Multi-notch filter application in laser inertial navigation system

The power spectrum characteristics of ring laser gyros in laser inertial navigation system (LINS) are analyzed, which suggests that three laser gyros' dithering frequencies will interfere with each other in LINS. A novel low-pass finite impulse response (FIR) filter with three-notch is proposed to filter the dither frequencies of the ring laser gyros. A multi-notch FIR filter is designed with frequency-domain design method by specifying the amplitude of three dithering frequencies to be a small quantity. Three notches are produced naturally in the FIR amplitude frequency characteristic curve. The filter adopts a standard FIR algorithm. Meanwhile, the low-pass filter for the three laser gyros' signal in LINS and notching for the dithered signal are realized. A 24-order multi-notch FIR filter is given as an example to process the data of a high-precision LINS. The amplitude-frequency characteristic analysis shows that the new filter provides extra attenuation by at least 80 dB in the possible dithering frequency band due to three notch points concentrated. The extra decay can effectively prevent the filter performance degradation due to the laser gyro's dithering frequencies drift. Experiments suggest that the data oscillation of the output from the new filter is decreased by 5~8 times compared with that of the old filter in the LINS. Furthermore, the three-axis wobbling test results show that the navigation precision can also be improved.