Digital Video Broadcasting An Overview Prof. Dr. Mehmet Şafak Hacettepe University Dept. of Electrical and Electronics Engineering 06800 Beytepe, Ankara, Turkey msafak@hacettepe. edu. tr 1
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 ? 14 July 2006 DVB - An Overview I could see the difference if they were on the TV 2
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. An Overview 14 July 2006 DVB - Developments 3
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 14 July 2006 interoperability. DVB - the world of broadcast 4 of An Overview
Data Broadcasting 5
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. 14 July 2006 DVB - An Overview 6
Data Broadcasting • nn 14 July 2006 DVB - An Overview 7
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 14 July 2006 DVB - An Overview sufficient for the transmission of HDTV 8
Data Broadcasting Components inside the DVB data container U. Reimers, DVB-the family of international standards for DVB, Proc. IEEE, vol. 94, no. 1, pp. 173 -181, Jan. 2006 14 July 2006 DVB - An Overview 9
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 14 July 2006 DVB Overview numbers into service. Annames and electronic 10
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 14 July 2006 DVB - An Overview 11 broadband downstream.
Integrated Receiver Decoders (IRD) 12
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- An Overview DVB and MPEG-4 AVC 14 July 2006 13
Integrated Receiver Decoders (IRD) • 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. 14 July 2006 DVB - An Overview 14
Integrated Receiver Decoders (IRD) • 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 DVB -record. to An Overview 14 July 2006 15
Transmission on Cable, Satellite and Terrestrially 16
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 14 July 2006 DVB - An Overview 17
Transmission • DVB-S – Published in 1993 – Modulation: QPSK and BPSK – Convolutional codes concatenated with RS codes • DVB-S 2 – 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) 14 July 2006 DVB - An Overview 18 – Professional services, such as digital satellite news
Transmission • DVB-S 2 – Best transmission performance • LDPC codes concatenated with BCH codes • Variable and adaptive coding and modulation (recovers rain margin) • Approximately 30 % capacity increase compared to DVBS – 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 14 July 2006 transport streams -(packets), continuous bit streams, 19 DVB An Overview
Transmission Performance of LDPC codes over AWGN channel 14 July 2006 DVB - An Overview (N=64800) 20
Transmission M. Eröz et al. , An innovative LDPC code design with near-Shannonlimit performance and simplementation , IEEE Trans. Communicatio ns, vol. 54, no. 1, pp. 13 -17, January 2006. Comparison of DVB-S 2 (LDPC+ BCH) codes to DVB-S (convolutional+ RS) and channel capacity 14 July 2006 DVB - An Overview 21
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-S 2 offers more than 30% capacity improvement • DVB-S 2 is, on average, about only 0. 7 -0. 8 d. B away from Shannon limits. 14 July 2006 DVB - An Overview 22
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 23 14 July 2006 DVB - An Overview time slicing
Transmission • DVB-T, published in 1997, uses OFDM transmissions – – OFDM has 2 K (subcarriers), 4 K and 8 K 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 14 July 2006 DVB - An Overview 24
SFN Range vs Mobility Tradeoff • OFDM with 2 K: – 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 8 K: – 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 4 K provides a trade-off between 14 July 2006 DVB - An Overview 2 K and 8 K 25
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 14 July 2006 DVB - An Overview 26
Hierarchical Modulation An example of a constellatio n diagram for hierarchical modulation HP bit strea m (QPS LP bit K) stream (64 QAM) 14 July 2006 DVB - An Overview 27
Hierarchical Modulation • 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. 14 July 2006 DVB - An Overview 28
Transmission Choice of parameters for non-hierarchical DVB-T transmission U. Ladebusch and C. A. Liss, Terrestrial DVB, Proc. IEEE, vol. 94, no. 1, pp. 183193, Jan 2006 14 July 2006 DVB - An Overview 29
Transmission • Useful bit rate (Mbit/s) for all combinations of guard interval, constellation and code rate for nonhierarchical systems for 8 MHz channels (irrespective of the transmission modes) 14 July 2006 DVB - An Overview 30
