Making the shift_to_mobile_hd_voice

TECHNOLOGY WHITE PAPER

Making the Shift to Mobile HD Voice

End-to-end voice management for a better mobile end user experience

Abstract To deliver a better quality voice signal, mobile service providers must consider how the signal is

delivered from the handset, through the access portion of the network, and then through the mobile

core. Unfortunately, although each stage of the call is important, mobile service providers cannot

control the quality of every end user’s handset. Fortunately, they can control the radio portion of

their network, which requires its own approach to quality assurance and which service providers

have addressed with RF planning. Service providers can also control the quality of the signal

through the mobile network core, which offers significant opportunity for enhancement. With

Adaptive Multi-Rate Wideband (AMR-WB), a new speech coding standard commonly referred to as

high definition (HD) voice, service providers can provide better fidelity voice signals from handsets

and deliver CD quality voice to end users through mobile networks. But even with this new codec,

the challenge is to deliver HD Voice end-to-end for all voice calls on an ongoing basis, and in a way

that optimizes the network to ensure continuing profitability.


Making the Shift to Mobile HD Voice Alcatel-Lucent 2

VOICE IS THE MAINSTAY OF MOBILE SERVICE .................................................................................. 3

THE NEED FOR BETTER QUALITY VOICE............................................................................................. 5

Demand for HD Voice expected to grow....................................................................................................................... 6

BUILDING BETTER VOICE QUALITY ...................................................................................................... 7

New codec supports higher quality voice ..................................................................................................................... 7

Codec management requirements................................................................................................................................ 8

ALCATEL-LUCENT AND HD VOICE........................................................................................................11

Alcatel-Lucent Mobile HDV Core................................................................................................................................. 12

CONCLUSION................................................................................................................................................14

ACRONYMS ...................................................................................................................................................16



Voice Is the Mainstay of Mobile Service

Multimedia. Data. Long Term Evolution (LTE).

It seems you can’t turn to a telecommunications outlet these days without one more article, analysis,

or dissertation about the effects these three issues will have on mobile networks and on mobile

service providers. Industry insiders, media, and analysts have devoted reams of printed and digital

text to explaining their importance to the long term viability of the mobile service provider business.

But ask any business or consumer end user to explain what is most important to them with respect

to mobile services and voice quality will probably be at or near the top of the list. The fact is that

after all the texting and Internet surfing are done, mobile end users turn to their mobile phone to

send and receive voice calls. And they expect the quality of each call with friends, family and

colleagues to be comparable to the quality of calls on their landline, from anywhere and at any time.

End user expectations of voice quality were confirmed by a market study conducted at the end of

2009, which reported that an end user’s perception of poor voice quality usually manifests itself as

dissatisfaction with the service provider.1 The study revealed that while 64 percent of those surveyed

would contact their service provider if they experienced poor voice service, 41 percent would switch

service providers (Figure 1).

Figure 1. Effect of poor sound quality on end user action and service provider loyalty

Sixty-six percent of those surveyed said they would have to experience poor sound quality usually

(25 percent), occasionally (27 percent), or seldom (14 percent) for them to switch their service

1 “Market Perceptions of Voice Quality in Mobile Networks: Understanding how mobile voice quality affects service provider business”, Alcatel-

Lucent, January 2010.



provider. While 44 percent of business users and 36 percent of high end consumers said it would

only have to occur seldom or occasionally (Figure 2).

Figure 2. Frequency of poor sound quality in order to switch service providers

Mobile service providers have always understood this simple fact and have, over the years, gone to

great lengths to maintain and improve voice quality. In the early days of mobile service the

emphasis was on providing more coverage to enable calls in more areas and satisfy end user

demand for true “voice” mobility. As mobile networks became more ubiquitous and coverage issues

were no longer a major concern, the emphasis shifted to maintaining the connection so users would

not experience dropped calls. Now, with more users on the network, coverage available virtually

everywhere and anywhere, and networks robust enough to ensure calls don’t get dropped, service

providers are turning to the last piece of the puzzle: clearer, more perceptible audio quality.

