# Nuts and Bolts of a Realistic Stochastic Geometric Analysis of mmWave HetNets: Hardware Impairments and Channel Aging

## TL;DR

This paper develops a comprehensive stochastic geometric framework to analyze the downlink performance of realistic mmWave HetNets, considering hardware impairments and channel aging, revealing their impact on coverage and spectral efficiency.

## Contribution

It introduces a novel analytical model for multi-tier mmWave HetNets incorporating hardware impairments and channel aging, with detailed impact analysis on key performance metrics.

## Key findings

- Hardware impairments significantly affect high SNR performance.
- Transmit distortions degrade system more than receive distortions.
- Fewer served users and higher beam directivity improve spectral efficiency.

## Abstract

Motivated by heterogeneous networks (HetNets) design in improving coverage and by millimeter-wave (mmWave) transmission offering an abundance of extra spectrum, we present a general analytical framework shedding light to the downlink of realistic mmWave HetNets consisting of $K$ tiers of randomly located base stations (BSs). Specifically, we model, by virtue of stochastic geometry tools, the \textit{multi-tier} \textit{multi-user multiple-input multiple-output (MU-MIMO) mmWave} network degraded by the inevitable \textit{residual additive transceiver hardware impairments (RATHIs)} and \textit{channel aging}. Given this setting, we derive the coverage probability and the area spectral efficiency (ASE), and we subsequently evaluate the impact of residual transceiver hardware impairments (RTHIs) and channel aging on these metrics. Different path-loss laws for line-of-sight (LOS) and non-line-of-sight (NLOS) are accounted for the analysis, which are among the distinguishing features of mmWave systems. Among the findings, we show that the RATHIs have a meaningful impact at the high signal-to-noise ratio (SNR) regime, while the transmit additive distortion degrades further than the receive distortion the system performance. Moreover, serving fewer users proves to be preferable, and the more directive the mmWaves are, the higher the ASE becomes.