Digital Terrestrial Television in India

Terrestrial transmission

Digital Television is the way of future, providing interference free  television reception and remarkable picture & sound quality. 

Digital Terrestrial Television (DTT) offers numerous advantageous over its analog counterpart viz. multi-channel operation; vastly superior and uniform reception quality; reception possible in moving vehicles; less power requirement. In addition, DTT is highly spectrum efficient. Ten to 12 channels can be accommodated in the bandwidth required for a single analogue channel. 

DTT has been launched in certain countries viz. USA; UK & certain other European countries; Australia; Japan; China. Various countries have set cut off dates for complete switchover to DTT and switching off analog transmission.

In fact the actual digital switchover in the world mandated in these countries by their governments has been in analogue transmission only and not on Cable TV as mandated in our country.

India had selected DVB-T system for introduction of DTT in the country and Doordarshan had commissioned four digital transmitters one each at Delhi, Mumbai, Kolkata & Chennai on 26 January, 2003, for an experimental service. Mobile TV service (DVB-H transmission) was started by Doordarshan in Delhi in May, 07. Digital transmitter set up at Delhi earlier in 2003 for experimental service was converted for carrying DVB-H signals. It is another story that because of certain unknown reasons and lethargy of the government machinery these projects have remained experimental till date. 

 Even though parallel technologies such as Digital Cable, DTH, IPTV and Multimedia broadcasting would be prevailing, terrestrial transmission will have to continue on account of various reasons. Doordarshan, being the public service broadcaster will have to migrate to DTT in the years to come. Doordarshan plans to start digitalization of terrestrial network in 11th Plan and complete it by end of 12th Plan i.e. by 2017. In the scheme of digitalization of terrestrial network, cluster of certain LPTs are envisaged to be replaced by HPTs & also certain HPTs at new locations are planned to be set up.

Analog transmission will have to continue alongwith digital transmission for quite sometime. Cut off date for switching off analog transmission will have to be decided taking into account the percentage of population switching over to digital mode of reception. The policy of switchover to DTT would also affect citizens all over the country as it will require additional investment on part of TV homes for acquiring set top boxes in the initial years and subsequently in form of somewhat higher cost of TV sets.

Before fulfilling its own task, government is forcing its population to migrate to either private DTH networks or private digital cable networks to avail of digital television service. It is sad that unlike other developed countries DTT in not on the priority list of our government for mass entertainment. 

History

Digital Terrestrial Television is aerial based, that a person should connect the TV with an aerial to watch TV channels. Each TV set requires a digital Set-Top-Box to convert digital TV signals to analogue as our TV sets are still analogue. For analogue terrestrial transmission of Doordarshan one does not need a Set-Top-Box.

 India adopted DVB-T system for digital television in July 1999. The first DVB-T transmission was started on 26 January 2003 Currently the terrestrial transmission is available in both digital and analog formats. 40 high power DVB-T transmitters were set up in the top 4 cities which are now being upgraded to DVB-T2 + MPEG4 and DVB-H standards. An additional 190 high power, and 400 low power DVB-T2 transmitters have been approved for Tier I, II and III cities of the country by 2017. The Indian telecom regulator, TRAI, had recommended the I&B to allow private broadcast companies to use the DTT technology, in 2005. So far, the Indian I&B ministry only permits private broadcast companies to use satellite, cable and IPTV based systems.

 Competing variants of broadcast television systems are being used around the world. Advanced Television Standards Committee created the ATSC standards that use an ATSC tuner in North America and South Korea. An evolution from the analog National Television Standards Committee (NTSC) standard. Integrated Services Digital Broadcasting (ISDB-T) is used in Japan, with a variation of it being used in most of South America.

DVB-T is the most prevalent, covering Europe, Australia, New Zealand, Colombia and some countries of Africa. DMB-T/H is China's own standard (including Hong Kong and Cuba, though Hong Kong's cable operators use DVB); the rest of the world remains mostly undecided, many evaluating multiple standards. ISDB-T is very similar to DVB-T and can share front-end receiver and demodulator components. Several European countries have switched from analog to digital terrestrial television, with the rest hoping to complete in the next two years. 

Advantages

• If signal strength is sufficient, digital video quality tends to be better overall, due to the elimination of interference and other effects such as ghosting. Obtaining an optimum analogue picture can require extensive experimentation.
  
• More channels can fit on the same spectrum under digital transmission (at the cost of reduced quality).
  
• Interactive (red button) services can be provided.

Disadvantages

• It can be quite difficult to adjust the antenna, because of the lack of feedback that would be provided by a gradually degraded analog picture. The picture is usually either totally ‘on’ or totally ‘off’, providing no information about which direction to move the antenna. A signal meter provided on most tuners helps considerably with this problem, but some televisions lack a signal meter. The same problem can also make it very difficult to select and test antennas.
  
• New additional equipment (set-top box) is required. However, digital TV doesn’t require an STB.
  
• Increased electricity consumption by the digital receiving equipment if both TV and additional set-top box are plugged in.
  
• An upgraded antenna installation may be required.
  
• Analogue requires lower signal strength to get a viewable picture. By extension, digital does not degrade as gracefully as analogue. This is because digital signal transmission suffers from the cliff effect; meaning that once the signal degrades beyond a certain point, the receiver fails to decode the signal and cannot present the expected output.
  
