Walter Fischer

Digital Television throughout the World — an Overview

The numerous technical details of the various digital television standards have now been discussed. The only thing that is still missing is a report about the current development and spread of these technologies, and a look at the future. Digital satellite television (DVB-S) is available in Europe over numerous transponders of the ASTRA and Eutelsat satellites. Many streams can be received unencrypted. Complete receiving systems for DVB-S are available at low cost in many department stores. DVB-C, too, has become well established in the meantime. Digital terrestrial television has also become widely used in numerous countries and above all in Great Britain, where DVB-T started in 1998. DVB-T first spread in Scandinavia where Sweden is covered completely by DVB-T. Australia, too, was one of the first countries to have introduced DVB-T. In Australia, DVB-T is available mainly in the population centers along the Eastern and Southern coast. DVB-T is also being built up in South Africa and in India. In Europe, the current status is as follows: Autumn 2002 saw the start of DVB-T in Berlin and in August 2003, 7 data streams with more than 20 programs were on the air and analog television was being operated in parallel for only a brief period in simulcast mode and then switched off completely in August 2003, which certainly represented a minor revolution! DVB-T was designed to implement portable indoor reception. Reception is possible using simple indoor antennas from the heart of Berlin out to the outer suburbs in some cases. Naturally, there are restrictions in indoor reception due to the attenuation of buildings and other shadowing. In the years of 2003, 2004 and 2005, this type of reception known as Anywhere Television then also spread to the North-Rhine-Westphalia, Hamburg, Bremen, Hanover and Frankfurt regions and since May 30th 2005 also to the Munich and Nuremberg conurbation areas in Germany. The data rates per DVB-T channel are 13.27 Mbit/s, providing space for about 4 programs per channel. In most cases there are about 4 -6 frequencies in the air at any time. Mecklenburg followed in autumn 2005, and Stuttgart in 2006. The networks implemented in Germany are all designed as small isolated SFN regions with few transmitters.

High Definition Television – HDTV

Das seit den 50er Jahren eingefuhrte SDTV = Standard Definition Television ist immer noch in allen Landern weltweit quasi der „Hauptstandard“ fur analoges und digitales Fernsehen. Moderne TV-Kameras und mittlerweile auch Endgerate wie Plasmabildschirme und LCD-Fernseher ermoglichen aber ahnlich wie im Computerbereich auch deutlich hohere Pixelauflosungen.

Measurements on the MPEG-2 Transport Stream

With the introduction of digital television, neither the hopes of the users nor the fears of the test equipment makers were confirmed: there is still a large need for test instruments for digital television, but of a different type. Where it was mainly video analyzers for evaluating the test lines of an analog baseband signal in analog television, it is mainly MPEG-2 test decoders which are being used in digital TV. Throughout the world, taking measurements directly at the transport stream has become the most important digital TV test technology with regard to turnover and demand. Thus, e.g., every MPEG-2 transport stream to be broadcast is analyzed and monitored by means of a MPEG-2 test decoder at almost every transmitter site of DVB-T networks in some countries.

Digital Video Signal According to ITU-BT.R.601 (CCIR 601)

Uncompressed digital video signals have been used for some time in television studios. Based on the original CCIR Standard CCIR 601, designated as ITU-BT.R601 today, this data signal is obtained as follows: nTo start with, the video camera (Fig. 4.1.) supplies the analog Red, Green and Blue (R, G, B) signals. These signals are matrixed in the camera to form luminance (Y) and chrominance (color difference CB and CR) signals.

Transmitting Digital Television Signals by Satellite – DVB-S/S2

Today, analog television signals are widely received by satellite since this type of installation has become extremely simple and inexpensive. Thus, in Europe, a simple satellite receiving system complete with dish, LNB and receiver is available for less than 100 Euros and there are no follow-up expenses. In the meantime, analog satellite reception in Europe is being replaced more and more by DVB-S - digital video broadcasting by satellite and also DVB-S2 since 2005. In this chapter, the method of transmitting MPEG-2 source encoded TV signals via satellite is described.

