136HS system are defined. In [30], the requirements for synchronization on the radio subsystem of the digital cellular telecommunications systems are presented.

The International Telecommunication Union (ITU) developed a family of standards for the 3G systems. Leading 3G standards are based on CDMA technology, though there are other standards based on FDMA/TDMA and TDMA-SC). Two main standards based on CDMA technology for 3G are Wideband CDMA (WCDMA) and CDMA2000. WCDMA standards are currently under review by 3GPP, 3GPP2 as well as Operators’ Harmonization Group. Till now no single base-station model is the standard. WCDMA base-station products started with 15-channel model designs. Recently products with 50- or 60-channel models have been produced by manufactures.

2.2.5. Frequency AllocationThe GSM standard contains several subsets:

P-GSM (Primary GSM) uses the channels 1-124

E-GSM (Extended GSM) uses the channels 975-1023 and 1-124

R-GSM (Railways GSM) uses the channels 955-1023 and 1-124

DCS 1800 (GSM 1800) uses the channels 512-885

PCS 1900 (GSM 1900) uses the channels 512-810

The frequency bands for GSM BSS defined in [27], [28], and [29] are given in Table V.

Table V. Frequency bands for GSM base station systems

TX: RX:P-GSM 900 935 MHz to 960 MHz 890 MHz to 915 MHzE-GSM 900 925 MHz to 960 MHz 880 MHz to 915 MHzR-GSM 900 921 MHz to 960 MHz 876 MHz to 915 MHzDCS 1800 1805 MHz to 1880 MH 1710 MHz to 1785 MHz

GSM 850 and MXM 850 869 MHz to 894 MHz 824 MHz to 849 MHzPCS 1900 and MXM 1900 1930 MHz to 1990 MHz 1850 MHz to 1910 MHz

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The BSS manufacturers declare the specific operating frequency range of their devices. This operating frequency range should be within the frequency bands defined in Table V. This frequency range comprises the transmit and receive operating bands. A BSS may support DCS 1800, PCS 1900, MXM 1900, GSM 850, MXM 850 and one of the GSM 900 bands, but should not be defined as supporting more than one of the GSM 900 bands [27].

The pico-BTS is an extension of the micro-BTS concept to the indoor environments. Micro-BTS and pico-BTS are different from a normal BTS in two ways. First, the range requirements are less strict, and the close proximity requirements are more stringent. Second, the micro-BTS and pico-BTS are required to be of small size and of low complexity to allow deployment in large numbers. Therefore, the micro-BTS and pico-BTS need a different set of RF parameters to be specified to guarantee their requirements [27].

Many pico-BTS products support GSM 900, DCS 1800 and PCS 1900 frequency bands, such as the BS-242 Pico by SIEMENS supports GSM 900, DCS 1800 and PCS 1900; the sub-pico CDMA IP-BTS by Halfdome Systems supports PCS 1900; and RBS 2401 Indoor Base Station by Ericsson supports GSM 900 and DCS 1800.

Different frequency bands are allocated in different parts of world for third generation mobile services. Figure 8 gives detailed information about the frequency allocation for IMT-2000. The frequency of operation of WCDMA base-stations will be as per the frequency allocated in that particular region. Base station specifications for WCDMA are yet to be finalized.

2.2.6. Power ManagementFor pico-BTS, the manufacturers declare the rated maximum power at the antenna connector. The class of a pico-BTS is defined by the highest output power capability for 8-PSK modulation, and the output power should not exceed the maximum output power of the corresponding class. The power classes of pico-BTS are in Table VI.

Table VI. Pico-BTS power classes

TRX Power Class Pico-BTS Maximum Output PowerGSM 900, GSM 850 &

MXM 850DCS 1800, PCS 1900 &

MXM 1900P1 (>13)-20dBm (>16)-23dBm

The tolerance of the actual maximum output power of the BTS can be pm 2 dB under normal conditions and pm 2.5 dB under extreme conditions. In order to be able to hop between any defined power levels on a time slot, the dynamic power control may optionally be implemented in GSM pico-BTS according to [31].

2.2.7. InterferenceThe spectrum allocation varies in different parts of the world. The availability of spectrum also varies greatly from operator to operator. Currently, no base station hardware supports all of worldwide frequency assignments [32]. Moreover, the addition

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of spectrum for 3G applications adds more complexity to the task of designing base station hardware. Figure 7 shows the worldwide spectrum allocation [33], which is a reference for BTS designers.

Figure 8. Worldwide spectrum allocation

Interference is the limiting factor for the capacity of wireless systems. There are three types of interference:

Co-channel interference: produced by users who transmit in the same frequency channel.

Adjacent channel interference: produced by users who transmit in the neighboring frequency channels.

Out-of-band interference: produced by non-linearities.

Due to the frequency reuse nature in cellular systems, there is co-channel interference. Co-channel interference arises when the same carrier frequency is used in different cells. In this case, the power density spectra of the desired and interfering signals completely overlap. So, in narrowband systems, intense frequency reuse is not possible due to co-channel interference which degrades the quality of the received signal to intolerable levels.

Frequency reuse also introduces adjacent channel interference. This type of interference arises when neighboring cells use carrier frequencies that are spectrally adjacent to each other. In this case, the power density spectrum of the desired and interfering signals partially overlap. Adjacent channel interference is usually avoided by means of selective filters. The system designer should not assign contiguous channels to the same cell. Adjacent channels are usually spaced by 6 other channels (not used in the cell).

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2.2.8. Environmental ConditionsETSI defined the following environmental conditions as the requirements for the BSS equipment [27]:

Normal environmental conditions:

Temperature Range: +15 to +35°C

Relative Humidity: 35% to 75%

Air Pressure: 86 kPa to 106 kPa

Extreme typical operating temperature ranges are:

Indoor Temperature Range: -5°cto +50°C

Outdoor Temperature Range: -40°cto +50°C

In addition, the BTS should not make ineffective use of the radio frequency spectrum and exceed the transmitted signal level as defined in [31] for extreme operation.

2.2.9. Major Suppliers and ProductsMany companies have pico-BTS products. Here we list some of the major products.

2.2.9.1. BS-242 Pico by SIEMENS

BS-242 Pico-BTS is a new base station solution for indoor applications. It allows easy and flexible deployment in any indoor segment. It provides flexible coverage areas and capacity allocation, easy modification and extension of existing deployments, and fast installation. The decentralized architecture comprises of one server (core part) and up to 24 agents (remote TRX). Multi-carrier cells may be built simply by configuration. The main features of BS-242 Pico-BTS are:

E-GSM 900/1800/1900

Dual band support by the same server

Internal and external antenna

RF frequency hopping

Output power up to 200 mW at antenna connector

2.2.9.2. RBS 2401 Indoor Base Station by ERICSSON

Ericsson's RBS 2401 Indoor Base Station is a self-contained design. It can reduce the cost of providing high-quality coverage for wireless office services in public buildings. It is small, consumes 65 Watts, and has enough capacity to serve around 100 typical office users. It is compatible with advanced GSM services. It supports GSM 900 and 1800 MHz frequencies, and fits into Hierarchical Cell Structure schemes. It may also be deployed as part of Ericsson's integrated GSM-over-IP business communications solution.

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2.2.9.3. Sub-Pico CDMA IP-BTS by Halfdome Systems, Inc.

This BTS enables service providers to extend the IP network to the RF unit. Service providers are able to offer high bandwidth IP services, including Internet access, to its mobile customers. This BTS supports better quality soft handoff procedures and voice/data services in an in-building environment. The sub-pico CDMA IP-BTS supports PCS 1900 and has an output power of 25 mW at antenna connector.

2.2.9.4. PicoBTS (TM) by Samsung

Samsung received the "Infrastructure Product Innovation Award" from the CDMA Development Group by its PicoBTS product in 1998. The PicoBTS is designed for the CDMA radio platforms. It provides open architecture to make CDMA an affordable option for smaller carriers. It allows the operators to fit their design needs while reducing initial network deployment costs. The PicoBTS provides the operators with a small, yet high capacity platform allowing for maximum deployment flexibility. It is designed for both indoor and outdoor applications, and is available for omni and sector deployments. It is the first CDMA product of its size to incorporate dynamic channel allocation and feature up to 64 channel elements that may be appropriate for any sector and/or frequency in a multi-carrier configuration.

The main features of the PicoBTS are:

Air-interface: IS-95 A/B

Operating frequencies: PCS and cellular frequencies

Configurations: omni multi-carrier, 2-sector multi-carrier, 3-sector single carrier, indoor or outdoor

Capacity: 64 channel elements

2.3. Types of Pico-BTS

According to the installation location, pico-BTSs can be categorized as indoor pico-BTS and outdoor pico-BTS. There are three types of pico-BTSs according to the underlying air interface:

pico-BTS supporting GSM (900/1800/1900)

pico-BTS supporting TDMA (IS-136)

pico-BTS supporting CDMA (IS-95)

2.4. Main Target Market Forecast

The pico-BTS technology is currently in use, and its future is even more promising. The growth of the wireless population along with the increasing demand for higher bandwidth due to new wireless applications pushes the network operators to have smaller cells. Smaller cells increase system capacity, and provide higher bandwidth to the subscribers. On the other hand, smaller cell sizes imply more frequent handoffs. In order to avoid the

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adverse effect of frequent handoffs, the pico-cells must be located at hot spots like downtown areas where the subscriber density is high and mobility is low.

2.4.1. Discussion of the Current Market SegmentsThe pico-BTS technology is being currently used for 2G systems at hot spots. It is also being considered for the 3G cellular systems. The major application of the pico-BTS technology is Samsung's award-winning product. Samsung Telecommunications America and Tecore, Inc. have merged their efforts to offer a modular solution to small second-tier PCS operators in North America. They have integrated Samsung's PicoBTS with Tecore's AirCore Platform MSC and transmission system. The decreased cost of the pico-BTSs, due to economies of scale, has enabled cdmaOne to compete with TDMA and GSM networks. Thus, it has become economically reasonable for the rural operators to invest in CDMA systems. Tecore's switching center is scalable from 500 to 100,000 subscribers. The PicoBTS, coupled with Tecore's switching center, allows small operators to affiliate with brand-name carriers while operating their own networks.

The Samsung-Tecore solution was initially developed for the US market where cdmaOne and PCS networks are expected to reach 28.2 million subscribers by 2002 [36]. However, the fact that Samsung is taking this product to South Korea, and Telstra is replacing its AMPS network with cdmaOne shows that the international market for pico-BTS is expanding. Samsung has also made a contract with AirTouch Communications (now Vodafone AirTouch Plc which operates in 28 other countries) in May 1999 for five years to deploy CDMA PicoBTS and BSC in the US.

2.4.2. A Forecast of the Target Markets and Estimated Market SizeOne of the major problems cellular operators encounter is getting approval from the local city committees for the construction of towers and outdoor shelters for the base stations. Pico-cell solution is different from the traditional micro- and macro-cell solutions in terms of deployment since pico-BTSs can be installed inside privately-owned buildings. The deployment characteristics reduce the problems encountered with the local regulatory agencies. They also decrease field maintenance costs by satisfying A/C and power requirements, and avoiding tower and shelter rents.

Samsung has invested over $200 million in the US market as a proof of its belief in the potential of pico-BTS technology. Pico-BTSs will be integrated with other networks in the future to bridge the gap between 802.11b WLANs and 3G cellular networks. Enterprises can install pico-cells in their premises and integrate it with their local PBX switchboards. This model will improve the in-building signal reception. The enterprises can utilize this model to switch the calls made in the office as local calls through their local PBXs. There will be a seamless handoff to the cellular network when the employee leaves the premise.

2.5. Health and Safety

People who live or work close to BTSs are concerned about health and safety issues. The government of United Kingdom investigated possible health effects posed by mobile

40

phones and base stations, and published the results as a report [34]. The conclusion in the report is: "The balance of evidence indicates that there is no general risk to the health of people living near base stations, on the basis that exposures are expected to be small fractions of guidelines."

Although none of the recent research activities have concluded that exposure to the RF fields from mobile phones or base stations causes any adverse health consequence, radio waves above a certain signal level can cause heating effects to the body. International guidelines have been set to keep exposure to radio waves below that signal level. Network operators should comply with these international guidelines. In addition, the base station antennas emit RF beams that are typically narrow in the vertical direction but broad in the horizontal direction. The network designer should mount the antennas at a certain height to ensure the RF field intensity at the ground directly below the antenna is low. The RF field intensity decreases as one moves away from the base station. Since the size of macro- and micro-cells is larger than the size of pico-cell, the base stations for the larger cells transmit at higher signal levels. Therefore, the individuals located close to such base stations will be subject to higher signal levels.

According to David Allen, Director of Wireless Systems for Samsung Telecommunications America, Inc, "environmental concerns are ever-present when attempting to gain construction approval from various government agencies," in addition to the health and safety concerns. He has also mentioned that the pico-BTS is "aesthetically pleasing to the eye and extremely unobtrusive in city or rural landscapes," because of its small size [37].

Overall, the network operator should take electromagnetic energy, safety level, and safety distances into consideration and follow the health and safety-based guidelines.

2.6. Technology Development Prospect Analysis

As the wireless multimedia communication becomes more popular, there is a trend in developing 3G base stations that enable users with various services. Making voice calls, surfing the web, checking e-mails, participating in video-conferences, and accessing a wide range of new services from their wireless devices are examples of such services. It is expected that the pico-BTS technology will follow the development of 3G wireless systems and improve in the following aspects:

3G CDMA pico-BTS

The underlying 3G innovation is Wideband Code Division Multiple Access (WCDMA) technology. To deliver the promise of WCDMA, 3G pico-BTS must be able to handle greater capacity, support higher data rates and multimedia standards, while reducing the cost and the power consumption. The difference in the bandwidth requirements of different services like voice, data, and video must also be considered in the design.

For 3G pico-BTSs, high channel density must be accompanied by low power consumption. Components of pico-BTSs should consume less power, dissipate less heat, and be packed more densely. In addition, pico-BTSs should be reliable to keep maintenance costs down. All of these requirements place great demands on the

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performance, scalability, programmability, and power efficiency of 3G pico-BTS. Overall, the 3G pico-BTS infrastructure requires high performance and better cost, space, and power consumption efficiency.

Several companies are working on 3G CDMA pico-BTSs, such as Samsung, Hyundai Electronics, and Texas Instruments.

ETSI selected W-CDMA and TD-CDMA as the radio interfaces for the outdoor and indoor environments, respectively. In [106], a link level simulation is provided to compare W-CDMA and TD-CDMA systems. Two vehicular and two indoor to outdoor scenarios with different channel responses are considered in the simulations. Voice and data (circuit-switched and packet-oriented) services are considered for both air interfaces. The simulation results are summarized in Figure 9.

Figure 9. Link-level simulation results [106]

The round trip delay of the power control algorithm in the TD-CDMA mode is higher than the delay in W-CDMA mode. Therefore, the link performance in the TD-CDMA mode is more influenced by the mobile speed than the W-CDMA mode. Furthermore, the absence of the antenna diversity in the downlink causes the link performance to be downgraded with respect to the uplink. This is especially true for circuit-switched data service.

Wireless Access to IP Network

The growth of the Internet and the success of mobile wireless networks lead to increasing demand for mobile wireless access to Internet applications. The IP-based pico-BTS enabling broadband multimedia mobile communications is a great solution for this demand. As we introduced previously, the product Sub-Pico CDMA IP-BTS from Halfdome Systems, Inc. [35] is an IP-based CDMA pico-BTS. The system architecture is shown in Figure 10.

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Figure 10. IP radio access wireless network

As shown in this figure, the pico-BTS is an element in the overall IP-based radio access network. The wireless access gateway connects the wireless network and the IP network to enable high bandwidth IP services to mobile users. With Internet access, high quality voice and data services are supported in an in-building environment.

Wireless IP communication is a promising field for future technology improvements. IP-based pico-BTSs have great potential in the future market. The need for pico-BTS will increase with the emerge of the next generation wireless networks. The cell size in the next generation wireless networks will decrease due to the many reasons. The increase in the number of subscribers will pose the need for more capacity. The system capacity can be increased by smaller cells, and frequency reuse. Furthermore, the increase in the bandwidth requirements per user can be satisfied in smaller cells and shorter distances.

Pico-BTSs will employ new technologies like the OFDM-CDMA technology in the air interface to provide high bandwidth. QoS provision will also be provided in the air link of the next generation networks.

2.7. Service Analysis

Providing in-building communications services using wireless technology and pico-cell base stations is a feasible alternative to wireline networks. It offers many advantages, including cheaper and easier installation since it does not require the laying of cables, etc. It can also provide as much bandwidth as a wireline network. The deployment of wireless networks will be much faster than that of wireline networks. Thus, wireless networks are more suitable for temporary events like exhibitions. Furthermore, it is the only solution for places such as historic buildings where laying cables or drilling holes is not allowed.

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Moreover, wireless network infrastructures such as 2.5G and 3G can be constructed using pico-cell base stations in buildings. In the near future, broadband multimedia services will be available over Internet as the IP convergence solution is getting more interest and the IP technology is moving toward the edge in the radio access network (RAN) [42].

2.7.1. Current Services (2.5G/3G)The deployment of pico-cell base stations enables cellular/PCS operators to offer enhanced system capacity, coverage. Pico-BTSs also enable high quality voice and high speed data services as in GPRS, cdmaOne and cdma2000 [39]. The users inside the buildings can use their mobile phones to benefit from high quality voice and additional services as well as data transmission capabilities.

2.7.2. Future ServicesPico-cell base stations will also enable multimedia services, voice and video mail, wireless virtual private network (VPN), and other competitive features with QoS guarantee. Additionally, it is possible that location-aware services will be provided considering the small cell size of pico-cellular networks which means better knowledge of the user's location. A pico BTS can provide the location information of enough precision for location-aware services without additional cost. In the future, Internet technology will also be immediately available for cellular transmission [42]. Thus, the mobile users in the buildings will have complete access to the Internet using their mobile devices, and various types of multimedia services will be provided through Internet and corporate LANs.

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2.8. Network Design Plan Analysis

Figure 11. In-building network

Given the expense and limitations of physical cabling, the idea of using wireless technology and pico-cell base station to construct an in-building network becomes an obvious alternative. In a wireless in-building pico-cellular network, the working place is partitioned into pico-cells defined by floors and major walls. Such a system can be implemented to save time and cost due to cabling. Figure 11 shows an example of an in-building wireless network using pico-BTS. The deployment approaches in constructing such an in-building network can be mainly categorized into two approaches according to the front-end used.

2.8.1. Distributed Antenna ApproachThe deployment for the distributed antenna system will involve an arrangement of central base stations feeding out to several of antennas over coaxial or fiber cables. The antennas could be directional or omni-directional depending on the need. Figure 12 shows how an in-building deployment is achieved by the distributed antenna approach. It shows the base station located in the basement feeding out to the distributed antennas of the building.

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Figure 12. Distributed antenna

This approach for deploying wireless in-building network involves lengthy cell and frequency planning and the installation of distributed antennas using coaxial or fiber cables [41]. A typical installation can take several weeks and can cause a certain degree of disruption to the workplace.

The typical decisions that a system integrator would consider in an in-building installation can be summarized as follows:

Whether the building will be supported by external antennas or it will require internal base stations.

The coverage and level of service that will be needed.

The number of cells and frequency band required to meet the specification.

In order to decide on these items, the system integrator will need to perform test measurements on the site to find out how RF signals attenuate throughout the building. The system can effectively be integrated and optimized by test measurements. This approach might not be well suitable for use in events requiring temporary deployment for it involves cabling work to some degree. It might not be able to deliver very large capacity because it depends on the central BTS's multiplexing capability.

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2.8.2. Distributed BTS Approach

Figure 13. Distributed BTS

The distributed BTS approach involves using a BTS as the front end to the wireless in-building network. While this is not the most cost-effective method for an antenna could be cheaper than a BTS, it is the most robust solution for deploying a wireless in-building network because it provides a capacity as large as the in-building system needs [40]. Additionally, as lower cost pico-cell BTSs will be available from various vendors, this approach will become more feasible. Figure 13 shows how an in-building deployment can be done with this approach. It shows the base stations distributed in the building.

Using a BTS as the front end of the system provides the flexibility to allocate capacity as needed. This approach also allows engineers to conduct frequency planning on a cluster basis with the rest of the external macro system, allowing the in-building system to be seen as its own separate and independent site within the carrier's system. Moreover, it is possible to introduce autonomous cell and frequency planning through extended operating and maintenance (O&M) functionality. The ability of each pico BTS to listen to the network and provide O&M information to a central controller will result in the production of a virtual map of the distributed BTS network and ensures efficient use of allocated frequencies within the building. With autonomous cell and frequency planning, each distributed BTS can adjust its power level and frequency to define its position in the network. It can also be used to minimize interference with the external macro cellular networks.

