Type-II CSI Feedback Codebook Restriction for 5G NR
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Solution Overview
Problem
The existing CSI reporting schemes in 5G NR systems, particularly Type-II, face high feedback overhead due to the need for precise quantization and reporting of combining coefficients for subbands, which increases linearly with the number of subbands, leading to significant computational and communication burdens.
Innovation Solution
The proposed solution involves a method for efficient CSI feedback reporting using a three-stage precoder matrix structure, where the UE estimates and reports a precoder matrix based on two codebooks, with the first codebook containing spatial beam components and the second codebook containing delay components, allowing for reduced feedback overhead by selecting identical beam vectors for subsets of transmission layers and aligning delay vectors with multipath components, and signaling capabilities to adjust oversampling factors and subband configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Type-II CSI reporting is used with dual-stage W1W2 codebook and subband-based combining coefficients, then CSI resolution and accuracy are improved, but feedback overhead increases approximately linearly with the number of subbands
Solution Approach 1:
The patent extracts and reports only the most significant combining coefficients (e.g., top K coefficients) instead of all coefficients. This selective extraction maintains the essential CSI information while significantly reducing feedback overhead. The UE identifies and reports only the dominant coefficients that contribute most to the channel state representation.
Solution Approach 2:
The patent changes the parameter of codebook configuration by introducing a codebook restriction parameter that limits the search space for combining coefficients. By restricting the codebook to a subset of relevant entries based on channel characteristics, the system reduces the number of coefficients that need to be reported while maintaining CSI accuracy.
2Measurement precision
If the number of subbands is increased to improve frequency resolution, then CSI accuracy is improved, but feedback overhead increases considerably
Solution Approach 1:
The patent extracts and reports only the most significant combining coefficients for each subband rather than reporting all coefficients. By identifying and reporting only the top K significant coefficients per subband, the system maintains frequency resolution while reducing the linear growth of feedback overhead with the number of subbands.
3Measurement precision
If comprehensive codebook search is performed to ensure accurate precoder selection, then CSI accuracy is improved, but computational complexity at the UE increases
Solution Approach 1:
The patent changes the codebook search parameter by introducing codebook restrictions that limit the search space. The UE is configured with parameters that define restricted codebook subsets, reducing the number of combinations to evaluate while maintaining sufficient accuracy for precoder selection.
Solution Approach 2:
The patent applies partial codebook search by evaluating only a subset of codebook entries rather than the complete codebook. This partial action is sufficient to achieve the required precoder selection accuracy while significantly reducing computational complexity at the UE.
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.