# Toward Spectral and Energy Efficient 5G Networks Using Relayed OFDM with Index Modulation

## TL;DR

This paper reviews relay-assisted OFDM with index modulation as a promising approach to enhance spectral and energy efficiency in 5G networks, discussing recent advances, challenges, and future directions.

## Contribution

It summarizes recent developments in relay-assisted OFDM-IM, highlighting its potential to improve spectral and energy efficiency in 5G networks, and discusses associated challenges and future research directions.

## Key findings

- Relay-assisted OFDM-IM improves spectral efficiency.
- Relay-assisted OFDM-IM enhances energy efficiency.
- Challenges include complexity and diversity gain limitations.

## Abstract

Next generation wireless networks are expected to provide much higher data throughput and reliable connections for a far larger number of wireless service subscribers and machine-type nodes, which result in increasingly stringent requirements of spectral efficiency (SE) and energy efficiency (EE). Orthogonal frequency-division multiplexing with index modulation (OFDM-IM) stands out as a promising solution to satisfy the SE requirement with a reasonable increase in system complexity. However, the EE of OFDM-IM is still required to be enhanced. Moreover, diversity gain is hardly harvested in OFDM-IM systems, which hinders further reliability enhancement. In this regard, relay assisted OFDM-IM, as a promising joint paradigm to achieve both high SE and EE, was proposed and has been studied since last year. The objectives of this article are to summarize the recent achievements of this joint paradigm, articulate its pros and cons, and reveal the corresponding challenges and future work.