DIRECT TO HOME

DTH stands for Direct-To-Home television.

DTH is defined as the reception of satellite programmes with a personal dish in an individual home.

A DTH network consists of a broadcasting centre, satellites, encoders, multiplexers, modulators and DTH receivers.

What is DTH ???

• The DTH utilizes a technology which enables a home to receive high speed internet broadband access data communication, voice over internet protocol (IP) telephony and much more using an open standard Digital Video Broadcasting (DVB) technology.

• The video channels are received with a suitable set top box capable of demodulating Moving Picture Experts Group (MPEG-2) standard videos. Hardware compatible with DVB-RCS technology is readily available in the market in both Ku-band and C-band.

• DVB-RCS is an international open standard for multimedia satellite network where the return data rates in access of 2 Mbps are possible using low cost user terminals.

• The forward ink is usually at 40 Mbps.

• A DTH service provider has to lease Ku-band transponders from the satellite. The encoder converts the audio, video and data signals into the digital format and the multiplexer mixes these signals. At the user end, there will be a small dish antenna and set-top boxes to decode and view numerous channels.

• DTH does away with the need for the local cable operator and puts the broadcaster directly in touch with the consumer.

• DTH is an encrypted transmission that travels to the consumer directly through a satellite.

• DTH transmission is received directly by the consumer at his end through the small dish antenna.

• A set-top box, unlike the regular cable connection, decodes the encrypted transmission.

• The way DTH reaches a consumer's home is different from the way cable TV does.

• In DTH, TV channels would be transmitted from the satellite to a small dish antenna mounted on the window available at the rooftop of the subscriber's home.

How does DTH really differ from Cable TV ?

• So the broadcaster directly connects to the user and the middlemen like local cable operators are not there in the picture.

• DTH can also reach the remotest of areas since it does away with the intermediate step of a cable operator and the wires (cables) that come from the cable operator to your house.

• Also, with DTH, a user can scan nearly 700 channels which is about seven times than that in Cable TV.

• Yes. DTH offers better quality picture than cable TV.

• This is because cable TV in India is analog. Despite digital transmission and reception, the cable transmission is still analog.

• DTH offers stereophonic sound effects.

Is DTH superior to Cable TV ?

• It can also reach remote areas where terrestrial transmission and cable TV have failed to penetrate.

• Apart from enhanced picture quality, DTH has also allows for interactive TV services such as movie-on-demand, Internet access ,video conferencing and e-mail.

• In DTH, the payments can be made directly by the subscriber to the satellite company offering the service.

• A big problem that broadcasters face in India is the issue of underreporting of subscribers by cable operators.

• Consider the cable operators pyramid. Right at the top is the broadcaster. Next comes the Multi Service Cable Operator (MSOs) like Siticable, InCable, etc.

• Below them are the Access Cable Operators (ACOs) or your local cable guy who actually lays the wires to your house.

• The local cable operators or the ACOs then allegedly under-report the number of subscribers they have bagged because they have to pay the MSOs something like Rs 30-45 per household.

• Showing a lesser number of households benefits ACOs.

• With no way to actually cross check, the MSOs and the broadcasters lose a lot.

• Broadcasters do not earn much in subscription fees and are mostly dependent on advertisement revenue to cover their costs, which is not sustainable and does not offer high growth in revenues for broadcasters.

• The way out of this is to use a set-top box so that it will be clear how many households are actually using cable or going for DTH where broadcasters directly connect to consumers and can actually grow revenues with a growth in the subscriber base.

• DTH services were first proposed in India in 1996. But they did not pass approval because there were concerns over national security and a cultural invasion.

• In 1997, the government even imposed a ban when the Rupert Murdoch-owned Indian Sky Broadcasting (ISkyB) was about to launch its DTH services in India.

What is the history of DTH in India ?

• Finally in 2000, DTH was allowed. The new policy requires all operators to set up earth stations in India within 12 months of getting a license.

• DTH licenses in India will cost $2.14 million and will be valid for 10 years.

• The companies offering DTH service will have to have an Indian chief and foreign equity has been capped at 49 per cent.

• There is no limit on the number of companies that can apply for the DTH license.

Current Scenario

Satellite television system transmit and receive radio signals using special antennas called satellite dishes.

Satellites are higher in the sky than TV antennas so they have much larger ‘line of sight’ range.

SATELLITE TV SOLUTION

• Positioned at exact height above the earth (36000km).

• Rotate around the earth at the same speed as the earth rotates.

• Has circular orbit.

GEOSTATIONARY SATELLITE

• Channels are first multiplexed.

• QPSK modulated before transmission.

