Simulation on performance of space time block code

Abstract

In a wireless communication system, time-varying multipath fading has become the main constraint that affects the reliability of a wireless system. The most effective technique that had been used to mitigate the multipath fading is diversity. Space time block coding (STBC) offers the diversity technique and uses multiple-input and multiple output (MIMO) concepts in order to overcome the problem of fading and interference in a wireless communication system. The use of antenna arrays at both transmitter and receiver for a MIMO system gives benefits in terms of rate and reliability. Therefore, this paper analyzes the capability of STBC to minimize the fading effect and also improve the capacity. Three simulation models have been developed using Matlab V 6.5 software. The MIMO capacity measurement is also analyzed using the same software. The designed models then have been simulated with different numbers of code rate and antenna. The proposed STBC in this thesis consists of interleaver and cyclic code with code rate 4/5, 4/6 and 4/7. The simulation model is then sent through an AWGN channel to analyze the performance in terms of BER. The simulation results show that the proposed 2 transmitter and 2 receiver antenna model improved 90% of BER and 73% capacity compared to the conventional one antenna system.

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First Edition 2008
© SHARIFAH HAFIZAH SYED ARIFFIN & NORULHUSNA AHMAD 2008

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daripada Timbalan Naib Canselor (Penyelidikan dan Inovasi), Universiti Teknologi
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perkiraan royalti atau honorarium.

All rights reserved. No part of this publication may be reproduced or transmitted in any
form or by any means, electronic or mechanical including photocopy, recording, or any
information storage and retrieval system, without permission in writing from Universiti
Teknologi Malaysia, 81310 Skudai, Johor Darul Ta’zim, Malaysia.

Perpustakaan Negara Malaysia Cataloguing-in-Publication Data
OFDM and MIMO-OFDM system / editors: Sharifah Hafizah Syed Ariffin,
Norulhusna Ahmad.
Includes index
ISBN 978-983-52-0660-3
1. Wireless communication systems. 2. Broadband communication
systems. 3. Wireless LANs. I. Sharifah Hafizah Syed Ariffin.
II. Norulhusna Ahmad.
621.382
Editor: Sharifah Hafizah Syed Ariffin & Rakan
Pereka Kulit: Mohd Nazir Md. Basri & Mohd Asmawidin Bidin
Diatur huruf oleh / Typeset by
Fakulti Kejuruteraan Elektrik
Diterbitkan di Malaysia oleh / Published in Malaysia by
PENERBIT
UNIVERSITI TEKNOLOGI MALAYSIA
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81300 Skudai,
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Selangor Darul Ehsan, MALAYSIA.

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Contents

v
CONTENTS





Preface
ix
Chapter 1

The PAPR Performance in WLAN-
OFDM System
Norhafizah Ngajikin
Sharifah Kamilah Syed-Yusof

PAPR Reduction of OFDM Signals using
Partial Transmit Sequences
Sharifah Kamilah Syed-Yusof
Norsheila Fisal
Tang Sze Yin

Code Repetition Technique in Reducing
Papr of WLAN-OFDM System
Norhafizah.Ngajikin
Norsheila Fisal
Sharifah Kamilah Syed-Yusof

Time-Domain Amplitude Manipulative
Papr Reduction Techniques on PRS-
OFDM System
Sharifah K. Syed-Yusof
Norsheila Fisal
Muladi

1
Chapter 2
9
Chapter 3 18
Chapter 4
29

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Contents

vi
Chapter 5 Peak-To-Average Power Ratio
Reduction Technique in PRS-OFDM
System
Sharifah Kamilah Syed-Yusof
Norsheila Fisal
Muladi

The Evaluation Of ICI Self-Cancellation
Techniques in OFDM Systems
Sharifah Kamilah Syed Yusof
Norsheila Fisal
Muladi

Simulation on Performance of Space
Time Block Code
Norhafizah Ngajikin
Wan. N. Ahmad
Norsheila Fisal
Sharifah Kamilah Syed-Yusof

