Patent Publication Number: US-2023144952-A1

Title: Control device and control method

Description:
TECHNICAL FIELD 
     The present invention relates to a control device and a control method. 
     BACKGROUND ART 
     Recently, techniques of authenticating a device on the basis of results of transmission and reception of signals between devices have been developed. For example, in Patent Literature 1, an onboard device authenticates a portable device by transmitting and receiving signals to and from the portable device using a first communication unit. The portable device is a remote controller that performs locking or unlocking of a vehicle and is also referred to as a smart key. The portable device is carried by a driver. Patent Literature 1 discloses a smart-keying system in which the onboard device determines whether to permit a vehicle operation by measuring a distance to the portable device using a second communication unit in addition to authentication using the first communication unit. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 2019-31871A 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in the technique disclosed in Patent Literature 1, when signals for authentication are transmitted and received between devices, power consumption in a party receiving a signal is forced in a signal reception waiting period. These circumstances are true of signals other than the signals for authenticating a device. 
     Therefore, the present invention has been made in consideration of the aforementioned circumstances, and an objective of the present invention is to provide a control device and a control method that are novel and improved and that can reduce power consumption for waiting for reception of a signal. 
     Solution to Problem 
     To solve the above problem, according to an aspect of the present invention, there is provided a control device comprising a controller configured to control a communicator such that the communicator performs wireless communication with another device, wherein the controller controls a reception waiting time of a predetermined signal which is transmitted from the other device by the wireless communication on the basis of acquired acquisition information. 
     To solve the above problem, according to another aspect of the present invention, there is provided a control method that is performed by a processor, the control method comprising controlling a communicator such that the communicator performs wireless communication with another device; and controlling a reception waiting time of a predetermined signal which is transmitted from the other device by the wireless communication on the basis of acquired notification information. 
     Advantageous Effects of Invention 
     As described above, according to the present invention, it is possible to reduce power consumption for waiting for reception of a signal. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a diagram illustrating an example of a configuration of a system according to an embodiment of the present invention. 
         FIG.  2    is a sequence diagram illustrating an example of a basic flow of an authentication process according to the embodiment. 
         FIG.  3    is a sequence diagram illustrating an example of a flow of a distance measuring process which is performed in the system according to the embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. In this specification and the drawings, elements having substantially the same functional configurations will be referred to by the same reference signs, and repeated description thereof will be omitted. 
     &lt;1. Example of Configuration&gt; 
       FIG.  1    is a diagram illustrating an example of a configuration of a system  1  according to an embodiment of the present invention. As illustrated in  FIG.  1   , the system  1  according to the embodiment includes a portable device  100  and a control device  200 . The control device  200  according to the embodiment is mounted, for example, in a vehicle. The vehicle is an example of a mobile object which is one object for use of a user. 
     A communication device that is an authentication target device and a control device that includes a controller configured to perform an authentication process of authenticating the communication device using information acquired through communication with the communication device are involved in the present invention. In the example illustrated in  FIG.  1   , the portable device  100  is an example of the communication device, and the control device  200  is an example of the control device. In the system  1 , for example, when a user such as a driver of a vehicle  20  approaches the vehicle with the portable device  100 , wireless communication for authentication is performed between the portable device  100  and the control device  200  mounted in the vehicle  20 . When the authentication succeeds, a door of the vehicle  20  is unlocked or an engine is started, and the vehicle  20  becomes usable by the user. The system  1  is also referred to as a smart entry system. The elements will be sequentially described below. 
     (1-1) Portable Device  100   
     The portable device  100  is configured as an arbitrary device. As an example of the arbitrary device, a device such as an electronic key, a smartphone, or a wearable terminal which is carried and used by a user such as a driver can be used. As illustrated in  FIG.  1   , the portable device  100  includes a first wireless communicator  110 , a second wireless communicator  120 , a storage  130 , and a controller  140 . 
     The first wireless communicator  110  has a function of communicating with the control device  200  based on a first wireless communication standard. The second wireless communicator  120  has a function of communicating with the control device  200  based on a second wireless communication standard which is different from the first wireless communication standard. Particularly, the second wireless communication standard is more appropriate for measuring a distance than the first wireless communication standard, and the second wireless communicator  120  mainly takes charge of communication associated with distance measuring. 
     Here, the first wireless communication standard may satisfy at least one of a condition that a gain is higher and a condition that power consumption on a reception side is lower in comparison with the second wireless communication standard. In a specific example in which such conditions are satisfied, carrier waves of a frequency higher than a frequency of carrier waves in the first wireless communication standard may be used in the second wireless communication standard. This is because attenuation according to a distance becomes larger and thus a gain becomes lower as the frequency of carrier waves becomes higher, attenuation according to a distance becomes smaller and thus a gain becomes higher as the frequency of carrier waves becomes lower, and the conditions for the gain are satisfied. When the frequency of carrier waves is high, an influence of a human body such as absorption in the human body increases and the gain decreases. 
     In consideration of that a sampling frequency is set based on a maximum value of the frequency of carrier waves, at least a condition that a maximum frequency of carrier waves in the second wireless communication standard is higher than a maximum frequency of carrier waves in the first wireless communication standard has only to be satisfied. 