• Dish receives the signal.

• LNBC converts KU band signals to intermediate frequency based on the local IF.

• Set top box receives signals and performs demodulation and D to A conversion and gives the RF output to TV.

FUNCTIONING OF DTH

• The DTH network consists of two parts :

1. Compression and Encoding

2. Encryption and Transmission

3. Communication Channel

4. Receiver Terminal

Basic DTH Network Concepts

Compression and Encoding

• Currently, most of the service providers use the MPEG-2 compressed video format - the same format used to store movies on DVDs.

• With MPEG-2 compression, the provider can reduce the 270- Mbps stream to about 5 or 10 Mbps (depending on the type of programming).

• With digital compression, a typical satellite cantransmit about 200 channels whereas without digital compression, it can transmit about 30 channels.

• At the broadcast center, the high-quality digital stream of video goes through an MPEG-2 encoder, which converts the programming to MPEG-2 video of the correct size and format forthe satellite receiver in your house.

• The MPEG encoder analyzes each frame and decides how to encode it.

• The encoder eliminates redundant or irrelevant data, and extrapolates information from other frames to reduce the overall size of the file.

Each frame can be encoded in one of three ways:

1. As an Intraframe - An Intraframe contains the complete image data for that frame. This method of encoding provides the least compression.

2. As a Predicted frame - A Predicted frame contains just enough information to tell the satellite receiver how to display the frame based on the most recently displayed intra frame or predicted frame.

3. As a Bidirectional frame - To display Bidirectional frame, the receiver must have the information from the surrounding intraframe or predicted frames.

• The rate of compression depends on the nature of the programming.

• If the encoder is converting a newscast, it can use a lot more predicted frames because most of the scene stays the same from one frame to the next.

• In other sorts of programming, such as action movies and music videos, things change veryquickly from one frame to the next, so the encoder has to create more intraframes.As a result, something like a newscast generally compresses to a much smaller size than something like an action movie.

Encryption and Transmission

• After the video is compressed, the provider needs to encrypt it in order to keep people from accessing it for free.

• Encryption is an electronic method of securing the video and audio of any TV program so that satellite, cable, and broadcast TV services can maintain control over the distribution of their signals.

• Encryption scrambles the digital data in such a way that it can only accessed be if the receiver has the correct decryption algorithm.

Bit Rate:

• The amount of data information being transmitted in one second of time is called the bit rate, expressed in bits per second (b/s).

• A bit rate of one thousand bits per second is called a kilobit per second (kb/s); one million bits per second a megabit per second (Mb/s); and one billion bits per second a gigabit per second (Gb/s).

• A bit rate of more than 200 Mb/s would be required to digitize a broadcast quality video service without any signal impairment.

• This would require the use of several satellite transponders to relay just one uncompressed digital video signal.

• It therefore is essential that some form of signal compression be used to dramatically reduce the number of bits required for digital TV transmissions.

Communication Channel

• In a communications system, the part that connects a data source to a data sink is known as channel.

• Bandwidth refers to the data transmission capacity of a communications channel.

• The greater a channel's bandwidth, themore information it can carry per unit of time.

• The required bandwidth can vary greatly according to the type of application.

• For example, the transmission of simple ASCII text messages requires relatively little bandwidth, whereas the transmission of high resolution video images requires a large amount of bandwidth.

• For DTH system, communication channel is air and Band-Width is :Ku Band Up link : 13.75 to 14.5 GHzKu Band Down links : 10.95 to 11.2 GHz11.45 to 11.70 GHz12.50 to 12.75 GHz

Receiver Terminal

• The receiver terminals are basically for the reception of the signals being beamed from the transmission station.

• The terminal consists of the following :

1. • Receive type solid offset antenna2. • LNB feed system3. • Interface cables & Set top box

• The terminal can be placed outside the window of a high rise building, on the ground or a roof mount.

• The terminals can be used as per the contents being beamed by the transmission stations.

• DTH can also reach the remotest of areas since it does away with the intermediate step of a cable operator and the wires (cables) that come from the cable operator to your house.

Receiver Antenna

The selection of the appropriate antenna size is

based on the following: • Satellite EIRP at the particular location.• Rain attenuation at the location.• Adequate Eb/No for reception of excellent

picture quality.

SATELLITE RECEIVING ANTENNA

The parabolic curve has the property of reflecting all incident rays arriving along the antenna reflector’s axis of symmetry to a common focus located to the front and centre.

Parabolic Reflector

• The parabolic reflector receives externally generated noise along with the desired signal.

• When the satellite dish tilts up towardsthe "cold" sky, the antenna noise temperature is at its lowest level.

