TV DIGITAL

CATV

Oleh :Andini Salsabilla (1101130024)Girta Rama (1101130025)Reni Dyah W (1101130026)Gusty Aditya A (1101130027)

Digital TV (DTV) transmission offers the same advantages as any other form of digital communications, including enhanced bandwidth efficiency through compression, improved signal quality, and more effective management and control. As a result, it offers advantages in terms of processing, storage, and manipulation.Those advantages include editing, alteration (e.g., morphing ), reproduction, compression, and store - and - forward capability. Digital video requires that the information be digitized through the use of a video codec.

A broadcast - quality video signal is extremely bandwidth and storage intensive. Despite all the advantages of digital technology as applied to TV production, storage, transmission, and reception, all of the TV sets were analog. A conversion from analog to digital broadcast TV is revolutionary and completely unthinkable, unless there exists a compelling reason for the changeout of untold millions of TV sets. According to the manufacturers and the FCC, that compelling reason is in the form of High - Defi nition TV (HDTV).

The reasons of discussing broadcast TV technology and standards and their evolution are: First, most of the same technologies and standards apply to interactive videoconferencing and multimedia.Second, although broadcast DTV and CATV (Community Antenna Television) do not necessarily have to follow the same rules of the road, it is likely that the CATV providers will carry broadcast TV signals in a digital format since they are upgrading their networks to digital anyway. The FCC has imposed must - carry rules on both the CATV and the DBS (Direct Broadcast Satellite) providers, thereby forcing them to carry local broadcast TV channels and to fairly compensate the local stations for that content.

Considering that service providers are deploying broadband digital local loops in support of the triple play of voice, data, and TV, that the backbones are digital, that data, image,and movie content are digital, and that the TV broadcast signal will be digital, it is pretty clear that the digital circle will be complete very soon.

TV DIGITAL AND CATV

The bandwidth required for video transmission is very signifi cant and is affected by frame rate, resolution, color depth, aspect ratio, and audio.

Digital video, on the other hand, can be compressed fairly easily. Because uncompressed, broadcast - quality digital video requires between 90 and 270 Mbps, compression is critical. Without compression, a 1 - Gbps fiber - optic network could accommodate no more than 11 digitized NTSC channels. To digitize and compress the video information stream, the analog video and data signal first must be digitized through the use of a codec. Clearly, it is possible to reduce the amount of bandwidth required to transmit digital video and the amount of memory required to store it by reducing the frame rate, resolution, or color depth. However, the result is less than pleasing. In order to maintain the quality of the video presentation, therefore, the data must be compressed by using an appropriate and powerful data compression algorithm.A number of steps are involved in video compression, including filtering, color – space conversion, scaling, transforms, quantization and compaction, and interframe compression.

BANDWIDTH AND COMPRESSION

BANDWIDTH AND COMPRESSIONFiltering

Color - space conversion

Scaling addresses

also known as image decimation , reduces the total frequency of the analog signal through a process of averaging the values of neighboring pixels or lines. For example, adjoining black - and - white pixels become gray pixels. Taps are the number of lines or pixels considered in this process; MPEG, for example, uses a seven - tap fi lter.

also known as color sampling , simply involves the reduction of color information in the image. As the human eye is not highly sensitive to slight color variations, the impact is not noticeable. Black and white, however, are prioritized because the human eye is very sensitive at that level.

the creation of the digital image according to the presentation resolution scale associated with the display device. Rather than digitizing the video signal in large scale, the codec is tuned to the scale of presentation in terms of horizontal and vertical pixels, thereby reducing the amount of data that must be digitized. In consideration of this factor, the aspect ratio must be standardized.

Transforms

convert the native two - dimensional video signal into data dimensions. Although they are beyond the scope of this book, the various approaches include Discrete Cosine Transform (DCT), vector quantization, fractal transform,and wavelet compression .

BANDWIDTH AND COMPRESSIONQuantization and compaction encoding

Interframe compression

simply reduce the number of bits required to represent a color pixel. Compaction techniques include run – length encoding, Huffman coding , and arithmetic coding .

considers and eliminates redundant information in successive video frames. The background of a movie scene, for example, might not change, even though the actors move around the set. While the motion of the actors must be refl ected, the background need not be retransmitted over the network. Rather, it can be compressed out of each frame until background changes must be refl ected. At the point of decompression at the receive end of the signal, the unchanged background can simply be reinserted over and over again.

CATV History• Poor frequency response. Some part of the received band had notably lower levels

than other parts. This is particularly true as the frequency increases. In other words, there was fairly severe amplitude distortion. Thus equalization became necessary.

• The mixing of two or more RF signals in the system caused intermodulation products and “beats” (harmonics), which degraded reception.

• When these TV signals carried modulation, cross-modulation (Xm) products degraded or impaired reception.

CATV Network ServicesBroadcast analogue services :• Broadcast TV analog.• Broadcast audio analog.

Digital broadcast services :• Digital Video Broadcast (DVB) :

video, audio, data.• Near Video on Demand (NVoD) • Pay per view Service. • Pay per Channel Service.

Interactive Multimedia Services :• Video On Demand.• Karaoke On Demand.• Audio On Demand.• Interactive Games.• Telemedicine.• Teleworking.• Telemeeting.• Telelearning.• Interactive Home Shopping.• Electronic Commerce.

Value Added Services

Cable Telephony based on Packet Cable

High Speed data Services :• Fast Internet Access• Data Over Cable

Services• Community LAN

Services