Object detection system, object detection device, object detection program

Abstract

To provide an object detection system that can improve detection accuracy. [Solution] The object detection system comprises a transmitter that transmits radio waves and a receiver that receives radio waves, and the receiver, which receives radio waves transmitted from the transmitter, detects objects that have reflected the radio waves. The receiver has a processor configured to acquire a received signal by receiving radio waves, estimate the Doppler shift of the radio waves that occurs according to the relative speed between the transmitter and the receiver, correct the received signal by canceling the estimated Doppler shift component from the received signal, estimate the speed of the object that reflected the radio waves from the corrected received signal, and correct the estimated speed in correlation with the Doppler shift.

Description

[Technical Field]

[0001] This disclosure relates to object detection technology. [Background technology]

[0002] Patent Document 1 discloses a method for detecting the location of an object based on bistatic radio. This method includes a receiving device determining the location of a remote transmitting device that transmits a WWAN reference signal. This method includes obtaining the Time of Flight (ToF) and angle of arrival of the reflected WWAN reference signal reflected by a remote object. This method includes determining the location of a remote object based on the location of the remote transmitting device, the ToF, and the angle of arrival. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Special Publication No. 2023-527637 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In bistatic object detection, if at least one of the transmitters or receivers is mounted on a moving object, noise caused by Doppler shift due to movement may be introduced into the received signal. In such cases, the accuracy of object detection may decrease.

[0005] The object of this disclosure is to provide an object detection system capable of improving detection accuracy. Another object of this disclosure is to provide an object detection device capable of improving detection accuracy. Yet another object detection program capable of improving detection accuracy. [Means for solving the problem]

[0006] The following describes the technical means of solving the problem described in this disclosure. Note that the claims and the reference numerals in parentheses in this section indicate the correspondence with the specific means described in the embodiments detailed later, and do not limit the technical scope of this disclosure.

[0007] A first aspect of the present disclosure is an object detection system comprising a transmitter (20) that transmits radio waves (W) and a receiver (30) that receives radio waves, at least one of which is mounted on a mobile body (3), and which detects an object (T) that has reflected radio waves, The receiver is The process of obtaining a received signal by receiving radio waves, To estimate the amount of Doppler shift (Δf) of radio waves that occurs depending on the relative speed between the transmitter and receiver, This involves removing the estimated Doppler shift component from the received signal to correct the received signal, and From the corrected received signal, we estimate the speed of the object that reflected the radio waves, Correcting the estimated velocity in correlation with the amount of Doppler shift, It has a processor (322) configured to perform the following.

[0008] A second aspect of the present disclosure is an object detection device having a processor (322), which receives radio waves from a transmitter (20) that transmits radio waves and detects an object (T) that has reflected the radio waves, The processor is The process of obtaining a received signal by receiving radio waves, To estimate the amount of Doppler shift (Δf) of radio waves that occurs depending on the relative speed between the transmitter and the receiver, This involves removing the estimated Doppler shift component from the received signal to correct the received signal, and From the corrected received signal, we estimate the speed of the object that reflected the radio waves, Correcting the estimated velocity in correlation with the amount of Doppler shift, It is configured to execute.

[0009] A third aspect of the present disclosure is an object detection program stored in a storage medium (321) and including instructions for causing a processor (322) to execute, in an object detection system (1) including a transmitter (20) that transmits radio waves and a receiver (30) that receives radio waves, at least one of which is mounted on a moving body (3), for detecting an object (T) that reflects radio waves, acquiring a reception signal by receiving radio waves; estimating a Doppler shift amount (Δf) of the radio waves that occurs according to a relative speed between the transmitter and the receiver; removing components of the estimated Doppler shift amount from the reception signal to correct the reception signal; estimating a speed of an object that reflects radio waves from the corrected reception signal; correcting the estimated speed in correlation with the Doppler shift amount; including instructions for causing the above to be executed.

[0010] According to these first to third aspects, the reception signal can be corrected by estimating the Doppler shift amount and removing it from the reception signal. Further, the speed of the object can be corrected in correlation with the Doppler shift. Therefore, while removing the components of the Doppler shift that can be a factor of noise from the reception signal, the speed changed by this removal process can be corrected in correlation with the Doppler shift amount. Therefore, it is possible to improve the detection accuracy of the object.

