Abstract:A new method of classifying and identifying sub-carriers is proposed for Orthogonal Frequency Division Multiplexing (OFDM) signals in non-cooperative communication systems, because there are many sub-carrier modulation types and some sub-carrier modulation types are difficult to be identified in OFDM signals. This method combined and improved the constellation cluster projection method and Logarithmic Likelihood Function (LLF) algorithm. The method first performed constellation clustering projection on different subcarrier modulation signals to recognize the common subcarrier modulation, then calculated the LLF to recognize Offset QAM (OQAM) subcarrier signal and common subcarrier signals. On the basis of the previous step, the LLF of subcarrier group was derived to make the LLF calculation easier to be classified by the decision threshold. Theoretical deduction and computer simulation results showed that the method could recognize the subcarrier modulation when the SNR is 15 dB.