Abstract
Code Division Multiple Access (CDMA) communication system is a promising candidate for the future third generation communication systems, where there are strongly demands on wider bandwidth, high date rates, and various service requirements, etc. In that case, due to some channel characteristics, such as inter-symbol interference, that are no longer negligible and some dynamic variations of the systems, most conventional designs on the receiver will not attend satisfactory performance. In this thesis, a more practical system model is considered, including frequency-selective multi-path fading effect, multiple access interference, and inter-symbol interference, to develop the receivers with linear complexity suit for the wideband and multi-service CDMA communication systems in the future. Two kinds of linear complexity multiuser receivers are proposed, the symbol-rate multiuser receivers and the chip-rate multiuser receiver. The complexities of these proposed multiuser receivers are set as low as possible and the delays are minimized to satisfy the critical requirements on delay in real-time applications. Mean-squared error criterion is used to develop the filter of the multiuser receiver operated at symbol rate and the filter is modified by the decision feedback technique to upgrade the performance in severe inter-symbol interference environments. To reduce the cost of parameter estimations that need to be updated frequently in time-varying channels, adaptive processing is applied to the receivers. The alternative linear receiver operated at chip rate is based on the scheme of Kalman filtering by modeling the multiuser signals after the chip-matched filter as a state transition model. Given the state transition knowledge, the algorithm of Kalman filtering performs the superior adaptive estimation performance in mean-square sense. The capability of the proposed multiuser receivers in time-varying multi-path fading wideband CDMA systems is demonstrated by numerical simulations. Finally, the proposed multiuser receivers are extended to the applications in multi-rate CDMA systems. The proposed symbol-rate multiuser receivers are operated under the concept of effective users and the operation structure of the chip-rate Kalman filtering receiver does not affected by the multiple data rate as well as in a single rate system. The felxibllity of the chip-rate Kalman filtering receiver in dynamic systems shows the potential for the applications in future multi-media communication systems.