Research On The Modulation Identification Of OFDM Based On The Wavelet Transform

The technology of signal modulation identification plays an important role in adaptive transmission, software defined radio, electronic war and spectrum survey. Orthogonal Frequency Division Multiplexing (OFDM) is one of the multi-carrier modulations and is a core technology in the wireless communication system,but few researches for OFDM modulation in multi-path Rayleigh fading channels.To these problems mentioned above, this paper studies the technology of signal modulation identification in low signal to noise ratio (SNR) and multi-path conditions. Wavelet Transform (WT) is suitable for detecting transient signals,by which the instantaneous features of digital signals will be easily presented when the symbols change. In this paper, an algorithm applying WT on OFDM and Single Carrier (SC) digital signals twice (WT-T) to extract the transient features of them, and then by using the transient features in WT-T domain, it is easy to identify the two types of signals. The principle of this algorithm is derived deeply, and the algorithm is simulated using the OFDM signal based on DVB-T standard and IEEE 802.11a standard respectively in multi-path conditions. In addition, the effects of the sample size, the sample rate and the symbol rate on the identification algorithm are analyzed and simulated. At last, the algorithm is simulated using the Morlet wavelet and db3 wavelet respectively in multi-path conditions. The simulation results show that the algorithm has good performances in low SNR and multi-path Rayleigh fading channels.