R1-2601865
discussion
Discussion on downlink transmission scheme(s) for downlink shared channels
From ZTE
Summary
This ZTE contribution to 3GPP RAN1#124 bis contains 33 proposals and 29 observations covering the 6GR downlink shared channel framework. It argues for prioritizing multi-TRP operation, unified DMRS design with up to 48 orthogonal ports, flexible codeword-to-layer mapping, and deprioritizing AI-based receiver and SIP studies at the beginning of 6GR.
Position
ZTE proposes that 6GR downlink MIMO framework study focus on multi-TRP operation from initial access, with CJT and sDCI-based mTRP prioritized for day 1 deployment to address coverage, UPT, and peak data rate. They require a unified DMRS design based on Comb-3 CDM groups with FD-OCC length=4 per RB per symbol, supporting up to 48 orthogonal DMRS ports plus non-orthogonal DMRS via different sequences, and explicitly deprioritize interleaved VRB-to-PRB mapping over the entire bandwidth part. For codeword-to-layer mapping, they propose studying three flexible options even for up to 4 layers, with particular emphasis on Option 2 (single CW with individual modulation order per layer) showing 36% SE gain. They present technical case against AI-based receiver for DMRS-based channel estimation, arguing the performance gain is trivial (0.5-1.5 dB) and may be eliminated by AI/ML model flaws, and deprioritize SIP study due to suboptimal performance compared to AI-based LD-DMRS with far higher computation complexity (31G vs 1.3G FLOPs).
Key proposals
- Proposal 2-1-1 (Sec 2.1): For 6GR downlink MIMO framework study, RAN1 should focus on key deployment scenarios (dense urban, urban macro, high speed train) and key performance indicators (coverage, user perceived throughput, peak data rate).
- Proposal 2-2-1 (Sec 2.2): RAN1 should study multi-TRP operation and ultra-massive MIMO to address coverage, UPT and peak data rate issues.
- Proposal 2-3-1 (Sec 2.3): Prioritize two specific BS antenna configurations at 7 GHz for SLS evaluation of PDSCH transmission: 128 TXRUs/768 AEs and 256 TXRUs/1536 AEs.
- Proposal 3-1-1 (Sec 3.1): RAN1 should study heterogeneous multi-layer network with both macro and micro stations working on the same frequency band (e.g., around 4 GHz + around 4 GHz, around 7 GHz + around 7 GHz).
- Proposal 3-2-1 (Sec 3.2): Multi-TRP should be prioritized for 6GR day 1 deployment based on its technical advantages and solid research foundation in 5G NR.
- Proposal 3-3-2 (Sec 3.3): For 6G PDSCH codeword-to-layer mapping up to 4 layers, fully study three options: Option 1 (CW per layer up to 4 CWs), Option 2 (single CW with single target code rate + individual modulation order per layer), Option 3 (two CWs with {1,1}, {1,2}, {2,2} mappings for 2-4 layers).
- Proposal 3-4-1 (Sec 3.4): Merge NR PDSCH mapping Type A and B into unified resource mapping with flexible start symbol S={0,1,...,13} and PDSCH length L={1,2,...,14}.
- Proposal 3-5-1 (Sec 3.5): Study Type 0, Type 1 and dynamic switch as starting point for FDRA, and study a solution for up to 400 MHz bandwidth with balanced tradeoff between scheduling flexibility and signaling overhead.
- Proposal 3-6-1 (Sec 3.6): Support non-interleaved VRB-to-PRB mapping as 6GR baseline, while deprioritizing interleaved VRB-to-PRB mapping over the entire bandwidth part in 6G Day 1.
- Proposal 3-7-1 (Sec 3.7): Dynamic scrambling ID update, e.g., along with TCI update, should be supported for intra-cluster interference randomization under a same PCI in 6GR.
- Proposal 3-9-1 (Sec 3.9): One TB can be mapped to up to 400MHz resources without any restriction for a unified solution for UEs with one RF chain and two RF chains.
- Proposal 4-1-1 (Sec 4.1): Strive for a unified and streamlined DMRS design in 6GR for both downlink and uplink data channels.
- Proposal 4-2-1 (Sec 4.2): Up to 48 orthogonal DMRS ports need to be fulfilled at the beginning of 6GR, with Comb-3 CDM groups with FD-OCC length=4 as the basic DMRS pattern.
- Proposal 4-2-6 (Sec 4.2): RAN1 needs to thoroughly study and carefully justify the practical needs of AI-based receiver for DMRS based channel estimation at the beginning of 6GR.
- Proposal 4-3-1 (Sec 4.3): Deprioritize the study on superimposed pilot (SIP) at the beginning of 6GR.