By enhancing the audio quality of voice calls, mobile service providers who understand the

importance of voice as the mainstay of their business, hope to improve the quality of the customer

experience. In this way they hope to establish a competitive edge and ensure end user loyalty,

increase average revenue per user (ARPU), and reduce churn.

To deliver a better quality voice signal, mobile service providers must consider how the signal is

delivered from the handset, through the access portion of the network, and then through the mobile

core. Unfortunately, although each stage of the call is important, mobile service providers cannot

control the quality of every end user’s handset. Fortunately, they can control the radio portion of

their network, which requires its own approach to quality assurance. Service providers have

addressed quality requirements in the access with RF planning, but this is not the subject of this

paper. This paper addresses how service providers can control the quality of the signal through the

mobile network core, which offers significant opportunity for enhancement.



New technologies are now available that allow mobile service providers to manage the quality of

voice signals as they travel through the network core. Adaptive Multi-Rate Wideband (AMR-WB) is

a new speech coding standard that can be used to enhance voice signals in mobile networks and

deliver CD quality voice to end users. Commonly referred to as high definition (HD) voice, this new

approach to voice delivery provides excellent speech quality because it samples the signal over a

wider speech bandwidth of 50–7000Hz compared to narrowband speech coders, which are based

on Plain Old Telephone Service (POTS) wireline quality of 300–3400Hz.

But even with this new coding standard, the challenge is to deliver HD Voice end-to-end for all voice

calls where the handsets support the codec, and in a way that optimizes the use of network

resources to ensure continuing profitability. By enabling effective digital conversion of the voice

signal, establishing Transcoder Free Operation (TRFO) and Tandem-Free Operation (TFO) where

possible or necessary to avoid transcoding in an integrated, end-to-end intelligent codec negotiation

framework, mobile service providers can establish true HD Voice quality for their end users.

Integrated properly as part of a complete HD Voice solution, these capabilities will give mobile

service providers the ability to take their mobile voice service to the next level and maintain a

competitive edge.

The Need for Better Quality Voice

Market studies show that voice continues to account for the majority of a mobile service provider’s

revenues. At the end of 2009 Gartner projected that even though voice revenues are declining, they

will still account for close to 60 percent of revenues in most markets by 2013.2 But despite the

continuing importance of voice to a mobile service provider’s business, the quality of the mobile

voice experience has not made much improvement over the past 15 years, except for price bundling,

discounts on volume and/or “in-circle” plans and fewer dropped calls. In fact, yearly studies show

that mobile voice quality continues to be a major concern for end users. A 2009 study by JD Power

and Associates revealed that mobile call quality decreased from 11 PP100 to 13 PP100 between June

2009 and January 2010.3

Yet, end user expectations of voice service continue to be high. The results of the market study noted

in the introduction revealed that mobile voice quality is important. End users are not only able to

perceive and characterize it, but they also recognize good voice quality when they hear it. In

addition, voice quality is a major contributor to the overall quality of experience (QoE) associated

with mobile voice service. Three-quarters of end users surveyed agreed completely that they hate

missing what someone is saying because they may miss something important. The majority of end

users also agreed they get frustrated if they can’t hear people they are calling. In fact, the results

2 “Forecast: Mobile Services, 2004-2013,” Gartner, June to September 2009.

3 “2010 Wireless Call Quality Performance Study—Volume 1”, J.D. Power and Associates, January 2010,

http://www.jdpower.com/telecom/articles/2010-Wireless-Call-Quality-Performance-Study-Volume-1/page-2/.



showed that half of the end users surveyed feel anxious when they can’t hear someone clearly on

their cell phone.4

It’s safe to say that as service providers roll out 4G Long Term Evolution technology end users will

expect that the quality of their mobile voice service will move out of the 20th century and into the

21st century. Recent trials of HD Voice by a number of service providers confirm end users not only

expect this, but they are willing to pay for it. As a result, the Global mobile Suppliers Association

(GSA) reports that there are already 10 commercial HD Voice networks up and running in nine

countries.5

For example, France Telecom/Orange tested the market for HD Voice in Moldova at the end of

2009 with the world’s first commercial mobile HD Voice service. The company reported that the

service resulted in longer phone usage by some subscribers when they were calling HD handsets.

