Analog television (ATV) transmits an analog signal whose amplitude values vary over a continuous interval. This signal carries the audio signal (sound), video signal (information about picture brightness and color) and synchronization information (horizontal, vertical). The audio signal is modulated using frequency modulation and the video signal is transmitted using amplitude modulation both on one channel frequency, i.e. one TV station occupies entire capacity of one channel frequency.
Analog nature of transmitted signal causes that analog television typically provides lower quality of picture. The analog signal is a subject of interferences and noises during transmission (physical principles of signal propagation, reflections, weather) resulting in ghosts and snow (noise, graininess) in final picture. With increasing a distance between user’s antenna and transmitter the analog signal lowers its intensity and it cannot be completely regenerated.
Digital television (DTV) transmits digital signal. Because source video and audio signals are analog signals they have to be digitized at first, i.e. converted to streams of 0s and 1s. As is mentioned in following section digitized signals have to be compressed and then combined to form a transport signal (stream) that is adjusted for broadcasting finally.
DTV signals are protected by error correction codes which enable to regenerate original signal and eliminate noise and interferences [1]. Therefore users can watch TV channels (picture and sound) in same quality how they were broadcasted (no ghosts). This technology provides users with picture in standard (SD) as well as high definition (HD) resolutions and sound in CD (Compact Disc) quality. Digital television can use capacity of one frequency channel more effectively. Compression (and multiplexing) algorithms allow operators to insert more TV (as well as radio) stations within the same capacity previously occupied by one analog TV station. Digital television offers a lot of innovations with a new operation model which significantly contributes to a convergence of computers, television and Internet. Benefits for customers are noticeable hundreds of TV channels and access to a wide range of new services.
DTV and ATV can use the same medium for broadcasting (cable, air, and satellite). They share the same frequency band but not the same frequencies at the same time. DTV is not backward compatible with ATV. Users have to buy a new digital set-top-box (STB) [3]. Fig 2 shows how picture quality behaves based on signal strength. Simply said, digital picture is either in perfect quality or there is no picture. There is long interval when digital picture remains in perfect quality whereas analog TV picture is gradually becoming more grainy and/or with ghosts.