Research On Energy-balanced Strategy In Wireless Sensor Networks

Wireless sensor networks (WSNs) can sense the physical world, such as sensingthe temperature and humidity changes of environment, traffic control etc. Theemergence of the internet of things makes the WSNs serve and satisfy the requirementof people better, and it has a vast application prospect in the field of industry,agriculture and medical treatment. The development of WSNs technology makeshuman’s life more intelligent, the human and physical world can achievecommunication with each other.In general, a certain number of nodes are distributed randomly in a monitoredarea. These nodes self-organize into a WSN without any control of infrastructure. Onebase station located around the monitored area is used to collect the sense data fromnodes for the user to use. The network has the basic characteristics of Ad Hocnetworks, such as dynamic topology, self-organized network, and as the basictechnology, WSNs has the characteristic of strong application correlation, with thevary of application, the network has different performance. But the nodes in WSNsare equipped with limited energy, WSNs usually has large scale, once the energy ofnodes exhausted, it is very difficult to replace or recharge the node’s battery. Theproblem of energy consumption should be considered when the protocols of differentlayer in the WSNs protocol stack are designed. How to prolong the lifetime ofnetwork maximaly is always the research hotpot.The early researchers are committed to improving the energy efficiency of nodesin the network to prolong the lifetime of network, but it still fail to postpone the deathtime of network maximaly. As WSNs adopt many to one data transmission pattern, allof sensor nodes should transmit their sense data to the sink nodes or base station. Ifsensor nodes communicate with the base station directly, the long distance communication will make the nodes that far away from the base station consumeenergy fast; if sensor nodes communicate with the base station in multi-hop mode, thenodes that near the base station consume energy fast as a result of undertaking moreloads. The two situations cause the existence of difference of energy consumption rateamong nodes, which is the phenomena of unbalanced energy consumption appeared.WSNs have the demand of coverage. Once the monitored area can’t be completelycovered, the accuracy rate of sensing data will drop. Thus, if there are nodes in thenetwork die early, it will cause the network fail to connect, and emerge the isolatedregion, the network can’t fully cover the monitored area, and the lifetime of network isend at this time. But the rate of energy consumption of nodes is different, the othernodes in the network are still have much remaining energy, therefore, how to makethe energy loss rate of nodes in the network consistent, that is achieving energyconsumption balance, will prolong the lifetime of network maximaly and effectively.Based on the necessity analysis of achieving energy consumption balance, in thisthesis, a flat routing strategy, an unequal clustering strategy based on single hoptransmission, an unequal grid clustering strategy and an unequal adaptive clusteringstrategy based on multi-hop transmission, and a transmission strategy for achievingenergy consumption synchronization are designed for balancing energy consumptionof nodes, and the goal that prolonging the lifetime of network is achieved. Thecontributions of this thesis are as follows:1. In flat routing strategy, nodes in the network are equal, the node can bothsense data and as a relay node to help other nodes to complete data transmission. Thus,the nodes near the base station usually undertake more loads, these nodes die earlierbecause of excessive energy consumption. In view of the imbalance energyconsumption phenomena, a transmission power feedback control mechanism forachieving energy consumption balance is present in this thesis, the problem of energyconsumption balance is expressed as nonlinear programming problem with discretemulti-constraints, which is solved by the relative difference method, and thus theoptimal transmission radius of nodes in the network can be obtained. Through gettinghistory information of network in real time, that is energy information, the transmission radius of nodes can be adjusted feedback periodically, which makes thetransmission power of nodes change with the network operation, the time-varyingcharacteristics of the network is considered. The load undertaken by nodes in thenetwork can be redistributed, the consistence of energy consumption rate of node canbe improved, and the dead time of the network is deferred effectively. This algorithmnot only decreases the energy consumption of nodes, but also balances the energyconsumption of nodes by redistributing the loads. On the base of the distance betweennodes and the base station, the nodes with high remaining energy will be exploited,and the nodes with low remaining energy will be protected.2. In single-hop clustering strategy, cluster heads transmit the fusion data to thebase station directly, and the long distance transmission will consume more energy.Under this communication pattern, the cluster heads far away from the base stationexhaust their energy early for long distance communication, the network can’t beconnected, the monitored area fail to be covered. In this thesis, through analyzingenergy consumption of clusters located at different positions in the network, theconclusion is that once the network is distributed, the energy consumption of eachcluster is related to the radius of cluster. Based on the analytic result, an unequalcluster strategy for single-hop transmission is proposed in this thesis that is the clusterfar away from the base station has small cluster radius, the number of clustermembers it manages is decreased, thus the energy can be saved for long distancetransmission, and the cluster head near the base station can add its cluster radius, thenumber of cluster members it manages is increased, thus the energy consumptionefficiency can be improved. In this way, the energy of nodes in the network decreaseuniformly.3. In multi-hop clustering strategy, through multi-hop transmission cluster headsin cooperative way to complete the communication with the base station. Although itimproved the energy consumption efficiency of nodes in the network, the clusterheads near the base station will die earlier owing to overmuch load unavoidable. Tosolve the problem of unbalanced energy consumption, an unequal grid clusteringstrategy is presented. The network is partitioned into grids with different lengths, and the network structure is divided based on the grid is conducive to a more accurateanalysis of the load of network. Furthermore, the optimized cluster radius can beobtained based on the load and energy consumption analysis in the network. Thelength of grid that near the base station is shorter than that far away from the basestation. At the same time, the cluster head election adopts recommendationmechanism. The cluster heads will recommend the cluster member with highremaining energy to be the new cluster head which decreases the energy consumptionof cluster head election effectively.4. In multi-hop unequal clustering strategy, cluster radius is usually fixed, butWSNs is changed in real-time, the fixed cluster will cause the fringe nodes of clusterdie earlier, the unbalance energy consumption phenomena is still existence. Thus, inthis thesis, a unequal clustering strategy with cluster radius adjust adaptively ispresented, based on the average energy comparison among the node and its neighbors,the sensor nodes can adjust its competitive radius adaptively, that is the node withhigh remaining energy can increase its competitive radius and the cluster head withlow remaining energy can decrease its competitive radius to protect its energy.Combining cluster head recommendation mechanism and the two division of clusterstrategy proposed in this thesis, the balanced energy consumption of nodes in thenetwork is achieved effectively.5. For achieving energy consumption synchronization, based on the complexnetwork synchronization theory, the relationship among nodes is represented ascoupling relationship in this thesis. Furthermore, we construct the node state equation,and the remaining energy of nodes and the distance between nodes and the basestation are transferred into coupling factor, which is used to describe the transmissioncost between nodes. The key nodes in the network limit the lifetime of network, andthe betweenness of nodes can describe its influence on the network primely. Thoughreducing the maximum betweenness of nodes in the network continuously in thisthesis, which decreases the influence by key node on the network, the synchronizationability of networks is enhanced, and data distribution in the network is uniform, theoptimal transmission routes can be obtained, the balance energy consumption of the whole network is achieved finally.In this thesis, though energy consumption analysis of WSNs under differentstructure, we describe energy consumption problem with different forms, with thehelp of nonlinear programming and the synchronization theory in complex network,the transmission power of nodes, cluster radius, and the amount of data in the networkis adjusted, the energy consumption of nodes in the network is declined uniformly, thepurpose of prolonging the lifetime of network is achieved.