Signals Ahead: VoLTE Performance and Analysis

  • ID: 2905381
  • Report
  • Region: Global
  • Signals Research Group, LLC
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We conducted a network benchmark study of AT&T's VoLTE service (Alcatel-Lucent provides the Radio Access Network, Core Network, and IMS infrastructure) in Minneapolis-St. Paul in collaboration with Spirent Communications who provided us with its test equipment and engineering support. In a forthcoming report due out later this fall, we will leverage data observations that we made in this study and apply them to a lab-based study where we can conduct additional testing in a very controlled environment.

KEY OBSERVATIONS INCLUDE THE FOLLOWING:

- VoLTE is pretty much everything that we hoped it would be.

- The call quality (MOS), based on the POLQA algorithm, greatly exceeded that of 3G CS Voice and it was measurably higher Skype (over Wi-Fi and LTE). With background applications running on the same phone and transferring data with the network the VoLTE results were considerably better than Skype - the latter seemingly showed no impact while the latter frequently failed to deliver the voice packets in many cases.

- Relative to 3G CS voice, VoLTE's big advantage was the call setup time with a CSFB call taking nearly twice as long to establish as a VoLTE call.

- VoLTE required substantially fewer network resources (DL/UL resource blocks, scheduled TTIs, PDCCH scheduling grants) than Skype and presumably other OTT voice applications. We attribute this advantage to QCI=1 features, such as RoHC, TTI bundling, and DTX/DRX, which are either not supported by an OTT application or which are supported less efficiently. Once SPS and short DRX are launched the differences should be even more substantial.

- The network savings also translates into VoLTE call requiring less current drain and power consumption than a Skype call, meaning a longer batter life. Presently 3G CS voice has a slight advantage over VoLTE in this category.

- Continued improvements in LTE network coverage will give VoLTE an even greater advantage in the future and it will reduce the number of eSRVCC handovers to the 3G CS network.

SIGNALS AHEAD SUBSCRIPTION INFORMATION

This report is included as part of a subscription to Signals Ahead or it can be purchased separately.

Signals Ahead is a research-focused product that is published on a periodic basis. Its clientele include all facets of the wireless ecosystem, including some of the largest mobile operators, the top handset suppliers, the major infrastructure vendors, subsystem suppliers, semiconductor companies and financial institutions, including Wall Street, Private Equity and Venture Capitalists, spread across five continents.
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1.0 Executive Summary

2.0 Key Observations and Conclusions

3.0 Voice Call Quality Analysis
3.1 Heavy to Moderate Network Loading - Stationary Testing
3.2 Moderately Heavy Network Loading, Including Background Application Downloads -
Stationary Testing
3.3 Skype Voice over Wi-Fi - Light and Heavy Loading
3.4 MOS Drive Test - VoLTE, Skype and 3G CS Voice

4.0 Network Resource Analysis

5.0 Call Reliability, Call Setup Time and IRAT Handover Analysis
5.1 Call Setup Analysis
5.2 Call Reliability Analysis
5.3 eSRVCC Handover Analysis

6.0 Battery Life, Current Drain and Power Consumption Analysis
6.1 Level Setting
6.2 Highly Favorable Network Conditions
6.3 Average Network Conditions
6.4 Challenging Network Conditions
6.5 LTE versus Wi-Fi
6.6 VoLTE and Skype - a likely explanation

