17.2 Cross-Link Interference Management

When different TDD DL/UL patterns are used between neighbouring cells, UL transmission in one cell may interfere with DL reception in another cell: this is referred to as UE-to-UE Cross Link Interference (CLI). In case of Sub-Band Full Duplex (SBFD) operation, UE-to-UE CLI can be present either within the same cell or across different cells: UL transmission may interfere with simultaneous DL reception within one cell or in another cell.

To mitigate UE-to-UE CLI, gNBs can exchange and coordinate their intended TDD DL-UL configurations over Xn and F1 interfaces; and the victim UEs can be configured to perform UE-to-UE CLI measurements. There are two types of UE-to-UE CLI measurements:

• SRS-RSRP measurement in which the UE measures SRS-RSRP over SRS resources of aggressor UE(s);
• CLI-RSSI measurement in which the UE measures the total received power observed over RSSI resources.

A gNB serving victim UEs may indicate to neighbour gNBs to report SRS resources. The neighbour gNB that receives the indication may signal the information concerning SRS resources potentially causing UE-to-UE CLI back to the neighbour gNB(s) that initiated the procedure.

Two types of UE-to-UE CLI reporting are supported: L1-based reporting and L3-based reporting. A UE is not expected to be configured with both L1 CLI measurement and reporting and L3 CLI measurement and reporting simultaneously.

For L3-based UE-to-UE CLI reporting, layer 3 filtering applies to CLI measurement results and both event triggered and periodic reporting are supported.

For L1-based UE-to-UE CLI reporting, the configuration is dependent on the reporting quantity:

• For SRS-RSRP, only aperiodic CSI reporting is supported;
• For CLI-RSSI, the CSI reporting can be periodic or aperiodic.

In addition to UE-to-UE CLI, gNB-to-gNB CLI may also be present when different TDD DL/UL patterns are used between neighbouring cells or when SBFD operation is configured: DL transmission in one cell may interfere with UL reception in another cell.

To mitigate gNB-to-gNB CLI, a victim gNB can report gNB-to-gNB CLI related information of its serving cells to neighbour gNBs. The neighbour gNB should evaluate the received information and it may take CLI mitigation actions when necessary. Additionally, a victim gNB can configure a UE with UL resource muting. When UL resource muting is applied in a symbol, either even or odd sub-carriers of the frequency resource of the PUSCH are available, and the other sub-carriers are not used for the PUSCH transmission.