Test measurements of the building will still be required but to a much lesser degree than the distributed antenna approach. The distributed BTS can be deployed exactly where the capacity is needed. Furthermore, by using standard IP auto-configuration protocols, the distributed BTS can locate the central base station controller (BSC) and then register and authenticate a secure connection. Upgrades and addition of

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capacity can be achieved by simply adding another distributed BTS, which, in turn, causes the internal network to recon to accommodate the new distributed BTS. With this approach, the installation process can be done in days.

2.9. Network Security Plan

Data security itself is a fundamental design consideration for any RF-based network technology. In wireless in-building network systems, there could be two ways in which data might be intercepted:

Out of the system.

Inside the system.

Preventing effective reception of system data by an outside receiver is an inherent benefit of a technology allowing spectrum reuse within a relatively short distance. To allow reuse of the same frequency by a system nearby, system power level is kept very low. Additionally, it needs to take advantage of the propagation characteristics of the system RF as used in the in-building system. With their reflectivity and ability to disperse, the low-power system signals provide whole coverage within the in-building pico-cellular environment, yet are greatly attenuated by continuous barriers such as building floors and walls and dissipate rapidly with distance. Moreover, the multipath problem will make the signal incoherent to an outside receiver.

To protect the in-building network system from an inside attack, a controller node concept could be employed. In this system, every user node is required to register with the controller node and authenticate a secure connection before it starts communicating. Each user node not only needs to register and authenticate, but also has to request and be authorized to transmit and receive. Any node without authorization that tries to communicate will be excluded from the system. User nodes can neither transmit nor receive unless they are told to do so by the controller node. This operational protocol will be buried securely within the source code of the system.

2.10. Network Deployment Scenarios and Analysis

A cellular operator considers how the subscribers are distributed over the service area, and their movement patterns in network design. Thus, the number of handoffs is minimized, and the system capacity and coverage are maximized. According to these criteria, the typical deployment scenario for a cellular operator in a major city is to cover the rural areas with macro-cells, and urban areas with micro-cells. Such a deployment provides coverage with fewer base stations in rural areas, reducing the network cost. However, deploying macro-cells in urban areas causes low system capacity in densely populated areas. Therefore, micro-cells are deployed in urban areas, resulting in more handoffs. Although micro-cells increase system capacity, they cannot solve the capacity and coverage problems completely. There will still be dead spots inside the micro-cells with almost no coverage. Such dead spots will typically exist inside the buildings where the walls obstruct the radio signals.

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In order to overcome the problem of dead spots and increase system capacity, another possible scenario is to place pico-BTSs inside the buildings. In this scenario, pico-BTSs are placed at different floors of a building in which the coverage is to be improved (Figure 14). Although the building may be inside another cell, the subscribers in the pico-cells will have better signal reception from the pico-BTS, and communicate with the pico-BTS. Although the pico-cells are very small, there will not be frequent handoffs since the subscriber speed inside the building will be very low.

Figure 14. Alternative deployment with pico-BTSs

2.11. Network Cost Analysis

There are three basic differences between the two scenarios, given in Section 2.10, that affect the network cost:

There are less base stations in the typical deployment, therefore the total investment in the equipment will be lower.

In the alternative deployment scenario, the pico-BTSs are placed inside the building where better coverage is required. Therefore, the cost of real estate to shelter the base stations and establishing the towers in the typical scenario is avoided. Thus, the overall cost of the alternative scenario will not be high.

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Since the system capacity is increased and coverage is improved with the alternative scenario, the revenues of the cellular operators increase.

As a consequence of the items above, the gain obtained by deploying pico-BTSs, in places where feasible, surpass the cost of the deployment. Therefore, pico-BTS deployment is a good solution as long as the number of pico-BTSs and their locations are determined after careful study.

2.12. Conclusions

In this chapter, the technology of the pico-BTS has been presented from both of the technological and business perspectives. Some technical aspects of pico-BTS including standards, frequency allocation, power, and interference have been discussed in detail. Current and future technological development prospects of pico-BTS and its market forecast have been investigated.

For cellular networks deployed in some challenging environments such as mountains or highways wireless repeaters seem to be more suitable due to its cost efficiency with respect to the coverage it provides. For instance, cellular coverage might be increased with the use of wireless repeaters instead of costly deployment of base stations in mountains. In highways, on the other hand, high coverage solutions must be deployed in order to maintain the acceptable handoff rate in network. Pico-BTS is not an efficient technology for those areas due to its relatively low coverage.

In-building network design, however, might well take advantage of the higher capacity and service quality pico-BTS offers. Wireless repeaters along with the pico-BTS might be utilized together for large in-building areas to obtain cost efficient, high capacity and increased service quality cellular network solutions. A base station per building, wireless repeater for each floor, and pico-cell BTS for each corridor or large meeting hall might be a simple network deployment scenario in which wireless repeaters and pico-BTS coexist.

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3. Wireless LAN

3.1. Overview

In local areas such as business buildings, campuses, malls, and homes, the ever-increasing demands of wireless access to next generation networks continuously motivate the quick evolution of wireless local area networks (WLANs). Via WLANs, users can access high speed multimedia applications anywhere at anytime. Due to the high speed and multiple traffic types that are expected to be supported in the future WLANs, last mile issues in a local area network (LAN) environment will be solved at the same time.

In order to achieve the objectives of easy implementation, low cost, and wide user acceptance, WLAN generally work in industrial, scientific, and medical (ISM) band, which is un-licensed and available for public. Currently, several types of WLAN products have already existed. They belong to different standardization groups and can be categorized according to their different protocol standards. Typical WLAN standards or draft proposals include IEEE 802.11 [9], [44], [45], Bluetooth [46], [47], HomeRF [48], IEEE 802.16 [10], HiperLAN [49], [50], and many others [51], [52].

To date, several challenging issues still exist in WLANs. Compared to 2G wireless networks, current WLAN products are able to support data applications. Some products can achieve very high data rate, e.g., the rate of IEEE 802.11 WLANs can be as high as 11Mbps, while some products such as Bluetooth can only achieve medium speed data rate. Moreover, current WLAN products are weak in providing real time services. As an example, IEEE 802.11 products, which are based on the CSMA/CA protocol [9], are unable to provide quality of service (QoS) guarantees for voice, video, and other real time services. Thus, IEEE 802.11 working group E is still working QoS enhancement for IEEE 802.11 WLAN [53]. HomeRF products cannot support other real time service except low speed isochronous applications [48]. Another issue of WLANs is that interference between different types of WLANs can greatly degrade the performance of WLAN [54]. Moreover, the interoperability between WLANs needs to be paid attention to. Otherwise, the global communication, which is one of the objectives of the next generation communication systems, cannot be achieved.

Although WLANs are still being researched in order to have more advanced features, basic techniques are mature enough for deployment. WLANs are now being widely deployed. It is expected that the market of WLAN will be huge because WLANs will provide tetherless, high speed, and QoS-guaranteed last mile access to backbone networks such as next generation Internet.

In this chapter, we give a comprehensive investigation of WLAN technologies. In Section 3.2, we first analyze the functions, techniques, and standards of wireless repeaters. Then, current applications of WLANs, interference, and environmental issues are investigated. In the final part of this section, major suppliers of WLAN are presented. In Section 3.2.7, types of WLAN are categorized. Characteristics of these types of WLAN are also addressed in this section. The target market forecast and technology development prospect are reported in Sections 3.4 and 3.5, respectively. Interworking and integration with IMT-2000 are discussed in Section 3.6. Services provided by WLAN

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technologies are presented in Section 3.7. Network design plan and network deployment technology based on WLAN are analyzed in Sections 3.8 and 3.9 respectively. In Sections 3.10 and 3.11, the network deployment scenarios and cost analysis are presented.

3.2. Technology, Standardization, Present Conditions of WLAN

3.2.1. The WLAN Technology and StandardsCurrently, different types of WLANs coexist. For some WLANs, standards have been finalized. However, due to the increasing demands on the next generation communication systems, more research efforts are necessary in order to enhance the performance of these products. Thus, it is expected that standards with more advanced features will be proposed for these WLANs. For certain types of WLANs, proposals have been proposed, but research is still being carried out to finalize the standards. Finally, some types of WLANs are still in the start-up phase. Lots of research efforts are required in order to have a standard. In this subsection, the investigation is focused on the WLANs that have been widely accepted or researched. In particular, we analyze the WLANs such as IEEE 802.11 [9], Bluetooth [46], HomeRF and shared wireless access protocol (SWAP) [48], and HiperLAN/2 [50]. To investigate these typical WLANs, we focus on the technologies in the data link layer. Other issues such as frequency spectrum, bandwidth, and propagation characteristics of WLANs will be described in Section 3.2.3, and interference issues are discussed in Section 3.2.4.

3.2.1.1. IEEE 802.11

IEEE has developed several specifications in the Wireless LAN (WLAN) 802.11 family. Among them, 802.11a and 802.11b use Carrier Sense Multiple Access with Collision Detection (CSMA/CD), as the medium access protocol. It means that if a card has something to send, it will listen until no other card is transmitting, then starts transmitting, and listens if no other card starts transmitting at the very same time. If another card began transmitting it will stop, wait for a random interval and try again. If a source station has a data packet to send, the station checks the system to see if the path medium is busy. If the medium is not busy, the packet is sent; if the medium is busy, the station waits until the first moment that the medium becomes clear.

IEEE 802.11 standards activities include followings:

802.11a - 5GHz- Ratified in 1999

802.11b - 11Mb 2.4GHz- ratified in 1999

802.11d - Additional regulatory domains

802.11e - Quality of Service

802.11f - Inter-Access Point Protocol (IAPP)

802.11g - Higher Data rate (>20mBps) 2.4GHz

802.11h - Dynamic Frequency Selection and

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Transmit Power Control mechanisms

802.11i - Authentication and security

In the IEEE 802.11 standard, the physical layer and the MAC protocol are specified [9]. The MAC protocol has two operation modes, i.e., distributed mode and coordinated mode. As shown in Figure 15, the distributed coordination function (DCF) works in a distributed fashion and is based on CSMA/CA protocol. The point coordination function (PCF) is implemented on top of DCF in order to support real time traffic. PCF is based on polling which is controlled by a centralized point coordinator.

Figure 15. Protocol architecture of IEEE 802.11

In addition to PCF and DCF, three interframe spaces (IFS) are defined in the IEEE 802.11: short IFS (SIFS), DCF-IFS (DIFS), and PCF-IFS (PIFS). The length of SIFS is the shortest, and PIFS has a shorter length than DIFS. Normally, SIFS is used for CTS and ACK messages; and CIFS and PIFS are for asynchronous data and real-time traffic, respectively. Based on IFS, DCF, PCF, and the mechanism of CSMA/CA, the main operation procedures of the MAC protocol is shown in Figure 16. It actually follows the mechanism of using RTS/CTS to avoid collisions and hidden nodes.

Figure 16. Main operation procedures of the IEEE 802.11 MAC protocol

The IEEE 802.11 can support both data and real time traffic. However, their design is not QoS oriented since only priority is assigned to different types of traffic. Also, in order to support real time traffic, a centralized coordinator is required, which is infeasible in some wireless LANs such as ad-hoc networks. Thus, in [55], a reservation CSMA/CA is proposed to support multimedia traffic over mobile ad-hoc networks. IEEE 802.11 Working Group E [53] is also working to enhance the QoS capability of IEEE 802.11.

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802.11 Compatibility

While 802.11a and 802.11b share the same MAC layer technology, there are significant differences at the physical layer. 802.11b, using the ISM band, transmits in the 2.4 GHz range, while 802.11a, using the -NII band, transmits in the 5 GHz range. Their signals travel in different frequency bands allowing both technologies to operate without interfering with each other, it’s even possible to operate both on the same network concurrently. This can allow both 802.11b and 802.11a to operate using the same access points.

Interoperability

To ensure crossvendor interoperability [91], WLAN purchasers can look for the Wi-Fi symbol (Wireless Fidelity). WECA (Wireless Ethernet Compatibility Alliance) is the organization behind Wi-Fi that certifies products meeting the 802.11b specification through compatibility testing. (ww.wirelessethernet.org)

3.2.1.2. Bluetooth

To have a wireless network which has a more localized purview, i.e., the personal area [47], IEEE 802 Executive Committee started another working group to create a new wireless personal area network (WPAN) in March 1999. This new working group is IEEE 802.15 [56]. In the process of creating a standard for WPAN, the IEEE 802.11 called for proposals. By July 1999, the only respondent was the Bluetooth Special Interest Group [57]. Due to conflicting interests between IEEE and Bluetooth group members, Bluetooth has not yet become a standard for WPAN. However, it is the most widely accepted proposal for WPAN.

The aim of Bluetooth is to enable design of low power, small-sized, and low-cost radios that can be embedded in the existing portable devices. The multiple access of Bluetooth is based on frequency hopping (FH) code division multiple access (CDMA). The reason of not using TDMA in Bluetooth is to avoid timing issues [46], while that of not using direct sequence (DS) CDMA is to avoid issues such as the coordinated power control and common timing references. The Bluetooth network is a scatter ad-hoc network in which multiple piconets exist, as shown in Figure 17. These piconets may overlap or be disjoint. In each piconet, there is a master and multiple slaves. The master controls the FH channels and hopping sequences, while slaves access network via the master.

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Figure 17. Scatter ad-hoc network of Bluetooth

Bluetooth network works in 2.45 GHZ ISM band. Both isochronous and asynchronous services are supported by a Bluetooth network. For each unit, the transmission rate is less than 1 Mbps.

The MAC protocol of Bluetooth is based on FH-CDMA/TDD and the piconet architecture. A master is associated with a piconet which is identified by hop sequence and system clock of the master. The master controls medium access so that only communications between master and slaves are possible. The medium access is based on the following scheme:

Polling-based MAC within a piconet. In a piconet, the master polls slaves slot by slot. When a slave is polled, it starts transmission. The polling can be done implicitly when the master has information to send. Otherwise, the polling has to be done explicitly via a short poll packet. Due to polling-based access, the transmissions of slaves are contention-free.

ALOHA-based MAC to avoid interference between piconets. Independent piconets may interference when they occasionally use the same hop carrier. A type of ALOHA is used to avoid this problem. The master transmits information without checking a clear carrier. If the information is received in-correctly, it is re-transmitted at the next transmission opportunity. Due to the short dwell time of FH channel, collision avoidance scheme cannot be used.

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Bluetooth is not QoS-oriented, so it cannot support multimedia applications. Moreover, the intra-piconet scheduling and inter-piconet routing schemes need to be developed. Also, the procedures of setting up connections are complex.

3.2.1.3. HomeRF and SWAP

Networking in the home is required to extend the reach of PC and Internet throughout the home and yard [48]. The Home RF Working Group was thus formed in early 1997 to enable inter-operable wireless voice and data networking within the home at consumer price points. A SWAP has been created by HomeRF group and is now being finalized.In SWAP, the home network consists of two types of terminals or networking devices: isochronous clients and asynchronous peer-to-peer devices, as shown in Figure 18. Both of them can be connected to a main home PC. The isochronous clients are connected to the main home PC via the HomeRF control point, while the asynchronous devices are connected to main home PC via an Internet gateway.

Figure 18. Home networking based on HomeRF

In the HomeRF, the isochronous clients are based on TDMA, but the asynchronous devices are based on CSMA. Thus, the MAC protocol of SWAP should consider the hybrid of the two different systems. The frame structure of the hybrid MAC protocol is shown in Figure 19. A superframe consists of five phases. The hop is used to switch the hopping frequency, while the beacon maintains network synchronization, controls the format of the frame, and manages when each terminal should transmit and

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receive data. The contention free period (CFP) 1 and CFP 2 are based on TDMA/TDD, while the contention period is managed according to the CSMA/CA access mechanism. It should be noted that TDMA/TDD of CFP 1 and CFP 2 is different from the classical TDMA/TDD structure. In CFP1 and CFP2, uplink and downlink are changed alternatively on the slot basis. Service slot is used to send connection requests. Since the SWAP is based on frequency hoping techniques, the frame length is equal to the duration of a hop period.

Figure 19. The frame structure of SWAP

The operation procedures of the MAC protocol for SWAP are as follows:

Isochronous services. For each node that wants to transmit the isochronous services such as voice data, it first sends a request to the connection point (CP), i.e., the control point in Figure 18, via the service slot. In the beacon period of the next frame, the assignment is sent back to the node. If it is allowed to transmit packets, it is assigned a pair of uplink and downlink slots in CFP 2. Otherwise, the node should send the request next time. In the CFP 2, a node which assigned a time slot can transmit packets to the CP via the uplink slot and receive packet from the CP via the downlink slot. Piggyback information is also transmitted in the header of each packet to acknowledge whether packets sent in the last frame have been successfully. If errors occur, retransmission is required, and thus a pair of uplink and downlink slots for retransmission is assigned in the CFP 1. It should be noted that retransmission can be performed for only one time.

Asynchronous services. The asynchronous services such as computer data access the channel according to the CSMA/CA mechanism. In this working period, the CP is not required and the network is of ad-hoc type. In order to avoid the hidden node issue, the RTS/CTS also needs to be included into the CSMA/CA.

The main contribution of the SWAP protocol is to combine the TDMA based MAC and CSMA/CA protocol. By this way, heterogeneous traffic can be supported. Also, high system utilization can be achieved. Another advantage of SWAP is that it uses retransmission for isochronous traffic. Low packet loss ratio of real time services can be achieved by the fast MAC retransmission without using complicated error control scheme. However, the TDMA based MAC in SWAP is still weak. For example, multi-

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slot allocation is not proposed and the resource allocation algorithm to guarantee the QoS is ignored. Moreover, retransmission of asynchronous traffic or other error control schemes need to be developed.

3.2.1.4. BRAN Project

ETSI has established a standardization project for Broadband Radio Access Networks (BRAN) in Spring 1997. ETSI BRAN is the successor of the former Sub-Technical Committee RES10 which developed the HIPERLAN/1 specifications.

The project prepares standards for equipment providing broadband (25 Mbps or more) wireless access to wire-based networks in both private and public environments, operating in either licensed or license exempt spectrum. These systems address both business and residential applications. Fixed wireless access systems are intended as high performance, quick to set up, competitive alternatives for wire-based access systems.

The specifications address the physical (PHY) layer as well as the data link control (DLC) layer (with medium access and logical data link control sublayers as appropriate). Interworking specifications that allow broadband radio systems to interface to existing wired networks, notably those based on ATM, TCP/IP protocol suites and UMTS, are or will be developed.

ETSI BRAN currently produces specifications for three major Standard Areas:

HIPERLAN/2, a mobile broadband short-range access network

HIPERACCESS, a fixed wireless broadband access network

HIPERMAN, a fixed wireless access network which operates below 11 GHz

3.2.1.5. HiperLAN/2

There was an opposite WLAN standard, called HiperLAN/1, which was finalized by ETSI. It works in dedicated bandwidth of 5.1-5.2 GHZ. The MAC protocol of HiperLAN/1 is similar to CSMA/CA, so no real time service can be supported. In order to enhance the performance of WLANs in the sense of supporting higher speed and multimedia applications, ETSI proposed another standard, called HiperLAN/2, which is the first WLAN standard that is based on orthogonal frequency division multiplexing (OFDM) technology. The transmission rate of HiperLAN/2 can be up to 54 Mbps in the physical layer and up to 32 Mbps in the network layer. HiperLAN/2 works in the 5.4-5.7 GHZ frequency band.

HiperLAN/2 network is an infrastructure-based, where services are connection-oriented. The access point (AP) in HiperLAN/2 acts like a base station, and controls the medium access, handover, and interconnecting to other networks [50].

The frame structure of HiperLAN/2 is dynamic TDMA/TDD, which is shown in Figure 20.

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Figure 20. The frame structure of HiperLAN/2

Each MAC frame consists of several control channels such as broadcast channel (BCH), frame control channel (FCH), random access channel (RCH), access feedback channel (ACH), and the downlink and uplink transmission phases. The functions of these control channels are described as follows:

BCH. Control information is sent via this channel. The information includes transmission power, starting points and length of other channels, and identifiers of AP.

FCH. This channel conveys resource allocation information.

RCH. It is used by mobile terminals to request resources in the downlink and uplink transmission phases.

ACH. It conveys the feedback information on the access attempts in the previous RCH.

The MAC protocol of HiperLAN/2 is operated according to the following procedure:

Connection request. Mobile terminals send connection requests in the RCH, and get feedback about access attempts in the ACH. In this process, random access protocol is used, and collision resolution scheme is needed.

Admission control. To determine whether a connection request can be accepted, an admission control scheme must be used. Since HiperLAN/2 is a type of wireless LAN network, the admission control schemes for ATM networks can be used. However, certain modifications are necessary in order to make them applicable to the wireless environments.

Broadcast resource allocation via FCH. The information of allocated time slots for each connection is sent back to mobile terminals via FCH in a broadcast way.

Data transmission. When a mobile terminal is allocated time slots, the packets from high layers are segmented into ATM cells, and transmitted in the assigned time slots.

