On the capacity of multicode and variable spreading gain access scheme for multicarrier CDMA systems supporting multirate services with transmit power control

In this paper, the multicode (mc) and the variable spreading gain (VSG) access schemes for asynchronous multicarrier code division multiple access (MC-CDMA) systems supporting multirate services are considered. The system capacities for these two multirate access schemes are investigated. A transmit power control is proposed to maintain the link quality and improve the system capacity. Simulation results verified the correctness of the theoretical bit-error-rate (BER) performance expressions derived for MC-CDMA systems using these access schemes. Numerical results show that mc access scheme using orthogonal Gold spreading sequences give the best performance, and its superiority increases when the ratio between the data rates of both service class increases. In case when non-orthogonal Gold codes are used, mc access scheme shows a degrading in the system capacity as compared to VSG, due to the presence of larger self-interference (SI) among the sequences used by each high rate user