Research On ADCP Signal Processing Method Based On FPGA

Our country has rich marine resources.The development of marine resources has a great influence on the economic development of our country and the improvement of people’s living standards.Acoustic Doppler Current Profiler(ADCP)has become the main flow measurement instrument for exploring marine resources because of its characteristics such as no change on flow field,short measurement duration,and large velocity range.The basic principle of the ADCP is to measure the Doppler frequency generated by the relative motion of scatterer in the water from the echo,and to layer and calculate the echo so as to obtain the cross-sectional flow velocity.This topic researches the theoretical of the ADCP current measurement technology,realizes the main function on the FPGA platform,and optimizes for the hardware implementation of the frequency measurement algorithm.The main contents are as follows:Firstly,the classification and basic structure of ADCP are described.The principle of Doppler current measurement and the way of ADCP layered measurement profile are briefly described.For the case that the echo signal may contain high noise components,theoretical studies on three currently used frequency-measuring algorithms,including zero-crossing detection method,complex correlation algorithm and fast Fourier transform method,and the simulation analysis is performed on three frequency measurement methods on the accuracy of frequency measurement under different signal-to-noise ratios and different sampling frequencies.Based on the conclusions obtained,the complex correlation algorithm is used to estimate the frequency.The advantages of the wideband encoding and measurement method are also analyzed,and the wideband encoded signal is selected as the emission signal.In terms of system design,the FPGA development board with EP2C35F484C8 as the core is used to realize the digital parts of the ADCP signal generation module and the signal processing module on the FPGA,and the generation of coded phase modulation signals and the orthogonal demodulation of the echo signals are completed in the digital domain,which increases the flexibility of the system and the accuracy of the frequency measurement,and it also contributes to the miniaturization of the entire ADCP system.In the frequency measurement section,a phase angle calculation method based on shift addition operation and look-up table suitable for hardware implementation is proposed.Under the premise of ensuring the accuracy of frequency measurement,the resources consumed for complex calculations are greatly reduced.Finally,the main function of ADCP is tested and verified on the FPGA platform.The signal generator module uses the frequency offset signal to simulate the Doppler shift echo signal in the actual measurement,and the signal processing module’s functionis verified through the signal.The frequency measurement results of different measured signal frequencies and related delays are collated,and the experimental results show that this frequency measurement method has good frequency measurement accuracy in the case of occupying less resources.The measurement error is within ±20Hz.