Key Technologies And Validation For Reliable Transmission In Air-sea Time-varying Channels

With the development of the"air-sea integrated warfare"theory in information warfare,joint warfare in the air and sea domain has become the focus of future military communications research.In view of the characteristics of fast-moving air-sea channel and changing environment,a reliable air-sea wireless communication system is urgently needed in a long-range,highly dynamic and large frequency deviation environment.In this thesis,based on the characteristics of air-sea channels and drawing on mature technologies and experiences at home and abroad,a spread spectrum communication waveform based on a single carrier system is designed to achieve real-time and reliable air-sea wireless communication data transmission.The main contributions of this thesis are as follows:First of all,we summarise the current status of research on air-sea wireless communication technology,combine the characteristics of air-sea channels and demonstrate the functional and performance requirements of the designed communication waveform.Firstly,the development status of air-sea wireless communication and its key technologies is outlined,and a single-carrier spread spectrum communication system based on variable rate switching is identified.Secondly,the air-sea time-varying channel is characterised,including path loss,Doppler effect and multipath effect.Finally,each communication function and technical index is demonstrated and analysed.In the next part,a single carrier spread spectrum communication waveform with variable rate switching is designed according to the air-sea time-varying channel characteristics and application requirements.Firstly,the overall scheme of the communication waveform is described in detail,and key algorithms such as variable rate modulation coding,direct sequence spread spectrum and time-frequency synchronisation are designed.Secondly,for the air-sea time-varying channel,a code-division channel estimation method is proposed to superimpose the data symbols on the guide symbols for real-time estimation and compensation of channel state information to achieve reliable data transmission under a large frequency deviation channel.Finally,Simulink simulation platform is used to simulate and analyse the full-link anti-interference performance,time-frequency synchronisation performance,noise estimation performance and communication performance,to verify the feasibility of the overall architecture of variable-rate single-carrier spread spectrum communication,and to determine the demodulation thresholds for the four transmission rates.In the end,the experimental verification of variable rate single carrier spread spectrum communication is completed based on the software radio platform.Firstly,the general implementation architecture of the hardware platform and the communication waveform is given.Secondly,the implementation scheme of key modules such as spread spectrum despreading,time-frequency synchronisation and channel estimation are presented in detail.Finally,the BER and anti-frequency bias performance of the designed waveforms are tested in laboratory and microwave darkroom scenarios respectively.The test results show that the demodulation thresholds are 0dB,2dB,7dB and 14dB for the four transmission rates designed in this thesis,and that the BER of the four waveforms is not less than1×10^-6 when the frequency bias is 42KHz.The reliability of the designed scheme is verified.For air-sea time-varying channels,this thesis designs a variable-rate single-carrier spread spectrum communication waveform,which effectively improves the reliability of air-sea wireless communication systems and provides a theoretical and engineering reference for air-sea joint warfare.