Distributed Beamforming in Wireless Multiuser Relay-Interference Networks with Quantized Feedback

TL;DR

This paper investigates quantized beamforming in wireless relay-interference networks, proposing schemes that maximize diversity gains with minimal feedback, and analyzing the impact of quantization on system performance.

Contribution

It introduces a generalized diversity measure, analyzes diversity loss in relay-interference networks, and develops quantization schemes that achieve maximal diversity with low feedback.

Findings

Relay-interference networks suffer second-order diversity loss.

Global quantizer with relay selection achieves maximal diversity.

Local quantizers can achieve maximal diversity with low feedback.

Abstract

We study quantized beamforming in wireless amplify-and-forward relay-interference networks with any number of transmitters, relays, and receivers. We design the quantizer of the channel state information to minimize the probability that at least one receiver incorrectly decodes its desired symbol(s). Correspondingly, we introduce a generalized diversity measure that encapsulates the conventional one as the first-order diversity. Additionally, it incorporates the second-order diversity, which is concerned with the transmitter power dependent logarithmic terms that appear in the error rate expression. First, we show that, regardless of the quantizer and the amount of feedback that is used, the relay-interference network suffers a second-order diversity loss compared to interference-free networks. Then, two different quantization schemes are studied: First, using a global quantizer, we show that a simple relay selection scheme can achieve maximal diversity. Then, using the localization method, we construct both fixed-length and variable-length local (distributed) quantizers (fLQs and vLQs). Our fLQs achieve maximal first-order diversity, whereas our vLQs achieve maximal diversity. Moreover, we show that all the promised diversity and array gains can be obtained with arbitrarily low feedback rates when the transmitter powers are sufficiently large. Finally, we confirm our analytical findings through simulations.