Improved Multistage Parallel Interference Cancellation Using Limit Cycle Mitigation

This paper describes a new technique for improving the performance of multistage parallel interference cancellation (PIC) multiuser detection. The focus of the paper is on the hard-decision multistage PIC detector due to the fact that it possesses two desirable properties: (a) very low computational complexity in binary communication systems and (b) the optimum (joint maximum likelihood) bit estimates are a fixed point of the hard-decision PIC iteration. Unfortunately, the hard-decision PIC iteration is also known to sometimes demonstrate two modes of undesirable convergence behavior: convergence to nonoptimum fixed points and limit cycles. This paper demonstrates that limit cycles tend to occur with much greater probability than convergence to nonoptimum fixed points. To improve the performance of the hard-decision multistage PIC detector, we propose a reactive limit cycle mitigation algorithm. The results suggest that significant performance improvements may be possible in some cases with only modest increases in computational complexity.