Joint Estimation of Frequency Offset and Doppler Shift in High Mobility Environments Based on Orthogonal Angle Domain Subspace Projection

Conventional frequency preshift technology cannot distinguish between the large Doppler shift and the frequency offset aroused by crystal oscillator, which significantly hinders the system performance improvement in high mobility environments when the frequency offset is present. In this paper, a joint frequency offset and Doppler shift estimation algorithm in high mobility environment based on orthogonal angle domain subspace projection is proposed, which can track the fast time-varying Doppler shift and separate the Doppler shift from the frequency offset. First, an orthogonal angle domain subspace projection algorithm is proposed to project the Doppler spread caused by high mobility into equivalent Doppler shifts in each orthogonal subspace. Second, it utilizes equivalent Doppler shift of all orthogonal subspaces to jointly estimate the maximal Doppler shift and frequency offset. Finally, the estimates are used to compensate the frequency error in the received signal. Moreover, the maximum Doppler shift estimation, together with the projection vectors and the received power on each orthogonal subspace, is fed back and exploited in the subsequent transmitted signal. Simulation results show that the proposed method can estimate the two parameters accurately and eliminate almost all the errors on the Doppler rapidly changing area when SNR is up to 15 dB. Compared with the conventional receiver with automatic frequency control, the receiver with our proposed method achieves better system performance even on the Doppler rapidly changing area.