Research On A Hybrid MAC Protocol For Ad Hoc Networks

Self-organizing mobile network (Ad hoc networks) is a wireless packet networks with dynamic topologic structure. It does not need the support of fixed communication facilities. Network nodes may function as communication terminals or intermediate nodes (routers). Ad hoc networks can self-organize and self-manage along with node's join, left and move. Despite the initial goal of Ad hoc networks is designed to meet the needs of military communication, but with the in-depth study, it was found that Ad hoc networks can be widely used, such as emergency rescue, provisional meeting, wireless home networks and other civilian communication fields. In Ad hoc networks protocol stack, media access control (MAC) protocol running on the physical layer,is the direct controller of all packets to send and receive on the wireless channel. MAC protocol is one of the key technology problems.The MAC protocols in Ad hoc networks were deeply researched in this dissertation. How to make multiple nodes share limited wireless resource efficiently and reasonably was resolved in MAC protocol. Because of having a direct impact on network throughput, latency and other performance,MAC protocol plays a decisive role in Ad hoc networks performance. According to the method access to media, MAC protocols in Ad hoc networks can be divided into three categories: contention protocol, allocation protocol and hybrid protocol. Hybrid protocol can remain the strengths of its combined protocols while offsetting their weaknesses.Referring other brought up MAC protocols and research experience, aiming to achieve much high overall system performance under diverse traffic loading conditions, a hybrid MAC protocol–MHTDMA that based on TDMA and CSMA/CA is proposed. MHTDMA adjust channel access strategy depending on the level of contention in the network. Under low contention, this protocol behaves like CSMA/CA. Under high contention, this protocol behaves like TDMA and uses GPS realizing global time synchronization in previous stage and uses much low cost local synchronization later on. Through combining the strengths of TDMA and CSMA/CA while offsetting their weakness,MHTDMA is shown to improve overall system performance under diverse traffic loading conditions. Based on the theoretical algorithm analysis, MHTDMA was efficiently simulated through network simulator (NS2). Simulation results show that this protocol improves network throughput and decreases average access delay.