Improving the Coverage and Spectral Efficiency of Millimeter-Wave Cellular Networks using Device-to-Device Relays

TL;DR

This paper proposes using two-hop device-to-device relaying in millimeter-wave cellular networks to improve coverage and spectral efficiency, analyzing different relay bands and propagation conditions with stochastic geometry.

Contribution

It introduces a stochastic geometry framework for analyzing relay-assisted mmWave networks with uplink D2D relays in mmWave and microwave bands, highlighting coverage and spectral efficiency gains.

Findings

Microwave D2D relays provide better coverage under NLOS conditions.

mmWave D2D relays excel in high interferer density scenarios.

Downlink spectral efficiency depends on relay mode selection strategy.

Abstract

The susceptibility of millimeter waveform propagation to blockages limits the coverage of millimeter-wave (mmWave) signals. To overcome blockages, we propose to leverage two-hop device-to-device (D2D) relaying. Using stochastic geometry, we derive expressions for the downlink coverage probability of relay-assisted mmWave cellular networks when the D2D links are implemented in either uplink mmWave or uplink microwave bands. We further investigate the spectral efficiency (SE) improvement in the cellular downlink, and the effect of D2D transmissions on the cellular uplink. For mmWave links, we derive the coverage probability using dominant interferer analysis while accounting for both blockages and beamforming gains. For microwave D2D links, we derive the coverage probability considering both line-of-sight (LOS) and non-line-of-sight (NLOS) propagation. Numerical results show that downlink coverage and SE can be improved using two-hop D2D relaying. Specifically, microwave D2D relays achieve better coverage because D2D connections can be established under NLOS conditions. However, mmWave D2D relays achieve better coverage when the density of interferers is large because blockages eliminate interference from NLOS interferers. The SE on the downlink depends on the relay mode selection strategy, and mmWave D2D relays use a significantly smaller fraction of uplink resources than microwave D2D relays.