Field Superposition System and Method Therefor

• US 20120229254A1
• Filed: 03/11/2011
• Published: 09/13/2012
• Est. Priority Date: 03/11/2011
• Status: Active Grant

• Current Assignee: NXP B.V. (NXP Semiconductors NV)
• Original Assignee: NXP B.V. (NXP Semiconductors NV)
• Inventors: Nowottnick, Juergen
• Granted Patent: US 8,570,144 B2
• Time in Patent Office: Days
• US Class Current: 340/5.61
• CPC Class Codes: B60R 25/24 using electronic identifiers containing a code not memorised by the user
• CPC Class Codes: G07C 2009/00555 comprising means to detect or avoid relay attacks
• CPC Class Codes: G07C 9/00309 operated with bidirectional data transmission between data carrier and locks
• CPC Class Codes: H04L 63/0876 based on the identity of the terminal or configuration, e.g. MAC address, hardware or software configuration or device fingerprint
• CPC Class Codes: H04W 12/06 Authentication
• CPC Class Codes: H04W 12/79 Radio fingerprint

Abstract

Wireless communications between a vehicle base station and a transponder are authenticated. Interior and exterior antennas are respectively driven using first driving currents, the interior antenna being separated from the transponder by a portion of a vehicle in which the vehicle base station resides. Separate vector components of the respective fields emitted by the interior and exterior antennas are received and detected at the transponder. Superposition factors are calculated for the interior and exterior antennas based upon the separate vector components. Each of the interior and exterior antennas is concurrently driven using the same phase, respectively using the driving currents multiplied by the superposition factors. Superposed vector components are detected for a superposed signal including signals from both antennas received at the transponder. The transponder is authenticated based on the detected superposed vector components for the superposed signal being within a noise-based range of the sum of the separate vector components for each of the interior and exterior antennas as multiplied respectively by the superposition factors for the interior and exterior antennas.

Claims

1. A method of wireless communication between a vehicle base station and a transponder, the method comprising:

driving interior and exterior antennas using first driving currents, the interior antenna being separated from the transponder by a portion of a vehicle in which the vehicle base station resides;

detecting separate vector components of the respective fields emitted by the interior and exterior antennas and received at the transponder;

calculating superposition factors for the interior and exterior antennas based upon the separate vector components;

concurrently driving the interior and exterior antennas using the same phase, respectively using the first driving currents multiplied by the superposition factors; and

detecting superposed vector components of a superposed signal including signals from both antennas received at the transponder; and

authenticating the transponder in response to the detected superposed vector components being within an error-based range of the sum of the separate vector components for each of the interior and exterior antennas as multiplied respectively by the superposition factors for the interior and exterior antennas.

2. The method of claim 1, wherein calculating superposition factors includes calculating factors for the external and internal antennas, the product of the factor for the external antenna and the separate vector components for the external antenna being equal to the sum of a random value plus the product of the factor for the internal antenna and the separate vector components for the internal antenna.

3. The method of claim 1, wherein authenticating the transponder includes enabling at least one of an ignition circuit and an entry circuit in the vehicle.

4. The method of claim 1, wherein authenticating the transponder includes transmitting, from the transponder, the detected superposed vector components to the vehicle base station, and authenticating the transponder at the vehicle base station.

5. The method of claim 1,

wherein concurrently driving each of the interior and exterior antennas using the same phase includes encrypting and transmitting the superposition factors to the transponder,

wherein authenticating the transponder includes detecting and using the encrypted superposition factors at the transponder, to determine whether the superposed vector components are within said error-based range of the sum of the separate vector components for each of the interior and exterior antennas.

6. A method for wirelessly communicating between a vehicle base station and a transponder, the method comprising:

driving interior and exterior antennas respectively using transmission currents I_I and T_O, the interior antenna being separated from the transponder by a portion of a vehicle in which the vehicle base station resides;

at the transponder, measuring x₁, y_I and z_I vector components of the field strength emitted by the interior antenna, measuring x_O, y_O and z_O vector components of the received field strength emitted by the exterior antenna, and transmitting a signal indicative of the measured vector components to the vehicle base station;

at the vehicle base station, calculating superposition factors n and m for respectively applying to the measured signals from the interior and exterior antennas, based upon the transmitted signal indicative of the measured vector components;

at the vehicle base station, encrypting the superposition factors and transmitting the encrypted superposition factors to the transponder;

concurrently transmitting signals from each of the interior and exterior antennas to the transponder using the same phase, respectively using transmission currents I_I*n and I_O1*m; and

at the transponder, measuring x_S, y_S and z_S vector components of a superposed signal including the signals from both antennas, and authenticating the transponder in response to each of x_S, y_S and z_S respectively being within an error-based range of the sum of the respective vector components of signals from each of the interior and exterior antennas, multiplied by the superposition factors.

