| 摘要 |
A system for preventing unauthorized access to a vehicle having a passive entry system uses a bi-directional radio frequency, or RF-RF, signal. When using a RF-RF signal system, the signal from vehicle to a driver's ID device is non-directional and not significantly distance limited. Consequently, a thief may be able to activate the entry system and gain access to the vehicle when the driver's ID device is simply within range. The inventive passive entry system interrogates the ID device periodically following parking and locking of the vehicle. The signal strength levels received by the vehicle from the ID device are stored and a signal strength threshold level is computed. Upon a request for entry to the vehicle, a current signal strength level is compared to the signal strength threshold level. Based on that comparison, it is determined whether the request is valid or unauthorized. If the request for entry is deemed unauthorized, then access to the vehicle is not granted.
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