Performance Analysis And Simulation Of IOV Cooperative Communication Based On OFDM

With the growing maturity of driverless,artificial intelligence and 4G communication technologies,Internet of Vehicles has become a research hotspot for the development of science and technology in the future.Vehicle-to-vehicle communication,as the central nervous system of IOV,faces two major challenges in dealing with the openness and time-variability of wireless channels: On the one hand,multipath effect caused by rich-scattering transmission environment in the urban area is easy to cause channel frequency-selective fading;On the other hand,Doppler effect in high-speed mobile environment can offset the carrier frequency of orthogonal Frequency Division Multiplexing(OFDM)system and the orthogonality among subcarriers is destroyed,which will result in serious inter-carrier-interference.In view of the above problems,the main work of this paper is as follows:(1)According to the moving state of the three vehicles in the actual relay scene,the wireless channel characteristics of V2 V communication are studied,and the multipath effect and Doppler effect in the cooperative communication model are analyzed deeply.Simulation results show that the performance of relay system is the worst when the channel from source node to destination node is frequency selective channel.(2)Based on the in-depth study of the principle of OFDM against multipath effects,a complete OFDM simulation system is built based on the V2 V relay motion model,including transmitter,channel and receiver.The performance of OFDM in combating frequency-selective fading when the time delay spread is smaller than the cyclic prefix is analyzed through simulation,and the system performance under different frame length,modulation mode,channel estimation and speed is compared.(3)Based on the influence of Doppler shift on the OFDM system in the relay scene,this paper points out the shortage of the frequency offset estimation algorithm based on the long and short sequence and Park algorithm.Aiming at a phenomenon that the timing function of Park algorithm the has sub peaks at N4 and 3N4,an improved training symbol structure based on PN sequence is proposed in time domain,which effectively solves the problem of timing inaccuracy of Park algorithm.(4)In order to solve the problem that the frequency offset estimation range of Park algorithm is small and the training sequence in frequency domain is difficult to realize,an improved algorithm in frequency domain is proposed.This algorithm designs a new timing function and the training sequence is a pseudo random real number generated by the ZC sequence in frequency domain,which is conjugate symmetric structure in time domain.The integer frequency offset is estimated in frequency domain based on self-correlation of ZC sequences,and the fractional frequency offset is estimated based on cyclic prefix in time domain,Finally,the performance of the algorithm was verified by experiments.