PERFORMANCE STUDY ON HIGH DATA RATES...

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PERFORMANCE STUDY ON HIGH DATA RATES

MODULATION TECHNIQUES OF W-CDMA IN MULTIPATH

FADING CHANNEL

MUHAMMAD NAJIB BIN ISMAIL

A project report submitted in partial fulfillment of the

requirements for the degree of

Master of Engineering (Electrical-Electronics & Telecommunication)

Faculty of Electrical Engineering

University Technology Malaysia

APRIL 2005

v

ABSTRACT

Downlink transmission (base station to mobile terminal) using high data rate M-

ary Quadrature Amplitude Modulation (QAM) and Quadrature Phase Shift Keying

(QPSK) modulation schemes are considered in a Wideband-Code Division Multiple

Access (W-CDMA) system. The performances of these modulation techniques are

evaluated when the system is subjected to a number of users as well as noise and

interference in the channel. Additive White Noise Gaussian (AWGN) and multipath

Rayleigh fading are considered in the channel. Computer simulation tool, MATLAB,

will be used throughout the research to evaluate Bit-Error-Rate (BER) for W-CDMA

system models. Two approaches are used in this simulation. They are simulations using

Simulink and simulations using M files. A study of different modulation techniques is

needed so that a W-CDMA system can choose suitable modulation technique to suit the

channel quality, thus delivering optimum and efficient data rate to mobile terminal. It is

discovered that the performance of 16-QAM is significantly degraded in AWGN and

multipath Rayleigh fading channel compared to that of QPSK. Error correction coding is

needed to be used in this system particularly with 16-QAM to ensure better performance

of WCDMA system.

Index Terms – Multipath Rayleigh fading, AWGN, Direct Sequence Spread Spectrum

(DSSS), Code Division Multiple Access (CDMA), BER, signal-to-noise ratio (SNR),

QPSK and 16-QAM

vi

ABSTRAK

Projek ini melibatkan kajian mengenai transmisi jalinan ke bawah (downlink)

(stesen tapak ke terminal boleh gerak) yang melibatkan penggunaan teknik-teknik

modulasi QPSK dan 16-QAM di dalam Pemodulatan Pembahagian Kod Pelbagai

Capaian Lebar Jalur Luas (Wideband Code Division Multiple Access, WCDMA).

Prestasi teknik-teknik modulasi ini dinilaikan ke atas sistem WCDMA yang dikenakan

hingar dan interferen pada saluran (channel) sistem ini. Pertambahan Bunyi Hingar Putih

Gaussian (AWGN) dan kelenturan pelbagai laluan Rayleigh (multipath Rayleigh fading)

dipilih untuk digunakan pada saluran di dalam sistem ini. Di dalam kajian ini, program

computer MATLAB telah digunakan untuk mensimulasikan sistem WCDMA untuk

menilai kadar kesilapan bit di dalam sistem WCDMA. Dua kaedah telah digunakan iaitu

simulasi menggunakan Simulink dan simulasi menggunakan file M. Penyelidikan

terhadap teknik-teknik modulasi adalah diperlukan bagi sistem WCDMA supaya teknik

modulasi yang sesuai dapat digunakan secara dinamik oleh sistem ini supaya ia dapat

disesuaikan dengan keaadaan saluran. Kaedah ini adalah untuk memastikan

penghantaran data daripada stesen tapak ke terminal boleh gerak adalah pada tahap yang

laju, efisyen dan optimum. Keputusan simulasi computer ini telah menunjukkan

penurunan prestasi bagi teknik modulasi 16-QAM di dalam saluran AWGN dan

kelenturan pelbagai laluan Rayleigh jika ia dibandingkan dengan QPSK. Kod

pembetulan kesilapan adalah diperlukan di dalam sistem ini terutamanya jika 16-QAM

digunakan untuk memastikan sistem WCDMA berada pada keadaan yang baik.

