final fiber based

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CHAPTER1

1. INTRODUCTION

There is a growing desire for being connected to any device, anytime, and

anywhere, which is causing an increasing demand for gaining access to the radio spectrum.

However, the spectrum resources being limited, to enable bandwidth-hungry services and

applications, future broadband access systems need to combine optical and wireless access

technologies in an effective way so as to benefit from their strengths, avoid their

shortcomings, and deliver the best of both worlds to the mobile users. This purpose is full

filled by fiber based wireless access system

1.1. FIBER BASED WIRELESS ACCESS SYSTEM

Fiber based wireless access systems support high-speed multimedia in real-time by

combining the capacity of optical fiber with the flexibility of wireless networks. As its name

suggests it is a means of getting access to any kind of information anytime, anywhere in

fraction of seconds developed from two complementary technologies wireless and fiber. By

seamlessly converging optical and wireless access technologies, fiber based wireless access

system hold great promise to support a plethora of future and emerging broadband services

and applications on the same infrastructure. These systems increase capacity, Quality of

Service and support wideband multimedia services and have the possibility of utilizing

existing fiber infrastructure. They aim at combining the huge amount of available bandwidth

of optical networks and the ubiquity and mobility of wireless access systems with the

objective to reduce their cost and complexity.With the ultimate goal of providing access to

information when needed, wherever needed, and in whatever format it is needed, the vision

of technological convergence of wireless and optical networks has only becoming a necessity

but also plays a key role in future communications networks. They can be implemented usingdifferent architectures.Functions such as modulation/demodulation, up/down-converting, and

data multiplexing, can be performed at a central office serving several wireless access points,

which in turn reduces operational costs, increases flexibility, and facilitates network

scalability. Furthermore, radio resources can be allocated dynamically to wireless sites where

they are mostly needed, thus making better usage of the available radio resources, and

simplifying mobility handling.

FIBER BASED WIRELESS ACCESS SYSTEM Page 1


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The consolidation of Rof and high-speed baseband signals transport over a common optical

infrastructure is foreseen to pave the way for a seamless broadband experience for the end-

users.

1.2. ACCESS SYSTEMS

Access system is defined as a means by which one may input or output data from information

source and get the required bit of information. There are two main types of access

technologies: wired and wireless. Wired technology are those which require physical

connection to your phone or cable company's central office. Typically, coverage of these

wired technologies are limited to the area in which they are already present, or only within

their area of coverage. Wired broadband technologies are also comparatively difficult to

maintain. Network problems are more difficult to isolate because of the different hops and

central offices your data passes through. Wireless technology, on the other hand, is not

hampered by the limitations of cables or of digging trenches to access your area therefore

making it possible to extend its service nationwide.

1.3. WIRELESS ACCESS SYSTEMS

Wireless access systems provide multimedia services as well as voice services. This system

concept considers the latest trends in technologies and user demand. Wireless systems aim

at meeting specific service requirements while coping with particular transmission

impairments and optimizing the utilization of the system resources to ensure cost-

effectiveness and satisfaction for the end user. Wireless access systems potentially go almost

everywhere, but provide a highly bandwidth constrained transmission channel susceptible to

a variety of impairments.Since wireless access systems are resource limited, it is important

that the network be efficiently managed so as to maximize its resource utilization while

maintaining the Quality of Service required by various users and traffic types; objectives that

raise significant challenges in providing feasible and effective deployment and operation of

these networks. The adverse effects of the wireless propagation environment on environment

include the increasing demands for busty traffic, the variability in terms of services and

applications, and the scarce radio resources. Moreover, emerging applications impose greater

resource-sharing and dynamism demands.

