CODE SHIFTED REFERENCE IMPULSE-BASED ...830388/...Ultra wideband (UWB) is a radio technology in...

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Blekinge Institute of Technology

School of Electrical Engineering

CODE SHIFTED REFERENCE

IMPULSE-BASED

COOPERATIVE UWB

COMMUNICATION SYSTEM

Pir Meher Ali Shah

Mohammed Abdul Rub

Ashik Gurung

This thesis is presented as part of Degree of

Master of Science in Electrical Engineering


Sweden September 2011


School of Engineering

Department of Applied Signal Processing

Supervisor: Muhammad Gufran Khan

Examiner: Dr. Jörgen Nordberg

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Abstract

Ultra wideband (UWB) is a radio technology in which the transmission of information is

done over a large bandwidth with very short pulses at low energy levels. UWB technology has

gained a high popularity in the field of short-range wireless communications. UWB provides

significant benefits like position location capability, reduced fading effects, and higher channel

capacity. UWB technology is very desirable because of its certain characteristics like low power

consumption, cost reliability and simple architecture. However, UWB systems face challenges

regarding system design to achieve low complexity and low cost. UWB systems need high

sampling frequencies and face problems while using digital signal processing technology.

In this thesis, first, the comparison of transmitted reference (TR), multi-differential

frequency shifted reference (MD-FSR) and code shifted reference (CSR) is done in terms of

BER performance and system complexity. The simulation results validate that the CSR-UWB

system has better BER performance and lower complexity than MD FSR-UWB system.

Secondly, cooperative communication is implemented for CSR-UWB. The system BER

performance of the CSR impulse-based cooperative UWB communication system is evaluated

for different number of relays and different average distances between source node and

destination node. The simulations are carried out under both line of sight (LOS) and non-line of

sight (NLOS) environments. The simulation results show that the performance of the system

decreases with the increase in average source-to-destination distance. We also observe that the

system performs better under an environment of LOS channel than under an environment of

NLOS channel. Finally, the results validate that the system performs better as the number of

relay nodes increases until it reaches an adequately large number.

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Acknowledgement

First of all, we would like to express our warmest thankfulness to our supervisor Muhammad

Gufran Khan. We are highly indebted towards him for giving us his valuable time, effort and

guidance throughout our entire thesis period. We would really want to appreciate his clarity in

his direction and high dedication as a key of our motivation towards our thesis. Without his help

and support, this thesis would not have been possible. We would also like to convey our

gratitude to our examiner, Dr. Jörgen Nordberg. Our thanks also goes to our teachers in

Blekinge Institute of Technology. We would like to thank our classmates and friends for all

their help and for making our life here enjoyable. We are really grateful to our parents, brothers

and sisters for providing good education and good environment to us. Lastly, we would like to

thank God for giving us the courage and strength to move ahead towards our destiny.

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Table of Contents

ABSTRACT………………………………………………………………………………………………………………………………………………….………...3

ACKNOWLEDGEMENT…………………………………………………………………………………………………………………………………..……..5

CHAPTER ONE………………………………………………………………………………………………………………………………………………..…….9

INTRODUCTION………………………………………………………………………………………………………………………………..…..10

1.1 OVERVIEW…………………………………………………………………………………………………………………………10

1.2 HISTORY AND BACKGROUND…………………………………………………………………………………………….10

1.3 DEFINITION OF UWB………………………………………………………………………………………………………….11

1.4 FEATURES AND ADVANTAGES OF UWB……………………………………………………………………………..12

1.5 UWB CHALLENGES……………………………………………………………………………………………………………..14

1.6 THESIS CONTRIBUTION………………………………………………………………………………………………………15

CHAPTER TWO……………………………………………………………………………………………………………………………………………………..16

UWB SYSTEMS, MODULATION AND MULTIPLEXING TECHNIQUES……………………………………………………….17

2.1 UWB SYSTEM TYPES…………………………………………………………………………………………………………..17

2.1.1 MULTICARRIER UWB………………………………………………………………………………………………………..17

2.1.2 IMPULSE RADIO UWB………………………………………………………………………………………………………17

2.2 UWB PULSE SHAPE…………………………………………………………………………………………………………….18

2.3 MODULATION TECHNIQUES USED IN UWB SYSTEMS………………………………………………………..20

2.3.1 PULSE POSITION MODULATION……………………………………………………………………………………….20

2.3.2 PULSE AMPLITUDE MODULATION……………………………………………………………………………………21

2.3.3 BINARY PHASE SHIFT KEYING…………………………………………………………………………………………..22

2.3.4 ON-OFF KEYING……………………………………………………………………………………………………………….22

2.4 MULTIPLE ACCESS TECHNIQUES USED IN UWB SYSTEM……………………………………………………23

2.4.1 TIME-HOPPING UWB……………………………………………………………………………………………………….23

2.4.2 DIRECT SEQUENCE UWB………………………………………………………………………………………………….25

CHAPTER THREE…………………………………………………………………………………………………………………………………………………..26

ULTRA WIDEBAND WIRELESS CHANNELS………………………………………………………………………………………………27

3.1 PROPAGATION MECHANISMS AND CHANNEL CHARACTERISTICS……………………………………..27

3.1.1 MULTIPATH……………………………………………………………………………………………………………………..27

3.1.2 DELAY SPREAD…………………………………………………………………………………………………………………28

3.1.3 COHERENCE BANDWIDTH………………………………………………………………………………………………..29

3.2 CHANNEL FADING DISTRIBUTIONS………….…………………………………………………………………………29

3.2.1 GAUSSIAN CHANNEL………………………………………………………………………………………………..………29

3.2.2 RAYLEIGH CHANNEL…………………………………………………………………………………………………………30

3.2.3 RICEAN CHANNEL…………………………………………………………………………………………………………….30

3.3 ULTRA WIDEBAND CHANNELS……………………………………………………………………………………………30

3.4 IEEE 802.15.4A UWB CHANNEL MODEL………..……………………………………………………………………31

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3.4.1 PATH LOSS……………………………………………………………………………………………………………………….31

3.4.2 SHADOWING……………………………………………………………………………………………………………………32

3.4.3 POWER DELAY PROFILE……………………………………………………………………………………………………32

3.4.4 SALEH AND VALENZUELA…………………………………………………………………………………………………33

3.4.5 DELAY DISPERSION…………………………………………………………………………………………………………..35

3.4.6 SMALL SCALE FADING………………………………………………………………………………………………………36

CHAPTER FOUR……………………………………………………………………………………………………………………………………………………37

IR-UWB RECEIVERS………………………………………………………………………………………………………………………………..38

4.1 INTRODUCTION………………………………………………………………………………………………………………….38

4.2 TRANSMITTED REFERENCE (TR) UWB RECEIVER………………………………………………………………..38

4.3 FREQUENCY-SHIFTED REFERENCE (FSR) UWB RECEIVER……………………………………………………39

4.4 CODE-SHIFTED REFERENCE (CSR) UWB RECEIVER………………………………………………………………41

4.5 BER PERFORMANCE COMPARISON OF THE TR-UWB, THE FSR-UWB AND THE CSR-UWB

SYSTEMS……………………………………………………………………………………………………………………………..45

CHAPTER FIVE………………………………………………………………………………………………………………………………………………………48

COOPERATIVE UWB COMMUNICTION SYSTEM…………………………………………………………………………………….49

5.1 INTRODUCTION………………………………………………………………………………………………………………….49

5.2 WHAT IS COOPERATIVE COMMUNICATION?…………………………………………………………………….49

5.3 COOPERATIVE COMMUNICATION PROTOCOLS: PROCESSING MODES OF RELAYS…….…..…51

5.3.1 DECODE-AND-FORWARD………………………………………………………………………………………….……..51

5.3.2 AMPLIFY-AND-FORWARD………………………………………………………………………………………….…….51

5.3.3 COMPRESS-AND-FORWARD……………………………………………………………………………………….……52

5.3.4 ESTIMATE-AND-FORWARD………………………………………………………………………………………….…..52

5.3.5 CODED COOPERATIONS……………………………………………………………………………………………….….52

5.4 COOPERATIVE UWB SYSTEM MODEL…………………………………………………………………………………53

5.5 PERFORMANCE EVALUATION FOR RELAY POSITIONING…………………………………………………...55

5.6 PERFORMANCE EVALUATION OF THE COOPERATIVE CSR-UWB SYSTEM UNDER DIFFERENT

CHANNEL CONDITIONS………………………………………………………………………………………………….…..57

5.6.1 Case I: 4M (LOS) VS. 7M (LOS) WITH 5 RELAYS…………………………………………………………………58

5.6.2 Case II: 4M (LOS) AND 7M (LOS) VS. 4M (NLOS) WITH 5 RELAYS………………………..………..….59

5.6.3 Case III: 4M (LOS), 7M (LOS) AND 4M (NLOS) VS. 7M (NLOS) WITH 5 RELAYS.……………..….59

5.6.4 Case IV: 4M (LOS) VS. 7M (LOS) WITH 10 RELAYS…………………………………………………………….60

5.6.5 Case V: 4M (LOS) AND 7M (LOS) VS. 4M (NLOS) WITH 10 RELAYS…………………….……………..61

5.6.6 Case VI: 4M (LOS), 7M (LOS) AND 4M (NLOS) VS. 7M (NLOS) WITH 10 RELAYS….…………....62

CHAPTER SIX………………………………………………………………………………………………………………………………………………………..64

CONCLUSIONS………………………………………………………………………………………………………………………………………..65

FUTURE WORK…………………………………………………………………………………………………………………………………………………….66

REFERENCES…………………………………………………………………………………………………………………………………………………………67

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CHAPTER ONE

Introduction

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Chapter 1: Introduction

1.1 Overview

The tremendous growth in wireless technology and the huge demand in achieving successful

deployment of wireless communication have significant impact on our daily lives. Since 1990,

wireless communication has come to rise in the field of communication technology

throughout the whole world because of its undeniable applications. The cellular

communication growth from analog to digital, the development of third and fourth generation

radio systems and the transition of wired connection to Wi-Fi are enabling customers to

access a broad range of information at any time and from anywhere [1]. The need of every

customer is faster service, higher capacity, and more confidential wireless connections. The

Ultra Wideband (UWB) technology fulfills those demands by introducing exciting new

features in radio communications.

1.2 History and Background

Ultra wideband (UWB) differs from other communication techniques because it uses

tremendously narrow radio pulses for the communication between transmitters and receivers.

The utilization of short-duration pulses as building units for communication can produce a very

large bandwidth and provide many advantages [1] like immense throughput, robustness, along

with the co-existence of current radio features [1].

Ultra wideband communications was first introduced by Guglielmo Marconi in the early

19th

century by employing spark gap radio transmitters for spreading Morse code sequences

over the Atlantic Ocean [2]. However, the advantage of a wide bandwidth and the potential of

implementation of multiuser systems presented by electromagnetic pulses were not taken in

account at that moment.

After about fifty years later, modern pulse based communication was introduced in the

form of radars. The technology was limited to military and defense departments for confidential

purposes like extremely secure communications. Development in the field of micro-processing

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and semiconductor technology has lifted UWB for commercial uses [1]. The demand for UWB

raised and developers of UWB system approached the Federal Communication Commission

(FCC) for an approval for commercial implementation. In 2002, FCC granted an approval to

UWB for commercial purpose [1].

1.3 Definition of UWB

Ultra wideband is a radio signal that can be employed with a very low energy in a high

bandwidth. FCC suggests a UWB system has a bandwidth that is larger than 500 MHz or it has

a fractional bandwidth more than 20% of the center frequency [3]. Fractional bandwidth is

defined as [3]

c

LHBW

f

fff

−= (1)

Here, fBW is the fractional bandwidth, fH is the highest cutoff frequency (at -10 dB emission

point) and fL is the lowest cutoff frequency (at -10 dB emission point). fc is the center frequency

that can be calculated as fc = (fH + fL)/2. According to FCC, the UWB range for unlicensed

frequency is 3.1 GHz to 10.6 GHz for both outdoor and indoor environments [5]. Figure 1.1

shows the comparison between ultra wideband communication system and narrowband.

