Wireless Communications: Principles and Practice by Theodore S. Rappaport

From the Publisher

The indispensable guide to wireless communications—now fully revised and updated!

Wireless Communications: Principles and Practice, Second Edition is the definitive modern text for wireless communications technology and system design. Building on his classic first edition, Theodore S. Rappaport covers the fundamental issues impacting all wireless networks and reviews virtually every important new wireless standard and technological development, offering especially comprehensive coverage of the 3G systems and wireless local area networks (WLANs) that will transform communications in the coming years. Rappaport illustrates each key concept with practical examples, thoroughly explained and solved step by step. Coverage includes:

• An overview of key wireless technologies: voice, data, cordless, paging, fixed and mobile broadband wireless systems, and beyond
• Wireless system design fundamentals: channel assignment, handoffs, trunking efficiency, interference, frequency reuse, capacity planning, large-scale fading, and more
• Path loss, small-scale fading, multipath, reflection, diffraction, scattering, shadowing, spatial-temporal channel modeling, and microcell/indoor propagation
• Modulation, equalization, diversity, channel coding, and speech coding
• New wireless LAN technologies: IEEE 802.11a/b, HIPERLAN, BRAN, and other alternatives
• New 3G air interface standards, including W-CDMA, cdma2000, GPRS, UMTS, and EDGE
• Bluetooth wearable computers, fixed wireless and Local Multipoint Distribution Service (LMDS), and other advanced technologies
• Updated glossary of abbreviations and acronyms,and a thorough list of references
• Dozens of new examples and end-of-chapter problems

Whether you're a communications/network professional, manager, researcher, or student, Wireless Communications: Principles and Practice, Second Edition gives you an in-depth understanding of the state of the art in wireless technology—today's and tomorrow's.

Product Details

• Table of Contents
• Forewords & Introductions
• Read an Excerpt

Table of Contents

Forewords & Introductions

The second edition of this text has been written to initiate the newcomer to wireless personal communications, one of the fastest growing fields in the engineering world. Technical concepts which are at the core of design, implementation, research, and invention of wireless communication systems are presented in an order that is conducive to understanding general concepts, as well as those specific to current and evolving wireless communication systems and standards. This text is based upon my experiences as an educator, researcher, technical trainer, and consultant, and continues to be modeled from an academic course first developed for electrical engineering students in 1990, when there were fewer than five million cellular subscribers worldwide. As we begin the 21st century, more than 600 million people, about 10% of the worldUs population, pay a monthly subscription for wireless telephone service, and this figure will approach 50% by the end of the first decade of the 21st century.

This text continues to evolve, and has been modified and updated since its first edition, making it a useful book for practicing engineers, as well as for researchers, graduate students, and undergraduate students. The text has been prepared to provide fundamental treatment about many practical and theoretical concepts that form the basis of wireless communications, and has been designed for easy but thorough treatment of vital material that all wireless practitioners must be comfortable with. I have tried to emphasize the technical concepts with worked example problems, and numerous, carefully crafted homework problems at the end of each chapter that are based on real-worldindustry issues. The second edition contains dozens of new homework problems and examples, as well as up-to-the minute technical details of the many emerging wireless standards throughout the world, making this book particularly useful for industry short-courses or state-of-the-art academic classroom use.

References to journal articles are used liberally throughout this text to enable the interested reader to delve into additional reading that is always required to master any field. To support newcomers to the wireless field, and at the request of the Institute of Electrical and Electronics Engineers (IEEE), I have also prepared a low-cost two volume compendium of many of the original journal articles that first taught the fundamentals that are now used throughout the wireless industryQthis compendium series is a useful, but not required, supplement to this text. Whether you intend to use this book for individual study, or for classroom use, or for use as a handbook, this text has been written as a complete, self-contained teaching and reference book. The numerous examples and problems found throughout the text have been provided to help the reader solidify the material.

This book has been designed for the student or practicing engineer who is already familiar with technical concepts such as probability, communication theory, and basic electromagnetics. However, like the wireless communications industry itself, this book combines material from many different technical disciplines, so it is unlikely that any one person will have had introductory courses for all of the topics covered. To accommodate a wide range of backgrounds, important concepts throughout the text are developed from first principles, so that readers learn the foundations of wireless communications. This approach makes it possible to use this book as a handbook or as a useful teaching tool in a classroom setting.

