A Study Of The Link Adaptation Algorithm For IEEE802.11a

Recently, with the introduction of the high-speed WLAN physical layer, link adaptation to dynamically select the PHY mode has been recognized as an effective way to improve the system throughput, but the link adaptation mechanism is not specified in the standards? The mechanism to select one out of multiple available transmission rates at a given time is referred to as link adaptation and the effectiveness of the implemented link adaptation scheme can affect the system performance significantly? In the scheme, the main issues are the choice of the parameter to be used for the link estimation(e.g. Packet error rate, signal to noise ratio, received signal strength, carrier to interference ratio, etc), and how to select the appropriate rate from measurements of the selected parameter.In this paper, with studying the link adaptation algorithm based on PER and the system performance of IEEE 802.11a PHY, an optimum threshold scheme is presented instead of an existing fixed threshold scheme . Simulation results indicate that the optimum threshold scheme is better than other algorithms in term of throughput.Then, we present a generic method to analyze the throughput performance of an 802.11a DCF system and derive a closed-form expression of the expected throughput .In order to achieve the best system throughput under a certain channel condition, we apply the PER threshold scheme into the system of IEEE802.11a DCF. There are two instances in getting the PER threshold, one is optimum PER threshold scheme, the other is the changed PER threshold scheme. The first scheme is simple and easy to deploy, but it assume the channel condition is constant over the MSDU delivery period includes all the retransmissions and the PHY mode cannot be changed for all the retransmissions , so this scheme cannot adapt quickly to the fast-changing wireless channel. Base on recognizing the limitations of the optimum PER threshold scheme, then we propose a changed PER threshold scheme . This scheme provide a set of changed PER threshold for each transmission or retransmission, so the wireless station can adapt the PHY mode for the next transmission attempt if there is any variation of the wireless channel...