Figure 1.1: Comparison between ultra wideband communication system and narrowband

[4]

Frequency (Hz)

Narrowband

fH fC fL

Po

wer

Sp

ectr

al d

ensi

ty

(dB

)

UWB

-10 dB

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1.4 Features and advantages of UWB

The main advantages of UWB are as follows:

• Channel capacity improvement

As mentioned earlier, UWB utilizes a very large frequency spectrum which improves the

channel capacity C (bits per seconds) or data rate. An increase in radio frequency (RF)

bandwidth also increases the capacity of band limited additive white Gaussian noise (AWGN)

channel [6].

),1(log2

oRF

recRF

!B

PBC += (2)

where C represents the capacity of the channel with its radio frequency (RF) bandwidth BRF.

Prec is the received power signal and !o is the noise of power spectral density (PSD).

• Ability to work with low SNR

The above channel capacity equation also denotes that it logarithmically depends on the signal

to noise ratio. Hence, the UWB system is able to work in rough communication channels with

low signal to noise ratio and provides better channel capacity which is the outcome of large

bandwidth [1].

• Accurate positioning and tracking or radar sensing

Larger the bandwidth, finer is the resolution. One of the key features of UWB technology is to

provide accurate positioning. This application is mostly used in radar sensing to detect the

targets [7].

• High Performance in Multipath Channels

Multipath is an unavoidable phenomena in wireless communication channels. Multipath

reflection of the transmitted signal can be caused when the transmitted signal gets reflected

from several surfaces like trees, buildings, people, etc as shown in figure 1.2. Multipath fading

is the variation in the attenuation of the signal caused when the signal reaches the destination

through multiple paths [1]. The effect of multipath fading is low in UWB communication

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system because UWB has short duration pulses, thus the effect of reflected pulses on the

signal is less degrading [1].

Figure 1.2: Multipath phenomenon in wireless transmission

• Simple Transceiver Architecture

The transmission in UWB communication system is carrier-less. That means the data need not

be modulated over the continuous waveform with any particular carrier frequency. Carrier-

less transmission needs smaller number of radio frequency components compared to carrier-

based transmission [1]. Mixers and oscillators are not required in UWB transceiver to

translate carrier frequency to required frequency band [1]. Because of these reasons, UWB

transceiver system architecture has lower complexity compared to other narrowband

transceivers and is less expensive to design.

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• Resistance to jamming

Processing gain (PG) refers to the resistance of a radio system against jamming. It is identified

as the ratio of RF bandwidth to information bandwidth of the signal.

BandwidthnInformatio

BandwidthRFPG = (3)

UWB spectrum accommodates a wide range of frequencies and provides a high processing

gain which in turn gives the UWB signals high resistance to jamming.

1.5 UWB Challenges

There are many challenges faced in the UWB technology by using very short pulses for

communications. Here we discuss only the important challenges observed in UWB

communication system [1].

• Channel estimation

The estimation of channel performance is very sensitive issue for designing a receiver in a

wireless communication system. Measuring the exact performance of each channel is not

possible in the field of wireless communication. To estimate channel parameters, it is essential

to employ training sequences such as delays and attenuations of the propagation path. Mostly

UWB receiver associate received signal with predefined signal model, which is not possible

without any prior knowledge of the wireless channel parameter. But, because of the large

bandwidth and lowered signal energy, UWB pulses face harsh distortion which makes channel

estimation very difficult [8].

• Multiple–Access Interference

In a multiuser environment, multiple users send information independently and

simultaneously through a shared transmission medium. On the receiving side, more than one

receiver should be set to separate users and receive information from the particular users. The

interference of multiple users leads to multiple-access interference (MAI). Increase in MAI

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tends to unavoidable noise that considerably degrades the UWB pulses and creates

complications in detection [1].

• Pulse Shape Distortion

UWB pulses can be distorted considerably by the transmission path. According to Friis

transmission formula, received signal power decreases when frequency is increased [1].

Because of the long range of frequencies of UWB spectrum, the received power immensely

changes and distorts the shape of the UWB pulse. This degrades the performance of the UWB

receivers [1].

• Synchronization of High Frequency

The synchronization of time is a very important challenge in UWB systems. But, as the UWB

pulses are tremendously short, flawless synchronization is hard to achieve. In such a case,

major issues can arise due to poor detection of the exact position of the received signal [1].

1.6 Thesis Contribution

This thesis presents introduction, back ground, features and challenges of UWB technology in

chapter 1.

Chapter 2 introduces types of UWB system such as Multicarrier UWB (MC-UWB), Impulse

Radio UWB (IR-UWB) and description of various modulation techniques

Chapter 3 gives brief outline about the different UWB channels and its mechanism as well as

equations for path loss. In addition, IEEE 802.15.4a channel model for low data rate UWB

systems is studied.

Chapter 4 presents the structure and implementation of different IR-UWB receivers such as

Transmitted Reference Shifting (TR) UWB, Frequency Shifted Reference (FSR) UWB and

Code Shifted Reference (CSR) UWB and the simulation results.

In chapter 5 we have discussed about Cooperative UWB communication system. We have

compared and analyzed computer simulation results of cooperative CSR-UWB systems under

different channels.

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CHAPTER TWO

UWB Systems, Modulation and Multiplexing

Techniques

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Chapter 2: UWB Systems, Modulation and

Multiplexing Techniques

2.1 UWB system types

UWB systems can be typically divided into two categories: one based on sending multiple

simultaneous carriers named as Multicarrier UWB and the other based on sending very short

duration pulses with relatively low energy called Impulse radio UWB [9]. These two systems

are discussed in the following sections.

2.1.1 Multicarrier UWB (MC-UWB)

The idea of using multiple carriers in sending UWB signal is to divide the channel bandwidth

into a number of small sub-channels with adequately small bandwidth for the efficient

utilization of the bandwidth of the system [10]. For multi-carrier transmission technique, OFDM

(orthogonal frequency division multiplexing) is employed which allows the sub-carriers to

overlap in frequency without interfering with each other that results an increase in spectral

efficiency [9]. Such a system is called Multi-band Orthogonal Frequency Division Multiplexing

(MB-OFDM) [11]. In such a technique, a spectrum is divided into further smaller sub-

spectrums with a minimum bandwidth of 500 MHz each. The data is then interleaved on these

small sub-spectrums and transmitted into the air using multi-carrier OFDM technique [11].

Thus, by using this system, multiple users can also be supported by the allocation a group of

sub-channel to each user [9]. A high throughput can be obtained by a reliable communication

system by the transmission of multiple streams of data in parallel on separate carrier frequencies

[9].

2.1.2 Impulse Radio UWB (IR-UWB)

In impulse radio UWB systems, transmission is based on a series of discontinuous short pulses

or a pulse wave form which is generally known as monocycle pulses that have relatively low

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energy level [11]. The monocycle waveform could be any function that fulfills the requirements

of spectral mask regulations. Such common pulses comprise of Rayleigh, Laplacian, Gaussian

or Hermitean pulses [12]. A Gaussian monocycle waveform is employed along with Binary

Phase Shift Keying (BPSK) as a data modulation scheme in this thesis. In such systems,

because of the short length of the pulses which is nearly in nanoseconds, the bandwidth of the

transmitted signal is in gigahertz [9]. Such pulses have ultra-wide frequency domain features

which do not need any carrier modulation for propagation in the radio channel [12]. This

approach is usually employed for a single user, but it can also be employed on multiple users by

using the techniques of time-hopping or direct sequence spreading [12].

For the purpose of attaining a proper processing gain which can be employed to handle

noise and different interferences from the environment, a single symbol which has to be

transmitted is stretched over ! number of monocycle pulses [12]. This processing gain can be

expressed as

)(log10 101 !PG = (1)

With the help of pseudorandom (PR) time-hopping code, consecutive pulses are transmitted in

air interface in a discontinuous time-hopped scheme which provides UWB communication

resistance against severe multipath propagation [12]. The short pulse length and relatively

lengthy pulse repetition time helps in reducing the inter-pulse interference. This allows the

multipath components related to the transmitted pulse to be attenuated prior to sending the next

pulse [12]. The inter symbol interference (ISI) can be avoided between the pulses by increasing

the time in between the pulses so that it becomes greater than the channel delay spread [12].

2.2 UWB Pulse Shape

Usually, the pulse shapes implemented in UWB communications consist of Gaussian pulse,

Gaussian monocycle and Gaussian doublet as shown in figure 2.1.

A Gaussian pulse [12] is expressed as

2)/))((2/1(

Re2

1)(

σµ

πσ−−= t

etP (2)

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where σ is the length of the pulse and µ represents the centre of the pulse. The Gaussian pulse

is practically not applicable in wireless communication systems because it consists of a DC

term. But, the higher derivatives of the Gaussian pulse are free from such type of DC terms, and

hence can be practically implemented in wireless communication systems.

The first derivative of Gaussian pulse is regarded as Gaussian monocycle. It is

commonly employed in impulse radio systems. A Gaussian monocycle in time domain can be

expressed as

2

2

12

12

1)(

−

−

−−= σ

µ

σµ

σπ

t

G et

tP (3)

For Gaussian monocycle, µ = 3.5σ and the effective time length Tp = 7σ .

The second derivative of Gaussian pulse is regarded as the Gaussian doublet. It contains

two Gaussian pulses which are opposite in terms of amplitude. A Gaussian doublet in time

domain can be expressed as

−=

−−

−

−

−22

2

1

2

1

2

1)( σ

µσµ

σπ

wTtt

GD eetP (4)

where Tw is the time gap between the maxima of each pulse. The effective time length is

σ14=pT at σ7=wT .

Figure 2.1: Waveforms for Gaussian pulse, Gaussian monocycle and Gaussian doublet

[12]

Am

pli

tude

0 -1 1 2 -2

-0.5

0.5

1

0

-1

Gaussian pulse

Gaussian monocycle

Gaussian doublet

Time [s] X 10-9

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2.3 Modulation Techniques Used in UWB Systems

The process of changing the characteristics of periodic waveform with an external signal by

changing its amplitude, phase, or frequency is known as modulation. In UWB communication

system, different modulation techniques are employed. The most commonly used modulation

schemes are pulse-position modulation (PPM), pulse amplitude modulation (PAM), On-Off

Keying (OOK) and binary phase-shift keying (BPSK). These modulation schemes are discussed

below.

2.3.1 Pulse Position Modulation (PPM)

In Pulse Position Modulation (PPM), the selected bit that is to be transmitted controls the

position of UWB pulse. PPM is concerned with the nominal pulse position. In PPM, two or

more positions in time encode the information, which is shown in the figure 2.2 [12] [13].

Those pulses which are transmitted at nominal position are represented as 0 and the ones that

are transmitted beyond the nominal position are represented by 1 [13]. In figure 2.2, 2-ary PPM

modulation is shown in which one bit is encoded in every impulse [12] [13]. Adding more

positions allows more bits per symbol. In general, the time delay in between the position of

pulses is a fraction of a nanosecond, which is much shorter than the one in between the nominal

positions. This aids in avoiding the interferences among the impulses [13]. For PPM signals, the

signal model is generally expressed as

∑+∞

=

±−=0

)()(k

pkf TkTtpts (5)

where p(t) represents the UWB pulse and little shifts Tpk in pulse position performs the data

modulation [13].

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Figure 2.2: 2-ary PPM signal [14]

2.3.2 Pulse Amplitude Modulation (PAM)

Pulse Amplitude Modulation (PAM) is concerned with the transmission of data in a time

sequence of electromagnetic pulses by changing the power amplitudes or the voltage of

individual pulses. It can also be defined as a technique in which the data to be transmitted is

encoded in the amplitude of a series of signal pulses. The 2-ary PAM signal is illustrated in

figure 2.3 in which the pulse with higher amplitude is represented by 1 and the one with lower

amplitude is represented by 0 [14]. The M-ary PAM signal with different amplitude levels of M

that consists of sequences of modulated pulses is expressed as

∑∞

−∞=

−=k

fm kTtpkats )()()( (6)

where am(k) is the amplitude of the kth

pulse that depends on the M-ary information symbol m

0,1,…,M-1, Tf is the frame interval and Tp is the pulse duration [14].

