Thomson Broadcast

DVB-T2 solutions

Transmitter

- Elite 11/100

- Futhura

- Gapfillers / Repeaters

- Transmitter upgrade available for

Optimum, Ultimate

Exciter

- Supporting MPLP up to 64 PLP’s

- DVB-T / DVB-T2 dualcast exciter

- Full DVB-T2 code rates / IFFT

sizes

- Full Time interleaver

implementation

- T2 MI SFN

- Dual IP Gigabit pro MPEG FEC

inputs

- Low PAPR using Tone

Reservation

- Easy remote upgrade and

operation

- Full DVB-T2 control via front

panel

- DVB-T2 modes : custom settings

or V&V profile selection

- SNMP v2, HTTP control

- Adaptive non linear correction

- Adaptive linear equalization

- Embedded GPS

- High stability low phase noise

OCXO

DVB-T2 system implementation and

DVB-T2 Lite extension

Comprehensive understanding of

the DVB-T2 system

July 2014

Jérôme DAVID - Strategic Marketing Manager

Bruno Le Breton – R&D Manager

2/16

Thomson Broadcast

contribution to

DVB-T2 standard

Thomson Broadcast has a continued

involvement in DVB activities since

early 90’s. Thomson Broadcast has

contributed to DVB-T2

standardization from 2006 until now.

Thomson Broadcast longstanding

experience in RF domain and in

broadcast distribution network was

particularly involved in the process of

selecting techniques for PAPR

reduction and has chaired T2 MI

modulator interface specification

activities.

References

Key facts :

Channel robustness close to theoretical Shannon limit

Up to 50% more bandwidth than 1st generation standard

Better Transmission quality/efficiency/reliability with PAPR

Larger and better SFN capabilities with distributed MISO scheme

Mobile / fixed network capabilities with MPLP

Future proof solution with Future Extension Frame concept

Flexible Time interleaver

Robustness adjustable per PLP for one or more services

Native IP based network distribution

DVB-T2 is the world’s most advanced digital terrestrial transmission system offering highest

efficiency, robustness and flexibility. It introduces the latest modulation and coding techniques to

enable highly efficient use of valuable terrestrial spectrum for the delivery of audio, video and data

services to fixed, portable and mobile devices. These new techniques give DVB-T2 a 50% increase

in efficiency over any other DTT system in the world. DVB-T2 will coexist for some years with

DVB-T transmission.

Similarly to the first generation standard (DVB-T, ISDB-T, DAB), DVB-T2 uses OFDM

(Orthogonal Frequency Division Multiplex) modulation, with a large number of sub- carriers

delivering a robust signal, the new specification offers a range of different modes making it a very

flexible standard.

DVB-T2 uses the LDPC (Low Density Parity Check) codes offering excellent performance in the

presence of high noise levels and interference.

Transmission quality and reliability is improved by the introduction of advanced clipping

functions, named PAPR techniques.

Service Specific coding based on Multi-PLP (Physical Layer Pipes) mechanism is provided

to separately adjust the robustness of each delivered service within a channel to meet the required

reception conditions for mobile, indoor and fixed reception in the same channel

Transmission diversity method, known as Alamouti coding, extends the coverage in small-scale

single-frequency networks.

Finally, DVB-T2 group has defined a method called FEF (Future Extension Frame) which can be

implemented over an existing DVB-T2 network. DVB-T2 offers a higher data rate, more robust

signal, flexibility and scalability than any other existing transmission standard. For example, in the

UK a DVB-T channel typically has a data rate of 24 MBit/s, whereas a DVB-T2 channel can carry

36 MBit/s, while keeping the robustness equal.

Air Interface

Specification

Network distribution

Specification

DVB blue Book

Implementation

Guidelines

EN302755

TS102773

DVB A133

TS102831

3/16

Thomson Broadcast

DVB-T2 highlights

DVB-T2 standard is built upon

more than 30 building blocks. All of

these are extensively simulated and

tested against reference golden

streams issued by V&V (Validation

and Verification) standardization

group.

DVB-T2 Key Concepts

A complex standard?

At a first glance, DVB-T2 is a complex standard. It is made of a lot of new building blocks and all

of them must be carefully adjusted. These new advanced signal processing techniques such as

rotated constellation, ACE (Active Constellation Extension) and TR (Tone Reservation) PAPR

reduction techniques, MISO (Multiple Inputs Single Output), Flexible time interleaver, FEF,

scalable frame structure are good examples of how to bring added value to a broadcast technology.

