Low delay, high quality wireless digital speech communications by shared time division duplexing

We examine various strategies to provide low delay, high quality digital speech communications in a high capacity wireless network. Multiple access schemes based an time-division and packet reservation are compared in terms of their statistical multiplexing capabilities, sensitivity to speech packet dropping, delay, robustness to lossy packet environments, and overhead efficiency. In particular, we propose a low-delay multiple access scheme, called Shared Time-Division Duplexing (STDD), which allows both the uplink and downlink traffic to share a common channel, thereby achieving high statistical multiplexing gain even with a low population of simultaneous conversations. Typically, with a total capacity of 1 MBaud, 2 ms frame and 8 kBaud speech rate, low delay STDD is able to support 48 pairs of users compared to 38, 35 and 16 for TDMA with speech activity detection, basic TDMA and PRMA respectively