Multirate techniques are commonly used in audio and video processing, communications systems, and transform analysis. In most applications multirate systems are used to improve the performance, or for increased computational efficiency. OFDM is a very attractive technique for wireless communication due to its spectrum efficiency and channel robustness. The major drawbacks of OFDM system are high peak-to-average power ratio (PAPR) and inter-carrier interference (ICI). In this book, several important aspects are described as well as a mathematical analysis is provided, including the distribution of the PAPR used in OFDM system. Here, different PAPR reduction techniques like clipping, selected mapping (SLM) and Partial transmit sequence (PTS) are used to reduce PAPR. The performances of PAPR reduction techniques are then compared. Secondly, the performance of OFDM systems in presence of frequency offset between the transmitter and the receiver has been studied in terms of the carrier-to-interference ratio (CIR).