Method and apparatus for protecting a transmission path between a base unit and a mobile key unit
US6469620B2 · kind B2 · utility
1Cited by
6References
22Claims
0Family size
Assignee
Inventor
Key dates
| Filing date | Jul 3, 2001 |
| Grant date | Oct 22, 2002 |
| Priority date | — |
| Expiry date | Jul 3, 2021 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG07C2009/00793
- WIPO fieldControl
- WIPO sectorInstruments
Abstract
The invention relates to a method and apparatus for protecting a transmission path between a base unit and a mobile key unit in an access control system, in particular for motor vehicles. A carrier signal which is modulated with a user signal is transmitted from a transmitting unit to a receiving unit. According to the invention, a separate reference signal, which has a fixed phase angle with respect to the carrier signal, is also transmitted. The phases of the reference signal and of the carrier signal are compared in a test circuit, and an alarm signal is emitted if a phase difference which varies with time is found.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.