Research On Channel Estimation Technology Of Time-frequency Modulation System In Time-varying Channel

In recent years,Orthogonal frequency division multiplexing(OFDM)technology is widely used in many wireless broadband communication systems.However,due to its high frequency offset sensitivity,OFDM will suffer great performance degradation in fast time-varying channels.Orthogonal Time Frequency Space(OTFS)technology is proposed to solve this problem.The innovation of this modulation technology is that it put forward the idea of signal multiplexing in the delay-Doppler domain and then the time-varying channel in time domain is converted into a time-invariant channel in the delay-Doppler domain.Therefore,this scheme can effectively combat the system performance degradation caused by the Doppler frequency shift in the fast time-varying channel.Focusing on the advantages of the OTFS system against Doppler frequency shift and its compatibility with the OFDM system,this paper studies the relevant content of the OFDM-based-OTFS system under fast time-varying channels,and proposes two effective implementation schemes and related channels estimation scheme,aiming at improve the performance degradation of the OFDM system under fast time-varying channels.The main results of the thesis research are as follows:1.Propose a equalization scheme of OFDM-based-OTFS based on time-frequency domain channel estimation:This paper proposes a implementation scheme that combines time-frequency domain channel estimation and delay-Doppler domain channel equalization for OFDM-based-OTFS systems under fast time-varying channels,compared with the traditional OFDM system and OFDM-based-OTFS system with frequency domain equalization,this scheme makes full use of the full time-frequency diversity characteristics of the OTFS system,thus it can improve the anti-interference ability of information symbols,thereby improving the system's bit error performance under fast time-varying channels and improving system stability.2.Propose the OFDM-based-OTFS system delay-Doppler domain channel estimation scheme:When the channel estimation work of OFDM-based-OTFS system is carried out in delay-Doppler domain,this paper proposes an‘all-non-zero pilot symbol scheme'based on sparse signal recovery.Comparing with the currently widely used "threshold method" channel estimation pilot scheme,this pilot scheme is more flexible with lower pilot load rate,and meanwhile has lower signal peak power ratio.In addition,based on the proposed pilot scheme,the block-OMP algorithm is proposed to estimate the channel response in the delay-Doppler domain with block-sparse characteristics,and simulation results indicate that the estimation scheme can achieve the similar system performance as the ideal channel.