Blind Modulation Classification for OFDM in the Presence of Carrier Frequency Offsets

In the orthogonal frequency division multiplexing (OFDM) systems, inter-carrier interference (ICI) caused by carrier frequency offset (CFO) is considered to be one of the most crucial problems for OFDM over multipath channels, which will bring difficulties in the modulation classification of OFDM. In order to deal with the influence of ICI on subcarrier modulation classification, this paper presents a novel blind modulation classification method of OFDM systems with CFO over multipath channels. The virtual subcarrier signals and the pilot subcarrier signals with CFO are classified by using the second-order moment, and then the modulation subcarriers are classified with the fourth-order cumulants and the sixth-order cumulants. Simulations are conducted to verify the proposed method not only has a good classification performance, but also has a low computational complexity. The proposed method can reduce energy consumption and is beneficial for green radios.