vii

TABLE OF CONTENT

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENT vii

LIST OF TABLES xi

LIST OF ABBREVIATION xv

LIST OF APPENDIX xvi

1 INTRODUCTION 1

1.1 Background of the Problem 1

1.2 Problem Statements 2

1.3 Project Objective 2

1.4 Scope of Work 4

1.5 Significant of the Project Research 5

2 MODULATION SCHEMES IN WCDMA 7

viii

2.1 Bit Rate and Symbol Rate 9

2.2 Quadrature Phase Shift Keying (QPSK) 10

2.3 M-ary Quadrature Amplitude Modulation (QAM) 11

2.4 Wideband-Code Division Multiple Access (W-CDMA) 12

2.4.1 Direct Sequence Spread Spectrum (DSSS) 12

2.4.2 Code Division Multiple Access (CDMA) 15

2.5 Noise and Interference 15

2.5.1 Additive White Noise Gaussian (AWGN) 16

2.5.2 Rayleigh Fading 17

2.6 Bit Error Rate (BER) 19

2.7 Signal-to-Noise Ratio (SNR) 20

2.8 DSSS-CDMA Bit-Error Probability Calculations 20

2.9 Theoretical DSSS-CDMA System and Channel Models 21

2.9.1 Transmitter Model 21

2.9.2 Receiver Model 23

2.9.3 Channel Model 23

2.9.3.1 AWGN 23

2.9.3.2 Rayleigh Fading 25

3 CONFIGURATIONS ON WCDMA SYSTEM 28

3.1 Simulation Methodology 29

3.2 Simulation Using Simulink 30

3.2.1 Simulation in Phase 1: WCDMA System in AWGN Channel 31

3.2.1.1 Assumptions in Phase 1 31

3.2.1.2 Transmitter Design 35

3.2.1.2.1 User Data Sequence Generator 35

3.2.1.2.2 Spreading Sequence Generator 36

3.2.1.2.3 Spreader 38

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3.2.1.3 Modulation Techniques 39

3.2.1.3.1 QPSK Modulator 39

3.2.1.3.2 16-QAM Modulator 42

3.2.1.4 Channel Design 43

3.2.1.5 Receiver Design 43

3.2.1.5.1 QPSK Demodulator 43

3.2.1.5.2 16-QAM Demodulator 45

3.2.1.6 Despreader 45

3.2.1.7 Error Rate Calculation 46

3.2.1.8 Display 47

3.2.1.9 Performance Analysis for Phase 1 48

3.2.2 Simulation Phase 2: WCDMA system in AWGN and Multipath Rayleigh

Fading 50

3.2.2.1 Channel 53

3.2.2.2 Performance Analysis for Phase 2 55

3.3 Simulation Using M file 56

3.3.1 Generation of Spreading Code 56

3.3.2 Code Generation by Linear Feedback Shift Register 58

3.3.3 M-Sequence 59

3.3.4 Configuration of Transmitter and Receiver 61

3.3.5 Steps Taken to Realize the Simulation in dscdma.m file 66

3.3.6 Assumption and Limitation 67

4 PERFORMANCE ANALYSIS ON WCDMA SYSTEM 68

4.1 Simulation Using Simulink 69

4.1.1 Performance Analysis of QPSK modulation technique of WCDMA in

AWGN 69


AWGN and Multipath Fading Channel 71

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4.1.3 Performance Analysis of 16-QAM modulation technique of WCDMA in

AWGN 74



4.2 Simulation Using M files 78


AWGN 78



4.2.3 Performance Analysis Comparison of QPSK modulation technique of

WCDMA Between AWGN and Rayleigh Fading Channel 83


AWGN 89



4.3 Analysis and Discussion 90

5 CONCLUSION 92

5.1 Conclusion 92

5.2 Suggestion for Future Work 93

REFERENCES 95

APPENDIX 98

xi

LIST OF TABLES

Table no. Title Page no.

