US Patent 7751957 Method of determining position of portable device

A vehicle controller or a portable controller has a memory that stores an inside data group having information on the intensity of request signals transmitted from a plurality of transmitting antennas when a position of a portable device is the inside of a vehicle, and an outside data group having information on the intensity of request signals transmitted from the plurality of transmitting antennas when the position of the portable device is the outside of the vehicle. The vehicle controller determines whether the information on the intensity of request signals is closer to the inside data group or the outside data group stored in the memory.