I. Introduction
An orthogonal frequency division multiplexing (OFDM) system has several advantages over a single carrier modulation system. The major advantages are robustness to multipath fading and high bandwidth efficiency. These facilitate OFDM to be widely used in various high-rate data transmission systems such as the asymmetric digital subscriber line (ADSL) [1], the digital audio broadcasting (DAB) [2], the terrestrial digital video broadcasting (DVB-T) [3], and the wireless local area network (WLAN) [4]. Recently, OFDM has been attracting a considerable attention as a strong candidate for the wideband mobile communication system providing advanced cellular Internet service [5].