More importantly, a survey of end users revealed that 72 percent of users on HD calls intended to

purchase an HD Voice phone the next time they upgraded their handset.6 Since then, Orange has

rolled out HD Voice service in France, Switzerland, Spain, the U.K., and Armenia, and the company

has announced that all its handsets will support HD Voice by the end of 2011.

Demand for HD Voice expected to grow

The seeds of end user expectations and demand for HD Voice have been sown by a variety of

services already available. Notably, end users worldwide have adopted some form of voice over IP

(VoIP) application, either as a supplement to their existing voice services, or as an enhancement to

social networks, or interactive online gaming. The majority of these VoIP calls are connected from

one wideband voice processor to another. However, more calls are increasingly being connected

from a wideband processor to traditional PSTN or mobile endpoints. When these types of

connections are made the call processing reverts to the lowest common denominator, the

narrowband used in the PSTN network or the mobile network. As a result, end users notice the

difference in quality compared to calls managed on both ends by a wideband voice processor.

For end users who have experienced these types of calls, quality is an issue. They have come to

expect a certain QoE from their VoIP connection and are unhappy when it is not available. This

expectation will fuel demand for better quality voice on mobile, especially as VoIP services gain

traction on mobile networks and service providers adopt the new AMR-WB codec. As noted by ABI

Research in a 2009 report, these factors will result in a substantial increase in HD Voice traffic on

mobile networks over the next five years (Figure 3).

4 “Market Perceptions of Voice Quality in Mobile Networks: Understanding how mobile voice quality affects service provider business”, Alcatel-

Lucent, January 2010. 5 “HD Voice: Global Update Report”, Global mobile Suppliers Association, November 16, 2010.

6 “Mobile HD Voice”, ABI Research, Q1, 2010.



Figure 3. Mobile HD Voice traffic by region, world market forecast, 2009 to 20157

Building Better Voice Quality

For end users, a high quality voice call is one where the conversation occurs without difficulty and

without any annoying or distracting effects. It is characterized by clear, audible speech without any

degradation (clicks, buzz noises, or static), periods of interruptions, or echo. Creating higher quality

voice is becoming a lot easier as a result of advancements in wideband codec standards.

New codec supports higher quality voice

Traditional narrowband telephony is based on sampling the sound stream 8,000 times a second,

and constraining the reproduction of the sound spectrum to the range between 200Hz on the low

end to 3.3 KHz on the high end. The sampled voice is then fit into a 64K bandwidth.

The Adaptive Multi-Rate (AMR) audio codec is the current standard used in Global System for

Mobile Communications (GSM) and Universal Mobile Telecommunications System (UMTS)

networks. It provides audio data compression optimized for speech, and it was adopted as a

standard by the 3rd Generation Partnership Project (3GPP) in October 1998. This codec is a little

more complex. Based on link conditions, it uses link adaptation to select the best codec mode from

one of eight available bit rates.

The new benchmark for a high quality voice experience on mobile is based on the Adaptive Multi-

Rate Wideband (AMR-WB) codec. This codec was standardized by the ITU-T in 2007 and adopted

7 “Mobile HD Voice”, ABI Research, Q1, 2010.



by most mobile phone manufacturers as the future basis of mobile voice encoding. It provides

excellent speech quality because it doubles the sampling rate and more than doubles the width of

the sound spectrum reproduced, from 50Hz to 7 KHz. This adds significant depth and nuance to the

transmitted sound, and it reduces the bandwidth requirement to 32Kbps, half that of a typical PSTN

transmission.

Because it delivers the highest quality voice experience available, AMR-WB is commonly referred to

as HD Voice. The GSA notes that HD-voice “provides significantly higher voice quality for calls

between mobile phones supporting the feature, and can be implemented in GSM and WCDMA

(UMTS) networks. The higher voice quality of HD Voice improves the call experience and allows

people to better share feelings, do business and communicate information.”8

But having the right codec is only part of the solution mobile service providers need to create a

higher quality voice experience for end users. To truly capitalize on the benefits HD Voice offers,

mobile service providers must also consider how the codec is managed end-to-end.

