Modulation and coding in DS/SSMA communication systems
Abstract
In this work, we consider several different issues concerning the design and the analysis of direct-sequence spread-spectrum multiple-access (DS/SSMA) communication systems. The performance of DS/SSMA systems can be improved with coding. We have proposed a new system that employs trellis coding and continuous phase modulation (CPM). The trellis code provides coding gain while CPM provides desirable spectral properties. An analysis of this system with deterministic sequences shows that significant improvement can be achieved over the standard binary DS/SSMA system. Besides the design of a new system, we also consider the analysis of different DS/SSMA systems under the random sequence model. A generalized quadrature DS/SSMA system is examined. An algorithm that determines tight upper and lower bounds on the average probabilities of error is derived. An approximation algorithm, called the Conditional Gaussian Approximation, and further approximations are also provided. Systems with random polyphase signature sequences are also considered. An asymptotic analysis is provided and an approximation algorithm, again called the Conditional Gaussian Approximation is derived to estimate the probabilities of error. Finally, through an asymptotic analysis, the Standard Gaussian Approximation is rigorously derived and the Conditional Gaussian Approximation is extended to cover most systems with linear modulation. The results of the asymptotic analysis also provide directions on the design of DS/SSMA systems.
Degree
Ph.D.
Advisors
Lehnert, Purdue University.
Subject Area
Electrical engineering
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