wimax radio network planning and analysis

VOL. 3, NO. 8, August 2013 ISSN 2225-7217 ARPN Journal of Science and Technology

©2011-2013. All rights reserved.

http://www.ejournalofscience.org

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WiMAX Radio Network Planning and Analysis Dauda Elijah Mshelia

Assistant Lecturer, Department of Computer Engineering, University of Maiduguri, Nigeria

ABSTRACT

This paper presents radio network planning of Worldwide Interoperability for Microwave Access (WiMAX) in the region of Annemasse, France. The WiMAX technology offers higher data rates, voice and data services as compared with the DSL and Wi-Fi technologies. In order to achieve these services, radio network planning is essential and important for a successful deployment of the WiMAX network.Radio network planning follows a stage by stage strategy to ensure the performance of the network. The work is carried out through the use of simulations. This involves the availability of enough radio resources to cover the intended area through coverage analysis. The capacity of the network is necessary to ensure that the assigned frequencies will minimize interference. The subscriber traffic is forecast to see the connectivity of the subscriber over a time interval. Keywords: WiMAX, Radio network planning 1. INTRODUCTION WiMAX, which stands for Worldwide Interoperability for Microwave Access is a telecommunication technology that provides both fixed and mobile internet services. It’s a technology based on the IEEE 802.16 standard. This Broadband Wireless Access (BWA) technology has the ability to allow high data rates, voice and as well video services [1].

WiMAX is considered as a key solution to bridging the digital divide compared with the existing technologies [2]. Such technologies include Wireless Fidelity (Wi-Fi), Digital Subscriber Line (DSL), Global System for Mobile Communications (GSM), and Integrated Services Digital Network (ISDN).

As the world is tending towards a global village, the demand for broadband access, multimedia and internet services increases and there is need for new communication technology to emerge in order to satisfy the global necessity. Such technology should have the advantage of easy accessibility at very low costs. It is in this regard that there should be a shift from the conventional cellular technologies such as the GSM and DSL to new emerging technology like the WiMAX is capable of satisfying the new demand.

With recent WiMAX deployments around the world to satisfy the demand for high data rates with increasing number of users, radio network planning is very essential and important in order to address the said objective. It gives a network operator or provider the ability to obtain the best service and coverage of an area. The topology, traffic distribution and existing infrastructure are taken into account for a successful network planning.

Effective radio network planning can be done in such a way as to achieve optimal performance. Deployment costs are reduced considerably and large geographical areas are covered in terms of capacity and cell radius. Subscriber forecast can also be foreseen before a network is deployed in a real world.

Network planning is essential to the accomplishment of a new technology because it is the last stage of preparation before a network is deployed. It is the duty of the network planning engineer to decide the locations of the base stations for coverage and capacity of the network.

Theoretical methods which could be used for

network planning came with the experience of the network planning engineer with no guarantee of optimal performance. More so, these methods use mathematical modeling, estimations, and predications which are tedious, time consuming and offer less accurate results. For a better, faster and accurate network planning, there is need for an advanced tool. This gives more realistic results and could handle large geographical areas and solve complex problems within a short period of time.

The paper is aimed at providing a work plan or a

system layout for a successful deployment for a WiMAX network in the region of Annemasse in France. It is also anticipated that it will be a viable and cost-effective solution for the WiMAX deployment. It would entail obtaining the best sites for the base stations using a line-of-sight (LOS) propagation model and the sectorization of the antennas for best functionality.

In addition, there would be an assignment of

frequencies to the base stations in such a way that there would be interference avoidance. There would also be a traffic analysis on a subscriber database peculiar to the region to enable one see the subscriber demands on the WiMAX network over a time period.

This paper is organized as follows: Section 2

discusses the literature survey. Section 3 is on radio network planning which can handle the capacity and coverage of a communication system while Section 4 summarizes the various radio propagation models that have been developed to suit different kinds of environment and our choice of model is the International Telecommunication Union (ITU) terrain model. In the following section viz; Section 5 we discuss coverage and capacity planning in which the aim is to get optimal




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locations for the base stations to build the coverage according to planning requirements. In Section 6 we present the simulation results while in the last section a summary and conclusion is given.

