CSI Feedback via Multiple RRIs for Spatial Multiplexing Gain

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Solution Overview

Problem

In LTE Release 13, multiple beams are not spatially separated effectively during spatial multiplexing transmission in single beamformed CSI-RS, leading to insufficient gain when CSI is transmitted from UE to eNB.

Innovation Solution

The UE selects and transmits multiple Reference Signal Resource Indicators (RRIs) associated with different radio resources, enabling either spatial multiplexing gain or beam diversity gain by feeding back multiple RRIs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If single CRI is transmitted from UE to eNB in beamformed CSI-RS system, then feedback overhead is reduced, but spatial multiplexing gain is insufficient

Engineering Contradiction:

Improvefeedback overheadVSAvoidspatial multiplexing gain

Core Design Contradiction:

Device complexityVSProductivity

Solution Approach 1:

The patent segments the single CRI feedback into multiple CRI indicators, allowing the UE to report multiple selected beams (e.g., CRI1, CRI2, CRI3) instead of a single beam. This segmentation enables the system to capture spatial multiplexing opportunities across multiple beams while distributing the feedback information across multiple fields, thereby resolving the contradiction between feedback overhead and spatial multiplexing gain.

Inventive Principle:

Principle #1Segmentation

2Productivity

If multiple beams are used in spatial multiplexing transmission, then spatial multiplexing gain is improved, but beams are not spatially separated properly in single BF CSI-RS

Engineering Contradiction:

Improvespatial multiplexing gainVSAvoidspatial separation of beams

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent introduces an additional dimension to beam identification by enabling multiple CRI reports simultaneously. Instead of relying on a single beam dimension, the system now operates in a multi-dimensional space where multiple beams can be identified and spatially separated through their respective CRI indicators. This dimensional expansion allows proper spatial separation of multiple beams while maintaining spatial multiplexing gain.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Reliability

If UE is configured with multiple BF CSI-RS resources, then beam diversity is improved, but effective utilization requires multiple CRI feedback

Engineering Contradiction:

Improvebeam diversityVSAvoidfeedback mechanism

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent implements an enhanced feedback mechanism where the UE feeds back multiple CRI indicators corresponding to multiple selected BF CSI-RS resources. This feedback approach ensures that the eNB receives information about the best multiple beams for spatial multiplexing transmission, enabling effective utilization of beam diversity while providing the necessary feedback complexity to support multiple CRI reports.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS10840991B2User equipment and method for selection of CSI reference signal and CSI reporting in a beam forming system with multiple beams

Publication Date: 2020.11.17 NTT DOCOMO INC

AI summary

A user equipment (UE) includes a receiver that receives multiple Reference Signals (RSs) transmitted using respectively different radio resources from a base station (BS), a processor that selects, out of RS Resource Indicators (RRIs) associated with the radio resources used for RS transmission, multiple RRIs, and a transmitter that transmits the multiple RRIs to the BS. The processor derives Channel State Information (CSI) in each of the RRIs using the RSs. The transmitter transmits the CSI corresponding to the multiple RRIs to the BS. The transmitter transmits the CSI corresponding to a part of the multiple RRIs. The transmitter transmits a RRI rank that indicates a number of the selected RRIs.