Released by the DVB Project in March

and to be made publicly available in the

middle of the year, the simple goal of DVB-

T2 is to improve on a ten-year old standard

and put terrestrial broadcasters in the 21st

century. It is the second generation digital

terrestrial transmission (DTT) standard,

succeeding DVB-T, which was developed in

1995 and is used by most of the DTT

implementations around the world.

The common consensus is that mass-

market DVB-T2 products will be available

by mid-to-late 2010, although prototypes

are expected to emerge in 2009. Chip

vendors are said to be working on it

already, and simulating the options in their

programmable arrays.

The headline figure is that DVB-T2

promises at least a 30% improvement in

capacity. According to Peter MacAvock,

executive director of the DVB Project Office,

simulations have shown that up to 60%

capacity improvement is attainable, although

exact performance gains depend on the

parameters that are chosen. Significant

innovations of the new specification

compared to DVB-T include new forward

error protection, high-order modulation

modes, variable modulation and coding of

services and increase in the number of

OFDM carriers.

Principally, the increase in data

throughput is achieved by employing

enhanced forward error correction (FEC)

schemes, such as LDPC schemes, as

opposed to just BCH convolution used in

DVB-T. It is essentially the same LDPC that

DVB-S2 introduced to improve DVB-S. This

suggests around a 2dB improvement, which

can be converted to capacity either through

using less error correction or moving to a

higher order constellation, such as

256QAM (DVB-T allows up to a 64-QAM

constellation per carrier).

As Darren Fawcett, chief technologist at

Pace Micro, points out, FEC schemes

ultimately improve the robustness of the

signal, but it's down to the broadcaster how

they choose to use LDPC. "They can use it

to improve the resilience but not choose to

exercise higher order modulation. Given the

drive is to increase the efficiency and

capacity of the network, it's likely they'll

move to higher order modulation."

Significantly, there is a 32k carrier mode,

in addition to 2k and 8k for DVB-T.

According to Simon Gauntlett, technology

director of the Digital Television Group

(DTG), the benefits this option brings is the

ability to use single frequency networks

(SFN) and increased robustness to impulse

interference. "This makes the 32k mode

extremely important as part of the DVB-T2

spec. The UK could in theory be covered by

a network of 100 or so transmitters using a

single frequency and so it's potentially much

more efficient that the current network."

Despite the benefits on offer, Mike

Brooks, head of R&D at Arqiva, sounds a

note of caution. "Nothing comes for free;

you can't get something for nothing and if

we're changing parameters we need to

understand what those impacts are. There

are consequences for doing that which

mean that, in the same way as DVB-T, you

have to pick and mix from the suite of

options that will be available within the T2

spec. The big thing about the DVB

standards is that they allow flexibility - they

are a toolkit of options that enable you to

trade robustness, and hence the number of

transmitters, against the data throughput.

And that philosophy is continuing with T2."

A competitive platform?

DTT HD services are the main driver behind

the specification, and it is likely that the

transition to DVB-T2 will be linked to roll-

out of these services. This makes

commercial sense. As Mathias Leutiger,

head of product marketing of broadcasting

T&M products at Rohde & Schwarz, points

out, one of the biggest challenges for a

successful introduction of new technologies

is adding value for and being accepted by

TV viewers. "Only when they perceive a

page sixteen www.csimagazine.com Cable & Satellite International march-april 2008

Terrestrial transmission

A look inside DVB-T2The new standard will empower DTT broadcasters and help them fight back against competing platforms,but many compromises are involved, says Goran Nastic

clear advantage will viewers be willing to

accept the added expenditure."

So while DVB-T2 doesn't mandate

MPEG-4, there are good reasons for

combining the two to ease transition.

“What’s being considered for the delivery of

HDTV is an MPEG-4 box so you may as

well add DVB-T2 to make that jump as far

as possible and avoid lots of mini

switchovers. That’s why the tie between

DVB-T2 and MPEG-4 is made. It makes it

more attractive to the consumer, as you

can’t really sell technology for technology’s

sake,” says DTG’s Gauntlett.

For this reason, it is likely that all T2

boxes will be H.264 based. It’s a matter of

bundling new technologies together at a

convenient point, with a new consumer

device that has enough of a value

proposition for them to change

The question is whether DVB-T2, even

hand in hand with H.264 encoding, will be

enough to make DTT a viable competitor to

cable and satellite, particularly with just one

multiplex as proposed by Ofcom in the UK?