Codec management requirements

Today’s mobile networks are engineered to deal with the typical network impairments to voice

quality. All mobile networks have integrated processes specifically designed to reduce or eliminate

echo, delay, jitter, and packet loss. In addition, to optimize network resources and deliver voice

between different types of devices, all networks include transcoding functions.

Transcoding is the direct digital conversion of a voice signal from one codec format to another. It

takes place in the network as the signal is delivered from one element to another and it can

adversely affect sound quality. That’s because when voice is initially compressed and encoded,

details of the voice transmission are stripped away. The lower the compression bit rate, the greater

the amount of information that is stripped. Transcoding from one codec format to another, further

compounds this problem because the compressed signal must be decompressed into a base format

and then recompressed into a second codec format, so more information is stripped away. In

addition, multiple transcoding stages degrade voice quality, add delay and amplify speech

degradation anomalies, such as noise and distortion, introduced by the codecs used for

compression.

In legacy circuit switched networks, transcoding does not adversely affect voice quality because

these networks have one or at a maximum two transcoding stages. However, packet voice networks

can easily have three or even four transcoding stages with two or more transcoders working in

tandem. As a result, the quality of the voice signal can be significantly reduced by the time it reaches

an end user’s mobile device. To properly manage the quality of a HD Voice signal, the original

encoding must be maintained as the signal travels from the sender to the recipient. Therefore,

8 “HD Voice: Global Update Report”, Global mobile Suppliers Association, November 16, 2010.



transcoding must be eliminated (Figure 4).

Figure 4. Transcoder Free Operation (TrFO) improves sound quality

But the compressed voice must still be managed as it travels through the network to and from end

user devices. By intelligently managing codec usage, a wireless call server (WCS) can maintain

compressed speech in its original state as it travels between a pair of call servers on a network

(Figure 5).

Figure 5. Intelligent codec negotiation allows calls to be established without unnecessary transcoding

TrFO Improvements

0

12

34

5

AMR Rate

MOS

TrFO On

TrFO Off

Improvement

TrFO On 4.18 4.07 3.91 3.89 3.83 3.77 3.57 3.48

TrFO Off 3.87 3.69 3.38 3.34 3.33 3.12 2.93 2.8

Improvement 0.31 0.38 0.53 0.55 0.5 0.65 0.64 0.68

12.2

K

10.2

K

7.95

K

7.40

K

6.70

K

5.90

K

5.15

K

4.75

K



Likewise, intelligent codec negotiation ensures the signal travels through the network using the

highest quality codec. So, if both ends of a call do not support the AMR-WB codec then the WCS

should be capable of finding a common codec for both. In this way, the WCS can eliminate the need

to transcode from AMR-WB to a lesser codec in the middle of a call and the same codec is used end-

to-end. This ensures the highest quality voice signal is sent and received and guarantees end users

always experience smooth, undistorted voice calls (Figure 6).

Figure 6. TrFO can interwork with TFO to preserve end-to-end voice quality

For voice calls made between a mobile handset capable of HD Voice and a wireline HD VoIP phone,

the network must also be able to efficiently support HD wireline interworking. Since this

transcoding cannot be avoided, it should be completed at the edge of the network — at the last

gateway before the call leaves the mobile core and enters a wireline network (Figure 7).

Figure 7. Transcoding at the edge of the network for HD wireline interworking



Efficient codec management also requires intelligent routing to ensure the HD Voice signals get to

their intended endpoint by following the shortest possible route. To do this, the network must limit

the number of gateways the call must travel through as it makes its way through the mobile core. In

addition, there must be a mechanism in place to intelligently detect the optimal path through the IP

network.

Finally, intelligent codec management requires support for a variety of coding and signaling

between call servers, as well as support for two types of bearer traffic, Internet Engineering Task

Force (IETF) framing and 3GPP.