3.1 Parameters for Bernoulli Binary Generator Block 35

3.2 Parameters used in PN Sequence Generator Block 36

3.3 Parameters used in QPSK Modulator Passband Block 40

3.4 Parameters used in M-QAM modulation block 42

3.5 Parameters used in AWGN block 43

3.6 Parameters used in QPSK Demodulator Passband Block 44

3.7 Parameters used in 16-QAM Demodulator Passband Block 45

3.8 Parameters used in Error Rate Calculation Block 46

3.9 Parameters used in Display Block 48

3.10 Parameters used in multipath Rayleigh fading channel 53

4.1 Simulation result for evaluation on BER vs. SNR for 2-ray

AWGN channel for 1 user when the number of data is

200,000

78

4.2 Simulation results for evaluation on BER vs. SNR for 2-ray

Multipath Rayleigh Fading channel for 1 user when the

number of data is 200,000 at 60 kmph

80

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80




81



200,000

83


Multipath Rayleigh channel for 1 user when the number of

data is 200,000

84



100,000

86


Multipath Rayleigh channel for 5 user when the number of

data is 100,000

87

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LIST OF FIGURES

FIGURE NO. TITLE PAGE NO.

2.1 Constellation diagram of a QPSK system 12

2.2 Constellation diagram of a 16-QAM system 12

2.3 CDMA 15

2.4 Relationship among channel correlation function and power

density function

18

3.1 Simulation process for W-CDMA system models 30

3.2 WCDMA Model using QPSK modulation technique in

AWGN channel

33

3.3 W-CDMA Model using 16-QAM modulation technique in

AWGN and multipath fading channel

34

3.4 W-CDMA Model with Multipath Raleigh fading channel and

AWGN channel using QPSK Modulation Technique

51

3.5 W-CDMA Model using 16-QAM in AWGN and Multipath

Raleigh fading channel

52

3.6 Three-stage M-sequence 61

3.7 WCDMA system configured using m files 62

xiv

4.1 Performance of WCMA system using QPSK in AWGN

channel

70

4.2 Performance of WCDMA system using QPSK in multipath

fading channel at 60 kmph

71


fading channel for 90 kmph

72


fading channel at 120 kmph

73

4.5 Performance of WCDMA system using 16-QAM in AWGN 74

4.6 Performance of WCDMA system using 16-QAM in

multipath fading channel at 60 kmph

75



76



77

4.9 Performance of WCDMA in 2-Rays AWGN Channels for 1

user

79

4.10 Performance of WCDMA in 2-Rays Multipath Rayleigh

Fading Channels for 1 user

82

4.11 Performance Comparison of WCDMA in 2-Rays Between

AWGN and Multipath Rayleigh Fading Channels for 1 user

85

4.12 Performance Comparison of WCDMA in 2-Rays Between

AWGN and Multipath Rayleigh Fading Channels for 5 user

88

4.13 Performance Comparison of 16-QAM in WCDMA system in

AWGN channel

89

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LIST OF ABBREVIATION

WCDMA Wideband Code Division Multiple Access

UMTS Universal Mobile Telecommunication System

GMSK Gaussian Minimum Shift Keying

GSM Global System for Mobile Communication

AWGN Additive White Noise Gaussian Noise

QPSK Quadrature Phase Shift Keying

QAM Quadrature Amplitude Modulation

BER Bit Error Rate

SNR Signal to Noise Ratio

PN Pesudo-Noise

AMC Adaptive Modulation and Coding

HSDPA High Speed Downlink Packet Access

PDF Probability Density Function

dB Decible

ISI Inter-Symbol Interference

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LIST OF APPENDIX

APPENDIX

NO.

TITLE PAGE NO.

1.1 Matlab Source Codes for Simulation Using Simulink 98

1.1.1 Generic Source Codes of Simulation for QPSK of WCDMA

system either in AWGN or Multipath Fading channel or both

98

1.1.2 Generic Source Codes of Simulation for 16-QAM of

WCDMA system either in AWGN or Multipath Fading

channel or both

99

1.2.1 Source Codes for Simulation of Sub-System of WCDMA 100

1.2.1.1 Source Codes for Simulation of Autocorrelation Function of

a Sequence

100

1.2.1.2 Source Codes for Simulation of Cross-correlation Function

of a Sequence

100

1.2.1.3 Source Codes for Simulation of Generation Function of M

Sequence

101

1.2.1.4 Source Codes for Simulation of Shifting the Contents of the

Register

102

1.2.1.5 Source Codes for Simulation of Data Spread Function 104

1.2.1.6 Source Codes for Simulation of Data Despread Function 105

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1.2.1.7 Source Codes for Simulation of a Function to Sample the

