On the Development of a Very Fast Simulator for TH-UWB Systems = Sobre el Desarrollo de un Simulador Rápido para los Sistemas TH-UWB

(1)

UNIVERSIDAD POLITÉCNICA DE MADRID

ESCUELA

TÉCNICA

SUPERIOR

DE

INGENIEROS

DE

TELECOMUNICACIÓN

T

ESIS

D

OCTORAL

Sobre el Desarrollo de un Simulador Rápido para

los Sistemas TH-UWB

P

H

D

T

HESIS

On the Development of a Very Fast Simulator for

TH-UWB Systems

Autora:

M

ARINA

M

ARJANOVIĆ

Director:

D

R

.

J

OSÉ

M

ANUEL

P

ÁEZ

B

ORRALLO

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UNIVERSIDAD POLITÉCNICA DE MADRID

ESCUELA

TÉCNICA

SUPERIOR

DE

INGENIEROS

DE

TELECOMUNICACIÓN

D

EPARTAMENTO DE

S

EÑALES

,

S

ISTEMAS Y

R

ADIOCOMUNICACIONES

T

ESIS

D

OCTORAL

Sobre el Desarrollo de un Simulador Rápido para

los Sistemas TH-UWB

Autora:

M

ARINA

M

ARJANOVIĆ

Director:

D

R

.

J

OSÉ

M

ANUEL

P

ÁEZ

B

ORRALLO

(3)

UNIVERSIDAD POLITÉCNICA DE MADRID

ESCUELA

TÉCNICA

SUPERIOR

DE

INGENIEROS

DE

TELECOMUNICACIÓN

D

EPARTAMENTO DE

S

EÑALES

,

S

ISTEMAS Y

R

ADIOCOMUNICACIONES

T

ESIS

D

OCTORAL

Sobre el Desarrollo de un Simulador Rápido para

los Sistemas TH-UWB

Autora:

M

ARINA

M

ARJANOVIĆ

Director:

D

R

.

J

OSÉ

M

ANUEL

P

ÁEZ

B

ORRALLO

El tribunal nombrado para juzgar la tesis arriba indicada, compuesto de los siguientes Doctores:

Presidente: _______________________________________________________ Secretario: _______________________________________________________ Vocales: _______________________________________________________

_______________________________________________________ _______________________________________________________

Acuerdan otorgarle

Calificación ______________________________________________________

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UNIVERSIDAD POLITÉCNICA DE MADRID

ESCUELA

TÉCNICA

SUPERIOR

DE

INGENIEROS

DE

TELECOMUNICACIÓN

D

EPARTAMENTO DE

S

EÑALES

,

S

ISTEMAS Y

R

ADIOCOMUNICACIONES

P

H

D

T

HESIS

On the Development of a Very Fast Simulator for

TH-UWB Systems

Author:

M

ARINA

M

ARJANOVIĆ

Adviser:

D

R

.

J

OSÉ

M

ANUEL

P

ÁEZ

B

ORRALLO

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ACKNOWLEDGMENTS

Acknowledgments

There are a number of people who had a major influence in my life for the past

four years. Personally, I believe that they have brought out the best in me and also have

provided the financial and moral support, which played a significant role in my life.

First and foremost, I would like to thank to my supervisor Dr. José Manuel Páez

Borrallo. It was indeed a stroke of enormous good fortune that led me to work with him.

Although extremely busy, professor Páez always could find a time to help me think

about research from a wider perspective. For all his advices, constant encouragements,

giving me the chance to participate in various international conferences where I had met

many interesting people that also had influenced on my work. It has been my privilege

and honour to collaborate with Páez from his days as an energetic professor and director

of ETSIT to his new role as a vice dean of Technical University of Madrid.

Furthermore, I can not skip mentioning many thanks to Dr. Enrique Calleja and

Dr. Angel Álvarez who helped me to become the part of research group GAPS, made

my life in a new country much easier and introduced me to professor Páez.

I like to thank to Dr. Santiago Zazo Bello especially, for offering me good

advices throughout these years, and for getting me project that enable me to cover my

living expenses for the last year.

I am thankful to “Telefónica Móviles” for providing financial support by

granting me a scholarship during the first two and half years; and my sincere gratitude

to “CEDINT”, particularly to its director Ms. Asunción Santamaría for giving me the

chance to attend several international conferences.

I like to thank to Dr. Mariano García Otero for reviewing my first accepted

paper that gave me encouragement to go on. Additionally, I would like to thank to all

anonymous reviewers at conferences who have taken the time to review my work and

provided constructive criticisms and positive feedbacks which have certainly raised the

standard of my work.

I thank to Dr. Santiago Zazo Bello from UPM, to Dr. Javier Ramos López from

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ACKNOWLEDGMENTS

Palmas de Gran Canaria’ for their interest in my work and for accepting to be members

of my thesis committee.

Friends that I like to thank include people from GAPS, especially Alberto

Jiménez Pacheco, José Manuel Diaz and Galo Nuño Barrau. Alberto has been very

helpful giving me many fruitful comments and criticism on various versions of my

papers and programs. José Manuel contributed with many handful advices. Of course, I

am thankful to Galo for starting with a wonderful idea and leaving me a space to

continue with working in a very young, interesting and fertile area.

Thanks to my friends Milica, Shiki, Goga, Vlada, Mare, Mica, Marija, Sale,

Jelena Ristic, Jelena Urosevic, Zorana, Zarko, Vaske, Vule, Maja, Grabi, Kum and

Kuma, Sofia, Ful for supporting me during the years towards this dissertation.

I want to thank Mar Díaz Peñalver, Julian Ayuso, Dolores Ajates Abellán, and

Ana Nohales for helping me out with all the administrative issues.

Deepest gratitude should go to my parents and grandparents since they always

have loved me, believed in me, and encouraged me in my study.

