Uplink capacity analysis of a spectrally overlaid multi-band CDMA system with inter- and intra-cell interferences

In a spectrally overlaid multi-band CDMA (SOM-CDMA) system, wide-band, medium-band and narrow-band CDMA subsystems with different spreading bandwidths are spectrally overlaid with each other. This system architecture has an advantage that different traffic types can exist together within a given band of spectrum, without having to allocate a separate spectrum band for each type of traffic. However, spectrally overlaid subsystems may also induce more interference on particular reference mobiles. Under this scenario, to study the effect of interference on the system capacity becomes necessary in order to ensure that the system can provide the required quality of service (QoS) for each type of service. Previous works on SOM-CDMA systems focused only on interference from mobiles in an isolated cell. In this paper, the capacity of SOM-CDMA cellular system in terms of aggregate data rate, by taking both inter-cell and intra-cell interferences into consideration, is investigated. Our results show that under the standard path loss model and ideal power control assumptions, the maximum aggregate data rate of SOM-CDMA systems will be degraded to approximately 50% of the isolated cell case. We also observed that the system capacity increases with the cell radius, while below a certain radius, spectral overlay becomes impractical. The bound of maximum mobiles admitted in SOM-CDMA with given SNR requirement and data rate of each frequency band can be a guide to system designers who design the call admission scheme