Iterative Data Detection And Channel
Estimation For Single-Parity Check-
Product Coded for Wireless MIMO
Communications Systems
Muladi, Norsheila Fisal
Sharifah Kamiah Yusof

Performance of Block Turbo Coded
MIMO Systems
Muladi
Sharifah Kamilah Syed-Yusof
Norsheila Fisal


38
Chapter 6
49
Chapter 7
58
Chapter 8 70
Chapter 9
85

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Contents

vii
Chapter 10 The Performance of PRS-OFDM in
Multiple Antenna System
Sharifah Kamilah Syed Yusof
Norsheila Fisal
Muladi

The Space-Time-Frequency MIMO-
OFDM System with Intercarrier
Interference Self-Cancellation
Anis Izzati Ahmad Zamani
Sharifah Kamilah Syed Yusof
Norsheila Fisal

96
Chapter 11
106
Index







115

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Page 9

Preface

ix
PREFACE




Wireless communication has become increasingly important not
only for professional applications but also for many fields in our
daily routine More and more computers use wireless local area
networks (WLANs), and audio and television broadcasting has
become digital. Many of the above-mentioned communication
systems make use of one of sophisticated technique that is known
as orthogonal frequency division multiplexing (OFDM). OFDM is
a digital multicarrier transmission technique that distributes the
digitally encoded symbols over several subcarrier frequencies in
order to reduce the symbol clock rate to achieve robustness against
long echoes in a multipath radio channel. The concept of
orthogonality between subcarriers is a key to the OFDM system.
There are two main setback of OFDM system are Peak-to-Average
Power Ratio (PAPR) and Intercarrier Interference (ICI).
This book is a compilation of the research work done on
OFDM and MIMO-OFDM systems. The book is organized as
follows. In Chapter 1 investigates the Peak-to-Average Power
Ratio (PAPR) in OFDM system. Chapter 2 to Chapter 5 explore on
some techniques to reduce the PAPR in OFDM system. ICI self-
cancellation techniques are explored in Chapter 6. MIMO-OFDM
systems are discussed in Chapter 7 to Chapter 11. Preliminary
study of space-time (ST) block code is covered in Chapter 7.
Iterative data detection schemes are discussed in Chapter 8 and
Chapter 9. Chapter 10 deals with the performance of partial
response signalling (PRS) OFDM technique in multiple antenna
system. A preliminary work on space-time-frequency (STF)
OFDM system with the employment of ICI self-cancellation is
covered in Chapter 11.

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Preface

x
We would like to express our greatest gratitude to the
authors of the individual chapters, without whom this book would
not exist. And to those who have helped in the completion of this
book, we greatly appreciate your assistance.


Sharifah Hafizah Syed Ariffin
Norulhusna Ahmad
Facuty of Electrical Engineering
Universiti Teknologi Malaysia
2008

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The PAPR Performance in WLAN-OFDM System

1
1
THE PAPR PERFORMANCE IN WLAN-
OFDM SYSTEM
Norhafizah Ngajikin
Sharifah Kamilah Syed-Yusof



1.1 INTRODUCTION

OFDM is a
communication channel into a number of equally spaced frequency
hands. This modulation scheme is derived from multi-carrier
modulation (MCM). A subcarrier that carries a portion of the user
information is transmitted in each frequency sub-band. In OFDM,
every subcarrier is orthogonal to each other subcarrier.
Due to the summation of signals from each subcarrier in
OFDM signal, Peak To Average Power Ratio (PAPR) problem
arises. Figure 1.1 illustrates the flow of signal in the OFDM
transmitter. ScN multiple subcarriers are added coherently and
might contribute a peak in signal envelope that can achieve several
dB above the average signal power. An example of power
spectrum of the transmitted OFDM signal is shown in Figure 1.2

