On the design of spectrally overlaid CDMA systems under a practical interference environment

This paper studies the capacity of a multiple chip rate (MCR) system under a practical environment. In our analysis, the use of non-orthogonal spreading codes, differences in carrier frequencies and power spectrum density of signals for different users, are taken into consideration. Capacities of the two MCR systems with different subsystem configurations are obtained. A comparison between the capacity of an MCR system and a multiple processing gain (MPG) system is also given. From the numerical results obtained, it can be concluded that for MCR systems, the full assignment configuration (a) can provide a higher system capacity than configuration (b), and configuration (b) with Δω = 0 achieves the same capacity as that of the MPG systems. Hence with good control of the spectrally overlaid structure, MCR systems can achieve higher capacity than MPG systems.