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  • i

    Indoor Cooperative Localization for Ultra

    Wideband Wireless Sensor Networks

    A Dissertation

    Submitted to the Faculty

    of the

    WORCESTER POLYTECHNIC INSTITUTE

    in partial fulfillment of the requirements for the

    Degree of Doctor of Philosophy

    in

    Electrical and Computer Engineering

    by

    __________________________________

    Nayef Alsindi

    April 2008

    APPROVED

    ____________________

    Prof. Kaveh Pahlavan, Advisor

    ________________________

    Prof. Fred J. Looft, Head, ECE Department

  • ii

    To My Wife

  • i

    Abstract

    In recent years there has been growing interest in ad-hoc and wireless sensor networks

    (WSNs) for a variety of indoor applications. Localization information in these networks

    is an enabling technology and in some applications it is the main sought after parameter.

    The cooperative localization performance of WSNs is ultimately constrained by the

    behavior of the utilized ranging technology in dense cluttered indoor environments.

    Recently, ultra-wideband (UWB) Time-of-Arrival (TOA) based ranging has exhibited

    potential due to its large bandwidth and high time resolution. However, the performance

    of its ranging and cooperative localization capabilities in dense indoor multipath

    environments needs to be further investigated. Of main concern is the high probability of

    non-line of sight (NLOS) and Direct Path (DP) blockage between sensor nodes, which

    biases the TOA estimation and degrades the localization performance.

    In this dissertation, we first present the results of measurement and modeling of UWB

    TOA-based ranging in different indoor multipath environments. We provide detailed

    characterization of the spatial behavior of ranging, where we focus on the statistics of the

    ranging error in the presence and absence of the DP and evaluate the pathloss behavior in

    the former case which is important for indoor geolocation coverage characterization.

    Parameters of the ranging error probability distributions and pathloss models are

    provided for different environments: traditional office, modern office, residential and

    manufacturing floor; and different ranging scenarios: indoor-to-indoor (ITI), outdoor-to-

    indoor (OTI) and roof-to-indoor (RTI).

  • ii

    Based on the developed empirical models of UWB TOA-based OTI and ITI ranging, we

    derive and analyze cooperative localization bounds for WSNs in the different indoor

    multipath environments. First, we highlight the need for cooperative localization in

    indoor applications. Then we provide comprehensive analysis of the factors affecting

    localization accuracy such as network and ranging model parameters.

    Finally we introduce a novel distributed cooperative localization algorithm for indoor

    WSNs. The Cooperative LOcalization with Quality of estimation (CLOQ) algorithm

    integrates and disseminates the quality of the TOA ranging and position information in

    order to improve the localization performance for the entire WSN. The algorithm has the

    ability to reduce the effects of the cluttered indoor environments by identifying and

    mitigating the associated ranging errors. In addition the information regarding the

    integrity of the position estimate is further incorporated in the iterative distributed

    localization process which further reduces error escalation in the network. The simulation

    results of CLOQ algorithm are then compared against the derived G-CRLB, which shows

    substantial improvements in the localization performance.

  • iii

    Acknowledgements

    I am extremely grateful to Professor Kaveh Pahlavan for his support and guidance

    throughout my graduate studies. What I have learned from him was truly beyond

    academics and research for he has spurred the growth of my professional career. I have

    learned from his experiences and stories that carry many lessons in dealing with lifes

    choices and struggles. I am sure that I will always revisit them to seek inspiration.

    I would like to thank my dissertation committee members, Professor John Orr,

    Professor Allen Levesque, Professor Alexander Wyglinski and Professor Xinrong Li for

    their valuable suggestions, comments and encouragements.

    My graduate experience at WPI was simply remarkable and for that I have to thank

    and acknowledge my best friends who shared with me all my setbacks and successes

    throughout the last 6 years. They are Engin Ayturk, Mohammad Heidari, Hamid

    Ghadyani, Bardia Alavi, Erdinc Ozturk, and Ferit Akgul.

    Finally, my accomplishments were only possible because of my wifes continuous

    support, encouragement and motivation. Dr. Abeer Al-naqbi has provided me with the

    strength to persevere and succeed in the face of many adversities. I am also indebted to

    my father, Dr. Ali Alsindi and mother Mrs. Manar Fakhri for their support and

    investment in my upbringing and education. Also I would like to thank my brother and

    sisters who are also my best friends: Dr. Fahad Alsindi, Noora Alsindi and Muneera

    Alsindi.

  • iv

    Table of Contents

    Abstract .......................................................................................................................... i

    Acknowledgements .......................................................................................................... iii

    Table of Contents ............................................................................................................. iv

    List of Figures.................................................................................................................. vii

    List of Tables .................................................................................................................... xi

    Chapter 1 Introduction................................................................................................... 1

    1.1. Localization in Wireless Sensor Networks ......................................................... 1

    1.2. Background and Motivation ............................................................................... 3

    1.3. Contributions of the Dissertation ........................................................................ 8

    1.4. Outline of the Dissertation .................................................................................. 9

    Chapter 2 Node Localization in Indoor Environments: Concepts and Challenges 11

    2.1. Evolution of Localization Techniques .............................................................. 11

    2.2. Localization Systems ........................................................................................ 13

    2.3. Popular Ranging Techniques ............................................................................ 16

    2.3.1. TOA-based Ranging ................................................................................. 16

    2.3.2. RSS-based Ranging .................................................................................. 20

    2.4. Wireless Localization Algorithms .................................................................... 21

    2.4.1. Background ............................................................................................... 21

    2.4.2. Least Squares (LS) Algorithm .................................................................. 23

    2.4.3. Weighted Least Squares (WLS) Algorithms ............................................ 26

    2.5. Practical Performance Considerations .............................................................. 26

    2.6. Cooperative Localization in WSNs .................................................................. 28

    2.6.1. Background ............................................................................................... 28

    2.6.2. Cooperative Localization Techniques....................................................... 31

    2.6.3. Challenges Facing Distributed Localization Algorithms.......................... 32

    Chapter 3 UWB TOA-based Ranging: Concepts, Measurements & Modeling ...... 35

    3.1. Background ....................................................................................................... 35

    3.2. UWB TOA-based Ranging Concepts ............................................................... 38

  • v

    3.2.1. Ranging Coverage..................................................................................... 40

    3.2.2. Ranging Error............................................................................................ 42

    3.2.3. Factors Affecting Ranging Coverage and Accuracy ................................ 44

    3.3. UWB Measurement Campaign ......................................................................... 45

    3.3.1. Background ............................................................................................... 45

    3.3.2. Measurement System................................................................................ 45

    3.3.3. Measurement Locations and Procedure .................................................... 46

    3.3.4. Post-Processing ......................................................................................... 49

    3.4. Modeling the Pathloss....................................................................................... 50

    3.5. Modeling the Ranging Error ...............................................

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