Spread-signature CDMA: efficient multiuser communication in the presence of fading

A new class of orthogonal code-division multiple-access (CDMA) systems is developed for efficient multiuser communication in environments subject to multipath fading phenomena. The key characteristic of these new systems, which we refer to as "spread-signature CDMA" systems, is that the associated signature sequences are significantly longer than the interval between symbols. Using this approach, the transmission of each symbol of each user is, in effect, spread over a wide temporal and spectral extent, which is efficiently exploited to combat the effects of fading. These systems generalize and improve on the spread-response precoding systems. Both efficient signature sets and efficient receiver structures for such systems are developed. Several aspects of the performance of the resulting spread-signature CDMA systems are presented, including both the achievable bit-error rate characteristics and the effective capacity of such systems. The results suggest that spread-signature CDMA may be an attractive alternative to conventional CDMA in a variety of application scenarios.<
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