In this paper

a new method which combines with covariation

cyclostationarity and FLOM for calculating low order spectrum based on FAM(FFT Accumulation Method) was proposed and the simulations were made for modulated signals(AM

QPSK)

and finally the cycle leakage and complexity of this method were analyzed.The result under

stable distribution shows that the spectrum instruction of two order cyclostationary signals is the same as under Gauss model.However

the methods constructed under stable distribution have better performance of anti-noise than under Gauss model.The low order cycle characteristic parameters are constructed in the field of cycle spectrum and a new method is given for modulation recognition and blind

separation in complex environment.