Two-Codebook CSI Reporting With Basis Subset Indication
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Solution Overview
Problem
The existing 3GPP Release 15 Type-II CSI reporting scheme for New Radio (NR) wireless communication systems suffers from high feedback overhead due to the increased reporting of combining coefficients on a subband basis, particularly for large numbers of subbands, which is not efficiently addressed by current feedback compression schemes.
Innovation Solution
A two-codebook CSI reporting scheme is introduced, utilizing a first codebook for spatial beam components and a second codebook for delay components, allowing for precoding operations in the delay domain to reduce feedback overhead by selecting a common delay domain basis subset and reporting layer-specific delay domain indicators, thereby reducing the number of combining coefficients to be reported.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Type-II CSI reporting reports combining coefficients on a subband basis, then measurement precision is improved, but feedback overhead increases significantly
Solution Approach 1:
The patent segments the combining coefficients into two parts: wideband coefficients (reported once for all subbands) and subband-specific coefficients (reported only for subbands where they differ from wideband values). This segmentation allows the system to maintain high measurement precision where needed while reducing feedback overhead in subbands where full precision is not required.
Solution Approach 2:
Instead of reporting full combining coefficients for all subbands, the patent applies partial action by reporting only the necessary subset of coefficients - specifically, only those subband coefficients that differ from the wideband coefficients. This reduces feedback overhead while maintaining adequate precision for accurate channel state information.
2Measurement precision
If the number of subbands is increased, then measurement precision is improved, but feedback overhead increases linearly
Solution Approach 1:
The patent divides the subband processing into wideband and subband-specific components. By segmenting the coefficient reporting this way, the system can support a large number of subbands for high measurement precision while avoiding linear growth in feedback overhead, as only differential subband coefficients need to be reported.
Solution Approach 2:
Instead of reporting full coefficients for each subband (the conventional approach), the patent inverts the approach by reporting wideband coefficients first and then only the differences for specific subbands. This inversion significantly reduces feedback overhead when dealing with large numbers of subbands.
3Quantity of substance
If feedback compression schemes are applied, then feedback overhead is reduced, but implementation complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-determining the wideband coefficients first, then using these as a baseline for subband-specific reporting. This preliminary wideband analysis simplifies the overall compression scheme by establishing a reference point that reduces the amount of additional information needed for subband reporting.
Solution Approach 2:
The patent changes the parameter representation by separating wideband and subband-specific coefficients, transforming the feedback structure from uniform subband reporting to a hierarchical wideband-subband format. This parameter change simplifies the compression scheme by exploiting the correlation between wideband and subband coefficients.
Data Source
Figure 1A~1B
Figure 2
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AI summary
The present disclosure relates to methods and apparatuses (UE, network node or gNB) for CSI reporting. The method performed by a UE comprises: receiving (201) from the gNB, a radio signal via a MIMO channel, wherein the radio signal contains at least one DL-RS according to a DL-RS configuration; estimating (202) said MIMO channel based on said received at least one DL reference signal for configured subbands; calculating (203) a precoder matrix or a CSI matrix for a number of antenna ports of the gNB and configured subbands; the precoder matrix being based on a first codebook and on a second codebook and a set of combining coefficients for complex scaling/combining one or more of vectors selected from the first codebook and the second codebook; and reporting (204), to the gNB, a CSI feedback report and/or a PMI/RI, used to indicate the precoder matrix or the CSI matrix for the configured antenna ports and subbands.