2. LITERATURE SURVEY

A stage-by-stage planning techniques for WiMAX was explained by [3] for a reasonable coverage, capacity and service requirement. It went further to discuss the difficulties involved in planning and introduced an in-house network dimensioning tool which was designed for WiMAX and 3G UMTS networks. The technique contains a graphical user interface (GUI) driven front end developed with visual basic software and a spreadsheet based data repository. This aids in the coverage and capacity analysis of the network. It also makes use of mathematical algorithms to calculate interference and coverage analysis.

The tool allows for the selection of design

parameters from a collection of different parameters and gives a near real life scenario in order to picture the network before the final deployment. This gives a limitation in which an experimental work should have been carried out to verify its findings.

A design of a fixed WiMAX network in the

region of Athens was presented [4]. The region is an urban area surrounded by mountains. The design of the WiMAX system is a point to multipoint deployment at an operating frequency of 3.5 GHz. It used a Geographic Information System (GIS) tool and a software palling tool for the network planning and performed a system evaluation to authenticate its findings.

There was an effective frequency assignment to

avoid interchannel interference. The coverage of Athens was considerably covered effectively by locating the sectors of the antenna to the edge of buildings. In terms of the signal strength received, the map showed that 80 % of the area is greater than 55 dBm which shows that the links are of high quality. Carrier to Noise and Interference ratio (CINR) map indicated a quality link was achieved when CINR is greater than 10 dB. When the signal level fades, the system shifts to a lower modulation in order to maintain quality and link stability.

In another development [5], gave a solution for

finding the best locations of BS from a given set of candidate locations. It also gave the performance evaluation of the network when WiMAX parameters are applied in order to optimize the system. The design of the network which depends on automatic planning and optimization tools is made up of three parts; propagation prediction, network stimulation and optimization. A set of data is collected manually such as the data collection of the digital map, network dimensioning, propagation model and the traffic model. These are then configured automatically using several mathematical iterations considering cost based on the network operator’s needs. The aim is to provide the network operator a practical

solution of optimizing the network. At the end the results obtained reflected that a number of BSs was minimized, the MSs had sufficient coverage, reasonable distance between the BSs and a good quality of service was attainable.

To find out the actual performance of a WiMAX

system through measurements in a suburban environment in Belgium, [6] studied different scenarios in which the height of the SSs and BSs were varied to see the effect on coverage. Other measurement parameters such as CINR, link throughput, indoor reception and outdoor reception of a proposed model were analyzed.

Work was carried out on the coverage

performance of an OFDM system in mobile WiMAX [7]. This was evaluated for both the uplink and downlink of the system. Fractional frequency reuse 1 and 3 was also used to evaluate the coverage. The method employed in the paper made use of mathematical formulas and algorithms to determine the propagation model and also to define the coverage.

In conclusion, mathematical solutions were

expressed by the authors in the papers discussed above. These solutions are lengthy, tedious and require a lot of mathematical knowledge for the objectives of radio network planning to be achieved. Radio network planning engineers are readily looking for practical and faster radio network planning methods in order to save time and energy. Since data rates and internet services are increasing by the day, engineers will be interested in utilizing tools and methods that could be efficient, practical and results could be obtained within short periods of time as compared to mathematical solutions and analysis. These kinds of tool are advanced software developed for radio frequency applications. 3. RADIO NETWORK PLANNING Radio network planning is now becoming a challenging task with an increasing demand for access to telecommunication technologies such as WiMAX and demand for high data rates on already existing technologies. These demands come with more complexities into the network. The challenge is to produce a radio network plan that will ensure that there are enough radio resources and the system should be able to handle the capacity, offer a good quality of service, provide adequate bandwidth and with less interference levels.

The main objective of radio network planning is to find the optimal number of base station sites required to cover a targeted geographical area. Apart from the coverage of the area, the base stations should be able to handle the capacity of the subscriber forecast. In the end the network plan should produce a cost effective deployment. The network plan is based on the assumption that the subscriber forecast has a uniform distribution, uniform topology and ideal base station location. For the required network planning to be achieved there are some




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inputs which must be known. These are the site equipment parameters, marketing parameters, and licenses regulation and propagation models [3]. The use of a network simulation software aids in the development of a radio network plan.

