Analysis And Optimization Of Communication Performance In Wireless Rechargeable Sensor Networks

Wireless rechargeable sensor network can capture and store the wireless power in the space which makes it possible to function without battery. Therefore, it is expected that such network can be widely used in various applications such as road and bridge monitoring systems, and etc.In typical wireless rechargeable sensor network, nodes are usually attached to different ob-jects for sensing and data processing. At the same time, the reader is deployed in fixed position or move along certain route for node communication and collect sensor nodes’information by backscatter communications. With the increase of network scale, large number of nodes may re-sponse to near reader’s data request at the same time, and lead to serious communication collision in network. On the other hand, different from traditional RFID tag, wireless rechargeable sensor nodes usually need to transmit much longer data packets with sensory information, which increase data transmission delay, and thus cause more serious communication collision.EPC ClG2 and ALOHA are major protocols that are implemented in RFID networks nowa-days. They decrease communication collision by node scheduling, but can not avoid communi-cation collision completely. However, the deeply coupled charging process and communication process makes any communication collision cause serious communication delay since the collided nodes have to be recharged for communication success. Such problem becomes even more serious when the network scale becomes larger. The voltage of general wireless rechargeable sensor nodes need to be charged above certain threshold to guarantee reliable sensing, computing and communi-cation. And charging delay is positive related to charging distance between the reader and the node. In this paper, we exploit the typical charging character of wireless rechargeable sensor network, and propose a series of new methods to realize entirely collision-free communication by reader control. Different from existing methods which decrease communication collision by modifying media access protocol, our methods make nodes transmit information once they reach threshold voltage, to avoid communication collision fundamentally and decrease communication delay espe-cially for large-scale networks. Meanwhile, our approach does not need any modification of MAC layer protocols and thus simplify the implementation at both the reader and the nodes sides.Our contribution is as follows.1)For the situation when single reader is able to cover all sensor nodes, this paper proposes optimal deployment strategy based on geometry method, and conducts optimal location of collision free to minimize communication delay.2)In scenery when the reader has to stop several positions in order to charge all nodes and collect the information, in wireless rechargeable sensor networks, this paper proves the problem is NP hard. By extending the definition of collision region, this paper proposes effective data collection strategy based on greedy algorithm, to decrease communication delay.3)This paper further investigates the collision-free communication in wireless rechargeable sensor networks by exploiting the power control capability of reader. We prove the condition of node distribution under which the collision-free communication can be achieved under power control design. The effectiveness of power control design is also verified through extensive simu-lations.