Research On Interference Analysis And Spread Function Design Of OTFS System

Orthogonal Time Frequency Space(OTFS)pre-modulation technology is considered to be an effective method to solve high-reliability communication in high-speed mobile scenarios due to its robustness to doppler spread,which can be mounted as pre-processing/post-processing to the receiving and sending ends of the multi-carrier communication system.Filter Bank Multi Carrier(FBMC)system is considered to be one of the powerful candidate waveforms for the next generation communication technology because of its low out-of-band leakage and high spectrum efficiency.The communication system(OTFS-FBMC)that combines OTFS technology with FBMC system will have low out-of-band leakage,high spectrum efficiency and robustness to doppler spread at the same time.And the research on OTFS-FBMC system is in its infancy,lacking the theoretical basis and mathematical models under different interferences,as well as the most important doppler diversity analysis of OTFS technology.Moreover,due to the influence of the expansion function,the OTFS-FBMC system introduces certain inherent interference,which causes loss of system performance.Accordingly,this thesis conducts a three-part study on OTFS-FBMC system.First,the interference analysis of OTFSFBMC system under Carrier Frequency Offset(CFO)and doppler shift interference is conducted.Secondly,the doppler diversity of OTFS-FBMC system under Continuous Doppler Spread(CDS)channel is studied and the corresponding law is summarized.Finally,the performance analysis of the extension function in OTFS-FBMC system is carried out,and the optimized design is carried out to improve the system performance.Firstly,this thesis establishes the matrix model of the OTFS-FBMC system,analyzes the interference of the OTFS-FBMC system under CFO and doppler frequency shift in detail,establishes a mathematical model under different interferences,and derives the estimated symbolic expression,Signal-Interference--Ratio and Signal-to-Interference-Noise-Ratio(SINR)closed-form expression,and its accuracy has been strongly verified by simulation results.This thesis subsequently analyzes the impact of different interferences on the performance of the OTFS-FBMC system and the interference structure,and then reveals the inherent characteristics of the OTFS-FBMC system to provide a theoretical basis for subsequent researchers and subsequent chapters of this thesis.Secondly,this thesis studies the doppler diversity of OTFS-FBMC system under CDS channel,and researches the law of diversity from two angles of theory and simulation.The theoretical analysis is based on the estimated symbolic expression under doppler frequency shift interference,and the estimated symbolic expression of the OTFS-FBMC system under the CDS channel is derived by using the numerical integral characterization method,i.e.,the mathematical expression between the modulated and demodulated signals.And then the Pairwise Error Probability(PEP)expression is derived to analyze the law of diversity.The simulation analysis uses the number of independent channels and the signal detection algorithm to test the OTFS-FBMC system under the CDS channel,and then obtains the diversity rule.The diversity rules obtained from theoretical analysis and simulation analysis are verified by each other,and finally the diversity rules of OTFS-FBMC system under CDS channel are obtained,so as to provide a guiding basis for parameter configuration of OTFS-FBMC system in practical applications.Moreover,the numerical integration characterization method used in the theoretical analysis allows the high-dimensional time-domain channel taps to be represented by low-dimensional vectors,which in turn reduces the channel estimation difficulty to some extent.Finally,the influence of the extended function on the performance of the system in the OTFS-FBMC system is studied,so that the optimization problem model with the extended function as the optimization variable is established,and the successive convex approximation method is used to optimize the solution.In addition,in view of the problem that the system performance is affected by the SINR fluctuation at different grid points of the OTFS-FBMC system during the research process,an iterative optimization algorithm is further designed to solve it.The simulation results show that the optimized spreading function is superior to the OTFS-FBMC system using the commonly used filter in the FBMC system as the spreading function and the Orthogonal Frequency Division Multiplexing system combined with OTFS technology in terms of stopband attenuation and system reliability.