digital terrestrial television dtt quo vadis .digital terrestrial television ebu technical review
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DIGITAL TERRESTRIAL TELEVISION
Ulrich H. ReimersTechnische Universitaet Braunschweig
This article looks at the prospects for DVB-T and DVB-T2 in Germany, in view of thefact that the future of classical terrestrial TV broadcasting in the country is underdiscussion and that it may even be terminated before the end of the decade. Thearticle also identifies solutions for media delivery to portable and mobile terminalssuch as in-car receivers or Tablet PCs which no longer rely on classical terrestrialbroadcasting.
Terrestrial broadcasting is the traditional means of delivering live video and audio content to view-ers. Whereas in the past, neither cable nor satellite or broadband networks both wired or wireless existed or were able to compete with terrestrial content delivery: today, terrestrial networks are justone of several means of reaching the radio and TV audiences.
As a result of the re-unification of Germany some 20 years ago, free-to-air satellite delivery of all rel-evant radio and TV programmes has become a reality. When Germany was reunited, the 18 millionpeople in the five new states, on the territory of the former German Democratic Republic, wanted tobe offered West-Fernsehen (western television) immediately and satellite delivery was the onlyway of making this happen. Since those days, whoever is able to set up a satellite dish on his/herbalcony or roof will have the full range of TV (and radio) programmes available free-of-charge, manyof them in HD.
It is important to be aware of this German speciality in order to understand the discussions that areon-going in the country. In many parts of Germany, cable TV is also widely accepted. The introduc-tion of DVB-T, which started in 2003 and which was finalized in 2008, took this situation into consid-eration. DVB-T parameters were chosen which turned classical terrestrial broadcasting into a meansof delivering TV content not only to stationary but also to portable and mobile receivers, thereby tak-ing advantage of the unique feature of terrestrial networks the ability to reach uncabled devices. Inconsequence, more than one million cars are equipped with DVB-T receivers and some six millionUSB sticks etc. with built-in DVB-T frontends have been sold. In many households, at least thesecond TV set in the kitchen, the nursery etc. receives DVB-T using just a small rod antenna.
Using DVB-T, the public broadcasters ARD and ZDF offer 12 TV programmes across Germany.Commercial broadcasters, on the other hand, have been sceptical regarding the commercial casefor DVB-T. They decided to transmit their programmes mainly in urban areas where they expected asignificant number of households to use terrestrial reception even in the living rooms. It is importantto understand that their income from the presentation of commercials is not simply correlated withthe number of people watching these commercials. What matters is the number of those peoplewatching their programmes which are part of the audience metering panel operated jointly by allpublic and commercial broadcasters. People watching TV in cars, on laptops etc., are not included inthe audience metering panel and therefore dont create income. In addition, the commercial broad-casters rightly assumed that, outside the urban areas, many people would have no problem settingup a satellite dish and would therefore watch free-to-air satellite TV on their primary television sets.
DTT Quo Vadis Germany as a case study
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Fig. 1 shows the percentage of households using DVB-T in the 16 Laender (federal states) of Ger-many. The left column represents the average of all states (12.5%) and indicates the number of TVhouseholds in the country (37.977 million) . This diagram carries an important message. In stateswhere commercial programmes are on-air (for instance HB: Bremen, B: Berlin), DVB-T reachessome 26% or 23% of the households. In states where only the programmes of ARD and ZDF are on-air, the percentage of households using DVB-T is very low (for instance SL: Saarland, SA: Sachsen-Anhalt). While considering this fact, it becomes clear that, for classical terrestrial TV broadcast to beaccepted by the public, both public and commercial broadcasters have to be present.
Preparing for the introduction of DVB-T2The second generation DVB system for terrestrial broadcasting (DVB-T2) is already in commercialuse in several countries around the world. The primary application of the networks operated inthese countries is the transmission of HDTV content to stationary receivers equipped with roof-topaerials. However, the DVB-T2 standard has been developed as a toolbox, offering a significantlywider range of potential application scenarios. Based on the deliberations guiding the introductionof DVB-T, a possible introduction of DVB-T2 in Germany would need to encompass portable andmobile receivers.
