Wireless energy transfer as a promising technology provides an alternative solution to prolong the lifetime of wireless rechargeable sensor networks (WRSNs). In this paper, we study replenishing energy on sensors in a WRSN to shorten energy expiration durations of sensors, by employing a mobile wireless charger to replenish sensors dynamically. We first formulate a novel sensor recharging problem with an objective of maximizing the charging utility of sensors, subject to the total traveling distance of the mobile charger per tour and the charging time window of each to-be-charged sensor. Due to the NP-hardness of the problem, we then propose an approximation algorithm with quasi-polynomial time complexity. In spite of the guaranteed performance ratio of the approximate solution, its time complexity is prohibitively high and may not be feasible in practice. Instead, we devise a fast yet scalable heuristic for the problem in response to dynamic energy consumption of sensors in the network. Furthermore, we also consider the online version of the problem where sensor replenishment is scheduled at every fixed time interval. We finally conduct extensive experiments by simulation to evaluate the performance of the proposed algorithms. Experimental results demonstrate that the proposed algorithms are very promising.

According to low earth orbit (LEO) satellite systems with users of different levels, a dynamic channel reservation scheme based on priorities is proposed. Dynamic calculation of the thresholds for reserved channels is the key of this strategy. In order to obtain the optimal thresholds, the traf c is predicted based on the high-speed deterministic movement property of LEO satellites rstly. Then, a channel allocation model based on Markov is established. Finally, the solution of the model is obtained based on the genetic algorithm. Without user location, this strategy effectively reduces handover failures and improves channel utilization by adjusting dynamically the thresholds according to traf c conditions. The simulation results show that the system's overall quality of service can be improved by this strategy.

Positioning is the foundation of wireless sensor applications. An attack method of multiple counterfeit identities in sensor network localization is proposed. At different times, attack nodes counterfeit different identities nodes, sending false reference coordinates, which leads to the failure of positioning. In the paper, we establish a normal localization system, which can accurately calculate the blind node's coordinate. Then, some attack nodes with multiple counterfeit identities was taken in localization system, which affect the result of calculating the blind node's coordinate. Through the experiment, we verify the feasibility of the proposed location attack based on multiple counterfeit identities technology.

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