iii

SIMULATION OF WCDMA RADIO OVER FIBER TECHNOLOGY

SITI HARLIZA BINTI MOHD RAZALI

A project report submitted in partial fulfillment of the

Requirements for an award of the degree of

Master of Engineering (Electrical-Electronics and Telecommunication)

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

APRIL 2007

ii

“I hereby, declare that I have read this thesis and in my

opinion this thesis is sufficient in terms of scope

and quality for the award of degree of

Master of Engineering (Electrical-Electronics and Telecommunication)

Signature : ______________________

Name of Supervisor : DR. RAZALI BIN NGAH

Date : 13 APRIL 2007

iv

I declare that this thesis “Simulation of WCDMA Radio Over Fiber Technology ” is the

result of my own research except for works that have been cited in the reference. The

thesis has not been accepted any degree and not concurrently submitted in candidature

of any other degree.

Signature : ______________________

Name of Author : SITI HARLIZA BINTI MOHD RAZALI

Date : 13 APRIL 2007

v

Dedicated to my loving husband & family, ABG HAKIM & MAMA,

ANGAH, NINI, AISHAH and my adorable baby HAZIQ.

vi

ACKNOWLEDGEMENT

Alhamdulillah, I am greatly indebted to ALLAH SWT on His blessing for

making this study successfully.

I would like to express my gratitude to honorable Dr. Razali Bin Ngah, my

supervisor, for his guidance, support and encouragement throughout my study. I am

also thank you to my colleagues for providing an enjoyable study environment at UTM.

Finally, I would like to thank my husband and my mum, angah, nini and aishah

for their full support and patience. For my baby, I hope to make up for all the lost time

that we have not spent together.

vii

ABSTRACT

The demand for broadband services has driven research on millimetre wave

frequency band communications for wireless access network due to its spectrum

availability, and compact size of radio frequency devices. However, the mm-wave

signals suffer from severe loss along the transmission as well as atmospheric

attenuation. In other words, upcoming wireless networks will use a combination of air-

interface methods in different channels and in different cells that can be changed

dynamically to meet variations in traffic conditions. One of the solution to overcome

these problem is by using low-attenuation, electromagnetic interference-free optical

fiber. Radio over Fiber (RoF) is integration of optical fiber for radio signal transmission

within network infrastructures that is considered to be cost-effective, practical and

relatively flexible system configuration for long-haul transport of millimetric frequency

band wireless signals. This project is about to simulate WCDMA Radio Over Fiber

using Matlab Simulink. By doing so, the efficiency can be measured by the performance

of BER (Bit Error Rate). The finding of this project is the WCDMA RoF is suite with

3G and 4G application along with increasing users every year whole the world. The

conclusion is the simulation of WCDMA RoF was success developed throughout

objective.

viii

ABSTRAK

Permintaan yang semakin tinggi dalam perkhidmatan jalur lebar telah membuka

ruang para penyelidik untuk mengkaji dan menyelidik dalam bidang komunikasi jalur

frekuensi gelombang milimeter untuk rangkaian penyampai tanpa wayar yang

bergantung pada ketersediaan spektrum dan saiz kompak sesuatu alat radio frekuensi

itu. Walau bagaimanapun, isyarat gelombang milimeter ini terancam kepada gangguan

sepanjang proses penghantarannya seperti gangguan atmosfera. Dengan kata lain,

perkembangan rangkaian tanpa wayar menggunakan kombinasi kaedah ruang

hubungkait udara dalam saluran yang berlainan dan sel-sel yang berlainan yang boleh

berubah secara dinamik untuk variasi penyesuaian dalam kondisi bebanan. Antara jalan

penyelesaian untuk mengatasi masalah tersebut ialah menggunakan pengecilan yang

rendah, gentian optik bebas gangguan elektromagnetik. Isyarat radio menggunakan

gentian diintegrasikan dari gentian optik untuk penghantaran isyarat radio dalam

rangkaian infrastruktur yang mempertimbangkan kos-efektif, praktikal dan sistem

konfigurasi fleksibel secara relatif untuk penghantaran jarak jauh isyarat jalur frekuensi

tanpa wayar. Projek ini berkisar dengan simulasi WCDMA isyarat radio dalam gentian

menggunakan perisian Matlab Simulink. Dengan itu, keberkesanannya boleh diukur

melalui kadar kesalahan bit (BER) yang diperolehi dari simulasi tersebut. Projek ini

menemukan penggunaan WCDMA isyarat radio dalam gentian ini sangat sesuai

digunakan bagi pembangunan sistem 3G dan 4G dengan pertambahan pengguna setiap

tahun di seluruh dunia. Kesimpulannya, simulasi ini berjaya dibangunkan mengikut

objektif projek.

