Noncoherent Multiuser Communications: Multistage Detection and Selective Filtering

We consider noncoherent multiuser detection techniques for a system employing nonlinear modulation of non-orthogonal signals. Our aim is to investigate near-optimum noncoherent multiuser detection techniques that utilize the received signal structure while retaining reasonable complexity. Near-optimum approximations of the maximum likelihood detector are investigated where the signal structure is reflected in the approximation techniques explored. Several implementations of noncoherent soft interference cancelers are proposed and investigated, each of which exploits the signal structure in a specific way. We propose a class of detectors that employ selective filtering, a technique that exploits the a priori information that each user selects one of M signals for transmission. We show that selective filtering offers improved performance over the noncoherent counterparts of the existing near-optimum multiuser detectors. Both deterministic as well as blind adaptive implementations of selective filtering are considered. Numerical comparisons are provided to demonstrate the near-optimum performance of the proposed detectors.