UAV Trajectory Planning for Data Collection from Time-Constrained IoT Devices

The global evolution of wireless technologies and intelligent sensing devices are transforming the realization of smart cities. Among the myriad of use cases, there is a need to support applications whereby low-resource IoT devices need to upload their sensor data to a remote control centre by target hard deadlines; otherwise, the data becomes outdated and loses its value, for example, in emergency or industrial control scenarios. In addition, the IoT devices can be either located in remote areas with limited wireless coverage or in dense areas with relatively low quality of service. This motivates the utilization of UAVs to offload traffic from existing wireless networks by collecting data from time-constrained IoT devices with performance guarantees. To this end, we jointly optimize the trajectory of a UAV and the radio resource allocation to maximize the number of served IoT devices, where each device has its own target data upload deadline. The formulated optimization problem is shown to be mixed integer non-convex and generally NP-hard. To solve it, we first propose the high-complexity branch, reduce and bound (BRB) algorithm to find the global optimal solution for relatively small scale scenarios. Then, we develop an effective sub-optimal algorithm based on successive convex approximation in order to obtain results for larger networks. Next, we propose an extension algorithm to further minimize the UAV's flight distance for cases where the initial and final UAV locations are known a priori. We demonstrate the favourable characteristics of the algorithms via extensive simulations and analysis as a function of various system parameters, with benchmarking against two greedy algorithms based on distance and deadline metrics.

I. Introduction

The vision of smart cities is currently being pursued by governments and municipalities of major cities across the world; this massively relies on information and communications technologies to gather information which is critical for the efficient use of existing assets and resources. To deliver the grand envisioned promises, there is a need to embrace a myriad of network connected devices (wearables, smart home appliances, embedded sensors, traffic and street lights, connected vehicles, cameras, etc.) deployed in very large numbers, spanning various verticals (health, transportation, energy, industrial, etc.), leaping us to the realm of the Internet of Everything (IoE). For example, multiple sensors, meters, and street lights may be combined to improve infrastructure, services, and public utilities in cities. Other example use cases include critical applications such as disaster management, search and rescue operations and border monitoring, where a large number of Internet of Things (IoT) devices are distributed across different geographical areas for detection and measurement purposes.