Research On Blind Demodulation Of MPSK Signal In Wireless Detection

As main part of intelligent receivers,blind demodulation is an important subject in electronic countermeasure.The contents are realizing function such as modulation recognition,parameter estimation and demodulation based on channelization.In this paper,the detail of recognition,estimation and demodulation will be discussed.The specific work description as below:(1)Based on the existing modulation recognition algorithm,the instantaneous feature extraction method combined with high cumulant is used to identification.Different with other method,high cumulant under frequency offset was calculated.We transform carrier frequency which has big influence on recognition to symbol rate just have little effect,and the identification in phase modulation signal was completed by improved instantaneous extraction method.(2)Carrier frequency and symbol rate are important parameter in identification and following demodulation.It is needed estimate these two while they are unknown in blind situation.Firstly,a rough estimation of carrier frequency is carried out by using correlation method to determine an approximate range.Then,we proposed an algorithm based on cyclic correlation function to estimate accurately.Another method.the characteristic of cyclic spectral density at small step was found to estimate symbol rate.(3)The huge difference between demodulation in blind situation and collaboration communication.Every parameter has to be adapt with corresponding signal in order to achieve the truly blind demodulation.We mainly discuss the synchronization in demodulation which determines the correction directly.Firstly,carrier synchronization is carried out by using Costas loop and the parameter like loop filter designed in blind environment.We use Gardner and Farrow structure interpolation algorithm to realize bit synchronization.(4)The algorithm proposed above and its performance is verified in Matlab.The recognition can be come true at low signal-to-noise ratio.The accurately estimation method we proposed have much better performance than general method.It also take short time to be tracked in synchronization module.We realize all the algorithm in software radio platform which design by ourselves,and it can meet the requirements of theoretical analysis compare with simulation result.The whole process of blind demodulation is completed in the sense of engineering.