Finally, my special thanks should go to Milosh who has been with me and has

been so supportive all these years. Without his love, presence beside me, his

encouragement, support, and technical guidance, this thesis would never have started or

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RESUMEN

Resumen

Los impulsos de radio de banda ultra ancha y salto en el tiempo (IR-TH-UWB)

es una tecnología relativamente nueva que puede tener un fuerte impacto en el

rendimiento de las comunicaciones inalámbricas. Resistencia a la propagación

multi-trayecto, bajos niveles de potencia, elevada capacidad, coexistencia con otros sistemas,

capacidad de penetración en paredes, son algunas de las características que hacen que

este sistema sea muy atractivo para Comunicaciones Inalámbricas de corto alcance,

tales como Redes de Área Local inalámbricas (WLAN) y Redes de Área Personal

inalámbricas (WPAN). Esta tecnología hace uso de pulsos de muy corta duración para

transmitir grandes cantidades de datos digitales sobre un rango de frecuencias muy

amplio a muy bajos niveles de potencia. Desafortunadamente, para el procesamiento de

señales de banda ultra ancha, es necesaria una razón de muestreo extremadamente

grande. En una aproximación sencilla, con una razón de muestreo constante, la longitud

del array que contiene las muestras de bits, puede ser muy grande, dependiendo de la

relación entre el ciclo útil y la tasa binaria. Ya que este array tiene que pasar a través de

la cadena de bloques que modela el canal y la respuesta del receptor, es obvio que un

elevado número de convoluciones tienen que ser realizadas. Por lo tanto, aun en

ordenadores muy rápidos, el tiempo total de cómputo para estimar la BER puede ser muy alto. Este hecho reduce considerablemente la eficiencia del simulador. Además,

como se menciona en esta tesis, aplicando descomposición de señal directa/ en

cuadratura a las señales de UWB, que es una técnica fundamental usada para acortar el

tiempo de simulación requerido, no es posible mitigar una elevada frecuencia de

muestreo.

En esta tesis, un sistema TH-UWB con modulación por posición de pulsos

(PPM) es simulado utilizando el simulador de sistema de alta velocidad, el cual

constituye una innovación de nuestro grupo de investigación. Este método aprovecha las

ventajas de algunas de las propiedades de estos tipos de sistemas para facilitar un

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RESUMEN

independientemente de la razón de muestreo. Comparándolo con los simuladores

previos, la frecuencia de muestreo puede ser tan elevada como se necesite, ya que el

tiempo de simulación no depende de esta. La señal transmitida es almacenada en el

vector de forma de onda llamado Transmitted Distorted Received (TDR), por lo tanto,

no es necesario operar con las muestras de señal en cada simulación. La única influencia

de la razón de muestreo es en la longitud del vector de forma de onda TDR. La

complejidad del algoritmo es lineal con el número de usuarios, tramas, componentes

multitrayectos y ramas del receptor RAKE.

Para desarrollar el código de simulación, un paso importante en cada proceso de

simulación, es la definición de los atributos del dispositivo físico que afecta los

productos de simulación requeridos, esto es, la tasa de bits erróneos (BER). Uno de estos atributos en sistemas IR-TH-UWB es la sincronización que produce la alineación

de los relojes de relojes en transmisión y en recepción, de manera tal que la información

puede ser intercambiada con exactitud. Particularmente con PPM, la sincronización es

esencial para la correcta demodulación de las señales recibidas, ya que la información es

portada en la posición que tienen los pulsos en el tiempo.

Otra tarea crítica para la operación satisfactoria de los sistemas de UWB es la

detección multi-usuario. Algunas publicaciones muestran que el receptor MMSE tiene

el mejor rendimiento en términos de SINR a expensas de una elevada complejidad de cómputo, ya que requiere de la inversión de la matriz cada vez que la secuencia de

esparcimiento cambia. Por lo tanto, no existe mucha literatura relacionadas con estos

tópicos, especialmente en sistemas de UWB en la presencia de entornos reales con

multitrayecto.

Desafortunadamente, ya que la señal transmitida es almacenada en el vector de

forma de onda TDR, resulta difícil extraerla. Por lo tanto la implementación de aquellas

tareas (sincronización, estimación de canal y detección multi-usuario) podrían ser un

gran problema en la simulación del sistema.

Por lo tanto, la presente tesis se compone de dos partes. En la primera parte se

propone un sistema del tipo PPM IR-TH-UWB con un procedimiento de sincronización

conjunta de símbolo, trama y chip, en un entorno multitrayecto denso. Se asume que el

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RESUMEN

dicha sincronización es lograda a partir de maximizar la energía del canal multitrayecto

estimado. Basado en este método para la sincronización en combinación con el método

PWAM para la estimación de canal, las operaciones FFT que son usadas en muchos

trabajos, son evitadas y el algoritmo presenta muy baja complejidad. Adicionalmente y

con la finalidad de incrementar aun más la velocidad del proceso de simulación, este

método es implementado en un algoritmo de ensanchamiento temporal. Por lo tanto, los

algoritmos que esta tesis propone, puede relacionarse con canales con un gran numero

de taps que son difíciles de estimar usando los algoritmos existentes. Gracias a esta

aproximación, una baja complejidad para la implementación en tiempo real y un buen

rendimiento en términos de BER contra relación señal a ruido (SNR) es obtenido. Las simulaciones muestran que estos sistemas sincronizados contribuyan a mitigar los

efectos del corrimiento temporal.

En la segunda parte de la tesis, el receptor MMSE para sistemas IR-TH-UWB

usando un simulador de sistema de alta velocidad, es simulado. La implementación de

cualquier detector multi-usuario fue también una tarea difícil (como lo fue para la

sincronización) ya que una señal transmitida es ‘rechazada’ en los TDR y no existe una

estructura multi-usuario típica con matriz de correlación. Por lo tanto, aplicando este

método en esta tesis, es lograda una nueva aproximación de una detección

multi-usuario. Ya que la forma de onda es almacenada en los TDR, no es necesario operar con

las muestras de señal en cada simulación. Por lo tanto, la matriz de correlación tiene que

ser recalculada solamente cuando las condiciones del canal cambian. Dependiendo del

tiempo de coherencia del canal y de la tasa binaria, es posible encontrar el número de

bits que pueden ser simulados sin alterar la matriz de correlación. La única influencia de

la razón de muestreo es en la longitud de los TDR. Los resultados derivados demuestran

que este efecto es despreciable. Por consiguiente, puede ser considerado que la

velocidad de simulación es aproximadamente independiente de la razón de muestreo.

Ventajas adicionales de esta aproximación es que la complejidad del algoritmo es lineal

con el número de usuarios, las tramas, las componentes multitrayecto y las ramas del

receptor RAKE.

Además, con esta aproximación, es posible reducir el proceso de simulación

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RESUMEN

mayor consumo de tiempo. Basados en esta aproximación, un número de operaciones de

simulación necesarias para evaluar la matriz de recepción MMSE son reducidas. Por lo

tanto, es posible procesar un gran número de muestras y estimar exactamente bajos

valores de BER en un corto tiempo. Además, se deriva una fórmula teórica del rendimiento del detector MMSE para PPM IR-TH-UWB basados en esta nueva

aproximación. Esta fórmula es validada a partir de la comparación de los resultados con

otros obtenidos en investigaciones previas.