ix

TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION iv

DEDICATION v

ACKNOWLEDGEMENT vi

ABSTRACT vii

ABSTRAK viii

TABLE OF CONTENTS ix

LIST OF TABLES xiii

LIST OF FIGURES xiv

LIST OF ABBREVIATIONS xvi

1 INTRODUCTION

1.1 Introduction 1

1.2 Objective of Study 3

1.3 Scope of Project 4

1.4 Research Methodology 5

1.5 Thesis Outline 7

x

2 RADIO OVER FIBER

2.1 Introduction 8

2.2 What Is RoF? 8

2.3 The Radio Over Fiber Technology 11

2.4 Radio Over Fiber System 12

2.5 Radio Over Fiber Concept 13

2.6 Advantages Of Using RoF In Mobile Communication Networks 15

2.7 Benefits of Radio over Fiber Systems 16

2.7.1 Low Attenuation Loss 16

2.7.2 Large Bandwidth 17

2.7.3 Immunity to Radio Frequency Interference 18

2.7.4 Easy Installation and Maintenance 19

2.7.5 Reduced Power Consumption 19

2.7.6 Operational Flexibility 20

2.7.7 Millimeter Waves 21

2.7.7.1 Advantages of mm-waves 21

2.7.7.2 Disadvantages of mm-waves 21

2.7.8 Radio System Functionalities 22

2.8 Applications of Radio over Fiber Technology 22

2.8.1 Cellular Networks 23

2.8.2 Satellite Communications 23

2.8.3 Video Distribution Systems 24

2.8.4 Mobile Broadband Services 24

2.8.5 Wireless LANs 25

2.8.6 Vehicle Communication and Control 26

2.9 Summary 26

xi

3 WIDEBAND CODE DIVISION MULTIPLE ACCESS (WCDMA)

3.1 Introduction 27

3.2 RoF Using WCDMA 27

3.3 Parameters Of WCDMA 32

3.4 WCDMA Overview 35

3.4.1 Direct-Sequence CDMA 35

3.4.2 Wideband 36

3.4.3 Synchronization Aspects 36

3.4.4 Modes of Operation 37

3.5 Basic WCDMA Transmission Technologies 42

3.6 Characteristics Of WCDMA (Technical) 42

3.6.1 Highly Efficient Frequency Usage 42

3.6.2 Freedom From Frequency Administration 43

3.6.3 Low Mobile Station Transmit Power 43

3.6.4 Resources Used Independently in Uplink and Downlink 44

3.7 The Wideband Properties Of WCDMA Allow Higher Efficiency

In The Following Aspects 44

3.7.1 Wide Range of Data Speeds 44

3.7.2 Improved Multipath Resolution 45

3.7.3 Statistical Multiplexing Effect 45

3.7.4 Reduced Intermittent Reception Rate 45

3.8 Summary 46

xii

4 SIMULATIONS

4.1 Introduction 47

4.2 Simulations 47

4.2.1 BPSK Modulation 48

4.2.2 QPSK Modulation 49

4.2.3 QPSK Modulation using RoF 51

4.3 Results and Discussion 52

4.3.1 BPSK vs QPSK 56

4.3.2 RoF with different of Fiber Length 57

4.4 Summary 60

5 CONCLUSION AND SUGGESTIONS

5.1 Conclusion 61

5.2 Suggestion For Future Research 62

REFERENCES 64

xiii

LIST OF TABLES

TABLE TITLE PAGE

3.1 Parameter of WCDMA 33

3.2 Comparison of 2G and 3G CDMA Systems 34

xiv

LIST OF FIGURES

FIGURE TITLE PAGE

1.1 Research methodology flow chart 5

2.1 Typical layout of a bidirectional analog optical link using direct

modulation of laser diodes 11

2.2 Radio over Fiber Concept 12

2.3 Optically fed remote antenna network for microcellular RoF

systems 14

3.1 The basic techniques of the Direct Sequence Spread Spectrum 38

3.2 Principles of DS-CDMA 40

3.3 Allocation of bandwidth in WCDMA in the

time-frequency-code space 41

3.4 Spreading and dispreading in DS-CDMA 41

4.1 Constellation Diagram for BPSK 48

4.2 Block simulink for BPSK Modulation 49

4.3 Constellation Diagram for QPSK 50

4.4 Block simulink for QPSK Modulation 50

4.5 Block simulink for WCDMA using RoF 51

4.6 Theoretical BER performance with AWGN channel 52

4.7 BER performance with AWGN channel for BPSK 53

4.8 BER performance with AWGN channel for QPSK 54

4.9 Comparison BER of BPSK and QPSK 55

4.10 Comparison BER of BPSK, QPSK and Theory 56

xv

4.11 BER performance for fiber length 0.2 km 57

4.12 BER performance for fiber length 1 km 58

4.13 BER performance for fiber length 48 km 59

4.14 Comparison BER between 0.2 km, 1 km and 48 km 59

xvi

LIST OF ABBREVIATIONS

AWGN Additive White Gaussian Noise

BER Bit Error Rate

BPSK Binary Phase Shift Keying

BS Base Stations

DWDM Dense Wavelength Division Multiplex

EDFA Erbium Doped Fiber Amplifier

FDD Frequency Division Duplex

GMSK Gaussian Minimum Shift Keying

GSM Global System for Mobile Communications

IF Intermediate Frequencies

IMDD Intensity Modulation and Direct Detection

ITS Intelligent Transport Systems

IVC Inter-Vehicle Communication

LAN Local Area Network

MBS Mobile Broadband System

MS Mobile Station

MVDS Multipoint Video Distribution Services

OFDM Orthogonal Frequency Division Multiplexing

OTDM Optical Time Division Multiplexing

POF Polymer Optical Fiber

PSK Phase Shift Keying

QAM Quadrature Amplitude Modulation

QPSK Quadrature Phase Shift Keying

xvii

RAP Radio Access Point

RF Radio Frequency

RFI Radio Frequency Interference

RHD Remote Heterodyning and Detection

RIN Relative Intensity Noise

RS Remote Station

ROF Radio Over Fiber

RVC Road-to-Vehicle Communication

SC Switching Centre

SMF Single Mode Fiber

TDD Time Division Duplex

UMTS Universal Mobile Telecommunication Systems

UTRA Universal Terrestrial Radio Access

WBMCS Wireless Broadband Mobile Communication Systems

WCDMA Wideband Code Division Multiple Access

CHAPTER 1

INTRODUCTION

1.1 Introduction

Radio over Fiber (RoF) application has attracted much attention recently because

of the increasing demand for capacity/coverage and the benefits it offers in terms of

low-cost base station deployment in macrocellular system. RoF systems are now being

used extensively for enhanced cellular coverage inside buildings such as office blocks,

shopping malls and airport terminal. RoF is fundamentally an analog transmission

system because it distributes the radio waveform, directly at the radio carrier frequency,

from a central unit to a Radio Access Point (RAP). Note that although this transmission

system is analog, the radio system itself may be digital such as GSM.

Mainstream optical fiber technology is digital. Telecommunication networks use

synchronous digital hierarchy transmission technology in their cores. Fiber-based data

networks such as fiber distributed data interface and gigabit Ethernet all use digital

transmission. Fiber transmission links to base stations in mobile communications

systems are digital. Digital optical fiber transmission links are therefore ubiquitous in

telecommunications and data communications, constituting a high volume market worth

billions of dollars worldwide.

2

Wideband Code Division Multiple Access (WCDMA), air interface can now is

regarded as a mature technology ready to provide the basis for the third generation

wireless personal communication systems, known as ‘Universal Mobile

Telecommunication Systems’ (UMTS). These systems will make extensive use of

microcells and picocells in order to deliver high bandwidth services to customers.

WCDMA also known as third generation systems. The systems are designed for

multimedia communication can be enhanced with high quality images and video and

access to information and services on public and private networks will be enhanced by

the higher data rates and new flexible communication capabilities of third generation

systems. This together with the continuing evolution of the second-generation systems

will create new business opportunities for manufacturers, operators and the providers of

content and applications using these networks.

In the standardization forum, WCDMA technology has emerged as the most

widely adopted third generation air interface. Its specification has been created in 3GPP

(the 3rd Generation Partnership Project), which is the joint standardization project of the

standardization bodies from Europe, Japan, Korea, the USA and China. Within 3GPP,

WCDMA is called UTRA (Universal Terrestrial Radio Access), FDD (Frequency

Division Duplex) and TDD (Time Division Duplex). The name of WCDMA being used

to cover both FDD and TDD operation.

The benefit of using RoF for WCDMA distributed antenna systems is expected

to be even more important, partly because of their higher frequency and bandwidth

requirements.

In this project, the simulation of WCDMA RoF using Matlab Simulink had

successful developed. In this simulation, the fiber was represented by gain and 3rd order

3

polynomial was represented laser diode. The complete simulink block successfully run

and get BER performance to rate it.

1.2 Objective of Study

Objective of this research is to simulate a WCDMA radio over fiber (RoF) for

microcellular mobile communication systems using Matlab Simulink.

To achieve this objective various simulink blocks are developed such as with

AWGN Channel, polynomial as laser diode and gain is present fiber using MATLAB

SIMULINK.

From the research, main cause of using RoF is to shift the system complexity

away from the remote base station antenna and toward centralized radio signal

processing installation. In a RoF link, laser light is modulated by a radio signal and

transported over an optical fiber medium. The laser modulation is analog since the

radio-frequency carrier signal is an analog signal. The modulation may occur at the

radio signal frequency or at some intermediate frequency if frequency conversion is

utilized.

The basic configuration of an analog fiber optic link consists of a bi-directional

interface containing the analog laser transmitter and photodiode receiver located at a

base station or remote antenna unit, paired with an analog laser transmitter and

photodiode receiver located at a radio processing unit. One or more optical fibers

connect the remote antenna unit to the central processing location.

4

1.3 Scope Of Project

The works undertaken in this project are limited to the following aspects:

i) Literature review.

Reviews on the WCDMA using RoF technology by specific parameters of

WCDMA .

ii) Modeling and simulation of the WCDMA downlink system with RoF using

suitable parameters for laser diode, fiber and photodiode.

iii) Perform a simulation works by using a MATLAB/Simulink to observe BER.

iv) Compare the performance of the normal AWGN channel and different length of

fiber by setting different value of gain that present fiber.

5

1.4 Research Methodology

The methodology of this research is shown in the flow chart in Figure 1.1 below:-

Figure 1.1 Research methodology flow chart

Start

Literature study Mastering in simulation tools

Research on Radio over Fiber system

Identify various parameters Setting strategy for evaluation

Design Block Simulink

End

Comparison between AWGN normal and AWGN

using RoF

Evaluate and verification BER using MATLAB

6

In the beginning, there are two tasks that need to be done simultaneously.

Besides of doing literature review, exercises and tutorials need to be done for mastering

the simulations tools and some preliminary simulations need to be carried out as well.

Then, the problem of this research will be stressed with radio over fiber system

that an alternative to increasing base station complexity is to move the complex portions

of the network to a central processing location where the number of expensive signal

processing elements can be reduced by greater sharing among users.

Thus, identify various parameters and set the strategy for evaluation that can be

used to develop the block simulink.

After the preliminary research, the design of block simulink are developed and

tested by several of parameters.

Then, comparison between normal case and new case is done to get the result.

All simulink is using MATLAB SIMULINK.

Finally, the proposed block simulink will be evaluated with BER (bit error rate)

to determine the performance.

7

1.5 Thesis Outline

The thesis is structured as follows. The Chapter 1 discusses the general

introduction of this project.

Chapter 2 outlines the project background of this project, which is including the

basic introduction of RoF (Radio over Fiber) and further knowledge about RoF and their

characteristics.

Chapter 3 outlines the literature review of this project that is introduce more to

WCDMA technologies and characteristics.

Chapter 4 contains simulation and result.

The conclusion of the results and recommendation for future works will be

presented in Chapter 5.

8

CHAPTER 2

RADIO OVER FIBER

2.1 Introduction

This chapter will inform further explanatory about radio over fiber. There will be

explanation about what is RoF, the technology, system and concept of RoF. The benefit

of radio over fiber also stated. Furthermore, there are also told the advantages using RoF

in the mobile communication networks and applications of using RoF.

2.2 What is RoF?

Upcoming wireless networks will use a combination of air-interface methods in

different channels and in different cells that can be changed dynamically to meet

variations in traffic conditions. The co-existence of access methods such as adaptive

TDMA, TD-CDMA and WCDMA in the network could employ software-radio

approaches in the implementation of the base stations, but this will increase the

complexity present at the base stations and may impact cost.