• Switching channels is slower because of the time delays in decoding digital signals.
  
• Interactive (red button) services are rarely provided.

DTTV is transmitted on radio frequencies through terrestrial space in the same way as standard analog television, with the primary difference being the use of multiplex transmitters to allow reception of multiple channels on a single frequency range (such as a UHF or VHF channel) known as subchannels.

The amount of data that can be transmitted (and therefore the number of channels) is directly affected by channel capacity and the modulation method of the channel. The modulation method in DVB-T is COFDM with either 64 or 16-state Quadrature Amplitude Modulation (QAM). In general, a 64QAM channel is capable of transmitting a greater bit rate, but is more susceptible to interference. 16 and 64QAM constellations can be combined in a single multiplex, providing a controllable degradation for more important program streams. This is called hierarchical modulation.

New developments in video compression have resulted in the H.264/MPEG-4 AVC standard which enable three high-definition television services to be coded into a 24 Mbit/s European terrestrial transmission channel.

What is the difference between DTT and DTH and Cable TV?   

Where transmission is from an earth tower, it is terrestrial and in space from a satellite, it is known as DTH.

With terrestrial transmitters, the aiming of antenna can be more forgiving and less clear line of site than satellite needs.

Terrestrial only supplies your local programming. Satellite can provide local programming from other regions.

Only Doordarshan provides terrestrial transmissions in India and they are not encrypted and free-to-air.

Prasar Bharati’s Free Dish DTH is also free to receive but all other DTH services in India are pay services. Cable is received via a cable from a distribution node in the street which is supplied from a distribution amplifier which is fed by fiber optic cable or coaxial cable. Both SD and HD TV channels can be transmitted on DTT.

You can’t use a satellite receiver on a cable delivery system, because satellite digital delivery uses QPSK, yet another different modulation scheme. Similarly a DTT STB cannot be used on Cable or satellite as the modulation is COF DM. 

Technology

DVB-T is an abbreviation for "Digital Video Broadcasting — Terrestrial"; it is the DVB European-based consortium standard for the broadcast transmission of digital terrestrial television that was first published in 1997 and first broadcast in the UK in 1998. This system transmits compressed digital audio, digital video and other data in an MPEG transport stream, using coded orthogonal frequency-division multiplexing (COFDM or OFDM) modulation.

DVB-T2 is an abbreviation for "Digital Video Broadcasting – Second Generation Terrestrial"; it is the extension of the television standard DVB-T, issued by the consortium DVB, devised for the broadcast transmission of digital terrestrial television. DVB has been standardized by ETSI.

This system transmits compressed digital audio, video, and other data in "physical layer pipes" (PLPs), using OFDM modulation with concatenated channel coding and interleaving. The higher offered bit rate, with respect to its predecessor DVB-T, makes it a system suited for carrying HDTV signals on the terrestrial TV channel (though many broadcasters still use plain DVB-T for this purpose).

DVB-H (Digital Video Broadcasting - Handheld) is one of three prevalent mobile TV formats. It is a technical specification for bringing broadcast services to mobile handsets. DVB-H was formally adopted as ETSI standard EN 302 304 in November 2004. From March 2008, DVB-H is officially endorsed by the European Union as the "preferred technology for terrestrial mobile broadcasting". The major competitors of this technology are Qualcomm's MediaFLO system, the 3G cellular system based MBMS mobile-TV standard, and the ATSC-M/H format in the U.S. DVB-SH (Satellite to Handhelds) now and DVB-NGH (Next Generation Handheld) in the future are possible enhancements to DVB-H, providing improved spectral efficiency and better modulation flexibility. DVB-H has been a commercial failure, and the service is no longer on-air. Finland was the last country to switch-off its signals in March 2012.

Indian DTT

Now with DTH, Cable TV and other technologies DTT will have a tough time in India. It will take some some time for improving it and getting to into competition. Nowadays only Doordarshan is doing it. But other companies if take opportunity, it will boom.  Also Free Dish Doordarshan’s FTA DTH venture will be its biggest competitor. This is one reason why the Indian Government is hesitating to exploit the technology. Moreover DTH can carry many more channels than on a DTT transmitter and can also reach every nook and corner of the country with just one satellite. 

However, DTT is excellent in providing local content to masses. There is a due shortage of transponders on satellites all over the world. With more than eight hundred channels in India it is not possible to accommodate all in DTH service. Even DD’s Free Dish beams only 59 channels today, although it plans to have about 200 channels in the future.

Satellite transponder hiring is also expensive. Many small channels can shift to DTT for regional transmissions. Government can auction these frequencies and earn revenue too. Also it will help small, local advertisers who cannot pay costly ad rates on satellite channels. With more than 1400 terrestrial transmitters available with Doordardshan, there is a huge potential for DTT in India. 

Future

Future of DTT in India is very good if properly used. Digital Terrestrial Television is a very strong medium and will take time to be fit. Give it a chance, so this technology also flourishes in realms of digitalization. Many companies have started researching on it and it will be improved day and day, month by month and year by year. Conclusion But Free-Dish is DTH of Doordarshan which leaves behind the Digital Terrestrial Television service.


Source: http://cablequest.org/articles/digitization/item/4845-digital-terrestrial-television-in-india.html
Source: http://cablequest.org/articles/digitization/item/4845-digital-terrestrial-television-in-india.html