Soft Decision Parallel Interference Cancellation for Multi-Carrier DS-CDMA

In this chapter, we propose a new scheme for Multi User Detection (MUD) using Parallel Interference Cancellation (PIC) technique. This technique provides a good complexity, latency, and performance compromise. Among spread-spectrum techniques, the most popular one is the Direct-Sequence Code-Division Multiple-Access (DS-CDMA), where each active user’s data is modulated (multiplied) by a unique code. This technique is suitable for Multi-Carrier (MC) Direct-Sequence Code-Division Multiple-Access (DS-CDMA) systems. We offer a new scheme of soft detectors whose performance is superior to that of the other famous suboptimal detectors. On each sub carrier, instead of making hard bit decisions of the other users in the current stage and regenerating and canceling the interference signal, a weighted sum of the soft outputs of the other users in the current stage is canceled from the soft output of the desired user. This is the input to the next stage, then at the last stage, the interference canceled outputs from all the sub carriers are combined (Maximal Ratio Combining) to form the decision statistics. We derived expressions for the Bit Error Rate (BER) on Rayleigh fading channels. Analytical results are found for different stages in the proposed PIC scheme. The simulation results show that the proposed scheme offers good interference cancellation than the other filter receiver. The complexity of this scheme grows linearly with the number of users. Moreover, this scheme is much faster than other receivers such as Successive Interference Cancellation (SIC). Soft Decision Parallel Interference Cancellation for Multi-Carrier DS-CDMA