## 5 Simulation and Results Analysis
The coverage rate of the EAER algorithm also decreases gradually over rounds, and the coverage rate of the CPCSS algorithm is much slower than others. At 518 rounds of the network, the EAER coverage is close to zero, and at this time the coverage ratio in CPCSS is still 61.2%. Until 591 rounds, the coverage rate of the CPCSS algorithm will drop to zero rather slowly. It is mainly beneficial of that each node can dynamically adjust its own state according to the residual energy and the coverage of the neighbor nodes in CPCSS. In EAER, the periodic asynchronous mode is repeated in the state estimation, which has a great effect on the energy consumption and reduces the energy efficiency. The performances of the proposed algorithm with 100 and 200 nodes uniformly deployed on a network field are shown in Figure 11. In the simulation scenario, the sensing range of the node is within the limits of 8 m to 12 m while the corresponding communication range of each node is about 16-24 m, and the other parameters are consistent with the simulation parameters in the previous experiments. As expected, sleep scheduling algorithms provide a remarkable gain and maintain a high coverage rate long-term with the network running. No matter how the network density changes, the high coverage of the target area can be guaranteed during the most of the lifetime of network. Figure 12 shows that the number of active nodes varies with the increase of the initial deployment node. As it can be seen, the number of active nodes increases with a different extent in case of different  
Figure 11: Comparison of the coverage ratio over rounds. Figure 10: Comparison of the coverage ratio over rounds. density of nodes deployed from 100 to 500. Theoretically, the number of active nodes required for sensing the target area should be approximately constant. The main reason for this phenomenon is the boundary effect of the target region, in which the nodes at the edge of the area usually have less chance to be hibernated nodes owing to hard to be replaced. When the number of initial nodes is 100, active nodes in EAER and CPCSS are 38 and 33 respectively, the latter can reduce about 13.16% of active node's deployment in the network. While the total number of nodes is 300, EAER need to deploy 52 active nodes, is much higher than 44 in CPCSS. In EEHC, all nodes are active which will result in energy depletion in advance. Figure 13 shows that the average number of active nodes in the network varies with the sensing range. With the increase of the node sensing range, the number of active nodes of the algorithms is gradually reduced in the premise of ensuring the network coverage. This is because the greater the sensing range of the node, less active nodes is required to achieve the same coverage effect; namely, fewer nodes can retain the network coverage. Simulation results indicate that the number of active nodes in CPCSS is less than EAER in different sensing range model, and the advantage is more obvious especially the sensing range is small. To investigate the sensor's performance in terms of energy consumption, we compare the energy consumption of the nodes in CPCSS, EAER, and EEHC. Figure 14 shows the variation of total energy consumption of the network over the number of rounds. Since the initial energy of each node is 2 J,  
Figure 12: The average number of active nodes versus number of sensor nodes. Figure 13: The average number of active nodes versus sensing range. there are 200 nodes being deployed in the network and the total energy is 400 J. As can be seen from the results, the energy consumption of CPCSS is much slower than the EEHC and EAER. Figure 15 shows the number of alive nodes over rounds. It can be seen that in contrast to the EAER and EEHC protocols, the number of alive nodes in CPCSS decreases more smoothly. This is because the reduction of working sensors in CPCSS can conserve energy and prolong their operation lifetimes. Subsequently, we examine the performance of energy efficiency of the whole network.