Figure 2.3: 2-ary PAM Signal [14]

t

1 0 1 0 1

1 0 1 0 1

t

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2.2.3 Binary Phase Shift Keying (BPSK)

In Binary Phase Shift Keying (BPSK) which is also known as bi-phase modulation scheme, the

binary data is carried in the polarity of the pulses [14]. A positive polarity is given to the pulse

that represents the information bit 1 and a negative polarity is given to the pulse representing the

information bit 0, which is demonstrated in figure 2.4. BPSK is the simplest version of Phase

Shift Keying (PSK) [14]. The Binary Phase Shift keying can be expressed as

∑∞

−∞=

−=k

fkTtpkdts )()()( (7)

where

−=

1

1)(kd (8)

Figure 2.4 BPSK Signal [14]

2.3.4 On-Off keying (OOK)

On-Off keying is also occasionally known as non-return-to-zero (NRZ) encoding. It is a binary

level modulation scheme that contains two symbols with equal probabilities [15]. It is a special

case of PAM, where m belongs to 0,1 with pulse amplitude as am (k) = m(k) [14].

t

1 0 1 0 1

if information bit is 1

if information bit is 0

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In OOK, a pulse or signal is transmitted only when the information bit is equal to 1 as shown in

figure 2.5. No pulse or signal is transmitted when the information bit is equal to 0. On-Off

keying is mathematically expressed as:

∑∞

−∞=

−=k

fkTtpkmts )()()( (9)

where m(k) is the pulse amplitude and Tf is the frame time [14].

Figure 2.5 OOK Signal [14]

2.4 Multiple Access Techniques used in UWB System

In single band UWB systems, multiple users share a single UWB spectrum simultaneously. For

accommodating those multiple users, a suitable multiple access technique is required [16].

There are two common multiple access schemes: Time hopping (TH) and Direct Sequence

(DS) spreading, which are used to allow the users in a single band UWB system [16]. The

difference between the two systems is that the TH technique is concerned with the

randomization of the location of the transmitted UWB impulse in time, whereas the DS

technique is concerned with the continuous transmission of pulses comprising a single data bit

[17]. The TH-UWB and DS-UWB are explained in detail in the subsections below.

2.4.1 Time-Hopping UWB (TH-UWB)

In TH-based system, the information verified by the TH sequence is transferred with a time

offset for each pulse [16]. TH-UWB makes use of low duty cycle pulses, where users are time

1 0 1 0 1

t

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multiplexed by spreading the time spreading in between the pulses [16]. Every frame duration is

split into multiple smaller segments of which only one carries the transmitted monocycle of the

user [16]. The user is assigned a unique code known as TH sequence to designate the segment

employed for transmission in every frame interval [16]. As the position of every impulse is

verified by a pseudo-random (PR) code, extra energy is added to the symbol because of which

the range of the transmission is increased [17]. In such a way, the identification of different

users is done by their unique TH-code that allows them to be transmitted at the same time [17].

TH-UWB for the jth

users for different modulation schemes of UWB can be expressed as

follows [17] [18]

For PAM modulation:

∑ ∑∞

−∞=

−

=

−−−=k

!

l

jkc

jlfs

js

dTclTkTtpts1

0

)()()( )()( (10)

For PPM modulation:

∑ ∑∞

−∞=

−

=

−−−−=k

!

l

jkc

jlfs

js

dTclTkTtpts1

0

)()()( )()( δ (11)

In these equations dk is the k-th data bit of jth

user, !s is the number of impulses transmitted for

every information symbol, Ts is the total symbol transmission time that is divided into !s frames

each of duration Tf and each frame is itself subdivided into slots of duration Tc [17]. The PR TH

code sequence cl (unique for the j-th user) determines the position of one impulse in each frame

to be encoded as shown in the figure 2.6 [17]. Because of the blank transmission in case of 0th

bit, OOK cannot be employed in TH spreading [17].

Figure 2.6: TH-UWB Signals [17]

Ts

Tp

Tc

Tf

t

P a g e | 25



2.4.2 Direct Sequence UWB

In Direct Sequence UWB system, data is carried by multiple pulses whose amplitudes are based

on a certain spreading code [16]. DS-UWB uses a train of high-duty-cycle pulses whose

polarities are based on pseudo-random code sequences [16]. Each user in the system is

specifically assigned a pseudo-random sequence that regulates pseudorandom inversions of the

UWB pulse train [16]. This sequence of UWB pulses uses a data bit to modulate. This results in

the transmission of continuous UWB pulses whose number depends on the length of the pulses

itself and a system defined bit rate [17]. DS-UWB scheme is only applicable in PAM, OOK and

PSM modulation. It is not suitable for PPM as it is a time-hopping technique [17] [16]. For

PAM and OOK modulation, DS-UWB can be expressed as following [17][18],

∑ ∑∞

−∞=

−

=

−−−=k

!

l

jk

jlcs

js

dclTkTtpts1

0

)()()( ))()( (13)

where dk is the k-th data bit, cl is the l-th chip of the PR code, p(t) is the pulse waveform of

duration Tp, Tc is the chip length which is equal to Tp as shown in figure 2.7, !s is the number of

pulses per data and j is the user index [17]. The PR sequence has values in -1,+1 and length of

the bit is Ts = !sTc [17].

Figure 2.7: DS-UWB Signals [17]

Ts

Tc = Tp

t

P a g e | 26



CHAPTER THREE

Ultra Wideband Wireless Channels

P a g e | 27



Chapter 3: Ultra Wideband Wireless Channels

3.1 Propagation Mechanism and Channel Characteristics

The design and analysis of UWB communication systems are based on the propagation features

of UWB radio channels [18]. Reflection, diffraction and scattering are the main propagation

mechanism in communication [24]. Reflection occurs when a propagating signal impinges on

an object which has comparatively large dimensions than the propagating signal. Reflection

may occur at surfaces of the floor, walls and buildings [24]. Diffraction occurs when the radio

path between the transmitter and the receiver is obstructed by objects with sharp edges. This

results in the bending of signal around the obstacle, even when the line of sight exists between

transmitter and receiver. Scattering occurs when the signal passes through a medium which

contains objects that have very small dimensions compared to the wavelength, and when the

number of obstacles per unit volume is quite large [24].

In this chapter, we will discuss about UWB wireless channels. The natures of these UWB

wireless channels are very important and helpful while designing UWB communication system

to predict the coverage of the signal, to reach maximum data rate, to find optimal location of

antennas and for efficient modulation [27].

3.1.1 Multipath

The purpose of any communication system is to convey the message from transmitter to

receiver. A transmitted signal in wireless communication takes multiple paths to reach the

receiver which causes multipath effects because of reflections from objects like mountains,

buildings, water bodies, etc. Multipath effect includes constructive and destructive interference

at the receiver antenna and phase shifting of these multipath components of the signal causes

multipath fading [27]. Fading is a common problem that occurs in a propagating wireless signal.

Any fluctuation in the received signal is referred to as fading. If fading occurs due to multipath

then it is referred as multipath induced fading [19] [20]. Fading is classified into two types:

slow fading and fast fading. Slow fading arises when the coherence time of the channel is

P a g e | 28



relatively larger than the delay constraints of the channel and fast fading arises when the

coherence time of the channel is relatively small than the delay constraint of the channel [21].

The fast fading transmitter takes the advantage of both channel variation and channel conditions

by the use of time diversity that helps to increase the strength of the communication signal.

Whereas in case of slow fading, time diversity cannot be used as an advantage due to single

realization of the channel within its delay constraint [22].

3.1.2 Delay Spread

When a signal transmits via a time-dispersive multipath channel, the signal arrives to the

receiver from different paths. This is the cause of delay spread. Delay spread depends on the

distance and the position of objects near the transmission path. Delay spread can be interpreted

as the difference between the arrival time of the first and last multipath components [23] [19].

Delay spread leads to inter symbol interference (ISI). ISI is a form of distortion in the

communication channels. In practice, communication channels have limited bandwidth, hence

the transmitted pulses spread during transmission. This spreading of pulses causes overlap over

the adjacent time slot that causes errors at the receiver. This phenomena is referred to as inter

symbol interference which is shown in figure 3.1.

Figure 3.1: Inter Symbol Interfernce (ISI) in digital transmission

P a g e | 29



3.1.3 Coherence Bandwidth

Coherence Bandwidth is a range of frequencies that are allowed to pass through the wireless

channel without any distortion. It can be regarded as a statistical measurement of the frequency

ranges on the channel which can be assumed as “flat” [24]. Alternately, coherence bandwidth

can be suggested as an approximate highest bandwidth at which two frequencies of the signal

will possibly go through similar or correlated amplitude fading [25]. Multipath interference can

be avoided by decreasing the signal bandwidth so that it is less than the coherence bandwidth

[19].

d

CT

BWπ2

1= (1)

3.2 Channel Fading Distributions

Channel fading distribution refers to the factors or conditions that distort the signal when it

transmits from source to destination through the channel. The performance of the channels plays

a very vital role in transmission [19].

3.2.1 Gaussian Channel

The Gaussian channel is particularly used in modeling the noise produced at the receiver when

the transmission path is ideal [19]. This model is moderately correct in few cases like wired

communications transmissions and space communications. This channel model is appropriate

for channels with single transmitter and single receiver. A condition when the information is

sent through a channel that can be subjected to an additive white Gaussian noise is

demonstrated in figure 3.2.

Figure 3.2: Gaussian channel model

Noise (Zi)

Channel

Encoder +

Channel

Decoder Xi Yi =Xi +Zi

Continuous values

P a g e | 30



Here, Yi is the output of the channel, Xi is the input of the channel and Zi is the noise which is

assumed to be independent of X. Zi is zero mean Gaussian with variance !: Zi N (0,!).

3.2.2 Rayleigh Channel

Rayleigh channel is a transmission channel which has a fading envelope in the form of Rayleigh

probability density function (pdf). Rayleigh fading occurs in an environment where there are

several obstacles that scatter the transmitted signal before it reaches the receiver [26]. Rayleigh

fading distribution is generally used to describe the statistical time. It varies in the nature of the

received envelope of flat fading. The envelope is a sum of two quadrature Gaussian noise signal

which follows the Rayleigh distribution [24].

3.2.3 Ricean Channel

Ricean channel is a transmission channel that has a line of sight (LOS) propagation path along

with a small scale fading envelope distribution [24]. In this channel, the signal reaches the

receiver at different angles or paths that result in multipath interference. Ricean fading takes

place when one LOS path signal is stronger than the others. The strong signal arriving with

several weak multipath signals results Ricean distribution [24]. Complex signals resemble noise

signals that have enveloped in Rayleigh channel. Ricean distribution degenerates to Rayleigh

distribution when the dominant signal fades away [26].

3.3 Ultra Wideband Channels

As mentioned in chapter 1, the UWB systems provide a promising technological application

across several commercial fields and military applications including radar, communication, and

medical instruments. This technology offers very high data rates to several users during short

range communication channels by allocating a large bandwidth. UWB channels demonstrate

two significant effects: pulse distortion and multipath propagation. Particularly, in the course of

propagation, each waveform can be discarded by any object that results in multipath

propagation. Pulse distortion is rather concerned with the variation in the original UWB pulse.

The main difference between narrow band channel and UWB channel is different radiation

P a g e | 31



bandwidth ranges. The narrowband is used to cover less than 20 MHz of bandwidth, where as

UWB channels can cover more than 10 GHz of bandwidth [27] [29]. The standard UWB

channel models are designed by IEEE 802.15 groups: SG3a and SG4a which are known as

IEEE 802.15.3a and IEEE 802.15.4a channel models, respectively.

