Performance analysis of rate adaptation scheme for data traffic in DS-CDMA systems

A rate adaptation scheme for data traffic in direct-sequence code-division multiple-access (DS-CDMA) system is studied. With the scheme, the received power of each active data user is maintained constant by using transmission power control to compensate for channel fading and path loss, while the transmission rate is dynamically adjusted to guarantee a target bit energy-to-equivalent noise spectral density (E_b/N_e) when interference varies. A continuous-time Markov chain (CTMC) with state-dependent parameter is used to model the user activities in the system. Analysis and simulation results show that the rate adaptation scheme outperforms the conventional SIR based power control scheme, in terms of a power gain and lower average delay for the data users to achieve the same throughput. Moreover, by applying back-off access control, the performance of the rate adaptation scheme can be further improved.