     For example, signals in a radio frequency (RF) band and signals in a low frequency (LF) band may be used in the first wireless communication standard. In a typical smart entry system, signals in the RF band are used for transmission from the portable device  100  to the control device  200  of the vehicle  20 , and signals in the LF band are used for transmission from the control device  200  of the vehicle  20  to the portable device  100 . In the following description, it is assumed that the first wireless communicator  110  is constituted as a communication interface that can perform communication using signals in the RF band and signals in the LF band. That is, in the following description, it is assumed that the signals in the RF band are used for transmission to the control device  200  of the vehicle  20  and the signals in the LF band are used for reception from the control device  200  of the vehicle  20 . 
     For example, signals in an ultra-wide band (UWB) may be used in the second wireless communication standard. Signals in an impulse manner in the UWB have characteristics that positioning and distance measuring can be performed with high accuracy using the signals. That is, an air propagation time of radio waves with a very short pulse width equal to or less than a nanosecond can be measured with high accuracy using the radio waves, and positioning and distance measuring based on the propagation time can be performed with high accuracy. In the following description, it is assumed that the second wireless communicator  120  is constituted by a communication interface that can perform communication using the signals in the UWB. 
     A signal in the UWB can be transmitted and received as a distance-measuring signal and a data signal. The distance-measuring signal is a signal that is transmitted and received in a distance measuring process which will be described later. For example, the distance-measuring signal may have a frame format not including a payload part in which data is stored or may have a frame format including a payload part in which data is stored. The data signal is a signal for carrying data. The data signal preferably has a frame format including a payload part in which data is stored. In the following description, it is assumed that the distance-measuring signal has a frame format not including a payload part in which data is stored. It is also assumed that the data signal has a frame format including a payload part in which data is stored. 
     The storage  130  has a function of storing various types of information for operating of the portable device  100 . For example, the storage  130  stores programs for operating of the portable device  100 , IDs (an example of identification information), passwords, and authentication algorithms for authentication, and the like. The storage  130  is constituted, for example, by a storage medium such as a flash memory and a processing device that performs writing and reading to and from the storage medium. 
     The controller  140  has a function of controlling the entire operations of the portable device  100 . For example, the controller  140  controls the first wireless communicator  110  and the second wireless communicator  120  such that communication with the control device  200  of the vehicle is performed. The controller  140  performs reading information from the storage  130  and writing information to the storage  130 . The controller  140  also serves as an authentication controller that controls an authentication process which is performed in cooperation with the control device  200  of the vehicle. The controller  140  is constituted, for example, by an electronic circuit such as a central processing unit (CPU) and a microprocessor. 
     (1-2) Control Device  200   
     The control device  200  is provided in correlation with a vehicle. Here, it is assumed that the control device  200  is mounted in the vehicle  20 . Regarding the mounting position, the control device  200  may be installed in a cabin of the vehicle  20  or may be incorporated into the vehicle  20  as a control module or a communication module. The control device  200  may be provided in a parking lot of the vehicle  20 . In this way, the control device  200  may be separate from an object to be used by a user. In this case, the control device  200  can wirelessly transmit a control signal to the vehicle  20  based on a result of communication with the portable device  100  such that the vehicle  20  can be remotely controlled. As illustrated in  FIG.  1   , the control device  200  includes a first wireless communicator  210 , a second wireless communicator  220 , a storage  230 , and a controller  240 . 
     The first wireless communicator  210  has a function of performing communication with the portable device  100  based on the first wireless communication standard. In the following description, it is assumed that the first wireless communicator  210  is constituted as a communication interface that can perform communication using the signals in the RF band and the signals in the LF band. 
     The second wireless communicator  220  has a function of performing communication with the portable device  100  based on a second wireless communication standard which is different from the first wireless communication standard. In the following description it is assumed that the second wireless communicator  220  is constituted as a communication interface that can perform communication using signals in the UWB. A plurality of second wireless communicators  220  may be mounted in the vehicle  20 . 
     The storage  230  has a function of storing various types of information for operating of the control device  200 . For example, the storage  230  stores programs for operating of the control device  200 , IDs (an example of identification information), passwords, and authentication algorithms for authentication, and the like. The storage  230  is constituted, for example, by a storage medium such as a flash memory and a processing device that performs writing and reading to and from the storage medium. 
     The controller  240  has a function of controlling the entire operations of the control device  200  and onboard devices mounted in the vehicle. For example, the controller  240  controls the first wireless communicator  210  and the second wireless communicator  220  such that communication with the portable device  100  is performed. The controller  240  performs reading information from the storage  230  and writing information to the storage  230 . The controller  240  also serves as an authentication controller that controls an authentication process which is performed in cooperation with the portable device  100 . The controller  240  also serves as a door lock controller that controls door lock of the vehicle and performs locking and unlocking of a door. The controller  240  also serves as an engine controller that controls an engine of the vehicle and performs starting/stopping of the engine. A power source provided in the vehicle may include a motor in addition to the engine. The controller  240  is constituted, for example, as an electronic control unit (ECU). 