Brief Description of the Drawings

[0011] [Figure 1] It is a schematic diagram showing the overall configuration of the object detection system. [Figure 2] It is a block diagram showing the schematic configuration of the communication device. [Figure 3] It is a schematic diagram for explaining a transmission signal transmitted from a communication device on the transmitter side. [Figure 4] It is a block diagram showing the functional configuration of the communication device on the receiver side. [Figure 5] It is a flowchart showing an object detection flow according to the first embodiment. [Figure 6]This is a graph for explaining the velocity spectrum when Doppler shift correction is performed. [Figure 7] This is a flowchart showing the object detection flow according to the third embodiment. [Figure 8] This is a flowchart showing the object detection flow according to the fourth embodiment. [Figure 9] This is a schematic diagram for explaining the synthesis of multiple frames. [Figure 10] This is a flowchart showing the object detection flow according to the fifth embodiment. **Embodiments for Carrying Out the Invention**

[0012] Hereinafter, multiple embodiments of the present disclosure will be described based on the drawings. In each embodiment, corresponding components may be given the same reference numerals, and redundant explanations may be omitted. Also, when only a part of the configuration is described in each embodiment, the configurations of other embodiments described previously can be applied to other parts of the said configuration. Furthermore, not only the combinations of configurations explicitly shown in the description of each embodiment, but also the configurations of multiple embodiments can be partially combined with each other as long as there is no problem with the combination, even if not explicitly stated.

[0013] (First Embodiment) Regarding the first embodiment of the present disclosure, it will be described with reference to FIGS. 1 to 6. The object detection system 1 shown in FIG. 1 includes at least two communication devices 20 and 30. The communication devices 20 and 30 are configured to be able to transmit and receive data to and from each other by wireless communication. The communication devices 20 and 30 utilize the radio wave W transmitted in wireless communication to detect an object T that reflects the radio wave W. That is, the object detection system 1 is provided by a wireless communication system for data exchange. In other words, in the object detection system 1 of the present embodiment, the communication function and the sensing function for detecting the object T are integrated.

[0014] The object detection system 1 performs bistatic sensing by receiving radio waves W transmitted from one of two communication devices 20 and 30 mounted on different objects on the other. In the following, it is assumed that communication device 20 functions as a transmitter and communication device 30 functions as a receiver during sensing. In this case, communication device 30 is an example of an "object detection device".

[0015] At least one of the communication devices 20 and 30 is mounted on a mobile device. For example, communication device 20 is mounted on base station 2, and communication device 30 is mounted on vehicle 3, which is a mobile device.

[0016] Base station 2 is a facility that conducts wireless communication with vehicle 3. Base station 2 is configured to enable wireless communication compliant with wireless communication standards such as LTE (Long Term Evolution), 4G, 5G, 6G, and Wi-Fi.

[0017] As shown in Figure 2, the communication device 20 comprises a communication unit 21 and a control unit 22. The communication device 20 functions as a transmitter in object detection. The communication unit 21 is a unit for performing the transmission and reception processing of communication signals in the wireless communication described above. The communication unit 21 has an antenna and a communication circuit (not shown). The antenna is, for example, an array antenna in which multiple antenna elements are arranged. In the transmission process, the communication unit 21 performs D / A conversion of the digital transmission signal generated by the control unit 22 using the communication circuit. The communication unit 21 transmits the D / A converted transmission signal from the antenna, thereby radiating the transmission signal into space as radio waves W. In the reception process, the communication unit 21 receives the radio waves W transmitted from the vehicle 3, etc., using the antenna and converts it into a received signal. The communication unit 21 performs A / D conversion of the received signal using the communication circuit and outputs the converted received signal to the control unit 22.

[0018] The control unit 22 is configured to include at least one dedicated computer. The dedicated computer comprising the control unit 22 has at least one memory 221 and at least one processor 222. The memory 221 is a storage medium that non-temporarily stores programs and data that can be read by the computer. The memory 221 is at least one type of non-transitory tangible storage medium, such as semiconductor memory, magnetic media, and optical media. Here, storage may be storage in which data is retained even when the power supply is turned off, or temporary storage in which data is erased when the power supply is turned off. The processor 222 includes at least one type as a core, such as a CPU (Central Processing Unit), GPU (Graphics Processing Unit), RISC (Reduced Instruction Set Computer)-CPU, DFP (Data Flow Processor), and GSP (Graph Streaming Processor).