9

User terminals are projected to have varying capabilities in terms of data

transmission rates and modulation levels supported, but for reasons of mobility, power

consumption, and cost, the majority of user terminals will operate on a single air-

interface and limited number of transmission parameters at a given time. In this

scenario, most of the complexity resides in the base stations. However, placing the

complexity in the base stations may incur significant cost if the number of base stations

required for network deployment is large. An alternative to increasing base station

complexity is to move the complex portions of the network to a central processing

location where the number of expensive signal processing elements can be reduced by

greater sharing among users.

By using highly linear optical fiber links to distribute RF signals from a central

location to radio access points (RAPs) RoF allows the RAPs to be extremely simple

since they only need to contain optoelectronic conversion devices and amplifiers. All

communication functions such as coding, modulation and up conversion can be

performed at a central location. A simple RAP means small and light enclosures (easier

and more flexible installation) and low cost (in terms of equipment cost and

maintenance costs). Centralization results in equipment sharing, dynamic source

allocation and more effective management. All of this adds up to an access technology

that makes life easier and cheaper for operators.

Reasoning why RoF is able to shift system complexity away from the antenna is

that optical fiber is an excellent low-loss (0.2 dB/km optical loss at 1550 nm) and high-

bandwidth (50 THz) transmission medium. Transmission takes place at the radio carrier

frequency rather than the more conventional digital base band systems. The optical links

in RoF are therefore analog in nature, in that they reproduce the carrier waveform. The

radio carrier can be modulated with a digital modulation scheme such as GMSK (in

GSM) or QPSK (in UMTS).

10

In a RoF link, laser light is modulated by a radio signal and transported over an

optical fiber medium. The laser modulation is analog since the radio-frequency carrier

signal is an analog signal. The modulation may occur at the radio signal frequency or at

some intermediate frequency if frequency conversion is utilized. The basic configuration

of an analog fiber optic link consists of a bi-directional interface containing the analog

laser transmitter and photodiode receiver located at a base station or remote antenna

unit, paired with an analog laser transmitter and photodiode receiver located at a radio

processing unit. One or more optical fibers connect the remote antenna unit to the

central processing location.

Reduction in base station or remote antenna unit complexity is an attractive

outcome of using radio-over-fiber links. Reducing the remote base station complexity is

attractive because equipment, construction, and maintenance costs may be reduced.

Base station and remote antenna unit density can therefore be increased economically,

leading to lower power mobiles and higher bandwidth transmission. Increased wireless

and optical network integration is therefore seen as a plausible means of decreasing

costs in voice and data networks, while increasing network capacity.

The layout of a simple bi-directional directly modulated RoF link are shown in

Figure 2.1. In each direction the input RF signal is applied to a laser diode where it

modulates the intensity of the output light. In most cases this light will have a

wavelength of either 1300 or 1550 nm for low transmission loss in silica fiber. The fiber

may be multimode or single mode, although the latter is preferred for links spans of

more than a few tens of meters for a p-i-n photodiode, which provides an RF power

output proportional to the square of the input optical power. This type of optical link is

known as intensity modulated-direct detection (IM-DD). Other types of link are possible

involving frequency or phase modulation, but for cellular applications the IM-DD links

are used for reasons of simplicity and cost.

11

Figure 2.1 Typical layout of a bidirectional analog optical link using direct

modulation of laser diodes [1]

2.3 The Radio Over Fiber Technology

Radio over Fiber concept is already shown in Figure 2.1. This solution increase

the frequency reuse enables broadband access by providing a micro/pico cell scenario

for cellular radio networks. The micro/pico cell scenario is possible through the use of

radio access point (RAP) in Figure 2.2. These inexpensive low power RAPs provide

wireless access instead of conventional base stations. It is important to keep the RAPs

complexity and cost at a minimum in order to allow for large scales deployment. By

doing so, a large cell can easily be split into smaller cells by dispersing RAPs

throughout. The robust RAPs are connected to the central base station via the RoF links.

12

Figure 2.2 Radio over Fiber Concept [2]

2.4 Radio Over Fiber System

Nowadays, optical fiber microcellular systems, in which microcells in a wide area are

connected by optical fiber and radio signals are over an optical fiber link among base

stations and control stations, has attracted much attention. This is because of

i) The low loss and enormous bandwidth of optical fiber

ii) The increasing demand for capacity or coverage

iii) The benefits it offers in terms of low-cost base station deployment in

microcellular systems.

All of above which make it an ideal candidate for realizing microcellular

networks. In such a system, each microcell radio port would consist of a simple and

compact optoelectronic repeater connected by an RF fiber optic link to centralized radio

and control equipment, possibly located at a preexisting macrocell site.

13

Use of RF antenna remoting allows changes to the system frequency plan or

modulation format to be done at a central location, without the need to modify any radio

port equipment. Antenna remoting should also simplify the provision of system features

such as rapid handover, dynamic channel assignment and diversity combining.

This system will make extensive use of microcells and picocells in order to

deliver high bandwidth. Such microcell systems can solve the frequency limitation

problems because a number of base stations can be installed, the zone radius can be

reduced and the radio frequencies can be reused effectively in many radio zones. The

much lower power level eliminates the need for the expensive frequency multiplexes or

high-power amplifiers currently employed at base stations. The limited coverage due to

low antenna height greatly reduces the co-channel interference from other cells. RoF

systems are now being used extensively for enhanced cellular coverage inside buildings

such as offices, shopping malls and airport terminals.

2.5 Radio Over Fiber Concept

A microcellular network can be implemented by using fiber-fed distributed

antenna networks as shown in Figure 2.3. The received RF signals at each remote

antenna are transmitted over an analog optical fiber link to a central base station where

all the de-multiplexing and signal processing are done. In this method, each remote

antenna site simply consists of a linear analog optical transmitter, an amplifier an the

antenna.

14

Figure 2.3 Optically fed remote antenna network for microcellular RoF systems [1]

15

2.6 Advantages of Using RoF In Mobile Communication Networks

The radio network is a distributed antenna system with the potential for adaptive

antenna selection as well as adaptive channel allocation to increase the spectrum

efficiency. The distributed antenna system provides an infrastructure that brings the

radio interface very close to the users and has the following benefits:

i) Low RF power remote antenna points (RAPs)

ii) Line-of sight (LOS) operation (multipath effects are minimized)

iii) Enabling of mobile broadband radio access close to the user in an

economically acceptable way

iv) Reduced environment impact (small RAPs)

v) Good coverage

vi) Capacity enhancement by means of improved trucking efficiency

vii) Dynamic radio resource configuration and capacity allocation

viii) Alleviation of the cell planning problem

ix) Reduction in the number of handovers

x) Centralized upgrading or adaptation

xi) The potential to deploy precision tracking of user equipment for safety/first

aid and other purposes

xii) Higher reliability and lower maintenance costs

xiii) Support for future broadband multimedia applications

xiv) Better coverage and increased capacity

xv) High-quality signals

xvi) Support for macro diversity transmissions

xvii) Low fiber attenuation (up to 0.2dB/km)

xviii) Reduced engineering and system design costs

xix) Multiple services on a single fiber

xx) Lightweight fiber cables

xxi) No electromagnetic interference

xxii) Reliability

16

The use of low RF power RAPs has following advantages:

i) Low generated interference

ii) Increased spectrum efficiency

iii) Easier frequency/network planning

iv) Increased battery lifetime of mobile terminals

v) Relaxed human health issues

vi) The potential to use RF complementary metal oxide semiconductor

technology in mobile terminals

2.7 Benefits of Radio over Fiber Systems

2.7.1 Low Attenuation Loss

Electrical distribution of high frequency microwave signals either in free space

or through transmission lines is problematic and costly. In free space, losses due to

absorption and reflection increase with frequency. In transmission lines, impedance rises

with frequency as well. Therefore, distributing high frequency radio signals electrically

over long distances requires expensive regenerating equipment. As for mm-waves, their

distribution via the use of transmission lines is not feasible even for short distances. The

alternative solution to this problem is to distribute baseband signals or low intermediate

frequencies (IF) from the Switching Centre (SC) to the Base Stations (BS). The

baseband or IF signals are then up converted to the required microwave or mm-wave

frequency at each base station, amplified and then radiated. Such a system places

stringent requirements (such as linearity) on repeater amplifiers and equalisers. In

addition, high performance local oscillators would be required for up conversion at each

base station. This arrangement leads to complex base stations with tight performance

requirements. An alternative solution is to use optical fibers, which offer much lower

losses.

17

Commercially available standard Single Mode Fiber (SMFs) made from glass

(silica) have attenuation losses below 0.2 dB/km and 0.5 dB/km in the 1.5 µm and the

1.3 µm windows, respectively. Polymer Optical Fiber (POFs), a more recent kind of

optical fibers exhibit higher attenuation ranging from 10 – 40 dB/km in the 500 - 1300

nm regions. These losses are much lower than those encountered in free space

propagation and copper wire transmission of high frequency microwaves. Therefore, by

transmitting microwaves in the optical form, transmission distances are increased

several folds and the required transmission powers reduced greatly.

