Distributed Transmit Beamforming using Feedback Control

The concept of distributed transmit beamforming is implicit in many key results of network information theory. However, its implementation in a wireless network involves the fundamental challenge of ensuring phase coherence of the radio frequency signals from the different transmitters in the presence of unknown phase offsets between the transmitters as well as unknown channel gains from the transmitters to the receiver. In this paper, we show that such phase alignment can be achieved using distributed adaptation by the transmitters with minimal feedback from the receiver. Specifically, each transmitter independently makes a small random adjustment to its phase at each iteration, while the receiver broadcasts a single bit of feedback, indicating whether the signal-to-noise ratio improved or worsened with the independent adjustments of the current iteration. The transmitters keep the `good' phase adjustments and discard the `bad' ones, thus implementing a distributed ascent a...

• Type: Journal
• Year: 2006
• Where: CORR
• Authors: Raghuraman Mudumbai, J. Hespanha, Upamanyu Madhow, Gwen Barriac
• Keywords: CORR 2006, Education, Phase Adjustments, Phase Coherence, Transmitters