Study On The Key Issues In The Wireless Multi-hop Networks

Wireless multi-hop networks (WMHN) consist of nodes that freely and dynamically self-organize into arbitrary and temporary network topology, where source nodes and destination nodes are connected by multiple wireless links. Each node in WMHN is both a host that is the source or sink of packets and a router that relays packets for other nodes. Wireless ad hoc network, wireless sensor network and wireless mesh network are three typical wireless multi-hop networks. Wireless multi-hop networks are self-forming, self-managing and self-healing networks, allowing the random entrance and exit of nodes, and automatically rerouting communications around points of failure. These features and benefits of WMHN have been attracting attentions of many researchers in last several years. Starting from the intense active areas of research in wireless multi-hop networks, network wide broadcasting mechanisms and the improvement of network capacity for wireless multi-hop networks are studied in this paper. The main research works and results are listed as follows:An efficient broadcast mechanism——maximum life-time distributed broadcast (MLDB) method is proposed in this paper. To complete a broadcast across the network, all nodes need only maintain relevant information of their one-hop neighbors in MLDB. With the aim of selecting as less rebroadcast nodes as possible, MLDB chooses nodes with more uncovered neighbors and with larger new coverage area to do rebroadcast, thus reducing the redundant rebroadcasted packets in the network. The optimized design determines the little overhead of MLDB, which is applicable in the special wireless environment of wireless ad hoc networks. Compared with other algorithms, MLDB is capable of saving more rebroadcasts and obtaining longer useful network life-time under all circumstances.Wireless sensor network is featured by small node size and memory, low computing capability, battery supplied constrained energy and high node density. In view of the above features of wireless sensor network, an effective broadcast protocol (EBP) is presented in this paper. Through the discussion on the induced rebroadcast of a node's rebroadcast, the times and locations of the optimized induced rebroadcast are analyzed. In EBP, optimized rebroadcast nodes are selected based on the above analysis results and each node needs not any neighbor information to complete a broadcast efficiently. Thus, the control and memory overheads are decreased greatly. The simple and effective EBP algorithm performs well in wireless sensor network.A new broadcast algorithm called least redundancy broadcast algorithm (LRBA) is presented for large scale wireless multi-hop networks with dense nodes deployment. To decrease redundant rebroadcast, the vertex rebroadcast mechanism and node degree are combined by LRBA. The theoretical analysis on the rebroadcast ratio is completed, and the theoretical maximum and minimum rebroadcast ratio of LRBA is obtained. Based on different self-delay mechanisms, two implementing methods of LRBA are proposed. They are LRBA1 and LRBA2. Though simulations and comparisons of the reachability, rebroadcast ratio, delay and energy consumption performances of the two methods, the better one in overall performance is pointed out. Simulation results show that LRBA is scalable in large scale wireless multi-hop networks with dense nodes deployment. Though it has more memory and computation overheads than EBP, LRBA obtains lower rebroadcast ratio than other algorithms. LRBA is especially applicable to dense, large scale wireless multi-hop networks with a certain node processing power, such as wireless mesh network.The sweeping based directional neighbor discovery algorithm is studied and analyzed. To obtain the potentials offered by smart antennas, an unaided directional neighbor discovery (UADND) algorithm is proposed for wireless multi-hop networks. With UADND, network nodes could independently discover neighbors that can be reached only when both of transmission and reception are directional, thus the capacity of the networks could be expanded. Additional information provided by GPS or other methods, such as node position or synchronization information utilized by other neighbor discovery algorithms is not necessitated in UADND. Cross layer design is used in UADND to integrate directional neighbor discovery with routing. Simulation results show that compared with other algorithms UADND completes directional neighbor discovery with less control overhead and energy consumption.