Regularised multi-stage parallel interference cancellation for downlink CDMA systems

A hybrid receiver scheme for downlink code division multiple access (CDMA) systems over frequency selective channels is proposed. The proposed receiver combines a linear regularised zero forcing (RZF) equaliser and a parallel interference cancellation scheme with a tanh decision function (TPIC). It is called the RZF-TPIC receiver. The RAKE receiver is used to reduce the channel effects and obtain an initial estimate of the data. Multi-stages of TPIC are then employed to mitigate the multiple access interference (MAI). At the final stage, the RZF equaliser is used to provide a better estimate of the desired user's data. The effect of the decision function used for symbol estimation in the PIC stage is investigated. The performance of the proposed scheme is evaluated and compared with the traditional RAKE receiver by computer simulations. It is found that the proposed scheme offers significant gains, even with a large number of interfering users.