Research On Node Cooperation Schemes For Mobile Ad Hoc Network

Mobile ad hoc network is a Multi-hop Wireless Network which is composed of anumber of mobile nodes and does not rely on any infrastructure communication facility.Due to the lack of infrastructure supporting, coupled with the limited transmission rangeof nodes, the source nodes can not often communicate directly with the destination nodes,so the helps of middle forwarding nodes are demanded. In mobile ad hoc network, ifthere is no cooperation between nodes, routing will not to be set up, packets will not betransmitted, and there cannot exist multi-hop communications between nodes.However, the cooperation between nodes, for example, forwarding data for othernodes, is not always guaranteed. For the purpose of saving their own resources (suchas energy), selfish nodes may refuse to forward packets for other nodes, thus showingthe non-cooperative behaviors, which can seriously affect the network performance. Thepurpose of cooperation scheme is to enforce or incentive the selfish nodes to participatein the network cooperation, maintaining the normal operations of the network.In this thesis, we have improved the reputation based cooperation schemesand proposed the common-neighbor monitoring enabled cooperation enforcementscheme(CMC). Through the introduction of common neighbor monitoring technique, thewatchdog not only monitors the behavior of next hop forwarding node, but also monitorsthe surrounding connections, speeding up the detecting rate to the selfish nodes. In theroute discovery phase, the CMC scheme filters the routing control messages, discardingthose messages which contain selfish nodes, making the route that the source node findsas far as possible bypass the selfish nodes, reducing the impact that selfish nodes have onnetwork performance.The CMC scheme calculates node reputations using the direct information, althougha higher detection accuracy and relatively easy to implement, the detection rate to self-ish nodes is slow. So this thesis further proposed the TORA protocol with cooperationenhanced scheme(TORA CE), which computes the node reputations using one-hop infor-mation, improving the detection rate to selfish nodes. The TORA CE scheme, which isbased on the TORA protocol, is a multi-path ad hoc network nodes cooperation scheme.Each node has multi paths leading to the destination node. After the discovery of a selfish node, the TORA CE scheme can switch route quickly, reducing the probability of drop-ping packets in data transmission phase. The TORA CE method has better distributedcharacteristics, and limiting the route changes that selfish nodes triggered in a smallerrange.Using the game theory and mechanism design theory to analysis and design nodecooperation schemes is the inevitable trend of the future, so this thesis has analyzed theVCG mechanism based cooperation scheme and proposed the low message-overhead co-operation protocol(LMOCP). The LMOCP protocol is an improvement to the Ad hoc-VCG and LOTTO protocol, modifying four drawbacks in the Ad hoc-VCG protocol, andhas a lower message overload. Through the introduction of neighbor discovery process,nodes periodically broadcast"hello"messages in maximum transmitting power, so thateach node can calculate the minimum transmission power from neighbors to itself. Atthe same time, the routing discovery process has been improved to reduce the number ofcontrol messages. This thesis also analyzed the correctness of the LMOCP protocol andproved that the LMOCP protocol is ex post Nash implementable. Under the assumptionthat all nodes are rationality, the optimal strategy for each node is to honestly report theirown forwarding cost.However, the message overhead of the LMOCP protocol is still huge, which isO(n~2), so this thesis further proposed a broadcast tree enhanced node cooperation proto-col (BEC). After the construction of a broadcast tree rooted at the destination node in therouting discovery process, the control messages are transmitted to the destination nodealong the broadcast tree, which can further reduce the control messages. For a broad-cast tree with its height equal to O(lg(n)), the message overhead in BEC protocol isO(n lg(n)), lower than that of LOTTO protocol which is O(n~2). In addition, in BEC pro-tocol, the destination node is responsible for collecting the network topology informationand calculating the minimum cost path from source to destination node, and do not needto assume that the source node is honest, which more satisfies the real situation of thenetwork.