HiperLAN/2 holds the following features [50]:

High data transmission rate is possible

Network is ATM-based and connection-oriented, so QoS of multimedia traffic is supported

Automatic frequency selection is performed at the AP, so no frequency planning is required

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Power saving management is embedded in the protocol

Mobility is supported

Flexible architecture to support different network environments

Plug-and-play radio network

Manageable and scalable bandwidth

However, HiperLAN/2 has several problems such as high protocol overhead for IP traffic, low-throughput for bursty and delay-insensitive traffic, because it is based on wireless ATM technology.

Table VII below summarizes the characteristics of 802.11, 802.11b, 802.11a, and HiperLAN/2 [93].

Table VII. Comparison between 802.11 and HiperLAN/2

Characteristic 802.11 802.11b 802.11a HiperLAN/2Spectrum 2.4GHz 2.4GHz 5GHz 5GHz

Max Physical Rate 2Mb/s 11Mb/s 54Mb/s 32Mb/sMax data rate layer 3 1.2Mb/s 5Mb/s 32Mb/s 32Mb/s

Medium access CSMA/MA TDMA/TDDConnectivity Conn.-less Conn.-less Conn.-less Conn.-oriented

Multicast Yes Yes Yes YesQoS support No No No Yes

Frequency selection FH/DSSS DSSS Single carrier Single carrier with Dynamic

Frequency Selection

Authentication No No No NAI/IEEE address/X.509

Encryption 40bit RC4 40bit RC4 40bit RC4 DES, 3DESHandover support No No No No

Fixed network support Ethernet Ethernet Ethernet Ethernet, IP, ATM UMTS, FireWire, PPP

Management 802.11MIB 802.11MIB 802.11MIB HiperLAN/2MIBRadio link quality

controlNo No No Link adaptation

HiperLAN/2 enables QoS, automatically frequency allocation, power saving and security support, and is network independent. However, as most major vendors produce their wireless LAN products according to IEEE 802.11 standard, IEEE 802.11 has become the practical standard for most markets. Market drives plays an important role in the competition between the two different standards.

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Currently, network operators intend to deploy 802.11x wireless LAN, especially 802.11b, instead of HiperLAN networks. Such a situation is caused by both technical and non-technical factors.

In terms of non-technical factors, many big manufactures and IEEE committee support 802.11 and try to have a global standard for wireless LAN. When they developed 802.11b techniques, they just pushed it to get the level of performance that was enough as needed. Thus, not so much engineering effort is required to create products. However, HiperLAN standard is too good to be true [104]. ETSI HiperLAn group tried to make the technique advanced. However, it turned out to be too advanced and too late. Finally, most of the WLAN manufactures tend to back IEEE 802.11 instead of HiperLAN. For example, Intel clearly pointed out that they like to support IEEE 802.11 and Bluetooth in their chip design, but they are not willing to back HiperLAN.

In addition to non-technical factors, there do exist non-technical factors. 1. ATM versus IP. HiperLAN/2 is a wireless ATM technique. Although it is able

to carry the IP traffic over ATM, most of the industrial companies do not like such a design, because IP seems to be dominant network solution in the world market.

2. Network Infrastructure. IEEE 802.11x supports both Ad-hoc and Client/Server network architecture. However, HiperLAN only supports the client/server architecture. Thus, IEEE 802.11 WLAN is much more flexible in industrial application.

3. Frequency Band. IEEE 802.11b works in ISM 2.4 GHz band. Such a band is globally license-free. Thus, IEEE 802.11b was quickly accepted by many manufactures, vendors, and companies. However, HiperLAN works in 5-GHz band. Such a frequency band has not been assigned to be free to use in many countries. IEEE 802.11a share the same problem with HiperLAN. Athough in the future, global license-free 5GHz frequency band believes to be available, the application of HiperLAN is much later than 802.11b.

4. Complexity and Price. HiperLAN is too advanced, which results in the complexity in implementation. It is generally expensive to implement HiperLAN protocol in a chip set of a PC, PDA, and other terminals. However, implementing IEEE 802.11x in a chip set is simpler, and thus low cost WLAN can be easily provided to different type of WLAN users.

However, although HiperLAN/1 is not an interest to any network operators, HiperLAN/2 is still in progress. Due to its high speed and QoS guarantees, it will be a strong competitor with IEEE 802.11a WLAN in the world of 5GHz frequency band. Which will be the winner is not obvious at the moment.

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3.2.2. Current Use of WLAN and Industry PracticesBecause of the mobility, flexibility and low cost of WLAN, it has numerous practices in many areas such as home, enterprises and public accesses.

Home wireless networks. WLANs are an ideal, no-hassle, no-wires alternative for networking computers and Internet appliances at home. They can be installed easily, expanded quickly and reduce the cost of setting up a wired network.

Enterprise wireless networks. WLAN save time and money for enterprises. They also enable dynamic movements, scalability, and easy implementation. And they are easily to be integrated to an existing LAN. Wireless Networking is used to connect disparate networks in different locations. Building-Building or LAN-LAN wireless networks are being used by many industries serving diverse applications. Point-to-point and point-multi-point connections allow users in different locations the opportunity to access the Internet, share files, and access network resources without wires.

Public access. Wireless Internet service providers (WISPs) now offer public WLAN access for at various locations such as airports, airline clubs, conference centers, hotels, restaurants, and cafes. Using a laptop or PDA, users can access the wireless Internet, or log into a company intranet through a VPN (virtual private network) client. Public access WLANs do not worry to search for a data port. Access speed that is 50-200 times faster than dial-up, thus it is practical to make large file transfer. And the service is affordable with flexible payment options and no long distance charges.

Here are more typical examples of current WLAN practices:

Hospitals. Hand-held devices and portable computers are able to deliver patient information to doctors and nurses in real time, providing information that can save lives. In addition, administrative productivity is bolstered through the elimination of redundant paperwork.

Warehouses. Workers use wireless devices to deliver instant updates regarding supplies and inventories to centralized databases providing more accurate information to the management team. Bar code readers with wireless, data links are used to enter the locations and to identify inventory, improving operational efficiency and reducing costs associated with physical inventory counts.

Consulting and audit teams. Small work groups can quickly establish private and integrated networks as they move from site to site.

Dynamic environments, ad agencies, etc. The cost of LAN ownership can be reduced significantly in dynamic environments with multiple additions and moves.

Universities. Many universities have implemented campus-wide WLAN technologies as students become increasingly PC dependent. New York University, for instance, provides each entering freshman with a laptop computer as part of his/her tuition. By implementing WLANs, colleges like NYU can provide accessible data to students, both as they travel around campus and when they are unable to access a wireline connection.

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Historic buildings, older buildings. Many government and otherwise historic buildings have regulations against changing the building infrastructure, denying the possibility of pulling new wiring through the walls. WLANs are, in these circumstances, the only possible form of data networking. Trade Shows-WLANs provide quick and flexible setup capabilities that allow trade show personnel and convention centers to constantly change the network structure from one show to the next.

Meeting rooms. Real-time information allows management to make more informed decisions during meetings.

Retail stores. WLANs enable frequent network reconfiguration.

Restaurants and car rental agencies. Real-time information transfer enables superior customer service. Examples include Avis and Hertz.

Data backup. Mission-critical applications can be implemented with a wireless backup in the case of malfunctions in the wired infrastructure.

3.2.3. Working Frequency, Typical Bandwidth, and Propagation Footprints of WLAN

The technologies of typical WLANs have been described in Section 3.2. In this subsection, we summarize these techniques in terms of working frequencies, typical bandwidth, and the propagation footprints.

Since IEEE 802.11 working group has proposed several physical layer specifications, the working frequency, available bandwidth, and propagation characteristics are dependent on the physical working modes, as listed in Table VIII.

Table VIII. Different Physical layers specified by IEEE 802.11

Operating Modes Frequency Band Transmission Rate Propagation Footprints

Radio based, legacy DSSS

2.4 GHZ ISM band 1 Mbps with BPSK2 Mbps with QPSK

cellular or ad-hoc

Infrared-lightbased, legacy DSSS

Infrared-light 1 Mbps with BPSK2 Mbps with QPSK

cellular or ad-hocLoS

Complementarycode keying (802.11b)

2.4 GHZ ISM band 11 Mbps/5.5 Mbps cellular or ad-hoc

OFDM (802.11a) 5 GHZ 6-54 Mbps cellular or ad-hoc

In Table VIII, the cellular propagation footprint means that the 802.11 network works in an infrastructure based architecture. In such a scenario, mobile terminals communicate with an AP. Thus, the mobile terminals controlled by an AP lie in the cell which is covered by this AP. Handoff is required when a mobile terminal cross cells. When the 802.11 network works in ad-hoc mode, mobile terminals communicate peer-to-peer, so there is not a fixed pattern of the propagation footprints.

In a Bluetooth network, FH-CDMA/TDD is used, so the core physical layer technique is FH-CDMA. The working frequency of HomeRF is in 2.45 ISM band. Since

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a piconet uses one FH carrier, each Bluetooth unit cannot support the transmission rate of up to 1 Mbps. Due to the scatter piconet concept used in Bluetooth, the propagation footprint is non-regular. However, in each FH period, there exists an irregular cell that is controlled and covered by the master. In such an irregular cell, all slaves must communicate with the master.

HomeRF network works in the 2.4 GHZ ISM band. The physical layer is based on FH, and modulation is 2-FSK or 4-FSK. HomeRF control point (CP) has low transmitting power and can be implemented on a single chip. It has native support of Internet access, and voice telephony access is provided through PSTN. The maximum transmission rate of HomeRF non-real time services is up to 1 Mbps. When devices communicate with each other peer-to-peer, no fixed propagation pattern exist. On the other hand, if the devices are controlled by the CP, the network has a cellular structure, in which all devices communicate through the CP.

The physical layer of HiperLAN/2 network is based on OFDM technique, which enables that the physical layer transmission rate can be as high as 54 Mbps. In the network layer, the transmission rate can be also up to 32 Mbps. HiperLAN/2 works in 5.4-5.7 GHZ frequency band, which is dedicated in Europe. In HiperLAN/2, the AP acts like a base station. So all mobile terminals communicating with such a base station actually work in the cell covered by the AP. When mobile terminals move from one cell to another cell, handoff procedure is invoked.

As described previously, almost all the WLANs work in the frequency band around either 2.4 GHZ or 5.3 GHZ. It should be noted that the radio wave propagation introduce a path loss penalty of 6.9 dB going from 2.4 GHZ to 5.3 GHZ [54]. This means that, for WLANs working in 5.3 GHZ frequency band, almost five times of RF power is required to cover the same distance as WLANs working in 2.4 GHZ frequency band. For the same reason, the RF propagation through barriers is poorer when 5.3 GHZ frequency is used.

3.2.4. Interference to WLANsInterference in wireless systems is always an important issue because users near the local vicinity occupy the same bandwidth and cause co-channel interference. For WLANs, in addition to co-channel interference, other types of interference exist because generally WLANs work in the unlicensed ISM frequency band. In the same ISM frequency band, one type of WLAN may coexist with other types of WLANs or devices such as microwave oven and ultrasonic equipment. Thus, the interference to WLANs comes from the following major sources:

Co-channel interference. Co-channel interference arises due to uncoordinated users occupying the same bandwidth within or near local vicinity [60]. In a WLAN environment, since the transmission distance is short, the time dispersion from the propagation channel is low [60]. Thus, co-channel interference becomes an important factor of determining the SINR of the received signal. According to the Shannon-Hartley Law [61], the normalized capacity can be derived as

= log2(1 + S/(I+N)) (1)

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where S is the received interference power, I is the received co-channel interference power, and N is the noise power. Thus, from this equation, we know that if co-channel interference arises, the normalized capacity is reduced. This causes the degradation of network performance of WLAN. For example, the throughput and transmission rate are reduced if a fixed BER is required. In other words, if a fixed throughput is required, the BER will be increased. There are two approaches for reducing the effect of co-channel interference. One is to use the MAC protocol to determine the level of co-channel interference and select an appropriate channel for each user. Thus, for each channel, during a certain period, only one user transmits signals and other users in the immediate vicinity stop transmitting. The other approach is to use co-channel interference rejection technique in the physical layer.

Interference from non-WLAN devices in the same frequency band. Most of WLANs work in the ISM band, i.e., the frequency band of 900 MHZ, 2.4 GHZ, and 5 GHZ, where have already been used by other ISM devices such as microwave ovens, medical diathermy, and ultrasonic equipment. It is known that such ISM band interference exhibits impulsive characteristics and seriously degrades the performance of WLANs [62]. Thus, new techniques are necessary to reduce the interference or make the WLANs be more robust to operate in the presence of ISM interference. For example, in a new multicode transmission technique is proposed for DSSS system so that good performance can still be achieved in the presence of ISM interference. Reducing interference in the MAC layer is possible, but it must be much more difficult than in the physical layer. The reason is that the other ISM devices such as microwave ovens are not network components and cannot communicate with WLANs.

Interference between different WLANs in the same frequency band. It is quite possible that different types of WLANs use the same ISM band. When they are deployed in the near vicinity, interference to each other will seriously degrade the performance of WLANs. Thus, coexistence of WLANs of the same ISM band is a challenging research topic. For example, in the 2.4 GHZ ISM band, the coexistence of Bluetooth and 802.11b has been widely researched.

In the 5 GHZ ISM band, the coexistence of HiperLAN/2 and IEEE 802.11a is also an issue. To reduce the interference between WLANs in the same ISM band, many schemes have been proposed [54], [63], [64], and [65]. In general, the coexistence of WLANs can be enabled in the following ways [55], [66], [67]:

Regulatory and standards. Rules can be used to change the operation frequency segment of a channel so that the interference can be reduced. This has been proposed by FCC for Bluetooth. For example, a piconet in the Bluetooth might hop one segment of the band instead of the whole 2.4 GHZ ISM band. In addition to rules, standard and industry bodies should work together to make a rapid progress toward providing a suite of coexistence tools.

Usage and practices. When one WLAN is working, others are banned. In such a way, interference can be greatly reduced. However, this is not practical. Thus, modal operation of WLANs can be a good alternative. However, when WLAN devices grow

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to a high density, this approach is not feasible either. Thus, this type of methods cannot really solve the interference issues between WLANs.

Technical approaches. Such approaches are implemented in different layers such as driver layer, MAC layer, and physical layer. In the driver layer, software above the MAC layer can be installed for different types of WLANs. Thus, software switch from one WLAN to another WLAN is required. However, the approach in this layer does not work when more than one WLAN are working in the same time period. Thus, the approach in the MAC layer is more attractive. To propose schemes in the MAC to reduce the interference between WLANs is still an on-going research topic. In the physical layer, signal processing techniques and anti-jamming schemes can be used to reduce the interference and keep the performance of WLANs. However, physical layer techniques tend to directly affect system costs more than the MAC layer techniques, because the MAC layer comprise digital hardware and software, and techniques employed here tend to be relatively inexpensive to implement. Therefore, the techniques of physical layer and MAC layer need to be balanced.

3.2.5. Environmental IssuesEffect of wireless technology on health is one of the most discussed and to be concerned issue, as the devices emit radio frequency electromagnetic energy. The radiation used by this technology, fall well within the limits of safety guidelines (both in terms of frequency content and power level) specified by Radio Frequency Safety Standards and Recommendations. Hence it has been proved that WLAN is safe for health.

Widely accepted and recognized standard bodies for health regulations are ANSI/IEEE, NCRP, NRPB, and IRPA/INIRC. The safety limits specified by these bodies are very much the same, with little differences. ANSI/IEEE Standard (ANSI/IEEE C95.1-1992) specifies safety levels with respect to Human Exposure to Radio Frequency Electromagnetic Fields, from 3 KHz to 300GHz. Radiation in this frequency range is non-ionizing (as they do not have enough energy to break the chemical bonds of genetic material of body cells). The limit set by ANSI/IEEE C95.1-1992, for radio power in the above frequency range is in terms of, whole-body averaged energy absorption rate (i.e. Specific Absorption Rate or SAR) and it is 0.4W/Kg of the body tissue in environments designated either occupational or "controlled" and 0.08W/Kg in environments designated either public or "uncontrolled".

WLAN Technology use frequency bands around 2.4GHz and 5GHz. Hence radiation is non-ionizing. Moreover, manufactures of WLAN products are designing their products to operate within the power limit set by the Safety Standards. In fact most of the products have power specifications which is much below the specified limits (typically in the range of 35mW [68]). Hence the technology is safe for health.

Apart from the fact that it is safe to use, there are many more added advantages, inherited to WLAN Technology. Some of these are absence of wire in network (which makes it convenient and quick for network setup, trouble shooting, relocation and expansion etc). Also WLAN looks much better and cleaner compared to the wired one. User mobility, reduced-cost of ownership, real-time-access to information, and positive

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impact on user psychology are the added differentiations that WLAN has over Wired LAN. All these features make WLAN a more friendly technology, for its user.

3.2.6. Major Suppliers of the WLAN ProductsThere are three kinds of product in the WLAN: access point, LAN adapters and LAN bridges. In Table IX, major suppliers of access points are compared. In Table X, major suppliers of LAN adapters are compared. In Table XI, major suppliers of LAN bridges are compared.

Some operators such as Nokia use GSM SIM card for authenticating the user. Each SIM card stores a standard GSM International Mobile Subscriber Identity (IMSI) code that identifies the user and the home operator. In Wireless LAN, the SIM is integrated within Wireless LAN Card fitted to the user's laptop. Typically, this SIM is used for Wireless LAN access, but it can also be used as a separate SIM card to make and receive GSM calls while using the Wireless LAN. Using SIM authentication also provides full GSM international roaming capability with GSM roaming partners.

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Table IX. Comparison of access point products of major suppliers

Major suppliers

Products Operating Frequency

Standard Throughput WEP Encryption

Agere AP-1000 2.4GHz 802.11b 11Mbps -Avaya I/700022270 2.4GHz 802.11b 11Mbps -Nokia A032 2.4GHz 802.11b 11Mbps 64- and 128-

bitNortel e-mobility

DSSS AP DR4000E02

2.4GHz 802.11b 11Mbps -

Intel PRO/Wireless 2011B

2.4GHz 802.11b 11Mbps 64- and 128-bit

Intel PRO/Wireless 5000

5.2 GHz 802. 11b 54 Mbps 64- and 128-bit

Siemens I-GATE 11M 2.4GHz 802.11b 11Mbps 11Mbps3Com Access Point

60002.4GHz 802.11b 11Mbps 64-bit

Fujitsu MBH8MB01 2.4GHz Bluetooth 732.2kbps -Compaq WL510 2.4GHz 802.11b 11Mbps 128bitAgere AP-1000 2.4GHz 802.11b 11Mbps 128bitApple AirPort 2.4GHz 802.11b 11Mbps -IBM AP500 2.4GHz 802.11b 11Mbps -Cisco Aironet 350

Series2.4GHz 802.11b 11Mbps -

Table X. Comparison of LAN adapter products of major suppliers

Major suppliers

Products Operating Frequency

Standard Throughput Range

Intel PRO/Wireless 2011B LAN

PC Card

2.4GHz 802.11b 11Mbps -

Intel PRO/Wireless 5000 LAN

PCI Adapter

5.2GHz 802.11a 54Mbps 100 feet

Compaq WL110 2.4GHz 802.11b 11Mbps -Agere ORiNOCO

PC Card2.4GHz 802.11b 11Mbps -

Apple Airport Client Card

2.4GHz 802.11b 11Mbps -

Cisco Aironet® 350 Series

2.4GHz 802.11b 11Mbps -

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Table XI. Comparison of LAN bridge products of major suppliers

Major suppliers

Products Operating Frequency

Standard Throughput Range

Intel Wireless Gateway

2.4GHz 802.11b 11Mbps -

Compaq WL310 2.4GHz 802.11b 11Mbps 160m(525feet)Agere RG-1100

Broadband Gateway

2.4GHz 802.11b 11Mbps 550m(1750ft)

Agere ORiNOCO PC Card

2.4GHz 802.11b 11Mbps -

Cisco Aironet® 350 Series Wireless Bridge

2.4GHz 802.11b 11Mbps 25 miles (40.2 km)

3.2.7. Radio Link Quality ControlRadio link in wireless domain is the path or combination of paths from the transmitter to the receiver. The radio link governs the communication quality in terms of BER for a specific transmitter power level or in other words, given the BER specification determines the required transmitter power. In case of WLAN this is very critical for system performance. As there exist a limit on maximum amount of power which can be transmitted as per FCC regulation, for different standards. The radio link quality along with the transmitter power determines the range of communication for a specific communication performance in terms BER. We will first discuss important system parameters and variables required for this analysis of indoor WLAN range, then talk about link budget, taking into consideration, one suitable path loss model into consideration.

3.2.7.1. System Parameters

The indoor coverage range depends on maximum allowable transmitted power and nominal sensitivity. Such specifications are as per IEEE 802.11a and IEEE 802.11b standards. Table XII compares the specific parameters that determine the indoor coverage range as per IEEE 802.11a and IEEE 802.11b standards in USA and Europe. It is to be noted that the Packet Error Rate (PER) of both these standards are same.

