Summary of S4-260136: Updates to Simulation Results for FS_ULBC

1. Introduction and Context

This document presents updated link-level simulation (LLS) results for Ultra-Low Bitrate Communication (ULBC) over Non-Terrestrial Networks (NTN). The simulations follow the NTN-TDL-C channel model as specified in TS 36.102. This revision adds:
- Missing simulation results for NTN-TDL-C 10 NPUSCH
- New simulation results for NTN-TDL-C 10 NPDSCH
- Updated TBS (Transport Block Size) values for both NPDSCH and NPUSCH with 10 degrees elevation angle

The simulations are based on parameters discussed in S4aA250038 and follow agreements from previous meetings.

2. Channel Model Assumptions

Key Parameters:
- Satellite elevation angle: 12.5 degrees for link budget calculations
- Channel model parameters (delay and power of each path) determined for 10 degrees elevation (approximation of 12.5 degrees)
- Channel model: NTN-TDL-C from TS 36.102

3. Link Budget Analysis

3.1 CNR Baseline Values (from RAN1)

Uplink:
- CNR = 2.6 dB (0 dBi UE antenna gain, 3.75 kHz SCS, 1 tone, 23 dBm UE TX power)

Downlink:
- CNR = -3.3 dB (0 dBi UE antenna gain, 15 kHz SCS, 12 tones, 1 RX antenna, 7 dB noise figure)

3.2 Additional UL CNR Configurations

| Configuration | SCS | UE Power | UL CNR |
|---------------|-----|----------|---------|
| Config 1 | 3.75 kHz | 23 dBm | 2.6 dB |
| Config 2 | 15 kHz | 23 dBm | -3.42 dB |
| Config 3 | 3.75 kHz | 26 dBm | 5.6 dB |
| Config 4 | 15 kHz | 26 dBm | -0.42 dB |
| Config 5 | 3.75 kHz | 31 dBm | 10.6 dB |
| Config 6 | 15 kHz | 31 dBm | 4.58 dB |

3.3 Additional DL CNR Configurations

| Configuration | Number of RX | G/T value | DL CNR |
|---------------|--------------|-----------|---------|
| Config 1 | 1 | -31.6 | -3.3 dB |
| Config 2 | 2 | -31.6 | -0.3 dB |
| Config 3 | 1 | -28.6 | -0.3 dB |
| Config 4 | 2 | -28.6 | 2.7 dB |

4. NPUSCH Simulation Results

4.1 Common Simulation Parameters

• Scenario: GEO orbit, 10 degree elevation
• Carrier frequency: 2 GHz
• Channel model: NTN-TDL-C with 5 ns delay spread
• Physical channel: NPUSCH format 1
• SCS: 3.75 kHz and 15 kHz
• Number of tones: Single tone
• Waveform: SC-FDMA
• MIMO: SISO (1T1R)
• DMRS: OS#4 per slot for 3.75 kHz, OS#3 per slot for 15 kHz
• UE velocity: 3 km/h
• Symbols per slot: 7
• Slots per RU: 16
• Modulation: π/4-QPSK
• Receiver: MMSE with real channel estimation
• Target BLER: 1%, 2%, 6%, 10%

4.2 Results Part 1 - Various TBS and Bundling Times

80 ms Bundling Time

144 bits (Cases 1-4):
- Case 1: 15 kHz, MCS 2, 4 RUs, 2 reps → SNR: -4.97 dB (10% BLER) to -4.35 dB (1% BLER)
- Case 2: 15 kHz, MCS 2, 2 RUs, 1 rep → SNR: 1.8 dB to 2.7 dB
- Case 3: 3.75 kHz, MCS 10, 1 RU, 2 reps → SNR: 1.5 dB to 2.30 dB
- Case 4: 15 kHz, MCS 10, 1 RU, 4 reps → SNR: -4.64 dB to -3.90 dB

256 bits (Cases 5-8):
- SNR ranges from -2.84 dB to 5.9 dB depending on configuration

328 bits (Cases 9-11):
- SNR ranges from -1.53 dB to 9.45 dB depending on configuration

