Tap Location Compression for NR CSI Feedback
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Solution Overview
Problem
Current signaling formats for channel state information feedback in massive MIMO systems, particularly in New Radio phase II, face challenges in efficiently conveying time-domain tap delays and beam indices with low feedback overhead, especially for users with high mobility where tap locations change rapidly.
Innovation Solution
The proposed solution exploits the common channel support assumption to compress the feedback by conveying the channel support information in two steps: first, the locations of significant taps are sent, and second, a bit mask indicates active taps within these locations, reducing the overhead and leveraging the sparsity of the time-domain channel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the UE sends back complete channel impulse response information including all tap locations and beam indices, then the channel state information accuracy is improved, but the feedback signaling overhead increases significantly
Solution Approach 1:
The patent extracts only the essential information needed for channel state feedback by identifying and reporting only the significant tap locations and their corresponding beam indices, rather than reporting all possible tap locations. This extraction approach maintains channel state information accuracy while significantly reducing feedback overhead by eliminating redundant zero or negligible tap information.
Solution Approach 2:
The patent applies local quality by differentiating between significant and non-significant taps, reporting detailed information only for significant taps where precision matters, while omitting or coarsely representing non-significant taps. This allows the system to concentrate feedback resources on the most important channel characteristics, achieving high accuracy where needed while minimizing overall overhead.
2Loss of information
If the UE reports all tap locations in the time domain channel, then the completeness of channel information is improved, but the feedback overhead and processing complexity increase
Solution Approach 1:
The patent segments the time domain channel taps into significant and non-significant groups based on their magnitude or importance. Only the significant segment is reported in detail with precise tap locations and beam indices, while non-significant segments are either omitted or reported coarsely. This segmentation reduces feedback complexity while maintaining completeness of essential channel information.
Solution Approach 2:
The patent applies partial action by reporting only the necessary subset of tap information rather than all possible taps. By identifying and reporting only the significant portion of taps that contribute meaningfully to channel state, the system achieves sufficient information completeness without the excessive complexity of processing and reporting all tap locations.
3Measurement precision
If the feedback format includes detailed tap location and beam index information for each path, then the channel description accuracy is improved, but the spectral efficiency decreases due to high overhead
Solution Approach 1:
The patent extracts and reports only the critical channel parameters - significant tap locations and their corresponding beam indices - while omitting redundant information. This extraction maintains channel description accuracy for the dominant propagation paths while reducing feedback overhead, thereby improving spectral efficiency without sacrificing essential channel knowledge.
Solution Approach 2:
The patent changes the feedback parameter representation by using compact indexing methods for significant taps and their associated beams. Instead of reporting full channel matrices or all possible tap-beam combinations, the system transforms the feedback into a compact format reporting only significant tap locations and their corresponding beam indices, improving spectral efficiency while preserving channel description accuracy.
Data Source
AI summary
Methods, apparatus, and computer program products for a user equipment receiving CSI-RS and computing channel support information. Based on the CSI, the UE derives tap locations of channel support, depending on the observed channel and used subcarrier spacing. The deriving can additionally be done in relation to power class and window size. The UE apprises a base station of those tap locations of the channel support and also informs the base station of the strongest tap locations, which can be done in various ways comprising a bit mask. Methods, apparatus, and computer program products for a base station to send CSI-RS to a UE for computing CSI feedback. The CSI-RS resources can be for one or multiple transmit receive points. The base station receives back an indication of tap locations and a bit mask and builds information on tap locations by combining that received indication and bit mask.