Research On Reduction PAPR In OFDM System

Orthogonal Frequency Division Multiplexing(OFDM),which transmits information at high data rate,provides greater immunity to multipath fading and high spectrum efficiency.Being one of multi-carrier systems,OFDM systems also suffer from the problem of Peak-to-Average Power Ratio(PAPR).OFDM transmitters therefore require linear amplifiers with wide dynamic range, resulting in unwanted out-of-band power and increased interference.Otherwise, the peak power enters into non-linear amplifiers range which results in aberrant signals, carriers intermodulation interferer, radiation of out-of-band, destruct orthogonal and reducing performance of systems.The problem will be deeply researched in this thesis and use MATLAB software to achieve simulation.The goal is finding the feasible ways to resolve the problem.Firstly, the principles of DFT-based OFDM system, its key techniques, advantages and disadvantages of OFDM technology are analyzed in this thesis.Secondly, the article analyzes the high PAPR's causation and distribution of the OFDM systems and introduces three kinds of method of reducing, which are clipping technique,coding technique and scrambling technique. Clipping technique includes direct-clipping and peak power windows; coding technique discusses Golay Complementary sequence and arithmetic; scrambling technique introduces two representative technique:SLM(Selected Mapping) and PTS(Partical Transmit Sequence) and analyzes theories, performance, advantages and disadvantages of reducing PAPR.Finally, the article discusses on the companding method, analyzes the companding theory, emphasizesμ-law companding method and discusses on how to chose the Companding parameters.Aim at reducing BER performance the article introduces two improved companding methodes. Research show thatμ-law companding transform method can decrease the PAPR of OFDM systems with few calculation and practicality.