Study On Reducing The PAPR Of OFDM System

Orthogonal Frequency Division Multiplexing (OFDM) technology has high spectrum efficiency and strong anti-frequency selective fading. And it will become the next generation of mobile communications in the most competitive as one of the key technologies. OFDM system has an inherent disadvantage is the higher peak-average power ratio (PAPR), led to the sending end of the power amplifier and receiver front-end amplifier linearity is demanding, obstructs the practical technology. This paper arounds to reduce the OFDM systems’PAPR, and use of MATLAB tool to simulate how to reduce the PAPR. What’s mare, the NC-OFDM system based on cognitive radio can intelligent use spectrum resources, we will deeply discuss NC-OFDM system in this thiese.This paper introduces the basic OFDM system model and the key technology. Deeply research the problem of the OFDM system, and discusses the definition and distribution of its PAPR. analyzes the Performance of clipping, PTS,SLM and TR in OFDM system about its PAPR, And using various parameters of the MATLAB simulation, To draw a variety of advantages and disadvantages and how to choose the appropriate parameters in practical applications of these four methods toreduce the PAPR of the OFDM system. Otherwise improved PTS and TR algorithm at the same time simulate in the MATLAB.what’s more, discuss the PAPR problem of NC-OFDM system which Bases on the cognitive radio(CR), Compare the four methods in performance and time complexity, the effect, Thus judgement gives more suitable for NC-OFDM systems method.The results of the study show that:Compared with amplitude limit filtering, the effect of reducing the PAPR using PTS, SLM and TR is more better, but PTS is quite high on the time complexity, and it can Infer that SLM and TR is more sutable in OFDM system. For improving the TR and PTS, The simulation results show that the improved method in reducing the OFDM systems are better than the effect of the peak on basic unchanged, But the time complexity is greatly decreased, the time complexity of TR gets1/6of the unchanged method, the time complexity of PTS become1/16of the unchanged method. What’s more, the changed method in this paper is better than the common changed method. For the NC-OFDM systems Based on cognitive radio, The simulation results show that SLM and TR is more suitable in NC-OFDM systems with the continuous sub-carrier.There are some new characteristics in this research, research Several classic several ways to reduce the PAPR in OFDM systems, and also improve the algorithm of the SLM and PTS, reducing the complexity of their time. And combined the cognitive radio and OFDM systems, discuss its PAPR problem.