When planning for a network to be deployed, the network planner has also to take into consideration environmental factors such as buildings, roads, and mountains. These factors have impact on the propagation of the radio waves. The kind of environment also matters such as rural, suburban, and urban.

WiMAX network deployments are normally done in a point-to-multipoint fashion. This is where a one BS provides coverage for a number of SSs within an area. The WiMAX technology can provide up to 30 km distance range under LOS scenarios and 8 km range under nLOS scenarios. Figure1 is a flow chart that shows the stages involved in conventional network planning. No Yes

Fig 1: Phases of a Conventional Network Planning (Adapted from [8])

4. RADIO WAVE PROPAGATION This is the behavior of radio waves when they are transmitted from the BSs to the SSs. The radio wave propagation can be affected by reflection, refraction, diffraction, absorption and scattering. These can be

caused by high buildings and structures in city centers and mountains, hills and even trees in rural environments. Water vapour in the atmosphere can also cause an effect on the propagation of radio waves.

These factors can have adverse effects on the signal strength of the transmitted radio waves. To this effect propagation models have been developed to estimate radio wave propagation. The models have been developed to suit different kinds of environments to estimate the path loss between the transmitter and receiver i.e. BS and SS. Some of the commonly used propagation models include; International Telecommunication Union (ITU) terrain model, Okumura-Hata model, Standard University Interim (SUI) model, and Cost 231-Hata model [9].

The ITU model is suitable for any kind of terrain for line of sight propagation. The terrain model can be used to predict median path loss which is based on diffraction theory. It predicts path loss with respect to the height of path blockage and the first Fresnel zone. The Fresnel zone is the path followed by a signal between a transmitter and receiver. The model is also suitable for any frequency and path length and takes into consideration obstructions in communication links. It can also be used in both urban and rural environments.

The Okumura-Hata model can be used in environments where there are so many building and structure obstructions. This model is based on measured values and these measured values are used to determine the height of an antenna in a base station, the antenna height of a subscriber station, terrain roughness and localized obstructions. A weakness of this model is that it does not put shadowing and reflections into consideration.

The SUI model is a statistical model based upon three basic terrain types which are:-hilly/moderate-to-heavy tree density, hilly/light tree density or flat/moderate-to-heavy tree density, flat/light tree density. Initially this model was an extension of the Hata model but it has been modified to be applied to the WiMAX system at 3.5 GHz. This model is most suitable in nLOS propagation. However, it can be used to predict the coverage probability of a sector of a base station. It can also be used to predict the number of base stations in a geographical area.

The Cost 231-Hata model is most widely used in commercial RF planning tools and one of the most elementary propagation models based on the Okumura propagation model. The model gives a path loss graphical representation between the transmitter and receiver antennas. The Okumura model is accurate in predicting path loss especially for cellular systems.

5. COVERAGE AND CAPACITY

PLANNING In the coverage planning, the focus is to get optimal locations for the base stations to build the

COVERAGE PLANNING

(Antenna positioning and configuration)

CAPACITY PLANNING (Frequency Assignment)

QUALITY EVALUATION

(Simulation)

TARGETS ACHIEVED?

OUTPUT PLAN




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coverage according to planning requirements. The terrain of the area could be a valley, highland, plateau, mountain or a combination of two or more. These terrain characteristics are put into consideration.

The simulation planning tool is used to perform coverage planning. The tool will need the digital map of the area, the propagation model, and antenna height as inputs/parameters for the coverage to be obtained. The output of the coverage plan will just be merely a coverage prediction based upon the set parameters.

