Research On Rate Adaptation For WLAN In The Ungreedy Mode

Recently, more people pay attention to Wireless Local Area Network(WLAN) based on IEEE 802.11, and more enterprises start to use itbecause of its facility and mobility. Unfortunately, even if the protocol ofWLAN is improving to support the higher rates, it does not define how toswitch between the rates, namely, the rate adaptation. Therefore, morescholars are devoting to researching it, and have gotten some results,especially, under the greedy mode. However, the outcome of the researchwhich is under the ungreedy mode is still blank. This paper analyses thereason why the existing rate adaptation can not work well under theungreedy mode, and presents two rate adaptations which are more adapt toworking under the ungreedy mode: the modified ARF algorithm which hasa changeable value of timer is on the basis of ARF algorithm, and changes the method of the timer which is used to choose the rate of the packet, inorder to make the change of the rate adapt to the change of the channel'scondition. The other is the mechanism of test frame. It fully utilizes thefeature of ungreedy mode, and uses the test frames to estimate thecondition of channel in order to choose the correct rate to transmit thepacket. Consequently, this mechanism can reduce packet loss rate and delayto minimum. At last, this paper uses the results of NS2's simulation tocompare the performances of four rate adaptations under the ungreedymode. It can prove that the two rate adaptations which are presented in thethesis are more efficient.