Orthogonal frequency division multiplexing (OFDM) is a multi-carrier transmission technique in which data from a single high data rate stream is transmitted over multiple sub-carriers at low data rate. Space-time block coding, applied to OFDM results in performance improvement to frequency selective fading. In time-varying environment, OFDM experiences inter-carrier interference (ICI) due to the Doppler spread of the channel. In this work, we propose a technique where pilot-assisted channel estimation is combined with differential ST-OFDM for reducing the performance degradation caused by ICI. A Rayleigh fading channel is considered, and channel estimation is performed using the method of modified local splines. The system is simulated and the performance has been observed for various Doppler conditions. The results show that the proposed system has improved performance over the differential ST-OFDM at high Doppler but has a 3dB decrease in performance compared to the coherent ST-OFDM.