JPL's Wireless Communication Reference Website
Author: Jean-Paul M.G. Linnartz.
Publisher: Artech House, London and Boston.
Publication: Boston, 1993, 345 pages.
Reviewed by Richard O. LaMaire, IBM T. J. Watson Research Center, Yorktown Heights, NY, IEEE Personal Communications, February 1995, pp. 8 and 10.
The design of wireless communications systems requires a broad spectrum of knowledge that includes an understanding of radio propagation effects, medium access control protocols and their interaction with the radio environment, network traffic flows, and the differing characteristics of voice and data traffic. This book considers all of these topics and more as it investigates, through both analytical and simulation methods, the design and performance of mobile radio systems with narrowband radio channels. Narrowband refers to the fact that the channel transfer function remains virtually constant over the transmission bandwidth unlike in say spread-spectrum systems in which the radio channel can have very different properties over the wide frequency band across which the signal is spread. The focus of this book are systems that use narrowband VHF or UHF propagation over ranges on the order of a few tens of meters to tens of kilometers. Most systems using this type of channel are cellular systems including the Advanced Mobile Phone System (AMPS), the TDMA IS-54 system, the Global System for Mobile Communications (GSM), and the Digital European Cordless Telephone (DECT) system. Although not mentioned in the book, wireless Local Area Networks (LAN) that use slow frequency hopping radios are essentially narrowband systems that periodically change their frequency. Thus, the results of this book can also be applied to these systems. However, true wide-band systems, specifically Code Division Multiple Access (CDMA) systems are not treated. Many parts of the book are oriented toward vehicle-based voice communications, although data traffic also is treated extensively and at points the specific characteristics of microcellular systems are discussed.
The author's Ph.D. work entitled "Effects of Fading and Interference in Narrowband Land-Mobile Networks" is the basis for the book. The emphasis on fading and interference carries over to the book and represents the strongest contributions of the work.
The book has ten chapters and a useful appendix with some supporting mathematical detail. Chapter 1 provides background and introductory material concerning the history of communications, traffic management in various layers of the Open System Interconnection (OSI) reference model, the effects of mobility on communication systems, and cellular networks. The detailed technical material begins in chapter 2, where physical layer effects are investigated.
Chapter 2 treats VHF and UHF propagation in land-mobile communication. This chapter begins with a review of the generally accepted statistical model for narrowband mobile propagation. This treatment includes a discussion with supporting mathematics of the large-scale attenuation effects of free space loss, ground wave loss, and diffraction loss. Shadowing with a log-normal distribution is introduced and various types of multipath fading are described. Specifically, the mathematical characterization of Rician, Rayleigh, and Nakagami fading are presented along with motivating derivations. In addition, the combined effects of shadowing and Rayleigh fading are considered in the form of the Suzuki distribution for the instantaneous received power. The remainder of chapter 2 deals with the assessment of deterministic propagation models and presents some six different models that are compared with experimental data.
Chapter 3 gives an analytical method for finding the probability of signal outage in multi-user mobile networks with narrowband radio channels. The robustness of practical systems to noise and co-channel interference is discussed and a criterion for signal outage based on the Carrier-to-Interference (C/I) ratio is defined. In this model, which is later called the capture ratio model in chapter 7, the quality of reception experienced by the user degrades below an acceptable value (i.e., there is an outage) when the C/I ratio becomes less than a threshold z. The probability of signal outage is derived for situations with multiple interfering users and in the presence of the shadowing and fading effects introduced in chapter 2. While the outage probability that is studied in chapter 3 describes the percentage of time that the C/I ratio on a mobile link is below a certain threshold, it is also important to know the duration of the outages. In chapter 4, the rate at which the threshold z is crossed and the average fade/nonfade duration are investigated. Knowledge of the fade duration is important for the design of the error detection/correction coding that is used for the channel. Drawing from the author's original work, a method is derived for a multiple interferer scenario in which the sum of multiple incoherent Rayleigh-fading signals is approximated as a joint interference signal with Nakagami fading.
