| 摘要 |
PURPOSE:To keep sure and stable frame synchronization even during ciphering communication by transmitting a frame synchronizing signal at a band different from that of a ciphering signal in a spectrum transposition ciphering system using Fourier transfor. CONSTITUTION:A Fourier transforming device 3, a transposition circuit 4 and a shift circuit 3 are controlled by a prescribed period signal fed from a counter circuit 11. A counter circuit 10 generates a frame synchronizing signal having a prescribed frequency relation with an output of the counter circuit 11 and an output of the circuit 10 controls a switching circuit 12. Spectrums of two frequencies f1, f2 different from the frequency band of a ciphering signal are outputted alternately in a frame period from a switching circuit 12 and given to the spectrum of the ciphering signal by an insertion circuit 32. An output of the circuit 32 is transmitted through an inverse Fourier transform device 7. The frame synchronization is taken by detecting the spectrum change in the two frequencies f1, f2 at the reception side. |
