Distributed Transmit Beamforming: Design and Demonstration from the Lab to UAVs

TL;DR

This paper presents a comprehensive design and experimental validation of distributed transmit beamforming systems, optimizing parameters like preamble length and number of radios to enhance reliable communication range, demonstrated from lab setups to UAVs.

Contribution

It introduces a novel optimization framework for distributed beamforming that accounts for estimation errors, validated through simulations and real-world UAV experiments.

Findings

Optimized the number of radios and preamble lengths for reliable beamforming.

Validated the design through simulations and UAV experiments.

Demonstrated effective beamforming from lab to UAVs.

Abstract

Cooperating radios can extend their communication range by adjusting their signals to ensure coherent combining at a destination radio. This technique is called distributed transmit beamforming. Beamforming (BF) relies on the BF radios having frequency synchronized carriers and phases adjusted for coherent combining. Both requirements are typically met by exchanging preambles with the destination. However, since BF aims to increase the communication range, the individually transmitted preambles are typically at low SNR and their lengths are constrained by the channel coherence time. These noisy preambles lead to errors in frequency and phase estimation, which result in randomly changing BF gains. To build reliable distributed BF systems, the impact of estimation errors on the BF gains need to be considered in the design. In this work, assuming a destination-led BF protocol and Kalman filter for frequency tracking, we optimize the number of BF radios and the preamble lengths to achieve reliable BF gain. To do that, we characterize the relations between the BF gains distribution, the channel coherence time, and design parameters like the SNR, preamble lengths, and the number of radios. The proposed relations are verified using simulations and via experiments using software-defined radios in a lab and on UAVs.