Research On Reliable Routing In Wireless Ad Hoc Networks

Wireless Ad Hoc network, composed of independent wireless nodes, is a kind of dynamic self-organized networks. Each node moves independently and works both as a communication terminal and a router. Wireless Ad Hoc network is arbitrary and dynamic. Thus, it can survive without any fixed infrastructures and is suitable for being applied in disaster relief and rescue, temporal meetings, battlefields, intelligent traffic and environment monitor.For wireless Ad Hoc network, the routing is the primary function for the deployment in the realistic scenarios. However, there are still some open issues on the reliability of existing routing techniques, which include:(1) transmission errors due to the collision and interference between transmitted packets; (2) the routing congestion on nodes with heavy traffics, due to the shared channel; (3) invalid nodes and links due to the consumption of energy and bandwidth; (4) weak reliability of long multiple hop routing, due to the maintenance overhead and high loss ratio in large scale wireless ad hoc networks.To address the mentioned issues, we start the research based on the network architecture and propose solutions in MAC, network and application layers respectively. Then an implementation of cross layer optimization is conducted based on the two solutions in MAC and network layers. The contributions in this dissertation, in terms of wireless Ad Hoc network architecture, can be categorized as follows:(1) In MAC layer, a threshold based distributed flow control (TDFC) mechanism is proposed. By setting the block threshold for each flow, the communication congestion can be detected immediately. Meanwhile, the packets of greedy data flows are blocked by the relaying nodes. Thus, TDFC reacts efficiently on congestion and avoids the flow starvation.(2) In network layer, an energy-balance connected dominated set (EB-CDS) mechanism is proposed. It constructs CDS based on the left energy and connectivity degree. The dominating node with fast energy consumption speed selects dominator candidates and splits the routing load. EB-CDS can prolong the network lifetime by saving the energy of dominating nodes.(3) In application layer, a distributed index algorithm based on the geographical hashing table (DI-GHT) is proposed. The network is partitioned into domains and DI-GHT distributes resource index in all domains. Routing is implemented in the local domain and the routing path length is reduced. The requestor finds the index information in the nearest domains using the hash function and then retrieves the resource. Thus, DI-GHT can reduce the maintenance overhead ob routing and index.(4) Based on TDFC and EB-CDS, a cross-layer flow control mechanism named CL-TDFC is implemented. By exchanging control messages in cross-layer method, the heavy routing load is balanced when flow congestions occur or the residual energy touches the threshold.Simulations are conducted on the ns-2 platform. The results show that the algorithms proposed in this dissertation outperform existing algorithms in terms of the concerned criteria.