5G • RAN
Rank Indicator (RI)
MIMO Rank Indicator
UE feedback specifying the maximum number of independent spatial data layers the channel can support.
Technical Explanation
The Rank Indicator (RI) is calculated by the UE from CSI-RS measurements and reported via UCI. An RI of 1 indicates rank-1 transmission (single spatial stream / beamforming), while an RI of 4 or 8 indicates rich multipath scattering capable of supporting 4 or 8 parallel data streams simultaneously on the same frequency.
Key Functions
- Indicates maximum number of spatial layers (up to 8 in DL, 4 in UL)
- Derived from eigen-decomposition of estimated CSI-RS channel matrices
- Directs gNodeB scheduler layer allocation for spatial multiplexing
Specifications
3GPP TS 38.214
Interfaces
Uu
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