RADIO WAVE PROPAGATION AND SMART ANTENNAS FOR WIRELESS COMMUNICATIONS

RADIO WAVE PROPAGATION AND SMART ANTENNAS FOR WIRELESS COMMUNICATIONS

THE KLUWER INTERNATIONAL SERIES IN ENGINEERING AND COMPUTER SCIENCE

RADIOWAVE PROPAGATION AND SMART ANTENNAS FOR WIRELESS COMMUNICATIONS by Ramakrishna Janaswamy Naval Postgraduate School Monterey, CA, U.S.A. KLUWER ACADEMIC PUBLISHERS NEW YORK, BOSTON, DORDRECHT, LONDON, MOSCOW

0-306-46990-1 0-792-37241-7 1

Contents Preface FUNDAMENTALS OF CELLULAR RADIO 4. 5. The Cellular Concept Multiple Access Schemes Traffic Engineering PRINCIPLES OF RADIOWAVE PROPAGATION 4. 5. 6. Plane Waves Classification of Electromagnetic Media Free-Space Transmission Plane Wave Reflections from Planar Interface 5.1 Surface Roughness 5.2 Equivalent Impedance of a Random Rough Surface 5.3 Fresnel Zones Radio Horizons xiii 1 1 2 5 8 12 15 15 15 18 20 23 26 29 31 35

vi RADIOWAVE PROPAGATION & SMART ANTENNAS 7. 8. 9. 10. 1 Two Ray Model Over Flat Earth Effect of Obstacles 8.1 Diffraction by Knife Edge 8.2 Knife Edge Over Ground 8.3 Rounded Hills 3D Diffraction (UTD) Forward Propagation 35 39 39 45 49 51 55 64 MEDIAN SIGNAL PREDICTIONS 67 4. 5. 6. 7. Scales of Fading Statistical Distribution of the Median Signal Level 1 Effect of Vegetation 2 Effect of Street Orientation 3 Signal Attenuation in Tunnels Determination of Coverage Area from a Base Station Empirical Models for Path Loss 5.1 Hata Model for Macrocells 5.2 COST-231-Walfish-Ikegami Model 5.3 Empirical Model for Suburban Areas 5.4 Empirical Model for Microcells Longley-Rice Model: 6.1 Calculation of Effective Antenna Heights 67 67 70 71 74 75 76 82 82 84 88 90 92 93 96 4. CHARACTERIZATION OF SMALL SCALE FADING 99 Spatial Distribution of the Field 99 100

4. 1 2 3 4 5 6 7 Statistical Envelope Model Angle of Arrival and Signal Spectrum Contents Autocorrelation and Spectrum of Signal Envelope Level Crossing Rate and Average Fade Duration Random FM Ricean Fading Spatial Correlation of Field vii 100 102 108 117 124 128 129 131 137 5. WIDEBAND CHARACTERIZATION OF THE RADIO CHANNEL 4. 5. 6. 7. 8. 9. A Simple Two-Ray Model Linear System Description 1 2 3 4 Input Delay Spread Function Time Variant Transfer Function Output Doppler Spread Function Delay-Doppler Spread Function Random Time-Variant Communications Channels Classification of Channels 5.1 5.2 5.3 5.4 Wide-Sense Stationary Channel Uncorrelated Scattering WSSUS Channels Scattering Function Description of Mobile Radio Channel Wideband Impulse Response of the Radio Channel Power Delay Profile Frequency Selectivity of Channel 141 141 142 144 145 146 147 147 148 148 149 149 150 151 153 156 159 160

viii RADIOWAVE PROPAGATION & SMART ANTENNAS 6. GEOMETRIC MODELS FOR ANGLE AND TIME OF ARRIVAL 4. 5. 6. General Formulation Elliptical Scattering Model Circular Scattering Model Gaussian Scatter density 7. SPATIAL DIVERSITY 4. 5. 6. 7. 8. 9. 10. 1 General Receive Array Theory Combining Techniques Selection Combining Maximal Ratio Combining Equal Gain Combining Diversity Gain Antenna Gain Effect of Branch Correlation Mutual Coupling 8. SMART ANTENNAS Capacity Increase with Switched Beam Antenna 1 2 3 4 Effect of Shadowing and Fading on Frequency Reuse Regions of Interference Six Co-channel Interferers Capacity of Switched Beam Antenna under Shadowing and Fading 163 163 164 167 171 177 184 185 185 186 189 192 195 200 202 203 205 207 212 219 219 222 225 229 231 235

