| Orthogonal Time Frequency Space(OTFS)modulation technology is a modulation technology used in wireless communication to improve the scheme of severe doppler effect and channel influence in high speed mobile communication system.By placing signals in the Orthogonal Frequency Division Multiplexing(OFDM)domain for modulation rather than in the time-frequency domain,OTFS is more effective in resisting the time-selective fading caused by doppler shift than traditional OFDM technologies.At the same time,it has lower signal peakto-average ratio and transmitter complexity,so it has good performance advantage in dual extension channels.It can effectively eliminate or improve the influence of OFDM by underwater acoustic double extension channel,and improve the performance of underwater acoustic communication system.In this paper,the key technologies of underwater acoustic communication system based on OTFS modulation mode are studied,and a hydroacoustic communication system based on OTFS modulation is constructed based on the advantages of OTFS technology that can be well combined with multi-carrier modem.Under the time-varying underwater acoustic channel,the theoretical simulation and practical tests are carried out from the aspects of noise intensity,multi-way and Doppler effect,and the performance of the OTFS-based underwater acoustic communication system is evaluated and verified through the simulation and measured data demodulation results.Firstly,the basic architecture of OTFS and OFDM modulation technology is introduced,and the theoretical simulation analysis is carried out from the aspects of attenuation and noise,multipath,Doppler effect and time-varying aspects according to the complexity of time-varying underwater acoustic channels.Based on the time-varying acoustic propagation model,a time-varying underwater acoustic channel model that can fully describe the performance of the channel test system is established.On the basis of the radioacoustic model,the influence of environmental factors such as the relative motion between the transmitter and the receiver and the influence of wind speed on the channel of the random undulating interface characteristics of the ocean is added,and the underwater acoustic channel characteristics under different parameter settings are simulated and analyzed,which more finely represents the characteristics of the underwater acoustic channel changes,which provides a channel hypothesis basis for the establishment of the subsequent underwater acoustic communication system.Based on the theoretical research,this paper constructs a hydroacoustic communication system based on OTFS.The basic architecture of OTFS underwater acoustic communication system is introduced in detail,and the simulation results show that under the harsh environmental conditions of dual extended channels,with the increase of signal-to-noise ratio,the OTFS system reduces the bit error rate more than that of OFDM system,and shows better resistance to Doppler frequency shift.When the bit error rate is on the order of 10-4,the system performance of the encoded OTFS-BPSK is improved by nearly 2dB compared with the OFDM-BPSK system.This method has been verified in shallow water experiments in Jingmen Zhanghe Reservoir,China in December 2022.Experimental data show that in the horizontal range of 0.5～1km,the sending and receiving parties are in a relative motion state,the bit error rate of the encoded OTFS-BPSK reaches 4.41 × 10-4,and when the bit error rate is in the order of 10-3,the performance of the encoded OTFS-BPSK is about 1.5dB higher than that of OFDM-BPSK.Simulation and experimental results show that OTFS underwater acoustic communication system can be used as an alternative to traditional OFDM system,which provides new ideas and research directions for improving the robustness of high-speed underwater acoustic communication system. |
