Choice of sampling frequency for Gps signal simulator calibration receiver and influence on spread-spectrum ranging

As the GPS signal simulator is applied more and more extensively, the test equipment of the GPS signal simulator is required higher and higher. Currently, the calibration using the standard instrument is the most important means, which severely restricts the test environment of the simulator. In order to meet the test requirements of the GPS signal simulator for diversified situation, this paper proposes a design of the calibration receiver using the direct RF sampling technology and gives the design scheme. Based on the bandpass sampling theorem, the determination method of the sampling frequency for multiband signal is analyzed and the sampling frequency of the calibration receiver is determined. In addition, the range accuacy is the critical factor influencing on the test performance of the calibration receiver, and the sampling noise becomes the main error source for the calibration receiver using the direct RF sampling technology, so the range error caused by the sampling noise is analyzed in detail. The results show that the range error caused by the sampling noise tends to be constant when the CNR is over 85dB-Hz. For L1 P code, L2 P code and L5 P code, the range error generated by the calibration receiver doesn´t exceed 5.2 mm, 4.3mm and 4.1mm, respectively, when the CNR of the test signal generated by the GPS simulator is set to 85dB-Hz.