1.4.MERGING OF FIBER AND WIRELESS ACCESS SYSTEMS



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Ultimate goal of internet and communication network in general is to provide access

to information when we need it, where we need it and in whatever format we need it in.to

achieve this goal, wireless and optical technologies play a key role. Traditionally wireless

and optical fiber systems have been designed separately from each other. Wireless

systems aimed at meeting specific service requirements while coping with particular

transmission impairments and optimizing the utilization of the system resources to ensure

cost-effectiveness and satisfaction for the end user. In optical systems, on the other hand,

research efforts rather focused on cost reduction, simplicity, and future-proof ness against

legacy and emerging services and applications by means of optical transparency. With the

ultimate goal of providing access to information when needed, wherever needed, and in

whatever format it is needed, the vision of technological convergence of wireless and optical

systems had not only becoming a necessity but also played a key role in future

communications networks.[4].Indeed, optical fiber does not go everywhere, but where it does

go, it provides a huge amount of available bandwidth. Wireless access systems, on the other

hand, potentially go almost everywhere, but provide a highly bandwidth constrained

transmission channel susceptible to a variety of impairments. But prohibitive cost of

supplying optical fiber to all end users premises as well as the spectrum limitation of wireless

access systems fiber based wireless access system seems to be more attractive than by relying

on either standalone. Clearly, as providers need to satisfy users with continuously-increasing

bandwidth demands, future access systems must leverage on both technologies and converge

them seamlessly, giving rise to fiber based wireless access systems. Thus by seamlessly

converging optical and wireless access technologies, fiber based wireless access system hold

great promise to support a plethora of future and emerging broadband services and

applications on the same infrastructure.



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Fig1.representation of fiber based wireless access system

Through merging of fiber and wireless access system

CHAPTER 2

2. LITERATURE SURVEY

2.1. HISTORY

Wireless access systems were discovered back in 1980s.The initial wireless access systems

were FWA (fixed wireless access systems) the scale of their installations was relatively

small. Then NWA (Nomadic Wireless Access) systems were used. They used 11-Mbps spot

access in airports, train stations, hotel lobbies, and other public places using 2.4-GHz

wireless LAN technology (conforming to IEEE802.11b).Then came mobile wireless access

(MWA) systems that could be accessed from moving vehicles. These Systems aimed at

higher transfer speeds (20 Mbps).Advantage of wireless service was that network access

could be provided to existing buildings without the need to wire them with optical fiber.

On the other hand, the scarcity of spectrum resources made it impossible to rely entirely on

wireless for access lines. As a general, higher frequencies mean more bandwidth and faster

Transmission, but also limit communications to line-of- sight (LOS),due to the slight

propagation characteristics of high-frequency waves. It therefore became important to

choose the frequency based on the type of service targeted, and to be able to configure

optical + wireless hybrid systems that combine the wireless advantages with the wide

bandwidth of optical fiber communications and this gave rise to fiber based wireless access

system.

2.2. TRENDS IN ACCESS TECHNOLOGIES



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Fig.2.2various access technologies available

2.2.1. Wired Access Systems

They are widely deployed and able to provide both high data rates and high reliability. These

features are of strong importance for many advanced applications. The popularity of these

access systems stems from the fact that they are easy to install, highly reliable, provide high

speed access and improved quality of service. There are majority of broadband access

subscribers have a wired access over telephone lines, in most cases a version of digital

subscriber line (DSL) are used. Another widely deployed wired access technology is the

hybrid fiber coax (HFC) solution that uses fiber running from the central office of a network

provider to a remote node (RN) and coaxial cable from the node to subscribers. An adequate

converter in the RN adapts the signal from one to the other transmission medium. HFC

systems reuse the widely deployed Cable TV (CATV) network infrastructure. Both these

access systems employ copper wires for transmission which have their own losses such as

low carrying capacity and complexity.So for better carrying capacity and higher bandwidth

fiber access systems are employed.

Optical fiber provides an unprecedented bandwidth potential that is far in excess of

the wireless and any other known transmission medium. A single strand of fiber offers a total

bandwidth of 25000 GHz. To put this potential into perspective, it is worthwhile noting that

the total bandwidth of radio on the planet Earth is not more than 25 GHz [10]. More

importantly, optical networks lend themselves well to offloading electronic equipments by

means of optical bypassing as well as reducing their complexity, footprint, and power

consumption significantly while providing optical transparency to modulation format, bitrate, and protocol.They majorly include PON(passive optical networks),AON(active optical



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networks) and P2P.But optical access systems are costly and more power consuming because

of use of fiber.

Fig.2.2.1.Wired access technologies.

