Basics of Code Division Multiple Access (CDMA)

Excerpt

Code division multiple access (CDMA) has proven itself to be a viable technique for enabling the simultaneous transmission and reception of data over a shared channel. Although CDMA is associated mostly with wireless cellular communication, it is currently being viewed with interest for optical channels as well. Among its key advantages are graceful degradation with traffic, low probability of intercept, and resistance to narrowband interference. The writing of this book has been motivated by a desire to provide a succinct tutorial treatment of CDMA. The book is aimed at the reader who has an undergraduate degree in electrical or optical engineering. The general emphasis is on the explanation of concepts, and as such, the book is intended to provide a quick lesson in CDMA rather than serve as a textbook in the field. There are already several excellent books on the subject that provide the in-depth treatment one might expect of a textbook. For those interested in learning about CDMA but who prefer material other than textbooks, the only other option is to gather tidbits from various sites on the worldwide web. We hope this book will address the needs of such readers.

The book is organized as follows. Chapter 1 provides an overview of the basic communication process by identifying the key components of the process. An attempt is made to provide the reader with a comprehensive understanding of the common multiple access schemes. Chapter 2 covers digital communication fundamentals. The essentials of digital communication such as data transmission and detection in noise, the relationship between bandwidth and data rate, pulse shaping, and channel capacity are explained. The concept of code division multiplexing is introduced in Chapter 3 through orthogonal waveforms, and the notion of direct sequence spreading is then explained. Chapter 4 explores the properties of various types of codes used in direct-sequence-spread CDMA. A brief tutorial of Galois field arithmetic is provided, followed by a treatment of pseudo random binary sequences. Diversity techniques used to combat the effects of multipath and fading are treated in Chapter 5. Chapter 6 introduces the near-far problem and recent attempts to mitigate near-far effect based on multiuser detection. The subject matter of Chapter 7 is cell phone systems based on the IS-95 CDMA standard. Two appendixes, one on matched filter reception and another on random signals, are provided for quick reference.

It is our pleasant task to thank those who have helped in making this book possible. We are thankful to the many undergraduate and graduate students with whom we have had interactions on the subject over the last several years. The reviews by Professor Edwin Chong of Colorado State University and Fred Kellerman of Harris RF Communications were enormously helpful. We thank our families for their support and sustenance throughout the project. Finally, we have discovered that there is such a thing called infinite patience and it can be found in Margaret Thayer of SPIE. Surprisingly for the writing of a short book such as this one, we encountered a lot of delays and she has endured them without complaints. We are very thankful to her and to SPIE for their support.

Raghuveer Rao

Sohail Dianat

June 2005