Research On High Dynamic Low Intercept Spread Spectrum Synchronization Technology

On June 23,2020,the last Beidou-3 global networking satellite was successfully launched.my country has established a world-class satellite navigation system to provide services to people all over the world.Due to the limitation of satellite size and weight,satellite transmission power is usually low,and satellite communication needs to transmit information in a communication environment with lower signal-to-noise ratio.Since the satellite communication system completes the communication in a highly dynamic environment,there is a relatively large relative speed between the sender and receiver,and due to the high-speed satellite flight,the relative speed of the sender and receiver changes with time,making the local receiver and the received signal have a larger Doppler frequency Offset and large frequency offset change rate.At the same time,because the satellite communication system widely uses military communication,but due to its open space channel characteristics,it has poor security and is easy to be detected and interfered by the enemy.Therefore,more and more scholars are studying the design of low interception systems.Aiming at the characteristics of the above-mentioned satellite communication,this article mainly studies the low-intercept synchronization acquisition technology in the low SNR and high dynamic environment.Aiming at the characteristics of satellite communication systems that need to complete signal transmission in a low signal-to-noise ratio and high dynamic environment,this paper proposes an MS-FFT synchronization acquisition algorithm with better anti-frequency offset performance,and builds a system model.Under this model,MS-FFT and the commonly used PMF-FFT synchronization algorithm are analyzed for capture performance,and it is concluded that PMF-FFT has better anti-noise performance and MS-FFT has better anti-frequency performance under the same complexity.Partial performance.Aiming at the disadvantages of poor anti-interception performance of satellite communications,this paper proposes a low-interception synchronization head design scheme,which adopts a joint randomization method in the time domain and frequency domain to avoid energy accumulation and greatly reduce the estimation of communication parameters by non-cooperative parties through high-order statistics.The probability.Taking into account the consumption of chip resources,the PMF-FFT synchronization acquisition algorithm was finally used as the system implementation algorithm,and some improvements were made to it.The large number of relevant peak position judgments were used to replace the threshold judgments,which improved the acquisition performance of the system;serial multiple frequency points Search to improve the system's anti-frequency offset performance;parallel multi-channel PMF-FFT receives low-intercept synchronization heads to improve the system's anti-intercept performance,and the system is implemented on an intermediate frequency board based on the XCKU085 chip.Through in-field testing,it is verified that the system can complete synchronization capture in an environment with a signal-to-noise ratio of-18 d B and a frequency offset of ±250KHz.It is also verified that the sync head with low intercept design has better anti-interception performance than conventional sync heads.It is confirmed that the synchronous acquisition system designed in this paper is suitable for the fast-developing satellite navigation communication system.