3.4 IEEE 802.15.4a UWB Channel Model

IEEE 802.15.4a UWB channel model provides a broad range of channel environments such as

industrial, residential, office and outdoor. It covers a frequency range from 2 GHz to 10 GHz.

[28]. This model suggests data rates from 1Kbps to several Mbps. The important features of

IEEE 80215.4a are:

3.4.1 Path Loss

Path loss is the ratio between transmit and receive signal power. In an end-to-end wireless

communication system, a transmitter communicates with a receiver by sending a signal over the

wireless medium. The signal strength attenuates when it travels through the medium. Thus it

becomes poorer or weaker as the propagation distance increases. The signal beyond a certain

distance becomes unacceptable. Then at a regular interval to reactivate the signal strength, we

need a booster or repeater. More challenging problems will occur when there are multiple

receivers in the communication and more complexity will arise when distance from transmitter

to receiver is varying [20]. Basically, path loss can be defined as:

r

tL

P

PP = (2)

where Pt is the transmitted power and Pr is the received power. Path loss in narrow band can be

defined as:

PTX

fcdPRXEdPL

),()( = (3)

where PTX is the transmit power and PRX is the receive power, d is the distance between the

transmitter and receiver, fc is the center frequency and E is expectation to averaging

shadowing and small scale fading [30].

P a g e | 32



3.4.2 Shadowing

Shadowing is the effect that arises upon the received signal power when it is attenuated because

of the obstacles in the propagation path in between the transmitter and the receiver. The nature

of shadowing in UWB communication is similar to that of narrowband systems [29] [30]. The

average path loss evaluated over a small scale fading in dB is given as [30]:

Sd

dnPLdPL +

+=

0

100 log10)( (4)

where, S denotes the shadowing Gaussian noise distributed random variable with zero mean and

the standard deviation s.

3.4.3 Power delay Profile

Power delay profile demonstrates the quality of the received signal passing through a multipath

channel as a function of time delay. The time delay is the difference of travel time with

multipath arrivals. Power delay profile can be described as the squared magnitudes of impulse

response by spatial averaging along a local area [24],

2);()( ττ thPDP = (5)

where, |h (t; )| is the modulus value of the impulse response of the signal. With the help of this

impulse response, we can get the received signal power as [27],

)()()(1

0

22

n

!

n

nn tthEPDP τδατ −== ∑−

=

(6)

P a g e | 33



Generally, the paths which come at the later stage in the power delay profile go through more

attenuation. Consequently, the power delay profile is usually a descending function of the

excess delay. Figure 3.3 shows multipath components with different delays and attenuations.

Figure 3.3: Multipath components with different delays and attenuations

3.4.4 Saleh and Valenzuela

Saleh-Valenzula is a simple multipath model developed for indoor propagation measurements.

The basic postulation of this model is the arrival of multipath components (MPC) in the form of

clusters. The MPC amplitudes are independent random Rayleigh variables with variance. The

variance decays exponentially with both the cluster and excess delays within a cluster. The

forming of clusters is concerned with building structure. The components inside a cluster are

made from multiple reflections from objects. The clusters and MPC within the cluster that can

be derived according to Poisson arrival processes with different rates have exponentially

distributed inter-arrival times [24].

IEEE 802.15.4a model is based on Saleh-Valenzuela (SV) model which is shown in

figure 3.4. In complex baseband, the impulse response based on SV model is defined as [31].

),()exp()( ,,

1

0

1

0

, lkllk

L

l

K

k

lkdiscr Ttjth τδφα −−=∑∑−

=

−

=

(7)

Amplitude

Delay

P a g e | 34



where, lk ,α is the tap weight of the k

th component in the cluster, Tl is the arrival time of the l

th

cluster, lk ,τ is the delay of the kth

multipath component relative to lth

cluster arrival time and

lk ,φ denotes the uniformly distributed phases. For a band pass system, the phase angle is taken as

uniformly random distributed in a range from 0 to 2π [30].

An important component of the model which is the number of clusters is represent by L,

which is supposed as Poisson-distributed.

[ ] 0,(exp)( )11 >−∧−∧= −− lTTTTp LLllLL (8)

where, ˄l is arrival rate of the cluster.

The arrival times of the ray are modeled with a mixture of two Poisson processes as follows,

[ ] [ ] 0,)(exp)1()(exp)( ),1(,22),1(,11),1(, >−−−+−−= −−− kP lklklklklklk ττλλβττλβλττ (9)

where, β is the mixture probability, and λ1 and λ2 are the ray arrival rates [30].

The mean power of different component’s exponential within each cluster is given as [30]

[ ] )/exp(1)1(

1,

21

1

2

, ll

E lklk γτβλλβγ

α −++−

Ω=

(10)

Figure 3.4: Principle of Saleh–Valenzuela model

Delay

Amplitude

∧/1

Clusters

Γ

λ/1

P a g e | 35



where, Ω1 is the integrated power of the lth

cluster and γl is the intra-cluster decay time constant.

The mean (over small-scale fading) mean (over cluster-shadowing) energy (normalized to γl) of

the lth

cluster adopts a general exponential decay which can be expressed as [30]

clusterMT +Γ−=Ω ))/log(exp(10)log(10 11 (11)

where, M cluster is a normal distribution random variables with cluster standard deviation around

it [30].

The scenarios for the non line of sight (NLOS) define the shapes of the power delay profiles

differently [29].

)1(

)./exp())./exp(.1(1

1

1

11),(),(

2,

xE

rise

riselkriselklk −+

Ω+−−−=

γγγγγ

γτγτχα (12)

The parameter χ represents the attenuation of the first component, γrise determines how fast the

power delay profile γ increases to its maximum and γ1 determines the decay at the last time.

3.4.5 Delay dispersion

Delay dispersion can be said to be occurring when the channel impulse response remains for a

finite quantity of time or the channel happens to be frequency-selective [32]. The effect of delay

dispersion can be expressed as the product of the delay spread and the bandwidth of the system.

If this product is below unity, then its delay dispersion effect will be low on the system design.

And, if the product is higher than unity, then it is said to have a strong delay dispersion effect in

the system performance [18]. In multipath channel, delay dispersion is featured by two

parameters: root mean square (rms) delays spread and mean excess delay [32]. The mean excess

delay is the first moment of the power delay profile (PDP) according to [30].

∫

∫∞

∞−

∞

∞−=

ττ

ττττ

dPDP

dPDP

m

)(

)(

(13)

P a g e | 36



The rms delay spread is the second moment of the power delay profile (PDP) according to [30].

22

)(

)(

)(

)(

−=

∫∫

∫∫

∞

∞−

∞

∞−∞

∞−

∞

∞−

ττ

τττ

ττ

ττττ

dPDP

dPDP

dPDP

dPDP

rms (14)

Delay spread depends upon the distance; nevertheless, for channel simplicity it is neglected.

3.4.6 Small scale fading

Small scale fading refers to the changes in amplitude, multipath delays or phase of the received

signals over a short period of time [29]. Small scale fading takes place because of destructive

and constructive interference of multipath components that reaches the receiver at fairly

different times [29]. The distribution of small scale amplitudes is Nakagami in this model [30].

,exp)(

2)( 212

Ω

−

ΩΓ

= − xm

xm

mxpdf mm (15)

where m ≥ 1/2 is the Nakagami m factor, gamma function is Γ (m), and mean square value of

amplitude is Ω. The parameter m modeled as a log generally random distributed variable. Both

values of logarithmic mean µm and standard deviation m [30].

ττµ mom km −=)( (16)

τσ mom km^^

−= (17)

Nakagami factor is deterministic and delay independent [30].

P a g e | 37



CHAPTER FOUR

IR-UWB Receivers

P a g e | 38



Chapter 4: IR-UWB Receivers

4.1 Introduction

The immense bandwidth of UWB systems can make the design of the receiver quite difficult in

conventional UWB systems that use antipodal or pulse-position modulation with very short

pulses [33] [34]. The analog to digital transformation of the whole signaling bandwidth in

simple low-power UWB receivers is very hard to implement [34]. Many digital UWB receivers

have certain number of analog correlators to accumulate signal energy in a front-end RAKE

receiver type architecture [34]. The efficient accumulation of energy in that kind of architecture

can be expensive because of a large number of resolvable paths in the standard UWB fading

environment. It can create problems in channel estimation even if allowable in the perspective

of circuit complexity [34]. Because of these problems encountered in traditional impulsive

UWB or DS-UWB, the approach regarding multiband UWB for short-range high data rate

applications has been favored [34]. In the following sections, three reference-based non-

coherent IR-UWB systems, i.e., Transmit-Reference (TR), Frequency-Shifted Reference (FSR)

and Code-Shifted Reference (CSR) systems are discussed.

4.2 Transmitted Reference (TR) UWB System

As UWB systems have pulses of short duration and they are characterized by limited power,

these characters cause extreme dependence of these systems on timing requirements [44]. These

difficult timing requirements make receiver design complicated. In such a situation,

Transmitted-Reference (TR) UWB systems can offer a “simple” and cheap receiver that collects

the energy from various multipath components for the correct detection of UWB data [35].

In TR-UWB systems, some amount of the transmitted energy is used for measuring

channel [36]. Each frame of the transmitted signals contains two different pulses which are

reference and data [37]. The reference pulse has a fixed polarity. The polarity of the data pulse

indicates the data bit [38]. These two segments of the signal are separated in time domain. The

transmitted TR-UWB signal can be mathematically expressed as the following [39],

P a g e | 39



( )∑ ∑∞

−∞=

−

=

−+−++−=j

!

i

ffjff

f

DTij!tpbTij!tptx

1

0

])([])([)( (1)

where )(tp is a UWB pulse with duration pT , fT is the frame length, f! is the number of

frames, f! >>1, ∈jb 1,-1 is the information bit transmitted during thj ff T! time duration.

D is the delay between the reference and data pulse. There is a UWB pulse per each frame

interval [39]. At the standard TR-UWB receiver side shown in figure 4.1, the received signal is

filtered and correlated with a delayed version of itself. The correlated signal is integrated from

ff Tij! )( + to Mff TTij! ++ )( to constitute a decision variable [48]. The value of MT ranges

from pT to fT .

Figure 4.1: Block diagram of the TR-UWB receiver [34]

4.3 Frequency-Shifted Reference (FSR) UWB System

The TR-UWB architecture is able to provide a simple receiver design for a UWB system.

However, the implementation of TR-UWB receiver can be quite a challenge. In a low-power

integrated circuit environment desired by the TR-UWB receiver, it is hard to construct the delay

that handles a wideband signal [34]. To solve this complexity problem of the delay element, a

new system called Frequency-Shifted Reference Ultra-Wideband (FSR-UWB) is introduced

[34]. The main idea behind FSR-UWB is to propose a TR-UWB system in the frequency

domain which excludes the delay element of the standard TR-UWB receiver. Frequency

translation of a wideband signal is much easier than implementation of its delay element. In

FSR-UWB, the reference signal is translated in frequency (instead of time) to be orthogonal to

the data signal [40].

Matched

Filter

Delay

D

∫++

+

Mff

ff

TTij!

Tij!

)(

)( ∑−

=

1

0

f!

i

sign )ˆ( jr jr jb )(tr

P a g e | 40



The key principle proposed in [34] is to enforce the frequency shift of the data signal

relative to the reference signal over a symbol period rather than over a frame period. This

permits a significant overlapping of the frequency bands occupied by the data-bearing and

reference signal. The transmitted FSR-UWB signal can be mathematically expressed as the

following:

( )∑∑∞

−∞=

−

=

+−++−=j

!

i

ffjff

f

Tij!tptfbTij!tptx

1

0

0 ])([)2cos(2])([)( π (2)


frames, f! >>1, sTf /10 = is the frequency shift of the data signal relative to the reference signal,

1,1 −∈jb is the information bit transmitted during thj ff T! time duration [39]. Figure 4.2

shows the FSR-UWB receiver structure. The detailed explanation about FSR-UWB receiver is

given in [34].

