1 Digital Video Broadcasting An Overview Prof. Dr. Mehmet Şafak Hacettepe University Dept. of...

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Digital Video BroadcastingAn Overview

Prof. Dr. Mehmet Şafak Hacettepe University

Dept. of Electrical and Electronics Engineering06800 Beytepe, Ankara, Turkey

[email protected]

14 July 2006 DVB - An Overview 2

Digital TV

How come a man can be so sensitive as to distinguish between resolutions 1024 x 678 and 1365 x 768, but can not see the difference between 15 totally different woman shoes ?

I could see the difference if they were on the TV


Outline

• Vision• Data Broadcasting• Integrated Receiver Decoders (IRD)• Transmission on Cable, Satellite and Terrestrially• Interaction Channels• The Multimedia Home Platform (MHP)• DVB-Handheld• Hybrid Networks• Prospects for Future Developments


Vision

• Initially, DVB concentrated on broadcasting of audio and video services.

• In later phases, DVB addressed areas which lie outside of the classical broadcast world.

• Vision defined in 2000:– DVB’s vision is to build a content environment that

combines the stability and interoperability of the world of broadcast with the vigor, innovation, and multiplicity of services of the world of the Internet

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Data Broadcasting


Data Broadcasting

• A 4:2:2 picture requires a raw transmission rate of 13.5 Msamples/s x 16 bits/sample =216 Mbps.

• The 216 Mbps just to transmit one digital TV channel is very high, so the need for compression is obvious.

• Using compression techniques, the data rates on the order of 3.2 Mbps per TV channel are currently used.


Data Broadcasting

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Data Broadcasting

• For real-time HDTV encoders, the rate of improvement in practice has been significantly less than for SDTV:– smaller number of channels per multiplex means that the

introduction of statistical multiplexing techniques did not yield as much of a benefit for HDTV as it did for SDTV.

– Today’s real-time HDTV encoders for H.264/AVC or VC-1 do not yet fully exercise all of the additional tools in the new algorithms, such as variable block sizes

• Within a year, 8-10 Mbps is expected to be sufficient for the transmission of HDTV signals.


Data Broadcasting

Components inside the DVB data containerU. Reimers, DVB-the family of international standards for DVB, Proc. IEEE, vol.94, no.1, pp.173-181, Jan. 2006


Data Broadcasting

• The output of the MPEG-2 multiplexer (transport stream) consists of 188-byte packets, where different video, audio and data channels are multiplexed.

• Depending on the usable data rate of the broadcast channel, the size of the container varies.

• The program specific information (PSI) provides a list of packet ID (PID) values of the corresponding program numbers.

• The service information (SI) contains the modulation parameters, translates program numbers into service names and electronic program guide.


Data Broadcasting

• Data services can be – program related (e.g., teletext), or – independent of any other service in the multiplex

(e.g., software download, MHP applications, information services).

• DVB data broadcasting offers fast Internet access via satellites.– Users may be connected to the Internet via standard

modems and in addition install a satellite receiver card into their PCs for broadband downstream.

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Integrated Receiver Decoders (IRD)



• SDTV or HDTV• Baseline IRD or IRD with digital interface

– whether or not they are intended for use with a digital bitstream storage device such as a digital VCR

• Video coding formats: – MPEG-2 video or MPEG-4 AVC (H.264)

• Audio coding formats: – Dolby AC-3, DTS and MPEG-4 AVC (H.264)



• Reception of DVB services delivered over IP-based networks

• DVB-TXT replaces Teletext – which is transported during the period of the vertical

blanking interval (VBI) of analog television.• DVB developed a generic means for the delivery

of all VBI data, e.g., – to enable the control of video recorders,– the signaling of wide screen programs.



• As part of DVB signals, it is possible – to provide a translation of original soundtrack in the

form of subtitles– add graphic elements to the transmitted images, e.g.,

station logos.• TV-Anytime information in DVB transport streams

– help personal digital recorders (PDR) to search, select and acquire the content, the viewer wishes to record.

