WLC24-5: Adaptive Multi-Rate VoIP for IEEE 802.11 Wireless Networks with Link Adaptation Function

With the deployment of IEEE 802.11 wireless LANs, there is a strong requirement to support real-time applications with stringent QoS requirements on these networks. In order to improve the throughput in fluctuating wireless link conditions, IEEE 802.11 supports the link adaptation technique, which allows a wireless transmitter to select an appropriate transmission rate on a packet basis according to the wireless link conditions. However, if a lower transmission rate is selected because of deterioration of the wireless link conditions, packet delays and losses will be increased due to the poor bandwidth availability, especially when the traffic load is high, and as a result, the quality of real-time applications will significantly deteriorate. In this paper, we propose an adaptive multi-rate VoIP control scheme, which adapts the voice encoding rate and packetization interval according to the transmission rate in the PHY layer. We show that the proposed scheme achieves a significant improvement in the end-to-end delay and packet loss ratio of voice traffic in fluctuating wireless link conditions.