Capacity evaluation of a mixed-traffic WCDMA system in the presence of load control

This paper deals with the capacity analysis of a direct-sequence code-division multiple-access (DS-CDMA) cellular system in the presence of heterogeneous traffic. We consider a distributed resource allocation strategy that uses a closed-loop control scheme to manage the processing gain, the signal-to-interference ratio (SIR), and the system load. In particular, each base station aims at maintaining the uplink load to its allowable maximum value in order to achieve the maximum throughput. A typical urban cellular system is considered in which the path loss depends on the (alpha)th power of the distance, shadowing is log-normally distributed, and short-term fluctuations due to multipath fading are present. Besides, a radio resourcemanagement scheme is considered, which is able to control transmission power and spreading gain values so as to maintain the total received power at the base stations at a maximum allowable level. In this scenario, this paper derives a novel analytical approach for the evaluation of system capacity of DS-CDMA systems in presence of different traffic sources. Biterror-ratio (BER) and bit-rate requirements have been considered for the different traffic classes. Simulation results have permitted to validate the developed analytical framework on a very comprehensive range of cases. The proposed analysis is finally applied to universal mobile telecommunications system (UMTS)-like traffic classes in order to evaluate the system capacity.