Apparatus for privacy transmission in system having bandwidth constraint
US4398062A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Feb 20, 1981 |
| Grant date | Aug 9, 1983 |
| Priority date | — |
| Expiry date | Feb 20, 2001 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04K1/02
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
Source intelligence within a predetermined bandwidth is normally provided to a transmission channel having a bandwidth constraint of the predetermined bandwidth. For privacy transmission, a first pulse train indicative of the source intelligence is derived and is enciphered by addition of pseudo-random values to the pulses, either directly or modulo some specified constant. The enciphered pulse train is converted to first and second symbol pulse trains at subharmonic frequencies of the first pulse train. Energy within a selected spectrum is derived from each symbol pulse train, such as by filtering, and used to modulate first and second channels of a quadrature modulator having a carrier frequency centered within the predetermined bandwidth. A suppressed carrier quadrature modulated output is transmitted along with a carrier frequency component. Receiving means include a quadrature demodulator and means for reconstructing symbol pulse trains and means for reconstructing an additively enciphered pulse train from symbol pulse trains. The enciphered pulse train is provided to an adaptive filter and deciphering means for provision of an output to an intelligence utilization means. A tr…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.