This book addresses theory of channel modelling and data restoration at the receiver end in orthogonal frequency division multiplexing (OFDM) communication systems designed to operate in the doubly selective wireless channel. A family of reduced-complexity pilot-assisted estimators for the single and multiple-antenna OFDM configurations is described, emphasising optimal design and analytic performance evaluation. The problem of optimal power allocation between the data and the pilot symbols is investigated in detail. The closed-form analytical expressions are presented, prescribing optimised power levels for the transmitted pilot sequences. This is followed by simulation-based symbol error rate improvement demonstration in case of a system with the proposed optimisations incorporated. The book is recommended for a broad audience interested in digital signal processing problems of the modern broadband wireless communication systems. It might be useful for the postgraduate students specialising in wireless communication system research as well as for the R&D engineers involved in the corresponding system design and manufacturing.