As LTE networks start to mature across the world, more and more carriers are looking to introduce voice services on LTE networks using a technology called Voice over LTE (VoLTE). However, making sure the VoLTE user experience is as good as—or preferably better than—legacy 2G/3G voice services is very challenging. This SlideShare presentation cover the following: - How VoLTE is different from legacy wireless voice services - The VoLTE user experience, and how to measure it - Key elements of a successful test and verification strategy

1. The VoLTE User Experience
Better or Worse?

2. 2
Challenge
VoLTE is
Different Quantify
The VoLTE
User
Experience
Solve
Making
VoLTE
Better
(not Worse)
Outline

3. 3
Sources
Facts
Q1 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
Trends
Highly 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 4th, 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 DIFFERENT
The 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 Service
Applications
MAC, RLC, PDCP
OFDM, WCDMA, etc.
Mobile Device Network2G/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 Service
Applications
MAC, RLC, PDCP
OFDM, WCDMA, etc.
Mobile Device Network4G 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).
MoreBits/s&HigherSNR
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%
5%
10%
15%
20%
25%
30%
35%
40%
45%
50%
PercentageofValuesinMOSRange
MOS Range
MOS Distribution Both Speech Paths
NB/Standard Mode
AMR-WB enabled
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 AMR
EFR
AMR
AMR-WB
EFR
EVRC
EVRC-B
EVRC-WB
Reference
Speech
Material
(sampling
frequency)
8 kHz 8 kHz
48 kHz
Applications POTS
VoIP
3G
HD Voice
Voice
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 BETTER
The 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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$$ $$$$
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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