Aperiodic CSI-RS QCL Selection for Dual-TCI PDSCH Overlap
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Solution Overview
Problem
The existing NR standard does not define the UE behavior when Aperiodic CSI-RS collides with PDSCH in scenarios where the PDSCH is indicated with two TCI states, particularly in cases involving single-PDCCH based NC-JT, FDMSchemeA, FDMSchemeB, and TDMSchemeA, leading to undefined QCL assumptions for the UE.
Innovation Solution
The proposed solution defines the UE behavior by specifying the QCL assumptions for receiving Aperiodic CSI-RS when it overlaps with PDSCH, considering scenarios like TDMSchemeA, FDMSchemeA, FDMSchemeB, and single-PDCCH based NC-JT, by determining appropriate TCI states based on scheduling offsets and default or indicated TCI states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If Aperiodic CSI-RS is triggered to overlap with PDSCH in time, then resource utilization and flexibility are improved, but the UE behavior becomes undefined and reception reliability deteriorates
Solution Approach 1:
The patent applies parameter changes by dynamically selecting QCL assumptions based on the scheduling offset value. When the scheduling offset is less than a threshold, the UE uses QCL assumptions from the PDSCH; when the offset is greater than or equal to the threshold, the UE uses QCL assumptions from the CORESET. This parameter-based conditional selection resolves the ambiguity and enables reliable reception of Aperiodic CSI-RS even when it overlaps with PDSCH in time, thus improving resource utilization without sacrificing reception reliability.
2Measurement precision
If QCL assumptions are defined for Aperiodic CSI-RS overlapping with PDSCH, then reception accuracy is improved, but system complexity increases
Solution Approach 1:
The patent uses parameter changes (scheduling offset threshold comparison) to select between different QCL assumption sources. This approach improves reception accuracy by providing clear, defined behavior for Aperiodic CSI-RS reception, while avoiding excessive system complexity by using a simple threshold-based decision rule rather than complex multi-step procedures.
Solution Approach 2:
The system enables self-service by allowing the UE to autonomously determine the appropriate QCL assumptions based on the scheduling offset value and the configured threshold. The UE independently selects between PDSCH QCL assumptions and CORESET QCL assumptions without requiring additional network signaling or complex coordination, thus improving reception accuracy while minimizing system complexity.
3Adaptability or versatility
If multiple TCI states are indicated for PDSCH, then transmission versatility is improved, but determining appropriate QCL assumptions for Aperiodic CSI-RS becomes more difficult
Solution Approach 1:
The patent resolves the difficulty of determining QCL assumptions when multiple TCI states are indicated by using a parameter-based selection rule. The UE compares the scheduling offset against a threshold and accordingly selects QCL assumptions from either the PDSCH or the CORESET. This parameter-driven approach maintains transmission versatility (support for multiple TCI states) while simplifying the detection and measurement process by providing a clear, deterministic rule for QCL assumption selection.
Data Source
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AI summary
Systems and methods for determining Transmission Configuration Indication (TCI) states for Aperiodic (AP) Channel State Information Reference Signals (CSI-RSs) overlapping with downlink transmissions are provided. In some embodiments, a method performed by a wireless device includes: receiving AP CSI-RSs in the same symbols as downlink transmissions scheduled by a DCI with two TCI states indicated in DCI; receiving triggering of the one or more AP CSI-RS with scheduling offset between the last symbol of the PDCCH carrying the triggering DCI and the first symbol of the AP CSI-RS resources, where the scheduling offset is smaller than a wireless device reported threshold; and determining that the downlink transmission is scheduled according to a scheme where different sets of layers of the downlink transmission are received with different TCI states. In some embodiments, the wireless device applies a QCL assumption for a PDSCH transmission occasion when receiving the AP CSI-RS.