Patent Publication Number: US-2021190907-A1

Title: Electronic device, method for controlling electronic device, and electronic device control program

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the priority of Patent Application 2018-165795 filed in Japan on Sep. 5, 2018, and the entire disclosure of this previous application is hereby incorporated for reference. 
     TECHNICAL FIELD 
     The present disclosure relates to an electronic device, a method for controlling electronic device, and an electronic device control program. 
     BACKGROUND 
     For example, in the field of industries related to automobiles, technique for measuring the distance between an own vehicle and an object is important. In particular, in recent years, RADAR (Radio Detecting and Ranging) technique, that measures the distance between the own vehicle and the object by transmitting radio waves such as millimeter waves and receiving reflected waves from the object such as an obstacle, has been studied in various ways. The importance of technique for measuring such distances and the like is expected to grow more and more in the future with the development of techniques that assist drivers in driving and related to automated driving that automates a part or all of driving. 
     Further, a technique that measures (estimates) an arrival direction of the reflected wave by receiving a reflected wave obtained by reflection of the transmitted radio wave, have also been proposed in various ways. For example, PTL 1 and PTL 2 propose a radar technique that can accurately estimate the arrival wave direction. Further, PTL 3 and PTL 4, for example, propose a radar technique that can reduce the amount of data or arithmetic operation in estimating the arrival wave direction. 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP 2009-162688 A 
     PTL 2: JP 2011-137650 A 
     PLT 3: JP 2009-162689 A 
     PTL 4: JP 2012-163403 A 
     SUMMARY 
     An electronic device according to an embodiment comprises a transmitting antenna that transmits a transmitted wave, a receiving antenna that receives a reflected wave obtained by reflection of the transmitted wave, and a controller. The controller generates a first sample based on a result obtained by subjecting a beat signal generated based on a transmitted signal based on the transmitted wave and a received signal based on the reflected wave to a first fast Fourier transform process. The controller generates a second sample based on a result obtained by subjecting the first sample to a second fast Fourier transform process, and estimates an arrival direction of the reflected wave based on the second sample. The controller shall set the first sample from the beat signals in which the peak in the result obtained by performing the first fast Fourier transform process is equal to or higher than a first threshold value. 
     An electronic device according to an embodiment comprises a transmitting antenna that transmits a transmitted wave, a receiving antenna that receives a reflected wave obtained by reflection of the transmitted wave, and a controller. The controller generates a sample based on a result obtained by subjecting a beat signal generated based on a transmitted signal based on the transmitted wave and a received signal based on the reflected wave to a Fourier transform process. The controller estimates an arrival direction of the reflected wave based on the sample. The controller selects the sample from the beat signals in which the peak in the result obtained by performing the Fourier transform process is equal to or higher than a prescribed threshold value. 
     An electronic device according to an embodiment comprises a transmitting antenna that transmits a transmitted wave, a receiving antenna that receives a reflected wave obtained by reflection of the transmitted wave, and a controller. The controller generates a first sample based on a result obtained by subjecting a beat signal generated based on a transmitted signal based on the transmitted wave and a received signal based on the reflected wave to a first fast Fourier transform process. The controller generates a second sample based on a result obtained by subjecting the first sample to a second fast Fourier transform process. The controller estimates an arrival direction of the reflected wave based on the second sample. The controller selects the second sample from the beat signals in which the peak in the result obtained by performing the second fast Fourier transform process is equal to or higher than a second threshold value. 
     A method for controlling electronic device according to an embodiment includes the following steps. 
     (1) A step of transmitting a transmitted signal as a transmitted wave from a transmitting antenna. 
     (2) A step of receiving a received signal from a receiving antenna as a reflected wave obtained by reflection of the transmitted wave. 
     (3) A step of generating a first sample based on a result obtained by subjecting a beat signal generated based on the transmitted signal and the received signal to a first fast Fourier transform process. 
     (4) A step of selecting the beat signals from the first samples in which the peak in the result obtained by performing the first fast Fourier transform process is equal to or higher than a first threshold value, among the beat signals. 
     (5) A step of generating a second sample based on a result obtained by subjecting the selected first sample to a second fast Fourier transform process. 
     (6) A step of estimating an arrival direction of the reflected wave based on the second sample. 
     An electronic device control program according to an embodiment causes a computer to perform the above steps (1) through (6). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a diagram for explaining a use of an electronic device according to an embodiment. 
         FIG. 2  is a functional block diagram schematically showing a configuration of an electronic device according to an embodiment. 
         FIG. 3  is a diagram for explaining a configuration of a transmitted signal according to an embodiment. 
         FIG. 4  is a flowchart for explaining an operation of an electronic device according to an embodiment. 
         FIG. 5  is a flowchart for explaining an operation of an electronic device according to an embodiment. 
         FIG. 6  is a diagram for explaining a threshold value set in an embodiment. 
         FIG. 7  is a flowchart for explaining an operation of an electronic device according to an embodiment. 
         FIG. 8  is a diagram for explaining a threshold value set in an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the technique of measuring an arrival direction of the reflected wave as described above, it is desirable to improve the accuracy of the measurement. An objective of the present disclosure is to provide an electronic device that improves an accuracy of measuring the arrival direction of the reflected wave, a method for controlling electronic device, and an electronic device control program. According to an embodiment, it is possible to provide an electronic device that improves an accuracy of measuring the arrival direction of the reflected wave, a method for controlling an electronic device, and an electronic device control program. Hereinafter, an embodiment will be described in detail with reference to the drawings. 
     An electronic device according to an embodiment, for example, by being mounted on a vehicle such as an automobile (mobile body), can measure (estimate) a direction of a prescribed object existing around the mobile body. For this reason, an electronic device according to an embodiment can transmit a transmitted wave from a transmitting antenna installed on a mobile body to the surroundings of the mobile body. Also, an electronic device according to an embodiment can receive the reflected wave obtained by reflection of the transmitted wave from a receiving antenna installed on the mobile body. At least one of transmitting antennas and receiving antennas may be provided, for example, in a radar sensor or the like installed in the mobile body. 
     Hereinafter, as a typical example, the configuration in which an electronic device according to an embodiment is mounted in an automobile, such as a passenger car as an example of a mobile body will be described. However, mobile bodies on which the electronic device according to an embodiment is mounted is not limited to the automobile. An electronic device according to an embodiment may be mounted on a variety of mobile bodies, such as automated driving cars, buses, trucks, motorcycles, bicycles, ships, aircrafts, tractors such as agricultural vehicles, fire trucks, ambulances, police vehicles, snowplows, street sweepers, drones, and pedestrians. Further, mobile bodies on which an electronic device according to an embodiment is mounted are not necessarily limited to mobile bodies that move by their own power. For example, a mobile body on which an electronic device according to an embodiment is mounted may be a trailer portion towed by a tractor. 
     First, an example of detecting a body by an electronic device according to an embodiment will be described. 
       FIG. 1  is a diagram for explaining a use of an electronic device according to an embodiment.  FIG. 1  shows an example in which a sensor comprising a transmitting antenna and a receiving antenna according to an embodiment is installed on a mobile body. 
