Performance analysis of multi-rate 802.11 WLANs under finite load and saturation conditions
In IEEE 802.11 WLANs, stations can transmit data on the channel at different data rates. The stations by default set their values to the maximum speed. As the distances between the stations and the access point increase, the transmitters start sending at lower speeds. For example, in 802.11b, wireless stations transmit at 11, 5.5, 2 and 1 Mbps. A station also changes its modulation type and transmits at a lower rate when it faces interference from the surroundings. In this paper we introduce an analytical model that includes the capability of the standard to operate at different data rates under both, finite load and saturation conditions. Many enhancements are also made in order to make the model more consistent with the standard than existing models. The proposed analysis applies to both the basic access and the RTS/CTS access mechanisms. We provide analytical expressions for the throughput gained by the stations and the average service time. We perform experiments and simulations to validate the model.