Research On Orthogonal Time Frequency Space Modulation Based On Scattering Communication System

Scattering communication is widely used in many fields such as military communication because of its advantages of long distance of transmission and strong anti-interference ability.However,the existence of multipath effect and Doppler shift will make the channel have frequency selective fading and time selective fading,which limits the efficient transmission of the system.In this paper,Orthogonal Time Frequency Space(OTFS)system is applied to the scattering communication scene.OTFS system converts a doubly-selective channels into a time-invariant two-dimensional channel in the delay-doppler domain through the twodimensional transformation,which has excellent performance in the scattering communication system.This paper mainly focus on the channel estimation scheme and signal detection algorithm for OTFS system.This article introduces the propagation mechanism,the characteristics and multiple representations of the wireless channel,analyzes the basic principles of the OTFS system,and derives the corresponding relation of the symbols in the delay-doppler domain.Simultaneously its channel diversity gain is analyzed by the comparison of OTFS system with OFDM,SC-FDMA system.Based on the simulation of the above three systems in the scattering communication system,the results show that the OTFS system has better BER performance.In the channel estimation aspect of OTFS system,this article mainly studies the traditional estimation method,and an improved channel estimation scheme is proposed.In this paper,the estimation methods based on pilot subframe,embedded pilot-aided channel estimation and two-dimensional matched filter are studied.The algorithm is analyzed and the performance is verified by simulation.The estimation methods based on pilot subframe estimation and embedded pilot-aided channel estimation both have poor performance under low signal-to-noise ratio,while two-dimensional matched filter estimation has poor performance under high signal-to-noise ratio because it often fails to identify weak paths with small channel coefficients.In this paper,a new pilot sequence is proposed based on the two-dimensional matched filter estimation method,and a joint channel estimation scheme is proposed in combination with the traditional methods.The simulation results show that the estimation error and BER performance of the newly designed pilot sequence under high signal-to-noise ratio are better than that of the original pilot sequence.In the signal detection aspect of the OTFS system,this paper mainly studies the traditional signal detection algorithm,and proposes a low-complexity frequency domain equalization scheme based on the scattering communication environment.This article focuses on the analysis of linear detection methods represented by MMSE equalizer and iterative detection methods represented by MP detection algorithm.Combined with the actual scattering communication environment,a low-complexity frequency domain equalization scheme based on Doppler precompensation and an information merging scheme are proposed.The simulation results show that the performance of the FDE scheme based on Doppler precompensation is similar to the MMSE equalizer in delay-Doppler domain,but has lower complexity.Compared with the traditional MMSE equalizer,the information merging scheme has better BER performance,which is similar to the MP algorithm.