2.2.2.Wireless Access TechnologiesWhile the wireless world is embracing different high-speed communications systems

with different radio access technologies (RAT) and complementary capabilities, such as 3G

cellular, WPANs, and WLANs, research is forging ahead to future communications systems

and networking architectures capable of providing ubiquitous packet-based connectivity for a

plethora of applications and services, with low-cost and low-power computing devices and

high security, e.g., triple play, video on demand, P2P audio/video file sharing and streaming,

multichannel HDTV, multimedia/multiparty on-line gaming, and telecommuting. To

accommodate the rapidly growing demand for multimedia services and extend the Internet

success to mobile Internet, future broadband wireless access systems are expected to provide

data rates up to 100 Mb/s with wide-area coverage and up to 1Gb/s with local area coverage,

and to be flexible enough to accommodate a wide range of transmission rates and different

degrees of traffic burstiness. Since wireless communications systems are resource limited, it

is important that the network be efficiently managed so as to maximize its resource utilizationwhile maintaining the QoS required by various users and traffic types; objectives that raise

significant challenges in providing feasible and effective deployment and operation of these

networks. They also include WiFi and Wimax. Wi-Fi suggests Wireless Fidelity the name of

a popularwireless networking technology that uses radio waves to provide wireless high

speed Internet and networkconnections. Another technology commonly used is

WiMAX (Worldwide Interoperability for Microwave Access) is a communication technology

for wirelessly delivering high-speed Internet service to large geographical areas. The adverse

effects of the wireless propagation environment on environment include the increasing

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demands for busty traffic, the variability in terms of services and applications, and the scarce

radio resources. Moreover, emerging applications impose greater resource-sharing and

dynamism demands.

Fig2.2.2.trends in wireless access system

2.2.3. Radio Over Fiber Access System

Radio over Fiber (RoF) refers to a technology whereby light is modulated by a radio signal

and transmitted over an optical fiber link to facilitate wireless access. Although radio

transmission over fiber is used for multiple purposes, such as in cable television (CATV)

networks and in satellite base stations, the term RoF is usually applied when this is done for

wireless access. In RoF systems, wireless signals are transported in optical form between a

central station and a set of base stations before being radiated through the air. Each basestation is adapted to communicate over a radio link with at least one user's mobile station

located within the radio range of said base station.

RoF transmission systems are usually classified into two main categories (RF-over-Fiber ;

IF-over-Fiber) depending on the frequency range of the radio signal to be transported. a) In

RF-over-Fiber architecture, a data-carrying RF (Radio Frequency) signal with a high

frequency (usually greater than 10 GHz) is imposed on a light wave signal before being

transported over the optical link. Therefore, wireless signals are optically distributed to base

stations directly at high frequencies and converted to from optical to electrical domain at the

base stations before being amplified and radiated by an antenna. As a result, no frequency

up/down conversion is required at the various base station, thereby resulting in simple and

rather cost-effective implementation is enabled at the base stations.

b) In IF-over-Fiber architecture, an IF (Intermediate Frequency) radio signal with a lower

frequency (less than 10 GHz) is used for modulating light before being transported over the

optical link. Therefore, wireless signals are transported at intermediate frequency over the

optical



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Fig.2.2.3. Radio Over Fiber Access System

2.2.4. WIPAS (Wireless IP access system)

WIPAS is an innovative wireless access system, easy to manage and with minimal

maintenance, offering an ideal solution to connectivity problems that require high speed

transmission in places with difficult access and at low cost.This technology can work with

two topologies to deploy the links: point-multipoint (P-MP) considering an access point (AP)

and up-to 239 wireless terminals (WT).point-to-point (P-P) made of two WT. Both

configurations offer high speed data transmission, reaching 46 Mbps for P-MP and 64 Mbps

for P-P. In addition, it has adaptive modulation schemes that adjust to environmental

conditions, reducing the probability to loose connectivity, making it a very reliable system.

WIPAS works at a frequency of 26GHz far in this term from any other wireless data

communication system and therefore having almost no impact in terms of interference.