     The control device  200  illustrated in  FIG.  1    is an example of a control device in the claims. The configuration of the control device according to the present invention is not limited to the example illustrated in  FIG.  1   , but may include, for example, a communication module including the first wireless communicator  210 , a communication module including the second wireless communicator  220 , and a control module including the controller  240 . The configuration of the control device according to the present invention may be realized as a communication module including the first wireless communicator  210 , a communication module including the second wireless communicator  220 , or a control module including the controller  240 . The modules are connected to each other via a wired or wireless communication network. The communication network may be an onboard communication network based on an arbitrary standard such as a controller area network (CAN), a local interconnect network (LIN), or a local area network (LAN). 
     The configuration of the devices illustrated in  FIG.  1    is an example. For example, in the configuration illustrated in  FIG.  1   , each of the portable device  100  and the control device  200  includes a first wireless communicator and a second wireless communicator, but the present invention is not limited thereto. Each of the portable device  100  and the control device  200  may include a wireless communicator that performs communication based on one wireless communication standard. A plurality of wireless communicators may be provided in the vehicle  20 . The wireless communicator performs transmission and reception of signals used for an authentication process. A frequency band which is used for the wireless communicator to transmit signals used for an authentication process is arbitrary. For example, a signal used for an authentication process may be transmitted as a signal in the UWB, may be transmitted as a signal in the LF band, may be transmitted as a signal in the RF band, or may be transmitted as a signal in Bluetooth low energy (BLE (registered trademark)). 
     &lt;2. Authentication Process&gt; 
     In a smart entry system, the portable device  100  may be authenticated on the basis of a distance between the portable device  100  and the control device  200  of the vehicle. The authentication process in this embodiment includes a process of measuring a distance between the portable device  100  and the control device  200  (hereinafter also referred to as a “distance measuring process” in this specification) and a process of performing authentication on the basis of results of distance measuring. By performing authentication based on a distance, it is possible to reduce camouflage of an authentication target device such as a relay attack in which communication between a portable device (the authentication target device) and a control device (an authentication device) of a vehicle is indirectly realized by relaying transmission signals of the control device using a relay and authentication of the portable device by the control device is illegally established or camouflage of a distance and to effectively enhance authentication accuracy. 
       FIG.  2    is a sequence diagram illustrating an example of a basic flow of the authentication process according to the embodiment. As illustrated in  FIG.  2   , first, the control device  200  starts waiting of reception of a distance-measuring trigger signal (Step S 100 ). In this embodiment, for example, a signal for instructing to transmit a first distance-measuring signal (a distance-measuring trigger signal) is transmitted from the portable device  100  before the first distance-measuring signal is transmitted from the control device  200 . For example, a signal in the UWB is used as the distance-measuring trigger signal. The distance-measuring trigger signal is transmitted, for example, from the second wireless communicator  120  by the portable device  100 . In the control device  200 , it is assumed that the distance-measuring trigger signal is received by the second wireless communicator  220 . In preparation of receiving the distance-measuring trigger signal, the control device  200  controls the second wireless communicator  220  such that the second wireless communicator  220  performs reception waiting. Reception waiting means a state in which a process of fetching a received signal is performed when the signal is received. The reception waiting is also referred to as a reception waiting state. The reception waiting includes various processes for acquiring a desired signal. Examples of the various processes include a process of causing an antenna constituting the second wireless communicator  220  to receive a signal, a process of causing the second wireless communicator  220  to sample the received signal, and a process of causing the second wireless communicator  220  to perform a process based on the signal acquired by sampling. Examples of the process of performing a process based on the signal acquired by sampling include subsequent processes such as a process of determining whether the signal received via the antenna is a desired signal and a process of ascertaining information included in the signal. A reception waiting time, that is, a period in the reception waiting state, is also referred to as a reception waiting period. 
     On the other hand, the portable device  100  transmits the distance-measuring trigger signal (Step S 103 ). For example, a signal in the UWB is used as the distance-measuring trigger signal. Specifically, the portable device  100  may transmit the distance-measuring trigger signal using the second wireless communicator  120 . 
     Subsequently, when the distance-measuring trigger signal is received, the control device  200  transmits a distance-measuring request signal for requesting a response for a distance measuring process as a first distance-measuring signal (Step S 106 ). The process of transmitting the distance-measuring request signal is an example of the subsequent processes. For example, a signal in the UWB is used as the distance-measuring request signal. Specifically, the control device  200  may transmit the distance-measuring request signal using the second wireless communicator  220 . 
     Then, when the distance-measuring request signal (the first distance-measuring signal) is received from the control device  200 , the portable device  100  transmits a distance-measuring response signal for responding to a distance-measuring request as a second distance-measuring signal after a time ΔT 2  has elapsed after the distance-measuring request signal has been received (Step S 109 ). For example, a signal in the UWB is used as the distance-measuring response signal. Specifically, the portable device  100  may transmit the distance-measuring response signal using the second wireless communicator  120 . The time ΔT 2  is a prescribed time. The time ΔT 2  is set to be longer than a time which is considered to be necessary for processes in the portable device  100  after the first distance-measuring signal has been received and until the second distance-measuring signal is transmitted. Accordingly, it is possible to reliably complete preparation of transmission of the second distance-measuring signal until the time ΔT 2  elapses after the first distance-measuring signal has been received. The time ΔT 2  may be known to the control device  200 . 