Figure 4.2: Block diagram of the FSR-UWB receiver [34]

A modified form of the traditional FSR-UWB is proposed in [41] which is called Multi-

Differential (MD) FSR-UWB, where multiple data carriers use a single reference carrier. Every

data signal is a slightly frequency-shifted version of the reference signal [41]. The data carrier

frequencies are cautiously selected such that all data signals and the reference signal are

orthogonal to each other over the symbol period [41]. This adjustment expands the amount of

freedom accessible for signaling in the system [41]. The transmitted MD FSR-UWB signal for

M carriers can be mathematically expressed as following [41],

∑∑ ∑∞

−∞=

−

= =

+−++−=

j

!

i

M

k

ffkjkff

f

Tij!tptfbTij!tptx

1

0 1

])([)2cos(2])([)( π (3)

)(tr Matched

Filter ∫++

+

Mff

ff

TTij!

Tij!

)(

)( ∑−

=

1

0

f!

i

sign )ˆ( jr jr jb

)2cos(2 0tfπ

P a g e | 41



∫++

+

Mff

ff

TTij!

Tij!

)(

)(

where ∈jkb 1,-1 is the thk information bit transmitted over thj ff T! time duration. The

carrier frequency of the thk data signal is expressed as sk Tkf /)12( += .

Figure 4.3 shows the MD FSR-UWB receiver structure. The detailed explanation about

MD FSR-UWB receiver is given in [41]. For moderate data rate applications, the FSR-UWB

scheme performs better than the TR-UWB scheme. However, it is not preferable for high data

rate systems, because of the presence of intersymbol interference [41]. Apart from this, when

there are many users in the system, the frequency oscillator requires a lot of power [34].

Figure 4.3: Block diagram of MD FSR-UWB receiver [41]

4.4 Code-Shifted Reference (CSR) UWB System

Recently a new scheme called Code-Shifted Reference (CSR) has been proposed for IR-UWB

systems. In this scheme, the reference and data pulse sequences are separated by a set of shifting

and detection codes instead of getting separated by time (TR) or frequency (FSR) [33]. In CSR-

UWB, a reference pulse sequence and a single or multiple data pulse sequences are

instantaneously transmitted [42]. Every pulse sequence is coded by a particular shifting code. A

set of detection codes are used to detect the information bits from the data pulse sequences at

the CSR receiver side. The CSR scheme has been able to remove the ultra wideband delay

element required in the TR-UWB transceiver because the separation of the reference pulse

sequence and the data pulse sequences is performed by the employment of code shifting rather

)(tr Matched

Filter

∑−

=

1

0

f!

i

sign )ˆ( 1jr 1

ˆjr 1

ˆjb

( . )2

)2cos( 1tfπ

)2cos( tfkπ

)2cos( tfMπ

∑−

=

1

0

f!

i

sign )ˆ( jkr jkr jkb

∑−

=

1

0

f!

i

sign )ˆ( jMr jMr jMb

)(ˆ tr

ijr

P a g e | 42



than time shifting [43]. As the CSR-UWB transceiver separates pulse sequences with digital

codes in place of analog carriers used in FSR-UWB, it reduces a lot of degradation that is found

in the performance of the FSR-UWB system [43]. Moreover, it offers a lower system

complexity. Figure 4.4 shows the block diagram of the CSR-UWB transmitter proposed in [42].

Figure 4.4: Block diagram of the CSR-UWB transmitter [42]

The CSR-UWB transmitted signal can be mathematically expressed as following [42],

∑ ∑∑∞

−∞= =

−

=

++−=j

M

k

ikjki

!

i

ff cbcMTij!tptxf

1

0

1

0

])([)( (3)


frames, ∈jkb 1,-1 is the kth

information bit transmitted over thj ff T! time duration, and

∈ikc 1,-1 is the ith

bit of kth

shifting code selected from Walsh codes. M number of

information bits are transmitted instantaneously over !f number of frames of UWB pulses.

UWB

Antenna

UWB

Pulse

Generator

1 1jb jkb jMb

0ic 1ic ikc iMc

M

| . |

P a g e | 43



Equation (4) gives the M+1 shifting codes that separate a reference pulse sequence and M data

pulse sequences.

(4)

Figure 4.5 shows the CSR-UWB receiver. The received UWB signal after being filtered is

squared. It is then integrated over the limits of (j!f+i)Tf to (j!f+i)Tf+TM. TM ranges from Tp to

Tf. Larger the TM, larger will be the collection of signal energy, but with larger amount of added

noise and interference. The integrated signal is respectively correlated with M number of

detection codes to detect the M number of information bits.

Figure 4.5: Block diagram of the CSR-UWB receiver [42]

=

−

−

−

M!iMM

k!ikk

!i

M

k

f

f

f

ccc

ccc

ccc

c

c

c

)1(0

)1(0

0)1(0000

)(tr Matched

Filter

∫++

+

Mff

ff

TTij!

Tij!

)(

)(

∑−

=

1

0

f!

i

sign )ˆ( 1jr 1

ˆjr 1

ˆjb

( . )2

1~

ic

ikc~

iMc~

∑−

=

1

0

f!

i

sign )ˆ( jkr jkr jkb

∑−

=

1

0

f!

i

sign )ˆ( jMr jMr jMb

)(ˆ tr

ijr

P a g e | 44



Equation (5) gives the M detecting codes in the CSR-UWB receiver.

(5)

A maximum of M=2!-1

number of information bits can be simultaneously transmitted for !f =2!

number of frames. Table 1 shows an example of the selection of the M+1 shifting codes and M

detection codes from Walsh codes [42].

Code Length Shifting Codes Detection Codes

!f=2 0c = [1,1]

1c = [1,-1]

1~c = [1,-1]

!f=4 0c = [1,1,1,1]

1c = [1,-1,1,-1]

2c = [1,1,-1,-1]

1~c = [1,-1,1,-1]

2~c = [1,1,-1,-1]

!f=8 0c = [1,1,1,1,1,1,1,1]

1c = [1,-1,1,-1,1,-1,1,-1]

2c = [1,1,-1,-1,1,1,-1,-1]

3c = [1,1,1,1,-1,-1,-1,-1]

4c = [1,-1,-1,1,-1,1,1,-1]

1~c = [1,-1,1,-1,1,-1,1,-1]

2~c = [1,1,-1,-1,1,1,-1,-1]

3~c = [1,1,1,1,-1,-1,-1,-1]

4~c = [1,-1,-1,1,-1,1,1,-1]

Table 1: Example of shifting and detection codes selected from Walsh Codes [42]

