Unmanned aerial vehicles have been widely used to assist wireless sensor networks due to ever-increasing demands for Internet-of-things applications. To support timely delivery of information characterised by a recently introduced metric, termed as the age of information, this paper explores freshness of data in an unmanned aerial vehicle assisted wireless sensor network. Specifically, the authors consider a limited-energy unmanned aerial vehicle moving towards the Internet-of-things devices to disseminate data packets provided by a data centre. Since the unmanned aerial vehicle cannot visit all the nodes in each flight turn due to its finite-sized battery, the best sequence of nodes, from an age of information perspective, should be selected at the beginning of each flight turn. Thus, an unmanned aerial vehicle trajectory planning for data dissemination is proposed taking into account both maximal use of energy and freshness of data. To minimise the weighted sum age of information metric, by utilising the well-known knapsack and travelling salesman problems, the authors propose an algorithm to efficiently select devices and the corresponding visiting order in each flight turn. Finally, to highlight performance of the proposed algorithm, and to investigate the effect of limited-energy unmanned aerial vehicles, the number of nodes and flight turns, and simulation results are also provided and compared with other benchmark algorithms.
INTRODUCTIONRecently, unmanned aerial vehicles (UAVs) have attracted a lot of research attention in many Internet-of-things (IoT) services such as real-time monitoring of traffic [1], disaster management [2] and crowd surveillance [3]. Due to the high mobility and lineof-sight (LoS) communication opportunities, UAVs can be used as a flying base station (BS) for data collection or dissemination, specifically enhancing connectivity when there is no good enough reliable communications link between IoT devices and a BS [4]. However, the deployment of UAVs as aerial BSs leads to several challenges such as optimal trajectory planning, placement and energy consumption [5]. These challenges have been extensively studied in the literature from various perspectives: minimising delay and flight time or maximising network coverage and throughput. For instance, Mozaffari et al. [6] studied optimal deployment of UAVs to maximise network coverage. In [7], the authors min-This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.