Adopting the isomorphic emphasis to speech security on the time domain scrambling

The authors report that isomorphic emphasis succeeds in preventing speech quality degradation during time domain scrambling without any expansion of frequency occupancy bandwidth over radio security speech channels. The isomorphic emphasis is realized with the canonical form, which consists of a cascaded differentiator, time domain scrambler with arbitrary sequential pattern, and integrator. This time domain scrambler degrades speech quality by changing the power ratio of speech signal to fading noise over subjective frequency domain. The isomorphic emphasis is shown to protect time scrambled signals from both expansion and degradation over all of the subjective frequency domain, even if there exists a discontinuity among input data according to time scrambling. These facilities of the isomorphic emphasis in the time domain scrambling for speech security are verified from theoretical analysis and computer simulations for poor fading channels.