Research On Noise Suppression Of Small Frequency Shitf LFM Modulated Signal Based On Fractional Fourier Transform

With the rapid development of communication technology, the contradiction betweenscarcity of the electromagnetic spectrum resource and surge in user demand is increasinglyprominent, and new efficient digital modulation technique having high energy concentrationhas broad application prospects and urgent requirements.Small Frequency Shift linear frequency modulation (SFS-LFM) is a class of efficientdigital modulation techniques with High bandwidth efficiency. However, this technologyimproves the effectiveness of the inevitable result of weakening of the system’s noiseimmunity.To resolve this problem, an efficient signal receiver solution for1/3Continuous PhaseChirp Keying (1/3-CPCK) which is a Special case of SFS-LFM communication system isproposed based on FrFT, making use of the difference between LFM signal and noise in FrFTdomain, aimed to enhance thenoise immunity.The study content is described below in detail.To begin with, the analysis has been made of the difference between modulated signaland noise in FrFT domain in1/3-CPCK modulation system, based on theoretical analysis andsimulation.Secondly, a noise suppression method for1/3-CPCK communication system is proposedbased on parameter estimation of FrFTFinally, to solve the defects of previous method, a noise suppression method for13-CPCK communication system is proposed based on FrFT pre-filter, which uses the differencebetween modulated signal and noise in FrFT domain, filter the signal in FrFT domain. Inaddition, a simulation platform on Matlab is built, in order toverify the effectiveness andfeasibility of the proposed method.