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DIGITAL VIDEO BROADCASTING -

SECOND GENERATION

TERRESTRIAL

By Susmita Pandey

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CONTENTS Dvb.

Dvb –t2 history.

Dvb-t2 modulator.

Architecture model.

Key technologies.

Comparison.

Conclusion.

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DVB

Include DVB-S, DVB-S2, DVB-C, DVB-T and DVB-T 2.

DVB-T stands for Digital Video Broadcasting – Terrestrial.

These standards define the physical layer and data link layer of the distribution system.

Transmits a compressed digital audio/video stream,

using OFDM modulation with concatenated channel coding .

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DVB-T2 HISTORY The first country that deployed DVB-T2 is the

UK, launched in March 2010.

Launched in Italy, Sweden, and Finland in 2010 and 2011.

Outside of Europe DVB-T2 pay-TV services were launched in Zambia, Nigeria, Kenya.

Trials are currently taking place across the globe, it is thought to be installed in India by 2014.

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DVB-T2 MODULATOR

Inputpreprocessor(

s)

Inputprocessing

Bit interleavedcoding &

modulation

Framebuilder

COFDMgeneration

MultipleTS or GSstreams

Up to 255 input streams

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ARCHITECTURAL MODEL

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PHYSICAL LAYER PIPES (PLPS)

Enable the transport of data independent of its structure.

Both the allocated capacity and the robustness can be adjusted.

Two general modes are defined.

Fig. Different PLP's occupying different time slices

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INPUT MODE A

Most simple mode can be viewed as a straightforward extension of DVB-T.

Not sub-divided into multiple PLPs.

Only a single PLP is used, transporting a single transport stream.

The same robustness is applicable to all content.

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INPUT MODE B

This more advanced mode of operation applies the concept of multiple physical-layer pipes.

Service -specific robustness. Offers potentially longer time-interleaving depth

as well as the option of power saving in the receiver.

Fig. T2- frame for single RF channel, multiple PLP mode (here: 5 PLPs)

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PREAMBLES (P1 AND P2)

The initial symbols of a DVB-T2 physical-layer frame are preamble symbols.

The frame starts with the highly robust differentially BPSK-modulated P1 symbol, with guard intervals at both ends.

P2 symbols provide all static, configurable and dynamic layer-1 signalling.

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INTERLEAVING STAGES

Bit interleaver after FEC based on a LDPC word.

Cell interleaver after mapping based on a FEC frame.

Time interleaver after cell interleaver based on a TI frame.

Frequency interleaver before IFFT based on a symbol

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INTERLEAVER IN DVB-T2

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TASK OF INTERLEAVERS

Bit interleaver interleaves code bits in a LDPC word.

Cell interleaver interleaves mapped I Q values in a FEC frame.

Time interleaver is a protection against long impulsive interferers.

Frequency interleaver is a protection against frequency selective interferers (e.g. notches).

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TRANSMISSIONS IN A T2-SYSTEM

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RECEIVER MODEL

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FRAME STRUCTURE OF DVB-T2

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SUPERFRAME

Largest entity of a DVB-T2 system.

Carries T2-frames and may also carry Future-Extension Frame (FEF).

The maximum number of T2-frames in a super frame is 255.

The maximum length of a T2-frame is 250 ms and the maximum length of a FEF part is 250 ms.

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T2-FRAME

T2-frame consists of a P1 symbol and a configurable number of data symbols.

Fig. Structure of the T2-frame

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COMPARISON

DVB-T DVB-T2

Input interfaceTransport stream

Transport and generic stream

Modulation 64-QAM 256-QAMFFT size 8 K 32 KGuard Interval 1/4 1/16FEC CC + RS LDPC + BCHCarrier mode Standard ExtendedCapacity 19 Mbit/s 33 Mbit/s

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CONCLUSION

The availability of the DVB-T2 standard brings new opportunities for the terrestrial television delivery platform.

Broadcasters consider offering new services on the DTT platform which would have been difficult given the limited frequency capacity available in the VHF and UHF frequency bands.

It can be expected that the DVB-T2 standard will be relevant for many years into the future.

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THANK YOU

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