Mobile TV: The Next Killer-App

There is presently a great deal of industry hype surrounding 'mobile
television'. Said by some to be the next 'killer app' of the mobile
sector, and dismissed by others as having no sustainable business model, mobile
TV is a conjure of possibilities. It lies at the eye of a maelstrom of
technologies, network models and frequency bands, waiting for many trials to end
and the manifestation of a clue as to the most practical and commercially viable
direction.

Experiencing TV on handheld devices raises a whole new set of
issues that have spawned several new broadcast technology platforms. Attracting
the most attention globally is the digital video broadcast to handhelds (DVB-H)
standard, which is derived from digital video broadcast terrestrial (DVB-T). The
important difference is that DVB-H transmits the signal in bursts in order to
conserve handset battery life. It also incorporates greater forward error
correction, essential for boosting handheld reception.

Another significant difference is the data encapsulation
technique. The DVB-H stream is an IP datacast at 200 to 500kbps/program,
yielding up to 50 programs in an 8MHz channel. This resolution is sufficient for
the tiny handset screen. In contrast, standard-definition DVB-T uses MPEG-2 (or
MPEG-4) encoding at 4 to 5Mbps/program, yielding up to five 'standard
resolution' programs per channel.

DVB-H is not the only mobile TV platform finding favor. Korea
and China are the first to embrace terrestrial digital multimedia broadcast (T-DMB),
derived from the Eureka 147 digital audio broadcast (DAB) standard. Moreover,
Qualcomm has developed the forward link only (FLO) technology for the delivery
of multimedia content. T-DMB, FLO and DVB-H have each addressed the same
handset-related issues-battery life, reception and screen resolution-albeit
in different ways.

It Starts with Delivery

The choice of technology platform is just one element of delivery-and
delivery just one consideration-in the riddle that is mobile TV. Commercial
imperatives drive all, and are also dependent on such aspects as consumer
viewing habits, handset development, content licensing and government regulatory
environment. Yet it is with delivery that the whole mobile TV enterprise gets
moving, and delivery infrastructure that represents a significant proportion of
capital outlay. Consequently, the question of which delivery model proves best,
and most cost-effective, is one of high interest.

Speculation is compounded by the existence of several different
industry players. On the one hand, there are the mobile communications carriers.
These have an existing subscriber base and perceive mobile TV as a means of
extending and differentiating their service. Many have introduced
third-generation (3G) mobile TV services based on universal mobile
telecommunications service (UMTS) in recent months, while at the same time
partnering broadcast-based mobile TV trials.

It is generally well accepted that UMTS-based mobile TV has
limitations. The service is here and available now, but the unicast (one-to-one)
nature of UMTS means that as the viewer base grows, mobile TV will not be
sustainable on this platform-even as UMTS heads towards '3G long term
evolution' (3G LTE) or in-band cellular broadcast techniques such as
multimedia broadcast/multicast service (MBMS). Recent reports have suggested
that it makes more sense to use the spectrum for wireless data services that can
be charged at a higher rate than can television.

Mobile carriers are therefore turning to broadcast models for
mobile TV. Their quest to utilize existing base station sites has led to the 'cellular
overlay' model for mobile TV, where broadcast infrastructure is deployed at
mobile base stations to provide mobile TV coverage in a similar way to a
cell-based mobile network.

Coverage Adjustments

The broadcast industry approaches mobile TV coverage from the other
direction. Conventional free-to-air TV is typically broadcast from centralized
high-power transmission sites, supported by supplementary repeater or 'gap
filling' stations. It is relatively straightforward to deploy a mobile TV
service in the same manner; however, there do need to be adjustments to coverage
planning.

Research indicates that the 'high-power terrestrial broadcast'
model for mobile TV will require more repeater sites than for conventional
television. One reason is because, owing to an increase in reflections at ground
level, the forward error correction applied to the signal is increased,
resulting in a trade-off in signal-strength that needs to be addressed.

Additionally, consumers have also come to expect their handsets
to work indoors and in moving vehicles. The provision of indoor coverage is
considered one of the main challenges of mobile TV networks.

A third infrastructure model, incorporating satellite blanket
coverage supported by low-power terrestrial repeaters, has been proposed. The
repeaters would be co-located at mobile base stations to supplement urban and
provide indoor coverage.

A unifying element in all three network models is the
convergence of industries that have been hitherto quite separate. Mobile
carriers will need to embrace broadcast technology and content; broadcasters (or
infrastructure/service providers) will need to team up with carriers, who
already have the subscriber base. In fact, it seems logical for mobile TV
systems to be intrinsically linked with mobile phone services, which can provide
a one-to-one back-channel for interactivity. This could even prove to be a
driver for consumer take-up.

The Band Debate

From a technical and practical standpoint, the other major delivery option
pertains to frequency band, of which several are being considered: VHF (170 to
240MHz), UHF (470 to 860MHz), L Band (variable depending on region, but
generally falls somewhere between UHF and S Band) and S Band (2170 to 2200MHz).

Most popular globally for digital terrestrial television is the
UHF band, which has also seen the most mobile TV activity to-date. It has good
propagation characteristics and, if deployed using the terrestrial broadcast
model, should be capable of providing coverage of a large city using 20 to 50
repeater sites. Qualcomm in the USA is using this model for its commercial
MediaFLO service (using the FLO platform), but, as other trials have shown, it
is also ideal for deploying DVB-H.