     In a mobile body  100  shown in  FIG. 1 , a sensor  5  comprising a transmitting antenna and a receiving antenna according to an embodiment is installed. Further, the mobile body  100  shown in  FIG. 1  shall be equipped with an electronic device  1  according to an embodiment (for example, built-in). A specific configuration of the electronic device  1  will be described later. The sensor  5  may comprise, for example, at least one of transmitting antennas and receiving antennas. Further, the sensor  5  may include at least one of the other functional parts such as a controller  10  included in the electronic device  1  ( FIG. 3 ), as appropriate. The mobile body  100  shown in  FIG. 1  may be an automobile vehicle, such as a passenger car, but may be an arbitrary type of mobile body. In  FIG. 1 , the mobile body  100 , for example, may be moving in the Y-axis positive direction shown in  FIG. 1  (traveling direction) or (traveling or slow traveling), it may be moving in other directions, or it may be stationary without moving. 
     As shown in  FIG. 1 , the sensor  5  comprising a plurality of transmitting antennas is installed on a mobile body  100 . In the example shown in  FIG. 1 , only one sensor  5  comprising a transmitting antenna and a receiving antenna is installed in front of the mobile body  100 . Here, a position where the sensor  5  is installed in the mobile body  100  is not limited to the position shown in  FIG. 1 , but may be other positions as appropriate. For example, the sensor  5  as shown in  FIG. 1  may be installed on the left, right, and/or rear of the mobile body  100 . Further, a number of such sensors  5  may be an arbitrary number of one or more, depending on various conditions (or requirements) such as the range and/or accuracy of the measurement in the mobile body  100 . 
     The sensor  5  transmits an electromagnetic wave as a transmitted wave from a transmitting antenna. For example, if there is a prescribed object (for example, object  200  shown in  FIG. 1 ) around the mobile body  100 , at least a part of the transmitted wave transmitted from the sensor  5  is reflected by the object and becomes a reflected wave. Then, by receiving such a reflected wave by the receiving antenna of the sensor  5  for example, the electronic device  1  mounted on the mobile body  100  can detect the object. 
     The sensor  5  comprising a transmitting antenna may typically be a radar (RADAR(Radio Detecting and Ranging) sensor that transmits and receives radio waves. However, the sensor  5  is not limited to a radar sensor. The sensor  5  according to an embodiment may be a sensor based on a technique of, for example, LIDAR (Light Detection and Ranging, Laser Imaging Detection and Ranging) by light waves. Such sensors can be configured to include, for example, a patch antenna. Because techniques such as RADAR and LIDAR have been already known, detailed descriptions may be simplified or omitted as appropriate. 
     The electronic device  1  mounted on the mobile body  100  shown in  FIG. 1  receives a reflected wave obtained by reflection of the transmitted wave transmitted from a transmitting antenna of the sensor  5 , from the receiving antenna. In this way, the electronic device  1  can detect a prescribed object  200  existing within a prescribed distance from the mobile body  100 . For example, as shown in  FIG. 1 , the electronic device  1  can measure the distance L between the mobile body  100 , which is its own vehicle, and the prescribed object  200 . Further, the electronic device  1  can also measure the relative speed between the mobile body  100 , which is its own vehicle, and the prescribed object  200 . Furthermore, the electronic device  1  can also measure an arrival direction (arrival angle θ) in which a reflected wave from the prescribed object  200  arrives at the mobile body  100 , which is its own vehicle. 
     Here, the object  200  may be at least one of, for example, oncoming vehicles traveling in a lane adjacent to the mobile body  100 , vehicles traveling in parallel with the mobile body  100 , and vehicles in front of or behind the mobile body  100  traveling in the same lane as the mobile body  100 . The object  200  may be an arbitrary body around the mobile body  100 , such as motorcycles, bicycles, strollers, pedestrians, guardrails, medians, road signs, sidewalk steps, walls, manholes, and obstacles. In the present disclosure, objects detected by the sensor  5  include inanimate objects as well as organisms such as humans or animals. The objects detected by the sensors  5  of the present disclosure include markers, including humans, objects and animals, which are detected by radar technique. 
     In  FIG. 1 , a ratio of the size of the sensor  5  to the size of the mobile body  100  does not necessarily represent an actual ratio. Further, in  FIG. 1 , the sensor  5  shows a state of being installed outside of the mobile body  100 . However, in an embodiment, the sensor  5  may be installed in various positions on the mobile body  100 . For example, in an embodiment, the sensor  5  may be installed inside of the bumper of the mobile body  100  so that it does not appear in the outer appearance of the mobile body  100 . The position where the sensor  5  is installed on the mobile body  100  may be either outside or inside of the mobile body  100 , or both. An inside of the mobile body  100  is, for example, an inside of the body of the mobile body  100 , an inside of bumpers, an inside of headlights, or an inside of spaces in a car. An outside of the mobile body  100  is, for example, a surface of a body of the mobile body  100 , a surface of bumpers, or a surface of headlights. 
     Hereinafter, as a typical example, the transmitting antenna of the sensor  5  will be described as transmitting radio waves in a frequency band such as millimeter wave (above 30 GHz) or quasi-millimeter wave (for example, around 20 GHz to 30 GHz). For example, the transmitting antenna of the sensor  5  may transmit radio waves with a frequency bandwidth of 4 GHz, such as 77 GHz to 81 GHz. The transmitting antenna of the sensor  5  may transmit radio waves in a frequency band other than millimeter wave (above 30 GHz) or quasi-millimeter wave (for example, near 20 GHz to 30 GHz). 
       FIG. 2  is a functional block diagram schematically showing an example of a configuration of the electronic device  1  according to an embodiment. Hereinafter, an example of a configuration of the electronic device  1  according to an embodiment will be described. 
     When measuring distance or the like by millimeter wave radar, a frequency modulated continuous wave radar (hereafter referred to as FMCW radar (Frequency Modulated Continuous Wave radar)) is often used. A FMCW radar sweeps a frequency of a radio wave to be transmitted, and thereby a transmitted signal is generated. Therefore, for example, in a millimeter wave FMCW radar that uses radio waves in the 79 GHz frequency band, the frequency of the radio waves used will have a frequency bandwidth of 4 GHz, for example, such as 77 GHz to 81 GHz. A radar in the 79 GHz frequency band is characterized by a wider usable frequency bandwidth than other millimeter/quasi-millimeter wave radars, such as those in the 24 GHz, 60 GHz, and 76 GHz frequency bands. Hereinafter, such an embodiment will be described. 
     As shown in  FIG. 2 , an electronic device  1  in an embodiment consists of the sensor  5  and an ECU (Electronic Control Unit)  50 . The ECU 50  controls various operations of the mobile body  100 . The ECU 50  may consist of at least one or more ECUs. The electronic device  1  according to an embodiment comprises the controller  10 . Further, the electronic device  1  according to an embodiment may appropriately include other functional parts such as at least one of a transmitter  20 , receivers  30 A to  30 D, and a storage  40 . As shown in  FIG. 2 , the electronic device  1  may comprise a plurality of receivers, such as the receivers  30 A to  30 D. Hereinafter, when the receiver  30 A, the receiver  30 B, the receiver  30 C, and the receiver  30 D are not distinguished, they are simply referred to as “receiver  30 ”. 
     As shown in  FIG. 2 , the controller  10  may comprise a distance FFT processor  12 , a speed FFT processor  14 , an arrival angle estimator  16 , and a determination processor  18 . These functional parts included in the controller  10  will be further described later. 
     The transmitter  20 , as shown in  FIG. 2 , may comprise a signal generator  21 , a synthesizer  22 , phase controllers  23 A and  23 B, amplifiers  24 A and  24 B, and transmitting antennas  25 A and  25 B. Hereinafter, when the transmitting antenna  25 A and the transmitting antenna  25 B are not distinguished, they are simply referred to as “transmitting antenna  25 ”. Further, other functional parts in the transmitter  20  may also be referred to collectively by omitting symbols such as A and B when a plurality of functional parts of the same type are not specifically distinguished, for example, such as the phase controllers  23 A and  23 B. 
