Digital Video Broadcasting
Digital Video Broadcasting (DVB) is a set of standards for the digital transmission of video and audio streams, and also data transmission. It distributes data through variety of approaches such as satellite, cables, terrestrial television or terrestrial television handheld, microwave etc.
As the things become more compact, we need mobile TV through which we can watch television from anywhere in the world. For implementing this requirement we have a new technology i.e digital video broadcasting- handheld (DVB-H). DVB-H is a technical specification for bringing broadcast services to mobile handsets. It is based on the DVB-T standard for digital terrestrial television but tailored to the special requirements of the pocket-size class of receivers. This white paper presents an overview of the DVB and its advance technique DVB-H with respect to features and technology.
Digital Video Broadcasting systems have been defined in terms of standards for a variety of broadcasting media, such as cable and direct satellite broadcasting, and for most stages of the broadcasting chain, from contents origination to decoding at the viewer’s television set. Such systems are now in the early stages of adoption.
Digital Video Broadcasting (DVB) has become the synonym for digital television and for data broadcasting world-wide. DVB services have recently been introduced in Europe, in North- and South America, in Asia, Africa and Australia. Digital Video Broadcasting (DVB) is a transmission scheme based on the MPEG-2 video compression / transmission scheme and utilizing the standard MPEG-2 Transmission scheme. It is however much more than a simple replacement for existing analogue television transmission.
DVB is a European initiative. Equipment conforming to DVB standard is now in use on six continents and is DVB rapidly becoming the world-wide standard for digital TV. DVB provides superior picture quality with the opportunity to view pictures in standard format or wide screen (16:9) format, along with mono, stereo or surround sound. It also allows a range of new features and services including subtitling, multiple audio tracks, interactive content, multimedia content – where, for instance, programs may be linked to world wide web material.
DVB is the European standard for digital TV and, as such, provides a very high-speed, robust transmission chain capable of the many Megabits per second needed for each of several hundred MPEG-2 digital TV channels. In the old days, a typical satellite transponder had about enough bandwidth for a single analogue PAL color TV channel. So if your satellite had 22 transponders, you could transmit 22 TV channels.
Using DVB digital technology and standards means the same transponder can transmit around 40 Megabits per second. A typical PAL VHS standard TV channel can be compressed by DVB MPEG-2 to around 4 Megabits per second. Channels can be mixed – or “multiplexed” – in the same transponder giving a rule-of-thumb of 10 TV channels (each around 4Mb/s) in a typical (40Mb/s) transponder.
The core system is the same for digital satellite, cable and terrestrial TV with different modulation methods for each mode. In the UK, for some reason, Cable companies have chosen not to adopt the DVB standard.
Digital Video Broadcasting (DVB) is a set of standards that define digital broadcasting using existing satellite, cable, and terrestrial infrastructures. A fundamental decision of the DVB was the selection of Moving Picture Expert Group-2(MPEG-2), one of a series of MPEG standards for compression of audio and video signals. MPEG-2 reduces a single signal from 166 Mbits to 5 Mbits allowing broadcasters to transmit digital signals using existing cable, satellite, and terrestrial systems. MPEG-2 uses the lossy compression method(it is the one where compressing data and decompressing it retrieves data that may well be different from the original, but is close enough to be useful in some way), so the digital signal sent to the television is compressed and some data is lost. This lost data does not affect how the human eye perceives the picture.
DVB also uses conditional access (CA) systems to prevent external piracy. Each CA system provides a security module that scrambles and encrypts data. This security module is embedded within the receiver or is detachable in the form of a PC Card. Inside the receiver, there is a smart card that contains the user’s access information. The following describes the conditional access process:
- The receiver receives the digital data stream.
- The data flows into the conditional access module, which contains the content provider’s unscrambling algorithms.
- The conditional access module verifies the existence of a smart card that contains the subscriber’s authorization code.
- If the authorization code is accepted, the conditional access module unscrambles the data and returns the data to the receiver. If the code is not accepted, the data remains scrambled restricting access.
