# Intelligent Reflecting Surface vs. Decode-and-Forward: How Large Surfaces Are Needed to Beat Relaying?

## TL;DR

This paper compares intelligent reflecting surfaces with decode-and-forward relaying, showing that large surfaces are necessary for the former to outperform the latter in rate and energy efficiency.

## Contribution

It provides a comparative analysis highlighting the conditions under which intelligent reflecting surfaces can surpass traditional relaying techniques.

## Key findings

- Large metasurfaces are required to outperform DF relaying.
- High rates and energy efficiency benefits depend on surface size.
- Relaying remains competitive unless surfaces are very large.

## Abstract

The rate and energy efficiency of wireless channels can be improved by deploying software-controlled metasurfaces to reflect signals from the source to the destination, especially when the direct path is weak. While previous works mainly optimized the reflections, this letter compares the new technology with classic decode-and-forward (DF) relaying. The main observation is that very high rates and/or large metasurfaces are needed to outperform DF relaying, both in terms of minimizing the total transmit power and maximizing the energy efficiency, which also includes the dissipation in the transceiver hardware.