UAV-Based Cell-Free Massive MIMO: Joint Placement and Power Optimization under Fronthaul Capacity Limitations

TL;DR

This paper introduces a UAV-based cell-free massive MIMO system that optimizes UAV placement and power control to enhance coverage and performance under fronthaul capacity constraints, comparing different functional splits and frequency bands.

Contribution

It proposes a novel framework for UAV-based cell-free mMIMO that addresses fronthaul limitations through joint placement and power optimization, including analysis of split options and frequency bands.

Findings

mmWave fronthaul outperforms sub-6 GHz in SINR and power efficiency

Optimal UAV activation depends on fronthaul bandwidth and split options

Minimum fronthaul bandwidth varies with split option and UAV deployment

Abstract

We consider a cell-free massive multiple-input multiple-output (mMIMO) network, where unmanned aerial vehicles (UAVs) equipped with multiple antennas serve as distributed UAV-access points (UAV-APs). These UAV-APs provide seamless coverage by jointly serving user equipments (UEs) with out predefined cell boundaries. However, high-capacity wireless networks face significant challenges due to fronthaul limitations in UAV-assisted architectures. This letter proposes a novel UAV-based cell-free mMIMO framework that leverages distributed UAV-APs to serve UEs while addressing the capacity constraints of wireless fronthaul links. We evaluate functional split Options 7.2 and 8 for the fronthaul links, aiming to maximize the minimum signal-to-interference-plus-noise ratio (SINR) among the UEs and minimize the power consumption by optimizing the transmit powers of UAV-APs and selectively activating them. Our analysis compares sub-6 GHz and millimeter wave (mmWave) bands for the fronthaul, showing that mmWave achieves superior SINR with lower power consumption, particularly under Option 8. Additionally, we determine the minimum fronthaul bandwidth required to activate a single UAV-AP under different split options.