| The recent advances in sensor technology, micro-electro-mechanism system (MEMS), modern network and wireless communication technology have augmented research in wireless sensor networks. A wireless sensor network is composed of tiny sensor nodes each capable of sensing some phenomenon, doing some limited data processing and communicating with each other. These tiny sensor nodes are deployed in the target field in large numbers and they collaborate to form an adhoc network capable of reporting the phenomenon to a data collection point called sink or base station. These networked sensors have many potential civil and military applications i.e., they can be utilized for object tracking, intrusion detection, habitat and other environment monitoring, disaster recovery and health related applications. In these applications, it is important for the sensor nodes to be aware of their own locations, because sensed data is always meaningless without relating to its physical position. Many protocols in WSN for example Location-Based Routing require location information for sensor nodes.The main purpose of network protocol design is to find the path between a source node and a destination node, and then messages in the network are delivered via these multi-hop routes through other sensor nodes. Geographic routing is widely used in wireless sensor networks. However the problem that most of the geographic routing algorithms which adopt greedy algorithm as their basic routing strategy have to face is the'local minimal Phenomena'. How to reduce the occurrence of local minimal and how to design the recovery strategy, is of great significance in the geographic routing.In this thesis we sum up some solutions to the routing void problem. We also discuss their performance, characters.In this thesis we deduce the probability of a node to be a routing void node theoretically within random deployment WSNs. On the basis of theoretical analysis results, a new geographic routing algorithm, Greedy algorithm based on the geographic information of 2-hop neighbors (GF-2) is accordingly put forward。GF-2 algorithm "increases" the number of neighbors of the dead-end node, so that the probability of encountering the routing voids is greatly reduced and the success rate is improved. When GF-2 fails, a hybrid algorithm based on the node density is proposed. When the node destiny is very low, we propose to perform flooding only at concave nodes, while every other intermediate node should act with the receiving messages, as in the corresponding basic routing algorithm. This system ensures the success rate as well as saves energy. Because energy consumption rapidly increases as the node density increases in this way, we recommend single-path strategies. When the node density is not high we propose Perimeter routing as a solution. Because face routing used in GPSR usually results in a large number of hops, which not only reduces network efficiency, but may also decrease delivery rate when packets are subject to the constraint of time to live (TTL). The routing path can be pruned by the active node listening to the channel all the time. When the node density is high and the protocol is loop-free, the packet can bypass the dead-end node only in the greedy mode. Simulation results show that the new routing algorithm has better characters on the packet delivery rate and the length of routing path than GPSR.In this thesis, we also propose a void avoidance algorithm-BWTR. It can be shown that the threshold value combined with the weight provide a tool to bypass any concave nodes, so the packet delivery rate is guaranteed. Furthermore threshold value can be adjusted to save energy by limiting the number of retransmitting nodes.At last, this text generalizes the conclusion from study, analyses the shortcomings and presents the direction and emphasis. |
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