Towards balanced energy charging and transmission collision in wireless rechargeable sensor networks

By integrating sensing and computing capabilities into the traditional radio frequency identification (RFID) tags, the wireless identification and sensing platform (WISP) opens up a new research area referred to as wireless rechargeable sensor networks (WRSNs). Since WISPs need to be fully charged and then can start communication with the reader, thus the energy charging and transmission collision of WISPs are different from those of RFID tags. If the reader power is large, WISPs will be charged fast and start data transmission almost at the same time, which results in heavy transmission collision and the communication delay would be extremely large. However, if the reader power is small, WISPs will be charged slow and start data transmission one by one even without collisionh between any two WISPs, but the charging period of the whole network would be extremely large. Therefore, this paper aims at determining an optimal reader power towards balanced energy charging and transmission collision, such that the total duration for all WISPs to be fully charged and completely communicated is minimized. Firstly, we investigate on dynamic reader power with transmission collision avoidance, and static reader power towards balanced energy charging and transmission collision. Then, we derive the optimal reader power in three cases: (i) One reader and ray-uniformly distributed WISPs; (ii) one reader and randomly distributed WISPs; and (iii) multiple readers and randomly distributed WISPs. Finally, the theoretical analysis is verified through extensive evaluations.