This feature brings a high quality and secure communication. Finally, the communication

devices are compact and lightweight; they can be installed in any facility, proving to work

continuously under heavy duty. It employs fiber based wireless access system and radio overfiber technology thus this can be considered as the most recent development in the wireless

access systems



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Fig.2.2.4.wireless IP access system in comparison with WiFi

CHAPTER 3

3.NEED OF FIBER BASED WIRELESS ACCESS SYSTEM

Wireless access systems and fiber access systems were in their own way sufficient for

meeting the needs of an people for speedy and reliable access. But both these characteristics

were achieved at the cost of reduced bandwidth and increased complexity. Wireless access

systems could not provide larger carrying capacity whereas fiber access systems architecture

got more complex with increased number of users and even the cost of construction and

power consumption increased.so there was a growing need for technology which could for

the disadvantages of both the technologies as well as include assets of both these

complimentary technologies which gave rise to development of a technology which could

provide the users with best of both worlds i.e. fiber based wireless access system. Thus

Though each of these systems have their own pros and cons still fiber based wireless access

system outcasts most of them with the improved quality of service (QoS) on account of use of

wireless system and enable wideband services because of employment of optic fibers in the

access system. Optical fiber based wireless access schemes receive renewed attention with



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the popularity of hot-spots. Although existing hot-spots are typically supported by Wi-Fi

access, a similar architecture is often useful to provide cellular services [1]. These optical

fiber based micro cells not only increase the capacity, but also improve the quality of service

(QoS) and enable wideband services. This approach is often useful in crowded areas such as

supermarkets, airport concourses and subway stations where the macro-cellular architecture

is inadequate. Furthermore the ability to use existing dark fiber for radio over-fiber solutions

will significantly reduce the deployment cost and time. Note that, most of the modern cities

have extensive fiber infrastructure and often there is additional dark fiber in the same conduit

that can be used for this purpose.There is an increasing demand from broadband

telecommunication end-users to have instant access to high-capacity information services,

whether from a fixed or a mobile terminal. Recently fiber based wireless technology has

attracted more and more attention to provide wireless connectivity due to its advantages of

low-transmission loss and high bandwidth of optical fibers

CHAPTER 4

4.WORKING OF FIBER BASED WIRELESS ACCESS SYSTEM

4.1.TWO MAJOR WAYS OF REALISING FIBER BASED WIRELESS ACCESS

SYSTEM

4.1.1.Use Of Most Cell Station

The basic configuration of such systems is shown in Fig. 1. They use optical fiber between

the access control equipment (ACE) and RAPs. Since the modulators and demodulators



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Fig4.4.1.basic figure of fiber based wireless access system

(MODEMs) and controllers for each microcell are centrally housed in the ACE, each RAP

consists of only a transmitter (TX), receiver (RX), electric-to-optic converter (E/O) and optic-

to-electric converter (O/E). This reduces RAP size and complexity. Other advantages include

higher transmission capacity, easier system deployment, and effective MODEM use.

4.4.2.Use of hot spots and wireless access points



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Fig4.4.2.Design of fiber based wireless access system using wireless access point

This type majorly uses wireless hotspots technique just as in case of wifi realisation.

Optical fiber based wireless access schemes receive renewed attention with the popularity of

hot-spots. Although existing hot-spots are typically supported by Wi-Fi access, a similar

architecture is often useful to provide cellular services [1]. These optical fiber based micro

cells not only increase the capacity, but also improve the quality of service (QoS) and enable

wideband services. This approach is often useful in crowded areas such as supermarkets,

airport concourses and subway stations where the macro-cellular architecture is inadequate.

Furthermore the ability to use existing dark fiber for radio over-fiber solutions will

significantly reduce the deployment cost and time. Note that, most of the modern cities have

extensive fiber infrastructure and often there is additional dark fiber in the same conduit that

can be used for this purpose

4.2MOSTcell station

The concept behind the fiber-oriented wireless system, called "MOST", is shown in Fig. 2.

Many MOST-cell stations (M-CSs) are connected to the access control station (ACS) by

optical fibers. The CS in each cell houses a radio transmitter and receiver (TX/RX) including

frequency converters, a supervisory control, electric-to-optic converters (E/ 0), and optic-to-

electric converters (O B). The ACS is fabricated using modulators / demodulators

(MODEM), time division multiple access (TDMA) circuits, operation software (CONT),

supervisory control, network interface (INT), E/O, and O B



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l

Fig.4.2.basic structure of MOST

. A small optical interface (O B and E/O) is key to achieving a compact commercial CS,

however, such an interface has not yet to be developed. A wide dynamic range is another

important point that must be provided for radio system applications. Both low noise and

linearity are required for this optical interface.