- The receiver then decodes the data and outputs it for viewing.
DVB is an open system as opposed to a closed system. In open systems such as DVB allows the subscriber to choose different content providers and allows integration of PCs and televisions. DVB systems are optimized for not only television but also for home shopping and banking, private network broadcasting, and interactive viewing. DVB offers the future possibilities of providing high-quality television display in buses, cars, trains, and hand-held devices. DVB allows content providers to offer their services anywhere DVB is supported regardless of geographic location, expand their services easily and inexpensively, and ensure restricted access to subscribers, thus reducing lost revenue due to unauthorized viewing.
The concept of DVB is come in mind because of the deficiencies of old Analog TV transmission. DVB is a very great invention against the Analog TV transmission. The reasons behind this are :
- If signals get week than it provided very bad quality.
- Analog TV transmission was very expensive because it needed many high power senders for good coverage.
- I gave bad mobile reception because Antennas were very small and unaligned.
- Sending extra information(for example teletext) was very difficult or we can say nearly impossible.
Advantages of using DVB are:
- Now High quality reception is provided. If signal is received undisturbed than image quality, we get is exactly as transmitted. Digital Audio is provided with the transmission( for example MP3 and Dolby Digital etc.)
- Using DVB Mobile reception is possible because of which DVB-H technique is in use.
- DVB uses Multiplexing so that multiple DVB programs can be transmitted instead of one analog TV channel.
- Now, by using DVB the content provider has also got the advantages in encryption of data. DVB provide good encryption of data for content provider
How It Works
The DVB systems use MPEG-2 compression for audio and video. The compressed audio and video streams are combined together along with the ancillary and control data. This process is called multiplexing. In pay-per-view cases also conditional access data is multiplexed. The multiplexer output is MPEG-2 transport stream. Channel coding is applied to transport stream before modulation and broadcasting.
Types of Broadcasting
- Digital Video Broadcasting-Satellite(DVB-S): In DVB-S, the signal is broadcasted through the satellite. Satellite TV uses geostationary satellites in an orbit about 36000 km above the equator. It works on Quadrature Phase Shifting Key(it is a system of modulating digital signals onto a radio-frequency carrier signal using four phase states to code two digital bits.) The frequency spectrum used in it is 10,7-12,75 GHz. DVB-S is the most widely used, because it doesn’t require cable to your home, and no terrestrial broadcast antennas.
- Digital Video Broadcasting-Cable(DVB-C): In DVB-C, the signal is broadcasted through the broadband coaxial cable. Cable Head-Ends inject the modulated signal into the cable segments and each cable segments serve around 500 to 1000 users. The frequency spectrum used is 47Mhz-470Mhz. Spectrum 0 – 46 MHz used for communication from user (e.g. for Internet access via cable modems). Sometimes ,lower frequencies disturbed, line sharing among users, cable modem signals can influence DVB-C quality. It works on QAM modulation system. QAM conveys data by changing (or modulating) the amplitude of two carrier waves which are out of phase with each other by 90°.
- Digital Video Broadcasting-Terrestrial(DVB-T): In DVB-T, the signal transmitted using terrestrial methods i.e. from aerial antenna to aerial antenna and then to home receiver. DVB-T broadcasters transmit data using a compressed digital audio-video stream, with the entire process based on the MPEG-2 standard. The transmissions includes all kinds of digital broadcasting. Not only television set receive the signal but also computer’s receiver receive the signal in DVB-T. It can also received on single computer or on network. DVB-T uses Orthogonal Frequency Division Multiplex(OFDM) modulation with concatenated channel coding(i.e. Coded Orthogonal Frequency Division Multiplex(COFDM)).
COFDM is a modulation scheme that divides a single digital signal across 1,000 or more signal carriers simultaneously. The signals are sent at right angles to each other (hence, orthogonal) so they do not interfere with each other. With the help of COFDM we can reduce multipath problem (i.e. phenomenon in which signal reaching the receiving antenna by two or more paths causing interference) .
