Frame selection algorithm with adaptive FFT input for OFDM systems

Orthogonal frequency division multiplexing (OFDM) systems transmit a cyclic prefix, called a guard-interval, which is inserted in front of the effective symbol period along with signals copied from some of the last parts in the effective symbol period. This guard-interval is then used to reduce distortions due to multipath conditions. However, conventional OFDM systems produce inter-symbol interference (ISI) under severe multipath or pre-ghost channel conditions even though they accurately estimate the effective symbol period. Accordingly, the current paper proposes a frame selection algorithm for a fast Fourier transform (FFT) operation in the OFDM receiver to remove the ISI produced in conventional OFDM systems under multipath conditions. The proposed algorithm replaces some of the rear parts of the effective symbol period with some of the guard-interval as an FFT input frame. The replaced period for the FFT input frame is changed according to the multipath environment. Four estimation methods for determining the replaced period are also presented. The proposed algorithm can increase the receiver performance by more than 3 dB under multipath conditions in a digital video broadcasting-terrestrial (DVB-T) system without changing the equalization method.