CSI Feedback Overhead Reduction in 5G NR
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Solution Overview
Problem
The current 5G New Radio (NR) CSI reporting schemes, particularly Type-II, face high feedback overhead due to the increased number of subbands, which complicates the compression and quantization of combining coefficients, leading to inefficient channel state information feedback.
Innovation Solution
The proposed solution involves a three-stage precoder matrix structure and optimized codebook configurations, including a first DFT-based codebook for spatial beam components and a second DCT-based codebook for delay components, allowing for efficient selection and reporting of precoder matrices, reducing feedback overhead by aligning beam vectors with multipath components and using oversampling factors to manage computational complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Type-II CSI reporting is used with increased number of subbands, then channel state information accuracy is improved, but feedback overhead increases significantly
Solution Approach 1:
The patent segments the feedback report into two distinct parts: a first part containing CSI for first subbands and a second part containing CSI for second subbands. This segmentation allows the UE to report CSI for different subband ranges separately, reducing the overall feedback overhead while maintaining comprehensive channel state information across all subbands.
Solution Approach 2:
The patent introduces a subband-based dimension for organizing CSI feedback, where CSI is reported per subband rather than uniformly across all bandwidth parts. This dimensional organization allows efficient compression and selective reporting of CSI for subbands with different channel conditions, reducing feedback overhead while preserving accuracy.
2Quantity of substance
If combining coefficients are compressed and quantized, then feedback overhead is reduced, but measurement precision of channel state information may be compromised
Solution Approach 1:
The patent applies different compression and quantization strategies to different subbands based on their specific channel conditions and requirements. Subbands with stronger channel conditions may use higher precision quantization while subbands with weaker conditions use lower precision, optimizing the balance between feedback overhead reduction and measurement precision preservation.
Solution Approach 2:
The patent dynamically adjusts quantization parameters and compression levels based on subband characteristics, channel conditions, and system requirements. By changing these parameters adaptively, the system reduces feedback overhead in regions where high precision is not critical while maintaining accuracy where needed.
3Measurement precision
If a three-stage precoder matrix structure is used, then channel state information accuracy is improved, but device complexity increases
Solution Approach 1:
The patent divides the precoder matrix into three distinct stages: a first stage for wideband spatial beamforming, a second stage for subband delay compensation, and a third stage for final combining. This segmentation allows each stage to be optimized independently for specific functions, improving overall CSI accuracy while managing complexity through modular design.
Solution Approach 2:
The patent implements a nested precoder structure where the second and third stages are combined within the codebook framework, with the second stage combining coefficients being applied after the first stage beamforming. This nested arrangement allows efficient integration of multiple processing functions while reducing overall system complexity through shared computational resources.
Data Source
AI summary
The embodiments herein relate to a method performed by a UE (900) for providing a channel state information (CSI) feedback in a wireless communication system including at least the UE and a gNB (800) or a radio network node. The UE (900) is operative, by means of e.g. the processor (910) to: estimate the MIMO channel between the gl'JB (800) and the UE (910) based on received DL reference signals for the configured resource blocks. The UE (900) is further operative to calculate, based on a performance metric. a precoder matrix, for a number of antenna ports of the gNB (800) 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 (900) is operative to report a CSI feedback and/or a PMI and/or a PMI/RI, to the gNB (800), used to indicate the precoder matrix for the configured antemia ports and resource blocks.