Summary of S4-260216: On Transmission Delay for Voice over NB-IoT NTN

Document Overview

This contribution from Qualcomm addresses gaps in TR 26.940's mouth-to-ear delay calculations for NB-IoT NTN systems, specifically highlighting the omission of NPUSCH/NPDSCH transmission durations and clarifying the distinction between propagation delay and transmission delay.

Main Technical Issues Identified

Problem Statement

1. Missing Transmission Duration: TR 26.940 did not account for the duration of NPUSCH transmission or NPDSCH transmission, which can be significant for NB-IoT (e.g., 64ms for NPUSCH)

2. Terminology Confusion: TR 26.940 confuses propagation delay with transmission delay, where:

3. Transmission delay: The interval from when the first bit leaves a transmitter to when the last bit leaves the transmitter
4. Propagation delay: The time for signal propagation through the medium
5. Processing delay (up to 3ms) can be ignored in mouth-to-ear calculations

Proposed Technical Changes

5.2.2.4 Propagation Delay Corrections

Key Change: Renamed "Transmission delay" to "Propagation delay" for GEO satellite link

• Maximum propagation delay: 280ms (per KPI requirement in clause 7.4.2 of reference document)
• Minimum propagation delay: 248ms (280ms - 32ms, accounting for UE location within beam)
• Assumes no retransmissions over GEO satellite link

5.2.2.5 Transmission Delay (New Section)

New Addition: Introduces proper definition and consideration of transmission delay

• Defines transmission delay as the interval from first bit to last bit leaving the transmitter
• Highlights significance for NB-IoT NTN (up to 64ms for NPUSCH in uplink)
• Must be accounted for in mouth-to-ear delay calculations
• Transmission delay for transport block size should be based on RAN simulation results

5.2.2.5/6 ULBC Delay Components

• Section renumbered from 5.2.2.5 to 5.2.2.6
• References existing algorithmic delays for IMS codecs (AMR and EVS: 5ms to 12ms)
• Notes that ULBC may have different delay values from codec processing and algorithmic delays
• Marked as FFS (Further Study)

5.1.3 Mouth-to-Ear Delay Estimation Updates

Editorial Note Added:
- Numbers in Table 5.1.3-1 will be updated once RAN simulation is completed to account for transmission delays in uplink and downlink
- Current values assume AMR and EVS algorithmic delays
- ULBC delay components still need to be addressed
- Minimum Delay_GSCN assumed as 20ms

Existing Table Structure Maintained:
- Frame sizes: 20ms, 40ms, 80ms, 160ms, 320ms
- Two scenarios: GEO-TN (main) and GEO-GEO (sub-scenario 1)
- Lower and upper bounds for mouth-to-ear delay
- Delay ranges from 428-712ms (20ms frame, GEO-TN) to 984-1455ms (320ms frame, GEO-GEO)

Dependencies and Next Steps

• Awaiting RAN simulation results to determine actual transmission delay values for different transport block sizes
• ULBC-specific delay components require further study
• Terminology alignment needed with clause 4 "Application Scenario"
• Table 5.1.3-1 values pending update based on RAN simulation completion