Adaptive Antennas 1 2 3 4 5 6 4. Interference Cancellation Optimal Weights for Narrowband Case Statistics of the output CINR Capacity Improvement in CDMA Weight Generation Reference Signal Generation 9. MULTIPLE INPUT MULTIPLE OUTPUT WIRELESS COMMUNICATIONS MIMO Channel Capacity 1 2 3 4 5 Appendices SISO Channel N-Parallel Transmission Lines SIMO Channel General Rayleigh Faded Matrix Channel Practical Considerations A Numerical Generation of a Random Process B Wideband Channel Model for N-Element Array C Distribution of Hermitian Quadratic Forms in Complex Gaussian Variates Matrix Preliminaries Transformation of Variables P.D.F. of Hermitian Quadratic Form Contents ix 239 240 244 251 258 262 265 265 269 269 270 272 273 275 276 278 278 279 279 287 293 293 294 296

x Index RADIOWAVE PROPAGATION & SMART ANTENNAS 311

One quarter of knowledge is attained from the Teacher One quarter is attained by one s own intelligence and effort One quarter is attained from fellow students One quarter is completed in time (sic. asymptotically).

Preface This book emerged from teaching a graduate level course in propagation and smart antennas at the Naval Postgraduate School. In its present form, it is suitable not only as a graduate level text, but also as a reference book for industry and research use. The area of radiowave propagation and smart antennas is highly interdisciplinary, extracting material from electromagnetics, communications, and signal processing. This book is useful to workers in electromagnetics who would like to supplement their background with relevant communicational aspects and to workers in communications who would like to supplement their background with relevant electromagnetic aspects. Anyone with a basic understanding of probability, wave propagation, digital communications, and elementary signal processing should be able to appreciate the contents of the book. The book consists of nine chapters with several worked out examples dispersed throughout. Chapter 1 covers the basics of cellular communications. Chapter 2 covers the basic principles of electromagnetic wave propagation relevant to path loss predictions in wireless communications. Students with little prior background in electromagnetics should find the first few sections of Chapter 2 self-sufficient. Empirical path loss models that are used in system design are treated in Chapter The chapter includes the traditional models as well as some of the newer models. Chapter 4 has a thorough discussion on the causes and characterization of small scale fading. The topic of spatial correlation that is very important for antenna arrays is discussed there in detail. Chapter 5 deals with a wideband characterization of the fading radio channel. The idea of characterizing the radio channel in terms of a linear time-varying filter is brought out in the chapter. Geometrically based single scattering models that are useful for developing spatial channel models for smart antennas

xiv RADIOWAVE PROPAGATION & SMART ANTENNAS applications are discussed in Chapter 6. The chapter includes some new results that have not yet appeared in the literature. Spatial diversity is usually employed to mitigate the ill-effects of fading. A thorough discussion of spatial diversity, together with the effects of antenna mutual coupling and element correlation, is presented in Chapter 7. Chapter 8 has a detailed discussion on the currently hot topic of switched beam and adaptive antennas. Detailed system performance results, including the effects of fading and shadowing for TDMA and CDMA, are presented in that chapter. A totally new viewpoint of exploiting multipath has emerged recently, wherein, multiple sensors placed at both the transmitter and receiver end result in unprecedented bit rates in a wireless medium. The principles of such MIMO communication system, with emphasis on information-theoretic channel capacity, are introduced in Chapter 9. A one quarter graduate course consisting of 11 weeks may cover selected topics from Chapters 2-5, and Chapters 7-8. For instance, at our School, students were taught the following topics, after having been exposed to a previous course in wireless communications covering the topics of Chapter 1 and wireless standards, Chapter 2: Chapter 3: All sections Chapter 4: Chapter 5: All except Chapter 7: Chapter 8: Problems are included at the end of every chapter to aid the student in learning basic material as well as in preparing for more advanced topics. The reference list at the end of the book is by no means complete. Any omissions are inadvertent and are entirely due to the author s ignorance. I am open to criticism and would appreciate if any glaring errors are brought to my attention. I hope that this book satisfies the curiosity of students and working professionals alike in the subject area. I would like to thank our Department Chairman, Professor Jeffrey Knorr for providing me with an opportunity to offer the course material at the Naval Postgraduate School. I would like to thank my publisher, Jennifer Evans, for encouraging me to take up this project and for letting me slip by the deadlines at several instances. My students LCDR Mario Silva and LCDR Leonardo Mattos deserve thanks for pointing out some errors in the original manuscript. Thanks are also due to Jim Alien, Naval Postgraduate School, for drawing a

Preface number of figures in the book. I must thank my Sanskrit teacher, Dr. Sarasvati Mohan, for providing me with the Sanskrit quotation found in the book. My wife and daughter deserve special mention for letting me to be confined to my office for long hours every day, without which, this book could not have been completed. xv R. JANASWAMY Monterey, August 2000

To the ladies in my life: Revathi, Bharathi, and Sarala.