- Digital Video Broadcasting-Handheld(DVB-H): In DVB-H, the broadcast services are given to the mobile handsets. DVB-H is based on the DVB-T standard for digital terrestrial television but takes into account the specific properties of typical terminals which are expected to be small, lightweight, portable and – very importantly – battery-powered. DVB-H can offer a downstream channel at a high data-rate which will be an enhancement to the mobile telecommunications network, accessible by most of the typical terminals. Therefore, DVB-H creates a bridge between the classical broadcast systems and the world of cellular radio networks. DVB-H uses a power-saving algorithm based on the time-multiplexed transmission i.e. time slicing, which results in a large battery power-saving effect. It also allows soft handover if the receiver moves from network cell to network cell with only one receiver unit. For reliable transmission in poor signal reception conditions ,an enhanced error-protection scheme on the link layer is introduced. This scheme is called Multi-Protocol Encapsulation – Forward Error Correction (MPE-FEC). MPE-FEC employs powerful channel coding on top of the channel coding included in the DVB-T specification and offers a degree of time interleaving. It also offering additional flexibility in designing single-frequency networks (SFNs) which still are well suited for mobile reception, and also provides an enhanced signaling channel for improving access to the various services.
Future of DVB
Internet has become the leader for the last couple of years in the market, and will continue to take the lead. With producer (companies) and consumer (buyer) going online, the whole market is going through a paradigm shift. The question of whether conventional television will continue to play an important role is questionable. Digital television will bring a new era to the market, but there is also no doubt that Internet is there to continue. With digital television being net enable, the next paradigm shift is whether the PC (personal computer) or the digital television will take the lead, or will they converge to form a new generation product.
In no time, it would be possible to run applications (e.g. word processor) on the digital television; in that sense, the definition between a PC and a TV would not be clear, hence overlapping.
DVB introduces the MHP (Multimedia-Home Platform) that propose to integrate all consumer appliances.
The DVB-MHP solution will allow service providers to access all consumers using DVB-MHP compliant receivers. It will also allow the consumers to access the service providers of their choice. MHP will be the foundation for a homogeneous digital TV market. The Multimedia Home Platform (MHP) consists of a user terminal, including different low to high functionality implementations, its associated peripherals and in-home digital network. The MHP solution encompasses the whole set of technologies necessary to ensure interoperable MHP implementations. Three application profiles have been de-fined as Enhanced Broadcast, Interactive Television and Internet access. The MHP specification has been completed and endorsed in July this year by ETSI (European Telecommunications Standards Institute).
Turbo Internet is the forerunner that commercialized one of the numerous applications of digital broadcasting. Internet bandwidth (connection speed) to uni-user (unicast) is on the rise. Using wired telephone dialup, a 56Kbps (Kilo bits per second) connection is already quite saturated. ISDN (Integrated Services Digital Network) try to increase this limited and achieve up to a connection speed of 128 Kbps. Others like ADSL (Asynchronous Digital Subscriber Line) tried to overcome this limitation (can achieve up to 1.54 Mbps), but still not very feasible for the rural areas with little or no basic infrastructure. Turbo Internet architecture is based on the both the telephone and digital television broadcast infrastructure. It aims to delivery large amount of data/video/audio data to all. This aims at high speed Internet content delivery, and aid the convergence of multimedia since it can delivery real time video. A wired telephone dialup connection is required in this architecture to delivery the small bandwidth of uplink traffic.
One of the main areas of interest is the transfer of large amounts of data/video/audio to a single user (unicast), or to a large numbers of users simultaneously (multicast or broadcast). The wide area coverage offered by a single satellite footprint ensures that millions of subscribers can receive data in seconds from just one transmission. Since much of the infrastructure is already in place, very little additional investment is needed from broadcasters or subscribers to take advantage of data broadcasts over satellite. This service is already available in U.S., many parts of Europe and even some Asia country such as Thailand.
The target user of this document are those firms or software companies which are working on older technologies related to broadcasting and to those industries which are working in the mobile technology and to those which are related to telecommunication like NOKIA, TATA SKY, Dish TV etc.