=

−

−

−

M!iMM

k!ikk

!i

M

k

f

f

f

ccc

ccc

ccc

c

c

c

)1(0

)1(0

0)1(0000

~~~

~~~

~~~

~

~

~

P a g e | 45



4.5 BER performance comparison of the TR-UWB, the FSR-UWB

and the CSR-UWB systems

The simulations have been performed with bit error rate (BER) of the transceivers as a function

of Eb/N0 under the IEEE 802.15.4a industrial LOS channel environment. The fame duration of

TR-UWB is Tf = TM = 120ns with Td = 60ns. The fame duration of FSR-UWB and CSR-UWB

is Tf = TM = 60ns. The number of frames is fixed at !f = 8. The pulse duration is Tp = 1ns. The

data rates at M=1, 2, 3 and 4 are 2Mbps, 4Mbps, 6Mbps and 8Mbps respectively. Figure 4.6

shows the BER performance of TR-UWB, MD FSR-UWB and CSR-UWB. Two observations

that can be obtained by looking at the plot are:

I. When the value of !f is fixed, the BER performance of the CSR-UWB system becomes

better with the increasing value of M. The reason for this is that the selection of the shifting

and detecting codes assures that all of the information bits are transmitted orthogonally to

each other. Thus, when the value of M is incremented, there is also an increment in the

power of reference pulse sequence. The power of the reference pulse sequence is shared

between all the data pulse sequences, but this does not bring in any additional interference

amongst the data pulse sequences. The CSR-UWB transceiver attains its best BER

performance at M=!f/2. At this point, the BER performance of the CSR-UWB system is

equivalent to that of the TR-UWB system.

II. While TM=Tf, the BER performance of CSR-UWB transceiver under a multipath channel is

equivalent to that of the FSR-UWB transceiver under the AWGN channel. Hence the BER

performance of CSR-UWB transceiver under a multipath channel is better than that of the

FSR-UWB transceiver under the multipath channel. The reason behind this is the existence

of phase offsets in between the analog carriers that are reproduced by the FSR-UWB

receiver because of the delay spread of the multipath channel, and the corruption of the

analog carriers in the received data pulse sequences by multipath channel [34] [41]. In the

case of CSR-UWB transceiver, there is the absence of phase offsets in between the detection

codes produced by the receivers and the shifting codes in the received data pulse sequences

as the shifting and detection codes are always constant (i.e, either 1 or -1) within a pulse

duration.

P a g e | 46



13 14 15 16 17 18 1910

-4

10-3

10-2

10-1

100

Eb/No (dB)

BE

R

CSR-UWB (M=1)

CSR-UWB (M=2)

CSR-UWB (M=3)

CSR-UWB (M=4)

FSR-UWB (M=1)

FSR-UWB (M=2)

FSR-UWB (M=3)

FSR-UWB (M=4)

TR-UWB

Figure 4.6: BER performance comparison of TR-UWB, FSR-UWB and CSR-UWB at

TM=Tf and f=8

Better BER performance can be attained by differing the value of TM in between Tp and Tf

rather than fixing it at Tf. Figure 4.7 shows the plot for the BER performances of CSR-UWB

transceiver under an IEEE 802.15.4a LOS industrial channel for Tf=60ns, M=4, !f=8 and

different values of TM. It can be observed that the BER performance of the CSR-UWB

transceiver improves with the decrease in the value of TM until it reaches 5ns. This is because,

decreasing the value of TM avoids unnecessary noise introduced by the channel. But after a

point, when TM is significantly small, there is loss in the original information itself. On the other

hand, the integration time should be fixed at Tf in the case of the FSR-UWB transceiver, for the

correlation of the reproduced analog carriers at the receiver with the ones in the received data

pulse sequences [34] [41]. Eventually, the BER performance of the CSR-UWB transceiver is

much higher than the BER performance of the FSR-UWB transceiver except when TM is near to

Tf , in a multipath channel having serious delay spread.

P a g e | 47



13 13.5 14 14.5 15 15.5 16 16.5 17 17.5 1810

-5

10-4

10-3

10-2

10-1

100

Eb/No (dB)

BE

R

FSR-UWB, Tm=60ns

CSR-UWB, Tm=60ns

CSR-UWB, Tm=30ns

CSR-UWB, Tm=15ns

CSR-UWB, Tm=7.5ns

CSR-UWB, Tm=5ns

Figure 4.7: Improvement in BER performance of the CSR-UWB transceiver for TM<Tf

It has been seen that CSR-UWB transceiver has numerous benefits over TR-UWB

transceiver and FSR-UWB transceiver. The system complexity of CSR-UWB transceiver is low

in compare to TR-UWB and FSR-UWB transceivers. The CSR-UWB transceiver does not use

any delay elements of ultra wide bandwidth or any analog carriers. The CSR-UWB transceiver

has a higher BER performance than FSR-UWB transceiver. The CSR-UWB transceiver has a

BER performance which is equivalent to that of the TR-UWB transceiver when M=!f/2. The

CSR-UWB transceiver can use more than two pulses to transmit information bits without

degrading its BER performance. Thus it is much more flexible regarding frame design than TR-

UWB transceiver. CSR-UWB transceiver shifts the UWB pulses by the use of digital codes

with various discrete values rather than analog carriers with continuous values. Therefore, less

power is required by the CSR-UWB transceiver than the FSR-UWB transceiver. Ultimately, all

of these benefits prove the CSR-UWB as an extremely desirable scheme to build less complex

and low power transceivers for wireless communications.

P a g e | 48



CHAPTER FIVE

Cooperative UWB Communication System

P a g e | 49



Chapter 5: Cooperative UWB Communication

System

5.1 Introduction

Impulse Radio UWB (IR-UWB) is capable of high speed information transmission,

immense multipath resolution, low power expenditure and is highly cost efficient [45]. These

features have made IR-UWB very popular in wireless communication. Federal Commission of

communication (FCC) has set a standard according to which the average transmitted power of

the UWB signal is pretty low [46]. The power of the received signal decreases after its

transmission through multipath fading channel, which makes it difficult to detect and

demodulate the UWB signals [45]. Therefore, cooperative communication technique has been

introduced in UWB system for efficiently increasing the power at the receiver side and upgrades

the performance of the UWB system [47]. Here, based on IEEE 802.15.4a channel model, we

have implemented cooperative communication with the CSR-UWB system using decode and

forward (DF) relay method, and the BER performance of the system is evaluated using different

scenarios.

5.2 What is Cooperative Communication?

The benefits of multiple-input multiple-output (MIMO) systems have been so largely

recognized that certain transmit diversity techniques have become a very important part of

wireless standards [48]. However, transmit diversity might not be a practical scheme for other

scenarios, even though it is highly beneficial for cellular base stations [49]. Wireless agents

might not be capable of supporting multiple transmit antennas because of certain factors like

cost, size and limitations of hardware [49]. This is the reason why cooperative communication

was introduced. Cooperative communication allows single-antenna mobiles to possess some of

the advantages of MIMO communication systems [50]. The basic concept of cooperative

communication is that single antenna systems within a multi-user set-up can share their

antennas in such a style that a virtual MIMO system is created [51].

P a g e | 50



It has been observed that channels in a wireless scenario are subjected to fading which

means that the signal strength can decay noticeably during the course of transmission [52].

Diversity can be generated by transmitting independent copies of the signal, and this can

efficiently reduce the injurious effects of fading [52]. Particularly, by the transmission of signals

from different locations, spatial diversity is generated. This gives different independent faded

copies of the signal at the receiver [53]. This diversity can be generated in a new and exciting

fashion by cooperative communication.

The idea of cooperative communication is to promote the broadcast feature of wireless

communication networks, in which the neighboring nodes “overhear” the signal from the source

and then relay the information to the destination [54]. In figure 5.1, A third-party terminal acts

as a relay by receiving the signals from the source and forwarding the overheard information to

the destination to expand the capacity and upgrade the reliability of the direct communication

[53]. The end-to-end transmission is separated into two different phases in time domain which

are: broadcasting and relaying [55]. In the broadcasting stage, all receiving terminals (i.e. relays

and destination) operate in the same channel (i.e. time or frequency). In the relaying stage, the

transmitting terminals (relay nodes) may work in separate channels to dodge co-channel

interference [55].

Figure 5.1: Basic cooperative communication comprising a single relay

R

S D

Relay

Source Destination

P a g e | 51



5.3 Cooperative Communication Protocols:

Processing Modes of Relays

The basic concept of cooperative relaying is that the signal is transmitted by the source to both

the relay and destination [51]. The relay receives the same signal from the source and then

retransmits it to the destination. The destination merges the received signal from both the relay

and source to boost reliability. This whole process can be carried out by various methods of

relaying protocols which are discussed in the following subsections.

5.3.1 Decode-and-Forward (DF)

In decode-and-forward scheme, using regenerative method, the relay node decodes the signal

received from the source, and then re-encodes it prior to forwarding it to the destination [51].

Possibly wrongly decoded information at the relay can considerably lower the performance of

the system because of error propagation [56]. Therefore, it is supposed that, relays helps direct

communication only if the source signal has been detected correctly. It is assumed that cyclic

redundancy check (CRC) code to be capable of perfectly decoding the information. Such a relay

using the approach of CRC can be called as adaptive DF [57]. Nevertheless, this approach is not

always practical because the relay is sometimes not capable of correctly detecting the signal

from the source. Hence, another approach called fixed DF mode is introduced where the relay

always forwards the decoded information to the destination irrespective of the received signal

quality [57]. When the quality of the channel between the source and relay is very fine, the relay

is capable of decoding very quickly and correctly.

5.3.2 Amplify-and-Forward (AF)

In amplify-and-forward scheme, using non-regenerative method, the relay node amplifies the

signal received from the source without decoding, and then forwards it to the destination [59].

The noisy form of the signal from the source is multiplied by the relay with the amplifying gain

with a constraint (e.g. power constraint) and the resulting version of the signal is transmitted to

the destination [59]. The complexity of hardware is lower in AF than DF as the decoding

section is excluded in AF [51]. Even though the noise is also amplified along with the signal,

P a g e | 52



the destination can still make a better detection of the information as it receives two

independent faded versions of the signal [60]. AF relay can be further divided into two

subcategories. If the relay has complete awareness about the channel state information (CSI),

the amplify gain can be changed [51]. Such a relay is called variable-gain AF relay or CSI-

assisted AF relay. Whereas, if the relay needs only the statistical characteristics of the channel

in between source and relay, the relay is called fixed gain AF relay or semi-blind AF relay [51].

The latter has less complexity, but lacks behind from the former with respect to performance

regarding error-rate.

5.3.3 Compress-and-Forward (CF)

Compress-and-Forward is another technique of relaying which does not require decoding in the

relay. In Compress-and-Forward relaying method, the signal received from the source is

quantized and compressed by the relay with the aid of Wyner-Ziv lossy source coding [61]. The

compressed version of the signal is then transmitted to the destination by the relay. The received

information from the source and the quantized and compressed form of that information from

the relay is merged by the destination. CF performs better than DF on the basis of achievable

rate when the relay is near to the destination and vice versa [61].

5.3.4 Estimate-and-Forward (EF)

Estimate-and-Forward is also another relaying method where decoding is not needed in the

relay. In Estimate-and-Forward, an analog estimate of the signal received from the source is

forwarded by the relay to the destination [62]. This estimation is done by entropy constrained

scalar quantization of the signal received from the source or with the help of an unconstrained

minimum mean square error (MMSE) technique [66]. DF performs better than EF with regards

to achievable rate when the relay is far from the destination and vice versa [62].

5.3.5 Coded Cooperations

Coded cooperation is distinct from other relaying techniques because in this scheme, the

channel coding is integrated into cooperation [51]. The data (codeword) of every user is divided

into two parts. At first, every user transfers the former segment of its own codeword and tries to

P a g e | 53



decode the other segment of its corresponding communication partner [63]. If the information is

successfully decoded as verified by the Cyclic Redundancy Check (CRC) code, the user creates

the left over portion of its partner’s codeword and sends it to the destination. Else, the user

sends the left over portion of its own codeword [63]. The user and its corresponding

communication partner should work in an environment of orthogonal channels. In coded

cooperation, various channel coding techniques can be assigned [63].

5.4 Cooperative UWB System Model

Cooperative UWB system generally follows ad-hoc network structure [64]. This is for reducing

the complexity of the system. In that sort of structure, every node can play any of the following

