Reliability and User-Plane Latency Analysis of mmWave Massive MIMO for Grant-Free URLLC Applications

TL;DR

This paper evaluates the reliability and latency of mmWave massive MIMO in 5G URLLC, showing significant failure probability reduction but highlighting limitations in meeting strict URLLC requirements.

Contribution

It introduces a mathematical model for mmWave MIMO URLLC performance and derives approximate expressions for latency and reliability metrics.

Findings

mmWave MIMO can reduce failure probability by up to 32 times

Beyond a certain number of antennas, reliability gains plateau

mmWave MIMO alone cannot meet the strictest URLLC performance standards

Abstract

5G cellular networks are designed to support a new range of applications not supported by previous standards. Among these, ultra-reliable low-latency communication (URLLC) applications are arguably the most challenging. URLLC service requires the user equipment (UE) to be able to transmit its data under strict latency constraints with high reliability. To address these requirements, new technologies, such as mini-slots, semi-persistent scheduling and grant-free access were introduced in 5G standards. In this work, we formulate a spatiotemporal mathematical model to evaluate the user-plane latency and reliability performance of millimetre wave (mmWave) massive multiple-input multiple-output (MIMO) URLLC with reactive and K-repetition hybrid automatic repeat request (HARQ) protocols. We derive closed-form approximate expressions for the latent access failure probability and validate them using numerical simulations. The results show that, under certain conditions, mmWave massive MIMO can reduce the failure probability by a factor of 32. Moreover, we identify that beyond a certain number of antennas there is no significant improvement in reliability. Finally, we conclude that mmWave massive MIMO alone is not enough to provide the performance guarantees required by the most stringent URLLC applications.