Research On OTFS Modulation Domain And Signal Detection Algorithm

Orthogonal Time Frequency Space(OTFS)technology has attracted much attention in future 6G high-speed mobile communication applications due to its good channel resolution capability in delay-Doppler(DD)domain.However,the channel modeling in DD domain has defects due to phase difference with actual channel.Then received signal based on DD domain channel is different from real received signal,and signal detection algorithm of this model has problems.In addition,DD domain signal is modulated and converted into a serial data stream into channel for transmission.At this time,the dimension of OTFS channel is equal to product of delay dimension M and Doppler dimension N,that is MN MN,which makes it face the problem of high-dimensional channel matrix processing,so the computational complexity of current detection algorithm is relatively high.Therefore,firstly,through theoretical analysis and derivation,this paper establishes the conversion relationship between time domain channel and DD domain channel,which provides a new idea for low complexity DD domain signal detection algorithm.Using this conversion relationship,signal detection is carried out directly in DD domain.Finally,combined with the idea of interference cancellation,a two-dimensional(2D)interference cancellation algorithm based on DD domain is designed.The main contents of this paper are as follows:1.Firstly,it explains research background and significance of this paper,introduces current research progress of OTFS modulation technique,focuses on existing different OTFS system models,and briefly analyzes several OTFS system signal detection algorithms and their advantages and disadvantages.2.Through analysis of OTFS system model,it is found that the effective channel matrix in DD domain and time domain have different structures.The effective channel matrix in DD domain has a block circulant structure so that it can be decomposed by eigenvalues.The time domain effective channel matrix does not have this structure.On this basis,the corresponding conversion relationship between time domain channel matrix and DD domain channel matrix is theoretically derived.Different from the existing signal conversion relationship,there is only a phase deviation between the two,so conversion relationship between the two is established through a phase matrix.Finally,the correctness of this conversion relationship is demonstrated from perspective of waveform.3.Since there is a 2D convolution relationship between transmitted signal and channel in DD domain,and channel matrix dimension of this model is only M N,which helps to reduce computational complexity of detection algorithm.At the same time,the impact of time-frequency dual dispersion channel on OTFS is actually reflected in 2D inter symbol interference(ISI)in delay-Doppler domain.Therefore,the signal detection in DD domain can also be understood as a 2D de-crosstalk process.Based on this,a 2D successive interference cancellation(SIC)signal detection algorithm in DD domain is proposed.The design of guard interval is introduced into signal structure in DD domain,so that some modulation symbols have no ISI to avoid global interference,and provide basic conditions for subsequent SIC.The simulation results show that proposed interference cancellation detection algorithm has certain advantages in computational complexity compared with message passing algorithm and minimum mean square error algorithm.