Summary of S4-260137: On eCall Scenario for ULBC

1. Background

This contribution addresses the eCall (emergency call) scenario for Ultra-Low Bitrate Codec (ULBC) work. Previous contributions (S4-251908, SA-251848, SA-251881) emphasized the importance of preserving background signals in emergency communications. China has developed a related national standard "On-Board Emergency Call System for Road Vehicles" expected to take effect on July 1, 2027.

The document highlights that eCall scenarios have special requirements and different conditions compared to regular call scenarios, necessitating different design constraints and test methodologies.

2. eCall Scenario Description

2.1 System Overview

The eCall system is an in-vehicle safety technology that:
- Automatically dials emergency numbers (e.g., 112 in EU) upon severe collision detection
- Sends minimum data set (MSD) including GPS location, VIN, collision direction and time
- Can be triggered by built-in sensors or manual SOS button
- Functions via GEO satellite even without terrestrial network coverage

2.2 Communication Architecture

The bi-directional voice data flow involves:
- Vehicle side: Integrated microphones and speakers communicating over GEO satellite network
- Emergency response center: Connected via terrestrial mobile network (VoLTE, VoNR), fixed-line, or other IMS-supported platform
- Key requirement: Background noise captured within vehicle must be delivered with fidelity to emergency response center
- Asymmetric requirement: Noise preservation may not be required in the opposite direction (emergency center to vehicle)
- Dedicated system: No mobile phones involved in the communication link

3. Key Observations

Observation 1: eCall is a dedicated system between vehicles and emergency response centers. Speech codec designed for eCall is not necessarily the same as that for regular call scenarios, allowing for separate design constraints or performance requirements for ULBC-eCall.

Observation 2: Vehicle and emergency response center have significantly different hardware capabilities compared to regular call scenarios:
- Less sensitive to power consumption
- Higher computational capability
- Higher storage capability
- This allows for relaxed design constraints and more critical performance requirements for ULBC-eCall

4. Proposed Changes to TR 26.940

4.1 New Clause 4.5: eCall Communication

The contribution proposes adding a new scenario (Scenario 4) to TR 26.940 documenting:

High-level Prerequisites for ULBC in eCall:

• Very low bitrate support
• Background noise preserved with no DTX during the call (at least for vehicle-to-emergency center direction)
• Error concealment
• Real-time implementation capability (encoding and decoding)
• Good audio quality for reasonable QoE
• Relaxed hardware constraints compared to mobile phones

4.2 Modified Clause 6.2: Design Constraint Parameters

The contribution proposes creating separate design constraint columns in Table 6.2-1:
- Design Constraint (regular call): Existing constraints
- Design Constraint (eCall): New column with eCall-specific constraints

Key Differences for eCall Design Constraints:

| Parameter | Regular Call | eCall |
|-----------|-------------|-------|
| Noise Suppression | Not required; noise suppression may be applied | Background noise preserved during call (at least vehicle-to-center direction); opposite direction may not require preservation |
| DTX Support | Support | No DTX support during call (at least vehicle-to-center direction) |
| Complexity/Memory | Standard mobile constraints | Relaxed constraints possible |

5. Technical Contributions

The main technical contributions of this document are:

1. Introduction of eCall as a distinct ULBC scenario with specific requirements different from regular call scenarios
2. Identification of asymmetric requirements for noise preservation (required vehicle-to-center, optional center-to-vehicle)
3. Proposal for relaxed design constraints based on different hardware capabilities of eCall endpoints
4. Explicit requirement for background noise preservation and no DTX in critical direction
5. Framework for separate performance requirements for eCall vs. regular call scenarios in TR 26.940

The document establishes that eCall scenarios justify different codec design approaches due to their dedicated nature, different hardware capabilities, and specific regulatory/safety requirements.