Research On Reducing PAPR In OFDM System Based On Coding And Probability Technology

In recent years, with the rapid development of the fourth generation mobilecommunication technology, the requirement of data transfer rate of a lot of businessis rising now. Orthogonal frequency division multiplexing (OFDM) becomes one ofthe key technology of wireless communication with its advantages, such as highspectrum effic iency and resistance of the multipath effect. However, since the outputis made of the superposition of multiple sub-channels in OFDM system, it is boundto make a big peak because of the phase superposition. Such high peak averagepower ratio (PAPR) may produce nonlinear distortion, resulting in systemperformance degradation. So it is very critical to study how to suppress peakaverage power ratio in OFDM system. This paper does a series of research on theproblem of high peak average power ratio in OFDM system, and put forward a kindof new method of cooperative reducing PAPR based on coding and probabilitytechnology.At first, this paper carries on a thorough analysis of the basic principle ofOFDM system, key technology, the causes and statistical characteristics of PAPR.And summarize some current main methods on reducing PAPR, such as clipping,coding and probability method. Then select one which has good performance as partof the probability methods, that is selective mapping (SLM), and focus on it in thispaper. Though traditional SLM method can reduce the system PAPR significantly, ithas defects from two aspects, on one hand it needs extra bandwidth to transmitsideband information, on the other hand, it has a high command about the reliabilityof sideband information. This paper does research on another kind of SLM withoutbandwidth to transmit sideband information based on the foundation of simulationanalysis of SLM method. Through processing random phase shift sequences, it canreach the purpose of transmitting without an extra sideband message. However,though such kind of method saves the band, the SNR distribution on each band isimbalance makes it losses in terms of BER performance. Complementarycumulative distribution function (CCDF) and bit error rate curve of the traditionalSLM method are simulated respectively and the simulation result confir ms thetheory analys is. So at the end of the paper, a new scheme combining coding andprobability technology is put forward, trying to reduce the high PAPR of OFDMsystem by adding coding method into the design of random phase shift sequences.This method can make the energy distribution on each channel more balanced bychoosing coding of0,1uniform distribution. The simulation tests and verifies the proposed scheme has a better BER performance than of the proposed scheme isbetter than SLM scheme of transmission without sideband message significantly,and the introduction of coding has the ability of rectifying error detection, provingthat it will help improve the BER performance of the OFDM system further.