     Subsequently, when the distance-measuring response signal (the second distance-measuring signal) is received, the controller  240  of the control device  200  calculates a distance between the portable device  100  and the control device  200  (Step S 112 ). Specifically, the control device  200  measures a time ΔT 1  from the transmission time point of the first distance-measuring signal to the reception time point of the second distance-measuring signal and calculates the distance on the basis of the measured time ΔT 1  and the known time ΔT 2 . The control device  200  can calculate a time required for transmission and reception in one way of the signals by dividing a value obtained by subtracting ΔT 2  from ΔT 1  by 2, and calculate the distance between the portable device  100  and the control device  200  by multiplying the calculated time by a speed of the signals. The time ΔT 2  may not be known to the control device  200 . For example, the portable device  100  may measure the time ΔT 2  and report the measured time to the control device  200 . This report can be performed by transmitting a data signal including information obtained by encrypting information indicating the time ΔT 2 . The data signal is another example of the signal used for the distance measuring process. The data signal is a signal for including and carrying data. The data signal has a frame format including a payload part in which data is stored. The data signal can be transmitted and received as a signal in the UWB. 
     Calculating a distance in Step S 112  may be performed by a controller of a communication unit when the second wireless communicator  220  is configured as the communication unit. In this case, the communication unit transmits the calculation results to the controller  140  via an onboard communication network. A plurality of second wireless communicators  220  may be mounted in the vehicle  20 . The controller  240  may calculate the distance between the portable device  100  and the control device  200  on the basis of data transmitted and received between the plurality of second wireless communicators  220  and the portable device  100 . 
     Then, the controller  240  of the control device  200  performs authentication of the portable device  100  depending on whether the calculated distance satisfies predetermined conditions (Step S 115 ). For example, the controller  240  determines that authentication has succeeded when the calculated distance is equal to or less than a predetermined value and determines that the authentication has failed otherwise. The controller  240  may determine that authentication for performing corresponding predetermined control has succeeded when the calculated distance is in a predetermined range. For example, when a distance between a user carrying the portable device  100  and the vehicle  20  in which the control device  200  is mounted is in the predetermined range, the controller  240  may determine that authentication for performing control for turning on a light provided in the vehicle  20  has succeeded and perform control for turning on the light. When the user becomes closer to the vehicle  20 , the controller  240  may determine that authentication for unlocking a door of the vehicle  20  has succeeded and perform control for unlocking the door. 
     &lt;3. Conclusion&gt; 
     The portable device  100  and the control device  200  according to this embodiment perform the distance measuring process for the purpose of authentication based on a distance. The distance measuring process according to this embodiment includes transmitting and receiving distance-measuring signals and calculating the distance on the basis of times required for transmitting and receiving the distance-measuring signals as illustrated in  FIG.  2   . The distance-measuring signals include, for example, a distance-measuring trigger signal for instructing to transmit a first distance-measuring signal, a distance-measuring request signal for requesting to transmit a response for the distance measuring process, and a distance-measuring response signal for responding to the distance measuring request. 
     The distance measuring process according to this embodiment may be performed a plurality of times. The control device  200  can acquire a measured distance value with higher accuracy as a representative value, for example, on the basis of results of the plurality of times of distance measuring. Since the control device  200  repeatedly performs the distance measuring process a plurality of times, though the distance measuring process fails once, the next distance measuring process may succeed. That is, it is possible to enhance accuracy of the measured distance value. Performing the distance measuring process a plurality of times includes re-transmitting the distance-measuring trigger signal from the portable device  100 . 
     In general, power consumption in a signal receiving party in the reception waiting period of the signal is forced. For example, in the example illustrated in  FIG.  2   , when the second wireless communicator  220  is in the reception waiting state and fails to receive a distance-measuring trigger signal transmitted from the portable device  100 , the reception waiting state is maintained until a next distance-measuring trigger signal is transmitted from the portable device  100 . Since the reception waiting period is continued in this way, power consumption increases. Particularly, in the UWB, since power consumption in the reception waiting state is high, power consumption of the control device  200  increases due to continuation of the reception waiting period. Accordingly, for example, it may serve as one reason for a phenomenon in which an amount of electric power stored in a storage battery that supplies electric power to devices mounted in the vehicle  20  including the control device  200  decreases and the engine cannot be started. These circumstances are true of signals other than the signals for measuring a distance between devices. These circumstances are true of signals other than the signals for authenticating a device. 
     Therefore, in the embodiment of the present invention, the reception waiting time of a signal in a reception-side party is controlled at an appropriate timing Specifically, in the embodiment of the present invention, control for starting and ending reception waiting of signals on the reception-side party at appropriate timings is performed. Accordingly, it is possible to shorten the reception waiting period and to reduce power consumption in the reception-side party. 
     Transition to the reception waiting state according to this embodiment is performed at an arbitrary timing. The control device  200  starts reception waiting, for example, on the basis of information acquired through responding between the portable device  100  and the control device  200  which is performed before the distance-measuring trigger signal is transmitted. This information is also referred to as acquisition information in the following description. The signals used for responding and the distance-measuring signals used for the distance measuring process may be transmitted and received on the basis of different wireless communication standards. For example, the first wireless communication standard is used for transmission and reception of the signals used for responding, and the second wireless communication standard is used for transmission and reception of the distance-measuring signals. 
     Technical features of the embodiment of the present invention will be described below in detail. 
