PT-RS Port Selection via CSI Feedback Layer Indication
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Solution Overview
Problem
New Radio (NR) systems face challenges in mmWave frequencies due to phase noise from local oscillators, which degrade performance, and existing solutions for phase tracking reference signals (PT-RS) either associate PT-RS with the DMRS port with worse SINR or require significant additional signaling.
Innovation Solution
A method where the wireless device indicates the preferred layer for PT-RS transmission in CSI-feedback, ensuring PT-RS is not transmitted in the DMRS port with the worst SINR, using a fixed association rule that does not require additional signaling in the downlink, by jointly encoding the layer indication with the rank indicator and using precoder weights corresponding to the preferred layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PT-RS is associated with the DMRS port with worse SINR, then phase tracking can be performed, but transmission reliability deteriorates
Solution Approach 1:
The wireless device performs preliminary assessment of DMRS port SINR conditions and provides feedback to the network node before PT-RS transmission. The network node uses this advance information to select the optimal DMRS port for PT-RS association, ensuring phase tracking is performed on the port with best SINR rather than worst SINR, thereby maintaining transmission reliability while combating phase noise
Solution Approach 2:
A feedback mechanism is implemented where the wireless device measures SINR on different DMRS ports and reports this information to the network node. This feedback enables the network node to make informed decisions about PT-RS port association, selecting the DMRS port with the best SINR conditions for PT-RS transmission, thus resolving the contradiction between reliable transmission and phase noise mitigation
2Reliability
If dynamic PT-RS port selection is implemented, then transmission reliability improves, but signaling overhead increases
Solution Approach 1:
The patent merges the PT-RS port indication with existing CSI feedback mechanisms. Instead of introducing separate dedicated signaling for PT-RS port selection, the port indication is combined with channel state information feedback that is already being transmitted from wireless device to network node. This combining approach enables dynamic PT-RS port selection based on actual channel conditions while avoiding additional signaling overhead
Solution Approach 2:
The CSI feedback mechanism is given multi-functionality by using it not only for channel state reporting but also for conveying PT-RS port selection information. This universal use of existing feedback channels allows the system to achieve dynamic port selection without requiring dedicated signaling resources, thus improving reliability without increasing overall signaling overhead
3Reliability
If PT-RS is transmitted on all DMRS ports, then phase tracking coverage is improved, but energy consumption increases
Solution Approach 1:
Instead of uniformly transmitting PT-RS on all DMRS ports, the patent applies local quality by selectively transmitting PT-RS only on the specific DMRS port that has the best SINR conditions. This localized approach ensures that phase tracking is performed where it is most effective, providing adequate phase tracking coverage while avoiding unnecessary energy consumption from transmitting PT-RS on ports with poor channel conditions
4Measurement precision
If additional signaling is used for PT-RS port indication, then port selection accuracy improves, but system complexity increases
Solution Approach 1:
The system uses self-service by leveraging existing feedback capabilities of the wireless device to provide PT-RS port indication information. Instead of requiring the network to implement complex downlink signaling mechanisms, the wireless device autonomously measures SINR on different DMRS ports and reports this information using existing uplink feedback channels. This self-service approach achieves accurate port selection while keeping the signaling system relatively simple
Data Source
AI summary
Methods and apparatuses are disclosed for PT-RS selection. In one embodiment, a wireless device is configured to determine a layer based at least on a precoder associated with a precoder matrix indicator, PMI; and transmit an indication of the determined layer to a network node as part of channel state information, CSI, feedback. In other embodiments, a network device is configured to receive an indication of a layer for a phase-tracking reference signal, PT-RS, transmission as part of channel state information, CSI, feedback; determine a precoder based at least on the indication of the layer for the PT-RS transmission; and transmit the PT-RS, the PT-RS transmission associated with the indicated layer and a PT-RS port.