Performance analysis of the multi-rate DS/CDMA communication systems

Abstract

In this dissertation, we investigate the performance of the multi-rate direct-sequence/ code-division-multiple-access (DS/CDMA) communication systems which can offer multi-media services at different bit rates and bit error rates (BERs). Due to the coexistence of signals of different bit rates in the same radio frequency (RF) bandwidth, the analysis of the multiple access interference (MAI) of the multi-rate DS/CDMA systems is much more complicated than that of a conventional DS/CDMA system. In the first part of this dissertation, we investigate the performance of an asynchronous variable-processing-gain (VPG)-DS/CDMA system where signals are transmitted at different processing gain and transmitted power according to their own bit rates and BERs. The MAI of a VPG-DS/CDMA system is developed, and the BER is evaluated by means of the Gaussian approximation (GA), the bounds method, and the Monte Carlo (MC) simulation. For a VPG-DS/CDMA system with random codes, the BER of the desired user is not relevant to the processing gain of the interfering users; it is relevant only to the processing gain of the desired user and the transmitted power of all users. When the number of users in a VPG-DS/CDMA system is large, the BER depends only on the bit energy of the user. The BER performance for a VPG-DS/CDMA system with short codes is better than that for a VPG-DS/CDMA system with long codes or random codes. In the second part of this dissertation, we investigate the performance of an asynchronous multiple-chip-rate (MCR)-DS/CDMA system where signals are transmitted at different chip rates, carrier frequencies, processing gain, and transmitted power according to their own bit rates and BERs. The MAI of an MCR-DS/CDMA system is developed, and the BER is evaluated by means of the GA and the MC simulation. Some quantitative results on the effects of chip rate and processing gain on the variance of the MAI for an MCR-DS/CDMA system with random codes are obtained. Also, the e...