Position determining device and method, and keyless entry system

1. A position determining device configured to determine a position of a portable device configured to receive one or more radio signals transmitted from one or more antennas inside a vehicle, respectively, the position determining device comprising:

a memory; and

a processor coupled to the memory, and configured to

determine an open or closed state of a door of the vehicle for getting in and out of the vehicle by receiving a signal from a door sensor configured to detect the open or closed state of the door;

calculate an evaluation value related to the position of the portable device based on a received signal strength of the one or more radio signals at the portable device; and

determine that the portable device is positioned inside the vehicle when the evaluation value satisfies a predetermined condition,

wherein the processor is configured to change at least one of the predetermined condition and a method of calculating the evaluation value in accordance with the determined open or closed state of the door.

2. The position determining device as claimed in claim 1 , wherein the processor is further configured to

calculate one or more distances between the one or more antennas and the portable device as the evaluation value based on the received signal strength of the one or more radio signals transmitted from the one or more antennas;

determine that the portable device is positioned inside the vehicle when the one or more distances satisfy a predetermined first condition, in a case of determining that the door is closed as a result of determining the open or closed state of the door; and

determine that the portable device is positioned inside the vehicle when the one or more distances satisfy a predetermined second condition different from the predetermined first condition, in a case of determining that the door is open as a result of determining the open or closed state of the door.

3. The position determining device as claimed in claim 2 , wherein the processor is further configured to

determine the open or closed state of each of a plurality of doors of the vehicle, the plurality of doors including the door; and

determine that the portable device is positioned inside the vehicle when the one or more distances satisfy the predetermined second condition, in a case of determining that at least the door among the plurality of doors is open as a result of determining the open or closed state of each of the plurality of doors, the predetermined second condition being set with respect to each of different combinations of the open or closed states of the plurality of doors.

4. The position determining device as claimed in claim 2 , wherein

the predetermined first condition includes a condition that d≤TH 1 or a condition that d<TH 1 , where d is a distance from one of the one or more antennas to the portable device and TH 1 is a first threshold, and

the predetermined second condition includes a condition that d≤TH 2 or a condition that d<TH 2 , where d is the distance from the one of the one or more antennas to the portable device and TH 2 is a second threshold, the second threshold being smaller than the first threshold.

5. The position determining device as claimed in claim 2 , wherein

the predetermined first condition includes a condition that d≤TH 3 or a condition that d<TH 3 , where d is a sum of distances from two of the one or more antennas to the portable device and TH 3 is a third threshold, and

the predetermined second condition includes a condition that d≤TH 4 or a condition that d<TH 4 , where d is the sum of the distances from the two of the one or more antennas to the portable device and TH 4 is a fourth threshold, the fourth threshold being smaller than the third threshold.

6. The position determining device as claimed in claim 1 , wherein

the processor is further configured to

calculate a first Mahalanobis distance and a second Mahalanobis distance as the evaluation value when determining that the door is closed as a result of determining the open or closed state of the door; and

calculate a third Mahalanobis distance and a fourth Mahalanobis distance as the evaluation value when determining that the door is open as a result of determining the open or closed state of the door,

the first Mahalanobis distance is a Mahalanobis distance between a first data group and the received signal strength of the one or more radio signals received at the portable device, the first data group indicating a received signal strength of one or more radio signals from the one or more antennas received at a plurality of points inside the vehicle with the door being closed,

the second Mahalanobis distance is a Mahalanobis distance between a second data group and the received signal strength of the one or more radio signals received at the portable device, the second data group indicating a received signal strength of one or more radio signals from the one or more antennas received at a plurality of points outside the vehicle with the door being closed,

the third Mahalanobis distance is a Mahalanobis distance between a third data group and the received signal strength of the one or more radio signals received at the portable device, the third data group indicating a received signal strength of one or more radio signals from the one or more antennas received at a plurality of points inside the vehicle with the door being open,