Time

106

1.2.1.8 Source Codes for Simulation of a Function to Add Gaussian

Noise

107

1.2.2 Source Codes for Simulation of Main-System of WCDMA 108

1.2.2.1 Source Codes for Simulation of the Main Program of DS-

WCDMA System

108

1.2.3 Source Codes for Simulation of BER vs EbNo of WCDMA

System

113

1.2.3.1 Source Codes for Simulation of QPSK of WCDMA System

in AWGN Channel

113


in Multipath Rayleigh Fading Channel with Doppler Shift

(60kmph, 90kmph & 120kmph)

113


for AWGN vs Multipath Rayleigh Fading Channel

115


for AWGN vs Multipath Rayleigh Fading Channel for a

Single User

117


for AWGN vs Multipath Rayleigh Fading Channel for a Five

(5) Users

118

1.2.3.6 Source Codes for Simulation of 16-QAM of WCDMA

System in AWGN Channel

119

CHAPTER 1

INTRODUCTION

1.1 Background of the Problem

W-CDMA system has been identified by Universal Mobile Telecommunication

System (UMTS) as the platform of the 3rd generation cellular communication system.

Unlike conventional narrowband signal of 2nd generation (2G) communication system,

W-CDMA uses noise-like broadband frequency spectrum where it has high resistance to

multipath fading. High data rate signal transmission can be transmitted over the air by

using W-CDMA system, thus enabling large data transmission of multimedia rich

applications such as high-resolution pictures and video to end-users. Thus, suitable

modulation technique and error correction scheme have to be used in W-CDMA system.

In 2G network, modulation scheme such as GMSK is widely used in Global System of

Mobile Communication (GSM). GMSK can only deliver data rate of 1 bit per symbol.

Obviously, such modulation scheme is not suitable for the next communication system.

Thus, there is a need to study the performance of new modulation technique that could

deliver higher data rate effectively in a multipath fading channel.

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1.2 Problem Statements

To deliver multimedia content application over cellular networks, a high data rate

modulation scheme is one of the important criteria besides good error correction coding.

However, the implementation of high data rate modulation techniques that have good

bandwidth efficiency in W-CDMA cellular communication requires perfect modulators,

demodulators, filter and transmission path that are difficult to achieve in practical radio

environment. Modulation scheme that capable to deliver more bits per symbol is

susceptible to errors caused by noise and interference in the channel. Moreover, errors

can be easily produced as the number of users is increased and the mobile terminal is

subjected to mobility.

1.3 Project Objective

The objectives and aims of this project are to look at the performance of high

data rate modulation techniques at channels that are subjected to Additive White

Gaussian Noise (AWGN) and multipath Rayleigh fading. Modulation schemes that will

be considered in this project are Quadrature Phase Shift Keying (QPSK) and 16-ary

Quadrature Amplitude Modulation (16-QAM). This performance study will be carried

out by varying the chip rate of pseudo-noise (PN) generator. Furthermore, multiple

access scheme i.e. WCDMA will be also studied by comparing certain number of users

under static and mobility environment that are subjected to AWGN and multipath

Rayleigh fading. The performances of WCDMA under these channels fading are based

on Bit Error Rate (BER) at downlink (base station to mobile terminal) transmission.

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There will be three WCDMA wireless cellular system models that will be used in

this project. The models are

1. WCDMA system in AWGN channel

2. WCDMA system in AWGN and Multipath Rayleigh Fading.

3. Multi-user WCDMA system in AWGN and Multipath Rayleigh Fading.

Relationship for multiple rays using QPSK and QAM in W-CDMA system models

for the followings parameters will be obtained using MATLAB. They are:

1. Bit Error Rate (BER) versus Signal-to-Noise ratio (SNR) in AWGN channel for

QPSK modulation technique.

2. BER versus SNR in AWGN channel for 16-QAM modulation scheme.

3. BER versus SNR in AWGN and multipath Rayleigh fading channel with Doppler

shift (60kmph, 90kmph and 120kmph) for QPSK modulation technique.

