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Application Notes
Single Frequency Network (SFN) television broadcasting systems have been widely deployed, especially for OFDM based systems like DVB-T and DVB-T2 [1][2], DTMB, and ISDB-T, due to their high frequency efficiency and simple frequency planning. However, building a successful SFN system is challenging because it requires precise transmitter deployment in order to ensure good coverage.
In an SFN, two or more transmitters radiate the same signal on the same frequency simultaneously and repeaters are used to ensure good signal coverage. The receiver is thus likely to receive multiple echoes from many of these transmitters. Echo scenarios in SFN systems in the real world can generally be categorized as one of the following: post-echoes, pre-echoes, pre-echoes and post-echoes.
For an OFDM system, a guard interval (GI) is inserted between symbols to prevent inter-symbol-interference (ISI). As long as the maximum delay of the echoes is within the GI, there should theoretically be no ISI. The principle behind SFN deployment is that the echoes from different transmitters must lie within the GI and echoes outside the GI must be low enough to avoid detection so that no interference is received.
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