Research On The Methods Of Reducing PAPR Of OFDM System

Due to its high band-width efficiency and its robustness to multipath, Orthogonal Frequency Division Multiplexing (OFDM) has been used widely in several areas, such as Digital Audio Broadcasting, Digital Video Broadcasting, Wireless Local Area Network. OFDM has the high Peak-to-Average Power Ratio (PAPR) which is its disadvantage and it can reduce the system's performance, So we must reduce the PAPR.In this paper, the definition and distribution of PAPR are introduced based on the analysis of the theory of OFDM technology, and the methods of reducing PAPR of OFDM system are studied thoroughly. Firstly, Clipping and Modified Companding Transform which are signal pre-distorting technology are described. Secondly, a coding scheme based on Golay Complementary sequences and Reed-Muller codes is proposed to reduce the PAPR. This scheme can control the PAPR to 3dB, and have forward error correction capability. Then, two typical algorithm of signal scrambling technology─Selective Mapping (SLM) and Partial Transmit Sequence (PTS) are analyzed. The two methods are compared by MATLAB simulation with respect to the capability of PAPR reduction and transmit signal redundancy. In order to reduce the large computation complexity, we propose a new SLM scheme by using an IFFT conversion and an improved PTS scheme by using suboptimal iterative algorithm. Because the SLM needs some IFFTs operating which have high system complexity, we propose a simpler algorithm to select the transmitted sequence by comparing randomness of sequences. This improved SLM only needs one IFFT, so it has lower complexity. In the end, CCS simulation of OFDM system baseband modulation is carried out at the platform of TMS320C5402, which shows the effectiveness of theoretical methods.