Research On Reducing The Peak-to-Average Power Ratio Method In OFDM System

Orthogonal Frequency Division Multiplexing (OFDM) is an effective transmission scheme to cope with much impairment, such as transmits high-rate data, high spectral efficiency, combating inter symbol interference (ISI) and mufti-path delay. However, OFDM system has its faults yet, sensitivity of frequency offset and high Peak-to-Average Power Ratio (PAPR) are the problems of an OFDM system that must be solved, which limit OFDM's wide applications.This dissertation explores the question of OFDM's Peak-to-Average Power Ratio primarily. High Peak-to-Average Power Ratio is a major drawback of OFDM's applications, which makes the intermediations distortion occurs due to the nonlinearity of the high power amplifier. The distortion severely deteriorates the performance of the OFDM systems. Firstly, the thesis analyzed the principle of DFT based OFDM system, its key techniques, advantages and disadvantages of OFDM technology. The definition and distribution of PAPR are introduced, and various techniques on reducing the PAPR are summarized. Probability techniques which do not make the signal distorted and are not limited by the number of the carriers are analyzed aiming to solve the large complexity problem. Secondly, a SLM method based on the DFT property of the time domain circular convolution is studied. And in this thesis, a new method is proposed based on the same principle,which can reduce the computing complexity a lot more. And we discussed the PAPR performance of two schemes of the new method under the different conditions. Based on the results of MATLAB simulations, the new method could reduce PAPR effectively almost as the same as conventional SLM but performs a little bit worse on BER. Finally, based on this method, we extend other schemes to get flex tradeoff among complexity, PAPR and BER performance.