Half-Duplex User Equipment Relaying Policies for Uplink Improvement in Beyond 5G Networks

We consider a 5G cellular system, in which cellular user equipments (UEs) are willing to assist a cell-edge UE with a weak uplink (UL). We aim to improve the UL coverage as well as the end-to-end spectral and energy efficiency when the assisting UEs follow a group or multihop half-duplex relaying policy. Specifically, we study the UL performance under different distance-dependent fading conditions to understand when it is beneficial to use UE relaying. This question is motivated by recent advances in the Third Generation Partnership Project that suggests exploring the technology potential of physical layer groupcast and unicast over the sidelink for improving the UL coverage. Somewhat surprisingly, half-duplex UE relaying policies that exploit sidelink groupcast or unicast have not been thoroughly compared in the literature. System evaluations indicate that spectral efficiency can be improved over six times (compared to the case without relaying) with only two relaying UEs, while great energy efficiency gains are also achieved, provided that the time used for reception and transmission over the half-duplex relays is properly allocated. We also find that when relaying is beneficial, group and multihop relaying have their distinct advantages depending on the path loss exponent and the geometry of the system.