BER-Optimal Linear Parallel Interference Cancellation for Multicarrier DS-CDMA in Rayleigh Fading

In this paper, the authors consider the design and bit-error performance analysis of Linear Parallel Interference Cancellers (LPIC) for MultiCarrier (MC) Direct-Sequence Code Division Multiple Access (DS-CDMA) systems. They propose an LPIC scheme where they estimate and cancel the Multiple Access Interference (MAI) based on the soft decision outputs on individual subcarriers, and the interference cancelled outputs on different subcarriers are combined to form the final decision statistic. They scale the MAI estimate on individual subcarriers by a weight before cancellation. In order to choose these weights optimally, they derive exact closed-form expressions for the Bit-Error Rate (BER) at the output of different stages of the LPIC, which they minimize to obtain the optimum weights for the different stages.