On the performance of linear parallel interference cancellation

This paper analyzes the performance of the linear parallel interference cancellation (LPIC) multiuser detector in a synchronous multiuser communication scenario with binary signaling, nonorthogonal multiple access interference, and an additive white Gaussian noise channel. The LPIC detector has been considered in the literature lately due to its low computational complexity, potential for good performance under certain operating conditions, and close connections to the decorrelating detector. In this paper, we compare the performance of the two-stage LPIC detector to the original multistage detector proposed by Varanasi and Aazhang (1990, 1991) for CDMA systems. The general M-stage LPIC detector is compared to the conventional matched filter detector to describe operating conditions where the matched filter detector outperforms the LPIC detector in terms of error probability at any stage M. Analytical results are presented that show that the LPIC detector may exhibit divergent error probability performance under certain operating conditions and may actually yield error probabilities greater than 0.5 in some cases. Asymptotic results are presented for the case where the number of LPIC stages goes to infinity. Implications of the prior results for code division multiple access (CDMA) systems with random binary spreading sequences are discussed in the "large-system" scenario. Our results are intended to analytically corroborate the simulation evidence of other authors and to provide cautionary guidelines concerning the application of LPIC detector to CDMA communication systems.