• The actual amount of noise increase in this case is a function of antenna f/D ratio and diameter.

• Minimum antenna elevation angles of 5 degrees, for C band, and 10 degrees, for Ku-band, above the site location's horizon usually are recommended.

• If the antenna must tilt downward to receive a low-elevation satellite, however, the antenna's noise temperature will increase dramatically because it is now able to intercept the "hot" noise temperature of the Earth.

Antenna f/D Ratio

• The f/D ratio of the antenna is the ratio of focal length to dish diameter, measured in the same units.

• The f/D ratio selected by the antenna designer also determines the depth of the dish itself, that is, the amount of contour or "wraparound" of the paraboloid within its fixed diameter.

• The deepest reflectors have a f/D ratio of 0.25.

• A long-focus (high f/D) paraboloid reflector will have a shallow contour, while a short-focus paraboloid reflector resembles a deep bowl.

• This places the focal point directly in the plane of the antenna aperture.

• An antenna design with a large value of f/D requires a feed horn that has a narrower beam width, so that the edge illumination ofthe antenna can be maintained.

• This typically is between 10 and 15 dB below the value produced at the center of the reflector.

DISH MATERIALS AND CONSTRUCTION

• The reflector's surface material must be constructed out of metal in order to reflect the incoming microwave signals.

• Some antenna reflectors appear to be manufactured out of plastic or fiberglass; however, these dishes actually have an embedded metal mesh material that reflects the incoming satellite signals to the front and center of the dish.

• One oval dish design that is the antenna of choice for most digital DTH satellite TV service providers is called the offset-fed antenna.

• The offset paraboloid eliminates aperture blockage, reduces antenna noise temperature, and resists the accumulation of ice and snow by placing the feed below the reflector and angling it upwards.

• The offset-fed antenna can achieve higher efficiency levels than prime focus antennas normally attain, usually in the 70 percent range.

Antenna Specifications

1. Reflector Size - 65cm2. Type – Offset Feed 3. Frequency - 10.7 to 12.75 GHz4. Antenna Gain - > 36.75dB @12.75 GHz5. 3dB Beam width - < 3.2 degree6. 10dB Beam width - < 5.2 degree7. Aperture efficiency - >70%8. Surface Accuracy - < 0.01"9. Noise Temperature - < 35 Kelvin10. Offset Angle - 25 degree11. F/d ratio - 0.6

Low Noise Blocker

• A low-noise block converter is the antenna of what is commonly called the parabolic satellite dish commonly used for satellite TV reception.

• It is functionally equivalent to the dipole antenna used for most other TV reception purposes, although it is actually waveguide based.

• The purpose of the LNB is to use the super-heterodyne principle to take a wide block of relatively high frequencies, amplify and convert them to similar signals carried at a much lower frequency.

• These lower frequencies travel through cables with much less attenuation of the signal, so there is much more signal left on the satellite receiver end of the cable.

LNB Specifications:

1. I/P Range - 1O.7 GHz to 12.75 GHz 2. Local Oscillator - 9.75 GHz or 10.6 GHz 3. Noise Figure - 0.5 dB 4. Noise Temperature - 35 Kelvin @ 290

degree 5. Gain - 55dB

Set Top Box

• The set top box accepts the entire down converted band and separates out the individual transponder frequency.

• Then signals are first converted to fixed IF and then QPSK demodulated.

• The bandwidth of QPSK signals is 27.5 MHz asthe bit rate is 27.5 Mb/s.

• It is observed that 11 digital channelsare multiplexed in 27.5 MHz bandwidth.

• The power supply for LNB, polarization selection signals as well as LO setting signals are send by the set top box itself by using the same cable between the LNB and set top box.

• After the QPSK demodulation, the digital bit stream obtained contains several multiplexed channels as well as error control bits.

• The bit stream is processed to correct and detect errors, deinterleaved , and decrypted.

• A digital demultiplexer then extracts the bits for wanted channel, and sends them to MPEG decoder.

Block Diagram of Set Top Box

DTH BENEFITS

• Cost effective communication , information and

entertainment to all.

• Small size terminals can provide upto 4000 TV channels and 2000 radio channels through a click of a button and thus brings world’s altest information , news , entertainment to your home.

• DTH services bypasses mediators and thus content provider comes with customer directly.

• DTH services are transparent providing digital quality to all at equal prices.

CONCLUSION

• DTH has made the hopes of the people of rural areas to come true.

• It helps to develop and explore the ignited mind of people of India to think beyond the scope of imagination.

• It also helps to develop the economic conditions of a country.