In this paper, we consider orthogonal frequency division multiplexing (OFDM) systems with severe Doppler effect. In the frequency domain, this effect destroys the orthogonality between subcarriers and introduces interchannel interference (ICI). In the time domain, fast time-varying channels make channel estimation difficult and degrade the estimation accuracy. Thus ICI-mitigating and improved estimation techniques are desired. We proposed a new equalization technique to suppress ICI in linear minimum mean square error (LMMSE) sense and complexity can be greatly reduced. A novel channel estimation technique with low complexity and free of training symbol design is also proposed to estimate time-varying channels. Numerical results show that our proposal has significant performance improvement over traditional estimation and equalization techniques.