MIMO Codebook Structure for Feedback Overhead Reduction

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Solution Overview

Problem

Current wireless communication systems face challenges in achieving high spectral efficiency with limited frequency bands, particularly in MIMO systems, where the feedback overhead for precoding matrices is high and the performance varies significantly with changing channel conditions.

Innovation Solution

The design of a codebook structure for 4 transmit antenna MIMO systems, where each precoding codeword is derived as a product of two matrices, optimizing the feedback overhead and performance by exploiting fundamental properties of spatial correlation matrices under uniform linear array and cross-pole antenna configurations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If codebook resolution is increased to improve precoding accuracy, then spectral efficiency is improved, but feedback overhead increases

Engineering Contradiction:

Improveprecoding accuracyVSAvoidfeedback overhead

Core Design Contradiction:

Measurement precisionVSLoss of information

Solution Approach 1:

The codebook is segmented into two parts: a first codebook containing a limited number of codebook subsets, and a second codebook containing multiple codebook subsets. The transmitter and receiver share knowledge of both codebooks, but the receiver only needs to feedback a subset index from the first codebook. This segmentation allows high-resolution precoding selection while maintaining low feedback overhead.

Inventive Principle:

Principle #1Segmentation

2Adaptability or versatility

If codebook size is increased to cover more channel conditions, then adaptability is improved, but device complexity increases

Engineering Contradiction:

Improvechannel condition coverageVSAvoidcodebook storage and search

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The first codebook is designed in advance to contain a limited set of codebook subsets that cover diverse channel conditions. This preliminary structuring allows the system to achieve high adaptability without requiring the receiver to store or search through a large number of individual codebooks during operation.

Inventive Principle:

Principle #10Preliminary action

3Reliability

If feedback rate is increased to track channel changes, then performance is improved, but loss of time increases

Engineering Contradiction:

Improveperformance under changing conditionsVSAvoidfeedback time interval

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The invention extracts only the essential information needed for precoding selection - the codebook subset index from the first codebook - and feeds back only this compressed representation. This extraction approach maintains performance under changing channel conditions while minimizing feedback time and overhead.

Inventive Principle:

Principle #2Taking out (Extraction)

Data Source

PatentUS10594372B2Codebook construction

Publication Date: 2020.03.17 NEC CORP

AI summary

A method implemented in a base station used in a wireless communications system is disclosed. The method comprises having 1-layer, 2-layer, 3-layer, and 4-layer codebooks for 4 transmit antenna (4TX) transmission, each codebook including a plurality of precoding matrices, precoding data with one of the plurality of precoding matrices, and transmitting, to a user equipment, the precoded data, wherein each of the 1-layer and 2-layer codebooks comprises a first codebook and a second codebook, and wherein each precoding matrix in the first codebook comprises a first index and a second index. Other apparatuses, systems, and methods also are disclosed.