Rake receiver analytical study for TD-CDMA downlink evaluation

DMA systems generate intra-cell interference due to multipath propagation and or asynchronous transmission. Whereas interference cancellers or joint detectors are envisaged to reduce the interference in the uplink, CDMA mobile handsets are more limited in complexity. This paper is focused on the evaluation of the RAKE receivers when spreading sequences have short periods in a synchronous downlink transmission with multipath propagation. The bit-error-rate evaluation based on the randomness assumption of spreading codes can not be applied. We show that exact evaluation of the bit-error-rate, exploiting the sequences properties for any multipath channel profile (considering fractionally chip delayed paths) is feasible. This proposed evaluation is applied to the TD-CDMA mode of UMTS. This analytical study can be easily implemented and gives the performances for different scenarios avoiding simulations. It can also be useful to optimize the channel allocation code strategy or to evaluate the equivalent interference factor needed for capacity evaluation.