What is 5G NR sidelink relay?

According to 5G Americas, NR sidelink relay is the use of device-to-device communication as a way to extend the network coverage outside the area directly covered by the network infrastructure

NR sidelink relay was included as a working item in the 3GPP Release 17 to further improve this technology compared to achievements recorded in the previous release.

“For Release 16, a first version of NR sidelink has been developed and it solely focuses on supporting V2X related road safety services. The design aims to provide support for broadcast, groupcast and unicast communications in both out-of-coverage and in-network coverage scenarios. On top of that, sidelink-based relaying functionality should be additionally studied in order for sidelink/network coverage extension and power efficiency improvement, considering wider range of applications and services,” 3GPP said.

“Release-13 solution on UE-to-network relay is limited to EUTRA-based technology, and thus cannot be applied to NR-based system, for both NG-RAN and NR-based sidelink communication. Regarding, UE-to-UE coverage extension, proximity reachability is currently limited to single-hop sidelink link, either via EUTRA-based or NR-based sidelink technology. However, that is not sufficient in the scenario where there is no Uu coverage, considering the limited single-hop sidelink coverage,” 3GPP said.

Overall, sidelink connectivity should be further extended in NR framework, in order to support the enhanced QoS requirements, 3GPP added.

3GPP also said that this study item aimed to study single-hop NR sidelink-based relay.

1.         Study mechanism with minimum specification impact to support the SA requirements for sidelink-based UE-to-network and UE-to-UE relay, focusing on the following aspects  for layer-3 relay and layer-2 relay [RAN2];

A.        Relay (re-)selection criterion and procedure;

B.        Relay/Remote UE authorization;

C.        QoS for relaying functionality;

D.        Service continuity;

E.        Security of relayed connection after SA3 has provided its conclusions;

F.         Impact on user plane protocol stack and control plane procedure, e.g., connection management of relayed connection;

2.         Study mechanism to support upper layer operations of discovery model/procedure for sidelink relaying, assuming no new physical layer channel/signal [RAN2];

According to 5G Americas, sidelink-based relaying is the use of device-to-device communication as a way to extend the network coverage outside the area directly covered by the network infrastructure.

”Release 17 recognizes the market demand for mission critical national security and public safety services. The 3GPP system architecture and radio network working groups are discussing the requirements of more general NR proximity services (ProSe). Release 17 can advantageously reuse the high-reliability and low-latency features of the NR cellular (Uu) interface and the advanced features of the PC5 interface developed for V2X applications. For ProSe, there is an inherent need to provide reliable out-of-coverage services, support communications among emergency rescue personnel, and quickly connect out-of-coverage areas to infrastructure nodes,¨ 5G Americas said.

“To meet the requirements of ProSe, 3GPP plans to extend the capabilities of the Release 16 NR PC5 interface by enabling UE-based relaying. UE-based relaying can be useful in both partial (spotty) coverage and out-of-coverage situations by establishing multi-hop communication paths, such as in UE-UE-UE or NW-UE-UE relaying situations. These relaying features may require some new solutions in network control, resource allocation, end-to-end QoS management and UE/relay discovery. At physical-layer and MAC level, it is expected to reuse the release-16 features, incorporating changes to reduce energy consumption critical for handheld devices,” 5G Americas said.

“Building on the 5G PC5 design from C-V2X (cellular vehicle-to-everything) of Release 16, Release 17 brings a slew of new and enhanced sidelink capabilities, such as optimized resource allocation, power savings, and new frequency band support. It also expands sidelink to new use cases such as public safety, IoT, and others by way of introducing sidelink relaying operation,” Qualcomm said.