CSI Feedback Codebook Structure Using FDD Angle–Delay Reciprocity
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Solution Overview
Problem
In frequency division duplex (FDD) systems, the downlink channel state information (CSI) cannot be directly obtained from uplink CSI, leading to challenges in determining an optimal precoding matrix due to non-reciprocity of uplink and downlink channels, necessitating a new codebook structure that leverages angle and delay reciprocity for reduced feedback overheads.
Innovation Solution
A channel state information feedback method using a codebook structure W=W1{tilde over (W)}2WfH, where W1 is a port selection matrix, {tilde over (W)}2 is a linear superposition coefficient matrix, and Wf is a right multiplication matrix, allowing the terminal to determine CSI based on angle and delay reciprocity, with indication information specifying the type of Wf to reduce feedback overheads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If a traditional codebook structure is used for CSI feedback in FDD systems, then the feedback process is simple, but the feedback overhead is high and system performance is limited due to non-reciprocal channels
Solution Approach 1:
The codebook W is segmented into three distinct matrices: W1 (spatial-domain basis vector matrix), Wf (frequency-domain basis vector matrix), and W2 (linear superposition coefficient matrix). This segmentation allows independent optimization of spatial and frequency dimensions, reducing feedback overhead while maintaining accuracy by exploiting channel correlations in both domains separately
Solution Approach 2:
The patent introduces a dual-domain compression approach by adding frequency-domain compression to the traditional spatial-domain compression. The frequency-domain basis vector matrix Wf exploits frequency correlations, creating a two-dimensional compression space (spatial × frequency) that significantly reduces feedback overhead compared to single-domain approaches
2Productivity
If dual-domain compression is applied to reduce feedback overhead, then feedback efficiency improves, but determining the optimal codebook structure becomes complex
Solution Approach 1:
The patent pre-defines codebook structures with specific properties (e.g., DFT-based spatial basis, discrete frequency basis) and stores them in codebook tables. The terminal can directly select and feed back codebook indices rather than computing optimal structures in real-time, reducing complexity while maintaining efficiency
Solution Approach 2:
The patent allows dynamic adjustment of codebook parameters such as the number of spatial basis vectors, frequency resolution, and superposition coefficients. By changing these parameters adaptively based on channel conditions, the system optimizes feedback efficiency without requiring complex real-time structure determination
3Reliability
If angle and delay reciprocity is exploited for CSI acquisition, then system performance improves, but compatibility with existing signaling protocols becomes challenging
Solution Approach 1:
The patent designs the codebook structure to be universally applicable across different FDD configurations and existing signaling frameworks. The dual-domain compression methodology can be integrated with existing CSI reporting mechanisms while simultaneously supporting angle-delay reciprocity exploitation, achieving multi-functionality without sacrificing compatibility
Data Source
AI summary
A channel state information feedback method includes: a terminal receives first indication information from a network device, and the terminal sends channel state information to the network device. The first indication information is used to indicate a type of a right multiplication matrix in a first codebook, and the first codebook satisfies a formula (I). W is the first codebook, W1 is a port selection matrix, (II) is a linear superposition coefficient matrix, Wf is the right multiplication matrix, and (III) is a conjugate transpose of Wf, and is used by the terminal to determine the channel state information based on the first codebook. According to the method, when there are a plurality of codebooks, the codebook used by the terminal to obtain the CSI can be clearly indicated.