…4 main guidelines for a comprehensive

understanding of DVB-T2 possibilities

Capacity increase, Flexible system design, Efficiency improvements and Mobility have driven

DVB partners in DVB-T2 standardization process.

4/16

Thomson Broadcast

DVB-T2 highlights

Thomson DVB-T2 exciter

implements All SPLP modes basic

parameter configuration:

- All IFFT sizes

- All guard intervals

- All constellation

- All LDPC code rates and code

types

- All time interleaver modes

support: I-JUMP, Static,

Dynamic, FEF

Thomson Broadcast Man Machine

interface is designed to be intuitive.

Thanks to its front panel, user can

select DVB-T2 transmission

parameter directly using the front

panel. Configuration is easy based on

preset modes taken from settings used

in V&V validation group. Automatic

parameter check forbids any

unauthorized configuration. Exciter

provides 3 different network type

configuration: MFN-TS is dedicated

to MPEG TS legacy network, MFN-

T2 MI is used for MPLP via a gateway

and SFN T2 MI is used for SFN

operations.

Capacity increase

In DVB-T2, benefiting from higher modulation order (256QAM) and more efficient DVB-S2,

LDPC FEC, up to 50% capacity gain is achieved compared to DVB-T performances

Figure 1: 256 QAM modulation

Figure 2: baseband frame

Beyond a simple constellation change, the number of pilots used to perform channel

equalization can be adjusted allowing further bitrates optimization. User can expect up to 8%

gain.

Pilot ratio DVB-T DVB-T2

Continual pilot 8.5% 4%

Higher FFT size means shorter guard interval ratio for a given SFN cell network.

Guard interval

duration DVB-T 8K DVB-T2

with 32K

224 us 25% 6,25%

112 us 12.5% 3,12%

Bandwidth extension: Less guard band carriers are used enabling a +2.6% bitrate gain

Figure 3: Bandwidth extension

5/16

Thomson Broadcast

DVB-T2 highlights

PAPR support

Thomson Broadcast exciter

implements PAPR natively improving

Quality / Efficiency / Lifecycle of the

transmission network. For instance,

efficiency is improved by more than

1% and power gain is above 0.4dB.

ACE techniques can be used in other

standards since Thomson Broadcast

proposed this PAPR technique in

order to be backward compatible

with others systems such as DVB-T or

DAB.

While Tone Reservation is highly

efficient for higher order QAM

constellations, ACE is particularly

efficient for low order constellation

such as QPSK or 16QAM modulation

schemes. It makes ACE a good

solution for reducing PAPR in

existing mobile networks relying on

QPSK or 16QAM modulation

scheme.

Beyond PAPR technique power

gain, when using either PAPR

Tone Reservation or Active

Constellation Extension, transistor

lifecycle is dramatically improved by

reducing transistor ageing effect

Efficiency increase with Tone reservation or ACE

Lower PAPR achieved with tone reservation or Active Constellation Extension. The goal

of these techniques is to achieve better RF performances and increase overall efficiency of the

RF power amplifiers. With this technique, the purpose is to achieve Peak to Average Power

Ratio below 10dB

Figure 4: PAPR reduction

More efficient SFN networks with distributed MISO

Flexible and robust system based on innovative frame structure

New T2 frame structure: A T2 frame is based on P1 preamble, P2 preambles followed by data

symbols. P1 preamble is used for fast parameters detection and raw equalization while P2

preamble symbols are used to discover the subsequent T2 frame parameters.

Figure 5: Frame structure

T2 frame is based on the same DVB-T frames using guard interval OFDM data symbols

Figure 6: Guard interval

MPLP mode offers a Service specific robustness while SPLP mode can be used in existing

distribution network based on MPEG2-TS

Time interleaver combined with Cell interleaver can be adjusted for each PLP and the depth

of the interleaver can be adjusted on 1 or several consecutive frames. This makes time

interleaver really robust against impulse noise.

Rotated constellation combined with cell interleaver improves signal robustness in corner

reception scenarios by de-correlating I & Q components of regular grey mapping scheme.

Figure 7: Rotated constellation

6/16

Thomson Broadcast

DVB-T2 highlights

The design of the Thomson Broadcast

exciter has taken into account from the

beginning the need of resources for

the evolution of the DVB-T2 standard.

T2-Lite is a software evolution

compatible with the existing hardware

T2-Lite

The mobile configuration of the DVB-T2 standard, also called T2-Lite, uses a limited number of

available modes which are optimized for mobile transmission and minimize the requirements for

the receiver.