4. BER versus SNR in AWGN and multipath Rayleigh fading channel with Doppler

shift (60kmph, 90kmph and 120kmph) for 16-QAM modulation scheme.

5. BER versus SNR to compare between AWGN channel and multipath Raleigh

fading channel for different number of user for QPSK modulation technique.

6. BER versus SNR to compare between AWGN channel and multipath Raleigh

fading channel for different number of user for 16-QAM modulation technique.

Once data for BER and SNR under various parameters are obtained, the data are

tabulated. Graphs of BER as a function of SNR under different modulation

techniques as well as different velocities of mobile terminal subjected to noise and

interference channel will be plotted. These graphs will be studied and compared so

that a conclusion on suitable high data rate modulation scheme can be drawn.

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1.4 Scope of Work

This project is an entirely simulation project using scientific computer simulation

software, MATLAB 6.5.2. Two approaches will be used in this project. They are

simulation using Simulink and simulation using m files. It will be simulated in multi-

user environment based on Direct Sequence Spread Spectrum (DSSS), Wideband-Code

Division Multiple Access (W-CDMA). There will be no error correction coding or

channel coding employed for this simulation models.

There are two extreme cases of channel noise and fading that will be subjected

to the W-CDMA system models. Firstly, the model is simulated with different

modulation techniques under thermal noise, represented by Additive White Noise

Gaussian (AWGN). Then, the channel is simulated with various different parameters

using Non-Line of Sight (N-LOS) multiple reflected rays represented as multipath

Rayleigh fading.

The performance of the modulation schemes are studied when the mobile

terminal is static and mobile with different speeds. The performance measurement is

based on BER. Thus, suitable modulations techniques will be determined and concluded

based on BER that will be plotted as a function of function of SNR.

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1.5 Significant of the Project Research

The current trend to achieve high data rate cellular communication drives the

interest of this research. There are many ways one can improve data rate in a W-CDMA

system. However, two significant areas that could give significant boost to the

improvement of W-CDMA system is modulation scheme and error correction or channel

coding.

There are many modulation schemes that have the potential to deliver higher data

rate but there is a trade off between data rate and multipath environment. Modulation

techniques that can deliver more bits per symbol normally generate lots of error when

they are subjected to multipath channels. Recently, there is intensifying research about

Adaptive Modulation and Coding (AMC) [14]-[16]. The principle of AMC is to change

the modulation and coding format (transport format) in accordance with instantaneous

variations in the channel conditions, subject to system restrictions. AMC extends the

systems ability to adapt to good channel conditions. Channel conditions should be

estimated based on feedback from the receiver. For a system with AMC, users closed to

the cell site are typically assigned higher order modulation with higher code rates (e.g.

64 QAM with R=3/4 Turbo Codes). On the other hand, users closed to the cell boundary,

are assigned lower order modulation with lower code rates (e.g. QPSK with R=1/2

Turbo Codes). AMC allows different data rates to be assigned to different users

depending on their channel conditions. Since the channel conditions vary over time, the

receiver collects a set of channel statistics which are used both by the transmitter and

receiver to optimize system parameters such as modulation and coding, signal

bandwidth, signal power, training period, channel estimation filters, automatic gain

control, etc [3].

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Thus, this project will scrutinize suitable modulation techniques that are capable

to deliver highest data rate without compromising errors in multipath fading

environment. The performance of these modulation techniques will be simulated by

using computer simulation tool, MATLAB.

REFERENCES

[1] Y. Rosmansyah, P. Sweeney, R. Tafazolli, “Air-Interface Techniques for Achieving

High Data Rates for UMTS”, IEEE 3G Mobile Communication Technologies,

Conference Publication No. 477, pp. 368-372, 26-28 March 2001.

[2] A.S. Madhukumar, Francois Chin, “An Efficient Method for High-rate Data

Transmission using Residue Number System based DS-CDMA”, IEEE.

[3] Min-yan Song, Yang Xiao, Joachim Habermann, “High Data Rate Wireless System”,

IEEE, pp. 1344-1350.