     As shown in  FIG. 2 , the receiver  30  may comprise corresponding receiving antennas  31 A to  31 D, respectively. Hereinafter, when the receiving antenna  31 A, the receiving antenna  31 B, the receiving antenna  31 C, and the receiving antenna  31 D are not distinguished, they are simply referred to as “receiving antenna  31 ”. Further, as shown in  FIG. 2 , a plurality of receivers  30  may comprise an LNA  32 , a mixer  33 , an IF part  34 , and an AD converter  35 , respectively. The receivers  30 A to  30 D may have the same configuration, respectively. In  FIG. 2 , as a representative example, the configuration of only the receiver  30 A is schematically shown. 
     The above-mentioned sensor  5  may comprise, for example, the transmitting antenna  25  and the receiving antenna  31 . The sensor  5  may also include at least one of the other functional parts, such as the controller  10 , as appropriate. 
     The controller  10  comprised by the electronic device  1  according to an embodiment can control an operation of the entire electronic device  1  including an control of each functional part constituting the electronic device  1 . The controller  10  may include at least one processor, such as a CPU (central processing unit), for example, in order to provide control and processing power for performing various functions. The controller  10  may be realized collectively by one processor, by several processors, or by individual processors. The processor may be realized as a single integrated circuit. An integrated circuit is also referred to as an IC (Integrated Circuit). A processor may be realized as a plurality of communicably connected integrated circuits and discrete circuits. A processor may be realized based on various other known techniques. In an embodiment, the controller  10  may be configured, for example, as a CPU and a program executed on the CPU. The controller  10  may appropriately include a memory necessary for an operation of the controller  10 . 
     The storage  40  may store programs executed by the controller  10 , results of process executed by the controller  10 , and the like. Further, the storage  40  may function as a work memory for the controller  10 . The storage  40  can be configured by, for example, a semiconductor memory, a magnetic disk, or the like, but is not limited to these, and can be an arbitrary storage device. Further, for example, the storage  40  may be a storage medium such as a memory card that is inserted in the electronic device  1  according to the present embodiment. Further, the storage  40  may also be an internal memory of a CPU that is used as the controller  10 , as described above. 
     In the electronic device  1  according to an embodiment, the controller  10  can control at least one of the transmitter  20  and the receiver  30 . In this case, the controller  10  may control at least one of the transmitter  20  and the receiver  30  based on various information stored in the storage  40 . Further, in the electronic device  1  according to an embodiment, the controller  10  may instruct the signal generator  21  to generate signals, or may control the signal generator  21  to generate signals. 
     The signal generator  21  generates the signal (transmitted signal) to be transmitted as a transmitted wave T from the transmitting antenna  25  under the control of the controller  10 . The signal generator  21  may assign a frequency of a transmitted signal, for example based on control by the controller  10  when generating a transmitted signal. For example, the signal generator  21  generates signals having a prescribed frequency in a frequency band, such as 77 GHz to 81 GHz, by receiving frequency information from the controller  10 . The signal generator  21  may be configured to include a functional part such as a voltage controlled oscillator (VCO). 
     The signal generator  21  may be configured as a hardware having the function, for example, may be configured as a microcontroller and the like, or for example, may be configured as a combination of a processor such as a CPU and a program executed by the processor. Each functional part described below may also be configured as a hardware having the function, or if possible, for example, as a microcontroller, or for example, as a combination of a processor such as a CPU and a program executed by the processor. 
     In the electronic device  1  according to an embodiment, the signal generator  21  may generate a transmitted signal (transmitted chirp signal) such as a chirp signal. In particular, the signal generator  21  may generate the signal (linear chirp signal) in which a frequency changes periodically and linearly. For example, the signal generator  21  may generate a chirp signal in which a frequency increases periodically and linearly from 77 GHz to 81 GHz with passage of time. Further, for example, the signal generator  21  may generate the signal in which a frequency periodically repeats linear increase (up chirp) and decrease (down chirp) from 77 GHz to 81 GHz with passage of time. The signal generated by the signal generator  21  may be preset in the controller  10 , for example. Further, the signal generated by the signal generator  21  may be stored in advance in a storage  40  or the like, for example. Because chirp signals used in technical fields such as radar are known, more detailed description will be simplified or omitted as appropriate. The signal generated by the signal generator  21  is supplied to the synthesizer  22 . 
     The ECU  50  equipped with the electronic device  1  according to an embodiment can control an operation of the entire mobile body  100 , including a control of each functional part comprising the mobile body  100 . The ECU  50  may include at least one processor, such as a CPU (Central Processing Unit), for example, in order to provide control and processing power for performing various functions. The ECU  50  may be realized collectively by one processor, by several processors, or by individual processors. The processor may be realized as a single integrated circuit. An integrated circuit is also referred to as an IC (Integrated Circuit). A processor may be realized as a plurality of communicably connected integrated circuits and discrete circuits. A processor may be realized based on various other known techniques. In an embodiment, the ECU  50  may be configured, for example, as a CPU and a program executed on the CPU. ECU  50  may appropriately include a memory necessary for an operation of the ECU  50 . Further, at least a part of a function of the controller  10  may be a function of the ECU  50 , or at least a part of a function of the ECU  50  may be a function of the controller  10 . 
       FIG. 3  is a diagram explaining an example of a chirp signal generated by the signal generator  21 . 
     In  FIG. 3 , the horizontal axis represents the passage of time, and the vertical axis represents the frequency. In the example shown in  FIG. 3 , the signal generator  21  generates a linear chirp signal in which a frequency changes periodically and linearly. In  FIG. 3 , each chirp signal is shown as c 1 , c 2 , . . . , c 8 . As shown in  FIG. 3 , in each chirp signal, a frequency increases linearly with passage of time. 
     In an example shown in  FIG. 3 , eight chirp signals such as c 1 , c 2 , . . . , C 8  are included to form one subframe. That is, the subframe  1  and the subframe  2  shown in  FIG. 3  are configured to include eight chirp signals such as c 1 , c 2 , . . . , C 8 , respectively. Further, in an example shown in  FIG. 3 , 16 subframes such as subframes  1  to  16  are included to form one frame. That is, one frame consists of 16 subframes respectively, such as frame  1  and frame  2  shown in  FIG. 3 . Further, as shown in  FIG. 3 , a frame interval having a prescribed length may be included between the frames. 
     In  FIG. 3 , frame  2  and beyond may have a similar configuration. Further, in  FIG. 3 , frame  3  and beyond may have a similar configuration. In the electronic device  1  according to an embodiment, the signal generator  21  may generate a transmitted signal as an arbitrary number of frames. Also, in  FIG. 3 , some chirp signals are shown omitted. Thus, a relationship between frequency and time of a transmitted signal generated by the signal generator  21  may be stored in the storage  40 , for example. 
     Thus, the electronic device  1  according to an embodiment may transmit the transmitted signal consisting of subframes including a plurality of chirp signals. Also, the electronic device  1  according to an embodiment may transmit the transmitted signal consisting of a frame including a prescribed number of subframes. 