     &lt;4. Technical Features&gt; 
       FIG.  3    is a sequence diagram illustrating an example of a flow of the distance measuring process which is performed in the system  1  according to the embodiment. The portable device  100  and the control device  200  participate in this sequence. In this specification, the “authentication process based on a distance” includes a distance measuring process of measuring a distance between the portable device  100  and the control device  200  and an authentication process of performing authentication on the basis of the distance measured in the distance measuring process. 
     The controller  240  in this embodiment causes the second wireless communicator  220  to transition to a reception waiting state of a distance-measuring trigger signal at an arbitrary timing and waits for reception of a distance-measuring trigger signal. The arbitrary timing is determined, for example, on the basis of communication between the portable device  100  and the control device  200  which is performed before a distance-measuring trigger signal in the UWB is transmitted from the portable device  100 . The communication which is performed between the portable device  100  and the control device  200  before a distance-measuring trigger signal is transmitted or received may be performed, for example, by the first wireless communicator that can perform communication using a signal in the RF band and a signal in the LF band. 
     In the example illustrated in  FIG.  3   , an example of the communication performed between the portable device  100  and the control device  200  before a distance-measuring trigger signal is transmitted or received is request-response authentication. In the request-response authentication, an authentication request signal and an authentication response signal generated on the basis of an authentication request are transmitted and received. By performing the authentication process by one step using another method before the authentication process based on a distance is performed, it is possible to further enhance authentication accuracy. 
     As illustrated in  FIG.  3   , first, the portable device  100  transmits an authentication request signal using the first wireless communicator  110  (Step S 203 ). Then, when the authentication request signal is received by the first wireless communicator  210 , the control device  200  transmits an authentication response signal as a response to the authentication request signal using the first wireless communicator  210  (Step S 206 ). 
     The request-response authentication is a system in which an authenticator generates an authentication request signal and transmits the authentication request signal to an authentication target, the authentication target generates an authentication response signal on the basis of the authentication request signal and transmits the authentication response signal to the authenticator, and the authenticator performs authentication of the authentication target on the basis of the authentication response signal. Typically, since the authentication request signal is a random number and varies every authentication, the request-response authentication has resistance to a replay attack. The authentication response signal is generated on the basis of information of the authentication target. The information of the authentication target is, for example, an ID or a password. Since the ID and the password are not actually transmitted or received, it is possible to prevent tapping. More specifically, for example, in response to a first authentication signal transmitted as an authentication request by the portable device  100 , a second authentication signal calculated on the basis of the first authentication signal and key information such as a password stored in advance by the control device  200  is transmitted as an authentication response. When it is ascertained that the second authentication signal transmitted as the authentication response indicates a regular value which is calculated on the basis of the first authentication signal which is the authentication request and the key information, the portable device  100  may determine that authentication in the control device  200  has succeeded. The control device  200  may be an authenticator, and the portable device  100  may be an authentication target. The portable device  100  which is the authenticator may notify the control device  200  which is the authentication target of the authentication result. 
     Subsequently, the controller  240  acquires information on the request-response authentication and performs control for starting reception waiting of a distance-measuring trigger signal in the second wireless communicator  220  at a predetermined timing on the basis of the acquisition information (Step S 209 ). The request-response authentication is an example of the communication which is performed before the distance-measuring trigger signal is transmitted as described above. The controller  240  acquires information on the communication performed before the distance-measuring trigger signal is transmitted as the acquisition information. 
     The acquisition information on the request-response authentication may include, for example, a transmission or reception time point of an authentication request signal, a transmission or reception time point of an authentication response signal, and results of the request-response authentication. The controller  240  may start reception waiting of the distance-measuring trigger signal, for example, at a time point at which a predetermined time has elapsed from the transmission or reception time point of the authentication response signal or a time point at which the request-response authentication has succeeded as the predetermined timing based on the acquisition information. The predetermined time may be set to, for example, a time shorter than a time required for the portable device  100  to perform the processes after the authentication response signal has been received and until the distance-measuring trigger signal is transmitted. That is, the controller  240  can predict the time in which the distance-measuring trigger signal is transmitted on the basis of the acquisition information and perform control for starting reception waiting of the distance-measuring trigger signal. Information on time synchronization of signals such as information of in what clocks (seconds) after the authentication response signal has been received the distance-measuring trigger signal is to be transmitted may be shared in advance by the portable device  100  and the control device  200 . 
     By causing the controller  240  to start reception waiting as immediately as possible before the timing at which transmission of the distance-measuring trigger signal is predicted, it is possible to shorten the reception waiting period and to further reduce power consumption in the reception-side party. 
     The acquisition information may be acquired from a plurality of sources. For example, the controller  240  may acquire the acquisition information on the transmission or reception time point of the authentication request signal and the transmission or reception time point of the authentication response signal from the first wireless communicator  210 . When the first wireless communicator  210  is provided in a device other than the control device  200 , the acquisition information can be acquired from the other device. The other device is, for example, a communication device mounted in the vehicle  20 . When request-response authentication is performed by a device other than the control device  200 , the controller  240  may acquire results of the request-response authentication from the other device. The other device is, for example, a combined ECU mounted in the vehicle  20 . When the controller  240  has a function of controlling the first wireless communicator  210  or a function of performing request-response authentication, the acquisition information is acquired inside the controller  240 . 
