Research And Implementation Of Digital Demodulation Algorithms For Multidimensional Modulated Signals Based On FPGA

Laser Doppler vibrometry represents a high precision measurement technology,which is extensively applied in military field and precision civil measurement.As compared with traditional contact tachometer and other measuring devices,laser Doppler vibrometry is capable of higher accuracy and sensitivity.The output of ideal heterodyne laser vibration measurement system can be considered as FM signal.Despite the merits as mentioned above,there remain some practical problems with it,like parasitic amplitude modulation and residual carrier.The laser Doppler signal is known as multidimensional modulated signal with frequency and amplitude modulation.The digital demodulation algorithm and the adaptive residual carrier elimination algorithm intended for laser Doppler signal were proposed in this thesis.The need for using intellectual property(IP)cores was eliminated for all functional modules except for multipliers and adders.It was designed to facilitate the transplantation of different FPGA platforms.In respect to the real-time demodulation of laser Doppler signal,an orthogonal demodulation system was adopted and optimized on FPGA.The noise of the system was reduced after digital down conversion by the filter.In order to save the limited multipliers and logic resources of FPGA,serial,parallel and semi-parallel FIR filters were designed to satisfy the processing needs of different rate signals.Based on the CORDIC algorithm in vector mode,a high-speed multidimensional demodulator was suggested for the demodulation of the amplitude information and the phase information.An adaptive notch filter based on FRLS algorithm was investigated for suppressing residual carrier from laser Doppler signal.The computation of FRLS algorithm reduced about 58%by making a reasonable approximation to conventional RLS algorithm.Based on CORDIC algorithm in rotation mode,a new strategy was proposed for a numerical control oscillator to generate two orthogonal reference signals.The algorithm was validated on MATLAB and then operated on the platform of FPGA by using the fixed-point computing method.According to the above methods and techniques,the practical implementation of digital demodulation system was performed using FPGA.In addition,the performance of the sub-module and the overall function was tested and analyzed.It has been demonstrated that the power of laser Doppler signal ought to be greater than-70 dBm without a low noise amplifier.The vibration measurement distance is found to be less than 50m.Residual carrier is significantly inhibited by the adaptive interference cancellation system based on FRLS algorithm with a rejection ratio of 20dB within 0.02ms.