Matched median detectors for DS/SSMA systems using complex signature sequences

Abstract

Direct-sequence spread spectrum multiple-access communication systems allow several users to share a common communication channel where the distinction between different users is achieved by assigning a distinct signature waveform for each user. Real-world noise-environment is seldom purely Gaussian, yet receiving systems generally are those that are optimal for white Gaussian noise (linear matched filters or correlation detectors). Matched median filters are robust detectors in impulsive noise environments forming a natural counterpart of linear matched filters. In this paper, matched median filters are extended to the demodulation of complex signature sequences assuming asynchronous communication and coherent single-user receivers. Monte Carlo simulations show that matched median filters for PSK codes outperform matched median filters for BPSK codes and linear matched filters for PSK and BPSK codes in the presence of multiple-access interference and impulsive channel noise.