Contents I. INTRODUCTION
OFDM is a popular multi-carrier modulation technique that offers very high transmission rates and utilizes efficiently the available spectrum and network resources. It is a promising choice for future high speed data rate systems and is already incorporated in many applications and standards such as WLAN, Digital Audio Broadcasting (DAB), Digital Video Broadcasting (DVB), the European HIPERLAN/2, Worldwide Interoperability for Microwave Access (WiMAX) and Digital Subscriber Line (DSL) [1]. In OFDM modulation scheme, multiple data symbols are modulated simultaneously by multiple carriers by breaking the wide transmission band into narrower, multiple sub-bands. This process allows OFDM to effectively combat frequency-selective fading usually encountered in wireless channels. Despite the great advantages OFDM offers, it has a few drawbacks, the most serious of which is the non-constant signal envelope with high peaks. These high peaks produce signal excursions into nonlinear region of the high power amplifier at the transmitter, thereby leading to nonlinear distortion. For a binary data stream with rate bps, modulated symbols, , are stored for an interval of using a serial-to-parallel converter. Subsequently, each one of the symbols modulates one sub-carrier and then all modulated sub-carriers are transmitted simultaneously [2]. The OFDM signal can be expressed as \eqalignno{&x(t) =\sum_{k=0}^{N-1}\alpha_{k}\exp(j2\pi(f_{c}+k\triangle f)t) \cr &=\ \exp(j2\pi f_{c}t)\sum_{k=0}^{N-1}\alpha_{k}\exp(j2\pi k\triangle) \cr &= \exp(j2\pi f_{c}t)\alpha(t), & \hbox{(1)}}