7.0 Test Methodology

8.0 Final Thoughts

9.0 Appendix

Index of Figures

Figure 1. VoLTE MOS Test Results - IKEA, June 17th 1940 Hours
Figure 2. VoLTE MOS Test Results - IKEA, June 17th 1930 Hours
Figure 3. Skype Voice over LTE MOS Test Results - IKEA, June 17th 2015 Hours
Figure 4. Skype Voice over LTE MOS Test Results - IKEA, June 17th 2005 Hours
Figure 5. VoLTE MOS Test Results with Multiple Applications doing Network Transactions on Different Phones and Datum Background Downloading on the Test Phone - IKEA, June 18th 1840 Hours
Figure 6. VoLTE MOS Test Results with only Angry Birds Downloading on a Different Phone - IKEA, June 18th 1920 Hours
Figure 7. Skype Voice over LTE MOS Test Results with Multiple Applications doing Network Transactions on Different Phones - IKEA, June 18th 1850 Hours
Figure 8. Skype Voice over LTE MOS Test Results with Multiple Applications doing Network Transactions on Different Phones - IKEA, June 18th 1900 Hours
Figure 9. Skype Voice over LTE MOS Test Results with Multiple Applications doing Network Transactions on Separate Phones and Datum Background Downloading on the Test Phone - IKEA, June 18th 1900 Hours
Figure 10. Skype Voice over LTE MOS Test Results with ONLY Angry Birds Downloading on a Separate Phone - IKEA, June 18th 1920 Hours
Figure 11. Skype Voice over Wi-Fi MOS Test Results - lightly loaded network
Figure 12. Skype Voice over Wi-Fi MOS Test Results - moderately heavy to heavily loaded network
Figure 13. VoLTE Drive Test MOS Results - geo plot of St. Paul drive route
Figure 14. VoLTE Drive Test MOS Results - histogram
Figure 15. Skype Voice over LTE and HSPA+ Drive Test MOS Results - geo plot of St. Paul drive route
Figure 16. Skype Voice over LTE and HSPA+ Drive Test MOS Score Results - histogram
Figure 17. 3G CS MOS Drive Test MOS Results - geo plot of St. Paul drive route
Figure 18. 3G CS Drive Test MOS Score Results - histogram
Figure 19. Summary of Drive Test MOS Results
Figure 20. VoLTE MOS Results versus RSRP - first portion of drive route
Figure 21. Skype Voice over LTE MOS Results versus RSRP - first portion of drive route
Figure 22. Skype Voice over LTE and HSPA+ MOS Results - second portion of drive route
Figure 23. 3G CS Voice MOS Results - first portion of drive route
Figure 24. VoLTE Drive Test Downlink MAC Layer Throughput versus Time
Figure 25. VoLTE Drive Test Uplink MAC Layer Throughput versus Time
Figure 26. Skype Voice over LTE Drive Test Downlink MAC Layer Throughput versus Time
Figure 27. Skype Voice over LTE Drive Test Downlink MAC Layer Throughput versus Time
Figure 28. Downlink Resource Block Requirements - VoLTE versus Skype Voice over LTE
Figure 29. Uplink Resource Block Requirements - VoLTE versus Skype Voice over LTE
Figure 30. Summary of Resource Block Requirements - VoLTE versus Skype Voice over LTE
Figure 31. Distribution of Downlink TTI Requirements - VoLTE versus Skype Voice over LTE
Figure 32. Distribution of Uplink TTI Requirements - VoLTE versus Skype Voiceover LTE
Figure 33. Summary of TTI Requirements - VoLTE versus Skype Voiceover LTE
Figure 34. The Impact of DTX and DRX on VoLTE and Skype Voice
Figure 35. The Impact of RoHC on VoLTE and Skype Voice over LTE
Figure 36. The Impact of VoLTE and Skype Voice over LTE on PDCCH Signaling Messages without SPS
Figure 36. PUSCH Transmit Power versus RSRP - VoLTE and Skype Voice over LTE
Figure 38. Call Setup and Reliability Drive Route
Figure 39. Circuit Switched Fallback Time Results - Histogram
Figure 40. VoLTE Call Setup Time Results - Histogram
Figure 41. Comparing VoLTE and CSFB Call Setup Times
Figure 42. CSFB Call Setup Time - by message activity
Figure 43. VoLTE Call Setup Time - by message activity
Figure 44. 3G Voice Call Reliability
Figure 45. VoLTE Call Reliability
Figure 46. eSRVCC Handover Drive Test Route - average results
Figure 47. eSRVCC Handover #5 Drive Test Route - VoLTE and 3G CS MOS comparison with RSRP
Figure 48. Estimated Battery Life in Airplane Mode with Different Backlight Settings
Figure 49. Estimated Current Drain and Power Consumption in Airplane Mode with Different Backlight Settings
Figure 50. Estimated Battery Life Near the Serving Cell Site - Highly Favorable Conditions
Figure 51. Relative Battery Life Near the Serving Cell Site - Highly Favorable Conditions
Figure 52. Estimated Current Drain and Power Consumption Near the Serving Cell - Highly Favorable Conditions
Figure 53. Estimated Battery Life Near the Middle of the Cell - Average Conditions
Figure 54. Relative Battery Life Near the Middle of the Cell- Average Conditions
Figure 55. Estimated Current Drain and Power Consumption Near the Middle of the Cell - Average Conditions
Figure 56. Estimated Battery Life Near the Edge of the Cell - Challenging Conditions
Figure 57. Relative Battery Life Near the Edge of the Cell - Average Conditions
Figure 58. Estimated Current Drain and Power Consumption Near the Edge of the Cell - Average Conditions
Figure 59. Estimated Battery Life - VoLTE versus Skype over Wi-Fi
Figure 60. Relative Battery Life - VoLTE versus Skype over Wi-Fi
Figure 61. Estimated Current Drain and Power Consumption - VoLTE versus Skype over Wi-Fi
Figure 62. Skype over LTE Power Consumption and Current Drain
Figure 63. VoLTE Power Consumption and Current Drain
Figure 64. VoLTE Test Area
Figure 65. Quantum Display
Figure 66. VoLTE Drive Test MOS Score Results - probability distribution
Figure 67. Skype Drive Test MOS Score Results - probability distribution
Figure 68. 3G CS Drive Test MOS Score Results - probability distribution
Figure 69. Skype over LTE MOS Results versus RSRP - second portion of drive route
Figure 70. 3G CS Voice MOS Results - second portion of drive route
Figure 71. eSRVCC Handover #1 Drive Test Route - VoLTE and 3G CS MOS comparison with RSRP
Figure 72. Skype Voice over LTE MAC Layer Throughput versus Time
Figure 73. VoLTE MAC Layer Throughput versus Time
Figure 74. CSFB Message Flow
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