Waveform And Verification Of High Speed Wireless Transmission For Limited Load Unmanned Surface Vessels

With the popularization of unmanned platforms,unmanned boats are increasingly used in maritime monitoring,transportation and fishery.In these applications,users need to quickly obtain information at sea,so it is important to study a communication system that can transmit at high speed by unmanned ships at sea.However,the low antenna caused by the low height of the unmanned boat platform,the platform instability caused by the waves,and the complex and variable channels have brought higher challenges to the wireless transmission of the unmanned submarine at sea.Aiming at the channel characteristics of unmanned vehicles under sea surface communication,this thesis adopts orthogonal frequency division multiplexing and adaptive modulation coding technologies to overcome the problems of sea surface multipath and Doppler effect,and realizes high reliability and high efficiency data transmission of limited load surface unmanned vehicles.The specific research content of this thesis includes the following three aspects:Firstly,the transmission function and performance index of limited load surface unmanned vehicle in the sea surface transmission scenario are analyzed in detail.According to the analysis results of transmission function index,adaptive modulation coding and orthogonal frequency division multiplexing technology are adopted in this thesis.According to the analysis results of three transmission performance indexes,namely propagation loss,Doppler frequency offset and multipath delay,it is determined that the signal-to-noise ratio of this thesis is 18 d B when the farthest communication distance is 10 km,frequency offset index is 1k Hz,and multipath delay index is 10 us.Secondly,an orthogonal frequency division multiplexing wireless transmission waveform scheme with adaptive modulation coding function is designed.The scheme includes four baseband transmission rate modes: 10.29 Mbps,15.44 Mbps,20.58 Mbps and30.88 Mbps.The simulation verification of these four transmission rate modes is completed with the help of MATLAB platform,and the simulation results of the comparison of bit error rate performance,signal-to-noise ratio estimation performance,time-frequency synchronization performance,adaptive and fixed modulation coding performance are given.Thirdly,the hardware realization and experimental verification of waveform are completed by FPGA platform.The demodulation thresholds of the four rate modes are8 d B,10 d B,14 d B and 18 d B respectively under the condition of direct wired connection in the laboratory,which is about 3d B lower than the simulation performance.In the wireless environment of the external field,when the signal-to-noise ratio is greater than or equal to 9d B,the bit error rate is lower than that of the system,and the switching thresholds of the four modes are 9d B,10 d B,15 d B and 20 d B successively,which is 0～2d B higher than the demodulation threshold of the wired laboratory test,verifying the feasibility of the scheme.The high-speed wireless transmission waveform of the limited load surface unmanned boat designed in this thesis is suitable for the sea surface channel within the level 3 sea state.It has adaptive modulation and coding function,improves the communication performance between small boats,and has been verified by engineering.It provides technical support for maritime wireless communication applications with high speed requirements.