Precoding Selection for Uplink MIMO HARQ Retransmissions
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Solution Overview
Problem
Existing methods for precoding selection in uplink MIMO hybrid ARQ for retransmissions in LTE-A systems fail to effectively assign precoding when the number of codewords in retransmissions is less than in original transmissions, particularly with imperfect channel state information available at the user terminal.
Innovation Solution
A method that involves obtaining a precoder for retransmission by using a known precoding matrix and modulation and coding scheme from the original transmission, forming an approximate channel covariance matrix, estimating the minimum mean square error receiver signal-to-noise-interference-ratio for each layer, and selecting a precoding matrix from a codebook that maximizes the sum-rate for retransmissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If non-adaptive HARQ retransmission is used in UL MIMO with reduced rank, then resource efficiency is improved, but precoding selection becomes problematic when codeword count changes
Solution Approach 1:
The patent changes the parameter of precoding matrix selection by introducing a mapping relationship between original transmission precoding matrices and retransmission precoding matrices. When rank reduces, the system selects appropriate precoding matrices from the codebook based on the original precoding matrix index and the desired retransmission rank, rather than using the same precoding matrix. This parameter change enables adaptive precoding selection for non-adaptive HARQ retransmissions.
2Loss of information
If channel state information is quantized to reduce overhead, then signaling overhead is reduced, but precoding selection accuracy deteriorates
Solution Approach 1:
The patent uses the original precoding matrix index as a reference copy to determine retransmission precoding matrices. Instead of requiring full channel state information, the system copies the precoding selection logic from the original transmission and adapts it to the retransmission rank. This copying approach maintains precoding accuracy while minimizing additional channel information requirements.
3Device complexity
If fixed precoding matrix is used for retransmission, then implementation complexity is reduced, but sum-rate maximization is compromised
Solution Approach 1:
The patent introduces dynamic precoding matrix selection for retransmissions by mapping the original precoding matrix index to appropriate retransmission precoding matrices based on the desired rank. The selection process dynamically determines which precoding matrix from the codebook to use, rather than fixing a single matrix for all retransmissions. This dynamic approach maximizes sum-rate while keeping the selection process manageable through the mapping relationship.
Data Source
AI summary
A method implemented in a user terminal is disclosed. The method comprises obtaining known precoding matrix P of rank r and modulation and coding scheme assignments used in an original transmission, and a desired retransmission rank r′, forming an approximate channel covariance matrix, estimating a minimum mean square error receiver SINR for each layer to be retransmitted responsive to said forming, and finding a retransmission precoding matrix from a preceding codebook that maximizes a sum-rate for enabling precoding selections for retransmissions in uplink multiple-input multiple-output MIMO hybrid automatic repeat request HARQ. Other methods, apparatuses, and systems also are disclosed.