Maximum bitrate of 4 Mb/s per PLP

Limitation of the FFT size to exclude 1K and 32K carriers mode

Allows only short FEC frames (Nldpc = 16200)

Limitation of the size of the time interleaver memory to approximately half the size of

normal DVB-T2 transmission

Reduces set of combinations of FFT size, guard interval and pilot pattern. PP8 pilot pattern is

not allowed

Prohibition of the use of rotated constellations in 256-QAM and addition of two new more

robust code rates (1/3 and 2/5),

Code rate Modulation

QPSK 16 QAM 64 QAM 256 QAM

1/3 X

2/5 X

1/2 X

3/5 X

2/3 NA

3/4 NA

: Combination authorised

X : Combination authorised but without rotated constellation

NA : Not authorised

The mobile services may be transmitted as a stand-alone signal but may also be transmitted on the

same radio frequency channel with other DVB-T2 services. This can be achieved thanks to the

Future Extension Frame (FEF) feature of the standard. In this case, the mobile transmission will be

ignored by normal DVB-T2 receiver and the standard DVB-T2 transmission, also called T2-base,

is ignored by the mobile receiver

Figure 8: Example of composite T2-base and T2-Lite signal

7/16

The following table provides an overview of the comparison of the main characteristics of the

different standards:

DVB-T2 DVB T2-Lite DVB-T/H

FEC LDPC + BCH LDPC + BCH CC + RS

Code rate 1/2, 3/5, 2/3, 3/4, 4/5, 5/6 1/3, 2/5, 1/2, 3/5,

2/3, 3/4 1/2, 2/3, 3/4, 5/6, 7/8

Constellation QPSK, 16QAM,

64QAM, 256QAM

QPSK, 16QAM,

64QAM, 256QAM

QPSK, 16QAM,

64QAM

Guard Interval 1/128, 1/32, 1/16,

19/256, 1/8, 19/128, 1/4

1/128, 1/32, 1/16,

19/256, 1/8, 19/128,

1/4

1/32, 1/16, 1/8, 1/4

FFT size

1K, 2K, 4K, 8K, 8K ext.,

16K, 16K ext., 32K, 32K

ext.

2K, 4K, 8K, 8K ext.,

16K, 16K ext. 2K, 4K, 8K

Scattered pilots 1%, 2%, 4%, 8% of total 1%, 2%, 4%, 8% of

total 8% of total

Continual pilots 0,35% of total 0,35% of total 2,6% of total

RF Bandwidth 1.7, 5, 6, 7, 8, 10 MHz 1.7, 5, 6, 7, 8, 10

MHz 5, 6, 7, 8 MHz

Max. TS Bandwidth 50 Mb/s 36,37 Mb/s 32 Mb/s

Typical TS

Bandwidth

(8MHz channel

raster)

40 Mb/s (MFN)

33 Mb/s (SFN)

26 Mb/s (Mobile / fixed /

portable)

20 Mb/s (Mobile /

fixed / portable)

24 Mb/s (Fixed)

10 Mb/s (Mobile)

And the following figure reminds the DVB-T2 version history

Figure 9: Version history

8/16

Thomson Broadcast

DVB-T2 highlights

Unique PLP solution

Thomson Broadcast is going beyond

common implementation by

providing up to 64 PLP in parallel

where 16 PLP is currently state of the

art. This allows unequalled flexibility

in tailoring different services for an

existing network.

For instance, you could provide in a

single channel 16 mobile services

requiring up to 10Mb/s and allowing

3 to 4 HD services in the same

broadcast channel.

Moreover PLP management in

Thomson exciter is dynamic so

it allows live reconfiguration. This is

supporting future statistical PLP

management in order to optimize

robustness in the channel.

DVB-T2 introduction scenarios DVB-T2 application is primarily dedicated to fixed HD /3D terrestrial networks over existing

DVB-T networks but it contains everything

DVB-T2 and multi services

The Multiple Physical Layer Pipes (MPLP) concept gives the possibility to have specific robustness

for different services on a single DVB-T2 channel. Each PLP may have its own modulation, code

rate and interleaving. This offers the opportunity, for example, to broadcast on an unique channel

HD services with high bit rate dedicated for fixed reception, SD services with lower bit rate for

indoor reception, and radio or mobile TV services with very low bit rate.

DVB-T2 and T2-Lite application

Using MPLP to broadcast services dedicated to fixed reception and to mobile in the same T2

multiplex is limited by the fact that the FFT mode and the pilot pattern cannot be adjusted during

the same T2 signal. Fixed reception services is transmitted with large FFTs and sparse pilot patterns

to optimize the bit rate. On the other hand, reception in mobile scenarios requires the utilization of

smaller FFTs and more dense pilot patterns to follow the rapid variations in the time and frequency

domain. T2-Lite standard gives a solution for this problem, with the possibility to transmit the

signal in the FEF parts. In this manner, the FFT, guard interval and pilot patterns are optimized for

mobile reception using the T2-Lite signal, and in the same time, these parameters are optimized for

fixed reception using the T2-base signal.

