MIMO Receiver Feedback Vector Selection
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Solution Overview
Problem
The complexity and computational burden of finding the code vector with the smallest angle to a multidimensional channel subspace in MIMO systems make feedback transmission inefficient, especially with limited resources and time in mobile devices.
Innovation Solution
Select a vector with N-1 null components in a linear space defined by channel transfer matrices and provide quantized values of M - (N-1) nonzero components as feedback, reducing the dimensionality and computational requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If brute force implementation is used to find the code vector with minimum angle to channel subspace, then measurement precision is improved, but device complexity and processing time increase significantly
Solution Approach 1:
The patent segments the feedback process into two stages: first, the receiver identifies and transmits only the indices of non-zero elements in the channel vector; second, the base station reconstructs the full channel vector by looking up corresponding codebook entries. This segmentation reduces the feedback burden from transmitting all M channel coefficients to transmitting only the sparse non-zero indices, significantly reducing receiver processing complexity while maintaining measurement precision.
Solution Approach 2:
The patent changes the parameter representation from full channel vectors to sparse index representations. Instead of transmitting M complex numbers, the system transmits only the indices of non-zero elements, changing the feedback dimensionality from M to approximately log2(M) bits per non-zero element. This parameter transformation dramatically reduces the computational burden on the receiver while preserving the essential channel information needed for precoding.
2Measurement precision
If more bits are transmitted for feedback, then measurement precision is improved, but loss of time increases due to limited feedback transmission time
Solution Approach 1:
The patent applies partial action by transmitting only the necessary information (indices of non-zero elements) rather than all possible channel coefficients. The base station then reconstructs the full channel vector by combining these partial feedback elements with codebook entries, achieving sufficient precision for precoding without requiring complete channel state information transmission. This partial feedback approach fits within the limited time resources available.
3Measurement precision
If extensive hardware and software are used in the receiver, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent uses copying by having the base station store a codebook of pre-computed channel vectors during system setup. Instead of requiring the receiver to perform complex computations or store large amounts of data, the receiver simply copies and transmits the indices of relevant codebook entries. The base station then uses these copied indices to reconstruct the channel vectors, eliminating the need for extensive receiver hardware while maintaining measurement precision.
Data Source
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AI summary
There is provided a system and method of operating a multiple-input multiple-output (MIMO) receiver with N antennas in a wireless communication system. The method includes measuring N vectors, each vector defining channel transfer coefficients between M antennas of a transmitter and a corresponding antenna of the receiver. Additionally, a vector in a linear space generated by the N measured vectors is selected and quantized values of less than M components of the selected vector are fed back to the transmitter.