Multi-channel PGC Demodulation Technology Research And Implementation Based On FPGA

Optical fiber hydrophone is a new kind of underwater acoustic detection sensor system with strong anti-jamming capability,high sensitivity and wide dynamic range.It has a great significance for national defense construction and scientific research.Optical fiber hydrophone system with superior performance based on phase generated carrier(PGC)method gets more and more attention of researchers.The system with PGC method is widely used in submarine monitoring,geological prospecting,optical fiber displacement and other vibration sensor,which can realize precise demodulation.Conventional demodulation system is implemented by DSP.Using DSP can demodulate data more accurate by the floating point arithmetic in the process of operation,but the slow speed of DSP demodulation becomes the disadvantage.The demodulation system implemented by FPGA will improve the ability of sampling rate and operation rate.Furthermore,the system supports parallel processing.The system based on PGC needs low pass filter with narrow transition bandwidth.The performance of the filter is very importance for the accuracy of the demodulation results.Adopt the method of improve the filter order can improve the performance of the filter,but the shortcomings of the method is the length of the filter becomes long prohibitively,reducing the computational efficiency.The interpolation and FRM technique are exploited and applied to the design of a high performance filter with very narrow transition bandwidth.It is shown that the resulting filter entails less computational complexity substantially and reduces multiplier resources consumption comparing to the conventional filter.The main content and innovation points of thesis research are as follows:Firstly,in this paper the applications and development of fiber-optic hydrophone is expounded,and the present situation of the core demodulation system is analyzed.The advantage of the demodulation system based on FPGA and PGC algorithm is discussed.A novel demodulation system with pipelining and parallel processing is proposed.Using the system,four roads PGC signal can realize high accuracy sampling and real-time phase demodulation.Secondly,PGC demodulation algorithm is analyzed in detail and the relevant formulas are derived.And the data process of the PGC algorithm is determined.By analyzing theimportance part,low pass filter,of the PGC algorithm,the relation of the filter performance and its computational speed and resources consumption is illustrated.The method using interpolation and FRM technique to obtain a high performance filter with very narrow transition bandwidth is proposed.And the resulting filter improves operation rate and reduces multiplier resources consumption comparing to the conventional filter.Thirdly,the system function is determined.The hardware design and software design of the system are analyzed in detail.Design of hardware circuit,select the required chips,and build the hardware circuit based on FPGA.Defining the PGC algorithm is correctness and feasibility by the simulation of Matlab.And the change resulting of the signal wave from different operating can be obtained.Write software programs using Verilog language and select FPGA modules to achieve demodulation modules.And define the connection between the various functional modules and the sequential.Finely,using the hardware platform and the tool of Signaltap?to test the demodulation system.Verify the performance of the demodulation system and obtain demodulation results.Show the advantage of high precision,wide dynamic range of the demodulation system based on FPGA.