     Hereinafter, the electronic device  1  will be described as transmitting the transmitted signal having a frame structure as shown in  FIG. 3 . However, the frame structure as shown in  FIG. 3  is an example, and a number of chirp signals included in one subframe is not limited to eight, for example. In an embodiment, the signal generator  21  may generate subframes including an arbitrary number of (for example, any plural) chirp signals. Further, the subframe structure as shown in  FIG. 3  is also an example. For example, a number of subframes included in one frame is not limited to 16. In an embodiment, the signal generator  21  may generate frames including an arbitrary number of (for example, any plural) subframes. 
     The synthesizer  22  raises a frequency of the signal generated by the signal generator  21  to a frequency in a prescribed frequency band. The synthesizer  22  may raise a frequency of the signal generated by the signal generator  21  to a frequency selected as a frequency of the transmitted wave T that is transmitted from the transmitting antenna  25 . The frequency to be selected as the frequency of the transmitted wave T that is transmitted from the transmitting antenna  25  may be set by the controller  10 , for example. Further, the frequency selected as the frequency of the transmitted wave T that is transmitted from the transmitting antenna  25  may be stored in the storage  40 , for example. The signal whose frequency has been raised by the synthesizer  22  is supplied to the phase controller  23  and the mixer  33 . When there are a plurality of the receivers  30 , the signal whose frequency has been raised by the synthesizer  22  may be supplied to each of the mixer  33  in a plurality of the receivers  30 . 
     The phase controller  23  controls a phase of a transmitted signal supplied by the synthesizer  22 . Specifically, the phase controller  23  may adjust a phase of a transmitted signal by appropriately advancing or delaying a phase of the signal supplied from the synthesizer  22  based on the control by the controller  10 , for example. In this case, the phase controller  23  may adjust the phase of each transmitted signal based on the path difference of each transmitted wave T that is transmitted from a plurality of the transmitting antennas  25 . By the phase controller  23  appropriately adjusting the phase of each transmitted signal, the transmitted waves T transmitted from a plurality of transmitting antennas strengthen each other in a prescribed direction to form a beam (beamforming). In this case, the correlation between the beamforming direction, and the phase amount to be controlled of the transmission signals transmitted from each of a plurality of transmission antennas  25  may be stored in the storage  40 , for example. The transmitted signal whose phase is controlled by the phase controller  23  is supplied to an amplifier  24 . 
     The amplifier  24  amplifies the power (electric power) of the transmitted signal supplied from the phase controller  23 , for example, based on the control by the controller  10 . Because the technique itself for amplifying the power of the transmitted signal is already known, a more detailed description will be omitted. The amplifier  24  is connected to the transmitting antenna  25 . 
     The transmitting antenna  25  outputs (transmits) the transmitted signal amplified by the amplifier  24  as the transmitted wave T. As described above, the sensor  5  may be configured to include a plurality of transmitting antennas, for example, such as the transmitting antenna  25 A and the transmitting antenna  25 B. Because the transmitting antenna  25  can be configured in the same manner as the transmitting antenna used in known radar technique, a more detailed description will be omitted. 
     In this way, the electronic device  1  according to an embodiment can transmit a transmitted signal (for example, a transmitted chirp signal) as the transmitted wave T from the transmitting antenna  25 . Here, at least one of the functional parts comprising the electronic device  1  may be housed in an enclosure of a structure that cannot be easily opened in a single enclosure. For example, it is preferable that the transmitting antenna  25 , the receiving antenna  31 , the amplifier  24 A and the amplifier  24 B are housed in an enclosure, and the enclosure cannot be easily opened. Further, here, when the sensor  5  is installed on the mobile body  100  such as an automobile, the transmitting antenna  25  may transmit the transmitted wave T to the outside of the mobile body  100  through a member such as a radar cover. In this case, the radar cover may be made of a substance that allows electromagnetic waves to pass through, such as synthetic resin or rubber. This radar cover may be, for example, a housing of the sensor  5 . By covering the transmitting antenna  25  with a member such as the radar cover, it is possible to reduce risks that the transmitting antenna  25  is damaged or malfunctions due to contact with external objects. 
     The electronic device  1  shown in  FIG. 2  comprises two transmitting antennas  25  such as the transmitting antenna  25 A and the transmitting antenna  25 B, and transmits the transmitted wave T by these two transmitting antennas  25 . Therefore, the electronic device  1  shown in  FIG. 2  is configured to include two functional parts required for transmitting the transmitted wave T from the two transmitting antennas  25 , respectively. Specifically, the electronic device  1  is configured to include two phase controllers  23  such as the phase controller  23 A and the phase controller  23 B. Further, the electronic device  1  shown in  FIG. 2  is configured to include two amplifiers  24  such as the amplifier  24 A and the amplifier  24 B. 
     The electronic device  1  shown in  FIG. 2  comprises two transmitting antennas  25 , but a number of transmitting antennas  25  comprised by the electronic device  1  according to an embodiment may be any plural, for example, three or more. In this case, the electronic device  1  according to the embodiment may comprise the same number of amplifiers  24  as that of the plurality of transmitting antennas  25 . Further, in this case, the electronic device  1  according to an embodiment may comprise the same number of phase controllers  23  as that of the plurality of transmitting antennas  25 . 
     The receiving antenna  31  receives the reflected wave R. The reflected wave R is the one obtained by reflection of the transmitted wave T on the prescribed object  200 . The receiving antenna  31  may be configured to include a plurality of antennas, such as the receiving antenna  31 A to the receiving antenna  31 D. Because the receiving antenna  31  can be configured in the same manner as the receiving antenna used in the known radar technique, a more detailed description will be omitted. The receiving antenna  31  is connected to the LNA 32 . The received signal based on the reflected wave R received by the receiving antenna  31  is supplied to the LNA 32 . 
     The electronic device  1  according to an embodiment, can receive the reflected wave R obtained by the reflection, that the transmitted wave T, transmitted as a transmitted signal (transmitted chirp signal) such as a chirp signal, is reflected by a prescribed object  200 , from a plurality of the receiving antennas  31 . Thus, when the transmission chirp signal is transmitted as the transmission wave T, the received signal based on the received reflected wave R is referred to as a received chirp signal. That is, the electronic device  1  receives the received signal (for example, the received chirp signal) as the reflected wave R from the receiving antenna  31 . Here, when the sensor  5  is installed on the mobile body  100  such as an automobile, the receiving antenna  31  may receive the reflected wave R from outside of the mobile body  100  through a member such as a radar cover. In this case, the radar cover may be made of a substance that allows electromagnetic waves to pass through, such as synthetic resin or rubber. This radar cover may be, for example, a housing of the sensor  5 . By covering the transmitting antenna  31  with a member such as the radar cover, it is possible to reduce risks that the transmitting antenna  31  is damaged or malfunctions due to contact with external objects. 
     Further, when the receiving antenna  31  is installed near the transmitting antenna  25 , these may be collectively configured to be included in one sensor  5 . That is, one sensor  5  may include, for example, at least one transmitting antenna  25  and at least one receiving antenna  31 . For example, one sensor  5  may include a plurality of transmitting antennas  25  and a plurality of receiving antennas  31 . In such a case, for example, one radar sensor may be covered with a member such as one radar cover. 
     The LNA  32  amplifies the received signal with low noise based on the reflected wave R received by the receiving antenna  31 . The LNA  32  may be used as a low noise amplifier (Low Noise Amplifier), and amplifies the received signal supplied from the receiving antenna  31  with low noise. The received signal amplified by the LNA  32  is supplied to the mixer  33 . 
     The mixer  33  generates a beat signal by mixing (multiplying) the RF frequency received signal supplied from the LNA  32  with the transmitted signal supplied from the synthesizer  22 . The beat signal mixed by the mixer  33  is supplied to an IF part  34 . 
