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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
ix
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
4.1.2 Performance Analysis of QPSK modulation technique of WCDMA in
AWGN and Multipath Fading Channel 71
x
4.1.3 Performance Analysis of 16-QAM modulation technique of WCDMA in
AWGN 74
4.1.4 Performance Analysis of 16-QAM modulation technique of WCDMA in
AWGN and Multipath Fading Channel 75
4.2 Simulation Using M files 78
4.2.1 Performance Analysis of QPSK modulation technique of WCDMA in
AWGN 78
4.2.2 Performance Analysis of QPSK modulation technique of WCDMA in
AWGN and Multipath Fading Channel 79
4.2.3 Performance Analysis Comparison of QPSK modulation technique of
WCDMA Between AWGN and Rayleigh Fading Channel 83
4.2.4 Performance Analysis of 16-QAM modulation technique of WCDMA in
AWGN 89
4.2.5 Performance Analysis of 16-QAM modulation technique of WCDMA in
AWGN and Multipath Fading Channel 90
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
xii
4.3 Simulation result 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 90 kmph
80
4.4 Simulation result 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 120 kmph
81
4.5 Simulation result for evaluation on BER vs. SNR for 2-ray
AWGN channel for 1 user when the number of data is
200,000
83
4.6 Simulation result for evaluation on BER vs. SNR for 2-ray
Multipath Rayleigh channel for 1 user when the number of
data is 200,000
84
4.7 Simulation result for evaluation on BER vs. SNR for 2-ray
AWGN channel for 5 user when the number of data is
100,000
86
4.8 Simulation result for evaluation on BER vs. SNR for 2-ray
Multipath Rayleigh channel for 5 user when the number of
data is 100,000
87
xiii
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
4.3 Performance of WCDMA system using QPSK in multipath
fading channel for 90 kmph
72
4.4 Performance of WCDMA system using QPSK in multipath
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
4.7 Performance of WCDMA system using 16-QAM in
multipath fading channel at 90 kmph
76
4.8 Performance of WCDMA system using 16-QAM in
multipath fading channel at 120 kmph
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
xv
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
xvi
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
xvii
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
1.2.3.2 Source Codes for Simulation of QPSK of WCDMA System
in Multipath Rayleigh Fading Channel with Doppler Shift
(60kmph, 90kmph & 120kmph)
113
1.2.3.3 Source Codes for Simulation of QPSK of WCDMA System
for AWGN vs Multipath Rayleigh Fading Channel
115
1.2.3.4 Source Codes for Simulation of QPSK of WCDMA System
for AWGN vs Multipath Rayleigh Fading Channel for a
Single User
117
1.2.3.5 Source Codes for Simulation of QPSK of WCDMA System
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.
2
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.
3
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.
4
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.
5
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].
6
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.
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96
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[15] Victor Wen-Kai Cheng, Wayne E. Stark, “Adaptive Coding and Modulation for
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[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
97
[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-
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[21] T. J. Moulsley, “Throughput of High Speed Downlink Packet Access for
UMTS”, Phillips Research Laboratories, 2002.
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Aspects of WCDMA Systems with High Speed Downlink Packet Access (HSDPA)”,
Nokia Networks, Aalborg R&D, Denmark, 2002.
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