An OFDM turbo equalizer for scattered pilot signals in multipath environments with delay difference greater than guard interval

This paper proposes an OFDM turbo equalizer with precise channel estimation for scattered pilot signal reception in large delay spread environments. The equalizer effectively eliminates inter-symbol interference (ISI) from the previous and following OFDM symbols and inter-carrier interference (ICI) within the symbol, in multipath fading environments with delay difference greater than the guard interval (GI). The proposed OFDM receiver consists of a coherent detection unit, a turbo equalization unit and channel estimators for the respective units. In equalization mode, conventional channel estimators cannot precisely estimate the large delay profile by only using the scattered pilot. The new channel estimator for the turbo equalization exploits the log-likelihood ratio fed back from the MAP decoder for data. Computer simulation demonstrates the effectiveness of the turbo equalizer with precise channel estimation in the scattered pilot OFDM system specified by the digital terrestrial television broadcasting (DTTB) standard.