# 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