Oversampled orthogonal frequency division multiplexing in doubly selective fading

A new oversampled orthogonal frequency division multiplexing (OFDM) system operating in doubly selective fading environment is proposed in this paper. The oversampled OFDM structure employs oversampling in time domain and linear signal processing in frequency domain. The time-frequency processing enables a two dimensional Doppler-frequency grid that allows each data symbol be transmitted at multiple subcarriers and various Doppler spreads simultaneously, without sacrificing spectral efficiency. As a result, both Doppler diversity and multipath diversity inherent in doubly selective fading are achieved with simple linear operations. A Doppler domain block decision feedback equalizer is designed to suppress the intercarrier interference (ICI) caused by time varying fading, as well as to collect the diversity benefits enabled by the oversampled OFDM system. Simulation results show that the new system outperforms conventional OFDM system with the same spectral efficiency by as much as 8 dB.