Filter-And-Forward Distributed Beamforming in Relay Networks with Frequency Selective Fading

TL;DR

This paper introduces a filter-and-forward distributed beamforming method for relay networks experiencing frequency selective fading, offering significant performance improvements over traditional amplify-and-forward strategies.

Contribution

It proposes a novel filter-and-forward approach with closed-form solutions for power minimization and QoS maximization, extending to joint power constraints via convex optimization.

Findings

Substantial performance gains over amplify-and-forward strategies.

Closed-form solutions for key beamforming problems.

Effective handling of frequency selective fading.

Abstract

A new approach to distributed cooperative beamforming in relay networks with frequency selective fading is proposed. It is assumed that all the relay nodes are equipped with finite impulse response (FIR) filters and use a filter-and-forward (FF) strategy to compensate for the transmitter-to-relay and relay-to-destination channels. Three relevant half-duplex distributed beamforming problems are considered. The first problem amounts to minimizing the total relay transmitted power subject to the destination quality-of-service (QoS) constraint. In the second and third problems, the destination QoS is maximized subject to the total and individual relay transmitted power constraints, respectively. For the first and second problems, closed-form solutions are obtained, whereas the third problem is solved using convex optimization. The latter convex optimization technique can be also directly extended to the case when the individual and total power constraints should be jointly taken into account. Simulation results demonstrate that in the frequency selective fading case, the proposed FF approach provides substantial performance improvements as compared to the commonly used amplify-and-forward (AF) relay beamforming strategy.