     Subsequently, the controller  240  ends the reception waiting after a prescribed time has elapsed after the reception waiting has started (Step S 215 ). The prescribed time is a first prescribed time in the claims. The controller  240  performs control for ending reception waiting after the first prescribed time has elapsed after the reception waiting has started. That is, when the distance-measuring trigger signal has not been received in the first prescribed time, the controller  240  ends the reception waiting without receiving a distance-measuring trigger signal. When a distance-measuring trigger signal is received before the first prescribed time has elapsed, the controller  240  ends the reception waiting at that time point. In the example illustrated in  FIG.  3   , a case in which a distance-measuring trigger signal has not been received during the reception waiting is described. 
     The first prescribed time may be set to, for example, a time longer than a time in which a distance-measuring trigger signal reaches the control device  200  when a distance in an allowable range in which authentication based on a distance succeeds is assumed. This “time longer than the time in which the signal reaches” can include an error. Accordingly, it is possible to enhance a probability of reception success. 
     After the reception waiting has ended, for example, the controller  240  performs control in a normal state in which power consumption is lower than that in the reception waiting state and reception and transmission of a signal from and to the portable device  100  are not performed. 
     Subsequently, the controller  240  causes the second wireless communicator  220  to start reception waiting for receiving a distance-measuring trigger signal after a prescribed time has elapsed after the reception waiting has ended without receiving a distance-measuring trigger signal (Step S 218 ). The prescribed time is a second prescribed time in the claims. The second prescribed time may be set to, for example, a time shorter than a time interval at which a distance-measuring trigger signal is re-transmitted. In this way, according to the embodiment, by performing control such that the reception waiting is not continued until a next distance-measuring trigger signal is received even when a distance-measuring trigger signal has not been received, it is possible to reduce power consumption in a reception-side party. The controller  240  continues to perform reception waiting until a prescribed time (period) elapses again. This prescribed time may be the same as the first prescribed time. 
     Then, a distance-measuring trigger signal is transmitted from the portable device  100  (Step S 221 ). 
     Subsequently, when a distance-measuring trigger signal is received during the reception waiting, the controller  240  of the control device  200  ends the reception waiting (Step S 224 ). When the first prescribed time elapses without receiving a distance-measuring trigger signal again, the controller  240  repeatedly performs the processes of Steps S 215  to S 218 . That is, the controller  240  acquires information indicating that the reception waiting has ended without receiving a distance-measuring trigger signal as acquisition information and performs control such that reception waiting starts again at a predetermined timing, specifically, after the second prescribed time elapses, on the basis of the acquisition information. By performing normal control in the second prescribed time, it is possible to reduce power consumption. The number of times Steps S 215  to S 218  are repeated until a distance-measuring trigger signal is received may be limited to an upper limit. 
     Subsequently, when a distance-measuring trigger signal is normally received, the controller  240  performs control for transmitting a distance-measuring request signal for requesting a response for the distance measuring process as the first distance-measuring signal using the second wireless communicator  220  in response to the distance-measuring trigger signal (Step S 227 ). When the distance-measuring request signal is transmitted, the controller  240  performs, for example, control in a transmission state. The transmission state is a state in which various processes of radiating a signal as radio waves from an antenna are performed. Examples of the various processes include generating a signal to be transmitted, modulation based on the signal to be transmitted, and transmitting of radio waves from the antenna. Power consumption in the transmission state is lower than that in the reception waiting state. 
     Subsequently, the controller  240  of the control device  200  starts reception waiting when the reception waiting has ended because a prescribed time has elapsed after a desired signal (the distance-measuring trigger signal herein) has been received (Step S 230 ). The prescribed time is a third prescribed time in the claims. The third prescribed time may be set to, for example, a time shorter than a time which is assumed to be required for processing in the portable device  100  after the distance-measuring request signal has been received and until a distance-measuring response signal is transmitted. 
     That is, the controller  240  in this embodiment performs control for acquiring information indicating that a desired signal (a distance-measuring trigger signal herein) has been normally received and causing the second wireless communicator  220  to start reception waiting of a desired signal (a distance-measuring response signal herein) at a predetermined timing (after the third prescribed time has elapsed herein) on the basis of the acquisition information (also referred to as normal acquisition information). The normal acquisition information may be acquired, for example, from the second wireless communicator  220 . When the controller  240  has a function of controlling the second wireless communicator  220 , the acquisition information can be acquired in the controller  240 . The normal acquisition information may include a reception time point of the distance-measuring trigger signal. 
     A measurement start time point in the third prescribed time is not limited to the reception time point of the distance-measuring trigger signal, but may be, for example, a time point after a distance-measuring request signal has been transmitted. In this case, the normal acquisition information may include a transmission time point of the distance-measuring request signal. 
     The reception waiting time (period) which has started at a predetermined timing on the basis of the normal acquisition information is set to a fourth prescribed time. The fourth prescribed time may be set to, for example, a time longer than a time in which a distance-measuring response signal reaches the control device  200  when a distance in an allowable range in which authentication based on a distance succeeds is assumed. The fourth prescribed time may be shorter than the first prescribed time. Since reception waiting starts at the predetermined timing based on the normal acquisition information, it can be said that a more accurate timing is predicted. Accordingly, even when the reception waiting time is set to the fourth prescribed time shorter than the first prescribed time, it is possible to receive a desired signal. The fourth prescribed time shorter than the first prescribed time is, for example, a time excluding an error considered in the first prescribed time. By further shortening the reception waiting time in this way, it is possible to reduce power consumption. 