2.7.2 Large Bandwidth

Optical fibers offer enormous bandwidth. There are three main transmission

windows, which offer low attenuation, namely the 850 nm, 1310 nm and 1550 nm

wavelengths. For a single SMF optical fiber, the combined bandwidth of the three

windows is in the excess of 50 THz . However, today’s state-of-the-art commercial

systems utilize only a fraction of this capacity (1.6 THz). But developments to exploit

more optical capacity per single fiber are still continuing. The main driving factors

towards unlocking more and more bandwidth out of the optical fiber include the

availability of low dispersion (or dispersion shifted) fiber, the Erbium Doped Fiber

Amplifier (EDFA) for the 1550 nm window, and the use of advanced multiplex

techniques namely Optical Time Division Multiplexing (OTDM) in combination with

Dense Wavelength Division Multiplex (DWDM) techniques.

The enormous bandwidth offered by optical fibers has other benefits apart from

the high capacity for transmitting microwave signals. The high optical bandwidth

enables high speed signal processing that may be more difficult or impossible to do in

electronic systems. In other words, some of the demanding microwave functions such as

18

filtering, mixing, up- and down-conversion, can be implemented in the optical domain.

For instance, mm-wave filtering can be achieved by first converting the electrical signal

to be filtered into an optical signal, then performing the filtering by using optical

components such as the Mach Zehnder Interferometer MZI or Bragg gratings), and then

converting the filtered signal back into an electrical signal. Furthermore, processing in

the optical domain makes it possible to use cheaper low bandwidth optical components

such as Laser Diodes (LD) and modulators, and still be able to handle high bandwidth

signals.

The utilization of the enormous bandwidth offered by optical fiber is severely

hampered by the limitation in bandwidth of electronic systems, which are the primary

sources and end users of transmission data. This problem is referred to as the

“electronic bottleneck”.

The solution around the electronic bottleneck lies in effective multiplexing.

OTDM and DWDM techniques mentioned above are used in digital optical systems. In

analog optical systems including RoF technology, Sub-Carrier Multiplexing (SCM) is

used to increase optical fiber bandwidth utilization. In SCM, several microwave sub

carriers, which are modulated with digital or analog data, are combined and used to

modulate the optical signal, which is then carried on a single fiber. This makes the RoF

system costs effective.

2.7.3 Immunity to Radio Frequency Interference

Immunity to electromagnetic interference is a very attractive property of optical

fiber communications, especially for microwave transmission. This is so because signals

are transmitted in the form of light through the fiber. Because of this immunity, fiber

19

cables are preferred even for short connections at mm-waves. Related to RFI immunity

is the immunity to eavesdropping, which is an important characteristic of optical fiber

communications, as it provides privacy and security.

2.7.4 Easy Installation and Maintenance

In RoF systems, complex and expensive equipment is kept at the SCs, thereby

making remote base stations simpler. For instance, most RoF techniques eliminate the

need for a local oscillator and related equipment at the Remote Station (RS). In such

cases a photo detector, an RF amplifier, and an antenna make up the RS equipment.

Modulation and switching equipment are kept in the SC at the head end and shared by

several RS. This arrangement results in smaller and lighter RS, effectively reducing

system installation and maintenance costs. Easy installation and low maintenance costs

of RS are very important requirements for mm-wave systems, because of the large

numbers of the required antenna sites. Having expensive RS would render the system

costs prohibitive. The numerous antennas are needed to offset the small size of radio

cells (microcells and picocells), which is a consequence of limited propagation distances

of mm-wave microwaves. In applications where RSs are not easily accessible, the

reduction in maintenance requirements has many positive implications.

2.7.5 Reduced Power Consumption

Reduced power consumption is a consequence of having simple RSs with

reduced equipment. Most of the complex equipment is kept at the central SC. In some

applications, the antenna sites are operated in passive mode. For instance, some 5 GHz

Fiber-Radio systems employing picocells (small radio cells) can have the RSs (BSs)

operate in passive mode. Reduced power consumption at the RSs is significant

20

considering that RSs are sometimes placed in remote locations not fed by the power

grid.

2.7.6 Operational Flexibility

RoF does offer operational benefits in terms of operational flexibility. Firstly,

depending on the microwave generation technique, a RoF distribution system can be

made signal format transparent. For instance the Intensity Modulation and Direct

Detection (IMDD) technique can be made to operate as a linear system and therefore as

a transparent system.

This can be achieved by using low dispersion fiber (SMF) in combination with

pre modulated RF sub carriers (SCM). When this happens, then, the same RoF network

can be used to distribute multi-operator and multi-service traffic, resulting in huge

economic savings.

Secondly, with the switching, modulation, and other functions performed at a

centralized SC, it is possible to allocate capacity dynamically. For instance in a RoF

based distribution system for GSM traffic, more capacity can be allocated to an area

(e.g. shopping mall) during peak times and then re-allocated to other areas when off-

peak (e.g. to populated residential areas in the evenings). This can be achieved by

allocating optical wavelengths as need arises. Allocating capacity dynamically as need

for it arises obviates the requirement for allocating permanent capacity, which would be

a waste of resources in cases where traffic loads vary frequently and by large margins.

Furthermore, having a SC facilitates the consolidation of other signal processing

functions such as mobility functions.

21

2.7.7 Millimeter Waves

Millimeter waves offer several benefits. However, mm-waves cannot be

distributed electrically due to high RF propagation losses. In addition, generating mm-

wave frequencies using electrical devices is challenging. These issues describe the

electronic bottleneck already discussed above. The most promising solution to the

problem is to use optical means. Low attenuation loss and large bandwidth make the

distribution of mm-waves cost effective. Furthermore, some optical based techniques

have the ability to generate unlimited frequencies. For instance, microwave frequencies

that can be generated by Remote Heterodyning and Detection (RHD) methods are

limited only by the bandwidth of photo detectors.

2.7.7.1 Advantages of mm-waves

They provide high bandwidth due to the high frequency carriers. Secondly, due

to high RF propagation losses in free space, the propagation distances of mm-waves are

severely limited. This allows for well-defined small radio sizes (microcells and

picocells), where considerable frequency re-use becomes possible so that services can

be delivered simultaneously to a larger number of subscribers.

2.7.7.2 Disadvantages of mm-waves

The negative side of mm-waves is the need for numerous BSs, which is a

consequence of high RF propagation losses. Unless the BSs are simple enough,

installing and maintaining the mm-wave system can be economically prohibitive owing

to the numerous required BSs.

22

2.7.8 Radio System Functionalities

As stated earlier, RoF technology is not only used for distributing RF signals but

for radio system functionalities as well. Among these, modulation and frequency

conversion have been mentioned above. However, application of RoF technology for

radio system functionalities goes beyond modulation and frequency conversion to

encompass signal processing at very high frequencies. These functions include filtering,

attenuation control and signal processing in high frequency phased array antenna

systems, just to name but a few. These functions are also referred to as microwave

functions. Many of these functions are difficult to achieve in the microwave (electrical)

domain due to limited bandwidth and other electromagnetic wave propagation

limitations. However, if the processing is done in the optical domain, unlimited signal

processing bandwidth becomes available. As a result, many microwave functions can be

performed by optical components without needing E/O conversion for processing by

microwave components and vice versa.

2.8 Applications of Radio over Fiber Technology

Some of the applications of RoF technology include satellite communications,

mobile radio communications, broadband access radio, Multipoint Video Distribution

Services (MVDS), Mobile Broadband System (MBS), vehicle communications and

control, and wireless LANs over optical networks. The main application areas are

briefly discussed next.

23

2.8.1 Cellular Networks

The field of mobile networks is an important application area of RoF technology.

The ever-rising number of mobile subscribers coupled with the increasing demand for

broadband services have kept sustained pressure on mobile networks to offer increased

capacity. Therefore, mobile traffic (GSM or UMTS) can be relayed cost effectively

between the SCs and the BSs by exploiting the benefits of SMF technology. Other RoF

functionalities such as dynamic capacity allocation offer significant operational benefits

to cellular networks.

2.8.2 Satellite Communications

Satellite communications was one of the first practical uses of RoF technology.

One of the applications involves the remoting of antennas to suitable locations at

satellite earth stations. In this case, small optical fiber links of less than 1km and

operating at frequencies between 1 GHz and 15 GHz are used. By so doing, high

frequency equipment can be centralized.

The second application involves the remoting of earth stations themselves. With

the use of RoF technology the antennae need not be within the control area (e.g.

