38 Ericsson Review No. 1, 2008
Mobile TV over 3G networks – Service and
enablers evolution
Juan-Antonio Ibanez, Thorsten Lohmar, Dalibor Turina and Aurelie Zanin
Drivers and challenges of
a mass-market mobile TV
service
Surveys show that end-users consider mobile
TV to be one of the most interesting mobile
applications on offer. Mobile TV is often
identifi ed with “linear TV” and scheduled
broadcast distribution, but the concept of
TV and especially that of mobile TV is rapidly evolving to embrace on-demand TV as
well as podcast TV.
Market surveys and feedback from numerous test and commercial installations around
the world confi rm that users expect to be
able to access TV content when and where
they want, for instance while they are commuting via bus or rail.
As mobile TV gains ground among operators and end-users, the need to deliver it in
a cost-effective way with guaranteed quality
of service (QoS) becomes paramount. These
two aspects are equally important: costeffective delivery is a must in order for operators to maximize their revenues, just as
adequate quality of service is necessary to
guarantee a satisfactory end-user experience.
At present, mobile TV services are delivered over unicast best-effort bearers. In
most cases, this form of delivery is adequate
provided there is suffi cient capacity in the
network. Notwithstanding, a surge in the
volume of packet data traffi c is putting pressure on the ability of networks to deliver
delay-sensitive streaming services. For mobile
TV services to succeed, a number of enablers
must be put into place that maintain and
improve the quality of the end-user experience. These enablers are
network capacity through proper dimensioning and enhanced technology;
improved QoS handling for streaming services (as compared with background interactive traffi c); and
effi cient broadcast capabilities in 3G networks – for example, multimedia broadcast/multicast service (MBMS).
Ericsson, followed by other companies, is
introducing these enablers into its networks
and terminals, and commercial deployments
are set to begin in 2008. High-speed downlink packet access (HSDPA), for instance,
brings exceptional capacity to unicast. Similarly, streaming QoS with guaranteed bit
•
•
•
rates is now being introduced into terminals
(it is already widely supported in networks).
And initial deployments of MBMS began in
2008, adding unique broadcast capabilities
to 3G networks.
Broadcast versus unicast
There has been a lot of talk lately about
broadcast technologies being adequate enablers of mobile TV services. While this
might be partially valid for traditional TV, it
is evident – with the evolution of mobile TV
service through on-demand TV, podcast TV,
and interactivity – that unicast bearers are
the true essential enablers.
The preferred solution for effi ciently delivering mobile TV services calls for a combination of unicast and broadcast bearers. With
unicast, operators can offer a broad selection of TV channels or content, even though
only a limited number of users will view
most channels. By contrast, operators can
boost system capacity by employing broadcast capabilities to deliver the most popular
channels in densely populated areas. The
combined use of 3G unicast and broadcast
capabilities enables operators to offer a virtually unlimited number of channels, as opposed to pure broadcast solutions, which put
a hard limit (dictated by the amount of available spectrum) on number of channels.
In a nutshell, unicast can be used effi -
ciently
to delivery a large number of niche TV
channels to individual end-users;
to deliver on-demand TV;
to time-shift the delivery of linear TV
(pause/play, fast-forward, rewind);
to deliver podcast TV to individual endusers; and.
to provide interactivity for, and facilitate
the personalization of, TV service.
Likewise, broadcast techniques are best used
to effi ciently deliver popular TV channels to a
large number of end-users in a given geographic
area and podcast TV to a large group of endusers.
Therefore, although unicast remains a
fundamental component for delivering
evolved mobile TV services, the addition
of broadcast gives operators the most fl exible and cost-effective solution for providing
these services over a 3G network. In this
context, the OMA BCAST standard plays
an important role by defi ning a framework
for global interoperability of mobile broadcast services.
1
•
•
•
•
•
User interest in mobile TV services is growing thanks especially to the
rapidly evolving multimedia capabilities of mobile terminals. Mobile operators are thus eyeing mobile TV services both as a new source of revenue
and as a way of increasing customer loyalty.
This article looks at some key components of a mobile TV solution
that capitalizes on the capabilities of third-generation (3G) networks – in
particular, built-in support of unicast and broadcast transmission, which
fosters and sustains a strong uptake of service.