     The IF part  34  decreases the frequency of the beat signal to an intermediate frequency (IF (Intermediate Frequency) frequency) by performing frequency conversion on the beat signal supplied from the mixer  33 . The beat signal whose frequency is decreased by the IF part  34  is supplied to the AD converter  35 . 
     The AD converter  35  digitizes the analog beat signal supplied by the IF part  34 . The AD converter  35  may be configured by any analog-to-digital conversion circuit (Analog to Digital Converter (ADC)). The beat signal digitized by the AD converter  35  is supplied to the distance FFT processor  12  of the controller  10 . When there are a plurality of receivers  30 , each beat signal digitized by the plurality of AD converters  35  may be supplied to the distance FFT processor  12 . 
     The distance FFT processor  12  estimates the distance between the object  200  and the mobile body  100  equipped with the electronic device  1 , based on the beat signal supplied by the AD converter  35 . The distance FFT processor  12  may include, for example, a processor that performs a Fast Fourier transform. In this case, the distance FFT processor  12  may consist of an arbitrary circuit or a chip that performs the fast Fourier Transform (Fast Fourier Transform (FFT)) process. The distance FFT processor  12  and the speed FFT processor  14  may perform a discrete Fourier transform or a Fourier transform. 
     The distance FFT processor  12  performs FFT process on the beat signal digitized by the AD converter  35  (hereinafter, appropriately referred to as “first FFT process”). For example, the distance FFT processor  12  may perform the FFT process on a complex signal supplied from the AD converter  35 . The beat signal digitized by the AD converter  35  can be represented as a time change in the signal strength (electric power). The distance FFT processor  12  performs the FFT process on such a beat signal, whereby it can be expressed as the signal strength (electric power) corresponding to each frequency. When the peak is equal to or higher than a prescribed threshold value in the result obtained by performing the first FFT process, the distance FFT processor  12  may determine that the prescribed object  200  is at a distance corresponding to the peak. The distance FFT processor  12  can estimate the distance to the prescribed object based on one chirp signal (for example, c 1  shown in  FIG. 3 ). That is, the electronic device  1  can measure (estimate) the distance L shown in  FIG. 1  by performing the first FFT process. Because the technique itself for measuring (estimating) the distance to the prescribed body by performing FFT process on the beat signal is known, a more detailed description will be simplified or omitted as appropriate. Results of the first FFT process performed by the distance FFT processor  12  may be supplied to the speed FFT processor  14 . 
     The speed FFT processor  14  estimates a relative speed between the mobile body  100  equipped with the electronic device  1  and the object  200  based on the beat signal on which the first FFT process has been performed by the distance FFT processor  12 . The speed FFT processor  14  may include, for example, a processor that performs the fast Fourier transform. In this case, the speed FFT processor  14  may consist of an arbitrary circuit or a chip that performs the fast Fourier Transform (Fast Fourier Transform (FFT)) process. 
     The speed FFT processor  14  further performs a FFT process on the beat signal on which the first FFT process has been performed by the distance FFT processor  12  (hereinafter, appropriately referred to as “second FFT process”). For example, the speed FFT processor  14  may perform FFT process on the complex signal supplied from the distance FFT processor  12 . The speed FFT processor  14  can estimate the relative speed with a prescribed object based on the subframe of the chirp signal (for example, the subframe  1  shown in  FIG. 3 ). When the first FFT process is performed on the beat signal as described above, a plurality of vectors can be generated. The relative speed with a prescribed body can be estimated by obtaining the phase of the peak in a result obtained by performing the second FFT process on these plurality of vectors. That is, the electronic device  1  can measure (estimate) the relative speed between the mobile body  100  shown in  FIG. 1  and the prescribed object  200  by performing the second FFT process. Because the technique itself for measuring (estimating) the relative speed with a prescribed body by performing the speed FFT process on the result of performing the distance FFT process is known, a more detailed explanation is appropriately simplified or omitted. The result of performing the second FFT process by the speed FFT processor  14  may be supplied to the arrival angle estimator  16 . 
     The arrival angle estimator  16  estimates the direction in which the reflected wave R arrives from the prescribed object  200  based on the result obtained by the FFT process performed by the speed FFT processor  14 . The electronic device  1  can estimate the direction in which the reflected wave R arrives by receiving the reflected wave R from the plurality of receiving antennas  31 . For example, the plurality of receiving antennas  31  shall be arranged at prescribed intervals. In this case, the transmitted wave T transmitted from the transmitting antenna  25  is reflected by the prescribed object  200  to become the reflected wave R, and each of the plurality of receiving antennas  31  arranged at prescribed intervals receives the reflected wave R. Then, the electronic device  1  can estimate the direction in which the reflected wave R arrives at the receiving antenna  31  based on the phase of the reflected wave R received by each of the plurality of receiving antennas  31  and the path difference of each reflected wave R. That is, the electronic device  1  can measure (estimate) the arrival angle θ shown in  FIG. 1  based on the result of performing the second FFT process. Various techniques for estimating the direction in which the reflected wave R arrives have been proposed based on the result obtained by performing the speed FFT process. Therefore, more detailed description of known techniques will be simplified or omitted as appropriate. The information (angle information) of the arrival angle θ estimated by the arrival angle estimator  16  may be output from the controller  10  to the ECU  50  or the like, for example. In this case, when the mobile body  100  is an automobile, communication may be performed using a communication interface such as CAN (Controller Area Network). 
     The determination processor  18  performs process for determining whether each value used in the arithmetic operation process is equal to or higher than a prescribed threshold value. For example, the determination processor  18  may determine whether the peak in the result obtained by performing a process in the distance FFT processor  12  and the speed FFT processor  14  is equal to or higher than a prescribed threshold value, respectively. 
     For example, the determination processor  18  may determine whether the peak in a result obtained by performing the first FFT process by the distance FFT processor  12  becomes equal to or higher than the first threshold value. That is, the determination processor  18  may determine whether the peak in a result obtained by performing the first FFT process on the beat signal generated based on the transmitted signal and the received signal becomes equal to or higher than the first threshold value. To set the first threshold value will be described later. In this way, when the peak in a result obtained by performing the first FFT process on the beat signal is determined to be equal to or higher than the first threshold value, the beat signal may be counted as the “first sample”. Counting the beat signal as the “first sample” means that the determination processor  18  selects the sample in which the peak in the result obtained by performing the first FFT process on the beat signal is equal to or higher than the first threshold value. 
     Further, for example, the determination processor  18  may determine whether the peak in a result obtained by performing the second FFT process by the speed FFT processor  14  becomes equal to or higher than the second threshold value. That is, the determination processor  18  may determine whether the peak in a result obtained by performing the second FFT process on the above-mentioned first sample becomes equal to or higher than the second threshold value. To set the second threshold value will be described later. Thus, when the peak in a result obtained by performing the second FFT process on the first sample is determined to be equal to or higher than the second threshold value, the first sample may be counted as the “second sample”. Counting the beat signal as the “second sample” means that the determination processor  18  selects the sample in which the peak in the result obtained by performing the second FFT process on the beat signal is equal to or higher than the second threshold value. 
