# Massive MIMO for Ultra-reliable Communications with Constellations for Dual Coherent-noncoherent Detection

## TL;DR

This paper explores a dual detection scheme in Massive MIMO systems to enhance ultra-reliable communications under imperfect channel knowledge, combining coherent and non-coherent methods for improved reliability.

## Contribution

It introduces a novel APK constellation with dual-stage detection, improving reliability in SIMO systems with imperfect CSI under high SNR conditions.

## Key findings

- Proposed constellation scaling improves performance at high SNR.
- Dual detection strategy enhances symbol reliability with imperfect CSI.
- Simulation confirms effectiveness of the scheme in realistic scenarios.

## Abstract

The stringent requirements of ultra-reliable low-latency communications (URLLC) require rethinking of the physical layer transmission techniques. Massive antenna arrays are seen as an enabler of the emerging $5^\text{th}$ generation systems, due to increases in spectral efficiency and degrees of freedom for transmissions, which can greatly improve reliability under demanding latency requirements. Massive array coherent processing relies on accurate channel state information (CSI) in order to achieve high reliability. In this paper, we investigate the impact of imperfect CSI in a single-input multiple-output (SIMO) system on the coherent receiver. An amplitude-phase keying (APK) symbol constellation is proposed, where each two symmetric symbols reside on distinct power levels. The symbols are demodulated using a dual-stage non-coherent and coherent detection strategy, in order to improve symbol reliability. By means of analysis and simulation, we find an adequate scaling of the constellation and show that for high signal-to-noise ratio (SNR) and inaccurate CSI regime, the proposed scheme enhances receiver performance.