Patent ID: 8155827

Claim:
A method of determining a position of a portable device in a keyless entry system, the system including: an on-vehicle device having an on-vehicle transmitting unit having a plurality of transmitting antennas attached to a vehicle, that transmits a request signal, at least one of the plurality of transmitting antennas being attached to a movable object installed on the vehicle or at a place where movement of the movable object affects a transmitted radio wave, an on-vehicle receiving unit that receives an answer signal; an on-vehicle control unit that performs a predetermined control operation after authenticating the answer signal transmitted from a portable device; the portable device having a portable device receiving unit that receives the request signal; a portable device transmitting unit that transmits the answer signal; a portable device control unit that detects a strength of each signal transmitted from the plurality of transmitting antennas in the on-vehicle device, wherein the on-vehicle control unit or the portable device control unit having a memory that stores data; the method comprising the steps of: the memory storing in advance a first data group or a first parameter, the first data group having signal strength information of each received signal transmitted from the plurality of transmitting antennas before and after the movement of the movable object when the portable device is placed along an inside portion of the vehicle, the first parameter used for comparing the first data group and signal strength information, and the memory storing in advance a second data group or a second parameter, the second data group having signal strength information of each received signal transmitted from the plurality of transmitting antennas before and after the movement of the movable object when the portable device is placed along an outside portion of the vehicle, the second parameter used for comparing the second data group and signal strength information; and wherein the on-vehicle control unit or the portable device control unit configured to determine using the first and second data groups or the first and second parameters, which of the first and second data groups the strength information obtained by receiving the signals transmitted from the plurality of the transmitting antennas by the portable device closely resembles.