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Transmission on Cable, Satellite and Terrestrially


Transmission

Block diagram of the DVB-T encoder(Blue blocks are used in DVB-C and DVB-S as well)

U. Reimers, Digital Video Broadcasting, IEEE Comm. Mag., pp.104-110, June 1998


Transmission• DVB-S

– Published in 1993 – Modulation: QPSK and BPSK– Convolutional codes concatenated with RS codes

• DVB-S2 – Published in 2003– Modulation: QPSK, 8-PSK (broadcast applications), 16-

APSK and 32-APSK (professional applications)– Backward-compatibity with existing DVB-S receivers – Reasonable receiver complexity – Interactivity (i.e., Internet access)– Professional services, such as digital satellite news gathering


Transmission

• DVB-S2– Best transmission performance

• LDPC codes concatenated with BCH codes• Variable and adaptive coding and modulation (recovers rain margin)• Approximately 30 % capacity increase compared to DVB-S

– Maximum flexibility• framing structure • variable and adaptive coding and modulation• can operate in any existing satellite transponder• accommodates any input stream format (188-byte MPEG-2 transport

streams (packets), continuous bit streams, IP, ATM)


Transmission

Performance of LDPC codes over AWGN channel (N=64800)


Transmission

Comparison of DVB-S2 (LDPC+ BCH) codes to DVB-S (convolutional+ RS) and channel capacity

M. Eröz et al., An innovative LDPC code design with near-Shannon-limit performance and simple implementation, IEEE Trans. Communications, vol.54, no.1, pp.13-17, January 2006.


Transmission

• For each code rate, a parity-check matrix is specified by listing adjacent check nodes for the first bit node in a group of M=360.

• Irregular LDPC codes are used, where degrees of bit nodes are varying.

• DVB-S2 offers more than 30% capacity improvement• DVB-S2 is, on average, about only 0.7-0.8 dB away

from Shannon limits.


Transmission

• DVB-C– Published in 1994– Modulation: M-QAM with M=16, 32, 64,128 or 256. – Only RS coding is used (no convolutional coding).

• DVB-H – Published in November 2004 – Enables the reception of digital TV signals by

handheld devices– Additional FEC, in-depth interleaving and time slicing


Transmission

• DVB-T, published in 1997, uses OFDM transmissions– OFDM has 2K (subcarriers), 4K and 8K versions– OFDM allows single-frequency network (SFN) operation– Modulation: QPSK, 16-QAM or 64-QAM.– Hierarchical modulation: High and low priority streams are modulated onto

a single DVB-T stream for SDTV and HDTV• Reception by roof-top antenna, portable and mobile reception• DVB-T is adopted in large parts of the world with

– built-in front-ends set-top-boxes– PCI cards and USB boxes for desk-top PCs– PCMCIA modules for lap-top PCs– DVB-T reception in cars in driving speeds


SFN Range vs Mobility Trade-off

• OFDM with 2K:– widest subcarrier spacing, hence least susceptible against

Doppler shifts (suitable for high-mobility applications)– shortest symbol duration, hence provides the minimum range

for SFN.• OFDM with 8K:

– narrowest subcarrier spacing, hence most susceptible against Doppler shifts (suitable for low-mobility applications)

– longest symbol duration, hence provides the maximum range for SFN.

• OFDM with 4K provides a trade-off between 2K and 8K


Hierarchical Modulation

• Two separate data streams modulated onto a single DVB-T stream, – high-priority (HP) (low data rate) stream is

embedded within a low-priority (LP) (high data rate) stream

• Receivers with good reception conditions can receive both streams

• Only HP streams are received in bad channel conditions, e.g., mobile and portable reception



An example of a constellation diagram for hierarchical modulation

HP bit stream (QPSK)

LP bit stream (64-QAM)



• Broadcasters can target two different types of DVB-T receiver with two completely different (LP or HP) services– LP stream is of higher bit rate, but lower robustness

than the HP one;• hence, a trade-off between service bit-rate versus signal

robustness

• A broadcast could choose to deliver HDTV in the LP stream.


Transmission

Choice of parameters for non-hierarchical DVB-T transmissionU. Ladebusch and C.A. Liss, Terrestrial DVB, Proc. IEEE, vol.94, no.1, pp. 183-193, Jan 2006


Transmission

• Useful bit rate (Mbit/s) for all combinations of guard interval, constellation and code rate for non-hierarchical systems for 8 MHz channels (irrespective of the transmission modes)


Transmission

• For the hierarchical schemes the useful bit rates can be obtained from the table as follows:– HP stream: figures from QPSK columns;– LP stream, 16-QAM: figures from QPSK columns;– LP stream, 64-QAM: figures from 16-QAM columns.


