FFT Based Analog Speech Scrambler using TMS320C6711 DSP

Secure speech communication has always been of much interest in commercial, civil and particularly military communication systems. In this paper we have proposed a two dimensional analog speech scrambling and descrambling scheme which is based on permutation and depermutation of FFT (fast Fourier transform) coefficients and subsequent implementation on Texas Instrument's 32-bit floating-point DSP (digital signal processor) TMS320C6711. This DSP provides an efficient solution to computational complexities of the scheme thereby making the system faster, accurate and reliable. In addition to speed, our algorithm focuses on three main parameters of speech privacy i.e., residual intelligibility, bandwidth expansion and encoding delay. Simulated results provide low residual intelligibility, good quality of recovered speech and low encoding delay. The work is an improvement in real-time secure speech communication systems in DSP environment