Ambas tareas, sincronización y la nueva aproximación de detección multiusuario

propuestas en esta tesis, aportan una buena realización en términos de baja complejidad,

procesamiento rápido y un adecuado comportamiento de la BER en función de la relación señal a ruido (SNR).

Todos los resultados son evaluados usando el algoritmo propuesto y las

simulaciones son facilitadas para validar esta implementación. Estas demuestran que el

tiempo de simulación crece linealmente con el número de usuarios y el número de

tramas. El principal logro de esta tesis es un algoritmo para el cálculo de un sistema

completo PPM IR-TH-UWB cuya complejidad es Nh veces inferior comparado con

resultados previos, donde Nh es un número de chips en aquellos sistemas. Por lo tanto,

asumiendo un factor de esparcimiento grande de las señales de UWB, este algoritmo

consigue salvar un elevado tiempo de cómputo comparado con los diseños previos.

Esta tesis está constituida por seis capítulos. En el primer capítulo se ofrece una

panorámica de los fundamentos de los sistemas de UWB y dentro de este, algunos

tópicos incluyen: historia de UWB, características y aplicaciones de estos sistemas.

En el segundo capítulo se incluye el diseño de un sistema de acceso múltiple

UWB, incluyendo el diseño de un transmisor es revisado. Este capítulo presenta el

modelo completo del sistema y el convenio de notaciones empleadas a lo largo de la

tesis.

También en el segundo capítulo se incluyen dos modelos estadísticos para

canales de UWB son presentados, basados en datos reunidos a partir de medidas

extensivas de la propagación UWB. Saleh-Valenzuela y basado en Saleh-Valenzuela,

modelo propuesto por Intel que será empleado con estos propósitos en la tesis, será

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RESUMEN

En adición, se proporciona una descripción de una estructura receptora de simple

usuario y multiusuario, asumiendo una sincronización y una estimación de la canal

perfecta que constituyen la contribución de esta tesis.

El capítulo cuatro cubre las siguientes tareas:

• Diferencias entre UWB y sistemas tradicionales de banda estrecha y dificultades

en el desarrollo del modelo.

• Una breve revisión de los fundamentos de las metodologías de simulación.

• Un nuevo simulador del sistema IR-TH-UWB que constituye un aporte de

nuestro grupo de investigación y que será utilizado en interés de esta tesis.

El capítulo cinco presenta la segunda parte de la contribución de esta tesis donde

he implementado un receptor RAKE MMSE para sistemas de UWB usando un nuevo

simulador de sistema de salto en tiempo, logrando una novedosa aproximación de

detector multiusuario (MUD). Adicionalmente, es presentada una nueva fórmula teórica

del rendimiento del detector MMSE para PPM IR-TH-UWB basado en esta nueva

aproximación y en investigaciones previas es presentado.

El capítulo seis presenta resultados de las simulaciones para verificar este

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ABSTRACT

Abstract

Impulse Radio-Time Hopping-Ultra Wideband (IR-TH-UWB) is a relatively

new technology that might have a big effect on improving wireless communication.

Multipath resistance, low power, high capacity, coexistence with other systems, ability

of penetrating walls are some of the characteristics that make this system very attractive

for a Short Range Wireless Communications, such as deployed in Wireless Local Area

Network (WLAN) and Wireless Personal Area Network (WPAN). This technology uses

short pulses in order to transmit large amounts of digital data over a wide spectrum of

frequency bands with a very low power. Unfortunately, in order to process

ultra-wideband signals, an extremely large sampling rate is mandatory. In a straightforward

approach, with the constant sampling rate, the length of the array that contains the bit

samples can be very large, depending on the relationship between the duty cycle and the

bit rate. Since this array should pass through the chain of blocks that model the channel

and receiver responses, it is obvious that a large number of convolutions should be

done. Thus, even in very fast workstations, the total computing time in order to estimate

BER can be very high. This fact significantly reduces the efficiency of the simulator. Furthermore, as mentioned in this thesis, applying direct/quadrature signal

decomposition to UWB signals, which is fundamental technique used to shorten the

required simulation runtime, it is not possible to mitigate a large sampling frequency.

In this thesis, a complete Pulse Position Modulation (PPM) TH-UWB system is

simulated using the high-speed system simulator, which is the innovation of our

research group. This method takes advantage of some of the properties of this kind of

systems in order to provide a very straightforward and fast processing that improves all

the previous designs several orders of magnitude, independently on the sampling rate.

Comparing to previous simulators, sampling frequency can be as high as needed, since

the simulation run-time does not depend on it. Transmitted signal is stored in the

Transmitted Distorted Received (TDR) waveform vector, thus it is not necessary to

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ABSTRACT

rate is on the length of the TDR waveform vector. The algorithm complexity is linear

with the number of users, frames,multipath components, and rake fingers.

In order to develop the simulation code, an important step in every simulation

process is definition of the attributes of the physical device that affect the required

simulation products, i.e. Bit Error Rate (BER). One of those attributes in IR-TH-UWB

systems is synchronization that produces alignment of transmitter and receiver clocks,

so information can be accurately exchanged. Particularly with PPM, synchronization is

essential to correct demodulation of the received signals because information is

conveyed in the time position of the pulse.

Another critical task for successful operation of UWB systems is a multiuser

detection. Some papers show that MMSE receiver has the best performance in terms of

SINR at the expense of high computational complexity since it requires the matrix inversion every time the spreading sequence changes. Thus, there are no many

literatures dealing with this topic, especially not in UWB systems in the presence of real

multipath environment.

Unfortunately, since the transmitted signal is stored in the TDR waveform

vector, it is very difficult to extract it. Thus, implementation of those tasks

(synchronization, channel estimation and multiuser detection) might be a big problem

for system simulation.

Therefore, this thesis has two main parts. In the first part of the thesis, a joint

symbol, frame and chip synchronization method for PPM IR-TH-UWB system in the

presence of dense multipath environment is proposed. It is assumed that the channel is

estimated using Pilot Waveform Assisted Modulation (PWAM), and that

synchronization is achieved by maximizing the energy of the estimated multipath

channel. Based on this method for synchronization in combination with PWAM method

for channel estimation, FFT operations that are used in many works are avoided and the

algorithm has a very low complexity. Additionally, in order to even more increase the

speed of simulation process; this method is implemented in the enhanced time

algorithm. Therefore, algorithm that this thesis proposes can deal with channels with a

large number of taps that are difficult to estimate using the existing algorithms. Thanks

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ABSTRACT

performance in terms of BER versus Signal to Noise Ratio (SNR) are achieved. Simulation shows that this synchronization system helps to mitigate the negative effects

of timing offset.