Transmission

Minimum C/N ratio in the transmission channel required for quasi-error-free (QEF) reception for DVB-T

• QEF reception: BER <10-11 at the output of the RS decoder

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Interaction Channels



• The data belonging to a certain interactive service is transmitted in the broadcast channel

• The interaction channel enables the user to respond in some way (for instance via the standard remote control ) to the interactive service.

• The service provider or network operator listens and reacts to that response.



Generic system reference model used by DVB for interactive servicesU. Reimers, DVB-the family of international standards for DVB, Proc. IEEE, vol.94, no.1, pp.173-181, Jan. 2006



• The user’s response may take the form of some simple commands, like – voting in a game show,– purchasing goods advertised in a shopping program.

• Interactive services may take the form of full Internet access at the receiver.



• DVB broadcast channels can deliver information at typical rates of – 20 Mbps per channel for terrestrial broadcast

networks, – 38 Mbps per channel for broadcast networks via

satellite and cable.• Capacity of interaction channel may range from

a few kbps to up to 10 Mbps in cable networks.



• Return Channel Terrestrial (RCT):– Multiple access: OFDMA– Coding: Turbo or RS+ convolutional– Several kbps per TV viewer in cells with 65 km radius– Can handle large peaks in traffic– Use any gaps or under-utilised spectrum– Serve portable and mobile devices– Can operate in 6, 7 and 8 MHz channels– Transmit power < 0.5 W rms– Time interleaving against impulsive interference



Simplified diagram of a network architecture for DVB return channel satellite systems (RCS)

V. Paxal, DVB with return channel via satellite, DVB-RCS200, www.dvb.org

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The Multimedia Home Platform (MHP)


The Multimedia Home Platform

• The MHP specification defines an interface between a digital TV and the network to be connected to in order to support interactive services.

• It provides features and functions required for the – Enhanced Broadcast, – Interactive Broadcast, – Internet Access.

• The right to use the MHP logo is only granted to those MHP implementations that pass some 10000 tests, defined by ETSI.



• MHP offers true multimedia services to TV users.

• MHP provides a technical solution for the user terminal enabling the reception and presentation of applications in an environment that is – independent of specific equipment vendors, – application authors, – broadcast service providers.



• Some examples:– Electronic program guides for the channels/services

provided by a broadcaster– Information services (superteletex, news tickers,

stock tickers)– Enhancements to TV content (sporting and voting

applications and local play-along games)– E-commerce, e-government and other applications

relying upon secure transactions– Educational applications

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DVB over IP-based Networks



• A typical IPTV service involves the delivery of broadcast television, radio and similar on-demand services over IP networks,– hence, a bi-directional IP communication.

• An open IP infrastructure is used to reach the customers that can not be reached via classical broadcast networks.– Thus, the geographical reach of DVB services can be

extended using broad-band IP networks.



Basic IPTV architecturewww.dvb.org



• The work on IPTV can be divided into three areas:– Set-top boxes and personal video recorders (PVR),– Home networking,– Additions to the Multimedia Home Platforms (MHP).

• A specification has been developed that describes the transport of MPEG-2 based DVB services over IP-based networks.

• Creation of a wireless home network segment is soon expected.

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DVB-Handheld


DVB-Handheld

• The system takes into account the specific properties of typical DVB-H terminals:– Battery-powered– User mobility – Handover between cells– Mobile multipath channels (antenna diversity)– High levels of man-made noise– Indoor and outdoor operation– Flexibility to operate in various transmission bands and

channel bandwidths (to operate in various parts of the world)


DVB-Handheld

• DVB-H requires some additional features in the link layer of the existing DVB-T standard;– Existing receivers for DVB-T are not disturbed by

DVB-H signals• The additional elements in the link layer:

– Time slicing• to reduce the average power in the receiver front-end

significantly (significant power savings in the receiver)• to enable smooth and wireless handover when the users

leave one service area as they enter a new cell


DVB-Handheld

The capacity of one DVB-T channel is split between three TV programs and an additional eight DVB-H services

Slice duration: 625 ms

Bit rate:3.2 Mbps

(=2 Mb/625 ms)Average bir rate:0.4 Mbps(=3.2/8)

625 ms

U. Reimers, DVB-the family of international standards for DVB, Proc. IEEE, vol.94, no.1, pp.173-181, Jan. 2006


DVB-Handheld

– Additional forward error correction (FEC) gives an improvement in

• carrier-to-noise (C/N) performance• Doppler performance in mobile channels• tolerance to impulsive interference

– e.g., ignition noise in cars.