The material and chapter sequence in this text have been adapted from an entry-level graduate course which I first taught in 1991 at the Virginia Polytechnic Institute and State University. Chapter 1 demonstrates the historic evolution of the wireless communications industry, and the evolution of wireless systems from first generation analog to second generation (2G) digital systems. Chapter 1 also documents the rapid early growth of cellular radio throughout the world and provides a state of the industry in the mid 1990s. Chapter 2 provides an overview of the major modern wireless communication systems of the 21 st century, such as third generation (3G), Wireless Local Area Networks (WLANs), Local Multipoint Distribution Services (LMDS), and Bluetooth. Chapter 2 causes the reader to see how wireless networks are beginning to penetrate our daily lives for data and multimedia applications, as well as voice service. Chapter 3 covers fundamental cellular radio concepts such as frequency reuse and handoff, which are at the core of providing wireless communication service to subscribers on the move using limited radio spectrum. Chapter 3 also demonstrates the principal of trunking efficiency, and how trunking and interference issues between mobiles and base stations combine to affect the overall capacity of cellular systems. Chapter 4 presents radio propagation path loss, link-budgets, and log-normal shadowing, and describes different ways to model and predict the large-scale effects of radio propagation in many operating environments. Chapter 5 covers small-scale propagation effects such as fading, time delay spread, and Doppler spread, and describes how to measure and model the impact that signal bandwidth and motion have on the instantaneous received signal through the multipath channel. Radio wave propagation has historically been the most difficult problem to analyze and design for, since unlike a wired communication system which has a constant, stationary transmission channel (i.e., a wired path), radio channels are random and undergo shadowing and multipath fading, particularly when one of the terminals is in motion. New material in Chapter 5 also teaches a fundamental and new way of modeling spatial-temporal channels, which is vital for the development of smart antennas and position location systems.

Chapter 6 provides extensive coverage of the most common analog and digital modulation techniques used in wireless communications and demonstrates tradeoffs that must be made in selecting a modulation method. Issues such as receiver complexity, modulation and demodulation implementation, bit error rate analysis for fading channels, and spectral occupancy are presented. Channel coding, adaptive equalization, and antenna diversity concepts are presented in Chapter 7. In portable radio systems where people communicate while walking or driving, these methods may be used individually or in tandem to improve the quality (that is, reduce the bit error rate) of digital mobile radio communications in the presence of fading and noise.

Chapter 8 provides an introduction to speech coding. In the past decade, there has been remarkable progress in decreasing the needed data rate of high quality digitized speech, which enables wireless system designers to match end-user services to network architectures. Principles which have driven the development of adaptive pulse code modulation and linear predictive coding techniques are presented, and how these techniques are used to evaluate speech quality in existing and proposed cellular, cordless, and personal communication systems are discussed. Chapter 9 introduces time, frequency, and code division multiple access, as well as more recent multiple access techniques such as packet reservation and space division multiple access. Chapter 9 also describes how each access method can accommodate a large number of mobile users and demonstrates how multiple access impacts capacity and the network infrastructure of a cellular system. Chapter 10 describes networking considerations for wide area wireless communication systems, and presents practical networking approaches that are in use or have been proposed for future wireless systems. Chapter 11 unites all of the material from the first nine chapters by describing and comparing the major existing second generation (2G) cellular, cord-ess, and personal communication systems throughout the world. The tradeoffs made in the design and implementation of wireless personal communications systems are illuminated in this final chapter. The compilation of the major wireless standards makes Chapter 11 particularly useful as a single source of information for a wide range of wireless systems that are commercially deployed today.

Appendices which cover trunking theory, noise figure, noise calculations, and the Gaussian approximation for spread spectrum code division systems provide details for those interested in solving many practical wireless communications problems. The appendices also include hundreds of mathematical formulas and identities for general engineering work. I have attempted to place numerous useful items in the appendices, so that this text may be easily used by students or practicing engineers to solve a wide range of problems that may be outside the scope of the immediate text.

For industry use, Chapters 1P5, 9, and 11 will benefit working engineers in the cellular/PCS system design and radio frequency (RF) deployment, operations, and maintenance areas. Chapters 1, 2, 6P8, and 11 are tailored for modem designers and digital signal processing (DSP) engineers new to wireless. Chapters 1, 2, 10, and 11 should have broad appeal to network operators and managers, business and legal professionals, as well as working engineers.