According to Tim Sheppard, senior

business development manager of

broadcast at Cisco, how many HD channels

are possible varies hugely by country, but a

realistic target would be at least four HD

channels in a terrestrial multiplex. Of

course, MPEG-4 encoders continue to get

better as well, he notes. “Also if you put

four into a multiplex you can take advantage

of statistical multiplexing between the

encoders, meaning that one can go as high

as five or six HD channels in a mux leading

to a position where you have as many

H.264 HD channels as you used to have in

MPEG-2 SD.”

A similar argument is made by Simon

Frost, business development director at

Tandberg. “The 30% increase in bandwidth

gives you around 30Mbps to play within an

8MHz RF channel. Taking 5-6Mbps as the

average bit rate for HD in H.264 in a

statmuxed environment by 2010, you are

looking at maybe five or six HD services in

a multiplex. For some countries, that might

be enough.

“You can also pack many more SD

channels through with T2 and H.264. If

your proposition is payTV, such as Malta,

Netherlands and Sweden, then it will

definitely be a technology that you will want

to use. For example, we see a very clear

split in the countries that want to do payTV

in terrestrial in that most are using MPEG-4

even though the STB costs are currently a

little higher. In the public service broadcast

model, which is more prevalent in DTT, the

majority are MPEG-2 and less aggressive in

the amount of channels they are trying to

pack into a multiplex. Ultimately, it is the

business model that drives the technology

choices, but MPEG-2 and MPEG-4 AVC

remain critical in terrestrial,” he adds.

In the UK, a splinter group from the DTG

proposes to use the spectrum efficiency of

SFNs, claiming Ofcom’s proposals could

seriously compromise DTT’s long term

viability They see eight HD channels as the

minimum level to keep DTT competitive,

and argue that up to 40 HD channels are

possible on DTT using this approach. In

addition, it would also free up spectrum for

other uses, such as portable TV, as can

already be found in SFN areas like Germany.

It is worth pointing out here that DVB-T2

is not exclusively about HD. The debate in

the UK is mainly HD-driven, and

significantly, that is where most of the

urgency seems to be coming from the UK.

Elsewhere, interest is in ultra mobile

(portable TV in trains, cars etc), as well as

SD capacity, according to DVB’s MacAvock.

page eighteen www.csimagazine.com

Terrestrial transmission

To MIMO or not to MIMO?Whenever a MIMO (multiple input

multiple output) approach is used, it is

reasonable to expect an improvement in

robustness and a reduction in

destructive interference in SFN.

Arqiva has, in fact, been working with

the BBC and National Grid Wireless

(NGW) on a trial in Guildford looking at

the benefits of MIMO and says there will

undoubtedly be capacity increases; in

some cases it effectively doubles the

capacity of a single channel.

The technology, however, falls foul

of one of the commercial requirements

of T2, which stipulates that the T2

broadcast will be compatible with

existing DVB-T (and by implication

analogue TV) domestic installations,

ie single antenna, single downlead.

The general consensus, driven

by the commercial module, is that

existing antenna system in peoples’

homes shouldn’t be disrupted,

and these legacy issues preclude

a MIMO type implementation.

There is an option to deal with

MISO (multiple input single output), and

there are techniques such as Alamouti

schemes which could allow that to

happen so those are incorporated,

according to Arqiva.

There is work to enable future

development of a MIMO technology to

be allowed, but MIMO will not be

incorporated from Day 1.

IPR issuesGiven the problems the DVB had with

MHP, any potential property rights

issues have to be considered upfront.

Indeed, MHP kicked off a whole

reinvestigation of DVB’s IPR policy.

As a part of the DVB-T2 work, a new

approach to the existing rules was

suggested in that an early formation of

the patent pool was being encouraged

so that any IPR issues would come to

light well in a advance of anybody

deploying a network.

The aim is to avoid licensing issues

down the line.

“Simulations have shown that up to60% capacity improvement isattainable, although exactperformance gains depend on theparameters that are chosen.”

Cable & Satellite International march-april 2008

Cable & Satellite International march-april 2008 www.csimagazine.com page nineteen

As some sort of guide to the level of

interest, MacAvock points to the fact that

while some 30 companies formed a subset

of actively involved members in DVB-S2,

this number is closer to 60 with T2, with

Russia, China, the US, and Korea to name

but a few all involved.

Although DVB-T2 does have the tools to

enable ‘mobile’ TV better than DVB-T, T2’s

commercial requirements are aimed

primarily at rooftop aerials, and the work

that supports handheld mobile phone type

TV is outside the scope of the T2 work,

according to Arqiva’s Brooks. “There is an

initiative within the DVB called Next-

Generation Handheld (NGH), which will be

looking at this aspect,” he says.

