The effect of channel estimation, interleaving and channel coding on RAKE receivers for mobile DS-CDMA systems

The performance of a DS-CDMA system over a multipath fading channel is evaluated. A RAKE receiver is employed to combat channel distortion introduced by multipath and temporal variation due to fading. Error-correction coding commonly employed in modern digital mobile systems, results in a substantial improvement for a system in fading channels. A combination of coding and interleaving effectively provides additional diversity, and minimizes the adverse effect of error bursts. In this paper, we study the impact of interleaver size on the error rate of a DS-CDMA system under different fading conditions. Closed-loop power control is employed with interleaving/coding to deal with slowly fading channels. This combination helps the system performance not to be too sensitive to fade rate. The effectiveness of using low rate convolutional code is also studied. Simulation results show that reducing the code rate does not always result in improved performance. In fact, constraint length must be increased while reducing the code rate so that the resultant code can provide on improved performance.