Switching Centre). They can be sited many kilometers away for the purpose of, for

instance improved satellite visibility or reduction in interference from other terrestrial

systems. Switching equipment may also be appropriately sited, for say environmental or

accessibility reasons or reasons relating to the cost of premises, without requiring to be

in the vicinity of the earth station antennas.

24

2.8.3 Video Distribution Systems

One of the major promising application areas of RoF systems is video

distribution. A case in point is the Multipoint Video Distribution Services (MVDS).

MVDS is a cellular terrestrial transmission system for video (TV) broadcast. It was

originally meant to be a transmit-only service but recently, a small return channel has

been incorporated in order to make the service interactive. MVDS can be used to serve

areas the size of a small town.

Allocated frequencies for this service are in the 40 GHz band. At these

frequencies, the maximum cell size is about 5 km. To extend coverage, relay stations are

required. In MVDS a transmitter serves the coverage area, which is located either on a

mast or a tall building. The rooftop equipment can be simplified by employing RoF

techniques. For instance, instead of using Gunn oscillators with their own antennas and

heat pipes for frequency stabilization, an optical fiber link may be used to feed either a

traveling wave tube or a solid state amplifier at the transmit frequency. This greatly

reduces the weight and wind loading of the transmitter. In addition, a single optical fiber

could feed the transmitter unit from a distance of several hundred meters.

2.8.4 Mobile Broadband Services

The Mobile Broadband System or Service (MBS) concept is intended to extend

the services available in fixed Broadband Integrated Services Digital Network (B-ISDN)

to mobile users of all kinds. Future services that might evolve on the B-ISDN networks

must also be supported on the MBS system. Since very high bit rates of about 155 Mbps

per user must be supported, carrier frequencies are pushed into mm-waves. Therefore,

frequency bands in the 60 GHz band have been allocated. The 62-63 GHz band is

allocated for the downlink while 65-66 GHz is allocated for the uplink transmission.

25

The size of cells is in diameters of hundreds of meters (microcells). Therefore, a high

density of radio cells is required in order to achieve the desired coverage. The micro-

cells could be connected to the fixed B-ISDN networks by optical fiber links. If RoF

technology is used to generate the mm-waves, the base stations would be made simpler

and therefore of low cost, thereby making full scale deployment of MBS networks

economically feasible.

2.8.5 Wireless LANs

As portable devices and computers become more and more powerful as well as

widespread, the demand for mobile broadband access to LANs will also be on the

increase. This will lead once again, to higher carrier frequencies in the bid to meet the

demand for capacity. For instance current wireless LANs operate at the 2.4 GHz ISM

bands and offer the maximum capacity of 11 Mbps per carrier (IEEE 802.11b). Next

generation broadband wireless LANs are primed to offer up to 54 Mbps per carrier, and

will require higher carrier frequencies in the 5 GHz band (IEEE 802.11a/D7.0).

Higher carrier frequencies in turn lead to microcells and picocells, and all the

difficulties associated with coverage discussed above arise. A cost effective way around

this problem is to deploy RoF technology. A wireless LAN at 60 GHz has been released

by first transmitting from the BS, a stable oscillator frequency at an IF together with the

data over the fiber. The oscillator frequency is then used to up-convert the data to mm-

waves at the transponders (Remote Stations). This greatly simplifies the remote

transponders and also leads to efficient base station design.

26

2.8.6 Vehicle Communication and Control

This is another potential application area of RoF technology. Frequencies

between 63-64 GHz and 76-77 GHz have already been allocated for this service within

Europe. The objective is to provide continuous mobile communication coverage on

major roads for the purpose of Intelligent Transport Systems (ITS) such as Road-to-

Vehicle Communication (RVC) and Inter-Vehicle Communication (IVC). ITS systems

aim to provide traffic information, improve transportation efficiency, reduce burden on

drivers, and contribute to the improvement of the environment. In order to achieve the

required (extended) coverage of the road network, numerous base stations are required.

These can be made simple and of low cost by feeding them through RoF systems,

thereby making the complete system cost effective and manageable.

2.9 Summary

More general knowledge about Radio over Fiber has been written in this chapter.

So the reader will become familiar with this system and know how the systems

operated. Generally radio-over-fiber have considered millimeter wave radio-over-fiber

transmission. Millimeter wave radio, operating at 26-28 GHz or 60 GHz, was seen as

the logical choice for high bandwidth data transmission. Radio waves operating at this

frequency are attenuated greatly by the atmosphere, and so fiber was employed as an

alternate transmission media. Fiber dispersion has limited the success of radio-over-fiber

transmission of signals at these frequencies, particularly for fiber lengths exceeding 10

km.

27

CHAPTER 3

WIDEBAND CODE DIVISION MULTIPLE ACCESS

(WCDMA)

3.1 Introduction

This chapter is further information and details about WCDMA as well. As a

chapter that consult in order to understand and investigate this research project, further

explanatory will discuss and describe the parameters of WCDMA, an overview of

WCDMA, basic WCDMA transmission technologies, characteristics of WCDMA which

is more on technical site and last but not least is about the wideband properties of

WCDMA that allow higher efficiency from several aspects.

3.2 RoF Using WCDMA

The WCDMA air interface can now be regarded as a mature technology that is

ready to provide the basis for the third-generation wireless personal communication

systems know as the UMTS [1]. These systems will make extensive use of microcells

and picocells in order to deliver high bandwidth services to customers. The benefit of

28

using RoF for WCDMA distributed antenna systems is expected to be even more

important, partly because of their higher frequency and bandwidth requirements.

Two key features are expects to be employed in the UMTS system to minimize

multiple-user interference: adaptive antenna arrays and fast closed-loop forward and

reverse power control techniques. Other important techniques that are used to reduce

multiple-user interference are cell sectorization and voice activity monitoring,

particularly in speech-oriented cellular systems.

The UMTS is designed to support simultaneous transmission of multiple

services and data rates including video. One of the major drawbacks in RoF systems is

laser diode nonlinearity, which gives rise to intermodulation distortion and clipping

noise. It is well known that intermodulation distortion and clipping noise are signal level

dependent. So WCDMA RoF systems, voice activity monitoring will have an impact not

only on multiple-user interference but also on intermodulation distortion and clipping

noise power.

There are several researchers that report on applications in WCDMA RoF. In

Hamed Al-Raweshidy paper about ‘Radio over Fiber Technology for The Next

Generation’ has presented the main elements of the optical devices and the parameters

related to radio over fiber; laser diode performance, intermodulation, RIN and clipping

noise [1]. This paper discusses in more detail the system performance of RoF on

UMTS/WCDMA system. He also reported that an analytical model for evaluating the

performance of WCDMA-based RoF systems with numerical results showed an

improvement in performance when the effect of voice activity monitoring on

intermodulation distortion and clipping noise was taken into account.

29

Another paper from Hamed Al-Raweshidy and Nazem Khashjori with title

‘System Level Performance of WCDMA with RoF access network’ was reported that

the system-levelperformance of WCDMA with Radio-over-Fibre (RoF) access network

is investigated [15]. This paper aims at addressing issues such as coverage and transmits

power reduction during Macrodiversity. The simulation results demonstrate that, for a

given service, the transmit power reduction is up to 50% (depending on the channel

model and the mobile speed) in the case of the RoF technique as compared to the

wireless link. Macrodiversity is a technique in which multiple antennas are employed at

the receiver to form the branches for the diversity combiner, has the ability to improve

both uplink and downlink performance of wireless communications systems. When

Macrodiversity is combined with the use of fiber optic feeders, the results are

exceptionally promising.

The main aim of the system-level simulations is to help to perform more

practical link level simulations, by providing information about the effect of the

environment in a given link. The information from the RoF link-level simulations

Khashjori is brought to the system level as look-up tables. The most important numbers

are the Eb/No requirement for the services used and for the chosen mobile speed, both

in the uplink and downlink and the orthogonality factor in the DL. The numbers in the

tables depend on the channel model [15].

This paper has presented an evaluation of the WCDMA network with radio over

fiber. All methods used in this system are according to 3GPP UTRA standards. The

System level of WCDMA with RoF and wireless access was investigated. The

propagation model effect and cell loading has been analysed. The results show that there

is significant power reduction available for each link (up to 50%) when using RoF

techniques. In conclusion of this paper, the use of RoF technology can he used to

improve the performance of WCDMA [15].

