Patent ID: 8587403

Claim:
A method of preventing relay attack of a passive entry system (PES) used within a vehicle to provide passive access to one or more vehicle systems, the method comprising: upon detecting a PES triggering event, transmitting a query message from one or more PES antennas included within the vehicle, each of the query messages including a continuous wave (CW) portion having an amplitude that decreases as the query message travels farther from the transmitting PES antenna; receiving a first response of a fob receiving one or more of the query messages, the response indicating the amplitude of each CW portion included within the one or more query messages being responded to by the fob; determining whether the fob is one of near field and far field from the vehicle based on the amplitude included in the response indicating a distance of the fob from the vehicle to correspond with one of the near field and the far field; transmitting a challenge query to the fob that is dependent on whether the fob is near field or far field, the challenge query providing a first test if the fob is near field and a second test if the fob is far field; and granting access to the one or more vehicle systems to be passively controlled according to the PES triggering event depending at least in part on a second response of the fob to the one of the first test and the second test provided by the challenge query.