Of course, the T2-Lite signal can be used as a stand-alone signal which occupies the full frequency

channel.

DVB-T2 and new services

About the content aspect, DVB-T2 will be introduced for new services such as HD and

Ultra-HD programs. Ultra-HD debate is not yet over but we can expect that higher bandwidth will

be required to broadcast Ultra-HD services even for frame compatible format. DVB-T2 is designed

to carry HD/ Ultra-HD services and offer the best signal efficiency (5.6bit/Hz in UK) even more

with SFN diversity transmission (MISO). In order to deploy 3D content efficiently, it is necessary

to work with DVB Ultra-HD TV specification where Ultra-HD TV program and 2D services can

share the same broadcast channel at different time of the day. In this case, Ultra-HD TV set must

be capable to switch between 2D and Ultra-HD application. Ultra-HD TV specification defines

some scenario and signalization over the MPEG to allow flexible Ultra-HD transport. For instance,

Ultra-HD side by side requires broadcasting a full HD definition service with a minimum rate of

8Mb/s. In the UK, this will lead up to 4-5 Ultra-HD services or full HD services.

Moving DVB-T to DVB-T2 – Dual Cast Concept

Where legacy DVB-T transmission exists, it is easy to introduce DVB-T2 for new services. Current

DVB-T2 set-top boxes are also able to perform DVB-T modulation enabling a smooth transition to

new services over a network. A user purchasing a DVB-T2 set top box or TV set can also watch

legacy DVB-T transmissions. On the network side, the transition from a DVB-T channel to DVB-

T2 is simplified when dual cast operation is available in the exciter because network operator only

has to manage a single network instead of managing 2 different networks. DVB-T and DVB-

T2 spectrum characteristics are closed because they share the same channel raster and both of them

are based on OFDM transmission with guard intervals.

9/16

When system is transitioned to DVB-T2 and PAPR is implemented, it is possible to increase the

coverage by 0.4dB compared to the same DVB-T coverage for the same performance (MER =

34dB at transmitter output). Combined with signal compression improvement, it is possible to move

MPEG2 services to MPEG4 and bundle them in new multiplexes. This can free up new frequencies

to deploy new services as VOD or 3D services.

10/16

Thomson Broadcast

DVB-T2 highlights

Thomson DVB-T2 exciter

implements IP interface using pro

MPE FEC. When used additional

large buffers are used to ensure a

robust IP interface.

How is DVB-T2 implemented? Broadcasters can easily get started with a DVB-T2 transmission. DVB-T2 can be initially

implemented on a primary DTV transmitter, leveraging existing capital expenditures on the RF

transmitter, f i l ter ing, t ransmiss ion l ine , and broadcast antenna. In MFN network,

DVB-T2 Thomson Broadcast transmitters can be operated with the existing MPEG distribution

network over ASI or Gigabit Ethernet using the SMPTE2022-1 pro MPEG FEC standard. When

T2 network is operated in SFN network or if service protected MPLP variable is used, it is

necessary to use T2MI interface to send video streams to the transmitter. In this situation, a T2 MI

(Modulator Interface gateway is needed at the head-end to parse signals into T2-MI packets. A

field-proven transmitter must be tested with several Gateway manufacturers and solution must be

highly robust to any kind of jitter (packet jitter or time source jitter) as very large hardware buffers

size are available in the exciter to process IP input or MPEG-2 TS.

Figure 10: DVB-T2 transmission chain example co-existing with DVB-T distribution network

11/16

Thomson Broadcast

DVB-T2 highlights

Thomson Broadcast played an active

role in the definition of the T2-MI

(Modulator Interface).

T2 Modulator Interface standard is

part of DVB-T2 validation and

verification group.

The standard describing DVB-T2

Modulator Interface is labeled TS

102773

How is SFN implemented? T2 SFN networks setup are similar to SFN DVB-T networks but they require a T2-MI gateway

and time reference equipments. All networks implementing SFN or / and MPLP must follow the

T2-MI stack protocol.

Figure 11: T2 Modulator Interface protocol stack

T2 Modulator protocol stack is relying on existing and proved MPEG-2 TS and MPEG2-GSE.

