R1-2601841
discussion
Other aspects of 6GR physical layer operation
From Nokia
Nokia's prior position on
10.5.3.3
at
RAN1#124
· AI-synthesized, paraphrased
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Questions the necessity of introducing a 6GR-specific TRS before use cases and corresponding requirements are clearly identified. Presents a technical case against periodic TRS inherited from 5G, arguing that periodic TRS contributes to system overhead and network energy consumption and experiences different channel characteristics than PDSCH DMRS due to cell-specific wide-beam transmission versus UE-specific precoded transmission. Proposes that 6GR should build upon aperiodic RS design associated with downlink transmissions that shares the same/similar radio channel characteristics as PDSCH DMRS. If TRS usage is retained, proposes studying mechanisms for more flexible TRS adaptation including not transmitting TRS or adapting TRS configuration/setting for overhead reduction and energy savings without compromising performance, noting that network-side lack of knowledge for timely TRS adaptation is available at the UE.
Summary
This 3GPP RAN1 contribution from Nokia presents 6 observations and 6 proposals regarding 6G physical layer operation, focusing on time/frequency tracking reference signal (TRS) design and joint DL/UL CSI acquisition. Nokia argues that 6G should prioritize aperiodic, on-demand DM-RS-based tracking over periodic CSI-RS-based TRS to reduce overhead and energy consumption while better matching PDSCH channel characteristics.
Position
Nokia proposes studying DM-RS based TRS as a candidate for time/frequency tracking in 6G, presenting a technical case that periodic CSI-RS-based TRS suffers from high overhead, constant network/UE energy consumption, and mismatch between wide-beam TRS and narrow-beam PDSCH channel characteristics (delay spread, Doppler spread). They require aperiodic RS design associated with downlink transmissions that shares the same radio channel characteristics as PDSCH DMRS. Nokia proposes studying techniques like comb-offset hopping to alleviate inter-cell interference when TRS configurations collide across cells. For CSI acquisition, Nokia proposes studying joint DL and UL based DL CSI acquisition in TDD systems using the new Rel-19 UE antenna model with candidate antenna locations and orientations, noting that SRS-based acquisition serves cell-center UEs while CSI-RS-based acquisition serves cell-edge UEs.
Key proposals
- Proposal 1 (Sec Time and Frequency Tracking Reference Signal): In the study for TRS like signal in 6GR, use cases and corresponding requirements should be clarified.
- Proposal 2 (Sec Time and Frequency Tracking Reference Signal): 6GR should strive on building upon aperiodic RS design associated with downlink transmissions to perform channel parameter estimations and that shares the same/similar radio channel characteristics as PDSCH (DMRS).
- Proposal 3 (Sec Time and Frequency Tracking Reference Signal): If TRS usage(s) is kept in 6GR, study the need to enable more flexible TRS adaptation for the purpose of overhead reduction /energy savings, without compromising performance.
- Proposal 4 (Sec Time and Frequency Tracking Reference Signal): Study techniques like comb-offset hopping for the TRS signal to alleviate inter-cell interference when TRS configurations of different cells are using the same time and frequency resources.
- Proposal 5 (Sec RS serving for T/F tracking purposes): Consider DM-RS based TRS as a candidate for TRS purposes.
- Proposal 6 (Sec CSI acquisition by jointly DL and UL): Study joint DL and UL based DL CSI acquisition in TDD system with focus on new Rel-19 UE antenna model with candidate antenna locations and orientations.