R1-2601834
discussion
On aspects of bandwidth operation in 6GR
From Nokia
Nokia's prior position on
10.5.1.3
at
RAN1#124
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Proposes a lean 6GR BWP configuration framework that reduces the number of BWP types and eliminates redundant functionality options, making as many parameters cell-specific rather than BWP-specific. Requires removing the existing 5G TDD coupling between DL and UL BWPs, enabling independent center frequencies and independent switching per link direction. Opposes timer-based BW adaptation and proposes a proactive DCI-based scheme using UL grant as trigger, where PUSCH acts as implicit ACK to confirm receipt of BW switch commands before the actual switch occurs. Proposes decoupling initial BWP bandwidth from CORESET0 bandwidth to enable wider broadcast PDSCH transmissions for network energy saving. Proposes studying carrier configuration simplification by replacing pointA and SCS-specific offset with a single absolute frequency parameter for the start of the network carrier, assuming single SCS per band.
Summary
This Nokia Tdoc analyzes 5G NR BWP shortcomings and proposes a simplified, robust bandwidth adaptation framework for 6G Radio (FS_6G_Radio), containing 14 numbered proposals and 9 observations across initial BWP, non-initial BWP, BWP switching, and network carrier configuration.
Position
Nokia presents a technical case that NR BWP operation suffers from unnecessary flexibility resulting in excessive complexity, non-robust switching, suboptimal UL coverage, and problematic TDD coupling between UL and DL BWPs sharing the same center frequency. They propose a lean 6GR BWP configuration reducing BWP-specific parameters in favor of cell-specific parameters, limiting to two non-initial BWPs per link direction (wideband and narrowband), and decoupling DL and UL BWP center frequencies in TDD assuming separate UE local oscillators for Rx and Tx. They require a proactive DCI-based BWP switching framework with implicit acknowledgement via PUSCH (the best signal for UL DTX detector performance), explicitly opposing timer-based BW adaptation. They propose minimizing the switching gap by splitting total switching delay into processing time and switching time components, and making gap presence conditional on link direction and whether the switch is baseband-only (Type 0) or involves RF retuning (Type 1).
Key proposals
- Proposal 1 (Sec 2.2): Consider simplification through lean configuration, reducing number of BWPs and BWP types, eliminating redundant functionality options; redesign BW adaptation framework to make it robust and minimize service interruption and switching delays; optimize UL coverage by revisiting UE RF requirements (RAN4); provide unified solution for SSB measurements when CD-SSB is outside initial BWP; remove coupling between UL and DL BWP in TDD.
- Proposal 3 (Sec 3): Study efficient network carrier configuration principles assuming single subcarrier spacing for a given band.
- Proposal 5 (Sec 4): Study supporting system design where initial BWP for broadcast PDSCH transmissions can be wider than bandwidth of CORESET0.
- Proposal 6 (Sec 4): Support configuration of initial UL BWP with different center frequency than for the initial DL BWP in 6GR TDD.
- Proposal 7 (Sec 5.1): Minimize the BWP specific parameters and configuration options. Make as many parameters as possible cell-specific.
- Proposal 8 (Sec 5.1): Maximize the coexistence and similarity between initial and non-initial BWPs for those parameters and configuration options that require BWP-specific adaptation, e.g. CORESET0 and other CORESETs.
- Proposal 9 (Sec 5.1): Remove the existing coupling between DL and UL BWPs in 5G TDD, whereby DL and UL BWPs are required to switch simultaneously and share the same center frequency.
- Proposal 10 (Sec 5.2.1): For robust BW switching, aim at a proactive scheme for mitigating the potential error cases.
- Proposal 11 (Sec 5.2.1): Do not support timer-based BW adaptation in 6GR.
- Proposal 12 (Sec 5.2.1): Consider DCI based BW-adaptation triggering for 6GR.
- Proposal 13 (Sec 5.2.1): Consider UL grant as a trigger for DL BW switch or UL BW switch.
- Proposal 14 (Sec 5.2.2): Minimize the switching gap due to BWP switching by dividing total switching delay into processing time only and switching time, making the presence of switching gap conditional on the link direction (DL/UL) during the switching, and making the presence of switching gap conditional on switching type (BB only or RF).
- Proposal 2 (Sec 3): Support common resource block grid in 6GR similar to 5G.
- Observation 7 (Sec 5.1): Two non-initial BWPs per link direction are sufficient per UE for one cell.