Type-II CSI Codebook Restriction for Lower Feedback Overhead
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Solution Overview
Problem
The existing 3GPP Release 15 Type-II CSI reporting scheme for New Radio (NR) wireless communications systems faces high feedback overhead due to the increased reporting of combining coefficients on a subband basis, which becomes significant for large numbers of subbands.
Innovation Solution
A method and apparatus for channel state information (CSI) feedback that involves configuring a precoder matrix using two codebooks, where the first codebook contains spatial beam components and the second codebook contains delay components, with optimized selection and reporting of beam and delay vectors to reduce feedback overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Type-II CSI reporting is used with subband-based combining coefficients, then measurement precision is improved, but feedback overhead increases significantly
Solution Approach 1:
The patent segments the codebook into two independent parts: a first codebook for spatial beam components and a second codebook for delay components. This segmentation allows the UE to report only the indices of selected codebook entries rather than all combining coefficients, reducing feedback overhead while maintaining precision. The spatial and delay dimensions are separated, enabling more efficient reporting.
Solution Approach 2:
The patent transforms the feedback from a full matrix of combining coefficients to a set of indices in a reduced-dimensional space. Instead of reporting all W2 combining coefficients (which would be Nsubbands × Nbeams complex values), the system reports only the indices of selected codebook entries, effectively mapping the high-dimensional coefficient space to a lower-dimensional index space.
2Measurement precision
If the number of subbands is increased, then measurement precision is improved, but feedback overhead increases linearly
Solution Approach 1:
The patent segments the feedback into spatial beam selection (first codebook) and delay selection (second codebook) components. This allows the system to handle increased numbers of subbands by reporting only the indices of relevant delay components rather than all subband coefficients, maintaining feedback efficiency even as subband count increases.
Solution Approach 2:
The patent applies partial action by reporting only the indices of the most significant codebook entries (K1 and K2 entries) rather than all possible combining coefficients. This selective reporting maintains sufficient CSI accuracy for practical purposes while dramatically reducing feedback overhead compared to full reporting.
3Measurement precision
If full codebook search is performed, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent segments the codebook search into two independent stages: first selecting spatial beam components from the first codebook, then selecting delay components from the second codebook. This segmentation reduces the search space complexity compared to a full exhaustive search through all possible combining coefficients, while still achieving high measurement precision through the structured two-stage approach.
Solution Approach 2:
The patent applies preliminary action by pre-configuring the first and second codebooks with representative spatial beam and delay components. The UE then performs a simplified search within these pre-organized codebook structures rather than performing a full exhaustive search, reducing computational complexity while maintaining precision through the pre-structured codebook entries.
Data Source
AI summary
Method performed by a UE for providing a channel state information (CSI) feedback in a wireless communication system including at least the UE and a gNB or a radio network node. The UE is operative to: estimate the MIMO channel between the gNB and the UE based on received DL reference signals for the configured resource blocks. The UE is further operative to calculate, based on a performance metric, a precoder matrix, for a number of antenna ports of the gNB and configured subbands, the precoder matrix being based on two codebooks and a set of combination coefficients for complex scaling/combining one or more of vectors selected from a first codebook and a second codebook, and the UE is operative to report a CSI feedback and/or a PMI and/or a PMI/RI, to the gNB, used to indicate the precoder matrix for the configured antenna ports and resource blocks.