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WELCOME

Seminar report on

DTH

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Introduction

DTH stands for DIRECT-TO-HOME television

DTH is defined as:

The reception of satellite programmers with a

personal dish in an individual home.

DTH does away with the need for the local

cable operator and puts the broadcaster

directly in touch with consumer .

Working of DTHThe DTH utilizes a technology which enables a home to receive video channel with a suitable set capable of demodulating mpeg-2 (4) standard video channel with a suitable set top box

The DTH service provider has to lease ku band transponders from the satellite .

DTH does away with the need of local cable operator and put the broadcaster directly in touch with consumer.

Network of DTH

Dth consist of three main parts

•Programming source

•Broadcasting center (dbs)

•The receiving terminal

The programming source are simply the channels that provide programming for broadcast. The provider doesn't create original programming Itself; it pays other companies(HBO, ESPN etc)Satellite TV provider get programming from two major source; international turnaround channels (such as HBO,ESPN&CNN) &various local channel ( sahara TV,doordarshan etc ). Turnaround channels usually have a distribution center that beams

there programming to a geostationary satellite .the broadcast uses large satellite dishes to pick up these analog & digital signal from several sources .

Broadcasting center

Encoders

multiplxersModulators Broadcasting

Satellite

(Central hub of the system)

Broadcast center The broadcast center converts all of this programming into high quality, uncompressed digital stream. At this point the stream contains a vast quantity of data about 270 mbps for each channel . In order to transmit the signal from there, the broadcast center has to compress it.

Encoder (MPEG-2)The base analog or the high quality digital video- audio are converted to the DVB standards of correct size and format .With digital compression the satellite can transmit about 200 channels .

Multiplexers Mixes these signals

Modulation The modulation converts the message signal into a form that is suitable for transmission over communication channel. This involve varying some parameters of a carrier wave in accordance with the message signal.

Encryption After the video is compressed, the provider needs to encrypt it in order to keep people from accessing it for free. Encryption scrambles the digital data in such a way that it can only be decrypted if the receiver has correct decoding satellite receiver with decryption algorithm and security keys

Transmission Once the signal is compressed and encrypted, the broadcast center beams it directly to one of its satellite. the satellite pick up the signal amplify it & beams back to earth where viewer can pick it up .

Receiving station ( for the reception of the signal being beamed from transmitted station)

Receive type solid offset antenna LNB feed

system

Interface cables

Set top box

When a beam hits the curved dish, the parabola shape reflects the radio signal inward onto a particular point, just like a concave mirror focuses light onto aparticular point. The curved dish focuses incoming radio waves onto the feed horn. In this case, the point is the dish’s feed horn, which passes the signal onto the receiving equipment.

Feed horn Receive type solid offset antenna

Advantages of using offset fed antenna

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

There is no feedhorn blockage an important consideration when the antenna aperture is less one meter in diameter the

The offset feed antenna can achieve higher efficiency levels then prime focus antenna normally attain , usually in the 70% range .

low noise blockdown converter, or LNB.

The central element in the feedhorn is low noise blockdown converter Low Noise Block-down convertor (so called because it converts a whole band or “block” of frequencies to a lower band).An LNB sits on the end of an arm and faces the parabolic reflector (“dish”) which focuses the signals from a satellite into the “feed horn” of the LNB (see pictures below). The LNB converts the signals to a lower frequency and sends them out to the cable connector, which you connect to your satellite receiver via coaxial cable.

Lnb amplifies the radio signal bouncing off the dish and filter out noise (radio signal not carrying programming and also converts the ku band frequency into if bassed on local if

LNB

Universal LNB“Universal” ku band LNB is available that can switch electronically between 10.7-11.7 and 11.75-12.75 GHz frequency spectra to provide complete coverage of entire ku- band frequency range.The receiver send switching voltage (13 or 17 V dc ) to the LNB that automatically changes the LNB input frequency range to the desired frequency spectrum.

Set top box (STB)

A set-top box (STB) or set-top unit (STU) is a device that connects to a television and an external source of signal, turning the signal into content which is then displayed on the television screen

Qpsk demodulation Digital demultiplexing Mpeg decoder DAC

LNBConventional

mixture ADC

Qpsk demodulation

Synchronizer

vitiebri

Mpeg transpor

t demultiplexing

Mpeg decoder

DAC

Control process

Conditional access Video

encoder

Smart

card

Block diagram of STB

Demodulation (Qpsk) the process of conversion of signal into its original form transmitted at the transmitter is called demodulation .

Digital demultiplexing After Qpsk demodulation the digital bit stream contain several multiplexed Channel as well as error control bits. The bit stream is processed to correct and detect error , de interleaved and decrypted. The digital demultiplexer then extracts the bits for wanted channels. Mpeg decoder It de-scrambles the encrypted signal. In order to unlock the signal, the receiver needs the proper decoder chip for that programming package (smart card having correct keys for decryption is required to view paid channels ) The provider can communicate with the chip, via the satellite signal, to make necessary adjustments to its decoding programs.DAC The DAC finally generates analog audio and video signals to derive TV sets

Some other important terminology related to DTH service Satellite Geostationary satellite plays an important role for DTH system They are positioned at an exact height above the earth about 36000km As they remain stationary and they are ideal for use as communication satellite and also for remote imaging as they can scan the same point on earth beneath them.The satellite solves the problem of range and distortion by transmitting broadcast signal from satellites orbiting the earth.

PolarizationPolarization is a way to give transmission signal a specific direction. It makes beam more concentrated .Signal transmitted by the satellite can be polarized in one of four different ways linear (horizontal and vertical ) or circular ( left hand or right hand )To use the channel available for broadcasting as efficiently as possible both horizontal and vertical polarization(and left and right circular polarization) can be applied simultaneously per channel In such case frequency of one of the two is slightly altered, to prevent interference.

Future technologies in DTH Enabling cable and DTH for internet and interactivity

IP TV Voice over internet protocol telephony

Benefits of DTHCost effective communication, information and entertainment to all Small size terminal can provide up to 4000 channels and 2000 radio channels through a click of button and thus bring worlds 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 video , audio, radio, and IP to all at equal prices and other benefits with reliabilty

Conclusion Direct to home connects urban , rural and remote areas of the country and provide desire information, communication, information, education and entertainment at the click of button.

Thank you