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.