A Study on the Rate Switching Algorithm for IEEE 802.11 Wireless LANs
Recent wireless LAN systems, such as IEEE 802.11a and 802.11b, have a multirate mechanism in physical (PHY) layer. In that case, a station selects the data rate to be used for each frame transmission by the rate switching algorithm. Despite the rate switching algorithm have a great impact on the throughput performance, the effect has not been discussed enough. This paper describes a general rate switching algorithm that is actually used in many products and evaluates its effect on the performance of the Medium Access Control (MAC) protocol. And, a new rate switching algorithm is proposed to improve the throughput performance. Although the IEEE 802.11a PHY is assumed in this paper, the proposed algorithm can be applied to the wireless systems that employ CSMA based access control and have a multirate mechanism in PHY layer. Throughput performance and system capacity of the IEEE 802.11 WLAN is analyzed based on the basic frame exchange sequence of IEEE 802.11 MAC protocol. It is shown that the IEEE 802.11 MAC will have much better throughput and system capacity with the proposed algorithm.