     As described above, the arrival angle estimator  16  estimates the direction in which the reflected wave R arrives from the prescribed object  200  based on the result of the FFT process performed by the speed FFT processor  14 . Further, the speed FFT processor  14  performs the second FFT process on the beat signal on which the first FFT process has been performed by the distance FFT processor  12 . In this case, the distance FFT processor  12  may generate the first sample according to the determination process by the determination processor  18 , based on the results obtained by performing the first FFT process on the beat signal generated based on the transmitted and received signals. Further, the speed FFT processor  14  may generate the second sample according to the determination process by the determination processor  18  based on the result obtained by performing the second FFT process on the first sample. Then, the arrival angle estimator  16  may estimate the arrival direction (arrival angle θ) of the reflected wave R based on the generated second sample. For example, the electronic device  1  may estimate the arrival direction (arrival angle θ) of the reflected wave R based on a covariance matrix obtained by the second sample. 
     The electronic device  1  shown in  FIG. 2  comprises two transmitting antennas  25  and four receiving antennas  31 . Thus, by comprising the plurality of transmitting antennas  25  and the plurality of receiving antennas  31 , the electronic device  1  may configure these antennas as eight virtual antennas array for example. Thus, the electronic device  1  may transmit and receive the reflected wave R including 16 subframes shown in  FIG. 3  by using the virtual eight antennas. 
       FIGS. 4 to 7  are diagrams explaining an example of an operation of the electronic device  1  according to an embodiment. Hereinafter, an example of an operation of the electronic device  1  according to an embodiment will be described. Hereinafter, an example in which the electronic device  1  is configured as a millimeter-wave type FMCW radar will be described. 
       FIG. 4  is a flowchart explaining an operation of the electronic device  1  according to an embodiment. The operation shown in  FIG. 4  may be started when, for example, the electronic device  1  detects a prescribed object  200  existing around the mobile body  100 , and estimates the direction (arrival angle θ) in which the reflected wave R arrives from the object  200 . 
     When the operation shown in  FIG. 4  starts, the controller  10  of the electronic device  1  controls to transmit the chirp signal from the transmitting antenna  25  of the transmitter  20  (step S 1 ). Specifically, the controller  10  instructs the signal generator  21  to generate a transmitted signal (chirp signal). The controller  10  controls the chirp signal to be transmitted as a transmission wave T from the transmitting antenna  25  via the synthesizer  22 , the phase controller  23 , and the amplifier  24 . 
     When the chirp signal is transmitted in step S 1 , the controller  10  controls to receive the chirp signal from the receiving antenna  31  of the receiver  30  (step S 2 ). When the chirp signal is received in step S 2 , the controller  10  controls the receiver  30  to generate a beat signal by multiplying the transmitted chirp signal with the received chirp signal (step S 3 ). Specifically, the controller  10  controls so that the chirp signal received from the receiving antenna  31  is amplified by the LNA  32  and multiplied with the transmitted chirp signal by the mixer  33 . The process from step S 1  to step S 3  may be performed, for example, by adopting a known millimeter-wave FMCW radar technique. 
     When the beat signal is generated in step S 3 , the controller  10  generates the above-mentioned first sample from each generated chirp signal (step S 4 ). 
     Hereinafter, the process of step S 4  will be further described.  FIG. 5  is a flowchart explaining the process of step S 4  in  FIG. 4  in more detail. 
     When the process of step S 4  shown in  FIG. 4  starts, the distance FFT processor  12  performs the first FFT process on the beat signal generated in step S 3  as shown in  FIG. 5  (step S 11 ). As described above, when the process of step S 11  is performed, the signal strength (electric power) corresponding to each frequency can be obtained. In step S 11 , the distance FFT processor  12  may perform the first FFT process on the digital beat signal supplied from the AD converter  35 . 
     When the first FFT process is performed on the beat signal in step S 11 , the determination processor  18  determines whether the peak in the result obtained by performing the first FFT process is equal to or higher than the first threshold value (step S 12 ), among the generated beat signals. 
     Here, to set the first threshold value will be described.  FIG. 6  is a diagram explaining an example to set the first threshold value. 
       FIG. 6  is a diagram showing an example of the result of performing the first FFT process on the beat signal in step S 11 , for example. In  FIG. 6 , the horizontal axis represents the frequency f, and the vertical axis represents the signal strength (electric power) P. In the example shown in  FIG. 6 , when the frequency is in the region of fr 1  and the frequency is in the region of fr 2 , the signal strength shows a value close to Pa. Further, in the example shown in  FIG. 6 , when the frequency is f 1 , the signal strength shows the peak value P (f 1 ). 
     In an embodiment, the determination processor  18  sets the power threshold value Pth so that the peak value of power P (f 1 ) can be detected for example. Here, the threshold Pth may be set based on the average value of the power when frequencies are in the region fr 1  and/or the region fr 2  other than the peripheral region including the frequency f 1  when the electric power reaches the peak value P (f 1 ) for example. For example, in  FIG. 6 , when the frequencies are in the region fr 1  and/or the region fr 2 , the average signal strength shows a value close to Pa. Therefore, the average value of the electric power shall be Pa when frequencies are in the region fr 1  and/or the region fr 2  other than the peripheral region including the frequency f 1  when the electric power reaches the peak value P (f 1 ). In this case, the average value Pa of the electric power plus a prescribed value may be set as the electric power threshold value Pth. Further, when setting the electric power threshold value Pth, the guard band may be excluded in the peripheral region including the frequency f 1  when the electric power reaches the peak value P (f 1 ). 
     Thus, by setting the power threshold value Pth, the determination processor  18  can determine whether the peak in a result obtained by performing the first FFT process on the beat signal is equal to or higher than the first threshold value. 
     In step S 12  shown in  FIG. 5 , it is determined whether the peak in a result obtained by performing the first FFT process on the beat signal is equal to or higher than the first threshold value. When it is determined in step S 12  that the peak is equal to or higher than the first threshold value, the determination processor  18  performs the operation in step S 13  and ends the process shown in  FIG. 5 . On the other hand, when it is determined in step S 12  that the peak is lower than the first threshold value, the determination processor  18  ends the process shown in  FIG. 5  without performing the operation in step S 13 . 
     In step S 13 , the determination processor  18  counts the beat signal in which the peak in the result obtained by performing the first FFT process has been determined to be equal to or higher than the first threshold value as the first sample. For example, in step S 13 , the determination processor  18  may store the first sample in an internal memory of the storage  40  or the controller  10  for later process. In step S 11 , the beat signal on which the first FFT process is performed may be a unit of, for example, one chirp signal (such as c 1  shown in  FIG. 3 ). Therefore, in step S 13 , one chirp signal may be counted as the first sample. 
     As described above, the distance FFT processor  12  may generate the first sample from one chirp signal in step S 4  shown in  FIG. 4 . 
     When the first sample is generated in step S 4 , the determination processor  18  determines whether the process of step S 4  has been performed on all of the chirp signals included in one subframe (step S 5 ). In step S 5 , the determination processor  18  may determine whether the process of step S 4  has been performed on eight chirp signals (for example, c 1  to c 8  shown in  FIG. 3 ) included in one subframe (for example, subframe  1  shown in  FIG. 3 ). 
     When it is determined in step S 5  that the process in step  4  has not yet been performed on some of the chirp signals included in one subframe, the controller  10  returns to step S 1  and continues the process. 
     On the other hand, when it is determined in step S 5  that the process in step  4  has been performed on all of the chirp signals in one subframe, the controller  10  performs the process in step S 6 . A case of proceeding to step S 6  means that, for example, the first FFT process has been performed on all of eight chirp signals (c 1  to c 8 ) included in the subframe  1  shown in  FIG. 3 . Then, when proceeding to step S 6 , among the eight chirp signals (c 1  to c 8 ) described above, chirp signals in which the peak in the result obtained by performing the first FFT process is equal to or higher than the first threshold value are counted as the first sample. 
