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Analog Station Digital Station

Analog television systems are severely limited by Analog television systems are severely limited by the bandwidth they have available.the bandwidth they have available.

Simply put, additional subscription service require Simply put, additional subscription service require additional bandwidth and if it is not available, additional bandwidth and if it is not available, revenue growth is limited.revenue growth is limited.

Introduction to Digital TelevisionIntroduction to Digital Television

Why Digital Television?Why Digital Television?

Degradation of analog Degradation of analog

SignalSignal

Multi path distortionMulti path distortion

Crystal Clear Picture and SoundCrystal Clear Picture and Sound

ANALOG SIGNAL

ANALOG SIGNAL

MulticastingMulticasting

Instead of transmitting Instead of transmitting a single program, a single program, broadcasters can use broadcasters can use this digital signal to this digital signal to transmit – on one transmit – on one channel- at least four channel- at least four programs in resolution programs in resolution of today’s standard-of today’s standard-definition TV.definition TV.

This is known as the This is known as the MulticastingMulticasting

Data Casting Data Casting

Digital Television also Digital Television also has the ability to has the ability to broadcast data broadcast data simultaneously.simultaneously.

This is called data This is called data casting. It means you casting. It means you will be able to use an will be able to use an on-screen menu to on-screen menu to access additional access additional information about the information about the running programrunning program

Other ServicesOther Services Local channels, news and information about area, Local channels, news and information about area,

Whether report, travel report, national news, home Whether report, travel report, national news, home shopping, games….shopping, games….

Sports service-the latest results, interviews with Sports service-the latest results, interviews with personalities, special offerpersonalities, special offer

Home banking, checking your balance, E-mail, Home banking, checking your balance, E-mail, paying bill….etcpaying bill….etc

In fact in the new world of Digital Television the In fact in the new world of Digital Television the only limit on the range of available service will be only limit on the range of available service will be the imagination of the service providers.the imagination of the service providers.

Technical Background Technical Background

Y-SignalY-Signal R-G-B- Camera outputR-G-B- Camera output R-Y & B-Y SelectionR-Y & B-Y Selection Weighting FactorsWeighting Factors R-Y R-Y V & B-YV & B-YUU U +V U +V QAM QAM C C Y + C Y + C Frequency Frequency

Interleaving Interleaving Composite Colour Composite Colour

Video Signal Video Signal

Digitization of Composite Colour SignalDigitization of Composite Colour Signal Video Signal QuantizationVideo Signal Quantization Compression Compression

It has been practically verified It has been practically verified that sampling of the analog that sampling of the analog video signal at 256 levels is video signal at 256 levels is sufficient to allow the sufficient to allow the reproduced signal to be almost reproduced signal to be almost undetectable form the original undetectable form the original analog signal.analog signal.

An 8 bits code word is An 8 bits code word is necessary due to 256 levels. necessary due to 256 levels.

In the proposed coding scheme In the proposed coding scheme for television signals, black level for television signals, black level corresponds to 64 (code corresponds to 64 (code 01000000) and peak white to 01000000) and peak white to level 204 (code 11001100) as level 204 (code 11001100) as labeled in the figure.labeled in the figure.

CompressionCompression

Composite Video signal can be thought of Composite Video signal can be thought of as an analog compression technique as it as an analog compression technique as it allows colour in the same bandwidth as allows colour in the same bandwidth as monochrome. monochrome.

Whilst digital compression schemes do exist Whilst digital compression schemes do exist for composite video, these effectively put for composite video, these effectively put two compressors in series which is not a two compressors in series which is not a good idea.good idea.

So solution So solution MPEGMPEG

Basic of Video CompressionBasic of Video Compression

MPEG and Video CompressionMPEG and Video Compression

The MPEG is the current standard used for The MPEG is the current standard used for digital video. In this system, only the digital video. In this system, only the difference between the current frame, and difference between the current frame, and the next frame is considered.the next frame is considered.

Block matching algorithms are employed to Block matching algorithms are employed to detect if an object has move in the scene.detect if an object has move in the scene.

mathematical process called Discrete mathematical process called Discrete Cosine Transform (DCT) is used to Cosine Transform (DCT) is used to compress the data.compress the data.

Why MPEG?Why MPEG?

Two adjacent frames in a motion picture Two adjacent frames in a motion picture sequence are usually very identical. Often the sequence are usually very identical. Often the only difference is that some parts of the picture only difference is that some parts of the picture have shifted slightly between the frames.have shifted slightly between the frames.

If the content of the current frame was mostly sent If the content of the current frame was mostly sent in the previous frame, why send it again?in the previous frame, why send it again?

Just send the instructions for shifting pieces of the Just send the instructions for shifting pieces of the previous frame to their new position in the current previous frame to their new position in the current frame.frame.

If the pixel points in the same area are all very If the pixel points in the same area are all very nearly the same colour why send the same colour nearly the same colour why send the same colour over and over? over and over?

Just send the colour for the whole area ones.Just send the colour for the whole area ones.

Video Compression TechniqueVideo Compression Technique

Set-Top Box With conditional Access Set-Top Box With conditional Access SystemSystem

Digital television has several advantages over traditional TV, the most Digital television has several advantages over traditional TV, the most significant being use of a smaller channel bandwidth. This frees up significant being use of a smaller channel bandwidth. This frees up space for more digital channels, other non-television services such as space for more digital channels, other non-television services such as pay-multimedia services and the generation of revenue from the sales pay-multimedia services and the generation of revenue from the sales of frequency spectrum taken by analog TV. As digital becomes more of frequency spectrum taken by analog TV. As digital becomes more popular it is likely that the existing analogue services will be removed.popular it is likely that the existing analogue services will be removed.

The digital terrestrial set-top-box has been demonstrated at The digital terrestrial set-top-box has been demonstrated at Doordarshan Delhi by receiving the 5 TV programs and 2 Radio Doordarshan Delhi by receiving the 5 TV programs and 2 Radio channels on 516MHz channel frequency using Yagi antenna.channels on 516MHz channel frequency using Yagi antenna.

In most 'digitalised' country, the switch-off of all analogue In most 'digitalised' country, the switch-off of all analogue terrestrial TV broadcasts is scheduled to begin in 2009.terrestrial TV broadcasts is scheduled to begin in 2009.

Conclusion Conclusion

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