Study On Key Techniques Of Mobile Ad Hoc Networks

Ubiquitous computing is a communication mode which can provide information services anywhere and anytime.The mobile ad hoc network is a new important technology to realize ubiquitous computing, in which the communication between nodes relies on mutual cooperation in the manner of wireless multi-hop.This technology has the characteristics such as self organized, fast deployment and independent of infrastructure, which make it have wide prospects in both the fields of civilian and military. Therefore this type of networking plays a more important role in many aspects of people's daily life and military applications.Under this background, this dissertation carries out deep researches in several important techniques of mobile ad hoc network, which include the mechanism of IEEE 802.11e EDCA, broadcast algorithm and publish subscribe routing algorithm for ad hoc network. The main contributions of this dissertation are as follows:(1)This dissertation proposes a dynamic access control algorithm which can provide end to end delay assurance in multihop wireless network. The design idea of this algorithm is:Individual node estimates the transmitting delay from itself to every destination for each access categories; This algorithm provides the function of estimating the transmitting time of each packet in MAC layer. By subtracting end to end delay requirement from the packet transmitting time, the remaining time of this packet is obtained; An intermediate node will compare the packet's remaining time and each access categories'transmitting delay when it receives a packet.Then the node adjusts packets'priority. The simulation results show that:compared with EDCA, this algorithm achieving the end to end delay assurance;compared with APHD, this algorithm improves the network throughput and transimting delay.(2) This dissertation proposes a dynamic broadcasting algorithm. Firstly, a mathematic model is proposed by which the contention problems and additional coverage area are analyzed.Inspired by these analysis results,a dynamic broadcasting algorithm for on-demand routing protocol is proposed, which computes the broadcast probability of control message by neighbor node density and relative distance.By dynamically adjusting the broadcast probability, the redundant control message is reduced and the contention problem is alleviated.The simulation results show that:by applying this algorithm to on demand routing protocol,control messages'overhead is reduced, the packet delivery ratio is improved and the end to end delay is decreased.(3)This dissertation put forwards a publish subscribe routing algorithm for the ad hoc network. The design idea of this algorithm is:a).Construct the forwarding mesh topology through publisher query packet originated by publisher and subscriber reply packet from subscriber.b).Implement the content based routing strategy and subscription cover strategy in network layer. Content based routing strategy can filter unnecessary events which are not subscribed by subscribers.Subscription cover strategy will improve this routing strategy and further reduce the transmission of unnecessary events. The simulation results indicate that:PSRBSC can reduce the total cost of the network, improve subscription rate and average routing delay for events.(4) Based on our research of PSRBSC, this dissertation integrates the gossip algorithm and publish subscribe routing algorithm for ad hoc network. A new algorithm is proposed, which can improve subscription rate for publish subscribe system. In this algorithm, the publishers and subscribers will buffer the events received from network. The subscribers will send Gossip Subscription packets to subscribe and the mobile nodes will response Gossip Event packets to subscriber if it buffered the corresponding events.The simulation results show that this algorithm improves subscription rate effectively.(5) Finally, some extened researches for publish subscribe system in wired network are carried out.An application level multicast routing protocol for publish subscribe system is proposed. Every publisher and subscriber will join the session group and construct a shared multicast tree.The subscriptions generated by subscribers will be delivered to every node of the multicast tree and the events generated by publishers will be selectively transfered on the multicast tree.Experiment results show that this protocol can effectively reduce the routing delay for events'transmission.