Research And Improvement Of Ad Hoc Networks' MAC Protocols

Mobile Ad Hoc Network (MANET) is a distributed packet radio network, which composed of a collection of mobile nodes without supporting by any established infrastructure and with characteristics of speedness, agility and convenience. It can be widely used in military action, emergecy search, disaster rescue,law execution, office meeting and so on.In MANET, multiple nodes may access to the wireless channel simultaneously , that may result in collisions among packets and make receivers can't distinguish the accepted data. Thus, channel resource can be wasted and throughput decreases notably. In order to resolve these problems, Medium Access Control (MAC) protocols is required to coordinate the access of the nodes to the channel and make it more effective ,orderly and fair.To start with, in this paper, we briefly introduce the newest reseach dynamic of MANET's development and MAC protocols at home and abroad. Then, on the base of the effection of wireless media to MAC protocols and hidden and exposed terminal problems, we research the typical MAC protocols , mainly analyse the backoff algorithms affecting fairness and improve Multiple Increase Linear Decrease(MILD) and Exponential Increase Exponential Decrease(EIED) backoff algorithms used in Wireless Local Area Network(WLAN). Furthermore, we improve Binary Exponential Backoff(BEB) algorithm used in IEEE 802.11 standard based on above, that we deal with the situation appearing after sending data frames successfully with two different methods. When the times that data frames is sended successfully is smaller than some threshold, contention window decreases rapidly by exponential to increase the throughput; while the times is larger than the threshold, contention window increases by linearity to improve the fairness of the channel access in MANET.Using NS2 to analyse the network's throughput and the fairness of the channel access of the improved algorithms, the simulation results show that, compared with BEB algorithm, improved MILD backoff algorithm can improve the fairness of the channel access, improved EIED backoff algorithm can increase the network's throughput ,while improved BEB algorithm can improve the fairness of the channel access and increase the network's throughput in a way at the same time.