The DVB-T2 standard foresees a variety of algorithms for potentially increasing its performance, e.g.Rotated Constellations, Multiple Physical Layer Pipes (M-PLPs), transmit diversity (Multiple InputSingle Output, MISO), or a sophisticated time-interleaver. Due to the fact that in other countries theintroduction of DVB-T2 focused on stationary reception, the performance of the available parameterconfigurations for portable and mobile reception was not really field-tested and only predictedthrough simulations. To verify the existing simulation results and to identify the optimal parameterconfiguration, a consortium of several institutions and companies evaluated DVB-T2 for stationary,portable and mobile reception in a DVB-T2 field trial in Northern Germany. The field trial started inAugust 2009 and ended in July 2012. Many participants were involved, e.g. German media authori-ties, public and commercial broadcasters and network operators. The Institut fuer Nachrichtentech-nik (IfN) of Technische Universitaet Braunschweig was the technical coordinator. The project wassupported by many guests, including equipment manufacturers, the car industry represented by VWetc. Besides evaluating DVB-T2 in all its facets, another main objective of the field trial was to definea potential introduction strategy for DVB-T2 in Germany.
In order to analyze the DVB-T2 system under realistic conditions, a DVB-T2 network was estab-lished in the region south of Hamburg. This trial network consisted of two transmitters which wereabout 45 km apart and which operated at 690 MHz. Furthermore, the transmitters were operated inan SFN (Single Frequency Network) mode, i.e. both transmitters radiated identical signals syn-chronized in time and frequency and used the same carrier frequency.
Figure 1Percentage of households using DVB-T in the 16 states of Germany
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One transmitter was located in Rosengarten (with an antenna height of about 150 m above the aver-age terrain level), operating at an output power of 10 kW ERP. The other transmitter was situated inLueneburg (antenna height about 130 m above average terrain) and was operated at a power of5 kW ERP. Both SISO (Single Input Single Output) and MISO operation were supported by this net-work. The signal transmitted from Lueneburg was vertically polarized, whereas the transmitter inRosengarten delivered a horizontally-polarized signal. During MISO operation, the transmitter inRosengarten transmitted MISO group 1 and the transmitter in Lueneburg MISO group 2.
The measurements carried out within the trial network focussed on portable and mobile reception.Fig. 2 shows the three different areas which were selected for portable measurements. Seevetal islocated near the Rosengarten transmitter. Therefore, this transmitter mainly contributes to thereception there. Winsen is located exactly in the centre of the SFN network. In Lueneburg, the signalfrom the Lueneburg transmitter was dominant. During the measurement campaign, which lasted forsix weeks, 35 sets of parameter configurations were investigated. Almost all parameter configura-tions were measured in all three measurement areas, leading to 87 measurement locations in theentire area. In total, 3162 individual results were collected.
For our evaluation of the mobile reception of DVB-T2, no test receivers were available on the mar-ket. Therefore, a mobile DVB-T2 measurement receiver was developed by the IfN team, which isbased on a software defined radio concept . This means that the actual decoding is performed insoftware on a high-performance standard PC. Thus, the measurements were done in two steps. Inthe first step, the complete channel was sampled using a generic hardware frontend and the result-ing data was stored on a hard disk. In the second step, the data was decoded in non-real-time onthis PC. In addition to the decoding of the recorded signal, the receiver is also able to determine thelocal and momentary characteristics of the transmission channel. During the measurements, GPSdata was simultaneously recorded. Hence, the receiver links the measurement data with their geo-graphical positions and depicts them on a map.
The route used for measuring the performance of mobile reception comprised different areas withdifferent reception characteristics (Fig. 3). These areas included town centres (e.g. Winsen) withheavy traffic, dense buildings and a maximum allowed speed of 50 km/h, as well as country roads(up to 100 km/h) and the Autobahn between Lueneburg and Rosengarten which has no speed
Figure 2Geographic location of the three measurement areas in the DVB-T2 trial networkOpenstreetmap (cc-by-sa)
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limit. The measurement route also included a tunnel (the El