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Table XII. System parameters

Transmit Power

Transmit Gain

Receive Gain

Receiver Sensitivity

IEEE 802.11aUSA 23dBm 6dBi 0dBi -82dBm to –65 dBm

Europe 23dBm 0dBi 0dBi -82dBm to –65dBm

IEEE 802.11bUSA 30dBm 0dBi 0dBi -70dBm

Europe 20dBm 0dBi 0Dbi -76dBm

3.2.7.2. Path Loss Model for Indoor WLAN

The indoor radio channel model differs from that of traditional outdoor wireless models because of two main reasons: small distance of coverage and large variation in environment for small within small distance. From various experiments it has been observed that path loss in indoor environments are strongly influenced by building features like building layout, material etc. Indoor propagation is dominated by reflection, diffraction, and scattering. Many different types of models are proposed for such signal propagation. When both the transmitter and receiver are on the same floor the propagation loss can be modeled as the Keenan-Motley or Devasirvatham model. This model predicts the path loss as the summation of free space path loss plus a factor which varies linearly with range. The average signal path loss model can be represented by the following equation [105]:

(2)

where d is the distance, f is the frequency of operation, PLFS is the free space path loss, and a is the linear attenuation coefficient (typical value of 0.47 [dB/m] for an office environment).

3.2.7.3. Link Budget for Indoor WLAN

The indoor coverage range is calculated using the link budget formula according to the parameters specified by standards (given in previous table). Using the formula we can given the transmitted power, the coverage distance d can be calculated. The received power is related to transmitted power, antenna gain and signal path loss by the following equation:

Pr[dB]=Pt[dB] + Gt[dB]-PL(d,f) [dB] –Gr[dB] (3)

where,Pr[dB] is the minimum received power to meet PER/FER (receiver sensitivity),Pt[dB] is the maximum allowed transmit power,Gt[dB] is the transmit antenna gain,Gr[dB] is the receiver antenna gain,PL(d,f) [dB] is the indoor signal path loss given by Equation 2.

Using the above equation for a particular standard we can fine the in-building coverage area. In the above case we have assumed one channel model (path loss model).

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But the link budget equation is valid for any path loss model. Using the above propagation model the range of indoor WLAN is found to be around 47.4 m at 5 Ghz at 11 Mbps as per IEEE-802.11a (Europe) and 57 m for (USA).

3.3. WLAN Types and Their Characteristics

WLANs are really diverse, and it is impossible to have a single standard for them. However, they can be categorized into several types according to certain criteria. For example, we can categorize WLANs according to working groups or standardization committee. We can also classify WLANs according to their different frequency bands. In this subsection, we use the multiple access schemes as a criterion to categorize and compare WLANs. Thus, WLANs can be categorized into the following types:

CSMA/CA based WLAN. Due to simplicity of CSMA/CA, many WLANs are based on this technique. For example, IEEE 802.11 belongs to this type. Since CSMA/CA has hidden node and exposed node problems, some mechanisms such as request to send (RTS) and clear to send (CTS) are needed to enhance its performance. The basic network topology of CSMA/CA-based WLAN is ad-hoc. To provide network access to backbone, an AP is required. Considering that CSMA/CA is weak in QoS guarantees of real time services, so AP also helps to support the real time services. However, how to really deliver QoS guarantees in this type of WLANs is still being researched.

ALOHA- and Polling-based WLAN. This type of WLAN is especially used in WPAN because of its simplicity. Also, due to the weakness of ALOHA in the sense of QoS guarantees, this type of WLAN is not applicable to wider areas. Bluetooth and IEEE 802.15 WPAN belong to this type. The typical network topology of this type of WLANs is ad-hoc. To control the medium access and provide access to backbone, a master is generally used. The master can be dynamically selected in order to have more flexibility, which has been done in Bluetooth. This type WLAN has low transmission rate, and is weak in QoS guarantees. Multimedia services cannot be supported by this type of WLANs.

TDMA or CDMA based WLAN. Compared to CSMA, TDMA and CDMA are more flexible in resource management. The resources such as time slots or codes of a network can be allocated to a user by a reservation scheme. Thus, TDMA or CDMA based WLANs are becoming more and more attractive to developers and network customers. However, because of the higher complexity existing in TDMA and CDMA techniques, the cost of developing, manufacturing, and deploying such WLANs is more expensive. As TDMA and CDMA techniques quickly develop, especially in the physical layer, their cost will become so low that it can be acceptable to local area environments and users. Thus, TDMA or CDMA based WLANs are a promising option to provide next generation WLANs. Currently, most of the proposals in IEEE 802.16 working group are based on TDMA or CDMA techniques. In ETSI, HiperLAN/2 is also based on the TDMA technology. Because of using TDMA as the multiple access scheme, resources in HiperLAN/2 can be reserved and a virtual connection can be established as in an ATM network. In such a way, the QoS of multimedia traffic can be guaranteed.

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Hybrid WLAN. TDMA or CDMA can be used in combination with other multiple access schemes such as CSMA or ALOHA. For example, in HomeRF, the MAC protocol is based on a hybrid frame structure, i.e., the whole frame consists of the TDMA phase and the CSMA phase. The delay-insensitive traffic can be sent in the CSMA phase, while real time traffic such as voice is transmitted in the TDMA phase. The hybrid WLAN has the advantage of flexibility. It provides the low access delay for data traffic, so that users can feel that the network is always on, which is the feature of Internet. Although the access time of real time traffic is generally larger due to the process of resource reservation, the QoS is guaranteed. Unfortunately, the TDMA-based MAC part is still very simple. Actually the real time service is supported via the PSTN. Thus, the current HomeRF protocol only supports single slot allocation to isochronous services, and it cannot support many types of real time traffic. To have a powerful hybrid WLAN depends on the advances of both physical layer and data link layer techniques.

3.4. Main Target Market Forecast

The unexpected growth of Internet over last few years has proved the fact that platforms/technologies that support data and resource sharing are boon for explosion in business and added personal convenience. This provided motivation to apply the concept of data and resource sharing to other domains of communication, which gave birth to Wireless Networking in the LAN space. Development and penetration of WLAN technology since its conception has further strengthened the above argument. The market for WLAN products is increasing more than predicted, and its future is forecast to be huge and it is going to be omni-present, starting from inside of home to offices, educational institutes, health care centers, warehouses, hotels, airports and many more.

3.4.1. Current Market Segments and Their Market PenetrationThough the ultimate aim of WLAN technology is to replace the wired infrastructure, at present it is a significant compliment to what currently exists. Corporate, educational institutes, health care centers, manufacturing companies etc are installing WLAN systems to increase both user and IT team productivity. The present market for WLAN Technology includes but not limited to the following sectors:

Corporate. Many companies are going for WLAN alternative, as it is providing a common working platform of shared files and shared resources. It has already proven (through market study) that WLAN is more convenient, productive, user friendly and cost effective for corporate.

Education. In educational institutes WLAN is expanding its presence with classrooms, laboratories, libraries, student center, sport complexes, getting connected to its backbone network through wireless links. The advantages provided by WLAN are more in-class-productivity, low-cost and wide-coverage network setup, convenient access to institute's network from anywhere inside the campus (which makes it possible for both faculty and students to setup group study/discussion through desktops/laptops even though members are physically far apart). Institutes

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are also saving lots of money by buying fewer computers as the same ones can be used alternatively in different classes and laboratories at different times.

Healthcare. To take the advantages of this most sought after technology, hospitals are centralizing their laboratories, resources through WLAN. This promising technology has shown to meet their needs by decreasing the length of hospital stay, speeding diagnostic and case analysis time (as doctors and nurses have access to patient's file irrespective of their physical separation), procedural costs, documentation etc.

Manufacturing. Because of its size, frequent changes in assembly line, changing work location, it is cost prohibitive and also not feasible to lay cables in manufacturing or factory floors. Also in such environments, workers and management many times need instantaneous access to accurate information to track production runs, and production quantities in real time. WLAN is offering all these, hence its use in this sector is growing steadily.

Warehouse. WLAN is enabling warehouse workers to input and access data in real-time using mobile devices, linked to the mainframes or servers with software applications (like inventory collection, order fulfillment, shipping/receiving applications etc.) running on them. This also reduces the paper work by a great extent and has proved to be convenient both for workers and management.

Retail. Use of WLAN in retail industries (such as restaurants, military stores, grocery stores etc) have proved to have many advantages like reduction of long lines of customers, faster rate in getting customer checkout and totaling orders, faster rate in receipts of goods and taking inventories. It is also very much helpful for the decision makers in retail, as it provides them real-time information about ordering, collection, distribution and sale of goods.

A study by Wireless LAN Association (WLANA) has the following data on WLAN market penetration in different segments [75] (as shown in Figure 21).

Figure 21. WLAN market share of different segments

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3.4.2. A Forecast of the Target Markets and Estimated Market SizeThe growth, user acceptance, user satisfaction of WLAN technology, since its presence in the market, strongly claims that, this is going to be "The Technology" of the future. Steady developments of WLAN technology are supporting two major causes: decrease of product price and increase of network speed, which are the reasons behind continuous increase in shipments of WLAN devices. Apart from current sectors, more and more new markets are opening up for this technology. Some of these are shipping and receiving area, distribution center, cafeteria, home, train, bus, airport, sport complexes, trade shows, coffee shops, etc. It is also under consideration, to make WLAN as a viable option to connect the developing nations to the developed part of the world, making the concept "Global Village" a reality. As its products are becoming cheaper, WLAN can be set up in different parts of these countries. These distributed networks can be connected to each other and also to rest of the world through satellite IP Network. This has huge market potential.

In the present market scenario Wi-Fi (IEEE802.11b) products are becoming increasingly popular and are looked upon as the driving force for future WLAN market. Taking into account the accelerated growth of WLAN market, several market research groups have estimated a five-fold increase in its market by 2005. This corresponds to a complete enterprise WLAN end-user revenue to reach about 3.2 billion dollars.

3.5. Technology Development Prospect Analysis

Future WLAN technologies should provide faster speed, better performance, more security and lower price. There are many areas requiring further developments:

WLAN will have higher speed. WLAN network data rates have increased from 1 to 11 Mbps for Wi-Fi known as IEEE 802.11b, referring to the 2.4-GHz. WECA(Wireless Ethernet Compatibility Alliance) is planning to test for Wi-Fi5 for IEEE 802.11a standard at 5-GHz. It provides up to 54Mbps and will provide greater system capacity. The 5.7-GHz band promises to allow for the next breakthrough data rate of 100 Mbps. Future generations of products should support both the two Wi-Fi products and make a smooth migration. IEEE 802.11g committee is trying to extend the 2.4-GHz technology to higher speeds.

To provide high-speed multimedia communications among different broadband core networks and mobile terminals ETSI's BRAN (Broadband Radio Access Networks) has developed HIPERLAN/ 2 as a flexible Radio LAN standard designed to provide high speed access (up to 54 Mbit/s at PHY layer) to 3G mobile core networks, ATM networks and IP based networks.

WLAN needs more security guarantees. 802.11a task group is addressing the WLAN security problems. Wired Equivalent Privacy (WEP) algorithm of 802.11 provides WLAN security by using secret key for authentication and encryption. However, such mechanism has a principal limitation: the standard does not define a key management protocol for distribution of the keys. Therefore, we need a key management protocol.

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Many new futures and applications will occur for WLAN. Many semiconductor and product vendors are driving to new architectures and new levels of integration to decrease the size, cost, power consumption of WLAN devices. At the same time, they are adding new futures and applications for various market demands. Researches are being performed to find ways to adjust 802.11 network parameters dynamically to improve throughput. Industry also needs a standard to addresses the tracking or management of mobile devices in its Management Information Base (MIB).

WLAN needs to improve its reliability. Reliability is also a challenge that many organizations face with WLANs. Currently, wired LANs are more reliable than WLANs. We need to address interference problems and enhance signal strength.

Efficient and concurrent uses of bandwidth. Wideband Orthogonal Frequency Division Multiplexing (W-OFDM) is a transmission scheme that enables data to be encoded on multiple high-speed radio frequencies concurrently. This allows for greater security, increased amounts of data being sent, and is claimed to be the industry's most efficient use of bandwidth. W-OFDM tries to solve the problem that Bluetooth and 802.11b networks have when operating in the same frequency range. It enables the implementation of low power multi-point RF networks that minimize interference with adjacent networks. This reduced interference enables independent channels to operate within the same band allowing multi-point networks and point-to-point backbone systems to be overlaid.

3.6. Interworking/Integration with IMT-2000

The issue of interworking/integration of WLAN can be analyzed from two angles. The first case is to establish a communication link between two devices one of which is in WLAN and the other one being in an IMT-2000 network. The second case is when a device in WLAN can smoothly move to IMT-2000 network and vice-versa, as shown in Figure 23. The first issue can be solved by using the Ethernet backbone between WLAN and IMT-2000 network by using suitable adapters in both sides, as shown in Figure 22. The second issue is still an open problem, though there are few solutions existing. As both technologies operate at different frequencies, the issue of seamless inter-system movement can be made possible by using a suitable interface which will take care of the frequency conversion and other issues while the mobile is moving from one network to the other. Birdstep Technology, a Norwegian software vendor, together with Ericsson has a solution which allows session transparent IP roaming for mobile users between UMTS and WLAN.

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Figure 22. Interoperation between WLAN and 3G

Figure 23. Inter-system movement between WLAN and 3G

Wireless ISPs can offer 2.5G/3G cellular networks and WLAN to mobile users. Some operators currently provide those services which simultaneously support multiple access technologies, i.e., IEEE 802.11 for high-bandwidth access in urban areas and GPRS for wide area access in rural areas. Each technology has its advantages and disadvantages. The 3G cellular systems are designed to carry voice, video and data simultaneously. It can provide 2 Mbps data rates for fixed users, 144 Kbps for fast-moving mobile users (such as in vehicles), and 384 Kbps for slower moving users (such as pedestrians). 3G cell can cover a very large area, but it works in a circuit-switched pattern. On the other hand, WLAN provides a much higher bandwidth. And it is works in an IP-alike pattern similar to wired Ethernet. However, WLAN operates within the local area, and can supports only best effort services. WLAN users share the unlicensed spectrum where few quality assurances can be guaranteed.

Currently, 3GPP is considering the interworking between WLAN and 3G network. Such an interworking should include security, mobility, QoS , charging, and also support different WLAN standards to interwork with 3G. More and more operators around

the world are evaluating and integrating WLAN into their current and next-generation networks. Ericsson and Telenor are devising a 3G/WLAN interworking solution, and developing standards for this integration.

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The interworking of services could result in numerous advantages, thus it can enable the operator to acquire more customers. However, Telenor has also identified two possible scenarios that could undermine the 3G/WLAN interworking business. First, the demand for WLAN services could fall away once 3G services are widely available. Second, the stand-alone public WLANs could take off and reduce demand for both 3G and integrated 3G/WLAN offerings.

3.7. Service Analysis

With the development of wireless industry and wireless application, a much wider variety of services will be available for WLAN.

Network adapter card. This is the primary function of WLAN devices provided for PCs, notebooks, and Access Points.

Convergence for voice and data networks. The wireless LAN infrastructure can be used for a mobile PBX handset. As voice, audio and video are shared among WLAN-enabled phones, MP3 players, web cameras, interactive TVs, etc, wireless applications will move beyond traditional computer networking.

Replacement of proprietary cables. Users can connect one device to another with one universal short-range radio link. For instance, Bluetooth radio technology built into both the cellular telephone and the laptop would replace the cumbersome cables used to connect among laptops, cellular telephones, printers, PDA's, desktops, fax machines, keyboards, joysticks and virtually any other digital device.

Portable access to wireless LAN. The increasing mobile users become WLAN candidates. Laptop and wireless NIC enable user to travel to various locations while remaining their access to networked data.

Multimedia over wireless networks. Wireless packet-switched LAN deal with real-time services like voice and video.

Wireless remote data access. People can access data or files stored on servers at home of office wherever he is physically be. The servers function as Internet data/file station.

Data Backup. Mission-critical applications can be implemented with a wireless backup in the case of malfunctions in the wired infrastructure.

3.8. Network Design Plan Analysis

There exist different alternatives for Wireless LAN setup. This can be simple or complex depending on the number of expected users, area of coverage, quality of service, service types. The network topology for WLAN can broadly be classified into the following two types [71]:

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Ad-Hoc WLAN. This topology is very simple. It consists of few devices (desktops, laptops etc) each equipped with wireless adapter cards (a NIC card such as an ISA or PCMCIA card installed through a PC card slot). This does not require a central server (or administrator) or preconfiguration, so long as all the devices in the network are within each other's range. This is not connected to the outside world, just that these devices in the network are connected to each other, as shown in Figure 24. Hence this has limited access and use. This type of network is also called wireless peer-to-peer network. This is very suitable for group meeting, conference etc. The range of this network depends on the products used, and data rate asked for. Table XIII shows possible ranges for different data rates for 802.11b products.

Figure 24. Ad-hoc WLAN

Table XIII. Ranges possible for different data rates

RANGE DATA RATE

100FT 11MBPS

150FT 5.5MBPS

300FT 2MBPS

Client-Server based WLAN. As already discussed ad-hoc WLAN has limited use and is confined to a small region. But most of the time a WLAN is implemented as a complementary extension to existing wired client server network. In such scenarios the devices in the WLAN are capable of getting connected to the outside network through wired backbone networks using Access Points (APs) along with a seamless

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connection among themselves (either a direct wireless connection or through one or more APs or Extension Points (EPs), as shown in Figure 25). AP acts as a connection point between WLAN and existing wired network (which is high speed Ethernet in most cases). Each AP effectively doubles the network range (compared to peer-to-peer network) at which devices can communicate. Each AP can accommodate a specific number of clients depending on nature of transmission involved, required QOS etc. At present, many real-world applications exist, where a single AP serves from 15-50 client devices [71]. These APs have finite range (in the order of 500 feet in indoor environments and 1000 feet outdoor environments, which put a limit on the coverage of network using one AP. To extend the area of coverage, multiple APs are used and to ensure seamless roaming the coverage areas of different APs are made to overlap. This type of network configuration is used in offices, educational institutes, warehouses, etc, where the coverage area is large. Up till now, we are considering that each AP is connected to the wired network, which is not a good and practical option always, especially in cases where the area to be covered by such a network is far from the wired network. To take care of such cases, Extension Points are used, as shown in Figure 25. EPs look and function like APs, but the difference is that they connect to APs not to the wired network. They extend the network by relaying the signal from a client to an AP or another EP.

Figure 25. Client-server based WLAN

Although network design requirements, building environments, building materials vary much, and different equipment vendors’ products have different parameters, there exist some common principles in WLAN design, for both IEEE802.11 and HiperLAN.

The overall coverage area and the throughput of the WLAN system are the two basic categories of performance metrics should been studied very carefully.

The overall coverage area is the region in which mobile users can receive signals from access points in the WLAN system. It can be evaluated in terms of received signal

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strength intensity (RSSI). Measuring RSSI could be performed by system monitoring software coming from equipment vendors. There also exist some simulation software to simulate and predicate the expected coverage area. After comparing the measured data and predicated data, WLAN architects may need to re-locate some access points to fulfill the design requirement and reduce signal leakage from the defined coverage area.

Throughput defines how quickly the mobile users can send and receive information over the WLAN. Measurements data should be collected from different locations of the coverage area. In most case, WLAN architects may establish a client-server communication link via TCP connection, to identify throughput at any location. Although there are some impacts (such as overhead of protocol, other traffic on the network), such data could tell what a user may experience in the actual network. The measure should be taken at any region during various periods, such as normal network traffic, a much less one and a much exceeding one. And then make an average throughput. The impact of loading on the access points needs to be performed too.

Implementations of handoff and dropping are the responsibility of manufacturers, since they vary according to different equipments.

A certain level of received signal strength must be present to enable a communication between mobile users and access points. In practice, this level may be –90dBm, and may vary among different manufacturers. Considering the impact of loading, increased traffic will shrink the service area, so this value may be changed to a increase signal strength of –75dBm.

Security issues need be considered carefully. Signal leakage is a major concern, and present a potential security threat. Signals transmitted in a WLAN can penetrate through building walls and floors. WLAN architects should keep the access points away from windows, thin outside walls and other building materials, which could be penetrated by signals easily and thus result in risk of security.

Currently, the traffic engineering issues are under research. Some projects plan to exploit the potential of IP-based wireless mobile multimedia networking for WLAN. One major purpose is to develop a set of enhanced/new IP-based techniques to support mobility and soft-guaranteed QoS for WLAN. They should also develop location-aware and QoS-aware application services for mobile users. UMTS Release 5 will add additional rationale for unique addressing and predictable performance delivery of realize wireless multimedia contents for WLAN.