30

For paper ‘Fiber-Wireless Solution for Broadband Multimedia Access’ that has

written by Stephen Z. Pinter and Xavier N. Fernando had reported about the increasing

demand for high-capacity multimedia services in real-time demands wireless broadband

access [10]. In order to meet this demand, a fiber based wireless access scheme using

radio-over-fiber (RoF) technology can be used and is discussed in this article. Fiber

based wireless (Fi-Wi) access schemes effectively combine the high capacity of optical

fiber with the flexibility of wireless networks. This approach enables rapid deployment

of microcells in cellular radio networks for capacity enhancement. Furthermore, a single

sub-carrier multiplexed RoF link can support wireless LAN, cellular radio, and CATV

services simultaneously. RoF technology can also transmit millimeter radio waves to the

surrounding neighborhood for LMCS type systems. The focus of research group

ADROIT is to investigate various issues in this scenario such that RoF becomes a

feasible technology to provide a cost-effective, high performance solution for broadband

access. They have devised a system identification technique for a concatenated fiber-

wireless channel, and have proposed various compensation schemes to equalize the time

varying linear wireless plus static nonlinear optical channel. Another of their projects

focuses on supporting both cellular CDMA and IEEE 802.11 signals over the fiber-

wireless channel. They have also performed various experimental studies on the RoF

approach and have been working with optical and electrical signal processing for

performance improvement. This article provides an overview of ADROIT research and

presents some noteworthy results [10].

In paper title ‘WCDMA-Based Radio over Fiber System Performance with

Multiple-User Interference in Multiple Service Transmission’ by H.S. Al-Raweshidy

and S.O. Ampem-Darko had reported about intermodulation distortion and clipping

noise due to laser diode nonlinearity constitute a major source of interference and noise

in radio-over-fiber systems [12]. These noises are known to be signal level dependent.

This paper proposes an analytical model for evaluating performance of radio-over-fiber

systems. Numerical results presented showed 4.5 dB improvement in performance when

31

taken into account effect of mobile radio discontinuous transmission mode on

intermodulation distortion and clipping noise.

RoF application has attracted much attention recently because of the increasing

demand for capacity/coverage and,the benefits it offers in terms of low-cost base

stations deployment in microcellular systems. RoF systems are now being used

extensively for enhanced cellular coverage inside buildings such as office blocks,

shopping malls and airport terminal. Wideband Code Division Multiple Access

(WCDMA), air interface can now be regarded as a mature technology ready to provide

the basis for the third generation wireless personal communication systems, known as

Universal Mobile Telecommunication Systems (UMTS). These systems will make

extensive use of microcells and picocells in order to deliver high bandwidth services to

customers. The benefit of using RoF for WCDMA distributed antenna systems is

expected to be even more important, partly because of their higher frequency and

bandwidth requirements. Two key features are expected to be employed in the UMTS

system to minimize multiple-user interference (MUI) namely, adaptive antenna arrays,

and fast closed-loop forward and reverse power control techniques [12].

32

3.3 Parameter Of WCDMA

Every multiple access has their parameter to suit the application that supported

by them. Thus, same to WCDMA that suit to radio over fiber application has their own

parameter. As written in Table 3.1 below is suitable parameter for WCDMA using RoF.

There also have comparison between various CDMA parameter. Table 3.2 show

that the similar and differences between three types of CDMA that normally use in our

communication systems. The differences are from their bandwidth, data rate, chip rate,

frame length, intercell synchronization, spreading codes, multirate capability and etc.

Besides that, there are several parameters using the same method but different in other

method.

The different factors that influence capacity in WCDMA and 3G mobile

systems, such as traffic type (data, voice, and SMS), propagation model, terrain, user

mobility, sectorization, and cell overlap.

33

Table 3.1 Parameter of WCDMA

Channel Bandwidth (1, 25), 5, 10, 20 MHz

Downlink Rf channel structure Direct spread

Chip rate (1.024) / 4.096 / 8.192 / 16.384 Mcps

Roll-off factor for chip shaping 0.22

Frame length 10 ms/ 20 ms (optional)

Spreading modulation Balanced QPSK (downlink) Dual channel (uplink) Complex spreading circuit

Data modulation QPSK (downlink) BPSK (uplink)

Coherent detection User-dedicated time-multiplexed pilot (downlink & uplink), common pilot in downlink

Channel multiplexing in uplink Control and pilot channel time-multiplexed I and Q multiplexing for data and control channel

Multirate Variable spreading and multicode

Spreading factors 4-256

Power control Open and fast closed loop (1.6 kHz)

Spreading (downlink) Variable-length orthogonal sequence for channel separation, Gold sequences 218 for cell and user separation (truncated cycle 10 ms)

Spreading (uplink) Variable-length orthogonal sequence for channel separation, Gold sequences 241 for user separation (different time shift in I and Q channel, truncated cycle 10 ms)

Handover Soft handover, interfrequency handover

34

Table 3.2 Comparison of 2G and 3G CDMA Systems

35

3.4 WCDMA Overview

WCDMA has emerged as the most widely adopted air interface technology for Third

Generation systems. The 3GPP consortium has created specifications for the use of

WCDMA technology in its networks, where it is referred to as the UTRA (Universal

Terrestrial Radio Access). Evolved from the CDMA radio access scheme, WCDMA is a

Wideband Direct-Sequence CDMA (DS-CDMA) system. To understand this definition,

it is imperative to understand some of the terms/concepts used with respect to WCDMA:

Direct-Sequence CDMA

Wideband

Synchronization Aspects

Modes of Operation

3.4.1 Direct-Sequence CDMA

The term ‘Direct-Sequence CDMA (DS-CDMA)’ stems from the ‘Direct-

Sequence Spread Spectrum (DSSS)’ technique used in DS-CDMA. The CDMA scheme

uses the concept of spreading codes to transform the user signal into a spread-spectrum-

coded signal. These spreading codes are used to provide access to multiple users

simultaneously. Multiple spreading techniques exist: notable among them are the DSSS

and the ‘Frequency Hopping Spread Spectrum (FHSS)’.

The DSSS uses a carrier that remains fixed to a specific frequency band. The

data signal is spread onto a much larger range of frequencies using a specific encoding

scheme, rather than being transmitted on a narrow band. This encoding scheme is

known as Pseudo-Noise sequence (PN sequence). Frequency Hopping Spread Spectrum,

on the other hand, attempts to achieve the same result by sending its transmissions over

a different carrier frequency at different times. DSSS is the simpler of the spreading

36

techniques, whereby the original signal is directly multiplied by a faster-rate spreading

code.

3.4.2 Wideband

In WCDMA, the term Wideband refers to the higher bandwidth carrier signal of

approximately 5 MHz. Original DS-CDMA systems, like the IS-95, used a carrier

bandwidth of about 1 MHz. These systems are referred to as Narrowband CDMA

systems. In contrast, WCDMA is a CDMA based access scheme, which uses the DSSS

spreading techniques with a carrier bandwidth of around 5 MHz. The higher carrier

bandwidth makes WCDMA a wideband system.

3.4.3 Synchronization Aspects

The proposal for WCDMA radio interface are broadly divided into two

categories, network synchronous and network asynchronous, depending upon whether

the base stations within the network are synchronized in time or not. A network where

the base stations are time synchronized with each other are categorized as synchronous

networks. If synchronization between base stations is not required, then such a network

is termed as an asynchronous network. Second Generation IS-95 systems are based on

the synchronous network concept. Though synchronized network provide more efficient

utilization of the radio interface, it requires a lot of functionality within the base station

and hence more costly hardware. Additional techniques, like Global Positioning System

(GPS), would be required to time synchronize the base stations. These further places a

restriction on deployment of base stations-indoor and micro base stations can only be

deployed if the GPS signals can be received indoors. While Third Generation systems

37

based on the 3GPP specifications utilize the asynchronous network based scheme,

CDMA2000 based proposals use schemes that are synchronous network based.

3.4.4 Modes of Operation

WCDMA supports two basic modes of operation: one for paired spectrum and

the other for the unpaired spectrum. Here, pairing refers to the frequency bands

available for communication. The Frequency Division Duplex (FDD) mode is used for

the paired spectrum, while for unpaired spectrum; it is the Time Division Duplex (TDD)

mode.

In the FDD mode of operation, separate 5 MHz carrier frequencies are used in

the uplink and the downlink direction. Since two frequency bands of equal bandwidths

are available, one is used for uplink direction (from mobile station to base station) and

the other for downlink direction (from base station to mobile station). Thus, the

information transfer in FDD mode is symmetric. Further, data can be exchanged in both

directions simultaneously. The traditional GSM uses the FDD mode.

In the TDD mode of operation, only one 5 MHz carrier is time-shared between

the uplink and the downlink. Since only one frequency band is available, The TDD is

said to use the unpaired spectrum. The data is alternated in the uplink and downlink

direction. The main benefit of TDD mode is that the bandwidths in forward and

backward direction can be altered. Thus, it is possible that the downlink bandwidth is

much more than the uplink bandwidth. This is helpful in certain applications (downloads

from the Internet) where a small request is followed by large amounts of information.

