Keyless entry system and vehicle-mounted device

1. A keyless entry system comprising a vehicle-mounted device and a portable device,

wherein the vehicle-mounted device includes:

a first control unit that sequentially generates request signals;

a plurality of transmission antennas;

a first transmission unit that sequentially transmits the request signals through each of the plurality of transmission antennas;

a first reception unit that receives response signals responding to the respective request signals, each response signal including reception characteristics of the corresponding request signal received by the portable device; and

a storage unit that stores a history of the reception characteristics included in the response signals received by the first reception unit for each of the plurality of transmission antennas,

wherein the portable device includes:

a second reception unit that receives the request signals sequentially transmitted through the plurality of transmission antennas from the vehicle-mounted device;

a second control unit that generates the response signals each including the reception characteristics associated with the corresponding request signal received by the second reception unit, and

a second transmission unit that transmits the response signals generated by the second control unit,

wherein, if the first reception unit receives a new response signal, the first control unit determines whether or not to cause the vehicle to perform a predetermined operation based on the reception characteristics included in the new response signal and the history of the reception characteristics included in at least one previously-received response signal and stored in the storage unit, and the first control unit determines to cause the vehicle to perform the predetermined operation if an amount of change in the reception characteristics included in the new response signal compared with the reception characteristics in the history of the reception characteristics stored in the storage unit is equal to or smaller than a threshold value.

2. The keyless entry system according to claim 1 ,

wherein one of the reception characteristics of the request signal is a reception strength of the request signal received by the second reception unit.

3. The keyless entry system according to claim 1 , wherein

the first control unit calculates a first estimated value from the reception characteristics of the request signal transmitted through each of the plurality of the transmission antennas included in the new response signal, and a second estimated value from the corresponding reception characteristics in the history of the reception characteristics stored in the storage unit, and determines an amount of change in the first estimated value with respect to the second estimated value.

4. The keyless entry system according to claim 1 , wherein

the history of the reception characteristics in the storage unit is a history of a value estimated from the reception characteristics included in the at least one previously-received response signal, and

the first control unit determines whether or not to cause the vehicle to perform the predetermined operation based on a value estimated from the reception characteristics of the request signal transmitted through each of the plurality of the transmission antennas included in the new response signal and the history of the estimated value stored in the storage unit.

5. The keyless entry system according to claim 1 , wherein

the reception characteristics include a value estimated from the request signal received by the second reception unit,

the history of the reception characteristics in the storage unit is a history of the estimated value included in the at least one previously received response signal, and

the first control unit determines whether or not to cause the vehicle to perform the predetermined operation based on the estimated value included in the new response signal and the history of the estimated value stored in the storage unit.

6. The keyless entry system according to claim 3 ,

wherein the first and second estimated values are any one of a distance from a reference position, a position of the portable device, and a direction from the reference position.

7. A vehicle-mounted device, comprising:

a control unit that sequentially generates request signals;

a plurality of transmission antennas;

a transmission unit that sequentially transmits the request signals generated by the control unit through each of the plurality of transmission antennas;

a reception unit that receives response signals responding to the request signals from a portable device, each response signal including reception characteristics of the corresponding request signal received by the portable device; and

a storage unit that stores a history of the reception characteristics included in the response signals received by the reception unit,

wherein, if a new response signal is received by the reception unit, the control unit determines whether or not to cause the vehicle to perform a predetermined operation based on the reception characteristics included in the new response signal and the history of the reception characteristics included in at least one previously-received response signal and stored in the storage unit, and the control unit determines to cause the vehicle to perform the predetermined operation if an amount of change in the reception characteristics included in the new response signal compared with the reception characteristics in the history of the reception characteristics stored in the storage unit is equal to or smaller than a threshold value.

8. The vehicle-mounted device according to claim 7 ,

wherein one of the reception characteristics of the request signal is a reception strength of the request signal received by the second reception unit.

9. The vehicle-mounted device according to claim 7 , wherein

the first control unit calculates a first estimated value from the reception characteristics of the request signal transmitted through each of the plurality of the transmission antennas included in the new response signal, and a second estimated value from the corresponding reception characteristics in the history of the reception characteristics stored in the storage unit, and determines an amount of change in the first estimated value with respect to the second estimated value.

10. The vehicle-mounted device according to claim 9 ,

wherein the first and second estimated values are any one of a distance from a reference position, a position of the portable device, and a direction from the reference position.

11. The vehicle-mounted device according to claim 7 , wherein

the history of the reception characteristics in the storage unit is a history of a value estimated from the reception characteristics included in the at least one previously-received response signal, and

the first control unit determines whether or not to cause the vehicle to perform the predetermined operation based on a value estimated from the reception characteristics of the request signal transmitted through each of the plurality of the transmission antennas included in the new response signal and the history of the estimated value stored in the storage unit.

12. The vehicle-mounted device according to claim 7 , wherein

the reception characteristics include a value estimated from the request signal received by the second reception unit,

the history of the reception characteristics in the storage unit is a history of the estimated value included in the at least one previously received response signal, and

the first control unit determines whether or not to cause the vehicle to perform the predetermined operation based on the estimated value included in the new response signal and the history of the estimated value stored in the storage unit.