Radio link performance analysis of overlaid CDMA communication systems

Abstract

Two approaches of CDMA techniques accommodating various types of services have been proposed for applications to second- and third-generation mobile communication systems. The first approach is to use either a single-code CDMA (SC-CDMA) transmission scheme or a multi-code CDMA (MC-CDMA) scheme in a single channel bandwidth. The second approach is to use a spectrally overlaid CDMA system with different spreading bandwidths. In this dissertation, we are concerned with reverse link performance analysis of overlaid CDMA communication systems for various types of services in terms of signal power, interference, and capacity. First, we investigate the link capacity and signal power of SC-CDMA and MC-CDMA systems considering various system parameters, such as spreading bandwidth, traffic load, the orthogonality factor, and the number of spreading codes assigned to a user. The capacities of both SC- and MC-CDMA systems are identical in the ideal case where spreading code channels are orthogonal. However, in real environments the orthogonality is lost due to multipath fading and different code channels in MC-CDMA systems interfere with each other. This mutual interference affects link capacity and user signal power, both of which are important factors for determination of the system performance. The degree of orthogonality loss is characterized by introducing the orthogonality factor depending on multipath delay power profiles of the propagation channel. The results show that the SC-CDMA system provides a larger link capacity and multi-code users require significantly more power than do single-code users. Second, we analyze the capacities of spectrally overlaid narrowband and wideband systems using the two CDMA techniques: a single-code and a multi-code. The capacity is defined here as the maximally achievable total throughput in the narrowband and wideband subsystems. User signal power in the overlay systems affects the performance of the systems. The signal power i...