MIMO Precoder Determination Using Covariance Feedback
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Solution Overview
Problem
Inaccurate calculation of precoders in multi-input multi-output (MIMO) systems leads to distorted physical downlink shared channels (PDSCHs) due to insufficient channel state information (CSI) estimation by user equipment (UE).
Innovation Solution
User equipment (UE) estimates covariance matrices from channel state information-reference signals (CSI-RS) at different times and frequencies, and transmits these matrices or associated parameters to the base station (BS) for reconstructing precoders, using techniques like eigenvalue decomposition or singular value decomposition (SVD) to improve precoder accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the UE calculates precoders based on downlink channel matrices using conventional methods, then the precoder calculation process is simple, but the precoder accuracy is insufficient leading to distorted PDSCH transmission
Solution Approach 1:
The UE performs preliminary estimation of covariance matrices from CSI-RS signals at different times and frequencies before precoder determination. This preliminary action captures channel statistics in advance, enabling the BS to compute more accurate precoders using eigenvalue decomposition or SVD on the reported covariance information, thereby resolving the contradiction between precision and complexity.
Solution Approach 2:
The patent introduces covariance matrices as an intermediary between channel state information and precoder determination. Instead of directly calculating precoders from channel matrices, the UE first computes covariance matrices from CSI-RS measurements and reports them to the BS. The BS then uses these covariance matrices to determine precise precoders through eigenvalue decomposition or SVD, achieving higher accuracy without excessive complexity at the UE.
2Reliability
If the UE reports compressed/quantized precoders using specified codebooks, then the feedback overhead is reduced, but the precoder accuracy deteriorates causing serious distortion in PDSCH transmission
Solution Approach 1:
The patent changes the parameter being reported from quantized precoder indices to covariance matrix elements or their parameters. By reporting covariance information instead of directly quantized precoders, the system maintains higher precision in channel statistics while reducing feedback overhead through selective reporting of covariance parameters, thus improving PDSCH reliability without excessive information loss.
3Measurement precision
If the UE estimates channel state information at multiple time and frequency points, then the channel representation becomes more accurate, but the estimation complexity and processing overhead increase
Solution Approach 1:
The patent extracts only the essential covariance matrix information from extensive CSI-RS measurements taken at multiple time and frequency points. Instead of processing all raw channel measurements, the UE extracts covariance statistics that capture the essential channel characteristics, thereby maintaining measurement precision while significantly reducing processing time and complexity.
Data Source
AI summary
Method and UE are provided for determining precoder of MIMO system. In particular, a BS can transmit at least one CSI-RS to the UE. The UE can receive the at least one CSI-RS, and estimate at least one covariance matrix of at least one downlink channel matrix according to the at least one CSI-RS at different times and frequencies. Then, the UE can transmit the at least one covariance matrix or at least one parameter associated with the least one covariance matrix to the BS for the BS to reconstruct at least one covariance matrix, and determine a precoder according to the at least one reconstructed covariance matrix.