Research And Verification Of Key Technologies For Single-carrier Spread Spectrum Adaptive Air-Sea Communication

Modern warfare has gradually evolved into a systemic confrontation.As one of the joint combat objectives,"Air-Sea Battle"has gradually become the focus of my country's national defense science and technology research.The air-sea wireless communication data link is the key technology of this strategy.In the air-sea joint combat environment,air fighters and ships at sea are in a state of high-speed movement,and the sea climate is changeable and the air density is uneven.Data transmission is facing long-distance,high dynamic,large frequency offset and time-varying selective fading series of questions.Thesis studies the data transmission problem in the air-to-sea wireless channel,and proposes a single-carrier spread spectrum adaptive air-to-sea wireless communication waveform design and verification scheme.The main contributions of thesis are as follows:First,analyze the research status of air-sea wireless communication,and determine the transmission system and key technology modules of air-sea wireless communication combined with channel characteristics.Firstly,the research status of the air-sea wireless communication waveform is analyzed,and the waveform design criterion based on the single-carrier spread spectrum system is determined according to the application background of air-sea wireless communication.Aiming at the time-varying channel environment of air-sea,an equalization method for superimposed transmission of pilot and data is proposed.Channel estimation is performed symbol by symbol in time resources,and channel changes are tracked in real time to improve equalization accuracy;For the large frequency offset problem caused by high-speed motion,a combined synchronization head based on single-tone signal and Gold repeating sequence is designed,which can correct the maximum frequency offset up to 42KHz;According to the quality of the transmission channel,combined with adaptive coding and modulation,4 transmission modes are designed,and the adaptive rate switching of four transmission modes of 2.65Mbps,3.55Mbps,5.31Mbps and 7.96Mbps is realized.Second,analyze the key performance indicators of the air-sea wireless communication waveform,and complete the air-sea wireless communication data link design.Firstly,the frame structure of the transmitter based on the single-carrier system is designed,which mainly includes signal processing units such as channel coding,modulation,spectrum spreading and framing;Then complete the frame structure design of the corresponding receiver,including signal processing units such as time-frequency synchronization,despreading,channel estimation and equalization,demodulation and channel decoding.Finally,the construction of the communication link based on the Simulink platform is completed,and the simulation verification is carried out.The four transmission modes of 2.65Mbps,3.55Mbps,5.31Mbps and 7.96Mbps achieve the bit error rate at the signal-to-noise ratio of-3d B,1d B,6d B and 12d B respectively performance below 10^6-.Third,complete the FPGA code implementation for the software radio platform,and conduct the transmission scheme index test in the laboratory environment.In the laboratory environment,when the signal-to-noise ratio is 0d B,4d B,8d B and 15d B for the four transmission modes tested,the bit error rate is lower than 10^6-.On the premise that the bit error rate meets the requirements,the key function performance indicators of the waveform are tested,including the bidirectional transmission rate test,the anti-frequency offset test and the rate adaptation test,to verify the feasibility of the single-carrier spread spectrum adaptive air-sea wireless communication scheme.The research results of the data transmission waveform of air-sea wireless communication in this thesis have theoretical and engineering reference significance for the design of data transmission waveform at high speed,long distance and large frequency offset.