The MPEG Data Stream

The abbreviation MPEG, first of all, stands for Moving Pictures Experts Group, that is to say MPEG deals mainly with the digital transmission of moving pictures. However, the data signal defined in the MPEG-2 Standard can also generally carry data which have nothing at all to do with video and audio and could be Internet data, for example. And indeed, throughout the world there are MPEG applications in which it would be futile to look for video and audio signals. Thus, in Wollongong, about 70 km south of Sydney in Australia, an Australian pay TV provider is operating a pure data broadcasting service using MPEG-2 data signals via MMDS (Microwave Multipoint Distribution System). “Austar” are here providing their customers with fast Internet links in the Mbit/s range.

DVB-Datendienste: MHP und SSU

Neben DVB-H gibt es im Rahmen von DVB weitere aktuelle Datendienste, namlich die Multimedia Home Platform, kurz MHP genannt und den System Software Update fur DVB-Receiver – kurz SSU. Parallel hierzu lauft auch noch MHEG (=Multimedia and Hypermedia Information Coding Experts Group) in UK uber DVB-T. All diese Datendienste haben als gemeisame Eigenschaft, dass sie uber sog. Object Carousels uberDSM-CC Sections ausgestrahlt werden. Uber MHP und MHEG werden Applikationen zum Receiver hin ubertragen, die dann ein speziell dafur ausgestatteter Receiver auch speichern und starten kann. Bei MHP sind dies HTML-Files und Java-Applikationen, die in kompletten Directory- Strukturen an das Endgerat ubertragen werden. MHEG gestattet die Ubermittlung und das Starten von HTML- und XML-Files.

Broadband Cable Transmission According to DVB-C

In many countries, good radio and TV coverage is provided via broadband cable, especially in densely populated areas. These cable links have either a bandwidth of about 400 MHz (approx. 50 - 450 MHz) or about 800 MHz (approx. 50 - 860 MHz). In addition to the VHF and UHF band known from terrestrial television, special channels are occupied. Analog television programs can be received easily with a conventional TV set without additional complexities which is why this type of TV coverage is of such great interest to many. The only obstacle in comparison with analog satellite TV reception is the additional monthly line charge with which a satellite receiving system would pay for itself within one year in many cases. If the satellite dish is large enough, the picture quality is often better than via broadband cable since intermodulation products sometimes result in visible interference due to the multiple channel allocation in broadband cable.

MPEG-2 Video Coding

Digital SDTV (Standard Definition Television) video signals (uncompressed) have a data rate of 270 Mbit/s. This data rate is much too high for broadcasting purposes, which is why they are subjected to a compression process before being processed for transmission. The 270 Mbit/s must be compressed to about 2…7 Mbit/s - a very high compression factor which, however, is possible due to the use of a variety of redundancy and irrelevance reduction mechanisms. The data rate of an uncompressed HDTV signal is even higher than 1 Gbit/s and MPEG-2 coded HDTV signals have a data rate of about 15 … 20 Mbit/s.

Digital Terrestrial TV to North American ATSC Standard

Although terrestrial radio transmission poses a variety of problems due to multipath reception and is best handled using multicarrier methods (Coded Orthogonal Frequency Division Multiplex - COFDM), North America opted in favour of a single carrier method under the Advanced Television Systems Committee (ATSC). In the years 1993 to 1995, the Advanced Television Systems Committee – with the participation of ATT the audio signal is Dolby digital AC-3 coded. In contrast to DVB, high definition television (HDTV) was favoured in ATSC. The input signal to an ATSC modulator, therefore, is a transport stream with MPEG-2 coded video and Dolby AC-3 coded audio information (AC-3: digital audio compression). Video signals are either SDTV (Standard Definition Television) or HDTV signals. The modulation mode used is eight-level trellis-coded vestigial sideband (8VSB). This is a single-carrier method based on IQ modulation using only the I axis. Eight equidistant constellation points are distributed along the I axis. The 8VSB baseband signal has eight discrete amplitude modulation levels. First, however, an 8ASK signal is generated (ASK: amplitude shift keying).