Research On QoS Issues In The Medium Access Control Layer Of Ad Hoc Networks

The Ad hoc network is a full-distributed wireless packet network. In this environment, a mobile node may function as a communication terminal and as a router node. In such network, a data packet is relayed hop-by-hop between two adjancent nodes, without any supports of infrastructure. The distinguish features of the network, which are self-organize, self-management, and multihop, make the Ad hoc network's constructing more convenient and flexible. As a result, the Ad hoc network technology has broad prospects in such communication scenarios as battlefield, hotels, public service, emergency rescue, intelligent transport, small office, venue and so on. Nowadays, the Ad hoc network is a hot research area both in home and abroad.With the increasingly use of the Ad hoc netowrk, especially after the bulk realtime applications emerging in Ad hoc network, the demanding for supporting qulity of service (QoS) in the network arises. Although the distribution feature makes the Ad hoc network's constructing more convenient and flexible, it also makes QoS supporting a huge chanllenge. So the supporting QoS is difficulty for Ad hoc reasearchers. Every layer, in the Open System Interconnect (OSI) model, must offer QoS support technology, because solving QoS problem in a certain layer is imposible. As a result, this dissertation conducts in-depth and systematical research in Medium Access Control (MAC) layer of the Ad hoc network, and makes some innovative research results:1,In the part of channel access control, to solve the problem of ignoring receive nodes' handling ability, a new receiver participated channel access control mechanism is proposed. This method can protecte the receive nodes, espcially the forwarding nodes, against congestion. Besides, it can protect the high priority flows by differentiated the reject probability between different prority flows.2,In channel contention control aspect, to solve the problem that effective means of the guarantee of a high priority flow's contention success probability are lack under high background loads in 802.11 and 802.11e protocol, a new multiple reservation mechanism is proposed. The method ensures that a high priority data has higher success probability in access channel process. When it used together with the receiver participated channel access control mechanism, the End-to-End performance of high priority flows is better guaranteed.3,In the part of QoS coordination mechanism, to solve the problem that a high priority flow cannot get more wireless resource in wireless channel contention phase, because there has no coordination mechanism, a distributed coorporation MAC protocol is proposed. This protocol coordinates the low priority flows which affects the transmitting process of high priority flows, and makes the low priority flows initiative release some wireless resources, to protect the proformance of high priority flows.4,In the part of access loads control, a new loads control mechanism base on fuzzy logical system is proposed. This mechanism is built on the base of coorporation MAC protocol, and provides a practical loads control method to protect the high priority flows' QoS.Through the research of the 4 aspects listed, the aim of this dissertation is to provide a complete solution for the MAC layer of Ad hoc networks.