In the second part of the thesis, MMSE receiver for PPM IR-TH-UWB systems

using a high-speed system simulator is implemented. Implementation of any multiuser

detector in this algorithm was also a difficult task (as was for synchronization), since a

transmitted signal is ‘hidden’ in TDR and a typical multiuser structure with a correlation

matrix does not exist. Therefore, applying this method, in this thesis, a new approach of

multiuser detection is achieved. Since the transmitted waveform is stored in the TDR, it

is not necessary to operate with the signal samples in every simulation. Thus,

correlation matrix should be recalculated only when the channel conditions change.

Depending on the channel coherence time and the bit rate, it is possible to find the

number of bits that can be simulated without alerting the correlation matrix. The only

influence of the sampling rate is the length of the TDR. Derived results show that this

effect is disregarded. Therefore, it can be considered that the simulation speed is

approximately independent on the sampling rate. Additional advantage of this approach

is that the complexity of the algorithm is linear with the number of users, frames,

multipath components, and RAKE fingers.

Furthermore, with this approach, it is possible to reduce the simulation process

significantly by avoiding any convolution operation, which is the most time-consuming.

Relaying on this approach, number of simulation operations needed to evaluate MMSE

receiver matrix are reduced. Thus, it is possible to process a large number of samples

and to estimate accurately low BER in a short time application. In addition, I derived a

theoretical formula of the performance of the MMSE detector for PPM IR-TH-UWB

based on this new approach. This new formula is validated by comparing results to

some other results based on some previous researches.

Both tasks, synchronization and the new approach of multiuser detection

proposed in this thesis, give a good performance in terms of low complexity, fast

processing and BER versus Signal to Noise Ratio (SNR) performance.

All results are evaluated using the proposed algorithm and simulations are

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ABSTRACT

time linearly grows with the number of users and the number of frames. The main gain

of this thesis is that the complexity of the algorithm in order to calculate the complete

PPM IR-TH-UWB system is Nh times lower comparing to previous methods, where Nh

is a number of chips in those systems. Therefore, assuming a large spreading factor of

the UWB signals, this algorithm yields a large saving of computational time comparing

to the previous designs.

With this accurate flexible simulation model; we might analyze the performance

of the TH-UWB system and the impact of different factors of TH-UWB systems (the

number of users, waveform design time-hopping codes, channel models, receivers…)

and achieve a low BER in a real time application even in the presence of reach multipath environment.

This thesis consists on five chapters. In the first chapter of this thesis, the

fundamentals of UWB system are overviewed. Within the following sections, topics

covered are UWB history, features and applications of UWB system, types of UWB

signals, UWB spectrum and regulations and some of the possible problems of this

system.

The second chapter gives an overview of MA UWB system design, including a

transmitter design. Additionally, this chapter presents the overall system model and

notation convention that I have used throughout this thesis.

In addition, two statistical models for UWB channel are presented based on data

collected from extensive UWB propagation measurements. Saleh-Valenzuela and based

on Saleh-Valenzuela, model proposed by Intel that will be employed for the purposes of

this thesis are described. This channel model was made with one slight modification

since the observations have shown that the lognormal distribution better fits the

measurement data.

Additionally, the second chapter provides a description of a single user and

multiuser receiver structure, assuming perfect synchronization and perfect channel

estimation. As an optimum single user receiver, selective RAKE receiver is used for the

purposes of this thesis and as a multiuser receiver, MMSE RAKE is employed.

In addition, as a one part of the contribution of this thesis low complexity

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ABSTRACT

time implementation and the good performance in terms of BER versus SNR are achieved.

Since the UWB system requires taking a second look at simulation

methodology, the chapter three covers the following tasks:

• Differences between UWB and traditional narrowband systems and difficulties

in model development

• A brief review of the fundamental simulation methodologies.

• New IR-TH-UWB system simulator that is the innovation of our research group

and will be used for the purposes of this thesis.

In Chapter four, I implemented a MMSE RAKE receiver for Ultra-Wideband

(UWB) system using a new time-hopping system simulator, achieving a novel approach

of MUD. With this approach, it is possible to reduce the simulation time significantly by

avoiding any convolution operation, which is the most time-consuming. Relaying on

this approach, number of simulation operations needed to evaluate MMSE receiver

matrix are reduced. Complexity of this algorithm is O(Nu*Nf*L*Lmax), while using

Monte Carlo method complexity is Nh times higher. Thus, for systems with a very large

spreading factor, as UWB is, this provides a large computational time saving.

Additionally, I have derived a theoretical formula of the performance of MMSE

RAKE receiver detector for PPM IR-TH-UWB based on this new approach and some

previous researches.

In chapter five, simulation results are provided in order to validate this approach.

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TABLE OF CONTENTS

Abbreviations

AGN Additive Gaussian Noise

AWGN Additive White Gaussian Noise

BEP Bit Error Probability

BER Bit Error Rate

DS Direct Sequence

FCC Federal Communications Commission

FH Frequency Hopping

FT Fourier Transform

GPS Global Positioning System

GSM Global System for Mobile

LAN Local Area Network

LPD/I Low Probability of Detection/Interception

MAC Medium Access Control

MC Multi Carrier

MMSE Minimum Mean Square Error

MRC Maximum Ratio Combining

MSE Mean Square Error

MUD Multi-User Detection

MUI Multiuser Interference

(N)LOS (Non) Line Of Sight

OFDM Orthogonal Frequency Division Multiplexing

OMAN Open Mobile Access Network

PAM Pulse Amplitude Modulation

PDF Probability Distribution Function

PPM Pulse Position Modulation

PSD Power Spectral Density

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ABBREVIATIONS

RF Radio Frequency

QoS Quality of Service

SINR Signal-to-Noise-plus-Interference-Ratio

SNR Signal-to-Noise-Ratio

SS Spread Spectrum

SUD Single-User Detection

TDMA Time Division Multiple Access

TDR Transmitted-Distorted-Received

TEM Transverse Electromagnetic

TH Time Hopping

TR Transmitted Reference

UAV Unmanned Aerial Vehicle

UGV Unmanned Ground Vehicle

UMTS Universal Mobile Telecommunication System

UWB Ultra-Wideband

WAN Wide Area Network

WLAN Wireless Local Area Network

WPAN Wireless Personal Area Network

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LIST OF FIGURES

List of Figures

Figure 1.1 Comparison of the Fractional Bandwidth of a Narrowband and Ultra

Wideband Communication System ...37

Figure 1.2. Spectrum of a Gaussian Monocycle- Based Impulse UWB Signal

(Data taken from [48])...38

Figure 1.3. Spectrum of an OFDM based MC-UWB Signal (Data taken from [48]) ....39

Figure 1.4. UWB Spectral Mask and FCC Part 15 Limits. (Data taken from [49])...40