The UHF band is also suitable for networks deployed using the
cellular overlay model, since UHF frequencies are just below conventional global
standard for mobile communications (GSM) or US 'Cellular' code division
multiple access (CDMA) frequencies. This type of network is being trialled in
many countries across Europe.

One of the main challenges associated with the UHF band is the
limited availability of spectrum in most parts of the world, but especially
Europe. Some governments are considering assigning two or three UHF frequencies
for DVB-H mobile TV services, which can be deployed as single frequency networks
(SFN). Although it makes network configuration more complex, an SFN is a highly
efficient use of spectrum, and a network of two or three overlapping SFNs could
be a promising option.

The VHF Band III has even better RF propagation characteristics
than UHF. It is not suitable for the cellular overlay model, since the antennas
would be too large for existing base stations; but it is an ideal candidate for
the terrestrial broadcast model, where city coverage could be achieved with just
a handful of repeaters. From a network deployment perspective, VHF would appear
to offer the lowest roll-out costs coupled with the best indoor coverage.

Factoring in Availability

Korea and China are both deploying commercial T-DMB mobile TV services in
VHF Band III, as per DAB services. To-date, there has been no move to deploy DVB-H
in VHF Band III; however, since DVB-T services operate in VHF Band III, there
seems little reason why DVB-H would not as well. The main obstacle is again one
of spectrum availability-of the four considered bands it has the most limited
availability in most countries-coupled perhaps with convention.

The other two bands-L Band and the satellite S Band-are
emerging as contenders. Both provide reduced terrestrial propagation and
in-building coverage compared with the lower frequency bands, but have the
advantage of being more readily available.

Irrespective of which frequency band is selected, the signal
polarization is also under examination. The FLO systems being deployed use
circular polarization (CP), which is a combination of vertical (VP) and
horizontal (HP) components. It has been speculated that a CP signal may
facilitate reception at the mobile handset regardless of orientation. This may,
however, be a moot point, since the multiple reflections experienced by HP and
VP signals can alter the polarization, effectively producing a mixture of
polarization components by the time the signal reaches the handset.

Vertical polarization is favored at present by both DVB-H trials
and T-DMB deployments. In the latter case, this probably harks back to the DAB
convention, since radio signals are often VP to enhance reception by car
antennas. Use of VP also enhances isolation from HP television signals at
similar frequencies. Most DVB-H trials are using VP, although at least one
utilizes a HP signal. Ultimately, the selection of polarization will depend upon
the receiver performance when faced with multiple signals from reflections, plus
the indoor penetration of the signal.

Which Way Forward?

The future of mobile TV depends on many factors; but if it is proved that
consumers want mobile TV-and are prepared to pay for it-then half the battle
is won. The network model will then be determined by how cost-effectively
networks can be deployed and the availability of frequencies and licenses. This
is likely to differ on a case-by-case basis.

Utilizing existing infrastructure will be a key element. It is
not difficult to incorporate mobile TV services into existing broadband
terrestrial broadcast systems, particularly if the systems were initially
designed to accommodate additional services or channels. The most significant
capital outlay would come with the deployment of additional repeater stations.

If, on the other hand, a mobile TV network is deployed as a
cellular overlay, this will involve a significant shift in broadcast
infrastructure philosophy. The quest to deploy television antennas at existing
mobile base stations (hundreds, perhaps thousands, of sites) will encounter the
same challenges as experienced by mobile phone carriers-the demand for
low-profile, environmentally friendly antennas; the mandate for low emissions;
site-by-site negotiations; and the trade-off between capex and opex. It could
also promote utilization of the higher-frequency L Band and its inherently more
compact infrastructure.

Co-location interference issues also need to be considered when
overlaying mobile TV and wireless communications services. With UHF frequencies
so close to the GSM 900MHz receive band (usually 890 to 915MHz) and the CDMA
800MHz receive band (usually 824 to 849MHz), careful frequency planning and
coordination will be required. Moreover, if the broadcast signal is too high in
power, it could cause 'blocking' in the sensitive GSM or CDMA receivers,
unless RF filtering is deployed. Similar situations arise with both the L Band
and S Band frequencies, which are all in the vicinity of high-band GSM, CDMA and
UMTS services.

In addition, it is likely that all mobile TV network topologies
will ultimately need to incorporate dedicated wireless indoor solutions (WINS)
to provide coverage inside multi-level buildings, large campuses and underground
road tunnels and metro systems. These could be integrated with existing
broadband WINS systems for mobile wireless communications.

True Convergence

Clearly, for mobile TV to succeed as a commercial venture, it will involve
many players in the wireless sector: mobile phone carriers, broadcasters,
handset manufacturers, content providers, infrastructure groups, base station
OEMs, government and licensing bodies.

The quest to maximize the bottom line will ultimately reveal
which network model, technology platform and frequency band combine to form the
most viable option for a specific country or market. And it will be dependent on
which provides the most attractive and accessible model for consumer uptake.
Whatever the outcome, it will represent a true convergence of multiple
technologies. From this will materialize the true meaning of mobile TV.

Mike Dallimore

VP, Broadcast, Towers and Defence Systems, Radio Frequency Systems

maildqindia@cybermedia.co.in