Multiple-User Interference in FHMA-DPSK Spread-Spectrum Communications

In this paper, we investigate the performance of a nearoptimum receiver in a frequency-hopped multiple-access (FHMA) differential phase-shift-keyed (DPSK) spread-spectrum communication system. We obtain upper bounds on the bit error rates (BER's) for the chipsynchronous system and the chip-asynchronous system in the presence of a single interfering signal which interferes in one time-chip. We also obtain upper bounds on the BER for the chip-synchronous system with multiple-user interference, for the special case where each time-chip has at most one interfering signal of the same power as the desired signal. We find that, for the chip-synchronous system, the upper bound on the BER when one time-chip has two interfering signals is larger than the upper bound on the BER when each of the two time-chips has a single interfering signal. We also discuss system performance for a large number of simultaneous users, and examine the additive white Gaussian noise (AWGN) approximation for the multiple-user interference. Finally, results for the chip-synchronous system with single interference in one time-chip over a Rayleigh fading channel are presented.