Security-Coded OFDM System Based on Multiorder Fractional Fourier Transform

This letter utilizes the fractional Fourier transform (FrFT) to achieve anti-multipath and anti-eavesdropping communication. Transmitting data are encoded by binary-resilient code and then decomposed into multiple orthogonal fractional-domains simultaneously to generate coded orthogonal frequency-division multiplexing based on multiorder FrFT (MFrFT-COFDM) symbols. In addition, transform-order (TO) signals are randomly spread by exploiting legitimate channel response and sent to the receiver in the physical layer. Due to channel reciprocity and spatial decorrelation, the legitimate user can access correct TOs, but the eavesdropper cannot. When all the TOs are correct, the MFrFT-COFDM can provide more reliable anti-multipath transmission than other related works because no additional interference is produced. However, as long as any one of the TO is wrong, the final decoding bit error rate will be 0.5. In order to retrieve desired data, the eavesdropper has to test a huge number of TO combinations, which is usually an impractical task. Computer simulations are carried out to validate this scheme.