Differential OFDM Employing AFC for Doubly-Selective Channels in the Presence of Time-Varying Doppler Shifts

Abstract

This paper proposes differential orthogonal frequency division multiplexing (OFDM) employing automatic frequency control (AFC) for severe time and frequency selectivities, i.e., double selectivity in the presence of fast time-varying Doppler shifts. With respect to double selectivity, differential encoding/differential detection (DE/DD) is effective for time selectivity, and OFDM is effective for frequency selectivity. However, differential OFDM suffers from serious performance degradation due to intercarrier interference (ICI) caused by fast time-varying Doppler shifts. In order to cope with doubly-selective channels in the presence of fast time-varying Doppler shifts, this paper proposes differential OFDM employing AFC which can compensate frequency offset. The proposed scheme employs a multiple open-loop frequency estimation (MOLFE), which has a good trade-off between frequency coverage and estimation accuracy in short observation time. Next, this paper proposes a simple time-varying Doppler shift simulation model for autonomous underwater vehicle (AUV) turning. Finally, computer simulation results confirm that the proposed differential OFDM employing MOLFE has excellent performance in doubly-selective channels in the presence of fast time-varying Doppler shifts.