Tandberg’s Frost notes that T2 had the

option of a mobile focus, but there was

general lobby against confusing it with an

emerging DVB-H market. “Having said that,

a DVB-H and T2 mix could be interesting.”

The road to IP

DVB-T2 further cements the arrival of IP in

the broadcast industry by including GSE

(Generic Stream Encapsulation), an

evolution from the traditional method of

putting IP over the MPEG Transport Stream

(TS) over physical layer. The use of GSE -

while not mandatory - contributes to the

30%+ gain in capacity, especially when

applied to IP-based services.

“IP over MPEG TS has never been that

efficient; it’s a little clunky in terms of

encapsulation overheads. One of the

evaluation areas was to look at a native IP

transport layer that could exist inside T2, so

that you may be able to handle IP data

more efficiently and easily within the overall

transport. It may apply to even transport

layers of interactive applications perhaps

that have previously been carouselled.

There is, however, no shift in concept that

the MPEG TS is dead and everything will be

streamed in IP,” says Frost.

This brings into question whether

terrestrial broadcasting will eventually adopt

an all-IP approach that includes

transmission. Arqiva’s Brooks acknowledges

that IP does provide a common layer across

all sorts of platforms and makes distribution

and contribution circuits easier to

implement. “So I can foresee a situation

where we may see an IP infrastructure

being deployed in the future. That said, I

have not heard of any specific plans to

make everything IP-based.”

Even Sheppard’s Cisco agrees that an all-

IP approach isn’t necessary, despite some

inherent benefits. “I’m not sure it’s

necessary to remove the TS from the core

video. But you can imagine services like

push VoD and interactivity besides the core

video and audio, which would logically

make sense to go over IP because that’s

the format that’s now contributed in,

distributed in and browsed in.”

Cisco commissioned an independent

study that forecast that 65%+ of spend in

three years time on video networks will be

IP-based, and Sheppard is confident that

some of that convergence story will leak

over into the end transmission side.

DVB-T DVB-T2Error correction BCH LDPC

Modulation QPSK, 16-QAM, 64 QAM Addition of 256-QAM

FFT sizes 2k and 8k Addition of 32k mode

Physical/link MPEG- 2 TS MPEG-2 TS or IP Baseband frames

layer interface

Bandwidth 5, 6, 7, 8Mhz 5, 6, 7, 8Mhz

Multiplexing Single TS per Multiplex Potential for bonded UHF channels

Transport ~24Mbps ~32.4Mbps (44Mbps+ with MIMO)

rate/RF

Codecs MPEG-2, MPEG-4 AVC, VC-1 MPEG-2, MPEG-4 AVC, VC-1

Source: Various; CSI

Terrestrial transmission

CSI

Time frequency slicingTFS is a technique that allows services to

be spread over more than one multiplex,

maximising the benefits of statistically

multiplexing more services, a harder issue

when moving from SD to HD. As with

MIMO, the concept of TFS is extremely

compelling, but it looks like it has not made

its ways into the original specification given

its broader complexity from a chipset point

of view. The compromise decision in the

DVB-T2 committee is to have the TFS as an

optional part of the spec.

Tandberg’s Frost believes because the

availability of silicon in the tuner and the

commoditisation of the pricing are critical

factors, TFS is unlikely to feature in

commercial products, at least for the time

being. “If it hasn’t made it in as a

mandatory profile there isn’t going to be a

lot of interest in adding that.”

For Luc Ottavj, chief scientist officer and

co-founder of UDcast, typical questions to

be checked are what the exact overhead is

for TFS compared to the statmux gain, and

- due to the network plannings - how many

UHF channels having exactly the same

footprint can be TFS-grouped in a network.

These are mere semantics, however. In

reality, it requires having more than one

DVB-T2 multiplex, which doesn’t fit with the

current Ofcom proposal.

CSI understands that while a number of

companies were known to be pushing for

this technology to solve their transmitter

problem, TFS has been dropped due to the

ambitious timescale of the Ofcom proposal

and that the BBC, the standard’s champion,

feared that including this method would

delay deployment.

These developments have led to

accusations that DVB-T2 has been modified

to suit UK interests. Because parts of the

Uk are already concerned and nervous that

DVB-T2 might impact the DSO, it arguably

would have been better to implement the

technology following DSO’s completion.

With this in mind, despite its many

advancements, it is in some ways hard to

escape the conclusion that DVB-T2 could

have been much more than the sum of its

parts, at least in its first incarnation.

CSI