Based On The Ieee802.11 Wireless Ad Hoc Network Research And Design Of The Mac Protocol

Ad Hoc network is becoming more and more popular due to its flexibility, fastnetworking and random mobility. At the same time, wireless shared medium is limited,so the performance of Ad Hoc Network MAC Protocol is the key to the development ofthe protocol.Nowadays, most of the wireless networks are assumed that the moving node isequipped with omni-directional antenna which is generally based on the improved MACprotocol of IEEE802.11. IEEE802.11adopts binary exponential back-off algorithm(BEB) whose performances in the throughput, time delay and fairness index are poor.This thesis analyzes the current improvement of some typical back-off protocols andtheir defects, and put forwards an improved random back-off algorithm based oncontention window (LIMI-SD). Comparing with the BEB algorithm, numeral resultshows that the throughput and fairness index in LIMI-SD algorithm has beensignificantly improved, on condition that there is not a significant increase in the timedelay.Compared with omni-directional antennas, the directional antennas haveadvantages of a relatively higher gain, lower interference and farther transmittingdistance, at the same time, they can fully improve the multiplexing capability ofnetwork. Today, most of wireless networks equipped with directional antennas usedirection medium access control protocol, which, to some extent, can alleviate thehidden terminal and exposed terminal problems of the network. However, it leads tosome new problems such as neighbor node location, directional hidden terminal anddeaf node. In this thesis, some of the current improved protocols based on directionalantennas and their defects have been analyzed and a new type of MAC protocol basedon neighbor position and back-off in directional antennas (NPBO-DMAC) has been alsoput forward. This protocol has effectively solved new problems due to directionalantennas by taking advantages of mechanism of DRTS/DCTS, direction of double busysignals, DNAV setting and back-off mechanism. Numeral result shows thatNPBO-DMAC protocol can effectively support the application of directional antennas in Ad Hoc network, and it can greatly improve the performance of the system.In a word, this thesis has designed the LIMI-SD back-off Algorithm based oncontention window, and the NPBO-DMAC protocol based on neighbor position andback-off in directional antennas. At the same time, a lot of experiments have been donefor the design. Because of their relatively simple structure and the use of a more maturetechnology, it has good application prospects.