# ULBC Re-Focus Proposal

## Background and Motivation

The FS_ULBC study item, initiated nearly a year ago, aims to establish a normative ULBC standard for voice communication over GEO within Rel-20. However, progress has been slow, with crucial issues such as end-to-end simulation parameters remaining unresolved. This contribution proposes a focused approach to meet 3GPP standardization timelines.

## Core Proposal: Two-Phase Standardization Approach

The document proposes separating ULBC standardization into two distinct phases to ensure timely delivery while accommodating future enhancements:

### Phase 1: Rel-20 ULBC Baseline
- **Scope**: GEO-focused functionality based strictly on stable Rel-19 service requirements
- **Rationale**: Ongoing 6G Media requirements in SA1, SA2, and SA4 have not yet produced consolidated or normative requirement sets suitable for codec design
- **Principle**: Following established 3GPP procedures, the ULBC work item shall not define new service requirements but rely on formally defined and stabilized upstream requirements

### Phase 2: Rel-21 ULBC Advanced
- **Scope**: Extended functionality aligned with finalized 6G Media requirements
- **Application scenarios**: Beyond Rel-20 IMS Voice Call over GEO
- **Compatibility**: Should be backward compatible extension of Rel-20 baseline

## Technical Configuration Comparison

### Application Scenarios

**Baseline (Rel-20)**:
- IMS Voice Call over GEO based strictly on Rel-19 service requirements

**Advanced (Rel-21)**:
- Multi-Party Voice Communication
- IMS Voice Call with ULBC over additional access types beyond GEO

### GEO Channel Characteristics & Simulation

**Baseline (Rel-20)**:
- Single baseline UE Tx/Rx capability
- Single CNR in UL and DL (e.g., UL single-tone 23 dBm: CNR=5.28 dB for SCS=3.75 kHz, CNR=-0.74 dB for 15 kHz; DL 12-tone single Rx: CNR=-0.61 dB)
- Single agreed target bitrate compatible with baseline UE capability enabling acceptable system capacity
- Reliance only on mandatory Rel-19 NB-IoT radio protocol features (except SPS)
- i.i.d. random block error patterns
- Single SPS/bundling period (160 ms)

**Advanced (Rel-21)**:
- Advanced UE capabilities (e.g., increased Tx power, multiple Rx antennas)
- Multiple CNR assumptions in UL and DL
- Codec designers may choose optimal bitrate/TBS per CNR
- Allow reliance on expected Rel-20 and selected non-mandatory NB-IoT features
- Simulated block error patterns based on advanced features
- Additional SPS/bundling periods (e.g., 80 ms, 320 ms)

### Design Constraints: Bitrate

**Baseline (Rel-20)**:
- Single target bitrate derived from Rel-19 GEO IMS voice service requirements
- Example: TBS=208 with SPS period 160 ms, achieving 950 bps net bitrate

**Advanced (Rel-21)**:
- Multiple target CNRs with bitrate as codec design choice
- Additional bitrates for future 6G-related scenarios

### Design Constraints: Sample Rate and Audio Bandwidth

**Baseline (Rel-20)**:
- Single sample rate: e.g., 16 kHz
- Audio bandwidth: up to WB
- Note: May depend on agreed target bitrate

**Advanced (Rel-21)**:
- Input/output sampling rates: at least 8, 16, 32, 48 kHz
- Audio bandwidth unconstrained (codec design choice)

### Design Constraints: Frame Length and Algorithmic Delay

**Baseline (Rel-20)**:
- Corresponding to SPS/bundling period (160 ms) or sub-multiples thereof
- Algorithmic delay excl. framing: e.g., ≤80 ms (0.5 × SPS/bundling period)

**Advanced (Rel-21)**:
- Frame structure and algorithmic delay aligned with advanced SPS/bundling options and future 6G Media requirements

### Design Constraints: Complexity and Memory

**Baseline (Rel-20)**:
- Limited; sufficiently low to not preclude deployment on current-generation smartphones
- TBD MMAC/s
- E.g., 3M parameters

**Advanced (Rel-21)**:
- Relaxed, enabling multiple models
- Addressing future 6G Media requirements while leveraging new UE hardware trends

### Design Constraints: Packet Loss Concealment

**Baseline (Rel-20)**:
- Required; capable of addressing single agreed-upon target bit rate and operation point of IMS Voice Call over GEO

**Advanced (Rel-21)**:
- Required; capable of supporting anticipated extended application scenarios beyond Rel-20 IMS Voice Call over GEO, while fulfilling potential 6G Media requirements

### Design Constraints: Noise Suppression and Robustness

**Baseline (Rel-20)**:
- No requirement to provide noise suppression
- Required capability to handle and reconstruct noisy speech input with moderate to high SNR
- Note: Noise reconstruction capability primarily enforced through performance requirements

**Advanced (Rel-21)**:
- No requirement to provide noise suppression
- Required capability to handle speech and generic input anticipated in extended application scenarios

### Design Constraints: DTX

**Baseline (Rel-20)**:
- No requirement to support DTX
- Note: No separate DTX-related performance requirement

**Advanced (Rel-21)**:
- DTX support may be required for certain extended application scenarios, depending on potential 6G Media requirements

### Performance Requirements

**Baseline (Rel-20)**:
- Requirements focusing on clean and noisy speech performance
- NWT AMR7.4 or NWT AMR-WB8.85 depending on target bandwidth for:
  - Clean speech
  - Noisy speech (AMR/AMR-WB references operated with DTX on)
  - Relevant transcoding cases with G.711, AMR, AMR-WB, EVS

**Advanced (Rel-21)**:
- Complex set of requirements considering required capability to handle speech and generic input anticipated in extended application scenarios

### Test Methodology and Test Plan

**Baseline (Rel-20)**:
- Subjective: P.800 DCR
- Note: Test methodology and test plan should be conceptually aligned with corresponding EVS codec standardization Pdocs (e.g., DCR test design, applicable SNRs and types of noises for noisy speech test cases)

**Advanced (Rel-21)**:
- Subjective: Suitable for critical evaluation of candidate codec(s) against expected complex set of performance requirements

## Proposal

SA4 is asked to adopt this phased approach for ULBC standardization as working assumption:

1. **Rel-20 ULBC Baseline**: GEO-focused functionality based solely on Rel-19 service requirements and mandatory Rel-19 features (except SPS), enabling completion of viable ULBC baseline standard within Rel-20 schedule

2. **Rel-21 ULBC Advanced**: Extended ULBC functionality aligned with finalized 6G Media requirements, supporting application scenarios beyond Rel-20 IMS Voice Call over GEO, possibly leveraging advanced UE capabilities, and providing backward compatible extension of Rel-20 baseline

This approach ensures deliverable ULBC baseline in Rel-20 while providing clear and orderly path toward enhanced ULBC design in Rel-21.