424 bits (Case 12):
- SNR: 1.44 dB (10% BLER) to 2.05 dB (1% BLER)

160 ms Bundling Time

208 bits (Cases 13-15):
- SNR ranges from -5.56 dB to 1.53 dB

424 bits (Case 16):
- SNR: -1.95 dB to -1.52 dB

600 bits (Case 17):
- SNR: -1.38 dB to -0.97 dB

808 bits (Cases 18-19):
- SNR ranges from -1.42 dB to 0.21 dB

320 ms Bundling Time

328 bits (Cases 20-25):
- SNR ranges from -6.80 dB to -0.22 dB

776 bits (Cases 26-27):
- SNR ranges from -2.48 dB to 6.46 dB

1000 bits (Cases 28-30):
- SNR ranges from -1.95 dB to 7.47 dB

1544 bits (Case 31):
- SNR: 0.48 dB to 0.76 dB

4.3 Results Part 2 - Additional Cases

Covers Cases 32-46 with various TBS values (440, 584, 680, 936, 1096, 1384, 1736 bits) for 80 ms and 160 ms bundling times. SNR requirements range from -3.6 dB to 8.0 dB depending on configuration.

5. NPDSCH Simulation Results

5.1 Common Simulation Parameters

• Scenario: GEO orbit, 10 degree elevation
• Carrier frequency: 2 GHz
• Channel model: NTN-TDL-C with 5 Hz Doppler spread
• Physical channel: NPDSCH
• SCS: 15 kHz
• Number of tones: 12
• Waveform: OFDM
• MIMO: SISO (1T1R or 1T2R)
• Symbols per subframe: 14
• Modulation: QPSK
• Receiver: MMSE with NRS-bundling and real channel estimation
• Target BLER: 1%, 2%, 6%, 10%

5.2 Results Part 1 - Various TBS and Bundling Times

80 ms Bundling Time

144 bits (Case 0a):
- 1R: SNR -6.6 dB to -5.3 dB
- 2R: SNR -9.3 dB to -8.1 dB

256 bits (Case 0b):
- 1R: SNR -4.3 dB to -3.1 dB
- 2R: SNR -7.1 dB to -6.1 dB

328 bits (Cases 1-2):
- SNR ranges from -11.8 dB to -4.0 dB

424 bits (Cases 3, 3b):
- SNR ranges from -11.6 dB to -5.0 dB

160 ms Bundling Time

208 bits (Case 4):
- SNR: -15.3 dB to -11.8 dB

424 bits (Cases 5, 5b):
- SNR ranges from -14.6 dB to -8.0 dB

600 bits (Case 6):
- SNR: -11.1 dB to -7.2 dB

808 bits (Cases 7, 7b, 8, 8b):
- SNR ranges from -11.0 dB to -1.1 dB

320 ms Bundling Time

328 bits (Cases 9-11b):
- SNR ranges from -17.7 dB to -8.1 dB

776 bits (Cases 12, 12b):
- SNR ranges from -14.8 dB to -8.1 dB

1000 bits (Case 13):
- SNR: -10.3 dB to -6.4 dB

1544 bits (Cases 14, 14b):
- SNR ranges from -11.7 dB to -5.0 dB

5.3 Results Part 2 - Additional Cases

Covers Cases 15-46 with various TBS values (440, 584, 680, 936, 1096, 1384, 1736 bits) for 80 ms and 160 ms bundling times.

1T1R Results:
- SNR requirements range from -10.9 dB to 1.1 dB

1T2R Results:
- SNR requirements range from -13.6 dB to -1.9 dB
- Approximately 3 dB gain compared to 1T1R configurations

6. Conclusions

The document recommends considering these simulation results for determining design constraints for ULBC. The results demonstrate:
- Performance across various TBS values (144 to 1736 bits)
- Multiple bundling times (80, 160, 320 ms)
- Different SCS configurations (3.75 kHz, 15 kHz)
- Impact of repetitions on SNR requirements
- Benefits of 2 RX antennas (approximately 3 dB gain)