# Terahertz-Band Ultra-Massive Spatial Modulation MIMO

## TL;DR

This paper explores the use of spatial modulation with graphene-based nano-antenna arrays at Terahertz frequencies to enhance capacity and spectral efficiency, overcoming propagation challenges of ultra-massive MIMO systems.

## Contribution

It introduces a novel application of spatial modulation in THz-band UM-MIMO systems using nano-antenna arrays, providing theoretical and numerical performance analysis.

## Key findings

- Significant error rate improvements over conventional SM.
- Feasibility of THz-band SM demonstrated through analysis.
- Guidelines for optimal SM configurations based on distance and frequency.

## Abstract

The prospect of ultra-massive multiple-input multiple-output (UM-MIMO) technology to combat the distance problem at the Terahertz (THz)-band is considered. It is well-known that the very large available bandwidths at THz frequencies come at the cost of severe propagation losses and power limitations, which result in very short communication distances. Recently, graphene-based plasmonic nano-antenna arrays that can accommodate hundreds of antenna elements in a few millimeters have been proposed. While such arrays enable efficient beamforming that can increase the communication range, they fail to provide sufficient spatial degrees of freedom for spatial multiplexing. In this paper, we examine spatial modulation (SM) techniques that can leverage the properties of densely packed configurable arrays of subarrays of nano-antennas, to increase capacity and spectral efficiency, while maintaining acceptable beamforming performance. Depending on the communication distance and the frequency of operation, a specific SM configuration that ensures good channel conditions is recommended. We analyze the performance of the proposed schemes theoretically and numerically in terms of symbol and bit error rates, where significant gains are observed compared to conventional SM. We demonstrate that SM at very high frequencies is a feasible paradigm, and we motivate several extensions that can make THz-band SM a future research trend.