Alcatel-Lucent and HD Voice

The Alcatel-Lucent Mobile NGN solution has been designed to ensure optimal voice quality in next-

generation mobile networks. This solution is built on two key components:

• The Alcatel-Lucent 5060 Wireless Call Server (WCS), which provides the call

control and signaling functions. It is designed specifically for 3GPP, R4/R5/R6-compliant

architectures and it significantly improves network simplicity, capacity and operational

efficiency.

• The Alcatel-Lucent 7549 Media Gateway (MGW), which is a high-density, multi-

service gateway designed with voice and data-bearer interfaces, including Time Division

Multiplexing (TDM), IP and Asynchronous Transfer Mode (ATM). It performs any-to-any

switching, including native TDM-to-TDM, native packet-to-packet and TDM-to-packet,

and delivers a dramatically simplified architecture that supports seamless evolution to an

IP Multimedia Subsystem (IMS).

Together, the WCS and the MGW include a variety of features designed to counteract the effects of

the network, and the environment on the quality of voice calls (Table 1). Key features include

electrical echo cancellation, automatic noise reduction (ANR), automatic level control (ALC),

adaptive jitter buffers, and packet loss concealment.9 In addition, these network components are

engineered to eliminate the effects of speech coding and compression, and transcoding on voice

signals. This is accomplished with the Alcatel-Lucent Mobile HDV Core, a new system

embedded in the solution’s WCS. This system intelligently determines what the voice call quality

should be and sends the information to the gateway to enable optimal routing of the signal through

a mobile core.

9 For more information about the Alcatel-Lucent Mobile NGN solution, see the “Mobile NGN Core-Voice Quality White Paper, Edition 1.4”, Alcatel-

Lucent, 2010.



Table 1. Alcatel-Lucent Mobile NGN solution voice quality features vs. voice quality impairment factors

Alcatel-Lucent Mobile HDV Core

The Alcatel-Lucent Mobile HDV Core brings support for the AMR-WB codec to the Alcatel-Lucent

5060 Wireless Call Server (WCS) and Alcatel-Lucent 7549 Media Gateway (MGW). With this

software, the 5060 WCS is able to recognize when a call should be delivered as an HD Voice call,

determine when to use coding techniques, how to use coding, and what information the gateway

needs to properly deliver the signal. Based on this information, the 7549 MGW establishes the

appropriate HD quality connection and acts as transport for the call between two end users.

The software allows usage of AMR-WB codec in intra-MSC 3G mobile to 3G mobile calls, with

packet or TDM interconnect trunks. The AMR-WB codec is selected whenever its usage is possible

end-to-end, thereby enabling true “wideband” sound quality, assuming all elements on the call path,

including end user devices, support the AMR-WB codec.

The Mobile HDV Core also supports TrFO and TFO operation. With TFO, it is possible to

transparently transmit the compressed speech frames from mobile station to mobile station and

bypass the transcoding function, when both end terminals are using the same speech coding.

For TrFO, the Mobile HDV Core eliminates transcoding on the media gateways in the

communication path. This reduces the port-to-port delay for mobile-to-mobile calls, which is

particularly dramatic given that without TrFO or TFO, a typical GSM mobile-to-mobile call could be

transcoded up to four times on a compressed packet backbone. More importantly, by eliminating

transcoding, the potential for voice impairment caused by transcoding is also eliminated, fewer

digital signal processing resources are needed in the network, and bandwidth is optimized.

As a result, core and access transport bandwidth savings are realized with TrFO because cost-



efficient transmission is achieved by reducing the use of transcoding equipment in the transmission

path (Figure 8). And, because wireless codecs are bandwidth efficient, these savings can be carried

end-to-end without any “processing”.

Figure 8. Alcatel-Lucent Mobile NGN solution TrFO

To take advantage of the benefits of both TFO and TrFO, the Alcatel-Lucent Mobile HDV core

supports TFO and TrFO interworking. This results in a communication path that is optimized with

the concatenation of both TrFO and TFO links (Figure 9).