7. The method of claim 6, wherein calculating superposition factors n and m includes calculating factors n and m with [x_O*m, y_O*m, z_O*m] being equal to [x_I*n, y_I*n, z_I*n+random value], and where the superposed combined field strengths are above a noise level of the transmission.

8. The method of claim 6, wherein authenticating the transponder in response to each of x_S, y_S and z_S respectively being within an error-based range of the sum of the respective vector components of each of the interior and exterior antennas, multiplied by the superposition factors includes authenticating the transponder in response to

x_O1*m+x_I*n−

dx<

x_super<

x_O1*m+x_I*n+dx,

y_O1*m+y_I*n−

dy<

y_super<

y_O1*m+y_I*n+dy, and

z_O1*m+z_I*n−

dz<

z_super<

z_O1*m+z_I*n+dz,

wherein dx, dy, dz are error factors corresponding to phase jitter, measurement accuracy, and driver current accuracy.

9. The method of claim 6, further comprising

normalizing the measured vector components x_I, y_I and z_I, and x_O, y_O and z_O,

subtracting the normalized vector components of the received field strength emitted by the interior antenna from the received field strength emitted by the exterior antenna, and

detecting a relay attack in response to the subtracted normalized vector components in each of the x, y and z directions respectively being less than expected errors in detected field strength in each of the x, y and z directions.

10. The method of claim 6, further including, enabling a circuit in the vehicle in response to the authentication of the transponder.

11. The method of claim 6, wherein

driving the interior and exterior antennas respectively using transmission currents I_I and I_O includes driving each of the antennas during a period when the other of the antennas is not driven, and

measuring x_I, y_I and z_I vector components of the field strength emitted by the interior antenna, and measuring x_O, y_O and z_O vector components of the received field strength emitted by the exterior antenna includes measuring x_I, y_I and z_I vector components of the field strength emitted by the interior antenna during a period when the exterior antenna is not driven, and measuring x_O, y_O and z_O vector components of the received field strength emitted by the exterior antenna during a period when the interior antenna is not driven.

12. The method of claim 6, wherein concurrently transmitting signals from each of the interior and exterior antennas to the transponder using the same phase includes transmitting the encrypted superposition factors to the transponder.

13. The method of claim 6, wherein transmitting a signal indicative of the measured vector components to the vehicle base station includes encrypting the measured vector components, and transmitting a signal indicative of the encrypted vector components.

14. The method of claim 6, wherein driving interior and exterior antennas includes driving two exterior antennas, and wherein the steps of measuring and using vector components includes separately measuring and using vector components from both of the exterior antennas.

15. The method of claim 6, further including, in response to a predefined number of unsuccessful access tries to the vehicle base station are made, detecting an attack and disabling an authentication-based function.

16. A system for authenticating a wireless communication, the system comprising:

a transponder configured to receive and detect separate vector components of respective fields emitted by interior and exterior antennas of a vehicle, the interior antenna being separated from the transponder by a portion of the vehicle;

a vehicle base station configured to

drive the interior and exterior antennas respectively using first driving currents for communicating with the transponder, and

concurrently drive each of the interior and exterior antennas using the same phase, respectively using the driving currents multiplied by superposition factors calculated for the interior and exterior antennas based upon the separate vector components;

the transponder being further configured to detect superposed vector components of a superposed signal including signals from both antennas received at the transponder; and

the vehicle base station being configured to authenticate the transponder in response to the detected superposed vector components for the superposed signal being within an error-based range of the sum of the separate vector components for each of the interior and exterior antennas as multiplied respectively by the superposition factors for the interior and exterior antennas.

17. The system of claim 16, wherein the vehicle base station is configured to calculate the superposition factors for the external and internal antennas with the product of the factor for the external antenna and the separate vector components for the external antenna being equal to the sum of a random value plus the product of the factor for the internal antenna and the separate vector components for the internal antenna.

18. The system of claim 16, wherein the vehicle base station is configured to enable at least one of an ignition circuit and an entry circuit in the vehicle in response to authenticating the transponder.

19. The system of claim 16, wherein

the vehicle base station is configured to encrypt and transmit the superposition factors to the transponder, and

the transponder is configured to detect and use the encrypted superposition factors to determine whether the superposed vector components are within the error-based range of the sum of the separate vector components for each of the interior and exterior antennas.

20. The system of claim 16, further including the interior and exterior antennas.