software TDMA for VoIP applications over IEEE802.11 wireless LAN

An emerging killer application for enterprise wireless LANs (WLANs) is voice over IP (VoIP) telephony, which promises to greatly improve the reachability and mobility of enterprise telephony service at low cost. Most commercial IEEE802.11 WLAN-based VoIP products cannot support more than ten voice conversations over a single IEEE 802.11b channel, even though its peak transmission rate is more than two orders of magnitude higher than an individual VoIP connection's bandwidth requirement. There are two main reasons why these VoIP systems' effective capacity is lower than expected: stringent latency requirement and substantial per-WLAN-packet overhead. Time-Division Multiple Access (TDMA) is a well-known technique that provides per-connection QoS guarantee as well as maximizes the radio channel utilization efficiency. This paper presents a software-based TDMA (STDMA) protocol that is designed to support VoIP applications and successfully works on commodity IEEE802.11 WLAN interfaces. The resulting STDMA prototype can support more than 50 two-way G.729 voice conversations over a single IEEE 802.11b channel.