Research On Nonlinear Distortion Methods For Reducing Peak-to-Average Power Ratio Of OFDM In Vehicular Channels

With the development of the artificial intelligence industry and the deepening of the new concept of the Internet,the network communication between vehicles and everything will inevitably become the trend of future development,and improving the efficiency and safety of vehicular communication is crucial.In vehicular channel,Orthogonal Frequency Division Multiplexing(OFDM)technology is an excellent multi-carrier modulation technology.This modulation technology has many excellent features,such as strong resistance to multipath fading,fast transmission rate of information,high spectrum efficiency,and simplicity in hardware implementation,so it has been widely used in mobile digital communication systems and has become one of the core technologies for researching digital communication based in vehicular channels.However,in the wireless OFDM system based in vehicular channels,the subcarriers of the transmitter will produce a large signal amplitude when superimposed,which will lead to a relatively high Peak Average Power Ratio(PAPR)of the system.When the PAPR value is larger,it means that the transmitter will send signals with a larger amplitude range.In practical applications,the linear working voltage range of the transmitter is limited,among which the linear dynamic range of the power amplifier module is also limited.The high PAPR will not only bring in-band distortion and outof-band radiation but also increase the cost of practical applications.Therefore,in order to suppress the high PAPR of OFDM system in vehicular channels,researching on PAPR suppression algorithms is needed.This thesis mainly focuses on the high Peak-to-Average Power Ratio problem of OFDM system based in vehicular channels and researches the PAPR suppression algorithm of OFDM system,especially the nonlinear distortion-based PAPR suppression algorithm.On the one hand,aiming to improve the PAPR suppression gain performance,the existing limiting technology and compression-expansion algorithms are optimized and deduced,and a joint algorithm based on limiting and normalized μ-law compression-expansion is proposed to suppress the high PAPR at transmitting terminal in vehicular channels of OFDM system.On the other hand,aiming to improve symbol error rate performance of the system,the Decision-Aided Reconstruction(DAR)algorithm is proposed to recover the non-linear distortion signal and reduce the symbol error rate.The main research work and results are as follows:1.This thesis studies the basic principles of both analog and digital OFDM systems,as well as the issue of high PAPR at the transmitting terminal.Three major categories of PAPR suppression algorithms are summarized and analyzed: signal distortion algorithms,coding algorithms,and probability algorithms.The advantages and disadvantages of these three types of algorithms in suppressing PAPR are investigated.In order to reduce the computational complexity of the research system,this thesis focuses on studying the limiting algorithm and the compression-extension transform algorithm on the nonlinear distortion method.2.The joint scheme based on clipping and normalized μ-law companding transform is proposed to address the issue of high Peak-to-Average Power Ratio at the transmitter of OFDM system in vehicular channel.Firstly,the signal at the transmitting terminal is clipped,and then the traditional μ-law companding transform is used.Furthermore,the joint scheme of clipping and normalized μ-law companding transform is proposed to further suppress the PAPR of the system.Simulation experiments are conducted in both Additive White Gaussian Noise(AWGN)and vehicular channel to validate the feasibility and effectiveness of the proposing method.The experimental results show that,comparing to the original system,the system with only clipping technique,and the system with joint algorithm based on clipping and traditional μ-law companding,the proposing joint algorithm based on clipping and normalized μ-law companding can efficiently reduce the PAPR in vehicular channel of OFDM system.3.The thesis studies the suppression of high Peak-to-Average Power Ratio using adaptive techniques combined with limiting algorithms.To address the signal distortion caused by adaptive limiting techniques of OFDM systems,the thesis proposes to use the DAR algorithm to reduce the noise generated by adaptive limiting,and then,the algorithm improves symbol error rate performance of the system.Experimental simulations in AWGN and vehicular channel verify the feasibility and effectiveness of the DAR algorithm on reducing nonlinear distortion.The experimental results show that the DAR-based adaptive limiting algorithm can effectively reduce the high PAPR of the transmitting terminal,and then reduce the impact of nonlinear distortion at the receiving terminal in vehicular channels,and improve symbol error rate performance of the overall system.This thesis studies the high Peak-to-Average Power Ratio problem at the transmitting terminal of OFDM system in the context of vehicular channels.The research focuses on nonlinear distortion methods to suppress PAPR,and the DAR algorithm is used to reduce nonlinear distortion in the algorithm system and improve bit error rate performance of the overall system.Therefore,in vehicular channels,using nonlinear distortion technology at the transmitting terminal to reduce the high PAPR of OFDM system,while employing a recovery distortion signal algorithm at the receiving terminal to improve bit error rate performance of the system,is a future research direction.