Figure 1.5. WPAN, WLAN, and Cellular Networks: Typical Link Ranges. (Data

taken from [49])...41

Figure 2.1. Frame Structure for TH Signals ...46

Figure 2.2. Example UWB Pulses ...47

Figure 2.3. PSD of the Different UWB Pulses ...48

Figure 2.4. Example of a PPM Modulate UWB Signal Using the Data Sequence

{1 -1} ...50

Figure 2.5. Example of a PAM Modulate UWB Signal Using the Data Sequence

{1 -1} ...51

Figure 2.6. Channel Impulse Response ...55

Figure 2.7. Exponential Decay of Mean Cluster Power and Ray Power Within

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LIST OF FIGURES

Figure 2.8. One LOS Channel Realization Generated From Intel Model Using the

Same Parameter as the Ones in Table 2.2. (Experimental Data taken

from [76]) ...61

Figure 2.9. One NLOS Channel Realization Generated from Intel Model Using

the Same Parameter as the Ones in Table 3.3. (Experimental data taken

from [76]) ...62

Figure 2.10. RAKE Receiver Structure Scheme ...67

Figure 2.11 Histogram of the distribution of the MUI for a PPM TH-UWB system

with Tc=1 ns, Nh= 1024slots, Nu=900 links, λ = 180 ps, Nf=64 and no

multipath. The number of simulations is 330.503. It can be noticed the

Gaussian distribution of the interference. (Data taken from [83]) ...69

Figure 2.12. Theoretical BER Performance versus SNR of a PPM TH-UWB

System Downlink Employing RAKE Receiver in a Multipath Channel;

L=100, Nf=64; Nh=128...70

Figure 2.13. Theoretical BER Performance of a PPM TH-UWB System

Employing RAKE Receiver vs. BER Performance of a PPM TH-UWB

System Employing MMSE Receiver in AWGN Channel; Nf=8; Nh=4;

Nu=5 ...75

Figure 2.14. Block Scheme of the Receiver (with Channel Estimation and Joint

Synchronization)...77

Figure 2.15. Illustration of the Transmitted Reference System...78

Figure 2.16. Illustration of the PWAM Scheme...79

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LIST OF FIGURES

Figure 2.18. Timing Offset Presentation ...84

Figure 3.1. Wideband Signal Spectrum...90

Figure 3.2. Schematic Representation of Implementation of Monte Carlo Method ...94

Figure 3.3. Importance Sampling Illustration...95

Figure 3.4. Diagram of a Semi-Analytic BER Calculation for BPSK...97

Figure 3.5. Conceptual Model of the UWB Receiver for the qthUser ...103

Figure 3.6. Signal Processing Flowchart ...104

Figure 4.1. Signal Processing Flowchart (as in [83]) ...112

Figure 4.2. Error Vector Calculation Flowchart...114

Figure 4.3. Simulator Flowchart...115

Figure 4.4. Position Vector Calculation Flowchart ...116

Figure 4.5.Comparison Between the Theoretical and Results Obtained with New

Approach for AWGN and NLOS Channel; Γ=16 γ=8.5, 1/Λ=11 ns,

1/λ=0.35 ns, L=400, Lmax=400;Nu=5; Nf=8; Nh=4 ...118

Figure 5.1. Number of Users Influence on BER performance employing Single

User Receiver; Second Derivative of the Gaussian Monopulse; AWGN

channel; Nf=32, Nh=64, fs=200/Tc...122

Figure 5.2. Number of Chips Influence on BER performance employing Single

channel; Nu=64, Nf=64, fs=200/Tc,...123

Figure 5.3. Monocycle Shape Influence on BER performance employing Single

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LIST OF FIGURES

Figure 5.4. Sampling Frequency Influence on BER performance employing Single

channel; Nu=64, Nh=64, Nf=8, Nh=4 ...125

Figure 5.5. BER performance employing Single User Receiver; Second Derivative

of the Gaussian Monopulse; Multipath Channel L=400, Nu=2, Nh=64,

Nf=32, fs=200/Tc...126

Figure 5.6. UWB Downlink System Model ...127

Figure 5.7. UWB Uplink System Model ...127

Figure 5.8. Channel Estimation Performance in the PPM TH-UWB System

Downlink employing RAKE Receiver in NLOS Multipath Channel

based on Intel Measurements from Figure 3.4; Lmax=18, Nu=13, Nf=32,

Nh=128, fs=200/Tc, Perfect Synchronization ...128

Figure 5.9. Channel Estimation Performance in the PPM TH-UWB System

Uplink employing RAKE Receiver in NLOS Multipath Channel from

Figure 3.4 based on Intel Measurements; Nu=13, Nf=32, Nh=128,

fs=200/Tc, Perfect Synchronization...129

Figure 5.10. BER Performance versus SNR of a PPM TH-UWB System Downlink

employing RAKE Receiver in NLOS Multipath Channel from Figure

3.4 based on Intel Measurements; Lmax=18, Nu=13, Nf=32, Nh=128,

Np=10000, fs=200/Tc...130

Figure 5.11. BER Performance versus SNR of a PPM TH-UWB System Uplink

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LIST OF FIGURES

Figure3.4 based on Intel Measurements; Nu=13, Nf=32, Nh=128,

Np=10000, fs=200/Tc...131

Figure 5.12. Relation between the Sampling Frequency and the Simulation Time

per Bit for a PPM-TH-UWB System with PWAM assuming

Synchronization; SNR=5dB, Np=1, fs=200/Tc...132

Figure 5.13. Effect of the Number of Multipath Components on the Simulation

Time per Bit for a PPM-TH-UWB System with PWAM assuming

Perfect Synchronization; SNR=5dB, Np=1, fs=200/Tc...133

Figure 5.14.Comparison Between Results from [85] and Results Obtained with a

New Approach; L=1 (AWGN); Nu=5, Nf=8, Nh=4, fs=200/Tc...134

Figure 5.15. Effect of the Number of Users on BER Performance for a

PPM-TH-UWB System with MMSE Receiver; Nh=4, Nf=8, Tc=2 ns, fs=200/Tc,

L=1 ...135

Figure 5.16. Effect of the Number of Chips on BER Performance for a

PPM-TH-UWB System with MMSE Receiver; Nu=5, Nf=8, Tc=2 ns, fs=200/Tc,

L=1 ...136

Figure 5.17. Sampling Frequency Influence on BER performance employing

MMSE Receiver; Second Derivative of the Gaussian Monopulse;