TERMS AND ABBREVIATIONS
3G Third-generation mobile system
3GPP Third Generation Partnership
Project
BM-SC Broadcast/multicast service center
DRM Digital rights management
DVB-H Digital video broadcasting –
handheld
ESG Electronic service guide
GBA Generic bootstrapping architecture
GGSN Gateway GPRS support node
HSDPA High-speed downlink packet access
HTTP Hypertext transfer protocol
MBMS Multimedia broadcast/multicast
service
MCCH MBMS control channel
MSK MBMS session key
MTK MBMS traffi c key
MUK MBMS user key
QoS Quality of service
RNC Radio network controller
SAP Service access protection
SGSN Serving GPRS support node
SIM Subscriber identity module
SMS Short message service
UE User equipment (mobile terminal or
handset)
VoD Video on demand
XML Extended markup language
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MBMS – the 3G broadcast
technology
As explained above, operators need broadcast
technology to cope with a high penetration
of mobile TV services; the technical solution
over 3G networks is called MBMS (multimedia broadcast/multicast service). Other
wireless broadcast technologies also exist
(such as DVB-H) but are not covered in this
article, whose focus is on the capabilities of a
3G network.
The article Multimedia Broadcast/Multicast
in mobile networks presented MBMS in some
detail.
2
At the time of publication (January
2005), the 3GPP standard defi ned just two
modes of transmission: broadcast and multicast. Toward the end of 2006, 3GPP introduced a new “counting” mode for broadcast,
also commonly referred to as enhanced broadcast. 3GPP designed the enhanced broadcast
mode to better suit the characteristics of mobile TV services (in particular, fast channel
switching) while achieving high spectrum
effi ciency. Below we provide an overview of
the enhanced broadcast mode. Readers who
what to learn more about the broadcast and
multicast modes of MBMS should refer to
the aforementioned article.
Figure 1 illustrates the principle of MBMS
enhanced broadcast mode. A tree-like transport plane bearer is established for each TV
channel from the broadcast/multicast service center (BM-SC), through the GGSN
and SGSN, to each radio network controller (RNC) that serves the target area. The
transport plane bearer carries the audio and
video components of the TV channel to the
RNC. The RNC signals the availability
of the TV channel on a common MBMS
control channel (MCCH), which is always
present in MBMS-enabled cells. When an
end-user selects a TV channel, the terminal
reads the MCCH information to determine
whether or not the TV channel is available
via MBMS in the cell. If the terminal does
not fi nd the TV channel on MCCH or there
is no MCCH (for example, when an end-user
is roaming in another country), the terminal
can ask the TV server to send the content via
unicast. The availability of the unicast alternative is indicated in the electronic service
guide (ESG).
The information provided over MCCH indicates whether the
• TV channel is delivered on a point-tomultipoint radio bearer, in which case the
terminal needs only “tune” to that radio
bearer; or
terminal needs to request a dedicated
point-to-point radio bearer. No radio
bearer is established until a terminal has
requested one (this way, unused radio resources are conserved for other purposes).
When the number of point-to-point radio
bearers for a given TV channel reaches a
predefi ned threshold, the RNC switches to a
point-to-multipoint radio bearer and releases
the point-to-point bearers (the threshold represents the breakeven point in terms of total
cell power consumed by either transmission
mode). After having switched to point-tomultipoint mode, the RNC randomly triggers terminals, inducing them to report their
interest in the TV channel. This “recounting” procedure allows the RNC to reassess
the appropriate transmission mode as users
move to other cells or stop watching the TV
channel.
•
BOX A, UNICAST, BROADCAST, POINT-TO-POINT, POINT-TO-MULTIPOINT
Unicast refers to a particular case of end-to-end, point-to-point communication between a
server and a client (or receiver). Broadcast communication is typically end-to-end, point-tomultipoint communication between a server and multiple receivers. MBMS-enhanced broadcast
mode extends this concept. It offers an end-to-end, point-to-multipoint communication service,
but may employ any combination of point-to-point or point-to-multipoint radio bearers to reach
the actual receivers.
Figure 1
Illustration of the MBMS enhanced
broadcast mode. In this example, the
RNC decides to distribute the content via
a point-to-multipoint radio bearer when
three or more users request the same TV
channel.
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Review108.indd 39 Review108.indd 39 08-01-21 16.12.26 08-01-21 16.12.2640 Ericsson Review No. 1, 2008
The RNC thus always employs the most
favorable transmission mode, conserving unused radio resources for other services. Note,
however, that MBMS-enhanced broadcast
does not make “plain” broadcast mode obsolete. In some cases – for instance, where a
large number of end-users with a common
interest are concentrated in a limited geographic area – MBMS broadcast (without
recounting) is the perfect solution. Typical
examples are local broadcasts in sports arenas
or at exhibitions where targeted content can
be distributed exclusively to the local audience. The MBMS service area concept defi nes
the distribution area of an MBMS service
with the granularity of one cell, allowing operators to defi ne precisely where content is to
be broadcasted.