4.3. Subcarrier multiplexing in fiber based wireless access system

The subcarrier multiplexing (SCM) technique has many advantages for wireless

systems applications, especially in cellular and microcell systems. This technique features

direct RF/IF signal transmission over an optical fiber. The flexibility of the wireless systems

is significantly enhanced enabling construction of a simple cell station (CS) located in each

cell to be achieved. The broadband characteristic of an optical fiber encourages High bit rate

communication, e.g., data and video transmission. Applying the SCM technique is the way to

enhance future personal multimedia communications.



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4.4. SEFA and SSM Technology

Since the technology involves fiber structure Signal to noise ratio play an important role

in case of fiber based wireless access systems. There are two signal to noise ratios involved,

the optical SNR (OSNR) and the electrical SNR. These two form the cumulative SNR in the

concatenated fiber-wireless channel. The OSNR is a function of the modulation index m,

E/O, O/E conversion losses and, the fiber length. Shot, RIN and thermal noises terms are

involved in the OSNR. The OSNR should be greater than the expected SNR at the cell

boundary for a reasonable link design. So in order to improve the overall performance signal

extraction frequency is used Signal extraction and frequency arrangement (SEFA) technology

is proposed in the trial system to improve the input dynamic range. In this technique, each

desired received signal is extracted by tuning in an M-CS, and then the frequency of each

extracted signal is converted for avoiding IM3. The frequency converted signals modulate the

LD. Since LD non-linearity can be ignored, SEFA can increase the optical modulation index

proportional to the electrical input power into LD. Of course, each extracted signal power

level can be adjusted by AGC or a limiter. That is to say, this improves the SNR. On the other

hand, conventional simple transmission cannot increase the optical modulation index, since

LD nonlinearity must be taken into account.Signal extraction with frequency arrangement

(SEFA) was proposed to prevent the optical modulation index from restricting performance.

This leads to large optical modulation index and large receiver gain .It was confirmed by

simulation that the SEFA provides great improvements in DUR. In SEFA, larger DUR

improvement was obtained with worse conditions in the optical feeder. A 5-dB improvement

was obtained using a DFB-LD (which provides good conditions). Even using an FP-LD,

which provides poor conditions in an optical feeder and which has not been investigated well

as an E/O device because of its undesirable characteristics, we obtained about 11 dB of DUR

improvement.

The superimposed subcarrier modulation (SSM) is amethod for reducing the

reflection noise induced by fiber connectors. For optimizing the input power and frequency of

the superimposed subcarrier, RIN and IM3 performance was measured under single-mode

and reflective-fiber conditions.SSM was confirmed experimentally to be effective for

reducing the reflection noise. The input power of the superimposed subcarrier corresponded

to an index value of less than 0.6 of the total optical modulation index including desired

signals. A RIN improvement of about 11 dB was obtained when fc=1GHz and pc=5 dBm.



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Combining SSM and SEFA, a larger improvement in DUR is obtained under worse

optical conditions, such as using FP-LDs may find application in wireless systems using

subcarrier optical transmission.

4.5. Signal Processing for Optical Fiber based Wireless Access

Wireless communications has entered a new phase. The focus is shifting from

voice to multimedia services, which need wideband radio links. Furthermore, new wireless

subscribers are signing up at an increasing rate demanding more capacity. Micro and pico

cellular architecture is an attractive solution for both of these issues because; it increases the

frequency reuse and enables wideband access. In this micro/pico cell scenario, low power

radio access points (RAPs) should provide wireless access instead of conventional base

stations for cost considerations. These radio access points should be robust and have low

complexity and connected to the central base station via radio-over-fiber (ROF) 1 links [1].

Figure 1 (left) shows such architecture and Figure 1 (right) gives a closer look at the

downlink. The focus of this work is to investigate various signal processing strategies to

provide a cost-effective, high performance solution for high-speed fiber based wireless

access. We have been investigating signal-processing strategies to improve the performance

of fiber based wireless access schemes cost-effectively.

Several observations can be made from Figure 1. First, the signal at the radio access

point (RAP) is either at optical frequencies or at radio frequencies, but not at baseband

frequencies. Therefore, baseband signal processing cannot be (cost-effectively) done at the

RAP 2.

Figure4.5. Architectural and functional schematics of the fiber based wireless access scheme



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Therefore, the (baseband) compensation should preferably be done at the portable

unit or at the central base station rather than at the RAP. Note that in both of these cases, the

optical fiber channel that is concatenated with the wireless channel should be handled jointly.