Another important area is the antenna of the base station. Small antennas can be used in urban centers whereas the large ones can be utilized in rural areas. The sectorization of the antenna could be 3 or 4 sectors. The sectors are determined by the kind of antennas used. The Omni-directional antenna usually covers a 360 degree footprint while the sartorial antenna covers a 120 degree footprint and hence 3 sectors to cover a 360 degree footprint. Each sector covers a determined number of SSs. The best locations of the base stations are determined from all possible locations that a base station can be sited. The best locations could be determined by the height of a point in an area. Also the positioning of the base station depends on the population density of the Customer Premises Equipments (CPE) or SSs i.e. in a city centre or in a rural settlement where the wider the coverage the better. Each base station should cover a prescribed cell radius.

The kind of propagation is also prescribed. It could be LOS or nLOS propagation. The LOS situation is where the transmitter and receiver are visible to one another. The NLOS is where the transmitter and receiver are not visible to each other. In this case for example, the base station is an outdoor environment and the SS could be located in a building.

The output plan of a calculated coverage using a planning tool gives composite coverage map and a best server coverage map. The composite plot shows specified thresholds (Fig.2). Gaps can easily be spotted and also overlapping areas can be investigated. To avoid such discrepancies the antenna height and the antenna down-tilt can be changed. The best server coverage map on the other side shows the coverage area of each cell with its unique color (Fig.3). Coverage thresholds are not used in this coverage. However, in capacity analysis, frequency assignment is essential to meet the traffic demand on the network. The capacity of the network ensures the network can handle the traffic and demand of the SSs. Each CPE is sufficiently covered depending on the kind of service plan. It could be for business, office or home use.

Fig 1: Composite coverage of an area

Fig 3: Best server coverage of an area 6. SIMULATION RESULTS 6.1 Base Station Locations

At the commencement of the simulations the most important input required for the successful radio




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planning is the digital cartography of the area. The digital cartography defines the geographical location of Annemasse. It contains information about the terrain of the map. Such information includes the buildings, structures, mountains, valleys, forests, and roads as shown in Fig. 4.

Fig 4: Digital Elevation Map

In this section, it is intended that a number of base stations will be selected from a pool of potential base station locations. Also, these base stations shall be considered to be on rooftops of buildings so that costs of constructing a telecommunication mast by the network operator shall be reduced.

The chosen base stations shall be spotted where

there is a high density of buildings because there will be an expectation of a high number of subscribers. The radio planning tool comes with a searching mechanism that aids in displaying all the possible locations of BS by selecting the wanted area and defining the parameters for the search site filter. The parameters used for the search site filter is shown below in Fig.5.

The search site filter was set to search 100 (max

random points) tests sites at 2m (source antennas) above ground level within the search area. The location of the base stations should be at 4m (destination antennas) above rooftops only. At the end of the search site calculation, a percentage map is displayed showing the quality of all the potential sites on rooftops of buildings (Fig.6). As seen from the map, it shows different patches of eleven colors ranging from blue to brown as shown by the lower left hand side of the map. These colors represent different assigned percentages. Each percentage value represents the percentage that can be seen out of the 100 by a high percentage of subscribers. For instance if the site has an 80% value, it means that the site can be seen by 80% of the 100 random points.

Fig 5: Search site filter

Fig 6: Base station locations In order to place or create base stations areas, the

spots with the highest percentages are noted as they reflect areas where a majority of receivers will be seen. From this map the best sites were placed for the base stations. It was also considered that the base stations should be placed where there is a high density of houses. The higher the density of houses the better for base stations to be placed. It is in this regard that our discretion that placing three (3) base stations with percentage values




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of 84%, 80% and 88% was suitable. The altitudes of the sites are 498 m, 440 m and 454 m respectively. 6.2 Base Station Setup

After the base stations have been located on the best locations, three sectors are created for the antennas. They have an azimuth spacing of 120°. Therefore three antennas will be placed at 0°, 120° and 240° coordinates. To ensure that the coverage is minimized the sectors were broken out on the rooftops at a distance of 20 m from the initial position. These parameters are set and are shown in the window below(fig.7). Note that it shows that the number of copy reflects 2 but in reality 3 sectors are created.

Fig 7: Sector Configurations The main and important parameters are the type

of signal used and the type of antenna. The signal used was a 3.5 MHz frequency division duplex (FDD). The antenna used was a multiple-input multiple-out (MIMO) antenna with 6 arrays. The other inputs such as the Tx/Rx parameters are shown in Table 1.

