An analog speech scrambler using the FFT technique with high-level security
Akira Matsunaga, Keiichiro Koga, Michihisa Ohkawa · 2003
A full-duplex analog speech-scrambling system is proposed for the application to mobile communication systems and public-switched telephone networks. The scrambling algorithm is based on the rearrangement of the fast Fourier transform (FFT) coefficients accompanied by adaptive dummy spectrum insertion and companding operations. Simulations results indicate that the scrambled speech has no residual intelligibility and the unscrambled speech quality is satisfactory. The hardware unit is implemented by using seven advanced digital signal processing (DSP) chips, including those for an echo canceller for full-duplex operation and an adaptive equalizer.>