Speech scrambler
US4747137A · kind A · utility
75Cited by
5References
10Claims
0Family size
Assignee
Inventor
Key dates
| Filing date | Jun 30, 1986 |
| Grant date | May 24, 1988 |
| Priority date | — |
| Expiry date | Jun 30, 2006 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04K1/00
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
A speech scrambler is disclosed, in which a frequency spectrum obtained by an orthogonal transform of a time domain signal is divided into a plurality of blocks in the frequency domain. One of the blocks which has energy less than a predetermined value is adaptively replaced by a dummy spectrum. The resulting spectrum is rearranged in accordance with a predetermined rule. The frequency spectrum is subjected to an inverse othogonal transform to obtain a time domain signal for transmission. The orthogonal transform is fast Fourier transform or fast Hadamard transform.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.