5G • RAN
MAC CE Spatial Relation
PUCCH Spatial Relation Activation MAC CE
MAC Control Element dynamically activating which spatial filter (beam) to use for PUCCH resources.
Technical Explanation
For mobile UEs in mmWave, the optimal uplink beam changes frequently. Rather than using slow RRC reconfigurations, the gNodeB transmits a PUCCH Spatial Relation Activation/Deactivation MAC CE to immediately command the UE to steer its PUCCH uplink beam toward a new reference signal (SSB or CSI-RS).
Key Functions
- Dynamically updates uplink PUCCH beamforming directions via MAC signaling
- Avoids heavy RRC reconfiguration overhead for beam mobility
- Essential for maintaining uplink control links in mobile mmWave environments
Specifications
3GPP TS 38.321
Interfaces
Uu
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