Figure 9. Alcatel-Lucent Mobile NGN Solution TFO and TrFO interworking



Finally, the Mobile HDV Core software has a dynamic codec selection feature, which provides codec

negotiation and selection that enables TrFO whenever possible. This minimizes the number of

required transcoding steps and compressed links present on a call path. With this feature, the

mobile service provider configures the use of codecs within the core network based on codec

configuration used in the network and the level of TFO/TrFO support present. The software then

uses this information to negotiate and select the best codec for the call path based on requirements

for voice quality and bandwidth optimization.

The Mobile HDV Core software supports standards based out-of-band codec negotiation as well as

TFO. It offers a rich set of configuration options to allow service providers to make intelligent

tradeoffs between selection and de-selection/prioritization of all relevant codecs in a core network

and mobile access trunk group for various call scenarios. Likewise it enables intelligent bandwidth

vs voice quality tradefoffs. And it provides seamless intelligent codec negotiation across any

combination of different access types (2G over IP, and TDM, 3G over IP and ATM) and core

network types (Session Initiation Protocol (SIP), SIP-I, Bearer Independent Call Control (BICC),

and ISDN User Part (ISUP)).

Conclusion

Voice quality is a major contributor to the overall QoE associated with mobile voice service. Because

better voice quality keeps end users happy mobile service providers need a new approach to the

management and delivery of every encoded digital bit as it travels the network end-to-end.

Because it delivers the highest quality voice experience available, AMR-WB, or HD Voice, is the new

benchmark for a high quality voice experience on mobile. It provides excellent speech quality

because it doubles the sampling rate and more than doubles the width of the sound spectrum

reproduced. In addition, it is more efficient because it reduces the bandwidth required for high

quality voice delivery.

But the difficulty with analog to digital conversion is maintaining digital coding through the

network so that the quality of the voice is consistent end-to-end. Therefore, to truly capitalize on the

benefits HD Voice offers, mobile service providers must ensure the AMR-WB codec is managed

properly. By enabling TFO and TrFO management of the voice signal, mobile service providers can

avoid the problems associated with decompression and recompression of the signal as it travels

through the network. As a result, service providers can deliver a higher voice service QoE for end

users based on this new coding standard. This was confirmed through the France/Telecom Orange

AMR-WB trials in Moldova. Orange chose the Moldovan network for the trials because it was built

on a next-generation 3G infrastructure that supported TrFO operation upon initial deployment.

As part of the Alcatel-Lucent Mobile NGN solution, the Alcatel-Lucent Mobile HDV Core brings

support for the AMR-WB codec to the Alcatel-Lucent 5060 Wireless Call Server (WCS) and Alcatel-



Lucent 7549 Media Gateway (MGW). With this software, the 5060 WCS is able to recognize when a

call should be delivered as an HD Voice call, determine when to use coding techniques, how to use

coding, and what information the gateway needs to properly deliver the signal. Based on this

information, the 7549 MGW establishes the appropriate HD quality connection and acts as

transport for the call between two end users. Most importantly, it supports TrFO and TFO operation

to ensure optimal HD Voice for all calls whenever usage is possible end-to-end.



Acronyms

Term Definition

3GPP 3rd Generation Partnership Project

ALC automatic level control

AMR Adaptive Multi-Rate

AMR-WB Adaptive Multi-Rate Wideband

ARPU average revenue per user

ATM Asynchronous Transfer Mode

ANR automatic noise reduction

BICC Bearer Independent Call Control

GSA Global mobile Suppliers Association

GSM Global System for Mobile Communications

HD high definition

IETF Internet Engineering Task Force

IMS IP Multimedia Subsystem

ISDN Integrated Services Digital Network

ISUP ISDN User Part

ITU International Telecommunication Union

ITU-T International Telecommunication Union-Telecommunication Standardization Sector

LTE Long Term Evolution

MGW media gateway

POTS Plain Old Telephone Service

SIP Session Initiation Protocol

TDM Time Division Multiplexing

TFO Tandem Free Operation

TrFO Transcoder Free Operation

QoE quality of experience

UMTS Universal Mobile Telecommunications System

VoIP voice over IP

wcs wireless call server

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