Sounding Reference Signal Precoding for Dynamic TDD Switching
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Solution Overview
Problem
Existing wireless communication systems face challenges in efficiently configuring precoding for sounding reference signals (SRS) in multi-antenna/multi-layer systems, particularly in scenarios where Time Division Duplex (TDD) is deployed, leading to suboptimal channel estimation and precoding.
Innovation Solution
Implementing a method that allows dynamic switching between codebook-based and non-codebook-based UL transmission by incorporating a DL RS resource indicator in SRS transmission settings, enabling the UE to derive precoding matrices based on DL channel estimation, thereby enhancing channel estimation and precoding accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If codebook-based precoding is used for SRS transmission, then the base station can determine precoders from a predefined codebook, but the system lacks flexibility to adapt to rapidly changing channel conditions
Solution Approach 1:
The system enables dynamic switching between codebook-based and non-codebook-based precoding methods. The UE can be configured to use codebook-based precoding with TPMI indication for stable channels, or switch to non-codebook-based precoding where the UE autonomously determines precoders based on DL channel estimates for rapidly changing channels. This dynamic adaptability resolves the contradiction by allowing the system to select the appropriate precoding mode based on current channel conditions.
Solution Approach 2:
The invention changes the precoding configuration parameters dynamically. When switching from codebook-based to non-codebook-based precoding, the system changes from using predefined codebook indices (TPMI) to using UE-derived precoders based on DL RS measurements. This parameter change enables the system to adapt to varying channel conditions while managing complexity through configurable switching mechanisms.
2Adaptability or versatility
If non-codebook-based precoding with UE-derived precoders is used, then the system achieves better adaptability to channel conditions, but increases UE processing complexity and overhead
Solution Approach 1:
The system implements dynamic precoding mode selection where the UE can switch between codebook-based and non-codebook-based precoding. In non-codebook-based mode, the UE derives precoders dynamically from DL channel estimates, providing better adaptability. The system manages UE processing complexity by allowing configurable switching between modes, so the UE only performs complex DL channel estimation and precoder derivation when necessary for optimal performance.
Solution Approach 2:
The base station performs preliminary channel estimation using SRS transmissions before indicating the precoding mode to the UE. This preliminary action allows the base station to assess channel conditions and determine whether non-codebook-based precoding would benefit the UE, thereby avoiding unnecessary UE processing complexity when codebook-based precoding would suffice.
3Measurement precision
If frequency-selective precoding with multiple TPMIs is used, then the channel matching accuracy is improved, but the signaling overhead and configuration complexity increase
Solution Approach 1:
The system segments the bandwidth into multiple subbands and applies different precoding strategies to each subband. For frequency-selective precoding, the base station can indicate multiple TPMIs corresponding to different subbands, improving channel matching accuracy. The segmentation approach manages signaling overhead by allowing selective application of frequency-selective precoding only where channel variations warrant the additional precision.
Solution Approach 2:
The system applies frequency-selective precoding partially, only when channel conditions justify the additional overhead. The base station can configure the UE to use frequency-selective precoding for specific subbands or transmission occasions, rather than uniformly across all resources. This partial application reduces the overall signaling overhead while maintaining high channel estimation accuracy where needed.
4Productivity
If TDD reciprocity is exploited for uplink precoding, then the system achieves efficient channel estimation, but requires accurate downlink-to-uplink channel calibration
Solution Approach 1:
The system uses downlink reference signals (DL RS) as an intermediary to transfer channel state information from downlink to uplink. The UE measures DL RS, derives channel estimates, and uses these to determine uplink precoders assuming reciprocity. This intermediary approach enables efficient channel estimation by leveraging the downlink channel measurements, while the base station can validate and adjust the reciprocity assumption through calibration procedures to maintain precoding accuracy.
Data Source
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AI summary
A method, wireless device (100) and network node (200) for for performing sounding reference signal, SRS, transmission. According to one aspect a method includes receiving a definition of one or more SRS resource sets to be configured, comprising at least one SRS transmission setting. The method further includes receiving an indication of a selected SRS resource set to use for a SRS transmission, from the one or more configured SRS resource sets and determining a precoding configuration for the SRS transmission based on the selected SRS resource set and the at least one SRS transmission setting. The method also includes transmitting a SRS according to the determined precoding configuration.