Wireless operators should provide transactional and multimedia environments for their customers with performance guarantees, especially for those time-critical and real-time applications. IPv6 has mobile IP concept. The IPv6 standard also use the Flow Label in header to enable QoS, and supports traffic engineering of flow in a MPLS (Multi Protocol Label Switching) fashion. So, both IPv6 and MPLS techniques should be utilized in the traffic engineering of WLAN. The combination of Differential Services (DiffServ), MPLS and proper network traffic engineering could provide application specific QoS.

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In order to offer dual IPv4 and IPv6 solutions, NAT-PT (Network Address Translation-Protocol Translation, RFC 2766) will be used to connect IPv6 mobile terminals and IPv4 ones during early deployment phase.

3.8.1. Description of Possible In-Building Network Design Alternatives using the WLAN Technology and possible external interference/interoperability

WLAN can be deployed inside of a building using the Client-Server based WLAN Configuration. In most cases one or two APs will be sufficient to cover each floor and then different floors can be connected through EPs. These APs can be connected to the existing wired infrastructure of the building, which is high speed Ethernet in most cases.

There exist many sources of potential interference, to in-building WLAN, because there are many more devices which also operate in the same ISM band used by the WLAN Technology. Microwave oven, which operates at 2.4GHz, is potential source of interference for WLAN devices, operating around same frequency. Also some cordless phone work at 5GHz, which are sources of interference to the WLAN devices designed to operate around 5GHz U-NII (Unlicensed National Information Infrastructure) band.

The interoperability issue can be looked upon from two angles: first is interoperability between WLAN devices from different vendors and then interoperability between different technologies (which exist or going to come in near future). The first issue is being taken care, by standard bodies and manufactures, making sure that products from different vendors can work with harmony. The second issue is still under research, with few existing solutions, as discussed in Section 3.6.

3.8.2. Coverage and Capacity Analysis as a part of Network Design Process

If the coverage area is small (less than 500ft in radius) and also only communication between the devices in the network is needed, ad-hoc WLAN can be used. Here the number of users will be limited by factors like required QOS, service types, and so on. But in most cases the Client-Server based WLAN is preferred. This can give coverage to a much bigger area, using appropriate number of APs and EPs. Typically one access point gives coverage of around 100m in 802.11b standard and can handle around 15-50 users [71].

3.9. Network Deployment Technology and Premise Network Security Plan

Compared to wired system, signal communication security over WLAN is an obvious challenge, since unauthorized eavesdroppers and hackers can access the data communicated over WLAN even they are not in the physical proximity. There are a set of secure WLAN solutions available for different customers to choose according to their own network.

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802.11 APs can be cond with a service set identifier (SSID), but it is not enough for security (???). For most enterprises, they can use VPN technologies built into or on top of WLAN products.

The wired equivalent privacy (WEP) option of 802.11 standards or the common 128-bit extension of WEP is useful for many WLAN implementations. WEP technique uses shared keys and a pseudo random number (PRN) as an initial vector (IV) to encrypt the data portion of network packets, but does not encrypt 802.11b WLAN network headers. Each station (clients and APs) has a number of keys to encrypt the data before it is transmitted through the airwaves. Each station can only receive a packet being encrypted with its appropriate key. Without proper key, the packet will be discarded by the station and never delivered to the host. Some vendors also provide key servers to implement centralized key management, such as Cisco.

The Internet Protocol Security (IPSec) specification defined by the IEEE is the most widely used mechanism or securing VPN traffic. IPSec can use DES, 3DES and other bulk algorithms for encrypting data, keyed hash algorithms (HMAC, MD5, SHA) for authenticating packets, and digital certificates for validating public keys. IPSec includes 3 main elements: Authentication Header (AH) Encapsulation Security Payload (ESP) Internet Key Exchange (IKE).

For business networks, a VPN solution for wireless access is the best security measure for WLAN. A VPN is a private network that creates a secure tunnel in which data can flow. Already widely used for remote access, VPNs employ various security mechanisms to ensure that only authorized users can access the network and that the data cannot be intercepted.

The combination of VPN and, IPSec is an ideal solution for today’s wireless networking security needs [90]. With this solution, wireless APs are simply configured for open access with no WEP encryption, because the VPN channel handles security. VPN servers provide authentication and full encryption over the WLAN. The use of digital certificates offers strong authentication, and even in the event of unauthorized access, the WLAN communications cannot be read or used.

Bluetooth also uses keys to encrypt data. There are several kinds of keys in the Bluetooth system to ensure secure transmission [72]. The most important one is the link key, which is used between two BT devices for authentication purposes. There are four types of link keys: unit key, combination key, master key and initialization key. All of them are 128-bit random numbers and are either temporary or semi-permanent. Encryption key can be derived by using link key. This secures the data of the packet and is regenerated for all new transmissions. Each time encryption is needed, the encryption key will be automatically changed.

Even if there is not a key, there is the PIN code, which can be used to help identify devices to each other. It is a user-selected or fixed number, normally 4 digits in length, but it can be anything between 1 to 16 octets. The user can change it to add security to the system.

Many vendors have their own optional security systems. For example, Ericsson provides a firewall unit attached to each radio access point to forces every wireless user

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to authenticate his or her identity, besides encrypting any data exchanged over the air by means of IP-layer encryption. The firewall unit prevents unauthorized users from accessing the LAN or from eavesdropping traffic that is broadcast in the corporate environment. To achieve this, the firewall unit uses a powerful encryption scheme that complies with the IPSec standard—set by the Internet Engineering Task Force (IETF)—which is designed to provide a security level sufficient even for companies with very high security standards.

Some operating systems have upgraded to simplify to address security for the WLAN. For example, Microsoft Windows XP operating system incorporates the new 802.1x-standard VPN security technology for authentication and encryption key exchange, so it may simplify the security decision-making [73].

3.10. Network Deployment Scenarios

WLAN deployment is easy compared to other types of networks. There are different types of topologies which are suitable for different applications. Out of all these, the following two configurations are most widely used.

Peer-To-Peer WLAN. This is the most basic form. It is also termed as an ad-hoc topology in which a LAN is created solely by the wireless devices themselves, with no central controller or access point. Each device communicates directly with other devices in the network rather than through a central controller. So such network just requires PCs equipped with wireless adapter, enabling the PCs to share resources with one another, as shown in Figure 24.

Client-Server based WLAN. In a Client-Server based WLAN, users are benefited from extended range. They also get connected to the outside networks through Access Points. The APs are connected to the wired backbone as a server to provide resources for users (as shown in Figure 25). The number of users supported varies according to different technologies and different kinds of transmissions. The typical number ranges from 15 to 50. In this configuration EPs are used to extend the network coverage to locations which are far away from the wired backbone network.

In-Building WLAN can be arranged in a peer-to-peer (ad hoc) topology using only client adapters. A wireless LAN transceiver acts as a hub to bridge between wireless and wired networks. When the range is enlarged, access points can be incorporated to act as the center of a star topology and function as a bridge to an Ethernet network. Within a building, WLAN support both mobile and connected computer. Users can move freely within a facility while maintaining access to the network.

Networks located in buildings with miles from each other can be integrated into a single local-area network with a wireless bridge, thus from a building-to-building WLAN. This is much more convenient than bridging between buildings in wired way in case of obstacles such as freeways, lakes, regulations of local governments. It is also economic to eliminate the fees of leased line. Immediate and easy installation is another benefit.

For HIPERLAN/2, it relies on cellular networking topology combined with an ad-hoc networking capability. It supports two basic modes of operation:

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Centralized mode. This mode is used in the cellular networking topology where each radio cell is controlled by an access point covering a certain geographical area. A mobile terminal communicates with other mobile terminals or with the core network via an access point. This mode of operation is mainly used in business applications, both indoors and outdoors, where an area much larger than a radio cell has to be covered.

Direct mode. This mode is used in the ad-hoc networking topology, mainly in typical private home environments, where a radio cell covers the whole serving area. In this mode, mobile terminals in a single-cell home "network" can directly exchange data.

3.11. Network Cost Analysis

It is very important to know the cost equations of a particular network type before going for its deployment. In fact, in the present scenario this has more practical meaning as there exist multiple options to satisfy one particular type of network needs. For example, to set up a small range we can either go for WLAN or Bluetooth or can decide to add our area to the larger cellular network using repeaters etc. WLAN is proved to be cost effective compared to its wired counter-part. Even though the initial cost of WLAN is more compared to the wired one, once installed it has little management, expansion, trouble-shooting and relocation expenses. Hence, comparing the overall cost involved WLAN has been proven to be cheaper compared to the wired alternative.

3.11.1. Identification of the cost of various components involved in Wireless LAN setup

Different components of WLAN are Access Points, PC card, PCI Adapter, Wireless Bridge. These components are manufactured by different vendors, e.g., 3Com, Apple, Avaya, Cisco, IBM, Nortel, Nokia, Symbol, Zoom, and many more.

The following table gives a brief price comparison of there various components [74].

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Table XIV. Price comparison of different components of WLAN provided by major suppliers

Vendor Name Access Points PC card PCI Adapter Wireless Bridge3Com $545.00 $169.00 $199.00 $1095.00Apple $301.00 $99.00 -- --Avaya $685.00 $144.00 $59.00 --Cisco $717.00 $193.00 $269.00 $458.00

Compaq $729.00 $166.00 $208.00 --Ericsson $929.00 $186.00 -- --

IBM $1015.00 $182.00 -- --Nokia $751.00 $212.00 $199.00 --Nortel $1065.00 $289.00 -- $638.00

Symbol $1025.00 $181.00 $271.00 $655.00Zoom $410.00 $136.00 $136.00 $1888.00

3.11.2. Analysis of the total Economics Involved in Deploying and Running such WLANs

In most cases the initial installation cost for the WLAN is more compared to an alternate wired network, but the running cost for the WLAN is much less. Because of this, the payback period of this is much less compared to wired one. Survey across industries using WLAN has shown that the typical payback period in case of WLAN is around one year [75]. This survey has also shown that on average the cost per user for WLANs is around $4,550.00. Market analysis has shown that WLANs are extremely cost-effective for organizations using this technology for large scale network deployment. For example organizations that implemented WLAN for around 300 users has been benefited from annual savings of up to $4.9 million which corresponds to per user saving of $15,989.00.

In some cases even the initial installation cost of WLAN has been found to be less than the wired alternative. University of Akron, covered their four-story library with WLAN with a total cost of $80,000, using Cisco Airnet 350 series and the estimated cost for wired network for that was $800,000 [76].

All these shows that along with other advantages WLAN alternative is also cost-effective. With the technology developing and more competition in market, WLAN products are becoming cheaper, which will make their deployment even cheaper.

3.12. Conclusions

In this report, the technologies of WLANs were comprehensively investigated. The issues such as interference and environmental problems were also analyzed. The network deployment scenarios and design plans were briefly discussed. Moreover, the market size, market penetration, and costs of WLANs were addressed. Because of its advantages, WLANs will be an important part of next generation wireless networks.

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4. Wireless PBX

4.1. Overview

A Private Automatic Branch eXchange (PABX or PBX) is a private telephone system within an enterprise that switches calls between the enterprise users on local lines automatically [84]. It allows all users to share a certain number of external phone lines. The PBX is owned and operated by the enterprise rather than the telephone company. Most mid-sized and large organizations use a PBX because it is much cheaper than connecting an external telephone line to each telephone in the organization. A wireless PBX (WPBX) does not function as a stand-alone PBX. Instead, a WPBX works together with a conventional wire-line PBX. It provides call forwarding to extensions, accessing voice mail, intelligent switching and end-to-end transmission. WPBXs enable users to carry their telephone handsets inside the building and be accessible wherever they are [85]. A WPBX system can be integrated with a wireline PBX to provide mobility capability to a conventional wire-line telephone system. When integrated into an organization's PBX, wireless service allows the user to use a portable handset as a wireless extension to his desktop telephone. This allows users to keep the same extension number, and features of their desktop handsets with the freedom, and convenience of a mobile phone.

A WPBX system typically involves three components: control unit, base station and wireless handset. The control unit functions as a gateway between the wireless system and the wireline PBX systems. The base stations of the WPBX are located within the building to relay wireless signals through antennas to wireless handsets. The wireless handset is a small digital telephone emulating the feature functionality of the PBX's traditional desktop phones. Wireless PBX systems provide seamless communications throughout the building, even in places like elevators, tunnels, or parking lots where the signal reception is poor. Wireless PBX users benefit from the same digital voice quality as conventional PBX users.

In this chapter, the technology, the characteristics, and the network deployment strategies of WPBX systems will be presented.

4.2. Technology Analysis

Wireless PBX systems provide users with a high degree of mobility. The wireless handsets can be used anywhere within the coverage of the system's base stations, and provide the voice quality of the wireline telephone network. The major components of wireless PBX systems such as base stations and antennas must be strategically placed within the coverage area to ensure seamless coverage and high-quality service.

4.2.1. Current Technology of WPBXA WPBX system consists of the following three components:

Control unit: The control unit routes all incoming and outgoing calls between the wired telephone switch, and the base stations. The control unit can be co-located with

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the telephone switch or connected to the switch with a twisted-pair wiring or optical fiber from several thousand feet away. Optional battery backup is usually available, permitting uninterrupted operation in case of a power failure. System control, management, and administration functions are provided by an attached terminal that is password protected to guard against unauthorized access. Since the control unit becomes an integrated part of the company's existing telephone system, users have access to most of its features through their portable phones. Users can even set up conference calls, forward calls, and transfer calls. Depending on the wireless system installed, up to several hundred handsets can be supported by a single WPBX. Additional control units can be added as necessary to support future growth.

Base station: The base stations are placed strategically within an enterprise to relay wireless signals via antennas to the wireless handsets in the coverage area. They are typically mounted on the ceiling or walls, and are connected by twisted-pair cables to the wireless controller. They send and receive calls between the wireless handsets and the control unit. As the user moves from one cell to another, the base station hands off the call to the base station into which the user moved. When the new base station is able to receive the signals from the user's handset, the channel of the previous base station becomes idle, and it can be used to handle another call. To facilitate the handoff process, each base station may be equipped with dual antennas to provide antenna diversity. Antenna diversity is used in narrow-band systems to deal with multi-path fading. Multi-path fading is a serious problem also for the in-building wireless systems because of the reflections from walls, furniture, etc. Antenna diversity improves signal detection, enabling the handoff to occur in a timely manner. The base station accomplishes this by sampling the reception on each of its antennas, and switching to the one that offers the best reception. This process is continuous, ensuring the best voice quality throughout the duration of the call. Some vendors offer optional external antennas for outdoor coverage or directional indoor coverage. Also, the use of spread spectrum technology by some vendors virtually eliminates the multi-path problem. In densely populated areas, the number of base stations can be increased to handle a greater number of calls.

Wireless handset: The wireless handset is a pocket-sized digital telephone that emulates the feature functionality of the PBX's traditional desktop phones. They can also be used independently by assigning telephone numbers of their own. Typically, each wireless handset has a unique identification number that must be registered with the control unit. This allows only authorized users to access the in-building wireless communication system. If the handset is assigned the same number as the user's desktop phone, both phones ring for an incoming call. The user can even start a conversation on one phone and switch to the other. If the wireless handsets and the desktop phones have different numbers, each can be programmed by the user to forward incoming calls to the other. In either case, the wireless handsets must be registered with the control unit. If the handset is equipped with a liquid crystal display (LCD), the unit can also be used to retrieve e-mail messages, faxes, etc. However, this requires a separate messaging interface or access to the PBX's integrated messaging capability through a digital station interface.

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4.2.2. The Frequency BandsIn-building wireless communications systems currently operate in several frequency bands. These include the 800MHz band used for narrow-band cellular service, the 900MHz band currently used for in-building systems, the 1920MHz-1930MHz band used for unlicensed Personal Communications Services (U-PCS), and the 2.4GHz band utilized by some vendors to integrate LAN and the wireless voice communication systems.

Systems operating in the 800MHz, the 1900MHz, and the licensed PCS bands can be frequency-coordinated with a cellular carrier to offer the advantage of roaming between the corporate network and the public cellular network. Thus, the same mobile handset can be used at work, on the road, and at home. However, this advantage is not available to U-PCS wireless solutions, because U-PCS systems operate with a completely different technology that is incompatible with any licensed service. Other wireless systems use the 902MHz-928MHz frequency band that is intended for wireless communication within very narrow geographical areas. Even if wireless systems use the same frequency band, they may not be interoperable because of different underlying transmission technologies like CDMA or TDMA. In fact, most in-building WPBX systems are incompatible.

4.2.3. Products by Leading Vendors

4.2.3.1. Link WTS by SpectraLink

The Link WTS (Wireless Telephone System) [86] connects to a facility's existing telephone system. A network of base stations is installed throughout the facility. The call center mobility is supported via SpectraLink's ccLink WTS. The technical specifications of this product are as follows:

Frequency band: 902MHz - 928MHz

Access technology: TDMA / Frequency-Hopping Spread Spectrum

4.2.3.2. Companion by Nortel

The Companion [87] portfolio of in-building wireless communications solutions provides cost-effective, mobile communications at work. It enables users to be anywhere within their workplace for both voice and WCTI data communications. The technical specifications of this product are as follows:

Frequency band: 1920MHz - 1930MHz

Access technology: FDMA / Time Division Duplex (TDD)

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4.2.3.3. MD110 by Ericsson

The MD110 [87] is a full-scale cordless PBX, supporting both physical and functional integration of DECT (Digital Enhanced Cordless Telecommunications) in a fully modular and distributed business communications system. The technical specifications of this product are as follows:

Frequency band: 1900MHz

Access technology: TDMA / TDD

4.2.3.4. NEAX WCS by NEC

NEAX WCS (Wireless Communication System) [89] provides the employees of an organization with a full-featured wireless extension to their desktop telephones. Access to advanced telephony features such as voice mail, call forwarding, and conferencing can also be provided. The technical specifications of this product are as follows:

Frequency band: 1920MHz - 1930MHz

Access technology: TDMA

4.3. Characteristic Analysis

There are various types of WPBX systems available in today's market. However, WPBX systems can be mainly classified according to two criteria: operating frequency and access technology.

WPBX systems are based on the following access technologies:

CDMA: CDMA is a spread spectrum technology that assigns a different code to each wireless phone call. The CDMA-based systems recognize each call by its code and process the call. The same frequency band is shared between all users simultaneously.

FDMA: FDMA works by allocating a separate frequency band to each user to support multiple, simultaneous wireless access. Several WPBX products, like Companion by Nortel, are based on this access technology.

TDMA: TDMA works by splitting each frequency band in the time domain into multiple time slots. This access technology is adopted by many vendors such as Ericsson, NEC, SpectraLink, Avaya, etc.

The WPBX systems operate in the 800MHz band, the 900MHz band, the 1920MHz-1930MHz band (U-PCS), and the 2.4GHz band. The following are the characteristics according to the frequency band used:

800MHz and 1900MHz: Systems operating in these bands can be coordinated with a cellular carrier to offer roaming between the corporate network and the public cellular network. This enables the same wireless handset to be used everywhere.

900MHz and 2.4GHz: Systems operating in these frequency bands may cause interference problems with other equipment operating in the same frequency bands.

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1920MHz-1930MHz: The U-PCS frequency band is allocated by the FCC. Systems operating in this frequency band cannot support roaming between the corporate network and the public cellular network. U-PCS systems do not encounter interference problems because this frequency band is allocated specifically for in-building wireless use.

4.4. Main Target Market Deduction

4.4.1. Current Wireless PBX Market SegmentsWireless PBXs have been on the scene for almost ten years. They are available from a wide range of suppliers such as Ericsson, Lucent, NEC, Nortel, Siemens, and Spectralink. In the year 2000, combined sales of WPBXs and wireless key systems reached $275 million. In some European markets, for example, in France and Italy, more than 10% of the new PBX stations are wireless; in Finland, Sweden and Denmark, WPBX stations account for more than 25% of the new station shipments [77]. However, in United States, wireless communications within the office, in particular wireless options for the PBX, have not taken off. Less than 5% of the new PBX station shipments are wireless.

There are several reasons for the relatively low shipment in the U.S. like pricing, technology, customer awareness and education. Among these, pricing is the main reason. The cost per user for a WPBX system is sometimes three times of a conventional wired desktop phone. However, since in-building wireless communications is growing rapidly, ample opportunity exists for manufacturers with innovative products and applications. Customers want cordless telephones, full roaming, and seamless handoff during calls. Multiple product lines, broader distribution channels, and increased roaming capability are the highlights of wireless vendors' current market strategies [80].

4.4.2. Market ForecastCurrently, the growing market trends are:

Wireless communications expansion outside the building.

Cellular communications expansion inside the building.

Wireless IP-based systems running over enterprise LANs for adding wireless communications to existing data network infrastructure.

Mobile data and voice communications from handheld devices such as pagers and personal digital assistants using WAP (Wireless Access Protocol) technology.

The market for WPBXs is changing rapidly. It is forecasted that by 2005, the market will have exploded to almost $840 million, over a factor of three to one from the base year of 2000 [78].

