Blind adaptive channel equalization for OFDM using the cyclic prefix data

In an orthogonal frequency division multiplexing (OFDM) system using DQPSK, such as DAB, channel equalization is considered to be unnecessary. The reason for this is that there is no relative phase rotation due to the multipath channel in successive OFDM symbols, provided the channel delays are all shorter than the guard interval of the OFDM symbol. However, delays greater than the guard interval result in inter-carrier and inter-symbol interference to the OFDM system. In this paper, we present a blind adaptive equalization algorithm which uses the cyclic prefix data of the OFDM signals to equalize the multipath channel. This algorithm is ideal for systems such as DAB in which no pilots are available for the channel estimation yet the long delays nevertheless can cause significant performance degradation if no channel equalization is done. Our simulation results shows improved BER performance for the equalized system over the non-equalized system when long channel delays are present.