The Key Technology Of Multiple Carriers Satellite Signal Monitoring System

Modern satellite signal monitoring system towards to automation and intelligence, such as automatic alarm, and informs the personnel on duty through the intelligent means, even intelligent handling of emergencies, which can greatly improve the efficiency of monitoring. The automatic frequency spectrum monitoring system designed in this paper can replace frequency spectrograph to process frequency spectrum display, and precisely extract and identify the parameters of multiple carriers satellite signal including carrier frequency, symbol rate, signal to noise ratio(SNR) and modulation mode of sub-carrier in each channel etc. And it also can detect interference, realizing automatic alarm.The satellite signal monitoring system designed in this paper consists of three parts: satellite receiver, signal processing server and remote client. The front end of the system is a conventional satellite signal receiver, including amplifiers, converters and tuners. The signal processing is the most critical part of the system, determining the performance of the system. Remote client is responsible for communicating user's instructions, and displaying the process results.The key technologies of multiple carriers satellite signal monitoring system were deeply studied including carrier synchronization, symbol rate estimation, SNR(signal to noise ratio) estimation and modulation recognition. Carrier synchronization is divided into carrier frequency estimation and phase estimation, in which the carrier frequency can be estimated based on fast Fourier transform method with small amount but low precision and phase lock loop method with complex calculation but high precision. Estimation precision of carrier frequency was significantly improved without any increase of calculation complexity providing necessary prerequisite for subsequent signal parameter estimation. Symbol rate estimation is not sensitive to frequency offset, and the used method of modulation mode recognition is high-order cumulates which requires high accuracy of frequency offset calibration. Frequency offset value should not be higher than 100 Hz was found by simulation. Good recognition effect was achieved even under the condition of high SNR by improving Modulation recognition algorithm. At the same time, the SNR estimation part was also made some improvements, making the stability of SNR estimate be higher which possesses good practical value.Eventually, the system was implemented by the C programming language, and successfully applied in practice. In order to improve the signal processing speed, monitoring system adopted CPU-GPU programming model which was based on operation platform of CUDA(Compute Unified Device Architecture). This programming model can make full use of powerful parallel computing ability of GPU(Graphics Processing Unit) and accelerate the calculating time of algorithm to realize the result of real-time monitoring. Actual test results show that this system possess high accuracy and precision.