Research On Transmission Technology Based On Orthogonal Time-Frequency Space Modulation In Internet Of Vehicles System

With the development of Internet of Vehicles(Io V)technology,the maximum single bicycle movement speed in the V2X(Vehicle-to-Everything)scenario defined by 3GPP is 140 km/h,and the maximum relative travel speed of vehicle-to-vehicle will reach 280 km/h.In subsequent evolutionary standards,the absolute movement speed of bicycles has been increased to 200 km/h,and the carrier frequency has been extended from the original 6 GHz to the millimeter wave band.It can be seen that the Doppler effect in e V2X/NR-V2 X will be more significant in the future.Orthogonal Time Frequency Space(OTFS)modulation technology is compatible with Orthogonal Frequency Division Multiplexing(OFDM)due to its robustness to time-varying wireless channels.It has become a candidate modulation method for the sixth generation(6G)wireless communication system.OTFS takes advantage of the full diversity gain under time-and frequency-selective channels in high-speed scenarios by placing the modulated data symbols in the delay-Doppler domain and extending them to the time-frequency domain.Therefore,this technology has significant research significance.Reconfigurable Intelligent Surface(RIS),due to its passive and controllable hardware structure,partially solves the problem of uncontrollable channels and is considered a key technology in 6G.In order to address the issue of the Doppler effect on communication quality in Internet of Vehicles systems,this paper proposes integrating RIS into the OTFS system and introduces the Doppler diversity algorithm based on matching filtering.A system geometry model is constructed that includes the transmitter,RIS auxiliary system,the relative position of the receiving end,and the user’s speed.Based on this model,the Doppler frequency offset of different path signals is estimated,and the received signal is Doppler spectrum shifted and then matched and filtered after migration.A multiRIS optimization scheme is proposed that maximizes the Doppler interference suppression ability based on the characteristics of this Doppler diversity scheme.Simulation results show that the proposed Doppler diversity algorithm based on matching filtering can achieve better bit error performance than the traditional OTFS system.Furthermore,compared to the random RIS selection algorithm,the multi-RIS optimization selection algorithm proposed in this paper can greatly improve the bit error performance.In order to address the issue of timing synchronization in high Doppler frequency shifts in Orthogonal Time Frequency Space(OTFS)systems,which inherit the sensitivity to synchronization errors from Orthogonal Frequency Division Multiplexing(OFDM),this paper proposes a timing synchronization method based on the delay-time domain pilot sequence characteristics in OTFS systems.Firstly,by analyzing the relationship between the pilot sequence in the delay-time domain and the Zadoff-Chu sequence,the conversion coefficient matrix for the pilot sequence is derived.Then,the pilot sequence in the delay-time domain is processed by the conversion coefficient matrix to convert it to the Zadoff-Chu sequence for transmission.At the receiver,the good auto-correlation and cross-correlation properties of the Zadoff-Chu sequence are utilized to estimate the offsets in the delay and time dimensions,respectively,and then the symbol starting position is determined based on their relationship.Simulation results demonstrate that the proposed timing synchronization algorithm has higher accuracy and lower complexity compared to traditional pilot-based timing synchronization methods and traditional timing synchronization methods.