Transmitter

Quantum mechanics

Control (management)

Engineering

Microeconomics

Real-time computing

Relay

Constraint (computer-aided design)

Telecommunications

Economics

Power (physics)

Computer science

Mathematical optimization

Computer network

Mechanical engineering

Trajectory optimization

Physics

Relay channel

Trajectory

Mathematics

Astronomy

Mobile telephony

Artificial intelligence

Mobile radio

Transmitter power output

Channel (broadcasting)

Wireless

Throughput

Control theory (sociology)

Maximization

IEEE Transactions on Communications

In this paper, we consider a novel mobile relaying technique, where the relay nodes are mounted on unmanned aerial vehicles (UAVs) and hence are capable of moving at high speed. Compared with conventional static relaying, mobile relaying offers a new degree of freedom for performance enhancement via careful relay trajectory design. We study the throughput maximization problem in mobile relaying systems by optimizing the source/relay transmit power along with the relay trajectory, subject to practical mobility constraints (on the UAV's speed and initial/final relay locations), as well as the information-causality constraint at the relay. It is shown that for the fixed relay trajectory, the throughput-optimal source/relay power allocations over time follow a “staircase” water filling structure, with non-increasing and non-decreasing water levels at the source and relay, respectively. On the other hand, with given power allocations, the throughput can be further improved by optimizing the UAV's trajectory via successive convex optimization. An iterative algorithm is thus proposed to optimize the power allocations and relay trajectory alternately. Furthermore, for the special case with free initial and final relay locations, the jointly optimal power allocation and relay trajectory are derived. Numerical results show that by optimizing the trajectory of the relay and power allocations adaptive to its induced channel variation, mobile relaying is able to achieve significant throughput gains over the conventional static relaying.

Throughput Maximization for UAV-Enabled Mobile Relaying Systems