# A Simple Receive Diversity Technique for Distributed Beamforming

## TL;DR

This paper introduces a simple space-time diversity transformation technique for distributed beamforming with a two-antenna destination, enhancing diversity order without needing channel state information at the receiver.

## Contribution

It proposes a novel front-end operation at the destination that extends distributed beamforming to a two-antenna receiver, doubling diversity order without additional channel information.

## Key findings

- Doubles the diversity order compared to single-antenna receivers.
- Retains array gain while eliminating the need for receiver channel state information.
- Applicable in ultra-reliable, low-latency communication scenarios.

## Abstract

A simple method is proposed for use in a scenario involving a single-antenna source node communicating with a destination node that is equipped with two antennas via multiple single-antenna relay nodes, where each relay is subject to an individual power constraint. Furthermore, ultra-reliable and low-latency communication are desired. The latter requirement translates to considering only schemes that make use of local channel state information. Whereas for a receiver equipped with a single antenna, distributed beamforming is a well known and adequate solution, no straightforward extension is known. In this paper, a scheme is proposed based on a space-time diversity transformation that is applied as a front-end operation at the destination node. This results in an effective unitary channel matrix replacing the scalar coefficient corresponding to each user. Each relay node then inverts its associated channel matrix, which is the generalization of undoing the channel phase in the classical case of distributed beamforming to a single-antenna receiver, and then repeats the message over the resulting "gain-only" channel. In comparison to a single-antenna destination node, the method doubles the diversity order without requiring any channel state information at the receiver while at the same time retaining the array gain offered by the relays.