Abstract:

Considering the difficulty in classifying quadrature amplitude modulation (MQAM) signals over rayleigh fading channel, an algorithm based on antenna arrays for identifying MQAM signals in Rayleigh fading channels is presented. The characteristic that spatial diversity reception can improve the SNR of received signals is used. First, the equal gain diversity model for modulation classification is given. Then, the nonlinear leastsquares estimator is presented to estimate the frequency offsets and phase offsets. Finally the normalized fourthorder and sixthorder cumulants of the signal at the output of the combiner are estimated, that can be used as modulation classification features. Simulations demonstrate that the proposed scheme is efficient in rayleigh fading channel. Compared to the existing quasi hybrid likelihood ratio test (qHLRT) method, the proposed method has lower computational complexity and stronger practicability.

Key words: modulation classification, rayleigh fading channel, cumulant, equal gain combining