Luận Văn The Impact of Signal Bandwidth on Indoor Wireless Systems in Dense Multipath Environments

Abstract


Recently there has been a significant amount of interest in the area of wideband
and ultra-wideband (UWB) signaling for use in indoor wireless systems. This interest is
in part motivated by the notion that the use of large bandwidth signals makes systems less
sensitive to the degrading effects of multipath propagation. By reducing the sensitivity to
multipath, more robust and higher capacity systems can be realized. However, as signal
bandwidth is increased, the complexity of a Rake receiver (or other receiver structure)
required to capture the available power also increases. In addition, accurate channel
estimation is required to realize this performance, which becomes increasingly difficult as
energy is dispersed among more multipath components.

In this thesis we quantify the channel response for six signal bandwidths ranging
from continuous wave (CW) to 1 GHz transmission bandwidths. We present large scale
and small scale fading statistics for both LOS and NLOS indoor channels based on an
indoor measurement campaign conducted in Durham Hall at Virginia Tech. Using newly
developed antenna positioning equipment we also quantify the spatial correlation of these
signals. It is shown that the incremental performance gains due to reduced fading of
large bandwidths level off as signals approach UWB bandwidths. Furthermore, we
analyze the performance of Rake receivers for the different signal bandwidths and
compare their performance for binary phase modulation (BPSK). It is shown that the
receiver structure and performance is critical in realizing the reduced fading benefit of
large signal bandwidths. We show practical channel estimation degrades performance
more for larger bandwidths. We also demonstrate for a fixed finger Rake receiver there
is an optimal signal bandwidth beyond which increased signal bandwidth produces
degrading results.

Acknowledgments

At this time I would like to thank Michael Buehrer, William Davis, Jeffery Reed, and
Raqib Mostafa for serving on my advisory committee and providing technical expertise
as well as encouragement along the way. I would also like to acknowledge the Via
family for the generous endowment provided by the Harry Lynde Bradley Fellowship
which allowed me to pursue this research almost completely un-tethered from the reins.
I would also like to express my appreciation to my fellow graduate students in MPRG,
especailly Joseph Gaeddert, Chris Anderson, Brian Donlan, Vivek Bharadwaj, Aaron
Orndorf and John Keaveny for their thought provoking discussions and technical
assistance with this research. Also my appreciation goes to Samir Ginde, Carlos Aguayo,
Nathan Harter and my other lab mates for keeping things in perspective while working at
MPRG. Of the MPRG staff, which was extremely helpful, I would like to thank Mike
Hill, Shelby Smith, Hilda Reynolds, and Shereef Sayed.

I am greatly indebted to Mike Coyle and the staff of the Industrial Design Metal Shop for
their help in designing and manufacturing the antenna positioning system. Without
Mike’s support the positioning system would not have proceeded beyond the conceptual
stage. For donating replacement couplers for the positioning system I would like to thank
the staff at Ruland. I also owe thanks to Josiah Hernandez for helping with the
measurement campaign. I must also thank Dennis Sweeney from CWT and Carl Dietrich
from VTAG for their insight and use of their equipment during the measurement
campaign.

I owe a very special thanks to Alexander Taylor, who has been my partner in Electrical
Engineering crime for the past five years at Virginia Tech and has been an honest friend
through it all. Also the friendships forged with Aaron Orndorf and Jeremy Barry have
made this experience an interesting one to say the least.
Without a doubt none of this work would have been possible without the tireless support
and understanding of my fiancé and soon to be wife Ashley K. Rentz. Her
encouragement, wisdom, and unwavering love were instrumental in completing this
work; thank you for understanding.
Finally, I would like to thank my parents Bob and Louise Hibbard, as well as my brother
Mark Hibbard for their generous support, love, and understanding throughout this work
as well as my entire life.