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4.5. Technology Development Prospect Analysis

As the wireless in-building communication becomes more common, it is expected that the WPBX technology will have the following advancements in the future:

Convergence of telephony with IP

There is an increased demand from employees who are mobile and require both wireless voice and data communications to perform their jobs effectively and productively. Wireless IP-based systems running over enterprise LANs for integrating wireless telephony with the existing data network is the trend of technological development. Enterprise networks will evolve to an IP-based architecture that can handle voice, video, and data. Considering the investment in wireless LANs, it is more economical for enterprises to overlay voice over the wireless LAN rather than installing a dedicated, WPBX. Because voice and data traffics are combined on a single network, the quality of the voice call should be maintained while data performance is kept high.

Currently, both SpectraLink Corporation [81] and Symbol Technologies [82] have released voice-over-WLAN products, named NetLink Wireless Telephone System and NetVision Phone System, respectively.

Integration of Enterprise and Cellular/PCS Systems

This solution is for both on and off-premises communications. It relies on cellular technology. The key to this solution is to program cellular service to function like a PBX. Compared to conventional WPBXs, users can save money because they need only one handset that can be used both inside and outside the office. In addition, users no longer need multiple business phone numbers.

Ericsson and AT&T are working to achieve this goal. We will discuss the services provided by this solution in detail in the next section.

Compatibility

Currently, WPBX portable telephones are specific to each system. Although different systems may operate in the same frequency range, each one conforms to different wireless transmission standards. Even systems from the same vendor may not be compatible. For example, Lucent's Definity Wireless System can not interoperate with its TransTalk Wireless System. The former operates in 1910-1930MHz frequency range, while the latter operates in the 900MHz range. Interoperability among in-building WPBX systems is one of the future research topics.

Telecommunications Industry Association (TIA) has a standard for IP telephones [79]. It specifies requirements for the interoperability, acoustic performance, supplementary services support. It also provides specifications for safety, electromagnetic compatibility, and environmental performance of Voice-over-IP Feature Telephones.

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4.6. Interworking / Integration Technology Analysis with IMT-2000

The International Telecommunications Union (ITU) defined the world standard IMT-2000 (International Mobile Telecommunications). IMT-2000 now consists of five standard committees:

IMT DS, widely known as UTRA (UMTS terrestrial radio access) based on W-CDMA

IMT MC, widely known as cdma2000

IMT TC, also called TD-SCDMA

IMT SC, also called UWC-136 (EDGE)

IMT FT (DECT)

The DECT (Digital Enhanced Cordless Telecommunications) standard is one of the core building blocks for 3G communications. It will play a central role in the convergence of fixed and mobile communication services. DECT is designed for short-range use as an access mechanism to the main networks. It offers cordless voice, fax, data, and multimedia communications, wireless local area networks, and WPBX. It supports applications like single-cell domestic cordless phones, multi-cell WPBX systems, and wireless local loop systems for fixed users.

Wireless PBX technology works efficiently with the DECT technology to cover large business complexes with a cellular structure using small cells. A multi-cell DECT WPBX system can form a seamless mobile communications environment. The DECT digital radio technology, designed for indoor coverage, can handle a large number of users getting both voice and high-speed data services with a single infrastructure. Wireless PBX systems will continue to inter-work with the DECT technology to follow the evolution of 3G wireless networks.

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IP Core Network

BTS BTSBTS

PBX

In-building WPABX system

BTS

3G network

IP Core Network

BTS BTSBTS

PBX

In-building WPABX system

BTS

3G network

Figure 26. WPBX inter-operation with 3G systems

Figure 26 shows how the in-building wireless PABX system can be inter-operated with 3G network system. The in-building WPABX system is connected through PBX to the IP core network. 3G network is also connected to the IP core network. When a user moves from 3G network to a building equipped with WPABX system, a smooth roaming can be provided via the BTSs in the building WPABX system which is connected through PBX to the IP core network. Thus, the users getting various services in 3G networks will be able to get the same services within the buildings equipped with WPABX system which has inter-operability with 3G systems.

4.7. Service Analysis

A WPBX adds the mobile capability to a conventional wireline telephone system. When integrated into an organization's telephone system, the WPBX enables users to use a portable telephone as a wireless extension to their desktop telephone. This allows users to keep the same extension number and features of their desktop handsets with the freedom and convenience of a mobile phone. This is called "on-site mobility". There can also be significant savings in wiring in areas that are difficult or expensive to wire, like elevator and parking lots.

Wireless PBX systems also allow the integration of mobile cellular services and local cordless PBX services. When the users are in their offices, their mobile phones

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serve as personal extensions to the company's PBX. Incoming calls to users are handled by the company's PBX system. When the users leave their offices, the phones function as ordinary mobile phones. Any incoming calls to users are routed to the mobile phones via public wireless network. This service allows users to carry just one handset with one number no matter where they are. It allows immediate and direct communication. This is called "off-site mobility". Off-site mobility eliminates delays and allows users to work away from their desks without fear of missing critical calls. It gives users great mobility and versatility. This service can increase the productivity in a company, reduce phone tag and paging load.

The integrated system also has the capability to map the four-digit PBX extension to users' cellular phones. It gives the users ability to call or be called by others in the office using just assigned extension numbers, regardless of their location. For example, if a user at home wants to get in touch with a colleague, he just needs to dial his colleague's four-digit company PBX extension number. If his colleague is out of the office, the call will be automatically relayed to the other party's wireless phone via the public network.

The improved intelligent billing service is another advantage of the WPBX system in addition to the flexible mobility capability. Calls within the company and calls using the PBX extension numbers are billed at a lower cellular rate for on-site services. For example, AT&T offers the Enhanced Personal Base Station (EPBS) option for its cellular network that provides personal base stations for the home. The base station consists of a small transceiver mounted on the exterior wall of the customer's premise. It communicates via the digital PCS cell sites to AT&T central offices. Users pay a flat monthly fee for the privilege of using their cellular phones at home, on the road, and at the office. When the user is on the road, calls are billed at regular cellular rates. When he arrives at work, the network automatically launches a cellular connection to the company's PBX. Calls are then billed at the company's on-site telephone rate.

4.8. Network Design Plan Analysis

Currently, there are three technology options for wireless telephone solutions depending on the services described in the previous section [80]:

Fully integrated in-building wireless voice systems from traditional PBX vendors, like Ascom, Avaya, Ericsson, Nortel Networks, NEC, and Toshiba, and adjunct systems from vendors like SpectraLink.

Cellular/PCS-based systems, like Ericsson Mobile Advantage and AGCS ROAMEO, which support both public cellular and in-building wireless calls from the same handset.

The 802.11-based networks, which integrate wireless voice communications with LAN infrastructures to support both voice and data communications over a single backbone. Examples are NetLink WTS from SpectraLink and NetVision Phone System from Symbol Technologies.

There is no interoperability among in-building wireless voice systems from different vendors, except those systems that support the 802.11 standard for wireless voice communications.

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Integrated wireless solutions have the wireless radio controller installed in the same cabinet with the telephone switch. Usually, the integrated wireless telephone solution is manufactured by the vendor of the switch. Wireless adjunct systems from third-party vendors, such as SpectraLink Corporation and Symbol Technologies, typically locate the radio controller near the telephone switch, where it is directly connected to the base stations.

In this section, we focus on the first and third network design options, i.e., integrated in-building wireless telephone system and 802.11-based voice/data communications. From the end user's perspective, these two options provide the same functionality and quality. The choice is based on the customer's infrastructure and management preferences. The first option is an economical choice for customers who need to implement a wireless voice-only solution. Because 802.11 is an international standard for WLANs, the third option is good for wireless telephony throughout the global enterprise. We choose the products from SpectraLink as examples to explain the network design alternatives. Network design plans from other companies are similar.

4.8.1. Wireless Telephone Solution for Mobile Communication in the Workplace

4.8.1.1. System Overview

The Link Wireless Telephone System (Link WTS) architecture developed by SpectraLink Corporation [81] is shown in Figure 27. By placing small digital radio transceiver systems called base stations throughout a building or campus, users can initiate and receive calls anywhere in the facility using portable wireless telephones. The wireless telephone system attaches to a local PBX, key system or Centrex service. Since all calls are routed through the local phone system, there are no air-time charges or monthly usage fee.

Figure 27. Link wireless telephone system architecture

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The Link Wireless Telephone System includes:

Master Control Unit

The Master Control Unit (MCU) is a compact and modular unit that connects the telephone switch to the wireless telephone system using digital and/or analog line interfaces. The digital interface technology makes advanced switch features available to wireless telephone users, such as multiple line appearances, and display features.

Base Stations

The base stations are fixed transceivers that provide radio coverage throughout the workplace. They are small and lightweight, and can be installed in a variety of locations. The base stations are placed to provide adequate overlap and coverage.

Wireless Telephones

The Wireless Telephone is specifically designed to meet the requirements of in-building mobile communications.

4.8.1.2. Capacity and Coverage

SpectraLink offers Link 150 MCU and Link 3000 MCU. The system capacity and area coverage of these two systems are listed in Table XV.

Table XV. System capacity and area coverage

MCU System Capacity Area Coverage Max. CoverageWireless

TelephoneBase Stations Simultaneous

CallsLink 150 64 16 32 1,500,000 sq. ft.Link 3000 3,200 1,000 1,600 100 million sq. ft.

4.8.1.3. Interfaces

Open Application Interface

SpectraLink's Open Application Interface (OAI) is an integrated applications programming interface for computer telephony integration. It enables third-party computer applications to communicate with the Link WTS. It is the information access for the WPBX system. This feature allows users to view and respond to alphanumeric messages that are displayed on the wireless telephone. Message exchange occurs in real-time. The benefit of the OAI is its ability to quickly respond to non-voice messages, enabling fast decision-making and increased productivity for wireless telephone users.

The OAI allows the application program to access the status and control features for the display, keypad, icons, and ringer of the wireless telephone. Using the OAI, the wireless telephone allows the user to receive and retrieve important information from external systems.

Digital Switch Integration

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SpectraLink offers digital interfaces to a wide variety of PBXs and key telephone systems. The LinkPlus technology implements digital interfaces by emulating proprietary digital telephone sets. It makes switch features available to wireless telephone users without requiring any switch upgrades or enhancements. Mobile users have the ability to screen calls, access multiple lines, and use switch features.

LinkPlus allows the WTS to connect to the host PBX or key system using the same digital station ports that are used for digital wired telephone sets. For each type of PBX or key system, the WTS emulates all the codec, display, control, and signaling functions of a specific proprietary digital telephone set.

4.8.2. Wireless Voice and Data Solutions Over Local Area Networks

4.8.2.1. System Overview

The NetLink Wireless Telephone System (NetLink WTS) by SpectraLink operates over IEEE 802.11-compliant WLANs, providing both voice and data communications over a single integrated network. The system architecture is shown in Figure 28. The NetLink WTS uses Voice-over-IP (VoIP). To ensure excellent voice quality, SpectraLink developed a voice prioritization mechanism for 802.11 access points and Wireless Telephones. Based on the IEEE 802.11 standard for wireless LANs, the NetLink WTS provides a single solution for wireless telephony throughout the global enterprise.

Figure 28. NetLink wireless telephone system architecture

The NetLink Wireless Telephone System includes:

NetLink Telephony Gateway

The NetLink Telephony Gateway provides an interface between the Ethernet LAN and the host telephone switch using digital and/or analog line interfaces. It manages

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all wireless telephones on the network and converts from voice packets on the LAN to voice circuits on the PBX. The NetLink telephony gateway also supports H.323-compliant clients, allowing third-party wireless devices to initiate and receive calls through the host telephone switch.

NetLink Wireless Telephones

The NetLink Wireless Telephone is specifically designed to meet the requirements of mobile workplace communications. It is available in both frequency hopping and direct sequence spread spectrum 802.11 versions.

Wireless LAN Infrastructure

Wireless LAN access points receive IP voice packets from wireless telephones and forward them to the telephony gateway over the wired LAN.

4.8.2.2. Capacity and Coverage

Each NetLink 150 telephony gateway supports 16 users and 8 simultaneous calls. Up to 4 gateways can be used on a network, maximizing the system at 64 Wireless Telephones and 32 simultaneous calls. Adding more wireless telephones to a WLAN increases the bandwidth requirement because of the increase in traffic. Depending on the manufacturer of Access Point (AP), 3 to 7 simultaneous calls can be supported on an AP, requiring approximately 450-1050 kbps of available bandwidth.

The range of the radio in the wireless handset varies according to internal wall construction, obstructions, AP output power, RF transmission type (frequency hopping or direct sequence), and AP vendor. The typical indoor range between the wireless telephones and AP is approximately 150 to 200 feet.

4.8.2.3. Interfaces

NetLink wireless telephones operate as clients on the WLAN, along with other mobile 802.11 devices. APs receive IP voice packets from wireless telephones and forward them to the NetLink telephony gateway over the Ethernet LAN. The telephony gateway connects to the host telephone switch using digital or analog line interfaces.

Since all devices are compatible with 802.11 standards, they are able to communicate in the same wireless network. SpectraLink developed a Quality of Service (QoS) mechanism, SpectraLink Voice Priority (SVP). SVP gives preference to voice packets over data packets on the wireless medium, when data and voice are competing for bandwidth. SVP is compliant with the IEEE 802.11 standard.

4.9. Security

The security goals of the wireless industry are to provide user authentication to deter fraud, and to provide over-the-air privacy to deter amateur and commercial snooping.

For in-building network design employing the wireless PBX technology, many companies add special features to their wireless PBX products to provide security support. For example, the SpiderNET wireless PBX System from NSM Technology Ltd.

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[83] employs Frequency Hopping Spread Spectrum (FHSS) Technology to support maximum security against eavesdropping. Each portable telephone typically has a unique identification number that must be registered with the control unit. This allows only authorized users to access the system. In addition, when wireless voice network integrated to IP, modifications should be made either to voice systems or data networks in order to ensure IP network security.

4.10. Network Deployment Scenarios

As discussed previously, there are several solutions for in-building wireless voice communications such as cordless telephones, WPBX options, integrated wireless voice communications with WLAN infrastructures, and cellular/PCS-based systems, etc. Main applications for WPBX systems include:

Health care

In hospitals and nursing homes, WPBX systems provide an immediate link between nurses and physicians. By eliminating paging delays, nurses spend more time with patients and less time traveling back and forth to a phone. Patient care is improved and information is shared promptly among hospital staff.

Retail

In the retail environment, WPBX systems reduce the long hold times customers often endure. Store managers can be reached directly to answer questions. Customers do not have to wait long for price checks or approvals. Overhead paging is also reduced, which creates a more pleasant shopping environment.

Manufacturing

Wireless PBX systems allow supervisors to roam the entire factory floor while remaining in direct contact. Production downtime is reduced because maintenance personnel are always reachable to address equipment problems, and to directly consult outside specialists.

Corporate

Wireless PBX systems increase efficiency and productivity of the corporate. With WPBX systems, customers can reach the right person directly rather than being transferred into voice mail. Managers are contacted quickly when a decision must be made. Employees have more time for their jobs, spending less time to return phone calls.

Warehouse

Personnel in warehouses can be in touch throughout the day wherever they are on the loading dock, conveying commodity via forklift, or pulling items from inventory.

Government

Office managers can be available at all times for decision-making issues.

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4.11. Network Cost Analysis

The main pricing elements of a WPBX system are the radio controller, base station and portable telephones. There is no standard industry price for these elements. System design and configuration requirements are also major factors contributing to the wide price variation.

A base station costs $1,000 to $2,000. The cost of the wired system, which provides the features/functions, and the cost of system switching and trunking must be added to this price. Cost of a wired connection ranges from $200 to $1,000, depending on the number of features (voice mail, speed dialing). A wireless connection starts at about $600 and can rise up to $2,000. The most variable cost in any installation is the base station, and the number required depends on traffic and cell coverage. The cost of the portable telephone and the battery charger unit is typically priced at about $500 to $700.

The price of different system designs vary. The list price of SpectraLink WTS is $1,000 per user. The specific price varies depending on the size of coverage area and building construction. For the integrated system of wireless voice communications with WLAN, the list price for a 16-port NetLink telephony gateway of NetLink WTS is $4,000. The NetLink Wireless Telephone list price is $750. For the cellular/PCS-based systems, i.e., programming cellular service to function like a PBX, the cost varies according to the number of user licenses and the number of radio heads that need to be installed. The price of Ericsson product, digital wireless office system (DWOS), is $800-$1,000 per user.

Pricing is a major issue in the in-building wireless voice system market. The long-term benefits of WPBX justify the initial cost of deployment. The increased availability, efficiency, and productivity of properly equipped mobile workers, as well as the enhanced customer service factor will outweigh the initial cost concerns.

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5. Comparison of Wireless Repeater and Pico-BTS

As the demand for mobile telephony, data and Internet is increasing at more than predicted rate, subscribers are not only expecting, but also demanding to be connected to the mobile network all the time. The blank spots in the network are becoming intolerable for users. Hence arise the need for total coverage by mobile network including shadowed regions of the network i.e. tunnels, highways, in-building locations etc. Both repeater and pico-BTS are the proposed technologies as a solution to the above issue. Even though both of these technologies can be used as a solution for universal coverage of mobile networks, each has certain advantages and disadvantages which makes each of those suitable to different network deployment scenarios. This section will briefly compare both these technologies from four major perspectives: network service, technical characteristics, cost and market potential for network deployment.

5.1. Comparative Service Analysis

Both the repeater and pico-BTS technologies have the advantages of providing enhanced system capacity, reduced network cost, and easy and flexible installation. There are some common services supported by both technologies, whereas differences are also obvious.

Both repeaters and pico-BTSs support traditional low bit-rate 2G services such as voice transmission, medium bit-rate 2.5G data services such as those provided by GPRS, and high bit-rate 3G multimedia services such as those provided by IMT-2000. They are able to provide low cost, great flexibility, and high bandwidth wireless services in local in-building environments.

However, there are great differences between these two technologies. Repeaters are low-level network devices that simply amplify or regenerate weak signals. A repeater just receives and retransmits signals to the destination. It does not correct corrupted data, differentiate traffic types, or provide any other intelligent control functions. Therefore, a repeater cannot add new control functions to the system except increasing the signal strength. On the other hand, pico-BTSs are high-level network devices that support traffic management, power management and mobility management. A pico-BTS has higher layer networking protocols to provide error control, call admission control, resource allocation, dynamic power control, and routing functions. QoS guarantees are achieved by these protocols.

Compared with pico-BTSs, repeaters can be used in wider areas. They are not restricted to the local or in-building areas. They are also suitable for mountains, highways, tunnels, and large buildings where wireless coverage gaps exist due to shadowed areas from base stations and/or the overall traffic is not very high, but deploying additional base stations is expensive and not necessary. In contrast, since pico-cells usually extend to only a few hundred meters in diameter, pico-BTSs are good for indoor mobile applications with high capacity. They are not suitable for large areas because of their coverage limitation. However, since pico-BTSs have smaller coverage, location-aware services can be provided and the system has better knowledge of users' locations.

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Overall, if the system design goal is to provide indoor cellular services with high capacity, pico-BTS is obvious the solution. If the requirement is to extend wireless coverage to the existing system, repeaters can satisfy this requirement while reducing the cost per coverage area.

5.2. Technical Characteristic Comparison and Analysis

Repeaters and pico-BTSs have some similar technical features. However, they also have some differences. We compare these two technologies in the following technical aspects:

Frequency bands

They both follow the standards which are compatible with current 2G/2.5G wireless systems, and also follow the standards which are forward-compatible with 3G wireless systems. Pico-BTSs are part of wireless cellular systems. They work in the typical GSM/PCS, TDMA/IS-136, and CDMA/IS-95 frequency bands such as 900 MHz, 1800 MHz and 1900 MHz. Future 3G pico-BTSs may follow IMT-2000/UMTS specifications to work in 2 GHz frequency bands. But besides wireless cellular systems, repeaters can also be used for WLAN. The frequency bands of repeaters working in WLAN environment are specified in different WLAN standards, such as 2.4 GHz and 5 GHz. Typical frequencies used by repeaters from leading wireless repeater providers are in the range of 300 MHz and 6 GHz.

Equipment structure

The structure design of pico-BTSs is more complicated than that of repeaters. Conceptually, a repeater can be viewed as a simple amplifier. It consists of a receiver, an amplifier, a transmitter, an isolator, and two antennas. However, a pico-BTS does not only contain elements for physical signal transmission, but also incorporates higher layer protocols for intelligent control, such as data link protocols, network protocols, and transport protocols. Both repeaters and pico-BTSs can use either directional or omni-directional antennas depending on applications and network configurations.

Coverage

The coverage of each repeater and pico-BTS vary. A pico-BTS usually covers a pico-cell size, which ranges from around 50 meters to several hundred meters in diameter. In present market, repeaters are available with ranges as small as 50 meters to that of 8,000 meters.

Interference

Both repeaters and pico-BTSs may experience interference from the equipments working in the same frequency band. So the deployment is very important in order to reduce interference. The surrounding areas of repeaters and pico-BTSs need to be clear enough to avoid interferences from other electronic devices. The repeaters and pico-BTSs should be placed with enough distance in-between.