AWGN channel; Nu=64, Nh=64, Nf=8, Nh=4...137

Γ=16, γ =8.5, 1/Λ=11 ns, 1/λ=0.35 ns, L=400, Lmax=400

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LIST OF FIGURES

Figure 5.19. Effect of the Number of Chips on the BER Performance for a

PPM-TH-UWB System with MMSE Receiver; Nu=5, Nf=8, Tc=2 ns,

fs=200/Tc, Γ=16, γ =8.5, 1/Λ=11 ns, 1/λ=0.35 ns, L=400, Lmax=400

(Channel2) ...139

Figure 5.20. Sampling Frequency Influence on BER performance employing

MMSE RAKE Receiver; Second Derivative of the Gaussian

Monopulse; Channel 2; Nu=5, Nh=4, Nf=8 ...140

Γ=33, γ =5, 1/Λ=2 ns, 1/_λ=0. 5 ns, L=400, Lmax=400 (Channel3)...141

PPM-TH-UWB System with MMSE Receiver with Nh=4, Nf=8, Tc=2 ns,

fs=200/Tc, Γ=33, γ =5, 1/Λ=2 ns, 1/λ=0. 5 ns, L=400, Lmax=400

(Channel3) ...142

Figure 5.23. Effect of the Number of Users on the BER Performance for a

PPM-TH-UWB System with MMSE Receiver in the presence of AWGN

channel vs. BER Performance for a PPM-TH-UWB System in the

presence of Channel 2; Nh=8, Nf=8, Tc=2 ns, fs=200/Tc, L=400,

Lmax=400 ...143

PPM-TH-UWB System with MMSE Receiver in the presence of AWGN

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LIST OF FIGURES

MMSE Receiver in the presence of Channel 2; Nu=8, Nf=8, Tc=2 ns,

fs=200/Tc, L=400, Lmax=400...144

Figure 5.25. Effect of the Number of RAKE Fingers on BER Performance for a

PPM-TH-UWB System with MMSE Receiver in the presence of

Channel 2; Nu=8, Nf=8, Nh=4, Tc=2 ns, fs=200/Tc, L=400 ...145

Figure 5.26. Effect of the Synchronization on BER Performance for a

PPM-TH-UWB System with MMSE Receiver in the presence of Multipath

Channel (Channel2) Nu=13, Nf=8, Nh=8, Tc=2 ns, fs=200/Tc, L=400,

Lmax=400. ...147

Figure 5.27. Relation between the Sampling Frequency and the Simulation Time

per Bit for a PPM-TH-UWB System employing MMSE RAKE

Receiver; Nu=5, Tc=2 ns, fs=200/Tc, Nf=8, Nh=4, L=400, Lmax=100...148

Figure 5.28. Effect of the Number of Users on the Simulation Time per Bit for a

PPM-TH- UWB System employing MMSE RAKE Receiver; Tc=2 ns,

fs=200/Tc, Nf=8 Nh=4, L=400, Lmax=100...149

Figure 5.29. Effect of the Number of Multipath Components on the Simulation

time per Bit for a PPM-TH- UWB System with MMSE Receiver;

Nu=5, Tc=2 ns, fs=200/Tc, Nf=8, Nh=4, Lmax=L...149

Figure 5.30. Effect of the Number of Frames on the Simulation Time per Bit for a

PPM-TH- UWB System with MMSE Receiver; Nu=5, Tc=2 ns,

fs=200/Tc, Nh=4, L=400, Lmax=100. ...150

Figure 5.31. MMSE Matrix Calculation Flowchart using our Algorithm vs.

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LIST OF FIGURES

Figure 6.1. Conceptual Model of the UWB Signal Generation...157

Figure 6.2. Conceptual Model of the UWB Receiver for the qthUser ...158

Figure 6.3 Optimum Combining UWB RAKE Receiver for IR-TH-UWB ...161

Figure 6.4. Error Vector Calculation Flowchart when Optimum RAKE Receiver

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LIST OF TABLES

List of Tables

Table 2.3. Simulated and Measured Results for NLOS UWB Channels Using

Intel’s Model. Simulation Results are Generated from Intel Model with

Γ=16 ns, γ=8.5 ns, _Λ=1/11 ns, _λ=1/0.35 ns, _σ =4.8 dB. (Experimental

data taken from [76]) ...61

Table 2.4. Example Multipath Channel Characteristics and Corresponding Model

Parameters (Experimental data taken from [76]). ...63

Table 5.1 Channel Estimation Performance in the PPM TH-UWB System

Downlink employing RAKE Receiver in NLOS Multipath Channel

based on Intel Measurements from Figure 3.4; Lmax=18, Nu=13, Nf=32,

Nh=128, fs=200/Tc, Perfect Synchronization ...128

Table 5.2 Channel Estimation Performance in the PPM TH-UWB System Uplink

3.4 based on Intel Measurements; Nu=13, Nf=32, Nh=128, Perfect

Synchronization ...129

Table 5.3. BER Performance versus SNR of a PPM TH-UWB System Downlink

3.4 based on Intel Measurements; L=400; Lmax=18; Nu=13; Nf=32;

Nh=128; Np=10000...130

Table 5.4. BER Performance versus SNR of a PPM TH-UWB System Uplink

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LIST OF TABLES

3.4 based on Intel Measurements; Lmax=18, Nu=13, Nf=32, Nh=128,

Np=10000, fs=200/Tc...131

Table 5.5. Comparison of the Algorithms Complexities...133

Table 5.6 Comparisons of the Algorithms Complexities in Single User Receiver ...151

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CHAPTER 1 SUMMARY

Chapter 1

1. Summary

1.1. Introduction

Ultra wideband (UWB) communication systems can be broadly classified as any

communication systems whose instantaneous bandwidth is many times greater than the

minimum required to deliver particular information. This large bandwidth is the

defining characteristic of those systems.

Within the past 40 years, advances in analog and digital electronics and UWB

signal theory have enabled system designers to propose some practical UWB

communications system. Over the past decade, many individuals and corporations

began asking the FCC for permission to operate unlicensed UWB system concurrent

with existing narrowband signals. In 2002, FCC decided to change the rules to allow

UWB system operation in a broad range of frequencies. In some of the FCC UWB

rule-making process proceedings, one of them can find a vast array of claims relating to the

expected utility and performance of UWB systems, some of them almost perfect.

Testing by the FCC, FAA, and DARPA has uniformly shown that UWB still conforms

to Maxwell’s Equations and the laws of physics.