the fourth Mahalanobis distance is a Mahalanobis distance between a fourth data group and the received signal strength of the one or more radio signals received at the portable device, the fourth data group indicating a received signal strength of one or more radio signals from the one or more antennas received at a plurality of points outside the vehicle with the door being open, and

the processor is further configured to

determine that the portable device is positioned inside the vehicle when the first Mahalanobis distance is shorter than the second Mahalanobis distance, in a case of determining that the door is closed as a result of determining the open or closed state of the door; and

determine that the portable device is positioned inside the vehicle when the third Mahalanobis distance is shorter than the fourth Mahalanobis distance, in a case of determining that the door is open as a result of determining the open or closed state of the door.

7. The position determining device as claimed in claim 1 , wherein

the door is a slidable door, and

the processor is configured to determine the open or closed state of the slidable door.

8. A position determining method for determining a position of a portable device configured to receive one or more radio signals transmitted from one or more antennas inside a vehicle, respectively, the position determining method comprising:

determining, by a processor, an open or closed state of a door of the vehicle for getting in and out of the vehicle by receiving a signal from a door sensor configured to detect the open or closed state of the door;

calculating, by the processor, an evaluation value related to the position of the portable device based on a received signal strength of the one or more radio signals at the portable device; and

determining, by the processor, that the portable device is positioned inside the vehicle when the evaluation value satisfies a predetermined condition,

wherein at least one of the predetermined condition and a method of calculating the evaluation value is changed by the processor in accordance with the open or closed state of the door determined by said determining the open or closed state of the door.

9. The position determining method as claimed in claim 8 , wherein

said calculating the evaluation value includes calculating one or more distances between the one or more antennas and the portable device as the evaluation value based on the received signal strength of the one or more radio signals transmitted from the one or more antennas, and

said determining that the portable device is positioned inside the vehicle includes

determining that the portable device is positioned inside the vehicle when the one or more distances satisfy a predetermined first condition, in a case where said determining the open or closed state of the door determines that the door is closed; and

determining that the portable device is positioned inside the vehicle when the one or more distances satisfy a predetermined second condition different from the predetermined first condition, in a case where said determining the open or closed state of the door determines that the door is open.

10. The position determining method as claimed in claim 8 , wherein

said calculating the evaluation value includes

calculating a first Mahalanobis distance and a second Mahalanobis distance as the evaluation value when said determining the open or closed state of the door determines that the door is closed; and

calculating a third Mahalanobis distance and a fourth Mahalanobis distance as the evaluation value when said determining the open or closed state of the door determines that the door is open,

the first Mahalanobis distance is a Mahalanobis distance between a first data group and the received signal strength of the one or more radio signals received at the portable device, the first data group indicating a received signal strength of one or more radio signals from the one or more antennas received at a plurality of points inside the vehicle with the door being closed,

the second Mahalanobis distance is a Mahalanobis distance between a second data group and the received signal strength of the one or more radio signals received at the portable device, the second data group indicating a received signal strength of one or more radio signals from the one or more antennas received at a plurality of points outside the vehicle with the door being closed,

the third Mahalanobis distance is a Mahalanobis distance between a third data group and the received signal strength of the one or more radio signals received at the portable device, the third data group indicating a received signal strength of one or more radio signals from the one or more antennas received at a plurality of points inside the vehicle with the door being open,

the fourth Mahalanobis distance is a Mahalanobis distance between a fourth data group and the received signal strength of the one or more radio signals received at the portable device, the fourth data group indicating a received signal strength of one or more radio signals from the one or more antennas received at a plurality of points outside the vehicle with the door being open, and

said determining that the portable device is positioned inside the vehicle includes

determining that the portable device is positioned inside the vehicle when the first Mahalanobis distance is shorter than the second Mahalanobis distance, in a case where said determining the open or closed state of the door determines that the door is closed; and

determining that the portable device is positioned inside the vehicle when the third Mahalanobis distance is shorter than the fourth Mahalanobis distance, in a case where said determining the open or closed state of the door determines that the door is open.