This is a challenging task because of the time varying dynamic nature of the multipath

wireless channel and nonlinear characteristics of the optical channel. Furthermore, the uplink

and downlink have different channel combinations in this scenario and require separate

solutions. Secondly, it is desirable not to modify the portable units because of the ROF link.

In other words, the portable unit should not be aware of the existence of the ROF link. This

deliberation makes seamless roaming between fiber-based and conventional wireless systems

possible and, reduces the cost of portable units. Thirdly, since one central base station

supports several radio access points and a large number of portable units, the cost of the

central base station is shared among many users. Therefore, by performing most of the signal

processing centrally rather than at portable units, or by asymmetric distribution of the

complexity, the overall system cost is reduced. In addition to the nonlinear distortion,

multipath dispersion of the wireless link is also a major factor that limits the system

performance.

The fiber-wireless uplink consists of a linear dynamic system (the wireless channel) followed

by a static nonlinear system (the ROF link). Therefore, it can be modelled as a Wiener systemfor Gaussian inputs. However, due to the practical difficulties in generating Gaussian inputs,

different approaches have been proposed. Pseudo noise (PN) sequences have white noise like

properties and, easy to generate and analyse. Their correlation properties are well understood.

Besides, maximal length PN sequences are widely used in spread spectrum communications.

Therefore, using PN sequence for channel estimation is very attractive in wireless

communications. The fiber-wireless channel has the following properties:

1. The wireless channel varies relatively fast. Therefore, the compensation should follow it in

real time.

2. The nonlinearity comes from the laser diode and from the RF amplifier. Hence, it is almost

stationary. That means the nonlinear compensation needs to be updated only occasionally.

3. When multiple users are supported by this fiber based wireless access scheme, each user

has a different wireless channel. But all of them will share the same ROF channel.



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CHAPTER 5

5. APPLICATIONS OF FIBER BASED WIRELESS ACCESS SYSTEM

Fiber based wireless access system is majorly employed in fields where we require speed as

well as large bandwidth. The major applications of fiber based wireless access systems may

be given as follows:

1. Broadband communication and access

2. FFTA

3.Telepresentations

5.1. Broadband communication and access

They can be employed for broadband mobile communications because of improve the

quality of service (QoS) and enabled wideband services. Optical broadband access

technologies providing high-speed optical connections to the end users, will play an essential

role in alleviating the last mile bottleneck for next generation access networks. With the cost-

reduction in optoelectronic technologies for the past few years, it becomes apparent that

optics will move deeper and deeper into the networks to provide the much-needed bandwidth.

Compared to the traditional connections via copper, optical systems can certainly offer at

least 10 to 100 times more bandwidth over a much larger coverage area, hence having the

potential to sign up a sufficient number of customers to support the upgrade efforts. The

point-to-multi-point topology further enables flexible deployment toward reaching a large

number of end points. Optical wireless technology can be a complementary solution to the

fiber-based access networks. The principle of optical wireless technology is to use laser

beams to transmit high-speed (mega-gigabit per second) data via point-to-point or meshtopologies through the air2. This is an attractive candidate to provide last-mile connections

(up to 5 km) where the buildings are close to the fiber-optic infrastructure but not directly

connected with fibers. The transmitting and receiving unit is a telescope with an incorporated

optical transceiver, thus allowing bi-directional transmission. Most vendors employ laser

beams at 780-920nm range to achieve lower cost while some others use 1550- nm lasers to

achieve better eye-safe operation. No FCC license is required for transmission at such optical

frequencies. As a line-of-sight technology, optical wireless systems are vulnerable to several

environmental factors, including bad weather, poor atmospheric visibility, building sway,



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scintillation, etc. However, these can be resolved by systems with built-in intelligence such

as automatic tracking and alignment, etc. To obtain even better reliability, unlicensed

frequency radio systems can be used to back up the optical wireless systems when the

weather condition is poor.

