EURASIP Journal on Applied Signal Processing 
Volume 2006 (2006), Article ID 62831, 15 pages
doi:10.1155/ASP/2006/62831

Estimation and Direct Equalization of Doubly Selective Channels

Imad Barhumi,1 Geert Leus,2 and Marc Moonen3

 1Electrical Engineering Department, United Arab Emirates University, Al-Ain 17555, United Arab Emirates
2Faculty of Electrical Engineering, Mathematics, and Computer Science, Delft University of Technology, Mekelweg 4, Delft 2628CD, The Netherlands
3ESAT/SCD-SISTA, Katholieke Universiteit Leuven, Kasteelpark Arenberg 10, Leuven 3001, Belgium
Received 15 June 2005; Revised 9 June 2006; Accepted 13 August 2006

Abstract

We propose channel estimation and direct equalization techniques for transmission over doubly selective channels. The doubly selective channel is approximated using the basis expansion model (BEM). Linear and decision feedback equalizers implemented by time-varying finite impulse response (FIR) filters may then be used to equalize the doubly selective channel, where the time-varying FIR filters are designed according to the BEM. In this sense, the equalizer BEM coefficients are obtained either based on channel estimation or directly. The proposed channel estimation and direct equalization techniques range from pilot-symbol-assisted-modulation- (PSAM-) based techniques to blind and semiblind techniques. In PSAM techniques, pilot symbols are utilized to estimate the channel or directly obtain the equalizer coefficients. The training overhead can be completely eliminated by using blind techniques or reduced by combining training-based techniques with blind techniques resulting in semiblind techniques. Numerical results are conducted to verify the different proposed channel estimation and direct equalization techniques.