Research On Channel Estimation Technology Of Time-Frequency Modulation System In High-speed Environment

Since the 4G era,Orthogonal frequency division multiplexing(OFDM)technology has been widely used in many wireless broadband communication systems with the advantages of flexible allocation of spectrum resources and effective reduction of frequency selective fading.In communications,such as the Internet of Vehicles,UAVs,aerospace,etc.,the ultra-high terminal movement rate makes the wireless signal transmission environment more complex,and the high sensitivity of OFDM technology to frequency offset in high-speed environments greatly reduces the performance of the communication system.The recently proposed Orthogonal Time Frequency Space(OTFS)modulation technology is known for its ability to effectively combat multipath and Doppler effects.OTFS modulation technology combines the common features of traditional time-domain modulation an d frequency-domain modulation,and can achieve low-latency and high-reliability communication goals in high-speed communication environments.Based on the research based on OTFS.according to the characteristics of OTFS system being compatible with OFDM system,this paper studies the channel estimation and equalization technology of OFDM-based-OTFS system under high-speed environment time-varying channel.The main contents of the research are as follows:1.Firstly,the system model of OTFS modulation is deeply analyzed,and the input-output relationship of the OTFS system is briefly deduced.Secondly,based on the traditional OFDM-based-OTFS system,a system scheme combining time-frequency domain channel estimation and delay-Doppler domain channel equalization is proposed.The implementation scheme makes full use of the full time-frequency diversity characteristics of OTFS modulation in the delay-Doppler domain.The simulation results also show that the proposed delay-Doppler domain channel equalization scheme not only reduces the high-speed environment compared with other equalization schemes It also improves the overall communication performance of the communication system under the fast time-varying channel.2.On the basis that the delay-Doppler domain channel equalization achieves a certain system performance improvement,a ZP-OTFS system delay-Doppler domain channel estimation scheme is proposed,and on this basis,an embedded pilot-assisted OTFS channel estimation scheme is proposed.In view of the fractional Doppler situation in actual high-speed communication,this paper proposes a channel estimation algorithm based on cross-correlation and a delay-Doppler domain channel equalization algorithm based on maximum ratio combining,and based on MRC theory and Gauss-Seidel theory in channel equalization The continuous over-relaxation method is introduced to improve the channel equalization algorithm in the delay-Doppler domain and propose a low-complexity channel equalization algorithm in the delay-time domain.The embedded pilot-assisted scheme can flexibly adjust the system pilot loading rate according to the time-varying characteristics of the channel,and has lower pilot signal overhead and peak-to-average power ratio.The simulation results also show that this scheme can improve the signal-to-noise ratio by about 1.5dB compared with the OMP-OTFS system at a bit error rate of 10^(-4).By introducing the over-relaxation parameter,the ZP-OTFS system has a more accurate channel The estimated performance and lower computational complexity can improve the anti-jamming performance of wireless communication systems in high-speed environments.