Impact of Multi-Rate VoIP on Quality of Service in IEEE 802.11e EDCA with Link Adaptation

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. IEEE 802.11e provides QoS mechanisms of wireless LANs in the MAC layer. IEEE 802.11 supports the link adaptation function, which allows a wireless transmitter to select an appropriate transmission rate on a frame basis according to the wireless link conditions, to improve the throughput in fluctuating wireless link conditions. However, if a lower transmission rate is selected, packet delays and losses will be increased due to the poor bandwidth availability, and as a result, the quality of real-time applications will significantly deteriorate. In order to improve the quality of such applications, the multi-rate VoIP control scheme has been proposed, in which the appropriate voice encoding rate and packetization interval are selected according to the transmission rate in the PHY layer. In this paper, we first examine IEEE 802.11e EDCA with link adaptation in fluctuating wireless conditions. Then we show that the multi-rate VoIP control scheme improves the quality of voice applications under such conditions even if best-effort traffic coexists.