OFDM with guard interval and sub-channel equalization in a 2-resolution transmission scheme for digital television broadcasting

The interest in a new digital terrestrial TV system, that allows improved quality and receiver portability, leads to the choice of a modulation system suitable for operation in a very hostile environment (interferences, multipath). A very effective solution, already experimented with digital audio broadcasting, is the orthogonal frequency division multiplexing (OFDM) technique with a guard interval. Unluckily such an interval grows from a few ten microseconds, sufficient for typical urban propagation environment, up to 600 microseconds, when the emerging single frequency network (SFN) is considered. A long guard interval (as required in a SFN) results in a excessive prolongation of the symbol period (T) and thus in bandwidth efficiency loss. In addition, the use of a too long symbol period is limited by the effects of time selectivity of the channel and by technological limitations. In this light, the use is suggested of a shorter guard interval and a low complexity equaliser at the output of each subcarrier to reduce the error produced by the echoes exceeding the guard interval duration. A multiresolution (MR) transmission scheme has been adopted in order to eliminate the sharp threshold effect in the fringes of the broadcast area. The system performances of a 2-resolution OFDM system have been evaluated by computer simulation on a frequency-selective channel for Rice and Rayleigh propagation environment