Performance improvement of the OFDM system based on fractional Fourier transform over doubly dispersive channels

Traditional orthogonal frequency-division multiplexing (OFDM) loses its optimality in high-mobility scenarios, intercarrier interference (ICI) occurs and the Doppler shifts destroy the orthogonality of the subcarriers. Many solutions are introduced by using complicated equalizers in the receiver to overcome this problem. The fractional Fourier transform (FrFT) has been suggested to improve the performance of the OFDM over doubly dispersive channels that cannot be achieved with traditional OFDM even with complex equalizers. In this paper the performance of OFDM based FrFT is studied with multiple fractional orders at different Doppler shift. Simulation results demonstrate processing improvement due to using FrFT instead of Fourier Transform (FT) in OFDM system. The same bit error rate (BER) is achieved without increasing the transmitting signal to noise ratio (SNR) and processing improvements are gained up to 3 dB for different Doppler frequencies.