Research On Backoff Algorithm For Ad Hoc Network

Backoff algorithm is an important method of contention resolution used in wirelessnetwork shared by multiple users and a major research point in Ad Hoc network. Asuccessful devised backoff scheme can effectively reduce collision probability, improvefairness and make system better. As a channel access regulation mechanism proposed byIEEE802.11, Binary Exponential Backoff(BEB) has some disadvantages such asunfairness, not to take retransmission times and multi-hop into account. In this thesis,backoff algorithms are studied. The main achievements are outlined as follows:Firstly, the defects of BEB are studied, then by devising simulations respectively formulti-hop and retransmission times, this paper studies both’s influence on BEB. Resultsshow that BEB is not suitable for Ad Hoc network, and system with retransmission timelimitation has better performance when network scale is moderate. Besides, according tostudy on exiting backoff algorithms, four backoff algorithms are simulated and resultsindicate that delicate evaluation of channel status is the key for the choice of contentionwindow, and integration of various change forms can strengthen varying diversity ofcontention window, reduce the probability of choosing the same backoff value betweennodes.Secondly, an adaptive backoff algorithm for Ad Hoc network on transmissionstatus(TSB) is researched. This scheme takes the number of contention nodes, the reasonsof transmission failure and retransmission time limitation into account, deepens theknowledge of channel state, and gives higher priority to data transmitted several times.Analysis and simulation results demonstrate that this algorithm has been greatly improvedon throughput, end-to-end delay and collision rate.Thirdly, transmission limited backoff algorithm(TLB) is studied for Ad Hoc network.By“reverse cross backoff”,“interpolation”and“combination of additive change andmultiplicative change”, TLB strengthens varying diversity of contention window, reducescollision probability, and increases the probability of successful transmission within threeretrials. Simulation results demonstrate that compared with BEB, TLB has advanced throughput, end-to-end delay and collision rate.