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Published in:
2011 | OriginalPaper | Chapter
Fading and Diversity
Author : Don Torrieri
Published in: Principles of Spread-Spectrum Communication Systems
Publisher: Springer New York
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Fading
is the variation in received signal strength due to a time-varying communications channel. It is primarily caused by the interaction of multipath components of the transmitted signal that are generated and altered by changing physical characteristics of the propagation medium. The principal means of counteracting fading are
diversitymethods
, which are based on the exploitation of the latent redundancy in two or more independently fading copies of the same signal. This chapter provides a general description of the most important aspects of fading and diversity methods. The rake demodulator, which is of central importance in most direct-sequence systems, is shown to be capable of exploiting undesired multipath signals rather than simply attempting to reject them. The multicarrier direct-sequence system, which is described in the final section, is an alternative method of exploiting multipath signals that has practical advantages.