# Timeplan for FS_ULBC Study Item

## 1. Introduction

This document outlines the timeplan for the Feasibility Study on Ultra Low Bitrate Speech Codec (FS_ULBC). The study focuses on developing a codec for ultra-low bit rate communication services, particularly for IMS Voice Call Using GEO Access as documented in TR 22.887.

### Study Item Objectives

The FS_ULBC study has nine main objectives:

1. **Application Scenarios**: Document ultra-low bit rate communication service scenarios based on TR 22.887 use cases and requirements for IMS Voice Call Using GEO Access
2. **GEO Channel Characteristics**: Study GEO channel characteristics and derive service-related dependencies (bitrates, mouth-to-ear delay, loss/delay/jitter profiles)
   - Note: NB-IoT services impact is out of scope
3. **Design Constraints**: Identify relevant design constraints in coordination with other WGs:
   - Bit rates
   - Sample rate and audio bandwidth
   - Frame length
   - Complexity and memory demands
   - Algorithmic delay
   - Packet loss concealment (PLC)
   - Potential noise suppression integration
   - Discontinuous transmission (DTX) including VAD and comfort noise
   - Speech quality
   - Robustness to non-speech input
4. **Feasibility Evidence**: Provide evidence that design criteria can be met using existing reference codecs
5. **Performance Requirements**: Define performance requirements and identify test methodologies for:
   - Speech quality and intelligibility
   - Conversational quality
   - Clean and noisy speech conditions
   - Tandeming with existing IMS voice codecs
   - Clean channel and GEO channel conditions
6. **Objective Measures**: Identify or develop objective measures to verify design constraints (e.g., complexity and memory measurements)
7. **Reference Codecs**: Identify relevant reference codecs for comparison and evaluation
8. **Coordination**: Coordinate with other 3GPP groups (SA2, RAN, CT1, etc.)
9. **Normative Work**: Define potential normative work item objectives and timeline

## 2. Current Progress Status

### Application Scenarios (85% Complete)
- **Scenario 1**: IMS Voice Call over GEO (TR 4.2, P-doc 4.1)
- **Scenario 2**: Multi-Party Voice Communication (TR 4.3)
- **Scenario 3**: IMS Voice Call with ULBC over other access types than GEO (TR 4.4)
- **Next Steps**: Finalize high-level prerequisites and resolve ENs
- **Dependencies**: SA2, RAN, CT

### GEO Channel Characteristics & Simulation (75% Complete)
- NB-IoT system design and simulation parameters documented (TR 5.1.4, P-doc 5.2.2)
- **SA4#135 Plans**:
  - Finalize remaining parameters
  - Gather candidate Transport Block Sizes (TBS)
- **Dependencies**: SA2, RAN

### Simulation Methodology (60% Complete)
- **SA4#135 Plans**: Discuss and confirm simulation methodology
- **Dependencies**: RAN

### Company Simulation Results (40% Complete)
- Companies providing simulation results (P-doc 5.2.3)
- **SA4#135 and Post Ad-hoc Plans**:
  - Select appropriate TBS
  - Collect company simulation results
- **SA4#136 Plans**:
  - Cross-check simulation results
  - Finalize feasible TBS values and loss traces

### Mouth-to-Ear Delay (95% Complete)
- Documented in TR 5.1
- **Next Steps**: Resolve ENs

### Design Constraints Progress

#### Bit Rates (0% Complete)
- **SA4#136 and Post Ad-hoc**: Decide bit rates for ULBC (dependent on simulation results)
- **Dependencies**: RAN

#### Sample Rate and Audio Bandwidth (5% Complete)
- **SA4#135 and Post Ad-hoc**: Discuss supported audio bandwidth
- **SA4#136 and Post Ad-hoc**: Decide supported audio bandwidth

#### Frame Length (0% Complete)
- **SA4#136 and Post Ad-hoc**: Decide frame length for ULBC

#### Complexity and Memory Demands (80% Complete)
- Documented in TR 6.2.1, P-doc 6.1.1
- **SA4#135 and Post Ad-hoc**: Finalize complexity measurement metrics and resolve ENs

#### Algorithmic Delay (0% Complete)
- **SA4#135 and Post Ad-hoc**: Discuss algorithm delay for ULBC

#### Packet Loss Concealment (15% Complete)
- Documented in TR 7.1.5
- **SA4#135 and Post Ad-hoc**: Discuss PLC for ULBC

#### Noise Suppression (15% Complete)
- Documented in TR 7.4
- **SA4#135 and Post Ad-hoc**: Discuss noise suppression for ULBC

#### DTX (0% Complete)
- **SA4#135 and Post Ad-hoc**: Discuss DTX support for ULBC

#### Design Constraint Verification (5% Complete)
- P-doc 6.3.1
- **Next Steps**: Verify design constraints

#### Other Considerations (5% Complete)
- TR 6.4.1
- **Next Steps**: Document additional design considerations and resolve ENs