Table of Contents
CHAPTER 1
INTRODUCTION AND THESIS OVERVIEW .1
1.1 Motivation 1
1.2 Background and Perspective . 2
1.3 Thesis Overview . 3
CHAPTER 2
RADIO WAVE PROPAGATION AND THE INDOOR PROPAGATION
CHANNEL 5
2.1 Introduction . 5
2.2 Propagation Overview . 6
2.2.1 Antennas and Radiation . 6
2.2.2 Propagation Mechanisms . 9
2.2.3 The Friis Transmission Formula and Basic Communication Link 14
2.3 The Indoor Propagation Channel . 17
2.3.1 Large Scale Effects . . 17
2.3.2 Small Scale Effects . . 19
2.4 Multipath Mitigation Techniques . 30
2.4.1 Basic Diversity Methods . 30
2.4.2 The Rake Receiver – An Overview . 31
2.5 Impact of Signal Bandwidth on Indoor Wireless Systems – Literature Review . 32
2.6 Summary . . 38
CHAPTER 3
SLIDING CORRELATOR CHANNEL MEASUREMENT: THEORY AND
APPLICATION . .40
3.1 Introduction . 40
3.2 Overview of Channel Measurement Techniques . 40
3.3 Sliding Correlator Theory and Operation . 42
3.3.1 Cross Correlation Theory 42
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3.3.2 Pseudorandom Noise Sequences and Generators 44
3.3.3 Swept Time Delay Cross Correlation (Sliding Correlator) Theory . 46
3.3.4 Practical Considerations in the Sliding Correlator Measurement System . 51
3.4 Implementation of a Sliding Correlator Measurement System . 53
3.4.1 Transmitter and Receiver Implementation 53
3.4.2 System Calibration 56
3.4.3 System Repeatability . 58
3.5 Mapping Power Delay Profiles to Received Power . 59
3.6 Summary . . 61
CHAPTER 4
DESIGN AND IMPLEMENTATION OF AN ANTENNA POSITIONING AND
ACQUISITION SYSTEM .62
4.1 Introduction . 62
4.2 Positioning System Design Issues 62
4.2.1 Approaches to Antenna Positioning 63
4.2.2 Overall System Constraints . 64
4.2.3 Electrical Impact of Positioning System . 66
4.3 Positioning System Design and Implementation . 67
4.3.1 Design . 67
4.3.2 Implementation . 73
4.4 Antenna Positioning and Acquisition (APAC) Software 74
4.4.1 Defining the 2-D Measurement Grid . 75
4.4.2 Software Implementation Using Labview . 77
4.4.3 Additional Functionality . . 81
4.5 Positioning System Verification and Calibration 83
4.6 Conclusion 85
CHAPTER 5
INDOOR PROPAGATION MEASUREMENTS AND RESULTS AT 2.5 GHZ 86
5.1 Measurement Overview . 86
5.2 Measurement Campaign 86
5.2.1 Omnidirectional Biconical Antennas . 86
5.2.2 Narrowband (CW) Channel Sounder Configuration . 87
5.2.3 Wideband (Sliding Correlator) Channel Sounder Configuration 88
5.2.4 Measurement Procedure 90
5.2.5 Measurement Locations and Site Information . 91
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5.3 Measurement Results and Processing 95
5.3.1 Large Scale Results . 95
5.3.2 Small Scale Results . 99
5.3.3 A Note on Site Specific Phenomena . . 118
5.4 Conclusion 121
CHAPTER 6
IMPACT OF SIGNAL BANDWIDTH ON INDOOR COMMUNICATION
SYSTEMS . 122
6.1 Introduction . 122
6.2 Overview of BPSK Modulation and BER in AWGN 122
6.3 BER performance for BPSK in Measured Channels 124
6.4 Required Fading Margin for Quality of Service . 128
6.5 Spatial Correlation and Two Antenna Selection Diversity . 130
6.6 Rake Receiver Implementation and Channel Estimation . 132
6.6.1 Rake Receiver Performance – Perfect Channel Estimation . 133
6.6.2 Rake Receiver Performance – Imperfect Channel Estimation 134
6.6.3 Selective Rake Receiver Performance . 138
6.6.4 Selective Rake Receiver Performance with Channel Estimation 142
6.7 Conclusions 144
CHAPTER 7
CONCLUSIONS .145
7.1 Summary of Findings . 145
7.1.1 Impact of Spreading Bandwidth on Channel Characteristics 145
7.1.2 Impact of Spreading Bandwidth on DS-SS BPSK Indoor Systems 146
7.1.3 Original Contributions and Accomplishments 146
7.2 Further Areas of Research 147
7.2.1 On the Impact of Spreading Bandwidth 147
7.2.2 On the Use and Processing of Sliding Correlator Measurements 147
7.3 Closing . . 148
APPENDIX A