Table 1: Technical parameters

PARAMETER(S) VALUE(S) Frequency 3500 MHz

Nominal Power 50 W Tx Antenna Gain 15 dBi Rx Antenna Gain 15 dBi

Tx losses 0 dB Equivalent Isotropically

Radiated Power (E.I.R.P) 31547.87 W

Antenna height 25 m above ground level Tx bandwidth 3500 kHz Rx bandwidth 3500 kHz Antenna tilt -5.000

Fig.8 and Fig.9 shows the horizontal and vertical radiation patterns in polar coordinates exhibited by the antennas at the base stations. The antenna is situated at the origin of the horizontal and vertical axis. The main beam of the antenna is indicated by region of the red and blue colors. This is the region of strong radiation. There is also weak radiation in other directions indicated by the region of the black line in fig. 9.

Fig 8: Horizontal radiation pattern

Fig 9: Vertical radiation pattern 6.3 Coverage Analysis

The coverage model now dimensions the WiMAX network. The coverage expected in this section is to cover the majority of the area with very good and high field strength. This will enhance the SSs to readily pick up signals without much difficulty. Multiple simulations were carried out in this section until a desired coverage was obtained. The propagation model was set to ITU-525 model. This model was specifically chosen because it is a line of sight (LOS) model. That means the transmitter has a direct visibility with the receiver. The Fresnel zone is clear of obstructions between the transmitter and receiver. In order to calculate the coverage, a set of coverage parameters have to be inputted. These are the receiving antenna height which was set at 2m, the maximum distance of calculation set at 5 km and the minimum receiving threshold set at 65 dBm. The coverage calculation window is shown in Fig.10.




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Fig 10: Coverage calculation parameters The calculation took a few seconds and a

composite coverage is displayed showing the best field strength received (Fig. 11). This is displayed according to a default color palette. Each color has its own field strength value. It shows that the field strength decreases in strength as you move away from the base stations. It can also be read from the map that the highest field strength on the map 120 dBuV/m covers most of the populated areas. This means that there would be a good coverage of potential subscribers. Also, best server coverage was also obtained (Fig. 12). This coverage shows the coverage of each antenna of the base station sector. The composite coverage was filtered to show the coverage on rooftops. This is shown in three-dimensional view (Fig. 13).

Fig 11: Composite Coverage

Fig 12: Best server coverage

Fig 13: Rooftops best server coverage




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6.4 Capacity Analysis The next stage was to deploy the subscribers

onto the map. The subscriber database which already exists comes with the radio planning tool and it is unique to the terrain of interest which is Annemasse. The database shows the name, addresses of the subscribers, their bit rates, and their horizontal as well as vertical coordinates on the map. Fig. 14 shows the subscriber deployment. The map shows that the subscribers have been parented to each base station accordingly. Table 2 shows the number of subscribers attached to each base station and the bandwidth requirement of each subscriber.

After the subscriber database was deployed it

was noticed that the base stations couldn’t cover the subscribers. Therefore the locations of the base stations were moved to better positions since the subscribers had fixed positions. The coverage and capacity analysis was re-examined and results shown in section 6.3 and section 6.4 are the final and satisfactory outcomes.

Fig 14: Subscriber deployment

Table 2: Subscriber traffic

Next the capacity of the network will now be analyzed according the modulation pattern. The modulation map was obtained from the coverage map obtained above by updating the color palette. Each color is assigned a modulation range. Fig.15 shows the modulation map. As expected from the literature review it shows that the best modulation was 64-QAM. It had an associated data rate of 12.71 Mbps.

Fig 15: Modulation map 6.5 Spectrum Analysis

Different frequencies are allocated to the sectors of the base stations. This is done to minimize the interference levels. The frequency spectrum is assigned with the assumption that no same frequency is allowed on the same site. The assigned frequencies are 3560 MHz, 3567 MHz, 3574 MHz, 3581 MHz, 3588 MHz and 3595 MHz

Now in order to validate and also check the

quality of the frequency assignment, network interference is calculated. Fig. 16 shows the frequencies assigned to the sectors as well as the network interference map. It




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shows that there is no interference between the sectors which would have been indicated with white color patches.

