Abstract
As the demands for multimedia services with different and higher data rates are growing rapidly, the concept and structure of conventional narrowband CDMA systems are no longer suitable for the third generation mobile communication systems. Methods of modifying the structure of current systems to provide different or even time-varying data rate services must therefore be presented. The technologies of space-time processing and multiuser detections should also be incorporated into future cellular systems to meet the requirement for higher capacities. Issues of space-time processing for multi-rate CDMA communications and capacity analysis of linear multiuser detectors in cellular systems are therefore studied in this research. The first issue of interest is the analytical performance of various proposed schemes to provide multi-rate services in wideband CDMA systems. By generalizing and extending the effective user data model for multi-rate access, we precisely study the general performance of various proposed multi-rate schemes for wideband CDMA systems. A linear space-time processing multiuser receiver structure that can fit all the considered multi-rate schemes is therefore presented. With the extended data model and the proposed receiver structure, each multi-rate scheme is only distinguished by the bandwidth requirement and the spreading codes used. The numerical results suggest that the decision on employing which multi-rate scheme can be viewed as a trade-off between the power consumptions and the hardware or computational complexity of the receivers, as well as operating scenarios. The second part of this research investigates the system capacities of linear multiuser detectors in CDMA cellular environment. The capacity of the conventional detector has been extensively analyzed in previous research and the results justify the application of CDMA technology for mobile cellular communications. Though it is believed that the linear multiuser detectors will definitely improve the link performance and increase the capacity in CDMA cellular systems, the exact capacity gain and the exact behavior of linear multiuser detectors in the presence of unexpected interference from adjacent cells are not clear yet. In this work, the robustness to other cell interference and the capacities of linear multiuser detectors are therefore analyzed. Numerical results demonstrate that the linear multiuser detectors do help to increase the system capacity in cellular environment though not much compared with their complexities. Our last issue of interest is the capacity analysis of a CDMA system supporting multimedia services with linear multiuser detectors. This work adopts the generalized effective user data model and the capacity analysis techniques used in the last two researches. The capacity analysis of CDMA systems supporting single class of service is extended to systems supporting multimedia services. The ideas of resource allocation or resource assignment are also developed. The resource management in a system supporting multimedia services controls the multi-dimensional capacity distribution and will be demonstrated to affect the efficiency of the system.