three types of role of nodes: (i) source node (SN), (ii) destination node (DN) and (iii) relay node

(RN) [65]. However, in a specific process of communication, every node can only play a single

role. In a process of communication, a cooperative UWB system comprises of a source node, a

destination node and some relay nodes. Figure 5.2 shows a communication process in a

cooperative UWB system where “M” represents the number of relay nodes.

Every communication process in cooperative UWB system model consists of following

three different stages [65]:

i. At first, the source node transmits pilot symbol to all of the relays. At this phase, because of

the obstructions in the links in between the source node and the relay nodes, the links aren’t

confirmed.

ii. From among all the relay nodes, only the relay with the best bit error rate (BER)

performance is chosen as the relay of that communication process. For the purpose of

minimizing the power consumption of the network, only a single relay node is selected for

each communication process.

iii. The communication in between the source node and the destination node takes place via the

selected relay node.

The second step is of the highest significance among all the three steps of

communication of cooperative UWB system model. It is essential to know the channel fading of

the source to relay link and relay to destination link respectively to decide the route with the

best BER performance [64].

P a g e | 54



In figure 5.2, the channel fading of the source to relay link is represented by hi(t), where

i=1, 2, …, M. The number of relays is represented by “M”. The channel fading can be calculated

once the pilot symbols are received by the relays. The pilot symbols along with the achieved

signal-to-noise ratio (SNR) are then retransmitted to the destination node from every relay node

in separate time slots [65]. The pilot symbols from separate relay nodes are demodulated at the

receiving side. At this point, the channel fading of the relay to destination link is evaluated. In

figure 2, the channel fading of the source to relay link is represented by gi(t), where i=1, 2, …,

M.

Figure 5.2: Cooperative UWB system model

After the selection of the relay node with the best BER performance, the source node

transmits the data signal to the destination node via this path [65]. Generally, RAKE receiver is

implemented for the collection of multipath energy, and better performance is achieved at the

expense of the complexity of hardware [64]. Because a UWB system requires to be simple and

low in cost, RAKE receiver is hardly employed in the adoption of UWB systems. Energy

detection receivers are capable of decreasing the complexity of the system [53]. However, in

that case, UWB system’s performance is degraded. Hence, we have used Code-shifted reference

(TR) receiver, which is based on the energy detection receiver and it is capable of balancing

system complexity with system performance.

SN DN

RN1

RN2

RNM-1

RNM

h1(t)

h2(t)

hM-1(t)

hM(t) gM(t)

gM-1(t)

g2(t)

g1(t)

selection of only a

single relay

P a g e | 55



If amplify-and-forward (AF) cooperative communication protocol is implemented, the

multipath component at the source-relay link is amplified and forwarded towards the destination

[59]. Several multipath components are resulted after passing via the dense multipath channel in

between the relay nodes and the destination node. These multipath components interfere with

each other and decrease the SNR at the destination node [60]. Therefore, taking the dense

multipath feature of UWB channel under consideration, we have implemented decode-and-

forward (DF) protocol in our cooperative UWB system model to transmit the data from the

source node to the destination node through the relay nodes. This decreases the complexity of

the system as well as avoids the distortion of waveform that results from multipath expansion.

5.5 Performance Evaluation for Relay Positioning

It has been said that the relay nodes are placed in between the source node and

destination node with an aim to give better BER performance of the UWB system [51]. But it is

important to know the particular position of a relay in between the source node and the

destination node that gives the best BER performance [53]. By the term “position”, here we can

relate to the distance at which a relay is located from the source and destination. Distance is an

important factor in signal transmission. The signal quality decreases with the increase in

distance because of factors like path-loss, power-loss, noise and interference [53]. We have

considered Dxi as the distance between the source node and the relay node, and, Dyi as the

distance between the relay node and the destination node, where i=1,2,…,M. The number of

relays is represented as M. Let D be the distance between the source node and the relay node.

Figure 5.3 shows the BER performance of the UWB system as a function of Eb/N0 under

the IEEE 802.15.4a office LOS channel environment with the relay node at different distances

from the source and destination. The source node and the destination node are kept at a distance

(D) of 10m. It is assumed that the relays are kept at certain points over a straight line in between

the source node and the relay node, so as to keep the overall transmission distance constant

(10m) for all cases to ease performance comparison, i.e. D = Dxi + Dyi. Simulations are done for

the BER performances of 5 relays which are kept at a distance (Dxi) of 2m, 4m, 5m, 7m and 9m

from the source node. Thus, the corresponding distances (Dyi) of these relays from the

P a g e | 56



destination node are 8m, 6m, 5m , 3m and 1m respectively. It can be noted that the third relay is

at an equal distance from the source node and destination node, ie. Dxi = Dyi = 5m. For

comparison, the BER performance for a case with no relay is also simulated, i.e. the direct

transmission of the data signal from the source node to the destination node without any relay.

The fame duration the CSR-UWB is taken as Tf = 60ns with the number of frames as !f = 8.

The data rate is Rb=8Mbps.

18 18.5 19 19.5 20 20.5 21 21.5 2210

-4

10-3

10-2

10-1

100

Eb/No (dB)

BE

R

Dxi=2, Dyi=8

Dxi=4, Dyi=6

Dxi=5, Dyi=5

Dxi=7, Dyi=3

Dxi=9, Dyi=1

!o Relay

Figure 5.3: BER performances with relays at different positions

The simulation results clearly show that the CSR-UWB system model performs better in

the presence of a relay than in the absence of a relay. It can be observed that the BER

performance of the cooperative UWB system model increases as the relay gets closer to the

centre point in between the source node and the destination node. Thus, we can say that for a

given channel model, the BER performance of the system depends on the distance between the

source node and the relay node (Dxi) and the distance between the relay node and the destination

P a g e | 57



node (Dyi). The BER performance of the cooperative CSR-UWB system model is the best when

Dxi = Dyi = 5m at D =10m. Thus, we can conclude that the BER of the cooperative CSR-UWB

system is the minimum when the relay is equidistant from the source node and the destination

node.

5.6 Performance Evaluation of the cooperative CSR-UWB

system under different channel conditions

In the previous section, it has been assumed that the relay is positioned just anywhere

over the straight line in between the source and the destination for performance comparison

purposes. However, in a practical situation, the relays may not exactly lie in the straight line

between the source node and the destination node. Therefore, we can assume the angle made by

that line with the line between the source node and relay node as θ , that is evenly distributed

from 0 to π [65]. We have come to know from the previous section that the BER performance

of the cooperative CSR-UWB system is the best when the relay is equidistant from the source

node and the destination node. So, let us suppose that Di= Dxi = Dyi (where i=1,2,…,M) is the

distance between the source node and relay node as well as the distance between the relay node

and the destination node. Hence, for a given value of Di , the average distance between the

source node and the destination node can be specified as the following [65]:

πθθ

π

πi

iiii

DdDDDD

4cos2

1

0

222 =−+= ∫ (1)

We evaluated the performances of cooperative CSR-UWB system for different number

of relays, in LOS (Line of Sight) and NLOS (Non-Line of Sight) environments and different

average distance between source node and destination node. The simulations have been done for

the BER performances of cooperative CSR-UWB system for the number of relays M=5 and

M=10. We have taken the CM3 and the CM4 with 100 channels from IEEE 802.15.4a channel

model in our simulations. The CM3 channel represent the LOS (Line of Sight) channels and the

CM4 channel represent the NLOS (Non-Line of Sight) scenario. We have assumed two

P a g e | 58



different values for the average distance between the source and the destination which are iD =

4m and 7m. The frame duration of CSR-UWB is taken as Tf = 60ns with the number of frames

as !f = 8. The data rate is Rb=8Mbps.

The simulation of the cooperative CSR-UWB system with 5 and 10 relays is performed

under LOS and NLOS channel environments with 4m and 7m average distance between source

and destination. Evaluation of the performances is given in the following subsections.

5.6.1 Case I: 4m (LOS) vs. 7m (LOS) with 5 relays

First, the performance of the system is compared between scenarios of average source-

destination distance 4m and 7m. Both simulations are performed with an IEEE 802.15.4a LOS

channel CM3. From figure 5.4, we can observe that, in LOS channel environment, at a BER

requirement of 10-3

, the cooperative CSR-UWB system with average source-to-destination

distance of 4m outperforms the one with average source-to-destination distance of 7m by 4dB.

18 20 22 24 26 28 30 32 34 3610

-3

10-2

10-1

100

Eb/No (dB)

BE

R

LOS (4m)

LOS (7m)

Figure 5.4: System BER performance at LOS (4m) and LOS (7m) for M=5

P a g e | 59



5.6.2 Case II: 4m (LOS) and 7m (LOS) vs. 4m (NLOS) with 5 relays

The performance of the system with 4m average source-destination distance in an IEEE

802.15.4a NLOS channel CM4 is compared with the ones with 4m and 7m source-destination

distance in an IEEE 802.15.4a LOS channel CM3. We can observe in figure 5.5 that, for the

same distance of 4m, at a BER requirement of 10-3

, the performance of the system in LOS

channel environment is 9dB better than that in NLOS channel environment.

18 20 22 24 26 28 30 32 34 36 38 4010

-3

10-2

10-1

100

Eb/No (dB)

BE

R

LOS (4m)

LOS (7m)

NLOS (4m)

Figure 5.5: System BER performance at LOS (4m), LOS (7m) and ALOS (4m) for M=5

5.6.3 Case III: 4m (LOS), 7m (LOS) and 4m (NLOS) vs. 7m (NLOS) with 5

relays

Simulations are done to compare the performance of the system with average source-

destination distance 4m and 7m for both LOS and NLOS channel environments. IEEE 802.15.4a

CM3 channels are used for LOS environment and IEEE 802.15.4a CM4 channels are used for

P a g e | 60



NLOS environment. Figure 5.6 shows that the BER performance of the system is the worst at

7m average source-to-destination distance for NLOS channel environment.

18 20 22 24 26 28 30 32 34 36 38 4010

-3

10-2

10-1

100

Eb/No (dB)

BE

R

LOS (4m)

LOS (7m)

NLOS (4m)

NLOS (7m)

Figure 5.6: System BER performance at LOS (4m), LOS (7m), ALOS (4m) and ALOS

(7m) for M=5

5.6.4 Case IV: 4m (LOS) vs. 7m (LOS) with 10 relays

The performance of the system is compared between scenarios of average source-destination

distance 4m and 7m. Both simulations are performed with an IEEE 802.15.4a LOS channel

CM3. We can observe that, figure 5.7 also shows similar results as in figure 5.4. Here also, at

10-3

BER requirement under LOS channel environment, the BER performance of the

cooperative CSR-UWB system with average source-to-destination distance of 7m is 4dB less

than the one with average source-to-destination distance of 4m.

P a g e | 61



18 20 22 24 26 28 30 3210

-3

10-2

10-1

100

Eb/No (dB)

BE

R

LOS (4m)

LOS (7m)

Figure 5.7: System BER performance at LOS (4m) and LOS (7m) for M=10

5.6.5 Case V: 4m (LOS) and 7m (LOS) vs. 4m (NLOS) with 10 relays

The performance of the system with 4m average source-destination distance in an IEEE

802.15.4a NLOS channel CM4 is compared with the ones with 4m and 7m source-destination

distance in an IEEE 802.15.4a LOS channel CM3 with 10 relays. We can observe in figure 5.8

that, at the same average source-to-destination distance of 4m, the cooperative CSR-UWB

system under LOS channel environment outperforms the one under NLOS channel environment

by about 9dB at a BER requirement of 10-3

.

P a g e | 62



18 20 22 24 26 28 30 32 34 3610

-3

10-2

10-1

100

Eb/No (dB)

BE

R

LOS (4m)

LOS (7m)

NLOS (4m)

Figure 5.8: System BER performance at LOS (4m), LOS (7m) and ALOS (4m) for M=10

5.6.6 Case VI: 4m (LOS), 7m (LOS) and 4m (NLOS) vs. 7m (NLOS) with 10

relays

Simulations are done to compare the performance of the system with average source-destination

distance 4m and 7m for both LOS and NLOS channel environments with 10 relays. IEEE

802.15.4a CM3 channels are used for LOS environment and IEEE 802.15.4a CM4 channels are

used for NLOS environment. Figure 5.9 shows that the channel with average source-to-

destination distance of 7m under LOS channel environment gives the poorest performance.

P a g e | 63



18 20 22 24 26 28 30 32 34 36 38 4010

-3

10-2

10-1

100

Eb/No (dB)

BE

R

LOS (4m)

LOS (7m)

NLOS (4m)

NLOS (7m)

Figure 5.9: System BER performance at LOS (4m), LOS (7m), ALOS (4m) and ALOS

(7m) for M=10

By the comparison of figure 5.6 and figure 5.9, we can observe that the cooperative

CSR-UWB system with 10 relays outperforms the cooperative CSR-UWB system with 5 relays

by about 4dB under a BER requirement of 10-3

for both LOS and NLOS channel environments.

This is because more number of relay nodes opens greater possibilities of getting the relay node

with the highest BER performance. Mostly, the relay node lying nearest or just in the straight

