In this thesis, first, an asymptotic analysis of asynchronous band-limited direct-sequence spread-spectrum multiple-access (BL-DS/SSMA) systems with random spreading sequences is performed. The main result is that, for any linear data modulation and spreading scheme, all components in the decision variable of a class of linear receivers are asymptotically jointly Gaussian conditioned on the delays and phases of the interfering signals. Second, performance bounds on the chip matched-filter (CMF) receivers are derived based on the asymptotic analysis. Closed-form expressions for optimum transmit-receive chip waveform pairs that maximize the conditional signal-to-interference ratio (SIR) are obtained. This leads to performance bounds on CMF receivers because maximum conditional SIR implies minimum probability of error as a result of the asymptotic analysis. The bounds are used to examine the dependence of the multiple-access interference suppression capability of the CMF receivers on system parameters. Third, we propose a technique to enhance the performance of a packet acquisition system for BL-DS/SSMA packet communications. The proposed packet acquisition technique exploits not only the preamble but also the message payloads that follow the preamble. Using the proposed method, we improve the probability of acquiring packets, which leads to an increase in the throughput of the packet system. Finally, a new class of BL-DS/SSMA systems with continuous phase modulation is defined. The signals are generated by adding a spreading phase to the information phase while maintaining phase continuity, constant envelope, and efficient bandwidth usage.
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