Fig 16: Interference map 6.6 Traffic Analysis

The traffic is analyzed based on the quality of service. This is done on a 24-hour period to check the demand of the subscribers on the network. Table 3 shows the quality of service in the uplink and downlink. Also Fig.17 shows the graphical plot of the quality of service percentage covered in every hour for the 24-hour period. It can be observed that the quality of service drops between the hours of 9:00 am and 18:00 pm but the subscribers still have a 100 % connection. The drop which is expected shows that during the peak hours of the day when there are activities in offices and homes majority of the subscribers are on the network trying to access network resources.

Table 3: QoS in the uplink and downlink

Fig 17: 24-hour QoS 7. SUMMARY AND CONCLUSION

Research was carried out on WiMAX radio network planning based on current research trends in order to obtain new developments. Furthermore, the project was then narrowed down for a WiMAX deployment in Annemasse. This was achieved through simulations. Coverage analysis was made to obtain the best coverage. The base stations were positioned on building tops and in areas where most subscribers were sited. This is to maximize the radio resources. Frequency assignment was also carried out in such a way to reduce the interference and also incorporate the subscribers. The traffic was obtained for the subscribers for a 24-hour period to see the demand on the network.

The results obtained were good and satisfactory

based on the fact that the simulations were carried out a multiple of times and in each case adjustments were made till the target of coverage and capacity were reached. It is worthy of note that site equipment parameters, marketing parameters, and licenses regulation are not within the scope of the research but can be included for future work. For further research, propagation impairments such as




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multipath propagation, diffraction, and reflection caused by buildings on the path of signals from the base station to the subscriber and vice versa can be investigated.

ACKNOWLEDGEMENT The author is grateful to Glasgow Caledonian University, United Kingdom for providing the ICS Telecom software and the environment to carry out this research during my master's degree program. REFERENCES [1] Zhang, Y., 2007. Mobile WiMAX: Towards

Broadband Wireless Metropolitan Area Networks. New York: Auerbach Publications.

[2] Yarali A., 2007. WiMAX: A key to bridging the

digital divide. IEEE Proceedings Southeast on, pp.159-164

[3] Upase, B., 2007. Radio Network Dimensioning and

Planning for WiMAX Networks. FUJITSU Science Technology Journal, 43(4), pp.435-450

[4] Theodoras, T., 2007.WiMAX Network Planning

and System’s Performance Evaluation. IEEE Wireless Communications and Networking Conference, pp.1948-1953

[5] Gordejuela-Sanchez, F., 2009.A Multiobjective

Optimization Framework for IEEE 802.16e Network Design and Performance Analysis. IEEE Journal on Selected Areas in Communications, 27(2), pp. 202-216

[6] De Bruyne, J., 2009. Field Measurements and

Performance Analysis of an 802.16 System in a Suburban Environment. IEEE Transactions on Wireless Communications, 8(3).

[7] Jalloul, L., 2008. Coverage Analysis for IEEE

802.16e/WiMAX systems. IEEE Transactions on Wireless Communication, 7(11), pp. 4627-4634

[8] Zhang, Y., 2009. WiMAX Network Planning and

Optimization. [online].pp.370 Available from:

http://www.crcnetbase.com/ISBN/9781420066630 [Accessed 28th

July, 2010] [9] Milanovic J., 2010. Radio Wave Propagation

Mechanisms and Empirical Models for Fixed Wireless Access Systems. [online].

AUTHOR PROFILE Dauda Elijah Mshelia received a bachelor's degree in Electrical/Electronics Engineering from Abubakar Tafawa Balewa University, Nigeria in 2008. He later on received a master's degree in Wireless Communication Technologies from Glasgow Caledonian University, United Kingdom in 2010. Currently he is an assistant lecturer at the Computer Engineering Department, Faculty of Engineering and Engineering Technology, University of Maiduguri, Nigeria.

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