In-vehicle device, recording medium, and keyless entry system

1. An in-vehicle device provided in a vehicle and comprising:

a plurality of transmitting antennas;

an in-vehicle device transmitter configured to transmit measurement signals via the plurality of respective transmitting antennas;

an in-vehicle device receiver configured to receive, from a portable device, a measurement result signal that includes measurement data of received signal strengths of the respective measurement signals that have been transmitted from the plurality of respective transmitting antennas; and

an in-vehicle device controller configured to calculate first distances from the portable device to a plurality of preset areas, based on differences between a reference received signal strength that is received from one transmitting antenna and each of the received signal strengths of the respective measurement signals that are received from a rest of the plurality of transmitting antennas included in the measurement result signal, and to identify an area to which the portable device belongs from the plurality of preset areas based on the first distances, said difference being calculated as dij=xi−xj,

wherein the xi is the reference received signal strength and xj is the each of the received signal strengths that are received from the rest of the plurality of transmitting antennas, and

wherein the reference received signal strength is received from the one transmitting antenna that is provided in a center of the vehicle.

2. The in-vehicle device according to claim 1 , wherein the first distances are Mahalanobis distances or Euclidean distances.

3. The in-vehicle device according to claim 1 , wherein the in-vehicle device controller calculates second distances from the portable device to the plurality of preset areas, based on the received signal strengths of the respective measurement signals included in the measurement result signal, and to identify an area to which the portable device belongs from the plurality of preset areas based on the first distances and the second distances.

4. The in-vehicle device according to claim 3 , wherein the second distances are Mahalanobis distances or Euclidean distances.

5. The in-vehicle device according to claim 1 , wherein the in-vehicle device transmitter includes one in-vehicle device transmitter connected to the plurality of transmitting antennas.

6. The in-vehicle device according to claim 1 , wherein the in-vehicle device transmitter includes a plurality of in-vehicle device transmitters each connected to a corresponding transmitting antenna of the plurality of transmitting antennas.

7. The in-vehicle device according to claim 1 , wherein the number of the plurality of transmitting antennas is 5 and the number of the rest of the plurality of transmitting antennas is 4.

8. A non-transitory recording medium storing a program for causing a computer to execute a process comprising:

transmitting measurement signals from a plurality of respective transmitting antennas;

receiving, from a portable device, a measurement result signal that includes measurement data of received signal strengths of the respective measurement signals that have been transmitted from the plurality of respective transmitting antennas; and

calculating first distances from the portable device to a plurality of preset areas, based on differences between a reference received signal strength that is received from one transmitting antenna and each of the received signal strengths of the respective measurement signals that are received from a rest of the plurality of transmitting antennas included in the measurement result signal, and identifying an area to which the portable device belongs from the plurality of preset areas based on the first distances, said difference being calculated as dij=xi−xj,

wherein the xi is the reference received signal strength and xj is the each of the received signal strengths that are received from the rest of the plurality of transmitting antennas, and

wherein the reference received signal strength is received from the one transmitting antenna that is provided in a center of the vehicle.

9. A keyless entry system including a portable device and an in-vehicle device, the keyless entry system comprising:

a received signal strength measuring unit configured to measure received signal strengths of a plurality of respective measurement signals that have been transmitted from a plurality of transmitting antennas;

a distance calculating unit configured to calculate first distances from the portable device to a plurality of areas, based on differences between a reference received signal strength that is received from one transmitting antenna and each of the received signal strengths of the plurality of respective measurement signals that are received from a rest of the plurality of transmitting antennas; and

an area identifying unit configured to identify an area to which the portable device belongs from the plurality of areas based on the first distances, said difference being calculated as dij=xi−xj,

wherein the xi is the reference received signal strength and xj is the each of the received signal strengths that are received from the rest of the plurality of transmitting antennas, and

wherein the reference received signal strength is received from the one transmitting antenna that is provided in a center of the vehicle.