Summary of S4-250275: On Device Capability Diversity for ULBC

Overview

This document (revision of S4aA260006) addresses UE capability diversity in NB-IoT NTN deployments for ULBC voice services. It proposes a capability-aware system design approach rather than assuming uniform baseline UE capabilities, accompanied by a pCR to TR 26.940.

Key Technical Contributions

1. UE Capability Diversity Framework

Identified Capability Dimensions:

• Transmit Power Classes:
• Baseline: PC3 (23 dBm)
• Enhanced: PC2 (26 dBm) or PC1 (31 dBm)

• Future: up to 37 dBm under study for Rel-20

• Receive Antenna Configurations:

• Standard: Single RX antenna

• Enhanced: Dual RX antennas (providing ~3 dB gain)

• Advanced Features:

• Improved RF sensitivity
• Multi-tone NPUSCH transmission capability

Key Insight: These capabilities are optional and vary across device categories, market segments, and implementations.

2. Benefits of Enhanced Capabilities

Enhanced UE capabilities enable:

• Reduced time-domain resource usage in half-duplex NB-IoT transmission
• Overcoming limitations of 80 ms SPS periods (excessive BLER and capacity constraints)
• Multi-tone NPUSCH transmission for:
• Higher ULBC bitrates
• Reduced time-domain resource usage
• Improved link robustness (reduced packet error rates)

3. Capability-Aware Multi-User SPS Scheduling

Proposed Scheduling Strategy:

• Dynamic SPS Assignment: Enhanced UEs use shorter SPS periods (80 ms) while baseline UEs use longer periods (160/320 ms)
• Multi-Tone Transmission: Enhanced UEs utilize multi-tone NPUSCH formats
• Load Balancing: Resource allocation prioritized based on UE capability
• Service Differentiation: Three-tier service model:
• Baseline Service: Conservative configurations (long SPS, single-tone NPUSCH)
• Intermediate Service: Moderate enhancements (shorter SPS, possible multi-tone)
• Enhanced Service: Higher bitrates and reduced latency (shortest SPS, multi-tone, dual RX)

Practical Example (Figure 1):

• UE Type A (Baseline): 160 ms SPS, 128 ms single-tone NPUSCH, 950 bits/s net bitrate (TBS 208 bits)
• UE Type B (Intermediate): 80 ms SPS, 64 ms NPUSCH (higher TX power), 1100 bits/s net bitrate (TBS 144 bits)
• UE Type C (Enhanced): 80 ms SPS, 64 ms NPUSCH, reduced NPDSCH duration (dual RX), 1100 bits/s net bitrate (TBS 144 bits)

4. ULBC Bitrate Differentiation

Proposed Approach:

• Leverage UE capability diversity for bitrate differentiation
• Align bitrates with service tiers and UE capabilities
• Recommended minimum set of 3 ULBC target bitrates:
• Basic tier: [600 - 1000] bits/s
• Intermediate tier: [1000 - 1800] bits/s
• Enhanced tier: [1800 - 3000] bits/s
• Higher bitrates may be considered in second ULBC standardization phase

Note: Actual bitrates subject to ongoing TBS discussions; values >3000 bits/s may become relevant.

Proposed Changes to TR 26.940 (pCR)

Section 5.2.4: New Clause on UE Capabilities

Documents capability variations for NB-IoT NTN:

• Transmit Power Classes: PC3/PC5 (Rel-18), PC1/PC2 (Rel-19), potential >31 dBm (Rel-20)
• Receive Antennas: Single (typical) vs. dual (enhanced)
• Enhanced Capabilities: Higher TX power, improved RF sensitivity

Section 5.2.5: Enhanced Multi-User Considerations

Replaces assumption of uniform UE configuration with capability-aware scheduling:

• Capability-Aware Resource Allocation: Different SPS periods based on UE capabilities
• Multi-Tone Transmission for Enhanced UEs: Increased bitrate and/or reduced resource usage
• Dynamic Load Balancing: Optimized capacity through capability-based prioritization
• Service Level Differentiation: Three-tier service model aligned with UE capabilities

Includes Figure 1 demonstrating practical multi-user scheduling scenario with three UE types.

Section 5.1.2.2: UE Delay Tables

Updates delay estimation tables (5.1.2-2, 5.1.3-1) to include:

• Voice bundling periods: 80, 160, 320 ms
• Codec frame sizes: 20, 40, 80, 160, 320 ms
• Mouth-to-ear delay estimates for GEO-TN and GEO-GEO scenarios

Recommendations

1. Adopt capability-aware ULBC system design rather than assuming single baseline configuration
2. Agree on minimum set of 3 ULBC target bitrates for codec evaluation (approximate ranges: [600-1000], [1000-1800], [1800-3000] bits/s)
3. Document agreed ULBC target bitrates in Pdoc
4. Consider higher bitrates in second ULBC standardization phase

References

Key dependencies: S4aA260006 (previous version), S4-260144 (TR 26.940 v0.5.1), S4-260255 (ULBC Re-Focus Proposal), TS 36.763 (UE radio transmission/reception), S4-251863 (system capacity), S4aA250112 (error trace methodology), S4aA250118 (RAN simulation results)