CHAPTER Estimation of Time-Varying Channels ­ A Block Approach 1 Delft 2 TNO 4 Geert Leus 1 , Zijian Tang 2 , Paolo Banelli 3 University of Technology, Delft, The Netherlands Defence, Security and Safety, The Hague, The Netherlands 3 University of Perugia, Perugia, Italy 4.1 INTRODUCTION For coherent detection in a wireless communication system, channel state information (CSI) is indis- pensable. Channel estimation has drawn tremendous attention in the literature (see Tong, Sadler, & Dong, 2004 and references therein), where the pilot-aided method is one of the most intensively stud- ied approaches. This method is especially attractive for time-varying channels because of their short coherence time.