Design And Implementation Of Chirp Spread Spectrum Covert Communication System With Performance Analysis

In recent years,wireless communication has developed rapidly,which becomes more and more importance in almost all kinds of fields.However,there are many risks transmitting information by wireless communication.For example,wireless signals are easily interfered or the information is intercepted by the enemy.Traditional covert communication usually uses direct sequence spread spectrum(DSSS)technology to increase the covert performance of the wireless signals.Currently,there are too many effective methods detecting DSSS signals.Therefore,it is necessary to find new covert communication methods.In order to achieve the purpose of covert communication,the Chirp signal is selected as carrier for spread spectrum communication.Because Chirp spread spectrum(CSS)technology has large spread spectrum gain,great performance on anti-interference and fading channels,the performance analysis and implementation of Chirp spread spectrum system is studied.The communication performance of Chirp signal is studied.The low probability of detection and low probability of interception performance of Chirp are analyzed and compared with the DSSS system.A multi-waveforms Chirp spread spectrum system is proposed to improve the resistance on information interception of the system.Finally,the CSS communication system is implemented based on the FPGA platform.The main contents of this paper are as follows:Firstly,the communication performance of the CSS communication system is studied based on interaction of information and adaptation of channel.The characteristics of Chirp carrier and the principle of spread spectrum are introduced in this paper.The potential of Chirp carrier for covert communication is analyzed.Then,the Chirp-BOK modulation scheme is introduced.The principles of transmitter and receiver of Chirp-BOK and the frequency conversion method are also introduced.The influence resulted by carrier phase deviation on the performance of demodulation is analyzed.The bit error rate(BER)performance of CSS system is modulated under the Additive White Gaussian Noise(AWGN)channels,multipath channels,and Doppler channels on the MATLAB platform.Secondly,the low probability of detection and low probability of interception of the CSS covert communication system is studied in this paper,which is compared with the direct sequence spread spectrum system based on the same parameters.Then,the detection method based on fractional Fourier transform for CSS communication system is introduced.The information anti-interception performance of Chirp signal is studied under different estimation accuracy of parameters.A multi-waveforms CSS(MW-CSS)convert communication scheme is proposed to improve the information anti-interception performance of the system.The bit error rate of MW-CSS system under the AWGN channel is given.The communication performance of the MW-CSS system is simulated and analyzed under fading channels.Finally,the implementation scheme of the CSS convert communication system is designed and completed based on the FPGA platform.The parameters of the communication system and the rate conversion scheme among the modules are designed according to the parameters of the radio platform.According to the parameters of the scheme,the frequency conversion scheme of the transmitter and receiver is verified based on MATLAB platform.According to the pulse compression characteristic of Chirp signal,a bit synchronization scheme based on sliding correlation and searching of peak position is designed.Then,based on the Vivado platform,the Verilog programming of each module is completed.The performance of each module is verified based on the Model Sim platform.Finally,the communication system is debugged on the hardware platform and achieved the communication function.