# Summary of S4-260271: ULBC Performance Requirements

## Document Information
- **Source:** Apple Inc.
- **Meeting:** 3GPP TSG SA WG4#135, Goa, India (09-13 February 2026)
- **Type:** Discussion and Agreement
- **Revision:** Revision of S4aA250135 addressing comments from SA4 #134 post-adhoc telco (Dec 02)

## Main Technical Contributions

### Performance Requirements Framework

The document proposes establishing minimum performance requirements for the Ultra-Low Bitrate Codec (ULBC) based on the following rationale:

- ULBC targets IMS voice service over GEO and NGSO satellite systems (per Clause 4, TR 26.940)
- Quality must be consistent with deployed VoLTE IMS voice services
- Current TBS discussions center on bitrates in the 1-3 kbps range
- AMR-WB 12.65kbps and EVS-SWB 13.2kbps are commonly deployed VoLTE operating points

### Proposed Minimum Performance Benchmarks

The document establishes two key performance anchors:

1. **At lowest operating range (~1 kbps):**
   - ULBC shall provide speech quality No Worse Than (NWT) AMR-WB @12.65kbps
   - Applies to: clean speech, noisy speech, and packet loss conditions

2. **At higher operating range (~3 kbps):**
   - ULBC shall provide speech quality No Worse Than (NWT) EVS-SWB @13.2kbps
   - Applies to: clean speech, noisy speech, and packet loss conditions

### Reference Codecs and Operating Points for Testing

The document proposes a comprehensive list of reference codecs and operating points for ToR comparison testing in subjective evaluation:

- **AMR:** 12.2kbps
- **AMR-WB:** 8.85kbps, 12.65kbps, 23.85kbps
- **EVS AMR-WB-IO:** 8.85kbps, 12.65kbps, 23.85kbps
- **EVS-WB/SWB:** 7.2kbps, 8kbps, 9.6kbps, 13.2kbps, 13.2kbps CA, 24.4kbps

## Text Proposal

The document proposes updates to **Clause 8 (Performance requirements)** of TR 26.940, adding:
- New **Clause 8.1 (General)** containing the performance requirements framework and minimum benchmarks
- New **Clause 8.1.1 (A List of Reference Codecs and Operating Points)** containing the reference codec list for subjective evaluation