Reply LS on RAN Simulation Assumptions for ULBC

Document Information

• Source: RAN1
• Target: SA4
• CC: RAN4, RAN2, SA2, CT1
• Meeting: RAN1 #122 (Bengaluru, India, Aug 25-29, 2025)
• Response to: S4-251584
• Release: Rel-20
• Work Item: FS_ULBC

Overall Description

RAN1 provides responses to SA4's liaison statement S4-251584 regarding evaluation assumptions for ULBC (Uplink Broadcast) simulations.

Response to Question 1: Evaluation Assumptions Confirmation

RAN1 generally agrees with SA4's proposed evaluation parameters with the following clarifications and comments:

Modulation Order

• Observation: MCS indices 0 and 1 use π/2 BPSK for single tone transmissions
• Action for SA4: SA4 to decide whether to evaluate π/2 BPSK with MCS indices 0 and 1

Downlink CNR Parameter Correction

• Issue identified: The relevant UE parameter for downlink is noise figure (and/or G/T), not transmit power
• Recommended correction: "DL CNR=-3.3dB, 0dBi UE antenna gain, 15kHz SCS, 12 tones, 1 UE receive antenna, noise figure of 7dB"

40ms Bundling Support

• RAN1 specifications may support 40ms bundling by assuming 15kHz SCS (single and multi-tone) in the uplink
• Decision point: SA4 to decide whether to include this case in evaluations

SPS Frame Structure

• Status: RAN1/2 have not yet started work on designing SPS
• Implication: RAN1 cannot currently confirm whether the example frame structure for SPS (related to Figure 5.2.2.3-2 and associated text) will be supported

BLER Target

• RAN1 precedent: Previous RAN1 evaluations for voice have considered 2% BLER as the target performance metric
• Decision point: SA4 to decide what values to use in their evaluations

Power Classes

• To be confirmed by RAN4

Frame Structure Supportability (Figure 5.2.2.3-1)

• General support: The example is supportable by RAN1 specifications in most scenarios
• Exception: May not be supportable when:
• Cell is very large (e.g., >3000km)
• UE does not support TA report
• Network does not support UE-specific K-offset
• Requirements: The example requires:
• UE configured with two HARQ processes
• HARQ feedback disabled

Response to Question 2: RX G/T Value for NB-IoT with GEO

G/T Calculation Method

The parameter G/T is calculated as follows (per TR 38.821):

Formula: G/T = G_rx - 10log₁₀(T₀ + T_a) - NF + G_rx

Where:
- G_rx = receive antenna gain
- NF = noise figure
- T₀ = ambient temperature
- T_a = antenna temperature

Value Derivation for -31.6 dB/K

The value is obtained with:
- G_rx = 0 dBi
- NF = 7 dB
- T₀ + T_a = 290K

Alternative Values and Consensus

• Lower values: Values smaller than -31.6 dB/K can be derived based on assumptions in TR 36.763 (e.g., NF=9dB)
• RAN1 recommendation: The value of -31.6 dB/K may be used by SA4 in their evaluations
• Higher values: Some companies in RAN1 consider that values higher than -31.6 dB/K can be supported in commercial implementations
• Consensus status: RAN1 could not reach consensus on these higher values

Action to SA4

RAN1 respectfully requests SA4 to take the above information into account.

Next RAN1 Meetings

• RAN1 #122-bis: Oct 13-17, 2025, Prague, CZ
• RAN1 #123: Nov 17-21, 2025, Dallas, US