16.21.1 General

In multi-path relay scenario, a MP Remote UE is connected to a single gNB via one direct path and one indirect path while the MP Remote UE is in RRC_CONNECTED state. For the indirect path, both L2 and L3 MP Relay architectures are supported for MP Relay using PC5 interface, and only L2 MP Relay architecture is supported for MP Relay using N3C interface. The L3 MP Relay architecture is transparent to the serving NG-RAN of the MP Relay UE, except for controlling sidelink resources. In the case of MP Remote UE using SL indirect path, mode 1 resource allocation is supported only for intra-DU case, with the SR/BSR and grant sent on the direct path.

In multi-path relay, the interface between MP Remote UE and MP Relay UE can be either PC5 or N3C. When the interface between MP Remote UE and MP Relay UE is N3C interface, the relationship of MP Remote UE and MP Relay UE is pre-configured or static, and it is up to the implementation of the MP Remote UE and MP Relay UE how to pre-configure or make it static. More than one MP Relay UEs can be configured to MP Remote UE via N3C interface.

Multi-path relay supports MP Remote UE and MP Relay UE when they are in the same gNB, and PCell is always on the direct path.

Multi-path relay is supported in the following cell deployment scenarios:

• The MP Relay UE and MP Remote UE are served by the same cell;
• The MP Relay UE and MP Remote UE are served by different intra-frequency cells of the same gNB;
• The MP Relay UE and MP Remote UE are served by different inter-frequency cells of the same gNB.

Multi-path relay is supported in the following sidelink scenarios:

• Sidelink TX/RX and Uu link share the same carrier at the MP Remote UE;
• Sidelink TX/RX and Uu link use different carriers at the MP Remote UE;
• Sidelink TX/RX and Uu link share the same carrier at the MP Relay UE;
• Sidelink TX/RX and Uu link use different carriers at the MP Relay UE.