To use this text at the undergraduate level, the instructor may wish to concentrate on Chapters 1P6, or Chapters 1P5, and 9, leaving the other chapters for treatment in a second semester undergraduate course or a graduate level course. Alternatively, traditional undergraduate courses on communications or network theory may find in Chapters 1, 2, 3, 4, 6, 8, 9, and 10 useful material that can be inserted easily into the standard curriculum. In using this text at the graduate level, I have been successful in covering most of the material in Chapters 1P6 and 10 during a standard half-year semester and Chapters 7P11 in a follow-on graduate course. In Chapters 2, 10, and 11, I have attempted to cover important but rarely compiled information on practical network implementations and worldwide standards.

Read an Excerpt

Chapter 3: The Cellular Concept—System Design Fundamentals

3.1 Introduction

As the demand for service increases (i.e., as more channels are needed within a particular market), the number of base stations may be increased (along with a corresponding decrease in transmitter power to avoid added interference), thereby providing additional radio capacity with no additional increase in radio spectrum. This fundamental principle is the foundation for all modern wireless communication systems, since it enables a fixed number of channels to serve an arbitrarily large number of subscribers by reusing the channels throughout the coverage region. Furthermore, the cellular concept allows every piece of subscriber equipment within a country or continent to be manufactured with the same set of channels so that any mobile may be used anywhere within the region.

3.2 Frequency Reuse

Figure 3.1 illustrates the concept of cellular frequency reuse, where cells labeled with the same letter use the same group of channels. The frequency reuse plan is overlaid upon a map to indicate where different frequency channels are used. The hexagonal cell shape shown in Figure 3.1 is conceptual and is a simplistic model of the radio coverage for each base station, but it has been universally adopted since the hexagon permits easy and manageable analysis of a cellular system. The actual radio coverage of a cell is known as the footprint and is determined from field measurements or propagation prediction models. Although the real footprint is amorphous in nature, a regular cell shape is needed for systematic system design and adaptation for future growth. While it might seem natural to choose a circle to represent the coverage area of a base station, adjacent circles cannot be overlaid upon a map without leaving gaps or creating overlapping regions. Thus, when considering geometric shapes which cover an entire region without overlap and with equal area, there are three sensible choices—a square, an equilateral triangle, and a hexagon. A cell must be designed to serve the weakest mobiles within the footprint, and these are typically located at the edge of the cell. For a given distance between the center of a polygon and its farthest perimeter points, the hexagon has the largest area of the three. Thus, by using the hexagon geometry, the fewest number of cells can cover a geographic region, and the hexagon closely approximates a circular radiation pattern which would occur for an omnidirectional base station antenna and free space propagation. Of course, the actual cellular footprint is determined by the contour in which a given transmitter serves the mobiles successfully.

When using hexagons to model coverage areas, base station transmitters are depicted as either being in the center of the cell (center-excited cells) or on three of the six cell vertices (edge-excited cells). Normally, omnidirectional antennas are used in center-excited cells and sectored directional antennas are used in corner-excited cells. Practical considerations usually do not allow base stations to be placed exactly as they appear in the hexagonal layout. Most system designs permit a base station to be positioned up to one-fourth the cell radius away from the ideal location.

To understand the frequency reuse concept, consider a cellular system which has a total of S duplex channels available for use. If each cell is allocated a group of k channels (k < S), and if the S channels are divided among N cells into unique and disjoint channel groups which each have the same number of channels, the total number of available radio channels can be expressed as

(3.1)

S  = kN

The N cells which collectively use the complete set of available frequencies is called a cluster. If a cluster is replicated M times within the system, the total number of duplex channels, C, can be used as a measure of capacity and is given by

(3.2)

C = MkN = MS

As seen from Equation (3.2), the capacity of a cellular system is directly proportional to the number of times a cluster is replicated in a fixed service area. The factor N is called the cluster size and is typically equal to 4, 7, or 12. If the cluster size N is reduced while the cell size is kept constant, more clusters are required to cover a given area, and hence more capacity (a larger value of C) is achieved. A large cluster size indicates that the ratio between the cell radius and the distance between co-channel cells is small. Conversely, a small cluster size indicates that co-channel cells are located much closer together. The value for N is a function of how much interference a mobile or base station can tolerate while maintaining a sufficient quality of communications. From a design viewpoint, the smallest possible value of N is desirable in order to maximize capacity over a given coverage area (i.e., to maximize C in Equation (3.2)). The frequency reuse factor of a cellular system is given by 1/N, since each cell within a cluster is only assigned 1/N of the total available channels in the system.

