R1-2601908
discussion
Considerations on 6G Radio for NTN
From Thales
Summary
Thales presents 12 proposals and 5 observations in this 6G NTN contribution, urging that NTN-specific requirements be integrated from the outset of 6G radio design rather than retrofitted as in 5G. The document covers harmonized TN/NTN design principles, deployment scenarios across multiple orbits and frequency bands, a concatenated BCH+LDPC coding scheme to eliminate LDPC error floors without HARQ, and refinements to the NTN channel model K-factor parameterization.
Position
Thales requires that NTN-related technical considerations be addressed from the outset of 6G radio design to avoid the non-optimized adaptations that occurred when NTN was retrofitted into 5G NR. They propose studying a concatenated BCH outer code with LDPC inner code (BCH t ≈ 8–10, LDPC block size 16896 bits / 44 columns) to achieve Quasi-Error-Free performance and eliminate HARQ retransmissions in long-RTT NTN links where LDPC error floors become problematic at extended block sizes. They identify the current TR 38.811 K-factor parameterization as physically inconsistent across environment types and frequency bands, and propose revisiting this modeling. They require support for all orbit types from Very LEO (300 km) through GSO (35,786 km) with earth-fixed steerable beams limited to 250 km maximum footprint diameter, all payload types from transparent through regenerative with functional BS split, and all duplex modes (FDD, HD-FDD, TDD) with GNSS-independent positioning and physical layer operation.
Key proposals
- Proposal 1 (Sec 3): NTN-related technical considerations should be addressed early in the 6G study, including waveform design, frame structure, channel coding, MCS, AI/ML, and evaluation assumptions, accounting for high Doppler shifts, large/variable RTT, low SNRs, and compatibility across Very LEO, LEO, MEO, and GEO orbits.
- Proposal 2 (Sec 4): For harmonized 6GR design for TN and NTN, RAN1 should study technical aspects affected by NTN characteristics including time/frequency synchronization (FFS on pre-compensation at UE and/or network), GNSS-independent physical layer operation, frame structure, coverage enhancements, beam management, ultra-low BLER avoiding HARQ, beam hopping with longer SSB/common channel periodicity, FDD/HD-FDD/TDD duplexing modes, positioning/navigation/timing, PAPR reduction for NTN downlink, and 6G NTN coexistence with IoT-NTN or NR-NTN in the same beam.
- Proposal 3 (Sec 5.1): The 6G radio interface/access shall support all practical NTN deployment scenarios across Very LEO (300 km), Medium LEO (600 km), High LEO (1200 km), MEO (8000 km), and GSO (35,786 km) orbits with earth-fixed steerable beams and maximum beam footprint diameter below 250 km.
- Proposal 4 (Sec 5.3): The 6G radio interface/access shall support all NTN payload types including transparent (RF repeater), semi-transparent (RU with fronthaul), regenerative embarking a full base station (with store-and-forward and/or ISL support), and regenerative with functional BS split (RU+DU with F1-like interface).
- Proposal 5 (Sec 5.5): The 6G radio interface/access shall support all duplex modes at UE and network level including full-duplex FDD, half-duplex FDD (HD-FDD), and TDD, with UE types covering smartphones/IoT and vehicle/building-mounted devices across paired and unpaired frequency bands.
- Proposal 6 (Sec 5.7): The 6G radio interface/access shall support NTN-capable UE types including smartphones/IoT devices (omnidirectional antenna, -5 dBi min gain, 20 dBm Tx power, 7 dB noise figure, 500 km/h ground speed, outdoor/light indoor coverage) and vehicle/vessel/aircraft/building-mounted devices (directional antenna with 20 cm aperture equivalent, 1W Tx power, 1500 km/h ground speed, outdoor-only coverage).
- Proposal 7 (Sec 5.8): The 6G radio interface/access shall provide high-accuracy and resilient positioning without GNSS service.
- Proposal 8 (Sec 5.11): Further study and refine the NTN fast-fading channel model in TR 38.811, with particular focus on revisiting K-factor modeling versus environment and frequency due to physically inconsistent dependence across rural/suburban/urban/dense urban scenarios and S-band/Ka-band.
- Proposal 9 (Sec 6.2): Study a concatenated BCH outer code to ensure Quasi-Error-Free (QEF) performance, motivated by the need to eliminate LDPC residual error floors that become more pronounced at code block sizes of 16896 bits, avoiding costly HARQ retransmissions in long-RTT satellite links.
- Proposal 10 (Sec 6.3): Evaluate a concatenated BCH+LDPC scheme where LDPC (16896 bits / 44 columns) remains the inner code and a short BCH outer code (t ≈ 8–10, e.g., n=16896, k=16700, t=10, parity overhead 196 bits) removes LDPC residual errors, focusing on post-decoding BER/BLER in the error-floor region, impact on HARQ retransmissions and latency, and implementation complexity overhead.
- Proposal 11 (Sec 5.9): For 6G NTN study, consider the SAN parameters across L-, S-, C-, Ku-, Ka-, and Q/V bands as provided in Tables 8 through 12, including satellite EIRP density, G/T, antenna aperture, and beam diameter per orbit/band combination.
- Proposal 12 (Sec 5.10): For 6G NTN study, consider the satellite phased-array antenna models across L-, S-, C-, Ku-, Ka-, and Q/V bands as provided in Tables 13 through 16, specifying equivalent aperture, array spacing, total array elements, and single element gain.
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