Patent ID: 8232863

Claim:
A mobile device for a vehicle, the mobile device comprising: a receiving unit configured to receive transmission signals, each of the transmission signals being transmitted from a corresponding one of a plurality of transmitting antennas of a vehicle-side device; a control unit configured to determine a distance to each of the plurality of transmitting antennas using a signal strength of a corresponding one of the transmission signals received by the receiving unit; and a transmitting unit configured to transmit, to the vehicle-side device, data items indicating the distances to the plurality of transmitting antennas determined by the control unit, wherein, in a time period in which communication is not performed between the mobile device and the vehicle-side device, the control unit measures a signal strength of a signal received by the receiving unit to obtain a measurement value and stores the measurement value as a noise element, and, when communication is performed between the mobile device and the vehicle-side device, the control unit performs correction for noise on the signal strengths of the transmission signals, each of the transmission signals being transmitted from a corresponding one of the plurality of transmitting antennas, and determines the distances to the plurality of transmitting antennas, wherein the control unit compares a distance Lsn calculated using the signal strength of each of the transmission signals including the noise element with a distance Ln calculated using only the noise element, and, when a ratio of the distance Ln to the distance Lsn is larger than a predetermined value, the control unit transmits, as the distance to a corresponding one of the plurality of transmitting antennas, an alternative data item with which malfunction in the vehicle-side device is prevented.