Aperiodic Tracking Reference Signal Reception in Unlicensed Spectrum
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Solution Overview
Problem
The transmission of periodic tracking reference signals (P-TRS) is often prevented by channel access mechanisms like LBT in unlicensed spectrum, leading to outdated quasi-co-location (QCL) sources for downlink and uplink signals, which negatively impacts performance.
Innovation Solution
Implementing an aperiodic tracking reference signal (A-TRS) resource dynamically assigned through a provided SSB index, triggered by a group common physical downlink control channel (GC-PDCCH), allowing for beam-specific transmission to client nodes and enabling efficient reception of A-TRS even when P-TRS transmission fails.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If periodic tracking reference signal (P-TRS) transmission is used, then downlink and uplink performance is maintained through up-to-date QCL sources, but transmission is blocked by LBT mechanism in unlicensed spectrum
Solution Approach 1:
The patent transitions from static periodic P-TRS transmission to dynamic aperiodic A-TRS transmission. The network node dynamically decides whether to transmit P-TRS based on LBT success, and if failed, triggers A-TRS transmission instead. This dynamic adaptation allows the system to maintain QCL source availability despite LBT blocking periodic transmissions.
Solution Approach 2:
The patent implements preliminary action by configuring both P-TRS and A-TRS resources in advance, along with monitoring windows for detecting trigger commands. When P-TRS transmission is blocked by LBT, the pre-configured A-TRS resources are immediately activated through a trigger command, avoiding service interruption.
2Reliability
If aperiodic tracking reference signal (A-TRS) is introduced to replace P-TRS, then QCL source availability is maintained despite LBT failures, but system complexity increases due to additional signaling mechanisms
Solution Approach 1:
The patent introduces a trigger command as an intermediary mechanism between the network node and A-TRS transmission. Instead of complex continuous monitoring, the network node simply sends a trigger command via PDCCH when P-TRS fails, and the UE monitors for this trigger within a predefined window. This intermediary simplifies the complexity management.
Solution Approach 2:
The trigger command mechanism serves multiple functions: it indicates A-TRS transmission timing, activates pre-configured resources, and provides fallback when P-TRS fails. This multi-functionality reduces the need for separate signaling mechanisms, thereby managing complexity while maintaining reliability.
3Measurement precision
If beam-specific A-TRS transmission is implemented, then tracking accuracy is improved for individual beams, but PDCCH overhead increases due to individual triggering commands
Solution Approach 1:
The patent merges multiple A-TRS trigger commands into a single group common PDCCH message that can trigger A-TRS for multiple UEs simultaneously. Instead of sending individual trigger commands to each UE, the network node uses a group common PDCCH with a monitoring window approach, reducing PDCCH overhead while maintaining beam-specific tracking accuracy for each UE.
Data Source
AI summary
Example embodiments provide a procedure to improve reception of an aperiodic tracking reference signal by a client node, for example, when a periodic tracking reference signal was prevented. The aperiodic tracking reference signal resource may be dynamically associated with the periodic tracking reference signal through a provided synchronization signal block index. Further, a group common physical downlink control channel may be configured to trigger a monitoring window for reception of the aperiodic reference signal in response to a failed transmission of the periodic tracking reference signal. Apparatuses, methods, and computer programs are disclosed.