Beam correspondence is a terminology that is used if the Beams selected for downlink transmission and reception can also be used for uplink transmission and reception. # i.e DL and UL will transmissions will happen on the same beam. It is one of the fundamental elements of the Beam Management Concept.
3GPP Defines Beam correspondence as to the ability of the UE to select a suitable beam for UL transmission based on DL measurements with or without relying on UL beam sweeping. The beam correspondence requirement is satisfied assuming the presence of both SSB and CSI-RS signals and Type D QCL is maintained between SSB and CSI-RS.
Tx/Rx beam correspondence at gNB holds if at least one of the following is satisfied:
- gNB is able to determine a gNB Rx beam for the uplink reception based on UE’s downlink measurement on gNB’s one or more Tx beams.
- gNB is able to determine a gNB Tx beam for the downlink transmission based on gNB’s uplink measurement on gNB’s one or more Rx beams.
Tx/Rx beam correspondence at UE holds if at least one of the following is satisfied:
- UE is able to determine a UE Tx beam for the uplink transmission based on UE’s downlink measurement on UE’s one or more Rx beams.
- UE is able to determine a UE Rx beam for the downlink reception based on gNB’s indication based on uplink measurement on UE’s one or more Tx beams.
- Capability indication of UE beam correspondence-related information to gNB is supported.
Does UE need to Indicate to the network that if Beam Correspondence is supported or not supported?
Yes, UE indicates to network in UE capability Information message by including the below parameter beamCorrespondenceWithoutUL-BeamSweeping
| Parameter | Explanation |
|---|---|
| CorrespondenceWithoutUL-BeamSweeping | Indicates whether UE supports FR2 beam correspondence. The Parameter is applicable to FR2 only and it is set per band capability. The UE that fulfills the beam correspondence requirement without the uplink beam sweeping sets the bit to 1 (Supported), If the UE does not support beam correspondence and instead support supports Uplink beam sweeping then the bit is set to 0. This is a Mandatory Parameter that UE needs to Include in the UE Capability information message. |
| beamCorrespondenceCA | This Parameter Indicates whether UE configured with CA supports the same beam correspondence across all CCs |
| uplinkBeamManagement | Defines support of beam management for UL. The capability includes an indication of the – A maximum number of SRS resources per SRS resource set configurable for beam management, supported by the UE. – A maximum number of SRS resource sets configurable for beam management, supported by the UE. If the UE sets beamCorrespondenceWithoutUL-BeamSweeping to 0, the UE shall set this field to 1. This feature is optional for the UE supports beam correspondence without uplink beam sweeping. |
Beam correspondence for CA
For intra-band CA in FR2, the same beam correspondence relationship for beam management is supported across CCs in Rel-15 and no requirement is specified. Beam correspondence performance for intra-band CA is fulfilled if the beam correspondence requirements are met for the non-CA cases.
References :
3GPP TS 38.101-2 NR; User Equipment (UE) radio transmission and reception;
3GPP TS 38. 306 User Equipment (UE) radio access capabilities