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Environmental issues

Both repeaters and pico-BTSs have advantages on environmental issues compared with macro-cell base stations. Because of their small size and low radiation of electromagnetic waves, repeaters and pico-BTSs are more suitable for in-building deployment. They have smaller effect to the health of human being and can be manufactured with more acceptable appearance. Both of them can be easily and flexibly installed on the ceiling or wall of buildings.

Security

As more new applications will appear in 3G wireless systems, data security becomes more important. Special designs are taken by repeaters and pico-BTSs for the protection of data. As mentioned in Chapter 2, each receiver in the repeater contains a security circuit for verification. In Chapter 3, we mentioned that the controller node concept could be adopted to prevent unregistered data interception inside the system.

5.2.1. Cost Comparison and AnalysisAs both repeaters and pico-BTS technologies are solutions for full coverage of mobile network, their cost comparison is necessary to select the best one suitable to an application. The cost of these two technologies can be compared with respect to their installation and operational cost.

Installation cost. At the system level, repeater is very simple (consisting of a receiver, a transmitter, an amplifier, an isolator and two antennas), compared to pico-BTS (which has hardware to take care of the physical transmission along with software for higher layers protocols. Pico-BTS also has added functionalities like power management, interference cancellation, space diversities, etc., inbuilt to it). All these makes the pico-BTS much more expensive compared to repeaters.

Repeaters and pico-BTSs have comparable ranges (of the order of few hundred meters), which tells that the number of repeaters or pico-BTSs required to cover a particular area is almost same. Apart from all these, pico-BTSs are connected to each other through high bandwidth cables (which adds to installation cost), whereas repeaters are mostly connected via wireless links. Repeater network has one CAP to take care of network functionalities, along with repeaters to provide required coverage. Hence the installation cost of the repeater network is much less compared to that of pico-BTS, in most cases. But this cost equation changes when the network capacity and coverage are beyond some specific values. In such cases the load on CAP increases making it more complex and hence costly, whereas in case of network using pico-BTS, each of those operates within their capacity. The cost of this complex CAP becomes more than the sum total of costs of pico-BTSs and that of the cables used in the case of pico-BTS based network. The increase in complexity of the CAP is because of several factors. One such is the complex modulation schemes (like quadrature amplitude modulation (QAM) or adaptive modulation) used to increase the capacity of CAP using fixed allocated bandwidth. Also when the capacity of the repeater network increases, the interference at CAP increases exponentially asking for more complex interference-cancellation techniques. In such cases, the installation of repeater network becomes more expensive than the one using pico-BTSs.

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Hence it can be concluded that repeater network has low installation cost compared to that of pico-BTSs until the network coverage and capacity are below some threshold value, after which pico-BTS network installation option becomes cheaper. This threshold value depends on factors like bandwidth available, types of services, required QoS, and also on cost of repeater, pico-BTS, CAP, and cable.

Operational cost. For a repeater network, part of the operational cost which includes real estate lease, electricity, hardware maintenance, software maintenance, T1 backhaul etc (as given in Table III) is much less compared to pico-BTS network. Similarly, there are other components of operational cost, where pico-BTS network has advantages. One such component is transmission signal power. In case of repeaters, signal to/from subscribers needs to travel the entire path from the subscriber to CAP, whereas in case of pico-BTS network, it only travels the path from the subscriber to the nearest pico-BTS, which implies for same amount of communication, the repeater network consumes more transmission power compared to the pico-BTS network. Also when the network capacity is more, the hardware and software maintenance cost of the CAP becomes comparable to the sum total of similar cost for all the pico-BTSs. From this it is clear that both these technologies have operational cost advantages over the other under different network deployment scenarios.

As both the installation and operational cost for the network using repeaters and pico-BTSs are a function of network design parameters, proper calculation must be done to decide the cost effective solution.

5.2.2. Comparison and Analysis of Main Markets and Network Deployment

Both pico-BTS and repeater technologies have many market segments common to each other. For some applications, either of these two technologies can be used, whereas, for some others, one of these provides a more cost effective solution compared to the other one. There are existing and future market segments where only one of the above two technologies can be used as a solution. The main segments can be categorized as follows:

In-building coverage by mobile network. Market research shows that the demand for in-building coverage by mobile network is going to increase. If the building to be covered is of small or of medium size, then repeaters are preferred because of low cost, no cabling requirement. In such cases, the CAP can be put in the ground floor and the entire building can be covered by repeaters. As discussed in Chapter 6, as the size of the building or the required capacity increases (for example in airports, stadiums, shopping malls etc.) beyond the threshold value, pico-BTS based network becomes cost-effective. This shows both these technologies have huge market potential in this segment.

Coverage of shadowed regions in cellular environment. Repeaters are a promising solution for coverage of shadowed regions in cellular networks, because as the network capacity is less, there is not need to use a pico-BTS. Also in most of the cases such regions are straight instead of circular (for example tunnels, parking ramps and so on), hence using a repeater with directional antenna gives a low-cost solution.

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Extension of mobile network. Now the demand for including highways, railways into mobile network is increasing. Apart from that, extension of mobile network across forests, mountains and also inter-city mobile network is gaining importance. In all these cases, use of repeaters gives the most cost effective solution.

4G mobile network. For 4G mobile network, where the data rate is going to be of the order of 10 Mbps, the cell size cannot be more than few hundreds of meters (because of propagation characteristics of electro-magnetic waves going to be used). Hence, pico-cells along with pico-BTSs are the proposed solution. Here repeaters can also be used, but they cannot support frequency reuse across pico-cells, which limit network capacity. Hence, pico-BTS technology is going to be preferred. This is a huge potential market for pico-BTS technology.

Extension of satellite network. The satellite network, which is gaining popularity in entertainment market, can extend its coverage area using repeater technology, also they can provide mobile access to their service in small areas around the repeater (which gets connects to the central distribution site via high bandwidth fiber cables).

The above discussion shows that both these technologies are going to see an increased market for them. But for each one to capture the market of the other one, it has to improve upon it. Like if the price of pico-BTS becomes less, then it will capture a substantial portion of the in-building network market. Similarly, if the repeaters are going to add certain functionalities like space diversity, interference cancellation, power management, then the market for repeater technology is certainly going to increase.

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6. Comparison of WLAN and WPBX

6.1. Comparative Service analysis

WPBX service. A WPBX system is integrated with a wireline PBX to provide mobile capability to a conventional wireline telephone system. It enables a user to use a portable handset as a wireless extension to his desktop telephone, thus letting users keep the same extension number and features as their desktop telephones. It supports call forwarding to extensions, accessing voice mail, intelligent switching and end-to-end transmission.

WPBX also allows the integration of mobile cellular service and local cordless PBX service. When a user is in his office, his mobile phone serves as personal extension to the company's PBX. After he leaves office, the phone functions as an ordinary mobile phone.

In order to realize convergence of telephone with IP data, wireless IP-based systems running over enterprise LANs should be a technical trend. IEEE 802.11-based network can integrate wireless voice communications with LAN infrastructure to support both voice and data communications.

WLAN service. WLAN products have a much wider services. Computers can use WLAN adapters to form an Ad-Hoc WLAN. Most WLANs are implemented as a complementary extension to existing wired client server network, in which access point functions as the server. One or more access points can be used as extensions points to enlarge such network. Because of the mobility, flexibility and low cost, WLAN has numerous uses such as home wireless network, enterprise network and public access.

In many applications, users use WLAN to connect between different devices, in order to avoid using cables. Such devices include cellular telephone, laptop, PDA, fax machine and printers. Therefore, it is easily to setup or expand a network of computers and Internet appliances at home and or office.

With WLAN, people can access data or files stored on servers at remote places, wherever he physically is. And the access speed is 50-200 times faster than dial-up, while he does not worry any more about to search for a data port or the long distance charges.

Wireless packet-switched LAN deals with real-time voice and video services. WLAN can also provide high-speed multimedia communications among different broadband core networks such as 3G mobile core networks, ATM networks, IP-based networks, etc.

A wireless LAN infrastructure can be used for a mobile PBX handset, thus converge voice and data networks. Voice, audio and video are shared among WLAN-enabled phones, MP3 players, web cameras, interactive TVs and so on. In this way, WLAN functions beyond traditional computer networking.

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6.2. Technical characteristic (capacity and coverage) comparison and analysis

WLAN and WPBX differ in many technical aspects such as operating frequency, access technology, interoperability, security, system capacity and area coverage.

Operating frequency.

For WLAN, different frequency bands are utilized for different proposals and physical working modes. IEEE 802.11b operates in 2.4GHz ISM band. IEEE 802.11a operates in 5GHz band. Bluetooth network's working frequency is in 2.45 ISM band. HomeRF network operates in 2.4 GHz ISM band. HiperLAN/2 works in 5.4-5.7 GHz frequency band.

WPBX systems operate in 800MHz (for narrow-band cellular service), 900MHz (for in-building systems), 1920-1930MHz (for unlicensed Personal Communications Services) and 2.4GHz (for integration with LAN).

Access technology.

WPBX systems are mainly based on CDMA, FDMA, and TDMA. While WLAN's operating modes are much more complex. There are CSMA/CA based WLAN, ALOHA/ Polling-based LAN, TDMA/CDMA based LAN, or hybrid LAN. IEEE 802.11b can use radio based legacy DSSS, infrared-light based legacy DSSS, or complementary code keying. IEEE 802.11a uses OFDM. Bluetooth network uses FH-CDMA/TDD. HomeRF network's physical layer is based on FH, and it uses 2-FSK/4-FSK modulation. HiperLAN/2 network is based on OFDM.

Interoperability.

Different WPBX products have very weak compatibility, even if they work in the same frequency or they are produced by the same vendor.

Different WLAN products of the same type are compatible to each other, such as WLAN adapters. Although different types of WLANs using the same ISM band may cause serious interference to each other, there are some schemes to solve the coexistence problem between them, such as for IEEE 802.11b and Bluetooth.

Security.

Many WPBX products use FHSS technology to support maximum security against eavesdropping. Each portable telephone is assigned a unique identification number registered with the control unit. Only authorized users can access the system.

For WLAN, both 802.11 standards and Bluetooth use keys to encrypt data. Wired Equivalent Privacy (WEP) technology is an option of 802.11 standard and widely used by most WLAN products. WEP uses shared keys and a pseudo random number as an initial vector to encrypt the data. Most current products use 128-bit WEP encryption.

System capacity and area coverage.

WPBX vendors have different series of products suitable for different needs. Such products could be integrated to a network to maximize the system. For example,

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SpectraLink's Link 3000 MCU supports 1000 base stations, 3200 wireless telephones, and its area coverage is 100 millions square feet.

In a typical Client-Server-based WLAN application, each access point can serve 15-50 client devices. The coverage range for a single access point is in the order of 500 feet for indoor environment, and 1000 feet for outdoor environment. Some WLAN gateway products can reach 25 miles, such as Cisco's Aironet 350 Series.

6.3. Cost Comparison

Table XVI. Cost comparison of WLAN and WPBX (unit: $)

Access Point Network CardWLAN 500 - 1,000 100 - 200

Base Station Handset Radio ControllerWPBX 1,000 - 2,000 500 - 700 2,000 - 4,000

A typical WLAN system consists of access points and network adapter cards. An access point costs around $500 - $1,000, and a network adapter card costs around $100 - $200. Typically, an access point can serve about 15 - 20 users at the same time. Thus, if we assume that we construct a WLAN system composed of 20 users, it will cost around $2,500 - $5,000. A typical WPBX system is composed of radio controllers, base stations, and wireless handsets. A radio controller costs around $2,000 - $4,000. A base station costs around $1,000 - $2,000, and a wireless handset costs around $500 - $700. Thus, if it is assumed that a WPBX system serving 20 users is constructed, it will cost around $13,000 - $20,000. Table XVI shows the cost comparison between WLAN and WPBX. From this, we can know that a WLAN system is cost effective compared to a WPBX system.

The initial installation cost of a WLAN system is much cheaper than that of a WPBX system as shown above. Moreover, once installed, the WLAN system has less management expenses than the WPBX system. A WPBX system cannot function as a stand-alone PBX. It works together with conventional PBX systems. Thus, it involves more installation and operational costs than the WLAN system. Hence, the overall cost including the installation and the operational costs of the WLAN system is much cheaper than that of the WPBX system.

6.4. Markets and Network Deployment Comparison

There is an increasing demand for WLAN technology. The WLAN market is mainly being driven by the growing demand for bandwidth from portable PCs to Web browser and corporate applications. WLANs provide high-speed services that make access to email and corporate applications feasible. The market for WLAN system that is intended for PC connectivity will be slightly less than $1.4 billion in 2001. The market is expected to grow to $3.2 billion in 2005. Some of the WLAN market opportunities include the following:

Use of WLAN technology to connect consumer goods such as set-top box, etc.

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Public access WLANs could remove the need for data connectivity provided by 3G cellular and packet data networks, therefore grabbing the market chance for public network access.

The advantages of 5GHz products such as increased bandwidth, QoS and reduced interference could force customers to go without 2.4GHz compatibility. This would shift the market away from less costly 2.4GHz-capable solutions to relatively more costly but cost-effective 5GHz solutions.

WLAN market development and growth has been delayed by overflow of standards, which confused potential customers. Moreover, decisions were delayed while market players waited for new standards. Supported by the interoperability testing services of the Wireless Ethernet Compatibility Alliance (WECA), the IEEE 802.11 standards are emerging as the leaders. The technology is expected to continue to evolve. Products complying with the 802.11a standard will be available during the first half of 2002, boosting maximum data rates from the 802.11b standard's 11 Mbps to 54 Mbps. By using the broader 5.0GHz unlicensed band, 802.11a will also address many of the spectrum congestion issues in the 2.4GHz band used by 802.11b.

The wireless options for the PBX have not shown much growth even though WPBXs have been on the market for almost 10 years. Less than 5% of the new PBX system shipments are WPBX. Some of the several reasons for the relatively low shipment for WPBX are pricing, technology, customer awareness and education. Among these, the main reason is the pricing problem. The cost per user for a WPBX system is expensive. Sometimes it is three times of a conventional wire-line desktop phone. It is even more expensive than that of WLAN system as shown above. However, since in-building wireless communications is growing rapidly, lots of opportunities exist for manufacturers with innovative products and applications. Customers want cordless telephones, full roaming, and seamless handoff while they are receiving calls. Multiple product lines, broader distribution channels, and increased roaming capability are the important issues concerning wireless vendors' current market strategies.

The market for WPBXs is changing rapidly. It is expected that the market will grow to almost $840 million by 2005, over a factor of three to one from the base year of 2000.

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7. Comparison of Pico-BTS and WLAN/WPBX

7.1. Comparative Service Analysis

In order to provide low cost and high traffic rate wireless services for local areas, several wireless systems have been developed independently. For example, pico-BTS is used to enhance the traditional cellular system in the indoor environments. By using low-cost pico-BTS, higher capacity and services with better quality can be supported in buildings. WLAN is another technique to provide high speed wireless services to local area users. For a conventional wireline telephone system, WPBX is used to provide the mobile capability to end users in a local area such as buildings.

Several services can be supported by pico-BTS, WLAN, and WPBX. Among them, some are the same, while others are different.

As investigated in Chapter 3, pico-BTS is a type of cellular system, and thus, it is a complimentary part of the wireless cellular system. All the existing services in the 2.5G and 3G cellular systems can be supported in a pico-BTS system. However, since higher capacity can be offered by a cell in a pico-BTS system, larger traffic rate than that in 2.5G and 3G systems can be provided by pico-BTS systems. In this sense, pico-BTS is closer to the objective of the next generation wireless communication system. However, to really achieve the goal of the next generation wireless communication system, efficient protocols to support multimedia services need to be developed. Moreover, pico-BTS has much smaller cell than the conventional cells in 2.5G and 3G system, which provides a possibility of developing more precise location-aware services. Pico-BTS can be integrated with 2.5G and 3G cellular systems in a seamless way, because it is actually the same type of system as conventional cellular network. However, to access Internet via pico-BTS does not have a direct solution. It must depend on the conventional cellular system that is connected to pico-BTS. If the cellular system connected to pico-BTS is a 2G network, Internet access is not available. When the pico-BTS is connected to 2.5G or 3G, Internet access is supported.

In contrast, WLAN is a network that can be totally independent from other networks, as descried in Chapter 4. Current WLAN systems can provide much higher traffic rate than pico-BTS system. For example, the traffic rate of IEEE 802.11b can be as high as 11 Mbps, while a pico-BTS is almost impossible to deliver such a high traffic rate. However, in the same situation as pico-BTS system, new protocols such as MAC need to be developed in order to really support multimedia services in WLAN. For example, most of the existing WLANs such as IEEE 802.11 series, HomeRF, and Bluetooth are very weak in QoS guarantees for real-time services, although the transmission rate of data applications can be very high. Some WLANs such as HomeRF can be connected to PSTN so that voice communication can be smoothly supported, while the WLANs such as IEEE 802.11 and Bluetooth do not have a good solution to deliver voice service. Normally, voice over IP should be used if voice service needs to be supported. However, Internet over WLAN is an obvious solution, because data services are supported in all WLANs. It is not so apparent to integrate WLANs with 2G or 2.5G cellular systems because WLANs are purely packet-based network. However, since 3G

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and the next generation cellular systems are also purely packet-based, the integration of such WLANs with cellular systems will be seamless, which is one of the objectives of the next generation communication system. WLAN can be ad-hoc or infrastructure-based, so network topology is very flexible. However, due to this flexibility, to provide location-aware service in a WLAN becomes more challenging. Another severe issue still exist in WLAN is interference. Although co-channel interference also exists in pico-BTS system, devices in pico-BTS systems do not experience interference from other devices working in the same frequency band. However, a WLAN device experiences such interference, which significantly degrades the performance of WLANs.

As pointed out in Chapter 5, current WPBX can only support voice service with either on-site or off-site mobility. Thus, data applications and multimedia services cannot be provided in a WPBX system. Base station is required in a WPBX system, so WPBX is also an infrastructure-based network. Interference could be an issue if WPBX works in an unlicensed frequency band. Location-aware service is difficult to provide in a WPBX, because WPBX is connected to PSTN instead of a cellular system.

Features and services provided by pico-BTS, WLANs, and WPBX are compared in Table XVII.

Table XVII. Comparison of the features and services of pico-BTS and WLAN

Features or Services Pico-BTS WLAN WPBXData Rate Medium High Low

Voice Service Supported Supported in some WLANs

Supported

Data Applications Depending on the conventional

cellular s

Supported Not supported

Multimedia Services Support

Supported in the future

Supported in some WLANs

Not supported

Location-Aware Service Provision

Supported To be developed Not supported

Integration with Cellular Systems

Seamless To be developed Infeasible

Network Topology Infrastructure Ad-hoc or infrastructure

Infrastructure

Interference Low Severe Severe in un-licensed

In the industrial practice, hybrid networks that combine pico-BTS with WLAN or WLAN with WPBX exist. Such hybrid networks hold features of both systems. For example, when WLAN is integrated with WPBX, both voice and data applications can be supported with good quality. In the hybrid network, if WPBX is used in an area with severe interference that could be experienced by a WLAN, the interference issue of WLAN can be improved.

In the next generation cellular system, the network is packet-oriented. Thus, integrating WLAN with the cellular system is straightforward. However, since pico-BTS

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is also used for indoor environments, it is more advantageous to integrate WLANs with pico-BTS system first and then the outdoor cellular systems are connected through pico-BTS.

7.2. Technical Characteristics Comparison and Analysis

The technical characteristics of the pico-BTSs, the WPBXs and various kinds of WLANs are compared below.

Standards

Different types of WLANs are standardized by different bodies. IEEE 802.11 is standardized by IEEE, and some working groups still continue working on the standardization process. Bluetooth standardization is driven by the Bluetooth Special Interest Group, and it is not complete yet. The HomeRF Working Group is about to finalize the standards for the HomeRF and SWAP networks. The standards for the HiperLAN/2 networks are set by ETSI. The ETSI organization also sets the standards for the pico-BTS networks.

Physical and MAC layers

IEEE 802.11 uses direct sequence spread spectrum, infrared and OFDM technologies in the physical network. Its MAC layer is based on CSMA/CA. The MAC layer in Bluetooth uses frequency hopping CDMA based on polling or Aloha protocol. In HomeRF, the MAC layer is TDMA-based for isochronous services, and CSMA/CA-based for asynchronous services. The MAC layer in HiperLAN/2 is TDMA/TDD-based. The pico-BTS system in 2G networks is designed mainly for voice, and its MAC layer is the same as the network it is integrated with. WPBX systems are voice-only networks and their MAC layers are determined by the access technologies.

Frequency bands

IEEE 802.11 systems operate at the 2.4 GHz, 5 GHz and Infrared frequency bands. Bluetooth operates at the 2.45 GHz ISM band. The frequency bands for HomeRF and HiperLAN/2 networks are at 2.4 GHz ISM and 5.4-5.7 GHz. Pico-BTS systems operate at 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz, depending on the type. The WPBX systems operate at 800 MHz, 900 MHz, 1920-1930 MHz U-PCS, and 2.4 GHz bands.

