Open-Loop SU-MIMO Precoding With Codebook Cycling
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Solution Overview
Problem
Existing methods for selecting precoding matrices in high-speed open-loop systems, particularly in MIMO communication systems, face challenges when Precoding Matrix Indication (PMI) feedback is unreliable, especially for high-speed scenarios and less than full rank cases, leading to inefficiencies in antenna correlation configurations.
Innovation Solution
The method involves selecting the precoding matrix W(k) based on feedback without PMI in the uplink for each User Equipment (UE), cycling through a SU-MIMO codebook or DFT submatrix, and applying the same W(k) across scheduled subbands, with options for changing the precoding matrix every p subcarriers or every subcarrier within the subband.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PMI feedback is used for precoding matrix selection, then precoding accuracy is improved, but system reliability deteriorates in high-speed open-loop scenarios where feedback is unreliable
Solution Approach 1:
The patent introduces a codebook as an intermediary between the channel state and precoding matrix selection. Instead of directly using PMI feedback which is unreliable in high-speed scenarios, the system uses a predefined codebook that both transmitter and receiver can access. The receiver selects the best codebook index based on channel conditions and feeds back this index, while the transmitter independently selects the same precoding matrix from the codebook based on the feedback index, ensuring consistency without relying on direct PMI feedback.
Solution Approach 2:
The patent changes the selection criterion from direct PMI feedback to codebook index feedback. By transforming the precoding matrix selection problem into a codebook indexing problem, the system can achieve reliable precoding in high-speed scenarios. The codebook serves as a shared reference that allows the receiver to convey channel quality information through a simple index while the transmitter reconstructs the appropriate precoding matrix without needing direct PMI feedback.
2Device complexity
If the same precoding matrix is applied across all subcarriers, then implementation complexity is reduced, but frequency-selective performance deteriorates
Solution Approach 1:
The patent segments the frequency spectrum into multiple subbands and applies different precoding matrices to each subband. Instead of using a single precoding matrix for all subcarriers, the system divides the bandwidth and selects appropriate precoding matrices for each segment based on channel conditions in that segment. This allows the system to adapt to frequency-selective fading while maintaining reasonable complexity by limiting the number of precoding matrix changes.
Solution Approach 2:
The patent introduces dynamic precoding matrix selection across frequency by allowing the precoding matrix to change from one subband to another based on channel conditions. The system dynamically adapts the precoding strategy to match the frequency-selective characteristics of the channel, improving performance in frequency-selective scenarios while maintaining implementation feasibility through structured codebook-based selection.
3Adaptability or versatility
If codebook cycling is performed frequently, then adaptability to channel changes is improved, but feedback overhead increases
Solution Approach 1:
The patent uses partial codebook cycling where not all codebook entries are exhaustively searched and fed back. Instead of performing complete codebook searches which would generate excessive feedback, the system performs limited searches or uses simplified selection criteria that provide sufficient adaptability to channel changes while keeping feedback overhead manageable. This partial action approach balances adaptability with feedback efficiency.
Data Source
AI summary
A method for data transmission is provided that includes selecting a codeword from a predetermined codebook based on a transmission rank, generating a precoding matrix based on the selected codeword, precoding a plurality of symbols with the precoding matrix, and transmitting the precoded symbols.