Research On Reducing Peak-to-average Power Ratio Of OFDM System

Orthogonal Frequency Division Multiplexing(OFDM) is a kind of multi-carriermodulation technology with high spectrum efficiency and the ability of anti multipahfading. However, OFDM systems have the high peak-to-average power ratio(PAPR).This paper mainly studies how to reduce the high PAPR of OFDM system.First at all, the basic principle of OFDM system are studied and analyzed,severalclassical methods such as methods based on algorithms by the using of block coding andprobabilistic schemes to reduce PAPR are analyzed and compared.Secondly, this paper focuses on the clipping method and the improvment method ispoposed.The improved clipping don’t clip all the signal when it exceed the threshold, itonly instead signal amplitude which is between the fist max and the nth max by a fixedamplitude, the fixed amplitude is the x times of the average amplitude IFFT signal, x andn are variable. Found the n max amplitude, we must record the index and it real value.We can send them to receiving end.The improved clipping not only can further reduce thePAPR, and the system BER perform is not lowered.Thirdly, this paper focuses on the selected mapping method(SLM) and theimprovment method is poposed. In SLM system, after the original signal multiply therandom phase sequence vector and before Inverse Fast Fourier transform(IFFT),multiplied by a precoding matrix. The group of signal with minmum PAPR will beenselected from the groups of signal which is come from IFFT. In the improved SLM, theprecoding matrix is composed of complementary Golay sequence.Finally, This paper focuses on partial transmission sequence(PTS) method and theimprovment method is poposed. The improved PTS method is that each subblock ismultiplied by a precoding matrix after the original signal was separated into severalsubblocks and before every subblock was applied the Inverse Fast Fourier Transform inPTS system, the precoding matrix is composed of the Discrete Hartley Transform matrix.Theoretical analysis and simulation results demonstrate that The improved SLM and theimproved PTS in this paper can further reduce PAPR of OFDM system.