ANALOG SPEECH SCRAMBLING TECHNIQUE WHICH DOES NOT REQUIRE FRAME SYNCHRONIZATION

摘要

A scheme for implementation of frequency domain analog speech scrambling system using FFT wasproposed by F.S.Lee et.al.in 1980.And then,in 1984,L.S.Lee et.al.proposed another cheme using DFT which does not require frame synchroinzation.In the latter scheme,three requirements in designing the frequency domain scrambling matrix were discussed.Firstly,recovery of speech should be ensured when the system is out of frame synchronization.Secondly,the value of the scrambled output must be real.Lastly,the bandwidth expansionof the scrambled speech signal must be small.On this basis,a form of scrambling matrix is proposed in this paper.Computer simulations have been performed for it.A system has been implemented,and various tests were performed.The results show that using such a form of scrambling matrix the recovered speech has high quality without frame synchronization.With the help of the average displacement and interrelated rank,the uniform permutation scrambling scheme is compared with the random permutation scrambling scheme.The conclusion if that the former is much better than the latter.