Method and device for speech encryption and decryption in voice transmission

US5778073A · kind A · utility

Assignee

• LITEF GmbH · DE

Inventors

• Wolfram Busching · Wertheim, DE
• Erhard Schlenker · Schallstadt, DE
• Gunter Spahlinger · Stuttgart, DE

Key dates

• Filing date: May 14, 1996
• Grant date: Jul 7, 1998
• Expiry date: May 14, 2016

Classification

• Technology area (CPC H): Electricity
• CPC primary: H04K1/006
• WIPO field: Telecommunications
• WIPO sector: Electrical engineering

Abstract

A digitized real voice signal is converted via complex filtering into a complex signal that is subjected to sampling rate reduction, the bandwidth of the respective complex filter corresponding to the sampling rate. The complex signal is phase-modulated by means of a code signal generated by a random-number generator and additively combined with a pilot signal (likewise phase-modulated in a random distribution) to form an encrypted useful signal for transmission. The useful signal is sequentially transmitted together with a preamble for synchronization and signal equalization at the receiver end. At the receiver end, clock synchronization is forced for a phase-modulated pilot signal produced at the receiver end and equalizer coefficients for an equalizer at the receiver end are calculated from the digitized received signal after complex filtering and corresponding sampling rate reduction, during a preamble recognition phase, at which point the phase of the useful signal decryption is initialized. The encrypted, transmitted signal is separated from its phase-modulated pilot signal, which is superimposed at the transmitter end, by linking to the synchronized pilot signal, which is pr…