TRS-Based CSI Reporting for Mobile MU-MIMO Precoding
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Solution Overview
Problem
Downlink MU-MIMO precoding performance degrades when co-scheduled UEs move faster than a few km/h due to outdated channel information, and existing Type-II CSI feedback is complex and not suitable for multi-TRP operation and Layer 1/2 mobility.
Innovation Solution
Measure and report time domain channel properties using existing TRS signals, which are low complexity and suitable for multiple TRPs, allowing integration with existing CSI reports to enhance precoding robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Type-II CSI feedback is used for downlink MU-MIMO precoding, then precoding performance is improved, but UE complexity increases and multi-TRP operation is not supported
Solution Approach 1:
The patent segments the channel state information into spatial domain (from CSI-RS) and time domain (from TRS) components. The UE measures spatial CSI using CSI-RS and time domain properties using TRS, then combines them to form enhanced CSI reports. This segmentation reduces complexity compared to full Type-II CSI while enabling multi-TRP operation through independent measurement of each TRP's TRS.
Solution Approach 2:
The patent makes the TRS serve multiple functions: it provides time domain channel properties for precoding enhancement and also enables multi-TRP operation. The same TRS mechanism can be applied across multiple transmission points, making the solution universally applicable to various deployment scenarios including single-TRP and multi-TRP modes.
2Measurement precision
If channel measurement resources are increased to track mobile UEs, then precoding accuracy is improved, but reference signal overhead increases
Solution Approach 1:
The patent reuses the TRS (Tracking Reference Signal) that is already configured for time domain synchronization purposes. Instead of introducing new dedicated measurement resources, the patent leverages the existing TRS to also provide time domain channel properties for precoding enhancement. This multi-functionality approach maintains measurement accuracy while avoiding additional overhead.
Solution Approach 2:
The patent merges the time domain measurement function with the existing TRS resource. Rather than separating time domain and spatial domain measurements into independent resources, the patent combines them by using TRS for time domain properties and CSI-RS for spatial properties, then integrating these measurements into a unified CSI feedback mechanism.
3Loss of information
If CSI reporting is based on TRS measurements, then time domain channel properties are obtained, but CSI reporting capability is not yet supported in NR specifications
Solution Approach 1:
The patent performs preliminary measurements of time domain properties using TRS before the actual precoding operation. The UE measures channel time domain properties (such as autocorrelation function) in advance and includes these measurements in the CSI report. This preliminary action enables the network to have up-to-date time domain information for enhanced precoding without requiring real-time complex measurements during data transmission.
Solution Approach 2:
The patent uses TRS as an intermediary signal that bridges the gap between existing NR specifications and the desired enhanced CSI reporting capability. TRS is already defined in NR for synchronization purposes, so it serves as a ready-made intermediary that can be leveraged to obtain time domain channel properties without requiring completely new signal definitions, thus easing specification implementation.
Data Source
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AI summary
There is provided a method performed by a user equipment (UE). The method comprises: receiving a reference signal over multiple time instances; determining time domain properties of a channel, based on the received reference signal; and sending a report to a network node, the report comprising information about the determined time domain properties of the channel. A UE for implementing this method is also provided.