– In view of the restricted data rates and small displays of handheld terminals, it is suggested to exchange MPEG-2 video by H.264/AVC.


DVB-Handheld

• The extensions to the physical layer of DVB-T:– Bits in transmitter parameter signaling (TPS) are upgraded to

indicate the presence of DVB-H service– A new 4K OFDM mode adopted for trading off mobility and

single-frequency network (SFN) size• All modulation formats (QPSK, 16QAM and 64QAM) with

nonhierarchical or hierarchical modes can be used

– A new way of using the symbol interleaver of DVB-T has been defined (to provide tolerance against impulsive noise)

– The addition to DVB-T physical layer of a 5-MHz channel bandwidth to be used in non-broadcast bands.


DVB-Handheld

• DVB-H is intended to use the same broadcasting spectrum, which DVB-T is currently using.

• DVB-H services can be introduced – in a dedicated DVB-H network

• now it is possible to select 4K mode or in-depth interleavers

– by sharing an existing DVB-T multiplex between DVB-H and DVB-T services

– by using the high-priority part of the DVB-T hierarchical modulation


DVB-Handheld

• Possible applications for DVB-H:– IP datacasting service to handheld terminals like mobile

phones– Broadcast services for the mobile phone users

• frequency allocation for simultaneous operation?

• DVB-H is very spectrum-efficient when compared with the traditional TV services:– One 8-MHz channel can deliver 30-50 video streaming

services to the small screen terminals• 10 times more than SDTV with MPEG-2• 20 times more than HDTV with AVC

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Hybrid Networks


Hybrid Networks

• Hybrid networks exploit the benefits of both DVB and mobile communications to enhance services provided to the consumer:– Broadcast networks typically involve wide area and

high throughput at the expense of high Tx powers.– Mobile communications offer low-power transmitters

covering smaller areas (cells)• Network cost per user is higher than for a broadcast

network


Hybrid Networks

Hybrid Networkswww.dvb.org


Hybrid Networks

• The IP datacast, used by DVB for a system under development, integrates DVB-H in a hybrid network structure consisting of – a mobile communications network such as GPRS or

UMTS, and– an additional DVB-H downstream.

• In the process of being standardized• A paid service• Possibility of handover


Hybrid Networks

• Architecture of the IP datacast system

U. Reimers, DVB-the family of international standards for DVB, Proc. IEEE, vol.94, no.1, pp.173-181, Jan. 2006

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Prospects for Future Developments


Future Developments

• Mobile communications, digital broadcasting and Internet are converging.

• Current achievements of DVB:– Broadcast delivery to fixed, portable and mobilr terminals– Interactivity-capability in receivers – Data broadcasting over IP-based networks – Multimedia home platform (MHP) to run software applications

on all sorts of terminal devices.• To understand a person’s current location, availability,

and preferred method of communication at that moment e.g., a mobile phone or a DVB-H terminal.


Future Developments

• The focus is now moving to the content itself:– The ubiquitous access to media content requires

• content management, and • copy protection measures

– Portable content formats• To deliver or update the content over fixed and mobile IP

networks (for portable video players)– TV anytime/anywhere


References

• Special issue of Proc. IEEE on global digital television, vol.94, number 1, January 2006.

• DVB-T: ETSI EN 300 744 V1.5.1 (2004-11)• DVB-S2: Draft ETSI EN 302 307 V1.1.1 (2004-

06)• DVB-S: EN 300 421 V1.1.2 (1997-08)• http://www.dvb.org• http://pda.etsi.org/pda/queryform.asp

http://www.dvb.org/

http://pda.etsi.org/pda/queryform.asp









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