The unpaired nature of TDD makes it use the spectrum more efficiently. Further, as the

spectrum becomes scarce, getting an unpaired spectrum will be easier as compared to

38

obtaining a paired spectrum. This will provide TDD an edge over FDD. It is presumed

that TDD will be used in hot spots (such as airports) to provide high data rate

connectivity efficiently.

In a certain sense, the FDD mode of operation can be considered as a hybrid

scheme that uses CDMA and FDMA schemes, since the CDMA scheme is applied

within each frequency channel. In other words, the TDD mode of operation uses a

hybrid scheme based on CDMA, FDMA and TDMA, as the same carrier frequency is

further time-shared for the uplink and the downlink direction. With this introduction to

WCDMA forming the basis of discussion. The underlying technique utilised in

WCDMA is the Direct Sequence Spread Spectrum (DSSS) whose main principles are

illustrated in Figure 3.1.

Figure 3.1 The basic techniques of the Direct Sequence Spread Spectrum [5]

39

Figure 3.2(a) shows how DS-CDMA works and Figures 3.4 shows how the

signal of DS-CDMA is spread. The transmitted data sequence is spread across the

spectrum after being encoded by spreading codes, each of which is assigned uniquely to

each user at a higher rate than the symbol rate of the information data. WCDMA spreads

the information data over a 5 MHz band per carrier. The spread high-speed data

sequence is referred to as chip and the rate at which the spread data varies is called chip

rate. The ratio of chip rate to symbol rate is called the spreading factor (SF). The

destination mobile phone uses the same spreading code as the one used for spreading at

the transmission point to perform correlation detection (a process called dispreading), in

order to recover the transmitted data sequence. As signal received by other users carry

different spreading codes, the signal power is reduced evenly to 1/SF. In DS-CDMA, all

users share the same frequency band and time frame to communicate and each user is

identified by a spreading code uniquely assigned to the user.

In contrast, as shown in Figure 3.2(b), FDMA assigns to each user a different

carrier frequency, depending on the frequency generated in the frequency synthesizer

and TDMA assign to each user not only a carrier frequency but also a time slot to

engaged in communications. At the reception point, the frequency generated by the

frequency synthesizer is set in such a manner that the signals in the assigned carrier

frequency can be down converted in the destination mobile phone and the transmitted

data sequence is extracted from specific slots with reference to the demodulated signals.

In DS-CDMA, there is basically no need to assign carrier frequencies or time slot as

such to the users.

40

Figure 3.2 Principles of DS-CDMA [4]

Figure 3.3 is shown an arrangement in WCDMA, which is a wideband Direct-

Sequence Code Division Multiple Access (DS-CDMA) system such as user information

bits are spread over a wide bandwidth by multiplying the user data with quasi-random

bits (called chips) derived from CDMA spreading codes. In order to support very high

bit rates (up to 2 Mbps), the use of variable spreading factor and multicode connections

is supported.

41

Figure 3.3 Allocation of bandwidth in WCDMA in the time-frequency-code space

[4]

Figure 3.4 Spreading and dispreading in DS-CDMA [5]

42

3.5 Basic WCDMA Transmission Technologies

WCDMA secures a wider bandwidth of 5 MHz by applying the DS-CDMA

radio-access technology with the aforementioned characteristics. The wider band makes

it possible to divide and combine reception signals propagated through multipath-fading

channels into more multipath components, which helps improve the reception quality

through RAKE time diversity. (As the chip rate is 3.84 Mcps and the length of one chip

is 0.26 µs, multipath division can be performed at this resolution.) It is merit include the

ability to accommodate a greater number of users who communicate at high speed-for

example, at 64 and 384 kbps. It also has been verified in experiments that high-quality

data transmission a 2 Mbps can be implemented using 5 MHz bandwidth. In addition to

the fruits of wideband as such, WCDMA harnesses the distinguishable radio-access

technologies explained hereunder.

3.6 Characteristics Of WCDMA (Technical)

3.6.1 Highly Efficient Frequency Usage

In principle, the potential capacity of the system should be regarded the same

even when multiple access technologies like Time Division Multiple Access (TDMA)

and Frequency Division Multiple Access (FDMA) are applied. While Code Division

Multiple Access (CDMA) is often claimed to have a high efficiency of frequency usage,

it should be interpreted as referring to how easy it is to improve the efficiency of

frequency usage. For example, CDMA can achieve a certain level of efficiency by

precise Transmit Power Control (TPC), whereas TDMA would have to resort to an

extremely sophisticated dynamic channel assignment to achieve the same level of

efficiency. Using the basic technologies of the CDMA system in the right way would

lead to a system with highly efficient frequency usage.

43

3.6.2 Freedom From Frequency Administration

As CDMA allows adjacent cells to share the same frequency, no frequency

allocation plan is required. In contrast, FDMA and TDMA require frequency allocation-

in particular, much difficulty is involved in frequency allocation because of the way in

which stations are located in practice, as irregular propagation patterns and topographic

features need to be considered. It should also be noted that imperfect frequency

allocation designs diminish the efficiency of frequency usage. CDMA requires no

frequency allocation plan as such.

3.6.3 Low Mobile Station Transmit Power

CDMA can improve reception performance and reduce the transmission power

of Mobile Stations (MSs) by technologies like RAKE reception and so on. In TDMA,

transmission is intermittent; the peak power required for the transmission of 1 bit is

multiple times the number of TDMA multiplexes compared to continual transmission.

On the other hand, the peak power may be small in CDMA, as continual transmission is

possible. The additional merit of this feature is that it minimizes the impact to the

electromagnetic field.

3.6.4 Resources Used Independently in Uplink and Downlink

In CDMA, it is easy to support an asymmetric uplink and downlink

configuration. For example, in other access systems such as TDMA, it is difficult to

assign time slots for uplink and downlink configuration because the carrier bandwidth in

uplink and downlink would have to be changed. In contrast, in CDMA, the Spreading

44

Factor (SF) can be set independently between uplink and downlink for each user, and

thereby set different speeds in uplink and downlink. This allows the efficient use of

radio resources even in asymmetric communications, such as Internet access. When

there is no transmission, no radio resources are used; therefore, if one user is executing

transmission in uplink only, and another user is performing transmission in downlink

only, the radio resources being used are equivalent to one pair of uplink and downlink

resources. Generally, TDMA and FDMA would have to assign two pairs of radio

resources in such cases.

3.7 The Wideband Properties Of WCDMA Allow Higher Efficiency In The

Following Aspects

3.7.1 Wide Range of Data Speeds

Wideband enables transmission at high speed. It also enables the efficient

provision of services when there is a combination of low-speed services and high-speed

services.

For example, in TDMA, various transmission speeds can be offered by varying

the setting of the assigned number of time slots, but a low-speed, speech-only mobile

phone would still require the same peak power as the peak transmission power required

for maximum-speed services.

45

3.7.2 Improved Multipath Resolution

RAKE diversity reception technology improves the reception performance by

separating multipaths into individual paths for reception and combining. As wideband

improves the resolution of the propagation path, the required reception power need not

be high because of the path diversity effect brought about by the increased number of

paths. This helps reduce transmission power and increase capacity. A typical example of

this has been demonstrated in a field test revealing that the required transmission power

at approximately 4 Mcps is about 3 dB less than at approximately 1 Mcps.

3.7.3 Statistical Multiplexing Effect

Wideband increases the number of users to be multiplexed by each carrier.

Hence, the capacity increases because of the statistical multiplexing effect. The

characteristics of the statistical multiplexing effect are particularly evident in relatively

high-speed data communication: the efficiency decreases in narrowband, as the number

of channels that can be accommodated by each carrier is limited, whereas in wideband,

the efficiency improves because of the statistical multiplexing effect.

3.7.4 Reduced Intermittent Reception Rate

Wideband accelerates the bit rate in the control channel, and makes it possible to

reduce the rate of intermittent reception, which makes the mobile phone receive limited

46

signals when it is in idle mode for saving power. This extends the standby time of the

MS (Mobile Station).

3.8 Summary

From the above explanation, WCDMA an ITU standard derived from Code-

Division Multiple Access (CDMA), is officially known as IMT-2000 direct spread. W-

CDMA also known as third-generation (3G) mobile wireless technology that promises

much higher data speeds to mobile and portable wireless devices than commonly

offered in today's market.

W-CDMA can support mobile/portable voice, images, data, and video

communications at up to 2 Mbps (local area access) or 384 Kbps (wide area access).

The input signals are digitized and transmitted in coded, spread-spectrum mode over a

broad range of frequencies. A 5 MHz-wide carrier is used, compared with 200 kHz -

wide carrier for narrowband CDMA. Therefore utilization for WCDMA is bigger than

CDMA and very suitable for next generation, which is, the population become big every

year.

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CHAPTER 4

SIMULATIONS

4.1 Introduction

This chapter will discuss simulations that already done by using RoF basic

design. There will be further explanation about simulations, result and discussion and

conclusion of this chapter.