5.2. FFTA (Fiber To The Antenna)

By using an optical connection directly to the antenna, the equipment vendor can gain several

advantages like low line losses, immunity to lightning strikes/electric discharges and reduced

complexity of base station by attaching light weight Optical-to-Electrical (O/E) converter

directly to antenna

5.3. Telepresentation

Telepresentation refers to substituting the step of transportation of a person to a destination

where his presence is necessitated solely for the purpose of exchange of information by

telepresence or videoconferencing or video telephony in order to minimize the anticipated

future traffic gridlocks which mandate that the burdens on the transportation infrastructure be

reduced to a fifth or at a minimum to a third of the current volumes. Term telepresence refers

to a set of technologies that allow a person to feel as if present, to give the appearance that a

person is present, without actually being there thus to have an effect, via telerobotics, at a

place other than their true location of the person. Telepresence requires that the users' senses

be provided with such stimuli as to give the feeling of being in that other location.

Additionally, users may be given the ability to affect the remote location. In this case, the

user's position, movements, actions, voice, etc. may be sensed, transmitted and duplicated in

the remote location to bring about this effect. Therefore information can travel in both

directions between the user and the remote location. A popular application is found in

telepresence videoconferencing, a higher level of video telephony which deploys greater

technical sophistication and improved fidelity of both video and audio than in traditional

videoconferencing.



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CHAPTER 6

ADVANTAGES AND DISADVANTAGES

6.1.ADVANTAGES:

6.1.1. Improved the quality of service (QoS) and immunity to low line losses

This technology combines the assets of two of the leading technologies and covers up

their shortcomings thus providing improved quality of service.

It provides immunity to low line losses such as lightning strikes/electric discharge

6.1.2. Large Bandwidth

Optical fiber provides an unprecedented bandwidth that is far in excess than any other

known transmission medium and offers significantly longer ranges without requiring any

active devices. Optical fibres offer enormous bandwidth. The enormous bandwidth offered by

optical fibers has other benefits apart from the high capacity for transmitting microwave

signals. The high optical bandwidth enable high speed signal processing that may be more

difficult or impossible to do in electronic systems

6.1.3. Economical and high speed system

Fiber based wireless access system aim at combining the huge amount of available

bandwidth of optical networks and the ubiquity and mobility of wireless access networks

with the objective to reduce their cost and complexity

6.1.4. Low Maintenance

Optical fiber has some further advantageous properties such as longevity and lowmaintenance which will eventually render fiber the medium of in wired first/last mile access

networks in most of todays green field

6.1.5. Flexibility

Since optical fibers are used in fiber based wireless access systems hence the system can

reach to any remote location thus providing a better flexibility. Thus flexibility is one of the

most prominent advantages of fiber based wireless system.



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6.1.6. Transparency

Fiber based wireless access system provide transparency against data rate and signal

format, which eased carriers worldwide into deploying future-proof passive optical network

(PON) outside plants that can be flexibly upgraded as new technologies mature or new

standards evolve and meet the requirements of future

6.2.DISADVANTAGES

6.2.1. Noise and losses in the signals

The single mode fiber has enough bandwidth to support radio-over-fiber transmission

up to several GHz. However, the RF power that can be transmitted over fiber is very limited.

Typically 40 dB signal loss occurs just due to E/O and O/E conversion only. Half of this loss

is contributed to impedance mismatch between the 50 ohm RF system and the low impedance

laser diode at the E/O converter and, the high impedance photo diode and the 50 ohm output

at the O/E converter. Reactive matching techniques decrease these losses at the expense of

bandwidth. In addition, due to square law detection, any loss in the optical domain appears

twice in the electrical domain in log scale. These factors make the received signal at the end

of the radio over fiber (ROF) link weak at which point optical noise is added to the signal.

This noisy signal is then amplified and radiated to the air where it is further attenuated and

polluted with noise. The challenge is to recover the original information at the portable unit to

provide adequate QoS.

The overall signal to noise ratio is a function of various noise mechanisms of the ROF

link, mainly the shot, thermal and relative intensity noise (RIN) and the wireless channel

noise. Of these noise mechanisms, shot noise is a function of the mean optical power while

the RIN is a function of the square of the optical power. The RIN dynamically increases with

the power of the modulating RF signal. In addition to the above are the wireless channel

additive noise and thermal noise that are signal independent. Furthermore, the higher the

radio signal bandwidth, the higher the noise power collected at the ROF link.



