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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
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The VoLTE User Experience
Better or Worse?
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Ch
all
en
ge VoLTE is
Different Q
uan
tify The
VoLTE User Experience
Solv
e Making VoLTE Better (not Worse)
Outline
3
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
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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%
5%
10%
15%
20%
25%
30%
35%
40%
45%
50%
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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