The Research And Algorithm Improvement Of The PAPR In The OFDM Communication System

OFDM technology divides the channel into multiple sub-channel with orthogonal subcarriers, and people have given more and more attention on it. However, it has an Intrinsic weakness of high Peak-to-Average Power Ratio (PAPR) of the transmitted signal. This weakness makes a high request for the linearity of Power amplifier in transmitter and receiver,and increases the complexity of A/D and D/A convertor,and also requires A/D converter and power amplifier to have a very wide linear operating range,result in energy waste and increase the cost of the equipment. And it is also one of the principal problems to restrict OFDM technology to practice. Therefore, it is actually significative to control the PAPR of the OFDM signal.Based on Introdueing the basie OFDM PrineiPle,we analyze the reason and influenee of high PAPR in OFDM systems,and compare three methods to reduce the peak to average power ratio of OFDM signal, which mainly includes the pre-distortion techniques, coding techniques and the probability techniques. For the problem of the traditional algorithms,This article focuses on the probability techniques present two kinds of new improved algorithm to reduce PAPR in OFDM system.including improved selective mapping method (SLM) and improved partial transmit sequence method (PTS).An improved SLM is proposed the phase sequence is embedding on the check symbols of the OFDM data block. Therefore, the data rate loss from the specially transmission of the side information is decrease. And The simulation proves the reducing PAPR of OFDM system without excessively complexity, the performance of the improved SLM method is better than that of ordinary SLM technique.The other improved method is proposed basing on the PTS algorithm,which combines PTS process in time domain with repeated clipping-filtering in frequency domain.The co-algorithm has all the advantages both in PTS and clipping-filtering methods. The results of simulation proves that The coalgorithm has at least1dB improvement more than only use PTS or clipping-filtering method on reducing PAPR in OFDM system without degrading BER (bit-error ratio) performance.