11. A non-transitory computer-readable recording medium having stored therein a program for causing a computer to execute the position determining method as set forth in claim 8 .

12. A keyless entry system, comprising:

a vehicle-side device configured to transmit one or more radio signals from one or more antennas inside a vehicle, respectively, and receive a response signal respondent to the one or more radio signals; and

a portable device configured to receive the one or more radio signals and transmit the response signal, the response signal including an evaluation value calculated in accordance with a received signal strength of the one or more radio signals,

wherein the portable device includes

a first memory; and

a first processor coupled to the first memory, and configured to

calculate the evaluation value based on the received signal strength of the one or more radio signals transmitted from the one or more antennas, the evaluation value indicating one or more distances between the one or more antennas and the portable device, and

wherein the vehicle-side device includes

a second memory; and

a second processor coupled to the second memory, and configured to

determine an open or closed state of a door of the vehicle for getting in and out of the vehicle by receiving a signal from a door sensor configured to detect the open or closed state of the door; and

determine that the portable device is positioned inside the vehicle when the one or more distances satisfy a predetermined first condition, in a case of determining that the door is closed as a result of determining the open or closed state of the door; and determine that the portable device is positioned inside the vehicle when the one or more distances satisfy a predetermined second condition different from the predetermined first condition, in a case of determining that the door is open as a result of determining the open or closed state of the door.

13. A keyless entry system, comprising:

a vehicle-side device configured to transmit one or more radio signals from one or more antennas inside a vehicle, respectively, and receive a response signal respondent to the one or more radio signals; and

a portable device configured to receive the one or more radio signals and transmit the response signal, the response signal including information on a received signal strength of the one or more radio signals,

wherein the vehicle-side device includes

a memory; and

a processor coupled to the memory, and configured to

determine an open or closed state of a door of the vehicle for getting in and out of the vehicle by receiving a signal from a door sensor configured to detect the open or closed state of the door;

calculate an evaluation value related to a position of the portable device based on the received signal strength of the one or more radio signals indicated by the information included in the response signal; and

determine that the portable device is inside the vehicle when the evaluation value satisfies a predetermined condition,

wherein the processor is configured to

calculate a first Mahalanobis distance and a second Mahalanobis distance as the evaluation value when determining that the door is closed as a result of determining the open or closed state of the door; and

calculate a third Mahalanobis distance and a fourth Mahalanobis distance as the evaluation value when determining that the door is open as a result of determining the open or closed state of the door,

wherein the first Mahalanobis distance is a Mahalanobis distance between a first data group and the received signal strength of the one or more radio signals indicated by the information included in the response signal, the first data group indicating a received signal strength of one or more radio signals from the one or more antennas received at a plurality of points inside the vehicle with the door being closed,

wherein the second Mahalanobis distance is a Mahalanobis distance between a second data group and the received signal strength of the one or more radio signals indicated by the information included in the response signal, the second data group indicating a received signal strength of one or more radio signals from the one or more antennas received at a plurality of points outside the vehicle with the door being closed,

wherein the third Mahalanobis distance is a Mahalanobis distance between a third data group and the received signal strength of the one or more radio signals indicated by the information included in the response signal, the third data group indicating a received signal strength of one or more radio signals from the one or more antennas received at a plurality of points inside the vehicle with the door being open,

wherein the fourth Mahalanobis distance is a Mahalanobis distance between a fourth data group and the received signal strength of the one or more radio signals indicated by the information included in the response signal, the fourth data group indicating a received signal strength of one or more radio signals from the one or more antennas received at a plurality of points outside the vehicle with the door being open, and

wherein the processor is configured to

determine that the portable device is positioned inside the vehicle when the first Mahalanobis distance is shorter than the second Mahalanobis distance, in a case of determining that the door is closed as a result of determining the open or closed state of the door; and

determine that the portable device is positioned inside the vehicle when the third Mahalanobis distance is shorter than the fourth Mahalanobis distance, in a case of determining that the door is open as a result of determining the open or closed state of the door.