communication technique that divides a

Figure 1.1 Transmitter

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OFDM and MIMO-OFDM System

2

Figure 2 Power Spectrum Of Multi Carrier System
Commonly in a complete transmission system, the signal
will be amplified before transmitted for example through an
antenna. This condition introduced by the summation of the
subcarriers will contribute to a high PAPR. A serious problem of
large PAPR occurs if cheap and energy-efficient nonlinear
power amplifiers are used in the communication system.
Frequent excursions into the nonlinear operating region
contribute to the increment of Bit Error Rate (BER) and spectral
regrowth outside the intended frequencies of operation.
Reduction of PAPR inconsistency behavior might overcome this
problem. The mathematical expression for PAPR is given by
equation (1).



In order to keep the PAPR small, the max |sc(t)|2 must be
minimized.
(1)

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The PAPR Performance in WLAN-OFDM System

3
This chapter is organized as follows. In section 1.2 we
described the OFDM communication model. In section 1.3, the
performance of PAPR in WLAN OFDM communication system is
investigated. Lastly, section 1.4 concludes the finding of this
chapter.

1.2 OFDM COMMUNICATION MODEL

Figure 1.3 shows the model of basic OFDM transceiver. In this
parallel data transmission scheme, the data is transmitted
simultaneously over N orthogonal subcarriers with equal space
within the desired transmission bandwidth.


Figure 1.3 OFDM Transceiver

The transmitter converts the input data Cn=C0, C1,…,CN-1
from a serial stream to parallel sets. Before performing the
Inverse Fast Fourier Transform (IFFT) this parallel data set are
arranged on each subcarrier the frequency domain.
The symmetrical arrangement about the vertical axis is
necessary when using the IFFT to change the data into time
domain. An IFFT converts the frequency domain data set into
samples of the corresponding time domain representation of this
data. Specifically, the IFFT is useful for OFDM because it
generates samples of a waveform with frequency components
satisfying orthogonality conditions. Then, the parallel to serial

Page 14

OFDM and MIMO-OFDM System

4
block creates the OFDM signal by sequentially outputting the
time domain samples. Mathematical expression of the
transmitted signal, sc(t) is



where
Ci ~ binary data vector
n ~ number of modulated function
f0 ~ lowest frequency of the carrier
N ~ no of carrier
t ~ OFDM symbol duration

The OFDM receivers basically do the reverse operation of the
transmitter. First, the OFDM data are split from a serial stream into
parallel sets. The Fast Fourier Transform (FFT) converts the time
domain samples back into a frequency domain representation.
Thus, the magnitudes of the frequency components correspond to
the original data. Finally, the parallel to serial block converts this
parallel data into a serial stream to recover the original input data.
There are two assumptions to simplify the analysis. First, it is
assumed that the transmission is perfect, where the received signal
is approximately similar to the transmitted signal. Secondly it is
assumed that synchronization for the whole system is also perfect
and will not contribute to ISI problem. In this paper, simulation of
OFDM system is based on wireless LAN standard. Numerical
values for OFDM parameters are given in Table 1.1 [7].

1.3 PAPR FOR WLAN OFDM SYSTEM

Figure 1.4 shows the power spectrum for OFDM system based on
WLAN standard. By sending 1000 random hit using 52 carriers, it
is found that the maximum peak is 26.6 W. The average power is
11. 6 W. Therefore the calculated PAPR for this signal is 3.6 dB.
(2)

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The PAPR Performance in WLAN-OFDM System

5
Table 1.1 OFDM Parameters for Wireless LAN Standard





Figure 1.4 Power Spectrum of WLAN/OFDM System

1.3.1 Codeword effect

There are 16 codeword, which are the combination of 4 binary bits.
Table 1.2 list the PAPR value for each code. From several
simulations using different combination of bit, it is found that
certain bits combination contribute to higher PAPR occurrence. As
shown from Figure, code 2, 4, 13 and 15 generate higher PAPR
(above 16 dB) compared to the other combinations. The lowest
PAPR can be achieved through codes 6 and 11.