[4] Haifeng Wang, Zhenhong Li, “Novel Soft-bit Demodulator with Multi-dimensional

Projection for High-order Modulation”, IEEE, pp. 2051-2054, 2002.

[5] Theodore S. Rappaport, "Wireless Communication: Principle and Practice", Pearson

Educational International, 2nd edition. 2002.

[6] Bernard Sklar, "Digital Communications: Fundamentals and Applications", Prentice-

Hall, 2nd Edition, pp. 30-33.

[7] Bernard Sklar, "Rayleigh Fading Channel in Mobile Digital Communication System

Part 1: Characterization", IEEE Communication Magazine, pp. 90-100, July 1997.

96

[8] Julian Cheng, Norman C. Beaulieu, “Accurate DS-CDMA Bit-Error Probability

Calculation in Rayleigh Fading”, IEEE Transactions on Wireless Communications,

Vol. 1, No. 1, January 2002.

[9] Michael B. Pursley, “Performance Evaluation for Phase-Coded Spread-Spectrum

Multiple-Access Communication-Part 1: System Analysis”, IEEE Transaction on

Communications, Vol. Com-25, No. 8, August 1977.

[10] Michael B. Pursley, “Performance Evaluation for Phase-Coded Spread-Spectrum

Multiple-Access Communication-Part 2: Code Sequence Analysis”, IEEE

Transaction on Communications, Vol. Com-25, No. 8, August 1977.

[11] Tony Ottoson, “Multi-rate Scheme and Multi-user Decoding in DS-CDMA

Systems”, Thesis for degree of Licentiate of Engineering of Chalmers University of

Technology, Technical report no. 214L, ISBN 91-7197-217-X, November 1995.

[12] John G. Proakis, “Digital Communications”, McGraw-Hill, 3rd Edition, 1995.

[13] H. Harada & R. Prasad, Simulation and Software Radio for Mobile

Communications, Artech House, 2nd Edition, 2002.

[14] J. M. Holtzman, “A Simple, Accurate Method to Calculate Spread-Spectrum

Multiple-Access Error Probabilities,” IEEE Trans. Communication, vol. 40, pp. 461-

464, Mar.1992.

[15] Victor Wen-Kai Cheng, Wayne E. Stark, “Adaptive Coding and Modulation for

Spread Spectrum”, IEEE Journal, 1997.

[16] Troels E. Kolding, Frank Frederiksen, Preben E. Mogensen, “ Performance

Aspects of WCDMA Systems with High Speed Downlink Packet Access (HSDPA)”,

Nokia Network R&D, Denmark, 2003

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[17] Troels Emil Kolding, Klaus ingemann Pedersen, Jeroen Wigard, Frank

Frederiksen, Preben Elgaard. Mogensen, “High Speed Downlink Packet Access

(HSDPA): WCDMA Evolution”, IEEE Vehicular Technology Society News,

February, 2003.

[18] E. Hossain, T. Issariyakul, “Performance bound of dynamic forward link

adaptation in cellular WCDMA networks using high-order modulation and multicode

formats”, IEEE Electronics Letters, Vol.40, No. 2, January 2004.

[19] Dong In Kim, Ekram Hossain, Vijay K. Bhargava, “Dynamic Rate and Power

Adaptation for Forward Link Transmission Using High-Order Modulation and

Multicode Formats in Cellular WCDMA Network”, IEEE Journal, 2003.

[20] R. K. Morrow and J. S. Lehnert, “Bit-to-bit Error Dependence in Slotted DS-

CDMA packet systems with random signature sequences”, IEEE Trans. Commun,

vol. 37, pp. 1052-1061, Oct. 1989.

[21] T. J. Moulsley, “Throughput of High Speed Downlink Packet Access for

UMTS”, Phillips Research Laboratories, 2002.

[22] Troels E. Kolding, Frank Frederiksen, and Preben E. Mogensen, “Performance

Aspects of WCDMA Systems with High Speed Downlink Packet Access (HSDPA)”,

Nokia Networks, Aalborg R&D, Denmark, 2002.

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