Efficient Symbol-Spreading Strategies for Wireless Communication
MASSACHUSETTS INST OF TECH CAMBRIDGE RESEARCH LAB OF ELECTRONICS
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Some efficient new classes of algorithms for compensating for fading in wireless systems are introduced. For single-user or frequency-division multiplexed wireless systems, we develop a technique we refer to as spread-response precoding which replaces the interleaver traditionally used in conjunction with coding in such systems. From the perspective of the coded symbol stream, spread-response precoding effectively transforms an arbitrary Rayleigh fading channel into a nonfading, simple white marginally Gaussian noise channel with no intersymbol interference. Furthermore, spread-response precoding requires no additional power or bandwidth, and is attractive in terms of computational complexity, robustness, and delay considerations. In the multiuser case, spread-response precoding generalizes to a new class of orthogonal codedivision multiple-access CDMA systems for efficient communication in environments subject to multipath fading phenomen 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. 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 as well as 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.
- Non-Radio Communications