Sustainable Wireless Sensor Networks with UAV-Enabled Wireless Power Transfer
Abstract : In this paper, we consider an unmanned aerial vehicle (UAV)-enabled wireless power transfer (WPT) network, where the UAV is responsible for sustaining the network with all devices on the ground. The sustainable charge process operates periodically, i.e., in each working period, the UAV flies from and back to a landing position. The initial remaining energy in the batteries and battery storage limits are considered in this study. We assume only the initial remaining network lifetime (RNL) known and no further lifetime updates available, and provide a sustainable design aiming at minimizing the average UAV consumed power while sustaining the network including all devices. We formulate the problem via determining the UAV trajectory and lengths of working period and charging phase, and introduce an iterative algorithm for an efficient solution. The repeats of designed working period are proved to guarantee the sustentation of the whole network. Moreover, when UAV behaves the same in all working periods, the obtained solution is strongly influenced by the initial RNL. To get rid of this influence, we further propose a second approach, namely a transition-based sustainable design, in which a transition state is introduced for improving the RNL, and the UAV updates its behaviour in each working period. The convergence and limit of this transition approach are addressed. After transitions, the network shifts to a steady state, and operates periodically as in the first design. Finally, through simulations, we validate the sustaining performance of both designs and the performance improvement via the transition approach.
? The multi-UAV aided wireless power and information transfer is a hybrid dynamic system, where the power transfer is continuous, and the information collection can be regarded as a discrete event due to its instantaneous completion.
? Although existing studies have made many achievements from the perspectives of charging time, data transmission delay, network utility, etc., more work is still needed, as the mobility and communication performance of mobile charging vehicles are affected by terrain and other factors, while UAV assisted charging is rarely limited.
? Moreover, the dynamic process triggered by the transition is not affected by the system parameters and network topology.
? In this regard, how to maintain the sustainable operation of these lowpower devices is becoming a more practically important as well as challenging problem to tackle.
? We first use a toy example with one single GD to show the benefit of trajectory design, and then present a generic utility maximization problem to maximize the energy amounts transferred to multiple GDs in a fair manner subject to practical UAV flight constraints.
? We formulate a generic trajectory optimization problem for the single-UAV-enabled WPT system as follows by taking into account practical UAV flight constraints.
? It is worth noticing that the trajectory optimization problem (P1) for the singleUAV-enabled WPT is different from that for the UAV-enabled multiuser wireless communications.
• In UAV-assisted RFET, RF transmitter is mounted on UAV, and path planning can be automated, as suggested by the proposed algorithm.
• Through system simulations it is demonstrated that, in a generalized setting, the charging sequence offered by the proposed variants perform increasingly better in comparison to the state-of-the-art TSP approach.
• Treating mobility as boon, the concept of mobile base station was proposed to prolong the lifetime of sensor networks.
• To overcome the battery replacement issue, energy harvesting from several ambient sources, such as solar, vibration, piezoelectric, and ambient RF, were proposed.
? We investigate the UAV trajectory design jointly with communication/computation resource allocations to optimize the system performance, subject to the energy availability constraints at GDs.
? To fully reap the benefits of UAV-enabled WPT, how to properly design the UAV trajectories to maximize the energy transfer performance is a new and challenging problem to tackle innovatively.
? To tackle the above challenges, there have been a handful of prior works in the literature that investigated the trajectory design for enhancing the energy transfer performance for UAV-enabled WPT when there is only one single UAV.
? These problems are all challenging to solve, for which the performance-complexity trade off should be considered properly.
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