A Novel Energy Efficient Topology Control Scheme Based on a Coverage-Preserving and Sleep Scheduling Model for Sensor Networks  
Binbin Shi  
1 School of Electronics, Suzhou Vocational University, Suzhou 215104, China 1,*  
the life cycle of the entire system. Among them, one effective method is to reduce the number of active nodes using a node sleep scheduling scheme. Only when the active node fails, some redundant nodes will be awakened. In the early stage, a certain number of nodes are selected randomly according to the nodes' sensing distances, and the other nodes can be turned to a dormant state. In order to reduce the uncertainty effects of random scheduling, several works have been implemented to operate a node set rotation method. In this way, all nodes are divided into multiple sets, and each set is rotated independently to undertake monitoring tasks. Once the number of nodes in each set is the least and the number of node sets is maximized, this will extend the time interval of nodes in an active state. The main idea is that the redundant nodes should shut down to save energy after a quantitative selection process, and at the same time the initial coverage of the network is guaranteed. With a controlled scheduling scheme, some nodes take turns to be in a dormant state with low power, which can conserve the node's energy and improve the network lifespan. The current control scheduling methods can be classified as follows: random scheduling [6] and sleep scheduling [7]. * _Random scheduling methods._ The nodes can autonomously sense and collect the information of the target area on the basis of a variety of factors, for example, location information, the number of neighbor nodes, node residual energy, etc. [8]. Then, according to the built-in algorithm, the sensor node can decide freely whether it should remain in working condition or close its function module into a state of dormancy. In addition, in clustered ESNs, the cluster head can control the working status of its member nodes by means of the hierarchical structure [9]. Generally speaking, in the stochastic scheduling method, all nodes can determine the appropriate status alone from their own actions, no matter what the other nodes do, which can effectively reduce the communication overhead between nodes. * _Sleep scheduling schemes._ By making a global and comprehensive judgment of the nodes based on the degree of coverage redundancy in the network, the redundant nodes may be closed according to certain rules so as to achieve a balanced energy consumption and prolong the network lifetime [10]. This type of scheduling approach demands that the nodes cooperate with each other to complete the tasks, and massive factors should be taken into account comprehensively to determine which nodes are redundant, for example, the coverage ratio, nodes' location information, the number of neighbor nodes, the distance between nodes, etc. [11; 12]. In this way, the sharing of state information between nodes will increase communication overhead, but the advantage is that the distribution of active nodes in the target area is more balanced. This can effectively avoid the problem of \"routing holes\" in some areas of the network which occurs more frequently with stochastic scheduling methods. By judging whether the node is redundant, the node sleep scheduling scheme can adjust the sleep-wake schedule of eligible nodes and reduce the sensors' energy consumption [13]. However, it will generate another problem, that is, whether the coverage and connectivity of the network can be guaranteed. ESNs are data-centric networks, and the leading performance indicator of the quality of the network is whether can obtain all the information in the monitored area [14], which is the most essential requirement for the design of ESNs. For example, in event monitoring applications, the primary concern is whether the deployed network can detect all the events occurring within the entire region [15; 16].