Combining Relaying and Reflective Surfaces: Power Consumption and Energy Efficiency Analysis

TL;DR

This paper analyzes the power consumption and energy efficiency of hybrid relaying networks combining relays and intelligent reflective surfaces, highlighting conditions where hybrid schemes are advantageous or less efficient.

Contribution

It provides a comparative analysis of hybrid relaying networks with IRS and relay, considering channel estimation overheads and environmental dynamics.

Findings

Hybrid relaying can save power with fewer IRS elements.

Non-hybrid schemes are more energy-efficient at lower rates.

Hybrid relaying is beneficial at high rates with nearby IRS.

Abstract

Hybrid relaying networks (HRNs) combining both a relay and an intelligent reflective surface (IRS) can lead to enhanced rate performance compared to non-hybrid relaying schemes, where only either an IRS or a relay is utilized. However, utilizing both the relay and the IRS simultaneously results in higher power consumption for the HRNs compared to their counterpart. In this work, we study the required transmit power levels and the energy efficiency (EE) of HRNs utilizing both a half-duplex decode-and-forward (HD-DF) relay and an IRS, and compare their performance with non-hybrid relaying schemes. The impact of the required channel estimation overheads is considered when the reflective beamforming design (RBD) at the IRS is carried out under both instantaneous and statistical channel state information models. Also, the investigation is performed for both slow- and fast-changing environments. In terms of the transmit power requirements, our results show that HRNs can lead to higher power savings if the number of reflective elements at the IRS is not very large. However, non-hybrid relaying schemes are shown to be more energy-efficient, unless the targeted rate is high and the IRS is distant from both transmitter and receiver but within a close proximity to the relay.