# Summary of S4-260149: Updates on Assumptions and Open Issues for NB-IoT GEO Simulation

## Document Overview

This contribution from China Mobile addresses outstanding assumptions and open issues for NB-IoT GEO satellite simulation work within the ULBC (Ultra-Low Bitrate Codec) study. The document consolidates discussions from multiple Audio Ad-hoc meetings (June 4, June 17, and July 11) and proposes updates to TS 26.940 clause 5.2.2.4.

## Main Technical Contributions

### Status Updates on Simulation Parameters

The document provides a comprehensive status table tracking 11 key simulation issues, with updates on their resolution status:

#### **Resolved Issues**

1. **UE Power Class (Issue 1)**: 
   - Previously pending decision between 23 dBm (specified for NTN NB-IoT) vs. higher commercial values (26-33 dBm)
   - **Resolution**: 37 dBm adopted based on RAN4 Reply LS S4aA250219
   - Note: 37 dB is under study in ongoing RAN work

2. **Latitude-Dependent Loss (Issue 2)**: 
   - Addressed scintillation loss variation (2.2 dB vs. 0 dB) based on latitude per TR 38.821
   - **Resolution**: Simulation accounts for latitude-dependent loss using X term
   - Additional note: New 10-degree channel model introduced, may increase feasible TBS

3. **Elevation Angles (Issue 3)**: 
   - Proposal to maintain both 2.3° and 12.5° elevation angles for worst-case scenarios
   - **Resolution**: Simulation accounts for elevation angles using X term

4. **Simulation Channel Model (Issue 8)**: 
   - Choice between NTN-TDL-C or NTN-TDL-C5
   - **Resolution**: NTN-TDL-C is used

5. **Repetition Numbers (Issue 10)**: 
   - Proposal to specify and report repetition numbers in simulation
   - **Resolution**: Solved

#### **Partially Resolved Issues**

6. **Protocol Overhead (Issue 9)**: 
   - Requires clarification of packet header overhead for different protocol combinations (user plane, control plane, IP vs. non-IP)
   - **Partial Resolution**: SA2 confirmed voice packets transported over User Plane
   - **Still Pending**: Overhead for User Plane (IP vs. Non-IP) needs RAN confirmation

7. **RX G/T for Downlink (Issue 11)**: 
   - Field measurements show 3dB better value than current RAN assumptions
   - **Status**: Editorial note added in P-doc 5.2.2.3 to capture field-measured data
   - **Current Status**: Listed as "Unsolved" in table

#### **Unresolved Issues**

8. **UL/DL Guard Time (Issue 4)**: 
   - Current assumption: 1 ms guard time for UL/DL switching
   - **Status**: Needs RAN confirmation on feasibility

9. **Determine Candidate TBS Values (Issue 5)**: 
   - Multiple proposals from different companies:
     - Xiaomi (S4aA250035)
     - Fraunhofer (S4aA250031)
     - Skylo (S4-251540)
     - Dolby (S4-251390)
     - Huawei (S4aA250230)
     - Qualcomm (S4-251548)
     - vivo (S4aA250215)
   - **Status**: Unsolved, requires further verification

10. **Approaches to Select TBS (Issue 6)**: 
    - Three approaches provided in S4aA250072
    - One approach detailed in clause 5.2.2.4.1
    - **Status**: Unsolved, requires further discussion

11. **Overall Simulation Methodology Description (Issue 7)**: 
    - Need for high-level description of simulation execution, including optimization parameters and result parameters
    - General description documented in P-doc Clause 5.2.2
    - **Status**: Unsolved, to be addressed after all simulation work completed

## Proposal

The document proposes to:
1. Update the P-doc (TS 26.940) based on the status updates provided
2. Continue tracking these issues until full resolution

## Key Dependencies

The document highlights several dependencies on other working groups:
- **RAN4**: UE power class confirmation
- **RAN**: UL/DL guard time feasibility, protocol overhead confirmation
- **SA2**: Protocol overhead for different transport configurations