It is a relatively new technology that might have a big effect on improving

wireless communications. Multipath resistance, low power, high capacity, coexistence

with other systems, ability of penetrating walls are some of the characteristics that make

this system very attractive for a Short Range Wireless Communications, such as

deployed in WLAN and WPAN [1]-[3]. This technology uses short pulses in order to

transmit large amounts of digital data over a wide spectrum of frequency bands with a

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SUMMARY CHAPTER 1

In this chapter, the fundamentals of UWB system are overviewed. Within the

following sections, topics covered are UWB history, features and applications of UWB

system, types of UWB signals, UWB spectrum and regulations and some of the possible

problems of this system.

1.2. UWB History

There is a comprehensive bibliography about the origins of the UWB technology

as in [5]-[34]. Dr. Henning F. Harmuth gave a descriptive history of no sinusoidal

electromagnetic technologies in [13]-[19]. In his work, it was found that in late 1950's,

there was a first effort made by Lincoln Laboratory and Sperry to develop phased array

radar system.

The analysis started in attempting to understand the wideband properties of the

needed network. The four-port interconnection of quarter wave TEM mode lines was

analysed.

The impulse response of these networks was a train of weighted and equally

spaced impulses, thus the response resembled what one would find at the output of a

sampled data system. About the same time, Schmidt and RWP King were measuring the

impulse response of the dipole and resonant ring radiating elements in the time domain.

The response in the far field and the driving ports was approximately a train of

uniformly spaced impulses that was well correlated with the work of Hallen. Dr. Hallen

found in the frequency domain that this class of radiating element had a periodic

amplitude spectrum. This fact made clear that working in the time domain, was correct

for analysis and provided a challenge. With the help of Dr. Barney Oliver at Hewlett

Packard, who had just developed the sampling oscilloscope, and the generation of very

short pulses using avalanche transistors and tunnel diodes, the UWB technology started

to evaluate. The former Sperry Research Centre Sudbury then continued the work, in

1965 where this writer formed a group of very talented engineers to help with the

further development of this technology. Dr. J. Lamar Allen expanded the analysis of

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CHAPTER 1 SUMMARY

Harry Cronson later extended the work to time domain metrology where the frequency

domain properties of passive microwave networks were found via their impulse

response and Fourier transforms (FT). Both the US Air Force at Rome Labs and the US

Army in Huntsville, Alabama supported this work. At this time, Drs. David Lamensdorf

and Leon Susman started the analysis of antennas using time domain techniques.

The final task that needed to be developed before real system development

began was the threshold receiver. In the early 1970's both avalanche transistor and

tunnel diode detectors were constructed in an attempt to detect these very short duration

signals. Dr. A. Murray Nicolson of the tunnel diode constant false alarm rate receiver

improved this work in the development. This improved version of this receiver detector

is still in use today. With all the system blocks in place, a short-range radar sensor was

developed as a pre-collision sensor for the airbag and used later in cars (1972). The

range of this sensor was about 8 feet. Later improvements in power generation

techniques resulted in a space docking radar (25-30 feet) and an aircraft runway traffic

sensor with a range of 300 feet. Many systems that require different range requirements

were developed, including a new class of altimeters. In the metrology area (1970-1980),

this writer together with Dr. Nicolson developed a narrow base band pulse fixture to

measure the properties of microwave absorbing materials directly from a single pulse

measurement. Most of the development of those stealthy materials done at Wright

Patterson AFB used this approach until the Hewlett Packard network analyzer became

available. This was used to develop an anti-collision system for unmanned vehicles in

work and later this technique was expanded to measure liquid levels in a tank.

Work in radar continued in the 1990's with the development of synchronized

arrays of short pulse sources. Peak powers in the order of 100 kW (peak base band

power) were achieved using low cost sources designed to radiate and scan in space

microwave pulse packets having pulse durations on the order of 1-3 ns. These systems

were used for the detection applications.

In 1978, efforts turned toward the communication of these signals. Voice signals

were transmitted reliably over hundreds of feet without the need for synchronization and

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SUMMARY CHAPTER 1

greater ranges using the 19 kHz sub carrier from classical music frequency modulated

stations in urban areas.

During the period 1984-1994, the work in communications was considerably

expanded working together with Dr. Robert J. Fontana.

Until now, over 200 papers were published in accredited IEEE journals and

more than 100 patents were issued on topics related to ultra wideband technology. Due

to the reach area of applications, the business interests for UWB technology are growing

exponentially.

1.3. Features and Applications of UWB

Since the duration of used monopulses is extremely short, there are many

features of the UWB system, summarized as follows:

• High data rate performance

This is important for communications where UWB pulses can be used to provide

extremely high data rate performance in multi-user network applications.

• Fine range resolution and precision distance

This fact allows quality for radar applications [35], [36].

• Multipath resistance

Consequently, UWB systems are well suited for high-speed, mobile wireless

applications. Multipath cancellation occurs when a strong reflected wave arrives

out of phase with the direct path signal, producing a reduced amplitude response

in the receiver. With very short pulses, the direct path has come and gone before

the reflected path arrives avoiding the cancellation. In addition, implementation

of the RAKE receiver improves multipath resistance [36], [38].

• Low interference with other systems

This fact is significant for both military and commercial applications, since this

low energy density translates into a low probability of detection (LPD) RF

signature. An LPD signature is of particular interest for military applications

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CHAPTER 1 SUMMARY

produces minimal interference to proximity systems and minimal RF health

hazards as it was shown in [39], [40].

• Low system complexity and low cost

UWB systems can be made nearly "all-digital", with minimal RF or microwave

electronics. Due to the inherent RF simplicity of UWB designs, these systems

are highly frequency adaptive, enabling them to be positioned anywhere within

the RF spectrum. According to [39], this feature avoids interference to existing

services, while fully utilizing the available spectrum.

• The UWB system always occupies a wide bandwidth (order of GHz)This

insures a high capacity multiple access and ultra high-speed transmission (<

Several hundreds of Mbps). According to the classification of [41], applications

of the UWB system can be divided on military and civil. In the military and

government marketplace, these applications include:

• Tactical Handheld & Network LPI/D Radios

• Non-LOS LPI/D Ground wave Communications

• LPI/D Altimeter/Obstacle Avoidance Radar

• Tags (facility and personal security, logistics)

• Intrusion Detection Radars

• Precision Geolocation Systems

• Unmanned Aerial Vehicle (UAV) and Unmanned Ground Vehicle (UGV)

• Data links

• LPI/D Wireless Intercom Systems

While civil applications include:

• High Speed (20+ Mb/s) LAN/WANs

• Altimeter/Obstacle Avoidance Radars (commercial aviation) Collision

Avoidance Sensors

• Tags (Intelligent Transportation Systems, Electronic Signs)

• Intrusion Detection Radars

• Precision Geolocation Systems

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SUMMARY CHAPTER 1

As for the commercial marketplace, however, there are currently no "approved"

applications within the United States, since the frequency approval for UWB operation

has yet to be acted upon by the Federal Communications Commission (FCC).

