Performance limits and optimal resource allocation for coded multi-user communication systems.

Abstract

In this thesis, a class of concatenated-coded multicarrier code-division multiple-access (CDMA) systems is presented as a framework for the unified optimization of coherent binary multi-user communication systems operating in a frequency-selective Rayleigh fading environment. It is demonstrated under the assumptions of perfect channel estimation and interleaving that the framework is general enough to include systems which model the performance of both resource-sharing allocation schemes such as direct-sequence CDMA (DS-CDMA) and exclusive resource allocation schemes such as frequency-hopped CDMA (FH-CDMA) with orthogonal hopping patterns. It is possible to optimize over the coded multicarrier framework for various objectives under a given set of system assumptions. This optimization is performed over both the number of users in the system and the amount of diversity allocated to the inner code of each user. The first objective considered is the multi-user throughput, defined as the total number of bits communicated across the channel by the aggregate of users when they are employing optimal hard-decision decoded outer codes. Tight bounds are obtained on the normalized multi-user throughput, and the systems which achieve these bounds are presented. The second objective is obtained by optimizing the multi-user throughput under the assumption that there is a fixed number of users in the system. This problem translates into the allocation of diversity slots so as to minimize the probability of error of the inner code for each user. It is observed that the optimal systems allocate either the smallest reasonable number of slots or the largest number of slots possible to the inner code of each user. The conditions under which each solution is preferable are considered. The optimizations are then reperformed when systems in the class employ a simple multi-user receiver where the inner codes of all of the users are decoding jointly, and the effects of a cellular environment supporting voice activity are considered.