     On the other hand, when a distance-measuring request signal is received from the control device  200 , the portable device  100  transmits a distance-measuring response signal responsive to the distance-measuring request as the second distance-measuring signal after the time ΔT 2  has elapsed after the distance-measuring request signal has been received (Step S 233 ). 
     When the distance-measuring response signal is received, the controller  240  of the control device  200  ends the reception waiting (Step S 236 ). Then, the controller  240  calculates a distance between the portable device  100  and the control device  200 . Specifically, as described above with reference to  FIG.  2   , the controller  240  measures the time ΔT 1  from the transmission time point of the distance-measuring request signal to the reception time point of the distance-measuring response signal and calculates the distance on the basis of the measured time ΔT 1  and the known time ΔT 2 . 
     When the fourth prescribed time has elapsed without receiving a distance-measuring response signal, the controller  240  ends the reception waiting. At this time, the controller  240  acquires information indicating that the reception waiting has ended without receiving a distance-measuring response signal and starts reception waiting of a distance-measuring trigger signal again at a predetermined timing based on the acquisition information. For example, the controller  240  may perform control for predicting a time at which the distance-measuring trigger signal is re-transmitted from the reception time point of the distance-measuring trigger signal and starting reception waiting of a distance-measuring trigger signal prior to that time. 
     The controller  240  may perform control in the reception waiting state at a predetermined timing in preparation of reception of a next distance-measuring trigger signal again after the reception waiting has ended because a distance-measuring response signal has been normally received. That is, the controller  240  acquires information indicating that the reception waiting has ended because the distance-measuring response signal has been normally received (an example of the normal acquisition information) and starts reception waiting of a distance-measuring trigger signal again after a predetermined timing based on the acquisition information. For example, the controller  240  may perform control for predicting a time at which a next distance-measuring trigger signal is re-transmitted from the reception time point of the previous distance-measuring trigger signal and starting the reception waiting of a distance-measuring trigger signal prior to that time point. The controller  240  may perform control for predicting a time at which a next distance-measuring trigger signal is re-transmitted from the reception time point of the distance-measuring response signal and starting reception waiting of a distance-measuring trigger signal prior to that time. The controller  240  may set the reception waiting time in this case to be equal to the fourth prescribed time. More specifically, the controller  240  may set the reception waiting time to a time which is longer than a time in which a distance-measuring trigger signal reaches the control device  200  when a distance in an allowable range in which authentication based on a distance succeeds is assumed and which is shorter than the first prescribed time. Since the controller  240  starts reception waiting at a predetermined timing based on the normal acquisition information indicating that the distance-measuring trigger signal has been normally received or the distance-measuring response signal has been normally received, it can be said that a more accurate timing is predicted. Accordingly, even when the reception waiting time is set to a time shorter than the first prescribed time, it is possible to receive a desired signal. 
     One second wireless communicator  220  has been employed in  FIG.  3    described above, but the number of second wireless communicators  220  may be two or more. The two or more second wireless communicators  220  perform transmission and reception of signals to and from the second wireless communicator  120  of the portable device  100 . In this case, the controller  240  can calculate a distance between each second wireless communicator  220  and the portable device  100 . 
     When at least one of the two or more second wireless communicator  220  has normally received a distance-measuring trigger signal but the other second wireless communicator  220  has not received a distance-measuring trigger signal, the controller  240  may perform control for ending the reception waiting in the other second wireless communicator  220 . Accordingly, it is possible to further shorten the reception waiting time and to reduce power consumption. 
     In the embodiment described above with reference to  FIG.  3   , the authentication request signal is transmitted in communication which is performed between the portable device  100  and the control device  200  before the distance-measuring trigger signal is transmitted and received, but the present invention is not limited thereto. For example, transmission and reception of a wakeup signal for instructing to start and a response to the wakeup signal may be performed between the portable device  100  and the control device  200 . The reception-side party can be returned from a sleep state using the wakeup signal. Examples of the response to the wakeup signal include an acknowledgement (ACK) signal indicating that starting is to be performed and a negative acknowledgement (NACK) signal indicating that starting is not to be performed. 
     Alternatively, before reception waiting of a distance-measuring trigger signal, both of responding to the wakeup signal and request-response authentication may be sequentially performed between the portable device  100  and the control device  200 . The control device  200  starts the reception waiting of a distance-measuring trigger signal on the basis of responding to the wakeup signal or request-response authentication. 
     In responding to the wakeup signal or request-response authentication, a signal transmitted from one device to the other device is also referred to as a first notification signal. A signal transmitted from the device having received the first notification signal to the device having transmitted the first notification signal is also referred to as a second notification signal. Each device determines that authentication of the other device has succeeded only when the regular second authentication signal corresponding to the first authentication signal has been transmitted as a response to the first authentication signal. 
