Research On PAPR Reduction Schemes For OFDM System

As the core technology of the fourth generation mobile communication and Wide Band Wireless Access(WBWA), Orthogonal Frequency Division Multiplexing (OFDM) has been widely adopted in many high-speed data transmission systems such as Digital Audio Broadcasting(DAB), Digital Video Broadcasting and Wireless Local Area Network(WLAN), for its high spectrum efficiency, multipath resistance, low impulse noise, high bandwidth utilization with high-speed transmission capacity, flexible sub-carrier modulation and power allocation based on Channel condition. OFDM uses multiple orthogonal sub-carriers to carry data; therefore the output signal on each sub-carrier may conflict with each other. Compared with the single carrier system, OFDM has many disadvantages such as synchronization problem and High Peak to Average Power Ratio (PAPR). The on-going technologies on reducing OFDM signal PARP can be generally divided into three categories: limiting class technologies, encoding techniques and signal scrambler technologies.This paper proposes a simple but practical algorithm of Companding transform. Companding transform is a simple amplitude-based technology. It reallocates the signal power in the transmitter by numerical transformation, namely using compression and extended transformation to decrease the amplitude of high signal and enhance small signal's amplitude; a reverse operation is done on the receiving side to restore the original signal. This paper proposes an sine function-based Companding transform method, comparing with the most widely used u law function-based one. The simulation result proves that the proposed method can reduce the OFDM system's PAPR and the computational complexity in the transmitter, improving the BRE performance greatly.