Reduce The Papr Study. Ofdm System

Orthogonal frequency division multiplexing (OFDM) is considered as one of the core technologies of the fourth generation mobile communication systems due to its high-speed data transmission ability,high bandwidth efficiency and robustness to multi-path interference. However, OFDM system has high peak-to-average ratio problem, which affects its applications in practical.This paper introduces the basic theory of OFDM system. Based on the researches of the traditional PAPR reduction methods, a new PAPR reduction algorithm based on Fourier coefficient mapping is designed through studying the relation between OFDM modulation system and the Fourier series expansion of periodic signals. This method modulates the transmit data into periodic signals and takes part of the Fourier coefficients for OFDM modulation. The simulation results show that the PAPR of this new method can be reduced about 3 dB compared with QPSK mapping. When the bandwidth efficiency is equal to QPSK mapping, The BER performance is slightly better than QPSK mapping with SNR less than 8 dB, and worse than QPSK mapping with SNR more than 8 dB, When the bandwidth efficiency is 1/2 times of QPSK mapping, the BER performance is much better than the QPSK mapping.At the same time, two joint algorithms are designed in this paper through the combination of the Fourier coefficient mapping with the Selective Mapping algorithm and the Companding algorithm respectively. The simulation results show that the PAPR of the two joint algorithms based on Fourier coefficient mapping could be improved better than the traditional methods respectively. When the companding coefficient is large, the BER performance of the Companding algorithm based on coefficient mapping is better than the conventional Companding algorithm based on QPSK under the same bandwidth efficiency.