The VoLTE User Experience

Better or Worse?

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Ch

all

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ge VoLTE is

Different Q

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tify The

VoLTE User Experience

Solv

e Making VoLTE Better (not Worse)

Outline

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Sources

FactsQ1 2013: 6.4 billion

mobile subscribers, with smartphones comprising

50% of new mobile device sales

Voice and SMS represent approximately

70% of all global wireless revenues

Voice-over-LTE (VoLTE) revenues estimated to

reach $2 billion by 2016

TrendsHighly competitive

market, ARPU no longer increasing

HD Voice is one way to seek competitive

advantage(73 networks so far)

Voice and other services moving to more efficient

all-IP LTE networks

• Ericsson Mobility Report – On the Pulse of the Networked Society – June 2013• Global Mobile Suppliers Association – Mobile HD Voice: Global Update Report – June 4 th,

2013

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• How can I compare the VoLTE voice experience offered by different suppliers and technology options?

• How can I know that new infrastructure will deliver high-quality VoLTE services, before it goes live?

• How can I ensure that my devices offer the VoLTE voice experience my customers expect?

• How can I ensure that my network offers the VoLTE voice experience my customer expect?

• How does the VoLTE Voice experience on my network and devices compare to my competitors?

VoLTE: Better or Worse?

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VOLTE IS DIFFERENTThe VoLTE User Experience: Better or Worse?

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Physical

Data Link

Network

Transport

Session

Presentation

Application

Physical

Data Link

Network

Transport

Session

Presentation

Application

SIP, RTP, RTCP

TCP, UDP, SCTP

IP, RRC, NAS

Voice ServiceApplications

MAC, RLC, PDCP

OFDM, WCDMA, etc.

Mobile Device Network

1

2

3

4

5

6

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2G/3G Dedicated Voice Bearers –

Layer 1-3

Legacy Voice Services Depend on Robustness of Layers 1-3

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Physical

Data Link

Network

Transport

Session

Presentation

Application

Physical

Data Link

Network

Transport

Session

Presentation

Application

SIP, RTP, RTCP

TCP, UDP, SCTP

IP, RRC, NAS

Voice ServiceApplications

MAC, RLC, PDCP

OFDM, WCDMA, etc.

Mobile Device Network

1

2

3

4

5

6

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4G Dedicated Data Bearers – Layer 1-7

4G Voice Services Depend on Robustness at All Layers

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QoS RAN IMS Codec

Dedicated vs. Non-Dedicated Bearers

Semi-persistent scheduling resource allocation

Session Initiation Protocol (SIP)

HD Voice (Wideband AMR)

Quality of Service Class Identifier (QCI)

Transmission Time Interval (TTI) Bundling

Policy and Charging Rules Function (PCRF)

Dynamic scheduler in eNodeB

Robust Header Compression (RoHC)

Real-time Transport Protocol (RTP)

 

    Real-time Streaming Protocol (RTSP)

 

Key Enablers of VoLTE Fall Into Four Categories

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QoS Enables VoLTE Packets to be Prioritized

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QCI Sets Specific Packet Loss & Delay Targets Quality of Service (QoS) Class Identifier indicates max

delay & packet error rates for each LTE bearer Various network functions rely on the QCI to make

prioritization & resource allocation decisions

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eNB scheduler dynamically allocates resource blocks

(RBs) across all users.

QoS delay budgets are a key factor in allocations

eNB Dynamic Scheduler Grants Resources

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Semi-Persistent Resource Allocation for VoLTE Semi-persistent scheduling reduces the signaling

overhead for RB allocation by granting periodic use of a set of RBs

VoLTE sends short packets on a regular basis: SPS ensures resources are available which match the periodicity of VoLTE

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16QAM Signal Constellation(4 bits per symbol)

64QAM Signal Constellation(6 bits per symbol)

Link adaptation manages the packet loss rate by adjusting the rate at which bits are transmitted up or down based on radio conditions (SNR).

More

Bit

s/s

& H

igh

er

SN

R

Link Adaptation is Key to Packet Loss

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HARQ & TTI Bundling Impact Packet Loss & Delay

HARQ Reduces Packet Loss / Increases Delay (Jitter)

TTI Bundling Reduces HARQ Latency

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IP Multimedia Subsystem

Session Initiation Protocol (SIP) Session

Bit rate

Packet size

Packet transport frequency

RTP payload

Bandwidth adaptation

Policy and Charging Rules Function (PCRF)

Policy rules (bandwidth, quality class, IP packet filters)

PDN Gateway (P-GW)

Interpret rules and establish EPC dedicated bearers for voice

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HD Voice (WB-AMR Codec)

Type of Channel Channel Bandwidth 

Type of Service

Narrowband 50Hz – 3.8KHz Narrowband Voice

Wideband 50Hz – 7.5KHz HD Voice (including VoLTE)

Super-wideband 20Hz – 14KHz HD Voice (including VoLTE)

Channel bandwidths for different voice services

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THE VOLTE USER EXPERIENCE

The VoLTE User Experience: Better or Worse?