Electronic service guide
MBMS service providers employ service announcements to inform user equipment (UE)
or terminals about available services and how
they can access them. In the context of TV
services (such as linear TV, VoD, and podcast
TV) the service announcements take the form
of an electronic service guide (ESG), which is
an XML fi le with technical information that
receiving devices use to request, receive, decrypt and render services. Ericsson promotes
the OMA BCAST standard, which defi nes a
service guide structure and describes ways of
accessing it – for instance, by using a push
mechanism over a broadcast bearer or a unicast pull mechanism.
3
The OMA BCAST ESG structure is made
up of numerous fragments. The core fragments contain the program guide – that is,
the information which is meaningful to endusers, such as a list of TV channels and programs (previous, current, next) on each TV
channel. The ESG also contains information
that is understood by the receiving application but is not rendered to end-users. This
includes the access fragments, which tell
UEs what alternative bearers exist for each
TV channel. The UEs select the most appropriate bearer in their current location, prioritizing broadcast bearers over unicast bearers
when both options are available. The ESG is
a key feature for offering mobile TV services
that seamlessly integrate unicast and broadcast delivery. Note that the ESG solely refers
to the access technology; the type of radio
bearer used in broadcast mode is dictated by
the information provided over MCCH.
Service access and
content protection
After the broadcast client has received access information via the service announcement, the system cannot restrict reception of
the media stream. The media streams must
thus be encrypted to limit reception to those
people/devices who have subscribed to the
service. In other words, all receivers can receive the media streams but only subscribing
clients can decrypt and render them.
An organized, layered hierarchy protects
access to the MBMS service as follows (Figure
2)
4
: Each broadcast media fl ow is encrypted
using an MBMS traffi c key (MTK). This key
is changed frequently and distributed, interleaved, in the actual broadcast fl ow. The
traffi c key is protected with an MBMS session key (MSK), which is distributed via unicast. Only devices that have registered and
BOX B: PODCAST TV
Podcast TV describes a service to which end-users subscribe to view some kind of video content
on a regular basis or as it becomes available. The video clips are pushed to subscribers. They are
downloaded in the background, without user intervention, and stored in the terminal for off-line
viewing. Examples include the last episode of a TV series, weather forecasts, news updates, and
so forth.
Figure 2
Service access protection principle.
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authenticated with the BM-SC may receive
the MSK. The MSK, in turn, is protected
against eavesdroppers by the MBMS user
key (MUK), which is derived from a shared
secret key (Ks’). This key is established during the authorization procedure, part of the
generic bootstrapping architecture (GBA).
5
The actual media-protection keys change
frequently and may thus solely be decrypted
by registered devices.
The MUK and MSK are stored on the SIM
card (more secure) or in device memory.
The OMA BCAST specifi cation delineates
the protection of service access and content.
6
Service access protection (SAP) is about limiting access to the service. Content protection
(also known as digital rights management,
DRM) is about the management of received
content. Usage rights objects might restrict
how end-users use content. An end-user, for
example, might be able to record a mobile
TV session but will be prevented from forwarding it. The OMA BCAST SmartCard
profi le complies with and further extends the
3GPP MBMS access-protection scheme described above.
Interactivity and
personalization
Several TV programs contain “interactivity
features” that help integrate the audience
with the show they are watching. Popular
TV shows like “Big Brother” and “American Idol” let the audience vote on its favorite contestants. Viewers typically cast their
votes via voice calls or premium SMS with
a keyword. The advantage of this approach
is that it reuses existing charging methods.
The price of a vote depends on the number dialed, and the charge is collected via a
phone bill.
OMA BCAST takes interactivity one step
further by specifying an interactivity enabler.
Interactivity with an end-user is triggered
by the reception of an interactivity media
document, which describes the interactivity sequence (Figure 3). Interactivity media
documents may be sent via unicast or interleaved with broadcast fl ows and transmitted
to all listening devices. User feedback is then
sent to the feedback collection server over a
standard 3G unicast bearer (for example, via
HTTP or SMS).
