High-rate coded modulation schemes for 16 kbps speech in wireless systems

Abstract

We investigate changing the coding and modulation scheme described in the IS-136 digital cellular telephony standard to support a 16 kbps speech coder for a high quality indoor wireless mode. A Rayleigh fading environment with a maximum Doppler shift on the order of a few Hz is assumed throughout the study. All 5 coding designs presented are based on an 8-PSK constellation, and gains are measured with respect to the performance of uncoded 8-PSK. We show that these systems are limited not by the minimum distance of the constituent codes, but by their large error coefficients. Simulation results are given for both one and two receive antennas, and we conclude that for high quality speech, a two-receive antenna diversity system operating with antenna selection diversity offers the best solution.