line between the source node and destination node gives the best BER performance for the

system. Nevertheless, at a point when the number of relays (M) becomes adequately huge,

adding more number of relay nodes does not make the BER performance of the system any

better.

P a g e | 64



CHAPTER SIX

Conclusions

P a g e | 65



Chapter 6: Conclusions

In this thesis, first, the CSR-UWB system has been compared with the TR-UWB and the

FSR-UWB systems in terms of complexity and BER performance. The system complexity of

CSR-UWB system is low in compare to TR-UWB and FSR-UWB system since it does not use

any delay elements of ultra wide bandwidth or any analog carriers. The BER performance

comparison shows that, the CSR-UWB system has a BER performance which is equivalent to

that of TR-UWB system when M=!f/2. When the value of TM is decreased in the CSR-UWB

system, it has a higher BER performance than the FSR-UWB system. Secondly, a cooperative

CSR-UWB communication system has been investigated and its BER performance is presented.

The BER performance of the cooperative CSR-UWB system has been evaluated for different

number of relays under different channel environments using IEEE 802.15.4a channel model.

The simulation results show that, under a LOS channel at a BER requirement of 10-3

, the

performance of the cooperative CSR-UWB system with 4m average source-to-destination

distance is approximately 4dB better in SNR than the one with 7m. This means the performance

of the system decreases with the increase in average source-to-destination distance. It has been

observed that with the same average-to-destination distance of 4m, the performance of the

system under a LOS channel environment is about 9dB better than that under a NLOS channel

environment. Hence, it can be said that the system performs better under an environment of

LOS channel than NLOS channel. It can also be observed that the system with 10 relays

outperforms the system with 5 relays by 4dB. This means that the cooperative CSR-UWB

communication system performs better as the number of relay nodes increases until it reaches

an adequately large number.

P a g e | 66



Future work

In this thesis, the BER performance of the Code Shifted Reference impulse-based

Cooperative UWB Communication System has been evaluated only under IEEE 802.15.4a LOS

channel CM3 and NLOS channel CM4. The system can also be tested using other IEEE

802.15.4a channel environments in future.

The CSR-UWB system spends half of its power to transmit the reference pulse

sequence. Differential CSR (DCSR) is another version of CSR-UWB which reduces the power

spent in transmitting the reference pulse sequence so as to improve the performance of the CSR

UWB system. For future work, cooperative communication can be implemented over DCSR-

UWB which can perform better than the Code Shifted Reference impulse-based Cooperative

UWB Communication System.

P a g e | 67



References

[1] F. Nikoogar, Introduction to UWB communication “Ultra Wideband Communications.

Fundamentals and applications,” The United Kingdom’s spectrum auction for next-generation

wireless application generated in April 2000.

[2] R. J. Fontana, on A Brief History of UWB Communications, Multispectral Solutions, Inc. –

History of UWB Technology [online]. Available:

http://www.jacksons.net/tac/First%20Term/A_Brief_History_of_UWB_Communications.pdf

[3]. L. Yang and G. B. Giannakis, “Ultra wideband communication”, IEEE Signal Processing.

Magazine, vol. 21, no. 6, pp. 2654, Nov. 2004.

[4] J. H. Reed, An Introduction to Ultra Wideband Communication Systems: Prentice Hall PTR,

2005

[5] Federal Communications Commission, First report and Order in the matter of revision of

part 15 of the Commission’s Rules Regarding Ultra- Wideband Transmission System, ET-

Docket 98-153, FCC 02-48, April 22, 2002.

[6] R. A. Scholtz, D. M. Pozar and W. Namgoong, Ultra Wideband Radio, Joural of Applied

Signal Processing, EURASIP publishing, 2005:3, pp. 252-272

[7] W. Hirt, “Ultra wideband radio technology: overview and future research”, Elsevier

Computer Communications vol. 26, no.1, pp. 46-52, 1 January 2003

[8] I. J. Lahaie, ed., “Ultra wideband Radar: SPIE Proceedings”, vol. 1631, January 1992.

[9] B. Sreedevi , “EMI Issues in UWB System,” in 9th

International Conference on

Electromagnetic Interference and Compatibility (I!CEMIC), 2006, pp-417.

[10] S. Hoyos, B. M .Sadler, G. R. Arce, “Ultra wide band Multi carrier communication

receiver based on analog to digital conversion in the frequency domain,” in IEEE Conference of

Wireless Communications and !etworking, 2005, pp 782-787.

[11] H.Nikookar, R. Prasad, ”UWB Technologies, ” in Introduction to Ultra Wideband for

Wireless Communications, Signals and Communication technology, Springer, 2008, pp.121-

125.

[12] M. Gabriella, T. Kaiser, A. F. Molisch, I. Oppermann, “Signal Processing,” in UWB

communication system-a comprehensive overview, New York: Hindawi, 2006, pp. 144-157.

P a g e | 68



[13] G.R. Aiello, G.D. Rogerson, “Ultra-Wide Band Wireless Systems”, IEEE Microwave

Magazine, June 2003. Vol: 4, pp. 36-47.

[14] W. P. Siriwongpairat & K. J. Ray Liu, Ultra-Wideband Communications

Systems:Multiband OFDM Approach, John Wiley& Sons, 2007.

[15] S. Hranilovic, Wireless Optical Communication Systems: Springer, 1st Ed, 2004.

[16] W. P. Siriwongpairat, K. J. R. Liu, Ultra-Wideband Communication Systems: Multiband

OFDM Approach: John Wiley and Sons Ltd, 2007.

[17]. S. M. S. Sadough, (2009. April) A Tutorial on Ultra wideband Modulation and Detection

Schemes, [online] Available: faculties.sbu.ac.ir/~sadough/pdf/uwb_tutorial.pdf

[18]. M. G. Di Benedetto, T. Kaiser, A. F. Molish, I. Opperman, C. Politano, and D. Porcino,

UWB Communication Systems A Comprehensive Overview, Series on Signal Processing and

Communications, EURASIP, 2006.

[19] Benny Bing, “Broadband Wireless Access”, Massachusetts: Kluwer Academic Publishers

2000.

[20] William Stallings, Wireless Communications and Networks. Pearson education, Prentice

Hall, 2nd

Edition, 2004

[21] William Stallings, Wireless Communication Principles and Practice, Pearson Education,

2nd

Edition, 2006.

[22] Lars Ahlin &Jens Zander, “Principles of Wireless Communications”, PP26-130.

[23] Goldsmith, Andrea (2005), “Wireless Communications”, Cambridge University Press.

[24] T. S. Rappaport, Wireless Communications: Principles and Practice, Prentice Hall PTR,

Upper Saddle River, NJ, USA, 2nd

edition, 2002.

[25] N.Yee, J. Paul, L. G.Fettweis, “Multi-carrier CDMA in Indoor Wireless Radio Networks,”

IEICE Transactions on Communications, pp.900-4, July 1994.

[26] John G. Proakis (1995). Digital Communications (3rd

ed.). Singapore: McGraw-Hill Book

Co.pp.767-768.

[27] Andreas F. Molisch, “UWB wireless channels-propagation aspects and interplay with

system design,” conference proceedings- European Microwave conference, Vol.2, pp 1101-

1104, 2004.

P a g e | 69



[28] B.V.Santhosh Krishna, International Journal of Computer Science and Technologies, Vol.2

(1), 2011, 587-596.

[29] W.Pam Siriwongpairat and K. J. Ray Liu, “Ultra- Wideband Communication Systems

Multiband OFDM Approach”, New Jersey: John wiley & Sons 2008.

[30] Andreas F. Molisch, Kannan Balakrishnan, Dajana Cassioli, Chia-Chin Chong, Shahriar

Emami, Andrew Fort, John Karedal, Juergen Kunisch, Hans Schantz, Ulrich Schuster, and Kai

Siwiak, “IEEE 802.15.4a channel model – final report,” july 2005 IEEE document number 15-

04-0662-02-004a.

[31] A. Saleh, R. Valenzuela, “A statistical model for indoor multipath propagation,” IEEE

Journal on Select. Areas Communication., vol. SAC-5, no. 2, PP. 128-137, Feb. 1987.

[32] A. F. Molisch “UWB Propagation Channels”, Book chapter 1, pp.1, 2005.

[33] M. Z. Win, R. A. Schultz, “Ultra-wide Bandwidth Time-Hopping Spread-Spectrum

Impulse Radio For Wireless Multiple-Access Communications,” IEEE Transaction

Communication, vol. 48, pp. 679–691, Apr. 2000.

[34] D. L. Goeckel, and Q. Zhang, “Slightly Frequency-Shifted Reference Ultra-Wideband

(UWB) Radio,” IEEE Transaction on communication, Vol. 55, No. 3, March 2007.

[35] H. Zhang, D. Goeckel, “Generalized Transmitted Reference UWB systems,” IEEE

Conference in Ultra Wideband Systems and Technologies, pp. 147-151, 16-19 Nov, 2003.

[36] T. Zasowski, F. Althaus, A. Wittneben, “An energy efficient Transmitted-Reference

Scheme for Ultra Wideband communications,” 2004 International Workshop on Systems and

Technologies, Ultra Wideband Systems 2004, 18-21 May 2004, pp. 146-150.

[37] W. Gifford, M. Win, “ Transmitted-Reference UWB Communications,” Asilomar

Conference on Signals, Systems, and Computers, 2004.

[38] Andreas F. Molisch, “Introduction to UWB Signals and systems,” 2006. [online].

Available: http://en.scientificcommons.org/42499369. [Accessed: Sept. 11, 2010]

[39] Z. Jian, H. H. Ying, L. L. kun, L. T. Feng, , "Code-Orthogonalized Transmitted-Reference

Ultra-Wideband (UWB) Wireless Communication System," in International Conference on

Wireless Communications, !etworking and Mobile Computing WiCom 2007, 21-25 Sept. 2007,

pp.528-532.

[40] Q. Zhang, D. L. Goeckel, J. Burkhart, B. K. Mui, N. Merrill, R. Jackson, “Effect of

Impulse Dithering and Experimental Results,” in 2006 IEEE International Conference on Ultra-

Wideband, 2006, pp. 315-320.

P a g e | 70



[41] Q. Zhang, D. L. Goeckel, “Multi Differential Slightly Frequency Shifted Reference Ultra

Wideband (UWB) Radio,” in 40th

Annual Conference on Information Sciences and Systems,

2006, pp. 615-620.

[42] H. Nie, Z. Chen, “Code-Shifted Reference Ultra-Wideband (UWB) Radio,” in the 6th

Annual Conference on Communication !etworks and Services C!SR, 2008, pp. 385-389.

[43] H. Nie, Z. Chen, “Performance Analysis of Code Shifted Reference UWB Radio,” in 2009

Radio and Wireless Symposium RWS’09, 2009, pp.396-399.

[44] C. K. Rushforth, “Transmitted-reference techniques for random or unknown channels,”

IEEE Trans. Inform. Theory, vol. 10, pp. 39 – 42, Jan. 1964.

[45] J. R. Fernandes, D. Wentzloff, “Recent Advantages in IR-UWB Transceivers: An

Overview,” in 2010 IEEE International Symposium on Circuits and Systems (ISCAS), 2010, pp.

3824-3287.

[46] M. Gabriella, D. Benedetto, G. Giancola, Understanding ultra wide band radio

fundamentals: Prentice Hall, New Jersey, 2004.

[47] G. N. Shirazi, P. Y. Kong, C. K. Tham, “A cooperative retransmission scheme for IR-

UWB networks,” In Proceedings of the 2008 IEEE international conference in Ultra-

Wideband, Hannover, Sept. 2008, vol.2, pp.207-210.

[48] L. Wang, N. R. Shanbhag,”Low Power MIMO Signal Processing,” IEEE Transaction on

Very Large Scale Integration (VLSI) Systems, vol. 11, pp. 434-445, 2003.

[49] S. Zhu, K. K. Leung, “Cooperative orthogonal MIMO relaying for UWB Ad-Hoc

networks,” in IEEE Globecom, New Orleans, Nov. 2007, pp. 5175-5179.

[50] E. Biglieri, R. Calderbank, A. Constantinides, A. Goldsmith, A. Paulraj, and H. V. Poor,

MIMO wireless communications,. Cambridge: Cambridge University Press, 2007

[51] A. Nosratinia, T. E. Hunter, A. Hedayat, “Cooperative Communication in Wireless

Networks,” IEEE Communication Magazine, vol. 42, pp. 74-80, 2004.

[52] G. Yu, Z. Zhang, Y. Chen, P. Qiu, “Adaptive Power Allocation For Cooperative Relaying

System in Fading Wireless Channel,” in International Conference on Wireless

Communications, !etworking and Mobile Computing, WiCOM 2007, 2007, pp. 1116-1119.

[53] J. N. Laneman, D. N. C. Tse, G. W. Wornell, “Cooperative Diversity in Wireless

Networks: Efficient Protocols and Outafe behavior,” IEEE Transaction on Information Theory,

vol. 50, pp. 3062-3080, 2004.

P a g e | 71



[54] Y. Gao, J. Ge, C. Han, “Performance Analysis of Differential Modulation and Relay

Selection with Detect and Forward Cooperative Relaying,” IEEE Communications Letters, vol.

15, pp. 323-325, 2011.

[55] H. P. Frank, Fitzek, and M. D. Katz, Cooperation in Wireless Networks: Principles and

Applications. Netherlands: Springer, Jul 2006

[56] Z. Yi, M. Kim, “Decode and Forward Cooperative Networks with Relay Selection,” in 66th

IEEE Vehicular Technology Conference VTC-2007, 2007, pp. 1167-1171.

[57] W. Lin, G. Wu, L. Zhang, S. Li, “Performance Analysis of Cooperative Networks with

Random Decode and Forward Relaying,” in 10th

IEEE International Conference on High

Performance Computing and Communication- HPCC 2008, 2008, pp. 526-531.

[58] S. S. Ikki, M. H. Ahmed, “Performance Analysis of Adaptive Decode and Forward

Cooperative Diversity Networks with Best-Relay Selection,” in IEEE Transactions on

Communications, vol. 58, pp. 68-72, 2010.

[59] Y. Qiuna, Y. D. Wu, Y. He, “Cooperative Diversity of Wireless Networks with Multiple

Amplify and Forward Relays,” in 2010 International Conference on Communications and

Mobile Computing (CMC), 2010, pp. 207-212.

[60] J. Jose, L. Ying, S. Vishwanath, “On the Stability Region of Amplify and Forward

Cooperative Relay Networks,” in 2009 IEEE Information Theory Workshop, 2009, pp. 620-624.

[61] J. Jing, J. S. Thompson, P. M. Grant, “Design and Analysis of Compress and Forward

Cooperation in a Virtual MIMO Detection System,” in 2010 IEEE GLOBECOM Workshops

(GC Wkshps), 2010, pp. 126-130.

[62] A. Chakrabarti, A. de Baynast, A. Sabharwal, B. Aazhang, “Half-Duplex Estimate and

Forward Relaying: Bounds and Code Design,” in 2006 IEEE International Symposium on

Information Theory, 2006, pp. 1239-1243.

[63] T. E. Hunter, A. Nosratinia, “Diversity Through Coded Cooperation,” IEEE Transactions

on Wireless Communications, Vol. 5, pp. 283-289, 2006.

[64] K. Vardhe, D. Reynolds, B. Woerner, “Power Allocation and Relay Selection in

Cooperative Wireless Networks,” in Military Communication Conference-MILCOM 2010,

2010, pp. 2108-2112.

[65] Q. H. Shen, X. Wu, D. Lin, X. Qiu, “Performance Analysis of Cooperative Ultra-wideband

Communication System,” in 2010 International Conference on Communication and Mobile

Computing (CMC), 2010, pp. 217-220.

P a g e | 72



[66] K. S. Gomadam and S. A. Jafar, “On the capacity of memoryless relay networks,” in Proc.

IEEE International Commun. Conf., Istanbul, Turkey, Jun. 2006, pp. 1580-1585

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