Doppler correction for digital modulation in a fading channel with SISO

In a high mobility wireless channel, the Doppler effect is compounded and must be corrected by using pilot-aided symbols. The pilot symbol rate depends on the severity of the Doppler effect. There are existing algorithms such as differential decision-feedback (D-DF) and double-differential decision-feedback (DD-DF) for single-input single-output (SISO) systems to improve channel tap estimation. Such algorithms improve the bit error rate (BER) performance of pilot symbol aided decision feedback demodulation. In this paper, minimum mean square error (MMSE) estimation was implemented to further improve the channel tap estimation for the D-DF and DD-DF algorithms. BER performance showed significant improvement for higher order modulation schemes. On the other hand, implementation of the new algorithm on quadrature phase-shift keying (QPSK) showed negligible improvement.