The interactive service content is distributed as a separate logical fl ow to receiving devices that then merge it into the actual preBOX C, ARCHITECTURE FOR MOBILE TV OVER 3G
Figure 4 gives a simplifi ed view of a typical architecture for mobile TV over a 3G network.
The BM-SC is a logical entity defi ned by 3GPP. In practice, its functionality is split among several
physical components. The gray box roughly illustrates the distribution of BM-SC functionality.
The TV server is the fi rst contact point for the terminal and the central control unit of the mobile
TV service. The ESG aggregator translates and combines program information from content
providers and inserts it into the ESG.
The media controller distributes content streams to UEs via unicast or broadcast. The encryptor
encrypts the broadcast streams under the supervision of the service access protection (SAP)
function (Figure 2). Unicast streams do not require additional access protection because
standard 3G unicast security mechanisms already apply.
The broadcast controller establishes and releases MBMS bearers through the core and radio
network.
The live encoder, podcast TV, and on-demand TV servers encode TV content in a format that is
suitable for mobile devices and encapsulate it in applicable protocols for distribution.
The interactivity server generates interactivity documents. The feedback collector processes
feedback from end-users.
Protocol names are mentioned for completeness. For further details, the reader is kindly referred
to the following documentation from 3GPP:
Multimedia Broadcast/Multicast Service (MBMS); Architecture and Functional Description
(3GPP TS 23.246).
Multimedia Broadcast/Multicast Service; Protocols and Codecs (3GPP TS 26.346).
•
•
Figure 3
Example of voting interactivity sequence:
(1) The device displays two alternatives. (2) After making a selection, the end-user is
asked to confi rm the charge. (3) The vote is then sent.
Vote
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sentation of the TV service. Therefore, one
may personalize the interactive service experience. Users may browse the ESG, choose
from a variety of interactive services and, by
means of personal settings, specify how they
want the service to be displayed.
“Voting” is but one example of an interactive service, and the interactivity enabler can
be used to realize other services, such as news
tickers or chat applications, or to distribute
personalized or location-dependent advertisements.
Conclusion
Mobile TV is often identifi ed with the “linear TV” of legacy, fi xed TV networks, but
Ericsson’s vision of Mobile TV also embraces the distribution of on-demand TV and
Podcast TV content. The client’s electronic
service guide (ESG) is a complete “content
browser” that presents live, recorded and locally stored multimedia content by combining linear TV, on-demand and Podcast TV
into a unifi ed service offering.
MBMS is a technical extension to 3G networks: it reuses deployed infrastructure and
spectrum. Moreover, Ericsson’s implementation of MBMS can be deployed as a software
upgrade.
MBMS is used to boost capacity for transmitting popular Mobile TV channels to large
audiences. The radio network determines
whether it should employ point-to-point or
point-to-multipoint radio-transmission resources. Mobile TV channels are thus solely
broadcasted as needed. Integration with
unicast makes it possible to offer a virtually
unlimited number of Mobile TV channels
and on-demand content. Consumer studies
of legacy TV systems and Mobile TV trials
have shown that users expect a large variety
of channels, but only a small set of channels
are especially popular at any given time.
Thanks to its inherent fl exibility and ef-
fi ciency, MBMS is Ericsson’s preferred choice
of broadcast technology for Mobile TV as
well as any other service that must deliver
the same content to a large group of users in
a 3G network.
Interactivity and personalization are powerful means of captivating an audience and
increasing TV viewing time. Mobile TV,
with its natural integration of unicast and
broadcast communication channels, introduces entirely new ways of interacting with
an audience and of creating a personalized
TV experience. This new approach will
become a key differentiator of Mobile TV
offerings.
REFERENCES
Mobile Broadcast Services. Open Mobile Alliance, OMA-TS-BCAST_Services-V1_0
Bakhuizen, M and Horn W.: Multimedia Broadcast/Multicast in mobile networks. Ericsson
Review, Vol. 82(2005):1, pp. 6-13
Service Guide for Mobile Broadcast Services. Open Mobile Alliance, OMA-TS-BCAST_ServiceGuide-V1_0
Security of Multimedia Broadcast/Multicast Service (MBMS). 3GPP TS 33.246
Generic Authentication Architecture (GAA); Generic Bootstrapping Architecture. 3GPP TS
33.220
Service and Content Protection for Mobile Broadcast Services. Open Mobile Alliance, OMATS-BCAST_SvcCntProtection-V1_0
1.
2.
3.
4.
5.
6.
Figure 4
Simplifi ed view of architecture for mobile
TV over a 3G network.
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