Due to the fact that the hexagonal geometry of Figure 3.1 has exactly six equidistant neighbors and that the lines joining the centers of any cell and each of its neighbors are separated by multiples of 60 degrees, there are only certain cluster sizes and cell layouts which are possible [Mac79]. In order to tessellate—to connect without gaps between adjacent cells—the geometry of hexagons is such that the number of cells per cluster, N, can only have values which satisfy Equation (3.3).

(3.3)

N = i2 + ij + j2

where i and j are non-negative integers. To find the nearest co-channel neighbors of a particular cell, one must do the following: (1) move i cells along any chain of hexagons and then (2) turn 60 degrees counter-clockwise and move j cells. This is illustrated in Figure 3.2 for i = 3 and j =2 (example, N = 19).

Example 3.1

Solution

Given:
Total bandwidth = 33 * MHz
Channel bandwidth = 25 kHz 2 simplex channels = 50 kHz/duplex channel
Total available channels = 33,000/50 = 660 channels
(a) For N = 4,
total number of channels available per cell = 660/4 = 165 channels.
(b) For N = 7,
total number of channels available per cell = 660/7 = 95 channels.
(c) For N = 12,
total number of channels available per cell = 660/12 = 55 channels.

A 1 MHz spectrum for control channels implies that there are 1000/50 = 20 control channels out of the 660 channels available. To evenly distribute the control and voice channels, simply allocate the same number of voice channels in each cell wherever possible. Here, the 660 channels must be evenly distributed to each cell within the cluster. In practice, only the 640 voice channels would be allocated, since the control channels are allocated separately as 1 per cell.

(a) For N = 4, we can have five control channels and 160 voice channels per cell. In practice, however, each cell only needs a single control channel (the control channels have a greater reuse distance than the voice channels). Thus, one control channel and 160 voice channels would be assigned to each cell.

(b) For N = 7, four cells with three control channels and 92 voice channels, two cells with three control channels and 90 voice channels, and one cell with two control channels and 92 voice channels could be allocated. In practice, however, each cell would have one control channel, four cells would have 91 voice channels, and three cells would have 92 voice channels.

(c) For N = 12, we can have eight cells with two control channels and 53 voice channels, and four cells with one control channel and 54 voice channels each. In an actual system, each cell would have one control channel, eight cells would have 53 voice channels, and four cells would have 54 voice channels.

3.3 Channel Assignment Strategies

In a fixed channel assignment strategy, each cell is allocated a predetermined set of voice channels. Any call attempt within the cell can only be served by the unused channels in that particular cell. If all the channels in that cell are occupied, the call is blocked and the subscriber does not receive service. Several variations of the fixed assignment strategy exist. In one approach, called the borrowing strategy, a cell is allowed to borrow channels from a neighboring cell if all of its own channels are already occupied. The mobile switching center (MSC) supervises such borrowing procedures and ensures that the borrowing of a channel does not disrupt or interfere with any of the calls in progress in the donor cell.

In a dynamic channel assignment strategy, voice channels are not allocated to different cells permanently. Instead, each time a call request is made, the serving base station requests a channel from the MSC. The switch then allocates a channel to the requested cell following an algorithm that takes into account the likelihood of future blocking within the cell, the frequency of use of the candidate channel, the reuse distance of the channel, and other cost functions.

Accordingly, the MSC only allocates a given frequency if that frequency is not presently in use in the cell or any other cell which falls within the minimum restricted distance of frequency reuse to avoid co-channel interference. Dynamic channel assignment reduce the likelihood of blocking, which increases the trunking capacity of the system, since all the available channels in a market are accessible to all of the cells. Dynamic channel assignment strategies require the MSC to collect real-time data on channel occupancy, traffic distribution, and radio signal strength indications (RSSI) of all channels on a continuous basis. This increases the storage and computational load on the system but provides the advantage of increased channel utilization and decreased probability of a blocked call....