[Paper Review] Energy Minimization for Wireless Communication with Rotary-Wing UAV

Yong Zeng, Jie Xu+1 more|arXiv (Cornell University)|Apr 6, 2018

UAV Applications and Optimization24 references75 citations

TL;DR

The paper develops an energy-minimizing framework for rotary-wing UAV-enabled wireless communication by modeling propulsion energy, formulating a joint trajectory and scheduling optimization, and solving via fly-hover-communicate and path discretization methods.

ABSTRACT

This paper studies unmanned aerial vehicle (UAV) enabled wireless communication, where a rotarywing UAV is dispatched to send/collect data to/from multiple ground nodes (GNs). We aim to minimize the total UAV energy consumption, including both propulsion energy and communication related energy, while satisfying the communication throughput requirement of each GN. To this end, we first derive an analytical propulsion power consumption model for rotary-wing UAVs, and then formulate the energy minimization problem by jointly optimizing the UAV trajectory and communication time allocation among GNs, as well as the total mission completion time. The problem is difficult to be optimally solved, as it is non-convex and involves infinitely many variables over time. To tackle this problem, we first consider the simple fly-hover-communicate design, where the UAV successively visits a set of hovering locations and communicates with one corresponding GN when hovering at each location. For this design, we propose an efficient algorithm to optimize the hovering locations and durations, as well as the flying trajectory connecting these hovering locations, by leveraging the travelling salesman problem (TSP) and convex optimization techniques. Next, we consider the general case where the UAV communicates also when flying. We propose a new path discretization method to transform the original problem into a discretized equivalent with a finite number of optimization variables, for which we obtain a locally optimal solution by applying the successive convex approximation (SCA) technique. Numerical results show the significant performance gains of the proposed designs over benchmark schemes, in achieving energy-efficient communication with rotary-wing UAVs.

Motivation & Objective

• Minimize total UAV energy consumption including propulsion and communication energy.
• Ensure each ground node achieves its target information throughput.
• Understand the trade-off between flying and hovering/communication energy in rotary-wing UAVs.
• Explore tractable solution approaches for both simple and general UAV communication protocols.
• Provide insights and algorithms for energy-efficient trajectory design under TDMA with rotary-wing dynamics.

Proposed method

• Derive an analytical propulsion power model for rotary-wing UAVs capturing blade profile, induced, and parasite power components.
• Formulate a non-convex energy minimization problem (P1) over trajectory, time allocation, and mission time with throughput constraints.
• Use a fly-hover-communicate protocol to reduce (P1) to a finite-variable problem and solve via TSP-based ordering and convex optimization.
• Introduce a path discretization method to convert the time-continuous problem into a finite-variable form suitable for successive convex approximation (SCA).
• Show convergence to a locally optimal solution that satisfies KKT conditions.
• Provide asymptotic/heuristic insights for single and multiple GN cases, including MR/MÉ constants and optimal traveling speeds.

Experimental results

Research questions

• RQ1 How to minimize total UAV energy (propulsion plus communication) while satisfying per-GN throughput requirements?
• RQ2 What are efficient algorithms for UAV trajectory and TDMA scheduling to optimize energy under rotary-wing propulsion dynamics?
• RQ3 How can fly-hover-communicate and path discretization approaches be used to obtain tractable, near-optimal solutions?
• RQ4 What is the trade-off between traveling energy and hovering/communication energy for rotary-wing UAVs in data collection/relaying scenarios?
• RQ5 How does the visiting order and hovering locations influence total energy consumption in multi-GN settings?

Key findings

• Propulsion energy for rotary-wing UAVs comprises blade profile, induced, and parasite components; hovering is not always most energy-efficient.
• For a single GN, an optimal balance exists between traveling to an optimal hover point and hovering to transmit, determined by MR speed and a one-dimensional D_tr trade-off.
• For multiple GNs, the energy is minimized by selecting appropriate hovering locations and visiting order, reducing to a TSP-like problem with convex optimization for waypoint placement.
• A path discretization approach with SCA yields a locally optimal solution to the general (P1) problem without pre-specifying mission time.
• Numerical results show significant energy savings of the proposed fly-hover-communicate and path-discretization designs over benchmarks.