21/23

Fig.6.2.1 block diagram of losses and added noise

6.2.2. Expensive

Since this system employs optical fiber hence it is more expensive as compared to

other wireless access systems though it is less costlier as compared to fiber access systems.



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CHAPTER 7

7.CONCLUSION

Fiber based wireless access systems support high-speed multimedia in real-time by

combining the capacity of optical fiber with the flexibility of wireless networks

The integration of optical and wireless systems is considered to be one of the most promising

solutions for increasing the existing capacity and mobility as well as decreasing the costs in

next-generation optical access systems.

By seamlessly converging optical and wireless access technologies, fiber based wireless

access systems hold great promise to support a plethora of future and emerging broadband

services and applications on the same infrastructure



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CHAPTER 8

REFERENCES

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[3] H. Ohtsuka, R. Ohmoto, T. Shimizu, and H. Arai, Fiber-optic wireless

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[4] K. Araki and H. Ohtsuka, Fiber-oriented wireless systems for intelligent

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[6] http://ieeexplore.ieee.org/xpl/freeabs_all.jsp

[7] Xavier Fernando, Signal Processing for Optical Fiber based Fiber Wireless Access, Ph.D.

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[8] R. Olshansky, V. A. Lanzisera, and P. M. Hill, Subcarrier multiplexed lightwave

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http://ieeexplore.ieee.org/search/srchabstract.jsp?tp=&arnumber=1313205&queryText%3DFIBER+BASED+WIRELESS+ACCESS+SYSTEM%26openedRefinements%3D*%26filter%3DAND(NOT(4283010803))%26searchField%3DSearch+Allhttp://ieeexplore.ieee.org/search/srchabstract.jsp?tp=&arnumber=1313205&queryText%3DFIBER+BASED+WIRELESS+ACCESS+SYSTEM%26openedRefinements%3D*%26filter%3DAND(NOT(4283010803))%26searchField%3DSearch+Allhttp://ieeexplore.ieee.org/search/srchabstract.jsp?tp=&arnumber=1313205&queryText%3DFIBER+BASED+WIRELESS+ACCESS+SYSTEM%26openedRefinements%3D*%26filter%3DAND(NOT(4283010803))%26searchField%3DSearch+Allhttp://ieeexplore.ieee.org/search/srchabstract.jsp?tp=&arnumber=1313205&queryText%3DFIBER+BASED+WIRELESS+ACCESS+SYSTEM%26openedRefinements%3D*%26filter%3DAND(NOT(4283010803))%26searchField%3DSearch+Allhttp://ieeexplore.ieee.org/search/srchabstract.jsp?tp=&arnumber=1313205&queryText%3DFIBER+BASED+WIRELESS+ACCESS+SYSTEM%26openedRefinements%3D*%26filter%3DAND(NOT(4283010803))%26searchField%3DSearch+Allhttp://ieeexplore.ieee.org/search/srchabstract.jsp?tp=&arnumber=1313205&queryText%3DFIBER+BASED+WIRELESS+ACCESS+SYSTEM%26openedRefinements%3D*%26filter%3DAND(NOT(4283010803))%26searchField%3DSearch+Allhttp://ieeexplore.ieee.org/search/srchabstract.jsp?tp=&arnumber=1313205&queryText%3DFIBER+BASED+WIRELESS+ACCESS+SYSTEM%26openedRefinements%3D*%26filter%3DAND(NOT(4283010803))%26searchField%3DSearch+Allhttp://ieeexplore.ieee.org/search/srchabstract.jsp?tp=&arnumber=1313205&queryText%3DFIBER+BASED+WIRELESS+ACCESS+SYSTEM%26openedRefinements%3D*%26filter%3DAND(NOT(4283010803))%26searchField%3DSearch+Allhttp://ieeexplore.ieee.org/search/srchabstract.jsp?tp=&arnumber=1313205&queryText%3DFIBER+BASED+WIRELESS+ACCESS+SYSTEM%26openedRefinements%3D*%26filter%3DAND(NOT(4283010803))%26searchField%3DSearch+Allhttp://ieeexplore.ieee.org/search/srchabstract.jsp?tp=&arnumber=1313205&queryText%3DFIBER+BASED+WIRELESS+ACCESS+SYSTEM%26openedRefinements%3D*%26filter%3DAND(NOT(4283010803))%26searchField%3DSearch+All

final fiber based

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