Modulation Recognition with Frequency Offset and Phase Offset over Multipath Channels

Modulation recognition becomes unreliable at low signal-to-noise ratio (SNR) over fading channel. A novel method is proposed to recognize the digital modulated signals with frequency and phase offsets over multi-path fading channels in this paper. This method can overcome the effects of phase offset, Gaussian noise and multi-path fading. To achieve this, firstly, the characteristic parameters search is constructed based on the cyclostationarity of received signals, to overcome the phase offset, Gaussian white noise, and influence caused by multi-path fading. Then, the carrier frequency of the received signal is estimated, and the maximum characteristic parameter is searched around the integer multiple carriers and their vicinities. Finally, the modulation types of the received signal with frequency and phase off-sets are classified using decision thresholds. Simulation results demonstrate that the performance of the proposed method is better than the traditional methods when SNR is over 5dB, and that the proposed method is robust to frequency and phase offsets over multi-path channels.