MPEG-2 GSE is a generic purpose encapsulation protocol dedicated to efficient IP distribution of

video services to the T2-MI gateway. The output interface of the gateway to the distribution

network is either IP encapsulated or directly in ASI format.

12/16

Thomson Broadcast

DVB-T2 highlights

Thomson DVB-T2 exciter

interoperability has been verified by

BBC R&D.

Beyond V&V verification and

validation, Thomson Broadcast

contributes to European Celtic

Engines project and is leading DVB-

T2 SFN interoperability activities

inside this project.

Thomson Exciter implements SFN

test modes easing interoperability

verification between exciters

DVB-T2 offers more scalability than a DVB-T network. It offers larger guard intervals. Same

infrastructure basis than a legacy network can be re-used provided that equipments in the legacy

distribution network are transparent to the transport stream. However it requires a gateway to

perform timestamp insertion and Physical Layer Pipe multiplexing.

Figure 12: DVB-T2 transmitter setup dedicated to SFN

Setting up a DVB-T2 SFN network requires different stages:

Modulator interoperability verification, especially when different modulator brands are used

Modulator – gateway system interoperability

Program Feed Transparency: bit-synchronous requirement for SFNs means that program feeds

have to pass transport streams transparently, without any modification to packet order.

Bit rate jitter must remain low. Large Bit rate jitter from distribution network may cause SFN

disruption.

Distribution

Network

Bit rate Jitter Network Delay

Sat. DVB-S/S2

+/- 200ns

250 ms

Off Air +/-750ns 30 ms / hop

ATM over SDH Up to 200 ns Depending on the

size of the network

MPEG over IP +/-20ms 30ms / switch

Figure 13: Typical delays experienced in SFN distribution

13/16

Installing a DVB-T2 SFN network requires having specific SFN test modes to verify timing

adjustment between transmitters. Once done, a transmitter in a SFN network can be modeled

using a triplet (P: power, d: delay, f: frequency). It is important to determine where the 0delay

area i s f a l l i n g . In the following example, we can observe that the 0delay area is

falling concomitantly to a 0dB echo area. This will result in destructive interference in the 0delay

area.

Figure 14: Example of destructive interference situation in a DVB-T2 SFN

One solution is to change the delay of one transmitter to make sure that this situation will not

occur.

Figure 15: Non destructive “0delay” situation in a DVB-T2 SFN

Once the SFN network is setup, main issues come from the timing drift or disruption in the GPS

signal reception or in transport stream. In SFN networks, transmitters must be carefully monitored

and it is important that the exciter has embedded capabilities to detect such events separately in

order to take the proper preventive or corrective action. Furthermore, on main strategic sites, it is

desirable that the transmitter offers at operator wish permanent transmission in case of time

reference loss or perturbation of the distribution network.

14/16

How is T2-Lite implemented? T2-Lite signal can be used as a stand-alone signal. In this case, the implementation is the same

that for other DVB-T2 transmission. But T2-Lite signal can also share a unique channel with a

T2-Base signal. In this case, there are two possibility for the network configuration.

The first solution consists to separate the distribution of the T2-Base and T2-Lite signals.

Even if this solution could be useful for preliminary laboratory tests or pilot networks, it is not

optimized for network implementation and maintenance:

Two gateways are used. They need to be set-up simultaneously and the time synchronization

between them is critical.

As two different streams are necessary for T2-Base and T2-Lite signals, four inputs are

mandatory at the exciter level to offer input redundancy

The recommended operational configuration is the following:

In this case, only one gateway manages the T2-Base and T2-Lite signals and a single T2MI stream

is sent to the transmitter.

15/16

The MISO concept Interest of MISO (Multiple Inputs Single Output)

In this mode, DVB-T2 is broadcasted on 2 different antennas. Hence, DVB-T2 signal is split in

main and complimentary components feeding the antennas. Main advantage is that the receiver

will benefit from an increased C/N if the receiver is able to see both signals. If the receiver is not

able to see one of the 2 signals, its performance remain equal to SISO (Single Input Single Output

antenna).

Figure 16: MISO co-sited

For instance, current DVB-T2 UK transmission is based on a LDPC code rate of 2/3. With MISO,

it might be possible to use LDPC code rate 3/4 leading to a bit rate gain of 5 Mb/s.

Figure 17: Performance Gain

16/16

Network Constraint and distributed MISO

If both transmissions were to be co-sited, the cost would be prohibitive from the network

operator point of view. That is the reason to introduce distributed MISO where complimentary

signals are sent from two different existing nearby sites. In this situation, the C/N gain can be up to

3dB and be converted into higher bitrates.

Figure 18: MISO in Distributed transmission