Infrastructure and organization

IEEE 802.11 and HomeRF systems work in both cellular and ad-hoc modes. In the cellular mode, each mobile terminal communicates with an access point. In the ad-hoc mode, the communication is peer-to-peer. In Bluetooth networks, there is a centralized organization; one master node and several slave nodes exist in each piconet. HiperLAN and WPBX systems have cellular infrastructures. The pico-BTS systems are also cellular by nature since they are part of larger cellular networks.

QoS support

IEEE 802.11 systems support only priorities for different types of traffic. However, work is under way to enhance the QoS capability of IEEE 802.11 systems. Bluetooth,

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HomeRF, HiperLAN/2, and WPBX systems provide do not support QoS specifications. Pico-BTS systems can provide limited QoS support, but extensive research is required to improve it.

Maximum transfer rate

The transmission rate of IEEE 802.11 systems ranges from 1 Mbps to 54 Mbps, depending on the type. HomeRF systems provide a transmission rate up to 1 Mbps while it is lower than 1 Mbps for Bluetooth. HiperLAN/2 systems provide a transmission rate of 54 Mbps at the physical layer, but it is only 32 Mbps at the network layer. The transmission rate of a pico-BTS system is determined by the cellular network it integrates with. WPBX systems are intended only as extension of the desktop telephones to provide voice communication, and their transmission rates are very low.

Integration with other networks

The integration of the WLAN systems requires more improvement. Since WLANs are considered to be a part of the next generation systems, there is increasing research on this issue. The pico-BTS systems are already part of larger cellular systems, and they are fully integrated. The WPBX systems, except those that operate at U-PCS frequency band, can be integrated with cellular systems.

7.3. Cost Comparison and Analysis

Costs of pico-BTS, WLAN, and WPBX have been analyzed in Chapters 3, 4, and 5, respectively. Here a more comprehensive comparison is performed again based on the results in Chapters 3, 4, and 5.

To deploy and operate a wireless network in an indoor or local area environment, the costs are generally determined by the following important factors:

Deployment costs. This type of costs is related to several other factors such as frequency planning, network design, and deployment difficulty.

Equipment costs. Such type of costs is determined by the number of devices and the prices of these devices.

Operation costs. Operation of a network includes configuration of networks, service provision and pricing, maintenance and management of network, and so on.

Based on these factors, the costs of pico-BTS, WLAN, and WPBX are compared in Table XVIII.

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Table XVIII. Comparison of the costs of pico-BTS, WLAN, and WPBX

Cost Index Pico-BTS WLAN WPBXFrequency Planning High Low Medium

Network Design High Complexity Low Medium Complexity

Deployment Complexity

High Low Medium

Number of Base Stations

Medium Low Medium

Price of Base Stations

Expensive Low Low

Price of Gateway Expensive Low ExpensivePrice of Mobile

TerminalsLow Medium Low

| Network Configuration

High Complexity Low Complexity Network Configuration |

High Complexity | Low Complexity |

Network Maintenance

Medium Complexity

Simple Simple

Service Provision and Pricing

Medium Complexity

Simple High

As shown in Table XVIII, the WLAN is much economical than the other two in terms of network deployment costs. The reason is that WLAN is a relative independent network and works in a public ISM frequency band. Because the techniques of base stations (or access points) of a WLAN is simpler compared with pico-BTS or WPBX, the price of WLAN base station is generally cheaper. The same reason causes the price difference in gateways of pico-BTS, WLAN, and WPBX. Since WLAN is very flexible in network topology, the network configuration of WLAN is simpler. The same reason can be applied to the different costs in network maintenance and service provision and pricing. From Table XVIII, WLAN is shown to be much more advantageous than the other two options for wireless networks in local areas. However, it should be pointed out that, when deploying a wireless network, cost is not the only criterion to decide which option can be used. Actually, the features and services are also important aspects that concern network designer and service provider. In other words, the comparisons of costs in this subsection should be considered together with the comparisons of network features and services in Subsection 7.1.

7.4. Comparisons and Analysis of Main Target Markets and Network Deployments

Pico-BTS provides low-cost and higher capacity to users in an indoor environment. It also provides a bridge between WLANs and 3G cellular networks. Thus, pico-BTS has been widely accepted. Its market is steadily increasing. For example, based on pico-BTS, cdmaOne is enabled to compete with TDMA and GSM networks.

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The market of WLAN is increasing more than predicted. WLAN is going to exist in all kinds of local area environments such as homes, offices, educational institutes, warehouses, health centers, hotels, airports, and many more. Thus, the market penetration of WLAN is promising.

However, WPBX does not hold a huge market. Currently, its market is just a small percentage of the whole PBX markets. Its capability to penetrate the market of other wireless products is not strong, because its simple function cannot satisfy the ever-increasing demands on the new services of wireless communication. However, since WPBX can be integrated with other networks, it will continue to hold some percentages of market for wireless products. For example, WPBX can be integrated with WLANs so that the hybrid networks can enhance the performance of both networks, which enhances the market penetration capability of WPBX.

The target market and network deployment of pico-BTS, WLAN, and WPBX are compared in Table XIX. In such a table, the following factors that affect the market and network deployments are considered:

Motivation. This factor is determined by the functionality, technology advantages, costs, and customer needs.

Current market percentage. Although a higher current market percentage cannot guarantee a big future market, it reflects the actual needs from users.

Network deployments. This reflects the usage of a wireless solution. If a wireless solution can be applied to various environments, it is expected to have a huge market.

Market development. This means if a market is increasing, decreasing, or stable.

Market penetration capability. This is a very important factor that determines the future of a wireless solution. If the market penetration capability of a wireless solution is high, the market must be very promising.

Table XIX. Comparison of the markets of pico-BTS, WLAN, and WPBX

Market Index Pico-BTS WLAN WPBXMotivation Moderate Strong Weak

Current Market Percentage

Medium High Low

Network Deployments

Buildings under coverage of conventional cellular

systems

All local areas Buildings with PBX

Market Development

Steadily increasing Increasing fast Stable

Market Penetration Capability

Moderate Strong Weak

From Table XIX, we know that WLAN is going to be the wireless solution with much bigger market than the other two solutions. However, pico-BTS will also hold a big percentage of market. Both pico-BTS and WLANs will be an important wireless solution in the next generation wireless networks. They can together as a hybrid network. In

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contrast, WPBX does not have a promising future market unless some innovative technologies are developed to enhance its functionality. However, it is going to exist for a certain period to provide the wireless voice services in a conventional telephone system.

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8. In-Building Deployment

8.1. Taking advantage of technological evolution and meeting customer demands

Most wireless system venders and service providers declare their supports and evolutions to 3G wireless systems. While they may take different technique approaches.

Europe and Japan support WCDMA system, which is a great improvement from GSM in terms of data delivery. Currently, the feature set of WCDMA has evolved from R99, through R00 to R01. NTT DoCoMo has launched its WCDMA system in the end of this year, which is a R99 version.

United States and Korea prefer the cdma2000 system, which is based on IS-95. But they are in different situations now. While Korea has the highest concentration of IS-95 users, the United States faces the problem of several incompatible systems in use. Even AT&T uses WCDMA system.

China’s TD-SCDMA is also proved by ITU as an IMT-2000 standard, though it has a narrower rate of 1.28 Mbps. In current Chinese market, two totally different service providers exist. China Mobile, with its 67.5 million GSM users, ranks number one in the Chinese wireless market. It also supports GPRS service. The second player, China Unicom, will launch the largest CDMA network all over the world on Dec 31 2001. The first deployment phase will have 15.15 million users, 188 switches and 14,500 base stations, based on an enhanced I-95A version. It plans to increase its capacity to 50 million users in 2003. One problem is the incompatibility of 4 kinds of different UIM card in use now.

At the same time, China Unicom will launch its first CDMA-1X commercial testing network covering 7 big cities including Beijing and Shanghai. Such network could be upgraded onto 3G system smoothly.

The interoperability between CDMA and GSM is a big issue. The CDMA network in Singapore failed recently shows the importance of this problem. Now Korean Telecom delivers a GSM-CDMA two-mode mobile phone which will support GSM’s SIM card to be used in Korea. It may be a potential solution. Another approach is to have a traffic control function that is able to handle all spectrums allocated by the two systems as one. Adaptive Traffic Control ensures full utilization of the combined spectrum and resources with a seamless handover, and transfer of connections between the GSM and CDMA systems.

No matter what kinds of technology to be used, successful service provider should provide customers with the following services:

Greater coverage

High-speed rates

Scalable and manageable bandwidth

Enable new (high-end) services (and keep running the good old ones)

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Service differentiation

Smooth deployment and low maintenance

Interoperable systems

Plug & Play

Extends the local area network

Freedom to access the corporate network

Comparable to those of wired networks

Secure access to important information (e-mail, corporate data, Internet)

More and more users prefer an integrated wireless network that could integrate different wireless systems together and use them seamlessly. Therefore, successful operators should offer a seamless handover between 3G and WLANs.

Currently, physical layer technologies for different wireless systems are incompatible. Each of them occupies a different frequency band and their physical interfaces are totally different. However, competitive service providers should provide customer integrated service among different wireless networks, such as WCDMA cellular systems, high speed WLANs, and home wireless networks. To achieve this goal, some companies and research centers are developing novice techniques to produce a seamless multitier network interface. A Multitier Network Interface Card (mNIC) for service continuity is a hot topic now. It is a multi-tier network interface card which could be reprogrammable to different physical and network-layer standards [100]. Researchers are now developing a reconfigurable testbed and a prototype. DSP processors, custom VLSI ASICs and FPGA techniques are involved.

In industry practice, another innovative concept is Always Best Connected (ABC). This concept is given by Ericsson [98]. It provides operator a multi-access solution that can integrate with CDMA, WLAN and Bluetooth. In this scenario, the CDMA system covers a wide area network, while WLAN supports services in smaller hot spots such as airports, and Bluetooth is used as a cost-effective access technology for a PAN.

IN Ericsson’s solution, Bluetooth is used as the common interface technology for all types of access. The different kinds of access should be identified and the optimal access should be chosen automatically, without user’s interaction. Ericsson's CDMA2000 1xEV demonstration has been implemented in Nov 2001.

However, since Bluetooth has a relatively lower bit rate (no more than 1Mbps) and its weak support for QoS, especially in real time communication such as video, some other research institute may choose other access technology as the common interface. The Broadband and Wireless Network Laboratory (BWN) of Georgia Tech will select WLAN as the common interface in its Next Generation Wireless Network project.

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8.2. Network deployment scenario (Technology, Market, Architecture, Implementation Phases, schedule, Resource estimates)

Since the customers have various requirements for their specific network environment and needs, service providers should offer them different network deployment accordingly, considering the network capacity, price, connectivity, and scale, etc.

8.2.1. Wireless PBX System deployment for corporateIn a corporate which have a great needs for its employees to access telephone in building frequently, it should have a wireless PBX system deployment. Wireless PBX is a mobile communication system which connects the outside PSTN and the inner wireless base stations. The wireless handsets can be used as extension telephones, so users can call anywhere and anytime under the coverage. The lower charge is also attractive, because the WPBX system is belong to run in the corporation’s own mobile communication network, no extra charge is required. Besides, this system provides the company broadcasting function, which is a necessary requirement in big buildings and malls.

Figure 29 shows an example fulfilling the needs of small size enterprises and home-offices [94]. It should provide the following features:

Reliable wireless mobility

User-friendly features

System administration

Plug-and-go installation

Flexible relocation for dynamic workplace

Both stand-alone system, and being able to be connected to an existing corded PBX

Support maximum security against eavesdropping

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Figure 29. A wireless PBX system for small size corporate

The system consists of three major components: the Master Base station, the Remote Base station (RBS), and the Wireless Handset. The diameter of each Remote Base station’s cell coverage is about one kilometer, and whole system coverage is three or more square kilometers. Typically, it is a multi-cell system supports four to eight analog trunk lines, 16 simultaneous speech connections and 70 wireless handsets.

8.2.2. WLAN internetworking with Wired NetworkSome vendors provide WLAN 11 Mbps system deployment architecture shown in Figure30, such as Ericsson [95].

Wireless LAN Guard will provide very high security protection. Besides, by using authentication and encryption process with 128 bit encryption, each user will have safe pre-shared keys and public certificate. The Wireless LAN Guard also functions as a central monitor from which one people can configure, track the traffic, and manage the whole system. A WEB based configuration of Access Points offers more convenience. The site management enables users to can move from one location to another and connect to the network.

By using a Virtual Private Network (VPN) service, the users could access the enterprise network. Service providers may also extend the service area for the enterprise user to certain public areas.

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Figure 30. WLAN 11Mbps system architecture

8.2.3. Unified 3G Wireless NetworkIn the future, customers may prefer a unified wireless 3G wireless network that integrates all the wireless technologies together, and provide the customers a complete, seamless and secure service. Unified 3G Wireless Network shown in Figure 31 will provide:

Flexibility for Internet-based Data & Multimedia Services

Bandwidth on Demand

Lower Cost Than 2G for “Basic” Services

Plus New Service Capabilities

Significantly Improved Operational Efficiency (esp. Capacity/Spectrum Efficiency)

Service Transparency/Global Roaming

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Figure 31. Unified 3G wireless network

The core of the network is a Multi-service IP network. Various services will be supported including provisioning, PBX, VoIP, Value added, Billing, Settlements, Call and Session control, Multimedia, etc. Users can select WLAN, or ADSL to access the core network. Besides, both WCDMA and GSM systems could be supported simultaneously.

8.2.4. Complementary Technologies of cdma2000 and 802.11QUALCOMM provides another prospective network deployment approach for in-building wireless communication [97]. This approach will provide benefits for ender users, service operators and vendors. End users benefit from seamless wireless Internet services, and such service will be affordable and runs everywhere. Operators function as the preferred wireless Internet providers. Device Vendors should provide different and utilities to fulfill the specific requirements for end users and operators.

Enterprise WLAN’s coverage should be included and integrated into the WCDMA/cdma2000 coverage. In this coverage, laptops, PDAs and cell phones should be supported everywhere at anytime. In order to achieve this deployment, two more requirements should be fulfilled:

Dual Mode Laptop/PDAs that work both on WCDMA/cdma2000 and WLAN

Integrated Authentication mechanism with the Enterprise Wired LAN

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There are some additional benefits for this deployment Compared to other WLAN approaches, especially for enterprise:

Portability within the Enterprise

Leveraging existing Enterprise LAN

Direct access to information on the Intranet

Easy maintenance with existing LAN management system

Same security mechanisms as wired LAN

No monthly service fees

WLAN owned and operated by Office

Free use of unlicensed spectrum

Sufficient coverage with LAN

Employees are concentrated in a few areas of Enterprise when away from desk

LANs can provide sufficient coverage within Enterprise

There are may be three kinds of network deployment scenarios for end users and service providers. Providers could select one to fulfill the users’ specific needs.

WLAN operators are different from the WCDMA/cdma2000 Operator and WLAN operators compete with each other. This is not a long-term proposition. The main reasons come from the complicated charge fees and the difficulties to integrate. There may more than 1 WLAN operators to provide service. Each WLAN location has its own monthly backhaul costs, and each WLAN operator has its own billing, and authentication scheme. WCDMA/cdma2000 Operator will also feel to setup roaming agreements with numerous independent WLAN operators.

WCDMA/Cdma2000 Operator and one WLAN operator are both offering commercial service but compete with each other. WCDMA/cdma2000 operator will dominate in this battle because their ubiquitous coverage advantage is overwhelming. Each WLAN location has a monthly backhaul cost associated with it.

WCDMA/cdma2000 operator provides both CDMA and WLAN Services. This scenario has integrated billing and authentication schemes. End users may find this service is easily to use, and the charge will be unified and cheaper. Such a combination enables end users to use wireless data everywhere easily. End user does not have to know or worry about which air link is being used. WCDMA/Cdma2000 operator may own the WLAN, or wholesales from one other WLAN Operator. For the latter, the advantage is that WCDMA/cmda2000 operator does not worry about operation and maintenance of the WLAN.

8.2.5. VPN security for Wireless CommunicationWhen choosing network deployment schemes, each corporate consider the security as one of the highest requirements. Currently, the combination of VPN (IPSec) and 802.11 is an ideal solution for wireless networking security needs. In such a scenario, the wireless access points do not need WEP encryption themselves. All the security

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considerations are carried out by the VPN. The VPN servers provide encapsulation, authentication and full encryption over the LAN. To the end users, they will have a fully secure access to their network resource as if the data transferred ‘transparently’. The VPN approach is flexible enough to be used in a variety of different scenarios. In each scenario, the user has a same login interface and procedure (shown in Figure 32).

Figure 32. VPN (IPSec) provides wireless network security

8.2.6. HiperLAN/2 deployment for Corporate LANSince HiperLAN/2 have good support for QoS, many corporate will select such network deployment to support real-time wireless communication. Figure 33 shows an example. In this scenario, the corporate network is built on ethernet LAN and IP routers. Then, a HiperLAN/2 network is used as the last segment between the mobile terminals and the network/LAN. In subnet A, the HiperLAN/2 network supports mobility within the same LAN/subnet. However, when the terminal is moving between different subnets (From A to B), the handover should be handled by a layer above HiperLAN/2 [93].

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Figure 33. HiperLAN/2 used in a corporate network

HiperLAN/2 can be used as an alternative access technology to a 3rd generation cellular network, especially to provide wireless coverage for hot spots. The combination of using HiperLAN/2 in hot spots and using WCDMA technology for wide area is potential approach. In this way, a user can benefit from a high-performance network wherever it is feasible to deploy HiperLAN/2 and use W-CDMA elsewhere. Handovers can be achieved between the two types of access networks.

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9. Conclusion

Most wireless communication operators declare they have plans to involve to 3G wireless systems and will provide the customers the best wireless access from anywhere at anytime, though they may take different technique standards. However, what the users want most is to have a mergence of the wireless communication services that they get from different operators currently. The market needs for integration with Bluetooth, WLAN and cellular system is increasing rapidly, thus brings a great opportunity for those competitive service providers who will have the strategy to integrate various wireless technologies, and provide end users a completed, seamless service. Today’s high-rate wireless communication technologies could enable the operators to achieve their strategies.

Some key issues should be handled carefully when service providers offer network deployment to their customers. Among them, the interoperability between different wireless network systems is a key issue requiring further breakthrough from novice technologies. The mNIC technology and Always Best Connected concept may be the potential approaches. Compared to fixed network, the security problem is another important and sensitive issue requiring more consideration when implementing network deployment. In WLAN scenario, most providers use encrypted WEP technologies. In practical use, the combination of VPN and IPSec is an ideal solution. To achieve the high-rate wireless network integration and support real-time and multimedia wireless communications with guaranteed QoS, many new modifications should be taken for wireless repeaters, Pico-BTS, and WPABX devices.

Various vendors and research institute have different technology standards to compete with each other. But the end users need a ‘transparent’ integration of those detailed technologies. Besides, since different countries’ operators may take different approach to involve to the 3G wireless systems, how to handover among different systems should be a great issue.

Further more, since the needs from various enterprises and end users are quite different from each other, the service providers should prepare various network deployments for them accordingly. Lots of issues need to be considered including the network capacity, the connectivity to wired network, the QoS, the security, the price and the performance.

A competitive solution should provide seamless end-to-end connectivity from mobile users to wired ones. A web-based, centralized network management is another consideration most customers want. The more usages brought to customers, the more revenue you get.

In short, the successful operators will be those who have strategy to deliver mobile data through high speed 3G networks, and provide end users seamless, guaranteed and affordable wireless access everywhere, anytime.

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10. References

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[4] White paper, "Exploring the Great Indoors," Repeater Technologies, 2001.

[5] White paper, "Extending Coverage a Country Mile," Repeater Technologies, 2001.

[6] ETSI, "Base Station System (BSS) Equipment Specification, Part 4: Repeaters," GSM 11.26, v.8.0.2, Release 1999.

[7] 3GPP, "URTA Repeater: Radio Transmission and Reception," 3GPP TR 25.106, V.4.1.0, Release 4, Sept. 2001.

[8] 3GPP, "URTA Repeater: Planning Guidelines and System Analysis," 3GPP TR 25.956, V.4.0.0, Release 4, March 2001.

[9] IEEE 802.11 Wireless LAN Working Group, "Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specification ns," IEEE Standard, Nov. 1997.

[10] IEEE 802.16 Broadband Wireless Access Working Group, "802.16.1 Air Interface Standard," IEEE Draft Proposal, Oct. 1999.

[11] White Paper, "AVITEC AB -- Radio Coverage Solutions," Avitec Inc.

[12] R. Hranac, "Wireless Dilemma," Communication Technology Magazine, July 2000.

[13] White Paper, "Wireless Repeater with Solar or AC Power," Davis Inc.

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