Partial parallel interference cancellers in CDMA systems employing coding [UMTS example]

Partial parallel interference cancellation (PPIC) is a simple and practical technique that can improve the performance of the CDMA uplink. In coded systems, cancellation is typically performed prior to decoding, to limit the complexity of the receiver implementation. This forces the canceller´s operating SNR to levels lower than is considered in much of the literature. We propose the use of a three-stage PPIC employing weighted hard-decisions at each stage. Weighting factors were chosen by ad hoc means. We compare the PPIC detector performance to ordinary Rake, ideal linear MMSE, and full-search maximum likelihood methods. Non-idealities such as: multipath reception, imperfect channel knowledge, power control error, soft handoff, and the presence of high-speed data users are considered. We find that the gains achieved by the canceller are typically only 20-30%. However, the PPIC is superior to MMSE, and achieves virtually the same performance as ML at these SNR levels.