What is Cross Link Interference (CLI)?

CLI (Cross Link Interference) is a problem in TDD when a base station receiving in the uplink is facing interference from another base station transmitting in the downlink.

It can happen across network operators due to out-of-band emissions.

CLI can be mitigated by time-synchronization across base stations, that is, they share a common clock, phase reference and frame structure.

Even within the same operator network, CLI can occur since cell neighbours may be using different TDD DL/UL patterns.

CLI can be mitigated by gNBs coordinating their configuration over Xn and F1 interfaces.

If capable, a 5G UE measures and reports CLI-RSSI.

These reports can also include SRS-RSRP measurements on Sounding Reference Signal (SRS), which are uplink signals coming from other UEs.

This quantifies interference on downlink due to nearby uplink transmissions.

Both CLI-RSSI and SRS-RSRP are measured within the active DL BWP. These are applicable only for RRC_CONNECTED intra-frequency in TDD mode.

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