     When it is determined in step S 5  that the process of step S 4  has been performed on all of the chirp signals included in one subframe, the controller  10  generates the second sample described above from the generated first sample (step S 6 ). 
     Hereinafter, the process of step S 6  will be further described.  FIG. 7  is a flowchart explaining the process of step S 6  in  FIG. 4  in more detail. 
     When the process of step S 6  shown in  FIG. 4  starts, the speed FFT processor  14  performs a second FFT process on the first sample generated in step S 4  as shown in  FIG. 7  (step S 21 ). In step S 21 , the speed FFT processor  14  may perform a second FFT process on the result obtained by the first FFT process performed by the distance FFT processor  12 . 
     After the second FFT process is performed in step S 21 , the determination processor  18  determines whether the peak in the result obtained by performing the second FFT process is equal to or higher than the second threshold, among the first samples on which the second FFT process has been performed (step S 22 ). 
     Here, to set the second threshold value will be described.  FIG. 8  is a diagram explaining an example to set the second threshold value. 
       FIG. 8  is a diagram showing an example of the result obtained by performing a second FFT process on the first sample in step S 21 , for example. In  FIG. 8 , the horizontal axis represents the speed v and the vertical axis represents the signal strength (electric power) P. In the example shown in  FIG. 8 , when the speed is in the region of vr 1  and the speed is in the region of vr 2 , the signal strength shows a value close to P′a. Further, in the example shown in  FIG. 8 , when the speed is v 1 , the signal strength shows the peak value P′(v 1 ). 
     In an embodiment, the determination processor  18  sets the power threshold value P′th so that, for example, the peak value P′(v 1 ) of the electric power can be detected. Here, the threshold value P′th may be set based on, for example, the average value of the electric power in the region vr 1  and/or the region vr 2  other than the peripheral region including the speed v 1  when the electric power reaches the peak value P′ (v 1 ). For example, in  FIG. 8 , when the speed is in the region vr 1  and/or the region vr 2 , the average signal strength shows a value close to P′a. Therefore, the average value of the electric power in the region vr 1  and/or the region vr 2  other than the peripheral region including the speed v 1  when the electric power reaches the peak value P′(v 1 ) be P′a for example. In this case, the average value of power P′a plus a prescribed value may be set as the power threshold value P′th. Further, when setting the power threshold value P′th, a guard band may be removed in the peripheral region including the speed v 1  when the electric power reaches the peak value P′(v 1 ). 
     Thus, by setting the power threshold value P′th, the determination processor  18  can determine whether the peak in a result obtained by performing the second FFT process on the first sample is equal to or higher than the second threshold value. 
     In step S 22  shown in  FIG. 7 , it is determined whether the peak in a result obtained by performing the second FFT process on the first sample is equal to or higher than the second threshold value. When it is determined in step S 22  that the peak is equal to or higher than the second threshold value, the determination processor  18  performs the operation in step S 23  and ends the process shown in  FIG. 7 . On the other hand, when it is determined in step S 22  that the peak is lower than the second threshold value, the determination processor  18  ends the process shown in  FIG. 7  without performing the operation in step S 23 . 
     In step S 23 , the determination processor  18  counts the first sample in which the peak in the result obtained by performing the second FFT process has been determined to be equal to or higher than the second threshold value as the second sample. For example, in step S 23 , the determination processor  18  may store the second sample in an internal memory of the storage  40  or the controller  10  for later process. In step S 21 , the first sample on which the second FFT process is performed may use chirp signals (for example, c 1  to c 8  shown in  FIG. 3 ) included in one subframe as a unit, for example. Therefore, the chirp signal included in one subframe may be used as a unit to be counted as the second sample in step S 23 . 
     As described above, the speed FFT processor  14  generates the second sample from the chirp signal included in one subframe in step S 6  shown in  FIG. 4 . 
     When the second sample is generated in step S 6 , the determination processor  18  determines whether the process of step S 6  has been performed on the chirp signals in all of the subframes included in one frame (step S 7 ). In step S 7 , the determination processor  18  may determine whether the process in step S 6  has been performed on all of the chirp signals in the 16 subframes (subframe  1  to subframe  16  shown in  FIG. 3 ) included in one frame (for example, frame  1  shown in  FIG. 3 ). 
     If it is determined in step S 7  that the process in step S 6  has not yet been performed on some of the chirp signals included in one frame, the controller  10  returns to step S 1  and continues the process. 
     On the other hand, when it is determined in step S 7  that the process in step S 6  has been performed on the chirp signals in all of the subframes included in one frame, the controller  10  performs the process in step S 8 . A case of proceeding to step S 8  means, for example, that the second FFT process has been performed on the 16 subframes (subframe  1  to subframe  16 ) included in frame  1  shown in  FIG. 3 . Then, when proceeding to step S 8 , among the first samples included in the 16 subframes described above, the first samples in which the peak in the result obtained by performing the second FFT process is equal to or higher than the second threshold value are counted as the second sample. 
     In step S 8 , the arrival angle estimator  16  estimates the arrival direction (arrival angle θ) of the reflected wave R based on the generated second sample (step S 8 ). In step S 8 , the arrival angle estimator  16  may estimate the arrival direction of the reflected wave R based on, for example, the covariance matrix obtained by the second sample. 
     For example, the covariance matrix for estimating the arrival direction (angle of arrival θ) may be obtained using the complex signal (cx) of the peak of the second sample in which the peak in the result obtained by performing the second FFT process in one frame (16 subframes) of the transmitted signal described above is equal to or higher than the second threshold. In this case, an arithmetic operation of the covariance matrix cr may be performed, for example, according to the following equation (1): 
     
       
         
           
             
               
                 
                   
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                             cx 
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     Here, cx represents the complex signal of the peak after the speed Fourier transform, and conj (cx) represents the conjugate complex number of cx. Further, k and 1 represent the antenna numbers, and N represents the number of samples in the covariance matrix. 
     As described above, the electronic device  1  according to an embodiment estimates the arrival direction (arrival angle θ) of the reflected wave R based on the transmitted signal and the received signal. The electronic device  1  according to an embodiment may generate the first sample based on the result obtained by performing the first FFT process on the beat signal generated based on the transmitted signal and the received signal. Here, the first sample may be, for example, a set of chirp signals. Further, the electronic device  1  according to an embodiment may generate the second sample based on the result of performing the second FFT process on the first sample. Here, the second sample may be, for example, a set of subframes. Then, the electronic device  1  according to an embodiment can estimate the arrival direction (arrival angle θ) of the reflected wave R based on the second sample. Here, the electronic device  1  may estimate the arrival direction of the reflected wave R based on the covariance matrix obtained by the second sample. Further, the electronic device  1  according to an embodiment may estimate the arrival direction (arrival angle θ) of the reflected wave R based on the covariance matrix obtained by the second sample. 
     Further, as described above, among the generated beat signals generated based on the transmitted signal and the received signal, the first sample may be one in which the peak in the result obtained by performing the first FFT process is equal to or higher than the first threshold value. Here, the first threshold value may be set based on an average of power (electric power) corresponding to a region excluding the prescribed region including the peak in a result obtained by performing the first FFT process. 
     Further, as described above, among the first samples, the second sample may be one in which the peak in the result obtained by performing the second FFT process is equal to or higher than the second threshold value. Here, the second threshold value may be set based on an average of power (electric power) corresponding to a region excluding the prescribed region including the peak in the result obtained by performing the second FFT process. 