### Existing Codec Technologies (85% Complete)
- Reference codecs documented (e.g., DAC, Lyra) in TR 7
- **SA4#135 and Post Ad-hoc**: Continue documenting evidence of existing technologies and resolve ENs

### Performance Requirements (0% Complete)
- **SA4#136 and Post Ad-hoc**: Define performance requirements

### Test Methodologies (50% Complete)
- Subjective test methodologies documented in TR 9.1.3
- **SA4#135 and Post Ad-hoc**: Identify appropriate test methodologies

### Coordination with Other WGs
- Analysis of current liaisons from RAN, CT, and SA2 available (S4aA250139)
- Ongoing coordination as needed

## 3. Detailed Timeplan

### TSG SA#107 (March 12-14, 2025, Incheon, KR)
- Approval of FS_ULBC study item

### SA4#131-bis-e (April 11-17, 2025)
- **Start** documenting application scenarios for ultra-low bit rate communication services
- **Start** studying GEO channel characteristics and service-related dependencies
- **Start** identifying relevant reference codecs
- **Start** coordinating with other 3GPP groups

### Audio SWG Telco (May 5, 2025)
- Focus on application scenarios and technical contributions

### SA4#132 (May 19-23, 2025, Fukuoka, JP)
- **Finalize** application scenarios documentation
- **Progress** GEO channel characteristics study
- **Progress** reference codec identification
- **Progress** coordination with other WGs
- **Start** identifying/developing objective measures for design constraint verification
- **Start** identifying relevant design constraints (bit rates, sample rate, frame length, complexity, algorithmic delay, PLC, noise suppression, DTX, speech quality, robustness)
- **Start** providing feasibility evidence using existing reference codecs
- **Start** defining performance requirements and test methodologies for speech quality
- **If time permits**: Start documenting additional application scenarios

### Audio SWG Telcos (June-July 2025)
Multiple telcos scheduled to:
- **Progress** GEO channel characteristics study
- Perform RAN-related simulations within SA4
- Align on RAN link-level simulations
- Power to send LS to SA2 and RAN WGs if needed

### SA4#133-e (July 21-25, 2025)
- **Progress** all ongoing work items:
  - GEO channel characteristics
  - Coordination with other WGs
  - Reference codec identification
  - Objective measures development
  - Design constraints identification
  - Feasibility evidence
  - Performance requirements and test methodologies
- **If time permits**: Progress additional application scenarios

### F2F Ad-hoc Meeting (September 23-25, 2025, Erlangen, Germany)
- Hosted by Fraunhofer IIS
- Electronic participation on best effort basis

### Audio SWG Telcos (October 2025)
- Opportunity for feedback from other WGs
- **Progress** work on:
  - GEO channel characteristics study
  - Existing technologies documentation
  - Design constraints identification
  - Performance requirements and test methodologies
  - Application scenarios if time permits

### SA4#134 (November 17-21, 2025, Dallas, US)
Major milestone meeting:
- **Finalize**:
  - GEO channel characteristics study
  - Coordination with other WGs
  - Reference codec identification
  - Design constraints: bit rates, sample rate, audio bandwidth, frame length, PLC, noise suppression, DTX
- **Progress**:
  - Feasibility evidence
  - Objective measures development
  - Design constraints: complexity, algorithmic delay, speech quality, robustness
  - Performance requirements and test methodologies
- **Start** defining potential normative work item objectives and timeline
- **If time permits**: Finalize additional application scenarios

### Audio SWG Telcos (December 2025 - January 2026)
- **Finalize** GEO channel characteristics study
- **Progress**:
  - Simulation parameters for end-to-end simulation
  - Existing technologies documentation
  - Design constraints identification
  - Performance requirements and test methodologies
  - Application scenarios if time permits
- Power to send reply LS for incoming LS postponed during SA4#134

### SA4#135 (February 9-13, 2026, India)
- **Finalize** objective measures for design constraint verification
- **Progress**:
  - Design constraints: complexity, algorithmic delay, speech quality, robustness
  - Feasibility evidence
  - Performance requirements and test methodologies

### TSG SA#111 (March 10-13, 2026, Japan)
- TR for information

### SA4#136 (April 13-17, 2026)
- **Finalize**:
  - Design constraints: complexity, algorithmic delay, robustness to non-speech input
  - Feasibility evidence
- **Progress**:
  - Design constraints: speech quality
  - Performance requirements for speech quality

### SA4#137 (May 11-15, 2026)
Final study meeting:
- **Finalize**:
  - Design constraints: speech quality
  - Performance requirements and test methodologies (clean/noisy speech, tandeming, clean/GEO channel conditions)
  - Potential normative work item objectives and timeline

### TSG SA#112 (June 9-12, 2026, Singapore)
- **TR for approval** - Study completion