Chapters 3 and 4 dealt with generic radio receivers and used the probability of outage as the performance criterion. In contrast, in chapter 5, a Binary Phase Shift Keying (BPSK) receiver is considered and the average Bit Error Rate (BER) is derived. The specific focus of chapter 5 is the development of an approximate simplified model (more complicated models have appeared in the literature) that considers the combined effect of multipath fading and co-channel interference. This analysis shows that the specular-to-scatter (Rician) ratio K of multipath fading and the standard deviation of any shadowing on the channel have a very significant effect on the average BER.
Chapter 6 marks a shift in the book as the author begins his treatment of random access protocols for mobile radio systems in which multiple users seek to transmit data packets over a common shared radio channel. This chapter begins with a review of the previous literature on random access protocols including treatment of slotted ALOHA, slotted and unslotted Carrier Sense Multiple Access (CSMA), and the less-known Inhibit Sense Multiple Access (ISMA) protocols. A spatial distribution is used to characterize the average number of attempted packet transmissions per unit time and per unit of area offered by terminals at a given distance from the central receiver. In chapter 6, the radio channel is described only by a capture probabilities that give the probability of successful reception of a test packet transmitted from a given distance from the central receiver, in the presence of the interference from a given number of other terminals. Expressions for total channel throughput and the individual terminal success probability are derived. Chapter 6 ends with a treatment of the effect of propagation delays on the throughput of the nonpersistent ISMA protocol.
Chapter 7 is devoted to the derivation of models for receiver capture in mobile random-access networks. The focus of this chapter is the determination of capture probabilities that can be used in the various throughput equations that are derived in chapter 6 for the different random access protocols. For this reader, chapters 7 and 8 were the most interesting parts of the book. Many sections of these chapters have been taken from the previously published original research work of the author and his colleagues. Chapter 7 begins with an excellent review of the various capture models that have been proposed in the literature, including the simple vulnerability circle model of Abramson and the more complex capture ratio model that was outlined above. In addition to these models, the author describes models that are based on the nonfade interval and on bit error probabilities for the BPSK model of chapter 5. Chapter 7 concludes with a simulation comparison of the various models and a conclusion that the capture ratio model provides both a convenient technique to compute the performance of mobile random-access networks and a good compromise of the estimates produced by a number of the other capture models that were investigated. In chapter 7, only a single spatial distribution, the quasi-uniform spatial distribution is considered. Chapter 8 broadens the treatment by considering several other spatial distributions of traffic including ring, uniform, and circular band distributions. Laplace image functions are used heavily in this treatment. Capture probabilities are derived for a receiver capture threshold model for both coherent and incoherent cumulation. The chapter concludes with a brief treatment of stability in a slotted ALOHA network.
In Chapter 9, the author focuses on the system issue of frequency reuse in wide-area packet-switched networks. Specifically, he considers a cellular system in which a slotted ALOHA protocol is used over Rayleigh fading channels. Spectrum efficiencies are computed for different cellular cluster sizes. Chapter 9 concludes with the presentation and analysis of a model for two-branch site diversity in which two different cellular base stations can successfully receive a packet. The final chapter of the book, chapter 10, briefly summarizes the contents of the book and then discusses future research directions.
In summary, I recommend this book to readers who seek a deeper understanding of the effects of the radio environment on access protocols and the overall system performance of narrowband systems. This book is rich in mathematical detail and requires some background in Laplace transforms and analytic and numerical integration as a prerequisite for understanding and exercising the material. The book keeps a system perspective throughout, but except for the brief discussion in chapter 5 concerning a generic BPSK system, does not deal much with system implementation issues. The graduate student or researcher will find this book to provide an excellent starting point in this area due to its extensive references to the research literature. The book could be used in a graduate course (particularly chapters 2-3 and 6-8), but needs to be supplemented by exercises, since the book provides none.