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End User Experience Key Performance Indicators (KPIs)

Ability to make and maintain calls 

Call Initiation Rate (%), Call Drop Rate (%) 

Time it takes for a phone to start ringing 

Call Setup Time (s)

Speech quality during a call 

Mean Opinion Score (MOS)

Mouth-to-ear delay or latency variations during a call  

Mouth-to-ear delay (s), Latency, jitter 

What to Measure?

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Packet Loss & Delay Drive QoE for VoLTE

VoLTE packet loss directly impacts speech quality

Source: “Validating voice over LTE end-to-end”, Ericsson Review, January 2012.

Speech Quality vs. Frame Error Rate

Packet loss rate of < 1% results in good

speech quality on avg.

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Packet Loss & Delay Drive QoE for VoLTE

VoLTE packet delay impacts mouth-to-ear delay, and packet delay variability (jitter) impacts both speech quality & mouth-to-ear delay

Speech Quality vs. Mouth to Ear Delay

Source: “Validating voice over LTE end-to-end”, Ericsson Review, January 2012.

ITU recommended end-to-end mouth-to-ear delay is <200 ms

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UE-Specific Delays Dominate Mouth-to-Ear Delay

Packet delay is strongly impacted by LTE scheduling & HARQ:

• Average E2E transport delay

• Jitter buffer delay

Breakdown of mouth-to-ear delay for VoLTE lab and field tests performed by Ericsson

Source: “Validating voice over LTE end-to-end”, Ericsson Review, January 2012.

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0%

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10%

15%

20%

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MOS Distribution Both Speech Paths

NB/Standard Mode

AMR-WB enabled

MOS Range

Perc

en

tag

e o

f V

alu

es i

n M

OS

Ran

ge

Source: Spirent Testing on Live Network with Nomad HD

Speech Quality Impacted by Codec

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PESQ (ITU-T P.862)

POLQA (ITU-T P.863)

Codecs AMREFR

AMRAMR-WBEFREVRCEVRC-BEVRC-WB

Reference Speech Material (sampling frequency)

8 kHz 8 kHz48 kHz

Applications POTSVoIP3G

HD VoiceVoice Enhancement Devices

POLQA has more robust quality predictions for …

Cross-technology quality benchmarking (e.g., GSM vs. CDMA)

Noise reduction and voice quality enhancement

Time-scaling, unified communication and VoIP

Filtering and spectral shaping

Recordings made at an ear simulator

Perceptual Evaluation of Speech Quality (PESQ) vs. Perceptual Objective Listening Quality Analysis (POLQA)

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  Downlink MOS Uplink MOS

Device Device A

Device B

Device C

Device D

Device A

Device B

Device C

Device D

Average 3.09 3.34 3.16 3.62 3.46 3.81 3.44 3.31

Standard Deviation

0.42 0.08 0.39 0.29 0.22 0.03 0.27 0.12

Maximum Score

3.56 3.45 3.43 3.84 3.65 3.85 3.83 3.45

% MOS less than 3.0

33% 0% 17% 0% 0% 0% 0% 0%

POLQA MOS Score Comparison for VoLTE Devices

Source: Spirent Testing on Live Network with Nomad HD

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Call Initiation and Setup Time Comparison for VoLTE Devices

Source: Spirent Testing on Live Network with Nomad HD

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Call Drop Comparison for VoLTE Devices

Source: Spirent Testing on Live Network with Nomad HD

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MAKING VOLTE BETTERThe VoLTE User Experience: Better or Worse?

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Quantify, Ensure, Measure, Verify, Troubleshoot, Benchmark …

Test

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Measuring device performance across multiple OS’s and technologies

Testing in both live and simulated network environments

Evaluating multiple devices simultaneously

Managing extensive testing projects from a centralized location

Measuring how a device’s performance will impact subscribers

Comparing VoLTE voice quality to circuit switched voice: Is it as good or better?

Common VoLTE Test Challenges

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Metrics that focus on what the end-users experience (including speech quality, the ability to make and maintain calls, and mouth-to-ear latency)

Use the same voice service measurement systems in the field and in the lab

Measurement systems that can test any device, on any network, anywhere in the world and still provide one central location for results collection and analysis

Lab test solutions that provide simple interfaces for LTE and VoLTE configuration while also enabling fast creation of automated VoLTE tests

Coverage of relevant compliance tests originating from operators and standards organizations

Characteristics of Ideal Test Strategy

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$$ $$$$

Time & Cost to Fix

Test Early and Often, in Lab & Live

Lab (Emulated Network)

Live

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Spirent Believes in “Better”How can we help you improve VoLTE

quality and time-to-market?

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For More Information

Spirent’s VoLTE and HD Voice web page:

• Application Notes for CS8 and Nomad HD Voice Quality testing

• Video demonstrations

http://www.spirent.com/go/VoLTE

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