Blind Modulation Recognition Algorithm for MQAM Signals
MQAM信号调制方式盲识别

A blind modulation recognition algorithm for MQAM signals is proposed. The method firstly estimates the signal carrier frequency and bandwidth from its spectrum to complete the frequency conversion and the low-pass filtering. Then the baud rate is estimated by calculating the frequency spectrum of the square envelope, and the baud rate sampling is done according the symbol timing. Finally the modulation type is identified by comparing the variance of sequences in the minimum ring of vectogram. It does not require prior information about carrier frequency and baud rate, and is not sensitive to the carrier offset. Moreover, there is no complex iterative process. So it is suitable for signal recognition of practical applications. Computer simulations show that the correct recognition probability is larger than 99% if SNR is greater than 16dB and using 2400 symbols. It verifies the validity of the algorithm.