4.2 Simulations

Several type of block simulink was designed and developed for this thesis

simulation. There are:

i) BPSK modulation (Figure 4.2)

ii) QPSK modulation (Figure 4.4)

iii) QPSK modulation using RoF.(Figure 4.5)

48

The performance of the simulink is measured using BER. BER (bit error rate) is

the percentage of bits with errors divided by the total number of bits that have been

transmitted, received or processed over a given time period. The rate is typically

expressed as 10 to the negative power. For example, four erroneous bits out of 100,000

bits transmitted would be expressed as 4 x 10-5, or the expression 3 x 10-6 would indicate

that three bits were in error out of 1,000,000 transmitted. BER is the digital equivalent

to signal-to-noise ratio in an analog system.

4.1.1 BPSK Modulation

For BPSK modulation the block simulink was developed to get the performance

of BER to compare with QPSK modulation. BPSK is the simplest form of PSK. It uses

two phases which are separated by 180° and so can also be termed 2-PSK. It does not

particularly matter exactly where the constellation points are positioned, and in this

figure they are shown on the real axis, at 0° and 180°. This modulation is the most

robust of all the PSKs since it takes serious distortion to make the demodulator reach an

incorrect decision. It is, however, only able to modulate at 1bit/symbol (as seen in the

figure) and so is unsuitable for high data-rate applications.

Figure 4.1 Constellation Diagram for BPSK [7]

49

Figure 4.2 Simulink Block for BPSK Modulation

4.1.2 QPSK Modulation

Sometimes known as quaternary or quadriphase PSK or 4-PSK, QPSK uses four

points on the constellation diagram, equispaced around a circle. With four phases,

QPSK can encode two bits per symbol, shown in the diagram with Gray coding to

minimize the BER twice the rate of BPSK. Analysis shows that this may be used either

to double the data rate compared to a BPSK system while maintaining the bandwidth of

the signal or to maintain the data-rate of BPSK but halve the bandwidth needed.

Although QPSK can be viewed as a quaternary modulation, it is easier to see it

as two independently modulated quadrature carriers. With this interpretation, the even

(or odd) bits are used to modulate the in-phase component of the carrier, while the odd

(or even) bits are used to modulate the quadrature-phase component of the carrier.

BPSK is used on both carriers and they can be independently demodulated.

50

Figure 4.3 Constellation Diagram for QPSK [7]

Figure 4.4 Simulink Block for QPSK Modulation

51

4.1.3 QPSK Modulation Using RoF

Figure 4.5 Simulink Block for WCDMA using RoF

For simulation block Figure 4.5 is present the RoF system as the QPSK is

represent WCDMA with 5 MHz bandwidth, third order polynomial modeled as laser

diode and gain is present fiber. Fiber 1, Fiber 2 and Fiber 3 just name that represent the

different length of fiber.

These length were controlled by the gain as for 0.2 km gain is set to 0.01 for

Fiber 1, 1 km set as 0.02 for Fiber 2 and 48 km set as 1 for Fiber 3. By doing so, the

simulations were produced BER performance for ease analyzed.

52

4.2 Results and Discussion

Figure 4.6 shows that the theoretical BER performance for AWGN channels as a

reference for every BER performance because the BER for AWGN is more stable than

others.

Figure 4.6 Theoretical BER performance with AWGN channel

53

Figure 4.7 shows the BER performance with AWGN channel by using BPSK

modulation. There is very similar with the BER performance for AWGN channel in

figure 4.6.

Figure 4.7 BER performance with AWGN channel for BPSK

54

Illustrate that shows BER performance for QPSK using AWGN channel as

Figure 4.8 is higher than BER performance for BPSK then.

Figure 4.8 BER performance with AWGN channel for QPSK

55

Figure 4.9 is shown the comparison between BER performance for BPSK and

BER performance for QPSK. For figure 4.10 shows both BER performance before

compare to theoretical BER performance.

Figure 4.9 Comparison BER of BPSK and QPSK

56

Figure 4.10 Comparison BER of BPSK, QPSK and Theory

4.2.1 BPSK vs QPSK

From figure 4.6 to figure 4.10 are shown the BER performance fro BPSK and

QPSK compared to theoretical BER performance. Between BER BPSK and QPSK is

shown BER performance for BPSK is lower and same as theoretical than QPSK. It is

because QPSK can be regarded as a pair of orthogonal BPSK systems, i.e. the real

component is one BPSK system, the imaginary components is the second BPSK

system. Because they are orthogonal, they don't interfere (to a good

approximation), hence the BER curves are largely equivalent but the value is higher

than BPSK. BER performance for BPSK and theoretical is same because BPSK is the

basic of PSK modulation so the theoretical is actually represent BPSK .

Usually BPSK is using for uplink in WCDMA and QPSK for downlink. It is

because to differentiate between uplink signal and downlink signal to avoid the

57

interference between two signals. BPSK also known as a type of digital transmission

where two phases of the signal are possible to represent binary one and zero. While

QPSK is known as a modulation scheme which uses four phase values to encode two

data bits per modulated signal.

4.2.2 RoF with different of Fiber Length

Figure 4.11 shows BER performance for the fiber length that represent as Fiber 1

for 0.2 km (200 m).

Figure 4.11 BER performance for fiber length 0.2 km

58

Figure 4.12 shows BER performance for the fiber length that represent as Fiber 2

for 1 km (1000 m).

Figure 4.12 BER performance for fiber length 1 km

Figure 4.13 shows BER performance for the fiber length that represent as Fiber 3

for 48 km (48000 m). For figure 4.14 shows the comparison between three different

lengths of fiber.

59

Figure 4.13 BER performance for fiber length 48 km

Figure 4.14 Comparison BER between 0.2 km, 1 km and 48 km

60

As the figure 4.11 to 4.14 shown the different BER performance between

different fiber length. As the fiber length increases the average BER also increase. This

is expected because as the fiber length increases, signal attenuation in the fiber increases

and this decreases the signal noise ratio in the RoF link. BER performance for 0.2 km

and 1 km is quite same because the range is very small and can be consider same so they

are same. But for 48 km BER performance shown very high because as the fact

mentioned above.

4.3 Summary

As the Chapter 4 summary, BER performance show lower is the best way to use

but must suitable with the function that they perform. So that WCDMA is using BPSK

and QPSK for their function as the two is the basic modulation that can be manipulated

to get use with the function that want to. As the fiber length increases the average BER

also increase.

61

CHAPTER 5

CONCLUSION AND SUGGESTIONS

5.1 Conclusion

As conclusion, the simulation of WCDMA Radio over fiber has been developed

successful. The BER performance shows the largest length is the largest BER measured.

The general concepts of WCDMA radio over fiber systems have been presented.

A simulation model of the downlink segment of a WCDMA radio over fiber system was

presented using Matlab simulink.

Combination of WCDMA and RoF represents a first demonstration of new

broadband applications using full radio over fiber environment. RoF will be suited to 3G

mobile networks due to the cost savings associated with providing many small cells

compared to conventional approaches. The input power and fiber length limits have

been established for WCDMA transmission and will not impose undue restrictions on

the use of RoF.

62

RoF has a very important role in cellular communications today and become

even more prevalent in the futures as more in-building systems are required. RoF

transmission technology needs to pay attention to the optical fiber length, the emission

wavelength of the laser & transmission frequency for RF signal (chromatic dispersion).

RoF network structure is more flexible & easy to expand when compared with

conventional network structures.

5.2 Suggestion For Future Research

The IEEE 802.11a standard is proposed for a range of data rates from 6 up to 54

Mbps using the OFDM modulation technique in the 5 GHz band. The 5 GHz band is

specifically designed for “Wireless Broadband Mobile Communication Systems

(WBMCS)”. The IEEE 802.11a WLAN standard is superior compared with current

technologies because of its greater scalability, better interference immunity and

significantly higher speed and at the same time allowing for higher bandwidth

applications and more users. The 802.11a standard utilizes 300 MHz of bandwidth in the

5 GHz unlicensed National Information Infrastructure (U-NII) band.

Orthogonal Frequency Division Multiplexing (OFDM) is seen as the modulation

technique for future broadband wireless communications because its provides increased

robustness against frequency selective fading and narrowband interference and is

efficient in dealing with multi-path delay spread. To achieve this, OFDM splits high-rate

data streams into lower rate streams, which are then transmitted simultaneously over

several sub-carriers. By doing so, the symbol duration is increased.

OFDM uses multiple sub-carriers to transmit low rate data streams in parallel.

The sub-carriers are modulated by using Phase Shift Keying (PSK) or Quadrature

63

Amplitude Modulation (QAM) and are then carried on a high frequency microwave

carrier such as 5 GHz.

64

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