Study On Topology And Routing Technologies Of Wireless Sensor Networks

Wireless sensor network (WSN) has been a new research area for some years. WSN consists of a large amount of wireless sensor nodes integrated with sensing, computing and communication modules. It senses information from physical world and transmits the messages to the users. The features of self-adaptive, ruin-resistant, easy deployment and low cost, enable WSN to conduct many special applications, such as environment surveillance, medical, smart homing and military application. To extend WSN's lifetime, ensure its easy usage and guarantee the effectiveness of its data transmission is an important issue for wireless sensor network. This thesis focuses on energy-efficient algorithms and protocols, including topology control algorithms, routing algorithms and data transmission protocols. The main contributions of the thesis are as follows:(1) Bottleneck node recognition and remediationA Bottleneck Nodes is the node connecting two or more network areas by itself alone due to the casual deployment. Compared to other nodes, the bottleneck node has more influence on the lifetime of whole network. How to find bottleneck nodes in a network is actually a problem about how to find the minimum cut set in graph theory. However, it is difficult to implement this theory in a distributed way. In this thesis we defined a new kind of nodes, named quasi-Bottleneck Nodes, which have similar influence on the performance of the wireless sensor network and can be found out much more easily. Theoretical analysis and extensive simulation show that quasi-Bottleneck Nodes have significant impact on the performance of the whole network, including the speed of energy consumption and packet lost ratio. Furthermore a distributed algorithm to find out all quasi-Bottleneck Nodes and two effective solutions to eliminate the bad impact of these nodes are presented.(2) Clustering based data dissemination for mobile sinkEmploying mobile sink in Wireless Sensor Networks (WSNs) can prolong the network's lifetime and meet some specific requirements. Nowadays algorithms for mobile sink presented need the support of localization algorithms. However, the current localization algorithms are too expensive, or too imprecise, to meet the need of the routing protocols. A novel routing protocol based on clustering named CBDD for WSNs is presented in this thesis. The communication between the sink and the source is divided into inter-cluster communication and intra-cluster communication. The breakups of communication path between the sink and the source due to the sink's mobility are limited in the intra-cluster communication. Extensive simulations shown that, CBDD outperformed AODV, TTDD in the aspects of the data's time delay, the node's average energy consumption and the data's success transmission.(3) Routing voids analyzing and resolveing in greedy forwardingGreedy Forwarding (GF) is an important routing strategy among those routing protocols based on location information in WSN. But there is routing void problem while using greedy forwarding. This thesis deduces the probability of a node to be a routing void node theoretically within deterministic deployed and random deployed WSNs, and gets the probability of encountering the routing void node while setting up a path randomly. Also a modified GF algorithm with backoff method to avoid the routing void nodes is presented. From the analysis the conclusion can be made that when the average number of neighbors is greater than 10, the success probability of the modified GF algorithm to set the routing path up is approximate 100% and is sufficient to meet the requirement of WSN applications.(4) A data dessimination mechanism based on confidence coefficientEnergy of nodes in a WSN is spent mostly on delivering the packets. In order to decrease the number of packets, while not increase the time delay, a model of data dissemination based on confidence coefficient is presented. Confidence coefficient is generated by the nodes based on the data sensed, and represents the authenticity and importance of the data. A backoff algorithm and a transmission filter based on the confidence coefficient have been designed. Extensive simulations have testified the effectiveness of the model in decreasing energy consumption as well as delay of data transmission.