When we talk about digital broadcasting we usually talk about better picture and sound, high definition television, MPEG compression and more choice. The roots of transition to digital television broadcasting lie in more effective use of radio-frequency spectrum. In analog television world we have radio-frequency channels (frequencies) where each frequency transmits one TV channel (program) and in order to avoid interference the same frequency can be used again only far away. Digital technology enables us to use advanced compression algorithms to compress audio and video signals, consequently we can use one frequency channel to transmit more than one service (usually three to ten and even more TV channels), and we can build a network of transmitters operating on the same frequency thus significantly lower the number of frequencies (channels) needed to cover a territory.
There are a few standards for digital television broadcasting. Frequency plans for DVB-T are based on allotments - areas where all transmitters transmit on the same frequency. It helps in demodulating the signal. During the guard interval the same symbols with varying arrival times can be received without any inter-symbol interference. This is the basic principle of Single Frequency Networks (SFN).
Of course, the maximum distance between transmitters operating on the same frequency depends on the length of the guard interval. It is obvious that digital broadcasting has many advantages. Digital networks need to be synchronized to operate properly in SFNs and this can be sometimes tricky.
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