Multiple-user interference in FHMA-DPSK spread-spectrum communications

This paper investigates the performance of a near-optimum receiver in a frequency-hopped multiple-access (FHMA) differential phase-shift-keyed (DPSK) spread-spectrum communication system. Upper bounds are obtained on the bit error rates (BER's) for the chip-synchronous system and the chip-asynchronous system in the presence of a single interfering signal which interferes in one time-chip. Upper bounds are also obtained 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. It is found 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. System performance for a large number of simultaneous users is also discussed, and the additive white Gaussian noise (AWGN) approximation for the multiple-user interference is examined. Finally, results for the chip-synchronous system with single interference in one time-chip over a Rayleigh fading channel are presented.