Topics in DS-CDMA systems

Direct-sequence code-division multiple-access (DS-CDMA) is one of the most promising multiple access techniques for wireless communications. This dissertation addresses two topics in DS-CDMA systems: (1) Non-cooperative blind multiuser detection; (2) Multi-rate DS-CDMA systems.; The problem of non-cooperative blind multiuser detection is concerned with the demodulation of transmitted data without the knowledge of the users' spreading sequences or the training sequences. Several different iterative algorithms are proposed for the estimation of the spreading sequences in both Gaussian and impulsive channels. Performance bounds for the optimal estimators are computed and it is demonstrated that the proposed algorithms approach these bounds. Some practical issues like timing acquisition and user number estimation are also addressed.; In the second part of this dissertation, two popular multi-rate schemes: the multi-code (MC) scheme and the variable-spreading-length (VSL) scheme are studied. Using random spreading sequence analysis, closed-form expressions for the output signal-to-interference ratios (SIRs) of the linear minimum-mean-square-error (MMSE) multiuser receivers under these schemes are obtained. User capacity regions of these schemes are then computed and compared. Partly motivated by the results of this comparison, a novel VSL scheme is proposed that facilitates the implementation of low-complexity linear adaptive MMSE multiuser receivers. It is demonstrated via analysis and simulation that this scheme achieves good performance.