     A frequency band which is used to transmit the first and second notification signals is arbitrary. For example, the notification signals may be transmitted using the same frequency band as the distance-measuring signals such as the distance-measuring trigger signal and the distance-measuring request signal or may be transmitted using a frequency band different from that of the distance-measuring signals. The notification signals may be transmitted as signals in the UWB, may be transmitted as signals in the LF band, may be transmitted as signals in the RF band, or may be transmitted as signals in Bluetooth low energy (BLE (registered trademark)). 
     &lt;5. Conclusion&gt; 
     While an exemplary embodiment of the present invention has been described above in detail with reference to the accompanying drawings, the present invention is not limited to the embodiment. It will be apparent to those skilled in the art to which the present invention belongs can think out various alterations or modifications within the technical spirit described in the appended claims and the alterations or modifications belong to the technical scope of the present invention. 
     For example, an example in which a first distance-measuring signal is transmitted from an authenticator party has been described above in the aforementioned embodiment, but the present invention is not limited to this example. The authenticator party is, for example, the control device  200  of the vehicle  20 . For example, an authentication target party may transmit the first distance-measuring signal. The authentication target party is, for example, the portable device  100 . When a first distance-measuring signal is received from the portable device  100 , the control device  200  transmits a second distance-measuring signal as a response to the first distance-measuring signal. When the second distance-measuring signal is received, the portable device  100  measures a time ΔT 1  from the transmission time point of the first distance-measuring signal to the reception time point of the second distance-measuring signal. Subsequently, the portable device  100  transmits a data signal including information obtained by encrypting information indicating the measured time ΔT 1 . On the other hand, the control device  200  measures a time ΔT 2  from the reception time point of the first distance-measuring signal to the transmission time point of the second distance-measuring signal. When the data signal is received from the portable device  100 , the control device  200  calculates a distance between the portable device  100  and the control device  200  on the basis of the time ΔT 1  indicated by the data signal received from the portable device  100  and the measured time ΔT 2 . For example, the time required for transmission and reception of the signals in one way is calculated by dividing ΔT 1 -ΔT 2  by 2, and the distance between the portable device and the communication unit is calculated by multiplying the time by a speed of a signal. In this way, when the directions of transmission and reception of the first distance-measuring signal and the second distance-measuring signal are interchanged, the control device  200  performs control for transitioning to the reception waiting state in which the first distance-measuring signal transmitted from the portable device  100  is waited for. The aforementioned embodiment can be applied to the control of the reception waiting state in which the first distance-measuring signal is waited for. 
     In the aforementioned embodiment, an example in which the authentication target is the portable device  100  and the authenticator is the control device  200  of the vehicle  20  has been described above, but the present invention is not limited to this example. The roles of the portable device  100  and the control device  200  of the vehicle  20  may be interchanged, or may be dynamically interchanged. Positioning and authentication may be performed between control devices  200  of vehicles  20 . 
     In the aforementioned embodiment, the portable device  100  is an example of the communication device and the control device  200  is an example of the control device, but the present invention is not limited thereto. The portable device  100  may be an example of the control device, and the control device  200  may be an example of the communication device. 
     For example, an example in which the present invention is applied to a smart entry system has been described above in the embodiment, but the present invention is not limited to the example. The present invention is applicable to an arbitrary system that performs distance measuring and authentication through transmission and reception of signals. Examples of an object which is used by a user include a drone, a vehicle, a ship, an aircraft, a building, a robot, a locker, and a home appliance. The building may include a house. The present invention is applicable to a pair including two arbitrary devices of a portable device, a vehicle, a ship, an aircraft, a smartphone, a drone, a building, a robot, a locker, and a home appliance. This pair may include two devices of the same type or include two devices of different types. In this case, one device operates as a first communication device, and the other device operates as a second communication device. 
     For example, an example in which UWB is used as a wireless communication standard has been described above in the embodiment, but the present invention is not limited to this example. For example, a communication standard using infrared rays may be used as a wireless communication standard. 
     For example, an example in which the controller  240  is configured as an ECU and controls the entire operations of the control device  200  has been described above in the embodiment, but the present invention is not limited to this example. For example, each of the first wireless communicator  210  and the second wireless communicator  220  may include an ECU. In this case, the first wireless communicator  210  and the second wireless communicator  220  are also referred to as communication devices mounted in a mobile object. Similarly to the aforementioned control device  200 , each communication device mounted in a mobile object may perform the processes based on authentication information included in a received signal or the processes of controlling transition to the reception waiting state. 
     A series of processes which is performed by the devices described above in this specification may be realized using one of software, hardware, and a combination of software and hardware. Programs constituting the software are stored, for example, in recording media (non-transitory media) which are provided inside or outside of each device in advance. For example, the programs are read to a RAM and executed by a processor such as a CPU when a computer executes the programs. Examples of the recording media include a magnetic disk, an optical disc, a magneto-optical disc, and a flash memory. The computer programs may be delivered, for example, via a network without using recording media. 
     Processes described above with reference sequence diagrams or flowcharts in this specification may necessarily not be performed in the illustrated orders. Some process steps may be performed in parallel. An additional process step may be employed or some process steps may be omitted. 
     REFERENCE SIGNS LIST 
     
         
           1  system 
           100  portable device 
           110  first wireless communicator 
           120  second wireless communicator 
           130  storage 
           140  controller 
           20  vehicle 
           200  control device 
           210  first wireless communicator 
           220  second wireless communicator 
           230  storage 
           240  controller