R1-2601880
discussion
Downlink transmission schemes for downlink control channels
From TCL
Summary
This TCL contribution to 3GPP RAN1 #124bis contains 7 proposals and 2 observations on 6G PDCCH design. TCL advocates preserving NR PDCCH flexibility while proposing enhancements for coverage (repetition, higher aggregation, longer CORESET), supporting SFN-based M-TRP, reusing NR DMRS as baseline, and studying MRSS options between 5G and 6G.
Position
TCL proposes preserving NR PDCCH flexibility through Search Space and CORESET concepts for 6G, with harmonized CCE and REG definitions across 5G and 6G to simplify multi-RAT spectrum sharing and PDSCH rate matching. They propose three specific coverage enhancement directions: flexible time domain repetition for PDCCH, larger CCE aggregation levels (e.g. AL32 or higher), and extending CORESET duration beyond the NR limit of three OFDM symbols—particularly targeting ~7GHz deployments with ~10dB additional path loss relative to 3.5GHz and narrowband 3-5MHz BWPs where NR aggregation limits are infeasible. TCL requires supporting the SFN-based M-TRP PDCCH mechanism for spatial diversity and reliability. They require 6G PDCCH DMRS design to use 5G NR as baseline (ZC sequence, single port, comb structure with 3 REs per REG), with any enhanced design needing sufficient justification. TCL proposes RAN1 study five MRSS options: 5G DTx-aware coordination, central multi-RAT node TDM/FDM sharing, unified SSB, common initial DL BWP, and RAT-specific non-overlapping BWPs.
Key proposals
- Proposal 1 (Sec 2.1): Preserve NR PDCCH flexibility in time-frequency structuring via Search Space and CORESET for 6G.
- Proposal 2 (Sec 2.2): Enable flexible time domain repetition for PDCCH in 6G.
- Proposal 3 (Sec 2.2): Enable PDCCH with larger CCE aggregation levels (e.g., AL32 or higher) for 6G.
- Proposal 4 (Sec 2.2): Enable PDCCH with larger symbols in the time domain (CORESET duration beyond 3 OFDM symbols).
- Proposal 5 (Sec 2.3): Support SFN-based M-TRP PDCCH mechanism for 6G and investigate further enhancements for reliability.
- Proposal 6 (Sec 2.4): Base 6G PDCCH DMRS design on 5G NR; new designs require justification of rationality and necessity.
- Proposal 7 Option 1 (Sec 2.5): RAN1 to study coordination where the 6G base station utilizes 5G spectrum during 5G inactive cell DTx intervals.
- Proposal 7 Option 2 (Sec 2.5): RAN1 to study TDM, FDM, or hybrid TDM/FDM spectrum sharing managed by a central multi-RAT node.
- Proposal 7 Option 3 (Sec 2.5): RAN1 to study unified or shared SSB with enhancements to carry both 5G and 6G system information.
- Proposal 7 Option 4 (Sec 2.5): RAN1 to study BWP-based MRSS using a common initial DL BWP shared by both RATs for initial access.
- Proposal 7 Option 5 (Sec 2.5): RAN1 to study RAT-specific, non-overlapping BWPs for data and control transmission between 5G and 6G.
- Observation 1 (Sec 2.2): 6G PDCCH coverage fundamentally constrained under higher frequency (~7GHz), narrowband (3-5MHz BWP), and NTN conditions.
- Observation 2 (Sec 2.5): MRSS between 5G and 6G faces resource conflicts, high overhead/complexity from DSS-type MRSS, and SSB collision risks.
- Proposal 1 (Sec 3): Preserve NR PDCCH flexibility in downlink control time-frequency structuring via Search Space and CORESET.