1.4. UWB Signal Definition

In order to define an UWB signal, the following definition for the fractional

bandwidth is employed:

2 H L

f

H L

f f

B

f f

− =

+

(1.1)

where f_L and f_H represent the lower and upper frequencies (3 dB points) of the signal

spectrum, respectively. Thus, as it was defined in [41] and [42], UWB signals are

signals that have a fractional bandwidth greater than 25% in contrast to narrowband

signals with fractional bandwidth less than 1%. Figure 1.1 presents the comparison of

the Fractional Bandwidth of a Narrowband and Ultra wideband communications

systems.

1.4.1. Types of UWB Signals

There are two forms of UWB. First is IR-UWB, based on transmitting

information sending a very short duration pulses and the second is MC-UWB, based on

using multiple simultaneous carriers.

1.4.1.1. IR-UWB Versus MC-UWB

The relative advantages and disadvantages of those two types of signal are

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CHAPTER 1 SUMMARY

One of the issues is minimizing interference transmitted by, and received by the

UWB system. In MC-UWB it is possible to choose carrier frequencies to avoid

narrowband interference or from narrowband system. Therefore, it might be considered

Figure 1.1 Comparison of the Fractional Bandwidth of a Narrowband and Ultra

Wideband Communication System

that MC-UWB is well suited for avoiding interference. The most common form of

multicarrier modulation, OFDM, has become the leading modulation for high data rate

systems.

In addition, MC-UWB vs. IR-UWB is more flexible and scalable, but requires

an extra layer of control in the physical layer. However, for both types of UWB signals,

IR-UWB and MC-UWB spread spectrum techniques can be applied in order to reduce

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SUMMARY CHAPTER 1

IR-UWB signals need fast switching time for the transmitter and receiver and

very high precise synchronization between them. Since IR-UWB has a high

instantaneous power during the very short interval of the pulse, it can better avoid

interference to UWB systems, but, on the other hand, this high instantaneous power

increases the possibility of interference from UWB to narrowband systems. In addition,

IR-UWB are very low-cost systems since they can be made nearly "all-digital", with

minimal RF or microwave electronics.

Figure 1.2. Spectrum of a Gaussian Monocycle- Based Impulse UWB Signal (Data

taken from [48])

On the other hand, MC-UWB systems have a number of advantages over their

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CHAPTER 1 SUMMARY

therefore higher bit communications. In addition, MC-UWB has simpler channel

synchronizations, which leads to low-cost transceiver implementation and has the

continuous variations in power over a very wide bandwidth. Therefore, implementing a

MC-UWB front end can be challenging. This might be particularly challenging for the

power amplifier. UWB-OFDM is a novel MC-UWB system that uses a frequency

hopping scheme for reliable high bit rate communication over multi-path fading

channels [46]. The main advantage of UWB-OFDM system over normal OFDM is its

fine time resolution and ability to resolve multipath. Changing a frequency selective to

several parallel flat fading channels, OFDM system has not such high multipath

resistance [47].

Figure 1.2 and Figure 1.3 illustrates a comparison of the spectrum of IR-UWB

and MC-UWB, respectively.

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SUMMARY CHAPTER 1

1.5. UWB Compatibility with Other Services

UWB technology offers simultaneously high data rate communication and high

accuracy positioning capabilities as it was mentioned before. These systems can utilize

low transmitted signal power level with extremely wide bandwidth. Due to the very low

PSD, UWB systems can co-exist with the other radio systems.

The FCC recently approved the deployment of UWB on an unlicensed basis in

the 3.1–10.6 GHz band [49]. The essence of this ruling is to limit the PSD measured in a

MHz bandwidth. UWB spectral mask and FCC part 15 limits are shown in Figure 1.4.

Figure 1.4. UWB Spectral Mask and FCC Part 15 Limits. (Data taken from [49])

The spectral mask allows UWB enabled devices to overlay existing systems

while ensuring sufficient attenuation to limit adjacent channel interference. Additional

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CHAPTER 1 SUMMARY

The first consequence of this spectral mask imposed by the FCC is to express the use of

base band pulse shapes without additional transmit filtering.

Figure 1.5. WPAN, WLAN, and Cellular Networks: Typical Link Ranges. (Data taken

from [49])

In summary, UWB communications are allowed at a very low average transmit

power compared to more conventional (narrowband) systems that effectively restricts

UWB to short ranges [50]. UWB is thus, a candidate physical layer mechanism for

IEEE 802.15 WPAN for short-range high-rate connectivity that complements other

wireless technologies in terms of link ranges. Typical Link Ranges limits of WPAN,

WLAN, and Cellular Networks is shown in Figure 1.5. One of the main problems,

according to the compatibility, is interference caused by UWB signals to other various

radio systems, as well as the performance degradation of UWB systems in the presence

of narrowband interference and pulsed jamming. An UWB system suffers most from

PAN

LAN

WAN

Short-Range

Range

0-10m 0-100m 0-1

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SUMMARY CHAPTER 1

narrowband systems if the narrowband interference and the nominal centre frequency of

the UWB signal are overlapping. This is proved in [41] by BER simulations in an AWGN channel with interference at global system for GSM and UMTS/WCDMA

frequencies. In the in-band interference study, the victim radio systems are

UMTS/WCDMA, GSM900, and GPS. It is shown that better results are achieved with

proper selection of UWB pulse waveform and their width for spectral planning. Using

short pulses, interference in the observed frequency bands is the smallest if the pulse

waveform is based on higher order Gaussian waveforms.

When the UWB system degradation is studied in the presence of an interfering

and jamming radio system, results show that the system performance suffers most if the

interference and the nominal centre frequency of the UWB system are overlapping.

Thus, the UWB performance depends on the pulse waveform and on the pulse width. It

is shown that for high data rates, short pulses should be used. Additionally, it is shown

that the third derivative of the Gaussian pulse performs better than the first derivative.

On the other hand, if the data rate demands are not so high, and long pulses can be used,

then lower order waveforms perform better.

1.6. UWB Problems

As with any technology, there are always applications that may be better served

by other approaches. Therefore, there are still some problems related to UWB systems.

• In order to process ultra-wideband signals, it is necessary to have an extremely large sampling rate.

As it was mentioned in the abstract, in a straightforward approach, with the constant

sampling rate, the length of the array that contains the bit samples can be very large,

depending on the relationship between the duty cycle and a bit rate. Since this array

should pass through the chain of blocks that model the channel and receiver responses,

it is obvious that a large number of convolutions should be done. Thus, even in very fast