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Summary: S4-260524 – NB-IoT GEO Simulation Assumptions for ULBC (Skylo Technologies)

Context: Contribution to the FS_ULBC (Ultra Low Bitrate Codec) feasibility study for voice over IoT NTN in GEO environments. The document derives simulation assumptions from existing 3GPP specs (TR 38.811, TR 38.821, TR 36.763) and real-world operator deployment data.

Key Technical Findings:

• Baseline CNR (worst case): UL CNR = −2.2 dB, DL CNR = −8.5 dB, derived from TR 38.821/TR 36.763 Set-2 parameters with UE profile 23 dBm / 7 dB NF.
• UE parameters: Class 3 handheld/IoT, 23 dBm Tx power, NF 7–9 dB, G/T range −30.42 to −36.6 dB/K (including polarization mismatch), 0 dBi omnidirectional antenna, 1Rx antenna as baseline.
• Satellite parameters (field deployment): EIRP 40.5–49 dBW per 180 kHz spot beam; satellite Rx G/T 8.8–20.5 dB/K; free-space path loss ~190.6 dB; near-negligible Doppler for GEO.

Simulation Assumption Proposals:

• Channel model: NTN-TDL-C at 10° elevation angle for worst-case modeling (NTN-TDLC5 delay profile per TS 36.102).
• Codec bitrate: Must support below 1 kbps (e.g., 0.8 kbps) to handle GEO NTN bandwidth constraints of 1–3 kbps.
• Voice bundling period: ≥160 ms baseline; 80 ms requires SPS, not yet supported in commercial NB-IoT NTN UE.
• DMRS bundling: Not recommended as baseline; informative evaluation only.
• UE power class: 23 dBm is the primary UL bottleneck; industry demand noted for 26/29/31 dBm classes for improved link robustness.
• Rx diversity: Single Rx antenna as baseline; 2Rx NB-IoT NTN devices not yet commercially mainstream.

Proposal: SA4 is asked to adopt observations 1–8 and the practical hardware constraints identified when defining ULBC simulation assumptions and performance targets.