     That is, the electronic device  1  according to an embodiment performs the speed Fourier transform process using a plurality of (for example, eight) chirp signals on a distance in which the peak in a result obtained by performing the distance Fourier transform process is equal to or higher than the threshold value. Further, the electronic device  1  according to an embodiment counts how many subframes, having the speed at which the peak in the result obtained by performing the speed Fourier transform process is equal to or higher than the threshold value, lasts. Thus, the electronic device  1  according to an embodiment estimates the arrival direction of the reflected wave by obtaining the correlation matrix using the complex signal in which the peak in the result obtained by performing the speed Fourier transform is equal to or higher than the threshold value. 
     According to an embodiment of the electronic device  1 , the accuracy of measuring the arrival direction (arrival angle θ) of the reflected wave R can be improved. 
     When the arrival direction (angle of arrival θ) of the reflected wave R obtained by the reflection, that the transmitted wave T is reflected by a prescribed object, is estimated by using the conventional radar technique, the error in the angle estimation may become large. In particular, when a plurality of reflecting bodies exist in the range having the same distance and the same relative speed, the angle estimation error of the arrival angle θ becomes large. Further, recently, the research has been conducted to apply an eigenspace analysis, such as MUSIC (MUltiple SIgnal Classification), to an array radar, which estimates the direction of the arrival waves incoming to the array antenna with high angular resolution. However, according to such a method, the larger the noise, the larger the detection error. 
     On the other hand, according to an embodiment of the electronic device  1 , the noise can be removed before calculation using an algorithm such as the MUSIC, for example. Therefore, according to an embodiment of the electronic device  1 , the estimation error of the arrival direction of the reflected wave R can be reduced. 
     Further, according to an embodiment of the electronic device  1 , when the peak in the result obtained by performing the second FFT process for obtaining the relative speed is equal to or higher than the second threshold, it is adopted as the second sample. Therefore, according to an embodiment of the electronic device  1 , interference waves from the objects other than those existing in the range having the same distance and the same relative speed can be reduced. 
     Further, according to an embodiment of the electronic device  1 , a plurality of samples are used for the covariance matrix, that is calculated when estimating the arrival direction of the reflected wave R. Therefore, according to the embodiment of the electronic device  1 , even when a plurality of objects exist at the same time in the range having the same distance and the same relative speed, the arrival direction of the reflected wave R from each of the objects can be estimated. 
     Also, in general, when the arrival direction of the reflected wave R from the object with a high relative speed is estimated by using the radar technique, the object does not necessarily exist in the distance range during transmitting and receiving the chirp signal for obtaining the covariance matrix. According to an embodiment of the electronic device  1 , the arrival direction of the reflected wave R from the object is estimated by adopting only the signal in the distance range. Therefore, according to an embodiment of the electronic device  1 , the influence of noise and/or interference can be reduced in estimating the arrival direction of the reflected wave R. Here, “that distance” described above is the distance indicated by the step of the distance FFT. When the relative speed between the object  200  and the sensor  5  is fast, the object  200  may move from that distance step to the next distance step during all subframe time. In this case, the object does not exist in the distance range during transmitting and receiving the chirp signal for obtaining the covariance matrix. 
     Next, other embodiments will be described. 
     In the embodiment described above, among the beat signals generated based on the transmitted and the received signals, only the ones in which the peak in the result obtained by performing the first FFT process is equal to or higher than the first threshold value are considered as the first samples. Further, in the embodiment described above, among the first samples, only the ones in which the peak in the result obtained by performing the second FFT process is equal to or higher than the second threshold value are considered as the second samples. However, in an embodiment, for example, when there are one or more prescribed number of beat signals, among the generated beat signals, in which the peak in the result obtained by performing the first FFT process is equal to or higher than the first threshold value, the first sample may be all of the beat signals in subframes that include the beat signal. Further, in an embodiment, for example, when there are one or more prescribed number of beat signals, among the generated first samples, in which the peak in the result of performing the second FFT process is equal to or higher than the second threshold value, the second sample may be all of the first samples in subframes that include the first samples. 
     Thus, in an embodiment, when there are any beat signals in which the peak in the result obtained by performing the first fast Fourier transform process is equal to or higher than a first threshold value, the first samples may be all of beat signals in subframes that include the beat signal. Further, in an embodiment, when there are any first samples in which the peak in the result obtained by performing the second FFT process is equal to or higher than the second threshold value, the second sample may be all of first samples in frames that include the first sample. 
     The present disclosure has been described based on the drawings and examples, but it should be noted that those skilled in the art will find it easy to make various transformations or modifications based on the present disclosure. Therefore, it should be noted that these transformations or modifications are included in the scope of this disclosure. For example, the functions and the like included in each functional part can be rearranged in a logically consistent manner. A plurality of functional parts and the like may be combined together or divided into one. Each of the embodiments described above according to the present disclosure is not limited to faithful implementation of the each embodiment described above, and may be implemented by appropriately combining the features together or omitting a part thereof. That is, the contents of the present disclosure can be transformed and modified by those skilled in the art based on the present disclosure. Therefore, these transformations and modifications are within the scope of this disclosure. For example, in each embodiment, each functional part, each means, each step and the like are added to other embodiments in a logically consistent manner, or can be replaced with each functional part, each means, each step and the like of other embodiments. Further, in each embodiment, it is possible to combine a plurality of each functional part, each means, each step, and the like into one or divide them. Further, each embodiment of the present disclosure described above is not limited to faithful implementation of each described embodiment, and may be implemented by combining each feature together or omitting some of them, as appropriate. 
     The above-described embodiment is not limited to the embodiment as the electronic device  1 . For example, the above-described embodiment may be implemented as the control method for the device such as the electronic device  1 . Further, for example, the above-described embodiment may be implemented as the control program for the device such as the electronic device  1 . 
     The electronic device  1  according to an embodiment may comprise, for example, only the controller  10  as the minimum configuration. On the other hand, in addition to the controller  10 , the electronic device  1  according to an embodiment may be configured to include at least one of the signal generator  21 , the synthesizer  22 , the phase controller  23 , the amplifier  24 , and the transmitting antenna  25 , as shown in  FIG. 3 , as appropriate. The electronic device  1  according to an embodiment may also be configured to include at least one of the receiving antenna  31 , the LNA  32 , the mixer  33 , the IF part  34 , and the AD converter  35 , as appropriate, in place of or together with the functional parts described above. The electronic device  1  according to an embodiment may be configured to further include the storage  40 . As described above, the electronic device  1  according to an embodiment can adopt various configuration modes. Further, when the electronic device  1  according to an embodiment is mounted on the mobile body  100 , for example, at least one of the above-mentioned functional parts may be installed in any appropriate places such as inside of the mobile body  100 . On the other hand, in an embodiment, for example, at least one of the transmitting antenna  25  and the receiving antenna  31  may be installed outside of the mobile body  100 . 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  Electronic device 
               5  Sensor 
               10  Controller 
               12  Distance FFT processor 
               14  Speed FFT processor 
               16  Arrival angle estimator 
               18  Determination processor 
               20  Transmitter 
               21  Signal generator 
               22  Synthesizer 
               23  Phase controller 
               24  Amplifier 
               25  Transmitting antenna 
               30  Receiver 
               31  Receiving antenna 
               32  LNA 
               33  Mixer 
               34  IF part 
               35  AD converter 
               40  Storage 
               50  ECU 
               100  Mobile body 
               200  Object (Body)