The Research For Rate Adaptation Algorithms In IEEE802.11b

Since IEEE association issued the first wireless local area network standard802.11in1997, the wireless local area network has been widely used because of itsadvantages such as flexible character、low cost、easy to expand. How to optimize thethroughput of wireless local area network is always the one focus of attention in theacademic circles. IEEE802.11supports different rates in the physical layer.But itonly provides different sending rates for different types of frame in the MAC layer. Itdoesn’t provide for specific rate in different channel. According to different channelenvironment to configure different transmission rate has been shown to be aneffective means to improve network throughput. How to choose different transmissionrate? What’s the condition for selecting transmission rate? Therefore, this paperexplores the improvement and optimization of CARA algorithm based on the theoryof the wireless local area network system. Main contents are as follows:(1) Stating the rate adaptive algorithm in detail And the rate adaptive algorithmis studied. This paper compares three kinds of algorithm. They are based on thestatistical and direct measurement data,or combination of them. Then we compare thealgorithms with the mistake bit rate and throughout.(2)According to the influence of collision to the wireless local area networkthroughput, we analyze the advantages and disadvantages of CARA algorithm. Thispaper puts forward a improved CARA algorithm named Strong-CARA. Thisalgorithm not only to be able to use Request-Send/Clear-to-Send (RTS/CTS) toeliminate the influence of collision for the system throughput, but also can adjustthreshold adaptively according to different channel conditions. So it can obtain higherthe system average throughput in a variety of channel conditions.(3) In a variety of channel conditions, we use the network simulation software tocompare the average throughput of Strong-CARA、ARF and CARA. The results show that the proposed algorithm’s performance is better than the other two classicalalgorithms.