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. 14 July 2006 DVB - An Overview 31
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 14 July 2006 DVB - An Overview 32
Interaction Channels 33
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. 14 July 2006 DVB - An Overview 34
Interaction Channels Generic system reference model used by DVB for interactive services 14 July 2006 DVB - An Overview 35 U. Reimers, DVB-the family of international standards for DVB, Proc. IEEE, vol. 94, no. 1,
Interaction Channels • 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. 14 July 2006 DVB - An Overview 36
Interaction Channels • 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. July 2006 networks. An Overview cable 14 DVB 37
Interaction Channels • 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 14 July 2006 DVB - An Overview 38
Interaction Channels V. Paxal, DVB with return channel via satellite, DVBRCS 200, www. dvb. o rg Simplified diagram of a network architecture for DVB return channel satellite systems (RCS) 14 July 2006 DVB - An Overview 39
The Multimedia Home Platform (MHP) 40
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. July 2006 MHP implementations that pass those 14 DVB - An Overview 41
The Multimedia Home Platform • 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 An Overview 14 July 2006 DVB - providers. 42
The Multimedia Home Platform • 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 Overview secure 14 July 2006 DVB - An upon 43
DVB over IP-based Networks 44
DVB over IP-based Networks • A typical IPTV service involves the delivery of broadcast television, radio and similar ondemand 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. 14 July 2006 DVB - An Overview 45
DVB over IP-based Networks Basic IPTV architecture www. dvb. org 14 July 2006 DVB - An Overview 46
DVB over IP-based Networks • 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. 14 July 2006 DVB - An Overview 47 • Creation of a wireless home network segment
DVB-Handheld 48
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) 14 July 2006 DVB - An Overview 49
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) 14 July • to enable smooth. An Overview 2006 DVB - and wireless handover when 50
DVB-Handheld 625 ms 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) U. Reimers, DVB-the family of international standards for DVB, Proc. IEEE, vol. 94, no. 1, pp. 173 -181, Jan. 2006 Average bir 51 rate: 14 July 2006 DVB - An Overview
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. 14 July 2006 DVB - An Overview 52
DVB-Handheld • The extensions to the physical layer of DVBT: – Bits in transmitter parameter signaling (TPS) are upgraded to indicate the presence of DVB-H service – A new 4 K OFDM mode adopted for trading off mobility and single-frequency network (SFN) size • All modulation formats (QPSK, 16 QAM and 64 QAM) with nonhierarchical or hierarchical modes can be used – A new way of using the symbol interleaver of DVBT has been defined (to provide tolerance against impulsive noise) DVB - An Overview 14 July 2006 53
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 4 K 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 14 July 2006 DVB - An hierarchical modulation. Overview 54
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 14 July 2006 DVB - An Overview 55
Hybrid Networks 56
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) DVB An Overview • Network cost per - user is higher than for a 14 July 2006 57
Hybrid Networks www. dvb. org 14 July 2006 DVB - An Overview 58
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 14 July 2006 DVB - An Overview • Possibility of handover 59
Hybrid Networks • Architecture of the IP datacast system U. Reimers, DVBthe family of international standards for DVB, Proc. IEEE, vol. 94, no. 1, pp. 173 -181, Jan. 2006 14 July 2006 DVB - An Overview 60
Prospects for Future Developments 61
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 14 July 2006 DVB - An moment e. g. , a mobile 62 communication at that. Overview
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) DVB - An Overview – TV anytime/anywhere 14 July 2006 63
References • Special issue of Proc. IEEE on global digital television, vol. 94, number 1, January 2006. • DVB-T: ETSI EN 300 744 V 1. 5. 1 (2004 -11) • DVB-S 2: Draft ETSI EN 302 307 V 1. 1. 1 (2004 -06) • DVB-S: EN 300 421 V 1. 1. 2 (1997 -08) • http: //www. dvb. org 14 July 2006 DVB - An Overview 64
Thanks 65
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