System and method for authorizing a remote device

1. A method for authorizing a passive vehicle function, the method comprising:

transmitting a first query signal for receipt by a plurality of remote transceivers proximate a vehicle;

receiving a first reply signal from each of the plurality of remote transceivers receiving the first query signal;

determining a challenge order for authenticating any one of the plurality of remote transceivers based at least in part upon a location classification for each remote transceiver determined from each first reply signal; and

transmitting a challenge signal to a selected remote transceiver of the plurality of remote transceivers based upon the challenge order, the challenge signal prompting a challenge reply signal for the selected remote transceiver.

2. The method of claim 1 , wherein the first query signal comprises a plurality of sequential signal bursts, each sequential signal burst transmitted from one of a plurality of antennas located on the vehicle.

3. The method of claim 2 , wherein the plurality of antennas transmitting the first query signal generate an authorization zone having boundaries defined using signal strength criteria for each of the plurality of antennas.

4. The method of claim 3 , wherein the first reply signal includes signal strength data sampled for each signal burst transmitted from the plurality of antennas.

5. The method of claim 4 , wherein the location classification of each remote transceiver is based upon the signal strength data.

6. The method of claim 5 , wherein the location classification is selected from one of the following locations: within the authorization zone, out of the authorization zone, and indeterminate.

7. The method of claim 6 , wherein the challenge order amongst remote transceivers classified as within the authorization zone is further based upon the signal strength data.

8. The method of claim 6 , further comprising:

transmitting a second query signal for receipt by at least one remote transceiver having an indeterminate location upon a determination that no remote transceivers within the authorization zone have been authenticated, wherein the second query signal is at least partially transmitted from at least one additional antenna different from the plurality of antennas;

receiving a second reply signal from the at least one remote transceiver in response to the second query signal; and

determining a new challenge order for authenticating the at least one remote transceiver based upon the second reply signal.

9. The method of claim 6 , further comprising:

receiving a valid challenge reply signal from the selected remote transceiver authenticating the selected remote transceiver;

evaluating the signal strength of the valid challenge reply signal if the location of the authenticated remote transceiver is indeterminate; and

authorizing the authenticated remote transceiver upon a determination that the signal strength of the valid challenge reply signal indicates that the authenticated remote transceiver is within the authorization zone.

10. A passive activation system for a vehicle, the system comprising:

a plurality of antennas arranged at various locations throughout the vehicle, the plurality of antennas configured to:

transmit a first query signal for receipt by one or more remote transceivers located proximate the vehicle, and

receive a first reply signal transmitted from each of the remote transceivers in response to the first query signal, the first reply signal including signal strength data sampled by the remote transceiver for each of the plurality of antennas; and

a controller on board the vehicle and in communication with the plurality of antennas, the controller configured to:

determine a challenge order for authenticating any one of the remote transceivers based upon the signal strength data transmitted in each first reply signal, and

instruct a challenge antenna to transmit a challenge signal to one of the remote transceivers based upon the challenge order.

11. The system of claim 10 , wherein the first query signal comprises a plurality of sequential signal bursts, each sequential signal burst transmitted from one of the plurality of antennas.

12. The system of claim 10 , wherein the signal strength data in each first reply signal indicates whether the location of the corresponding remote transceiver is included within an authorization zone, excluded from the authorization zone, or indeterminate.

13. The system of claim 12 , wherein boundaries of the authorization zone are defined using signal strength criteria for each of the plurality of antennas.

14. The system of claim 13 , wherein remote transceivers located within the authorization zone are challenged before remote transceivers having an indeterminate location.

15. The system of claim 14 , wherein remote transceivers having stronger signal strength data are challenged before remote transceivers having weaker signal strength data.

16. The system of claim 12 , further comprising at least one additional antenna different than the plurality of antennas, the at least one additional antenna configured to:

at least partially transmit a second query signal for receipt by at least one remote transceiver having an indeterminate location, and

receive a second reply signal from the at least one remote transceiver in response to the second query signal, the second reply signal including signal strength data sampled by the at least one remote transceiver for each of the plurality of antennas, wherein the signal strength data in each second reply signal indicates whether the location of the corresponding remote transceiver is included within an authorization sub-zone, excluded from the authorization sub-zone, or still indeterminate.

17. The system of claim 16 , wherein the controller is further configured to determine a new challenge order for authenticating the at least one remote transceiver based upon the second reply signal.

18. The system of claim 12 , wherein the challenge antenna is configured to receive a valid challenge reply signal from one of the remote transceivers to obtain an authenticated remote transceiver; and

wherein the controller is further configured to:

evaluate the signal strength of the valid challenge reply signal if the location of the authenticated remote transceiver is indeterminate, and

authorize the authenticated remote transceiver upon a determination that the signal strength of the valid challenge reply signal indicates that the authenticated remote transceiver is within the authorization zone.

19. A method for authorizing a passive vehicle function, the method comprising:

querying for the presence of a remote transceiver within an authorization zone using a number of antennas positioned throughout a vehicle that each transmit a signal burst;

receiving a response from at least two remote transceivers proximate the vehicle, each response including an RSSI value for each signal burst;

determining a location for each remote transceiver with respect to the authorization zone based on the RSSI value;

classifying each remote transceiver as either included in the authorization zone, excluded from the authorization zone, or indeterminate based on the determined location;

determining a primary challenge order for challenging each remote transceiver individually based upon the classification;

determining a secondary challenge order for challenging remote transceivers included in the same class based upon the RSSI value;

determining an overall challenge order based upon the primary challenge order and the secondary challenge order; and

sequentially challenging the at least two remote transceivers by transmitting an encrypted challenge signal from a challenge antenna to each remote transceiver in accordance with the overall challenge order until a valid challenge response signal is received with matching encryption from one of the at least two remote transceivers.

20. The method of claim 19 , further comprising:

querying for the presence of an indeterminate remote transceiver within a sub-zone using at least one additional antenna upon a determination that no remote transceivers within the authorization zone have been authenticated;

receiving a second response from the at least two remote transceivers; and

determining a new challenge order for challenging the at least two remote transceivers based at least in part upon the second response