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:
- 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
-
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