Capacity analysis of spectrally overlaid multiband CDMA mobile networks

The future (third-generation) mobile communications system will provide not only voice and low-speed data services, but also video and high-speed data services. It will eventually have the capability for wireless multimedia communications. As a radio-access technique for such a system, the code-division multiple access (CDMA) has been considered in many potential third-generation systems including CODIT and the proposal of Ohno, Sawahashi and Adachi (see Proc. IEEF VTC'95, Chicago, IL, p.779-83, 1995). We model those CDMA systems as the spectrally overlaid multiband CDMA (SOM-CDMA) system. In an SOM-CDMA system, several CDMA (sub)systems with different spreading bandwidths are spectrally overlaid with each other. The reverse-link capacity of an SOM-CDMA system is calculated, and some numerical results are presented with discussion. As a result, we demonstrate how much capacity the SOM-CDMA has and how we can achieve an optimal allocation of frequency and power between (sub)systems. The results can be used as a guideline in designing the radio network of SOM-CDMA systems as well as a means to assess the performance of given systems. The results can be applied to any CDMA system with an SOM-CDMA concept, including CODIT and the proposal of Ohno et. al.