Type II Port Selection Codebook for Low-Overhead FDD CSI Reporting

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing 5G NR communications do not effectively exploit partial channel reciprocity in frequency division duplex (FDD) to optimize channel state information (CSI) reporting, leading to overhead issues in UE CSI measurements.

Innovation Solution

Implementing methods to leverage partial channel reciprocity in FDD by reconfiguring CSI resources, including wideband PMI reporting, larger sub-band sizes, and selective CSI reporting to reduce overhead at the UE.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of information

If traditional CSI reporting methods are used in FDD communications, then channel state information can be obtained, but reporting overhead and computational complexity are increased

Engineering Contradiction:

ImproveCSI reporting overheadVSAvoidchannel state information accuracy

Core Design Contradiction:

Loss of informationVSMeasurement precision

Solution Approach 1:

The base station performs downlink channel estimation before CSI reporting based on received uplink SRS signals. By preliminarily obtaining channel state information through channel reciprocity in TDD or uplink-downlink correlation in FDD, the system reduces the amount of CSI that needs to be reported by the UE, thereby reducing reporting overhead while maintaining measurement precision.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent introduces an intermediary processing step where the base station uses received SRS signals to estimate the downlink channel characteristics. This intermediary estimation acts as a bridge between uplink training and downlink CSI reporting, allowing the system to infer downlink channel state without requiring complete uplink-downlink reciprocity, thus reducing reporting overhead while preserving accuracy.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If full CSI reporting is performed, then accurate channel state information is achieved, but computational complexity and processing overhead increase

Engineering Contradiction:

Improvechannel state information accuracyVSAvoidUE computational complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent extracts only the essential CSI components that are most critical for downlink performance from the complete CSI set. By identifying and reporting only the most relevant channel parameters (such as dominant eigenvectors or selected precoding matrix indicators), the system reduces computational complexity at the UE while maintaining sufficient measurement precision for effective downlink communication.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Instead of performing complete CSI measurement and reporting, the patent applies partial action by having the UE measure and report only a subset of CSI parameters. The base station complements this partial reporting with its own channel estimation derived from SRS, achieving full CSI accuracy through combined partial measurements without requiring the UE to perform computationally intensive complete CSI analysis.

Inventive Principle:

Principle #16Partial or excessive action

3Loss of information

If channel reciprocity is exploited in FDD, then reporting overhead is reduced, but frequency selectivity and channel variations are not fully captured

Engineering Contradiction:

Improvereporting overheadVSAvoidfrequency selectivity handling

Core Design Contradiction:

Loss of informationVSAdaptability or versatility

Solution Approach 1:

The patent applies dynamic adaptation by adjusting the degree of reciprocity exploitation based on channel conditions. When frequency selectivity is high, the system reduces reliance on reciprocity and increases CSI reporting detail. When channels are more static, the system exploits reciprocity more aggressively to reduce overhead. This dynamic approach allows the system to adapt to varying frequency selectivity while maintaining efficient reporting.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes reporting parameters dynamically based on channel characteristics. By monitoring channel variation rates and frequency selectivity, the system adjusts CSI reporting granularity, resolution, and content. This parameter adaptation enables the system to reduce overhead through reciprocity when appropriate while maintaining adaptability to capture frequency selectivity when channel conditions require more detailed CSI.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS12621028B2Type II port selection codebook enhancements

Publication Date: 2026.05.05 APPLE INC

AI summary

A user equipment (UE) configured to report Channel State Information (CSI) to a wireless network. The UE transmits a first sounding reference signal (SRS) on an uplink (UL) channel, receives a first channel state information reference signal (CSI-RS) on a downlink (DL) channel, wherein the first CSI-RS includes a first configuration of CSI-RS parameters based on the first SRS, performs first CSI-RS measurements based on the first configuration of CSI-RS parameters, transmits a first CSI report including the first CSI-RS measurements, transmits a second SRS on the UL channel, receives a second CSI-RS on the DL channel, wherein the second CSI-RS includes a second configuration of CSI-RS parameters based on the second SRS, performs second CSI-RS measurements based on the second configuration of CSI-RS parameters and transmits a second CSI report including the second CSI-RS measurements.