Study And Implementation Of Carrier Recovery Technique In Non-Cooperative Communication

In order to obtain the best demodulation performance,the coherent demodulation method is often used in digital communication receiver.However,due to the Doppler effect,the different vibration sources of the receiver and transmitter,and the instability of the local oscillator will lead to the frequency offset between the local carrier and the received signal carrier.In addition,in the non-cooperative communication system,the lack of the priori information about the carrier frequency of the signal,it brings forward higher requirements for the carrier recovery technology.Therefore,it is important to study fast carrier recovery method with high precision and wide frequency range.Based on the analysis and summary of the carrier recovery technology study status at home and abroad,the paper made a deep study in the non-cooperative communication system in wideband carrier recovery.A new model of carrier recovery loop based on a combination of FFT carrier frequency estimation,maximum likelihood estimation and Costas loop is built to achieve high-precision and wideband fast carrier recovery and the model is realized in FPGA hardware.The main work and study contents of this paper are as follows:In the first part,the study background of carrier recovery technology is summarized,the study status of carrier recovery technology at home and abroad is outlined,and the characteristics of non-cooperative communication system are analyzed.In the second part,carrier recovery technology is studied.For one thing,carrier recovery method based on phase locked loop: study on the quadratic loop and Costas loop,decision feedback loop of carrier recovery;for another thing,open loop aided carrier recovery method: study on the FFT carrier frequency estimation algorithm,maximum likelihood criterion algorithm of frequency offset estimation.And advantages and disadvantages of the various carrier recovery methods are briefly analyzed.In the third part,according to the advantages and disadvantages of various carrier recovery methods,combined with the broadband and high precision requirements of carrier recovery project,this paper designed a new carrier recovery loop based on Costas loop: at first,use FFT transform to estimate carrier frequency cursorily,and the maximum likelihood frequency offset algorithm is used to correct the carrier frequency of the coarse estimation,then use modified estimated carrier frequency to instruct the Costas loop to achieve carrier recovery.Besides,use MATALB software to simulate the carrier recovery model.In the fourth part,FPGA implementation of the new carrier recovery loop is studied.The designed new model is divided into three modules,FPGA implementation method of each module is studied.MOEDLSIM software is used for simulation and hardware download test to verify the feasibility of the designed carrier recovery loop.Through the simulation,the absolute value of recovery carrier frequency offset is small,performance is great,and can meet the project requirements.