Open-Loop Distributed Beamforming Using Wireless Phase and Frequency Synchronization

Coordinating the operations of separate wireless systems at the wavelength level can lead to significant improvements in wireless capabilities. We address a fundamental challenge in distributed radio frequency system cooperation—inter-node phase alignment—which must be accomplished wirelessly and is particularly challenging when the nodes are in relative motion. We present a solution to this problem that is based on a novel technique combining high-accuracy ranging and frequency transfer. We demonstrate the system in the first fully wireless open-loop coherent distributed beamforming experiment. Inter-node range estimation to support phase alignment was performed using a two-tone stepped frequency waveform (TTSFW) with a single pulse, while a two-tone waveform was used for frequency synchronization. The approach was implemented on a two-node dynamic system using Ettus X310 software-defined radios (SDRs), with coherent beamforming at 1.5 GHz.