[0019] The dedicated computer constituting the control unit 22 may have at least one of the digital circuit and analog circuit as a processor 222. Here, the digital circuit is at least one of the following, for example, ASIC (Application Specific Integrated Circuit), FPGA (Field Programmable Gate Array), SOC (System on a Chip), PGA (Programmable Gate Array), and CPLD (Complex Programmable Logic Device). Furthermore, such a digital circuit may have a memory 221 that stores a program.

[0020] In the transmission process, the control unit 22 modulates the transmission data to generate a transmission signal and outputs it to the communication unit 21. For example, the control unit 22 modulates the transmission data using orthogonal frequency division multiplexing (OFDM). Specifically, the control unit 22 divides and modulates the transmission data into multiple data signals Sd, which are subcarrier signals of different frequencies within the transmission band. The frequency of each data signal Sd is set such that the spectral peaks substantially coincide at the position where the intensity of other data signals Sd is zero. The control unit 22 defines the bits of the transmission data by the phase of each data signal Sd. In the following, each of the divided data signals Sd may be referred to as a symbol. The control unit 22 generates multiple frequency-divided data signals Sd for each symbol transmission period Ts within a specified frame FR.

[0021] In addition, the control unit 22 generates a reference signal Sr within the frame FR, in addition to the data signal Sd which is the modulated transmitted data. The reference signal Sr is a signal generated for the receiver to perform channel estimation, etc. The reference signal Sr may also be called a pilot signal. The reference signal Sr has a pre-set phase (set phase) at the time of transmission and is a signal that is shared with the receiver as known information.

[0022] The reference signal Sr is repeatedly generated at a predetermined time interval within a single frame FR, as shown in Figure 3, for example. Furthermore, multiple reference signals Sr are generated at a predetermined frequency interval within a single symbol transmission period Ts in which they are generated. In other words, multiple symbols of the reference signal Sr are generated in both the time domain and the frequency domain.

[0023] In the control unit 22, the processor 222 executes a number of instructions included in the processing program stored in the memory 221 to control the transmission signal generation process described above. The processor 222 is also configured to execute a number of instructions included in the processing program stored in the memory 221 to demodulate data from the received signal.

[0024] The communication device 30 is mounted on the vehicle 3. The communication device 30 functions as a receiver in object detection. The communication device 30 comprises a communication unit 31 and a control unit 32. The communication unit 31, like the communication unit 21, is a unit for performing the transmission and reception of communication signals in wireless communication. The communication unit 31 has an array antenna and a communication circuit. In the reception process, the communication unit 31 receives radio waves W transmitted from the base station 2, etc., with its antenna and converts them into a received signal. The communication unit 31 performs A / D conversion of the received signal with its communication circuit and outputs the converted received signal to the control unit 32.

[0025] Here, the received signal may include a direct signal derived from a direct wave Wd, which is received when the radio wave W transmitted from the communication device 20 arrives directly at the object T without being reflected. The received signal may also include a reflected signal derived from a reflected wave Wr, which is received when the radio wave W is reflected at the object T.

[0026] The control unit 32 processes the received signal to acquire the transmitted data and detect the object T. The control unit 32 is configured to include at least one dedicated computer. The dedicated computer comprising the control unit 32 has at least one memory 321 and one processor 322. The memory 321 is a storage medium that non-temporarily stores programs and data that can be read by the computer. The memory 321 is at least one type of non-transitional physical storage medium, such as semiconductor memory, magnetic media, and optical media. Here, storage may be storage in which data is retained even when the power supply is turned off, or it may be temporary storage in which data is erased when the power supply is turned off. The processor 322 includes at least one type as a core, such as a CPU, GPU, RISC-CPU, DFP, and GSP.

[0027] The dedicated computer constituting the control unit 32 may have at least one of the digital circuit and analog circuit as a processor 322. Here, the digital circuit is at least one of the following, for example, ASIC, FPGA, SOC, PGA, and CPLD. Such a digital circuit may also have a memory 321 that stores a program.

[0028] In the control unit 32, the processor 322 executes multiple instructions included in the object detection program stored in the memory 321 to control the communication device 30. This causes the control unit 32 to construct multiple functional blocks for object detection. These functional blocks, as shown in Figure 4, include an acquisition block 110, a Doppler estimation block 120, a Doppler correction block 130, an object estimation block 140, an object correction block 150, and a demodulation block 160.

[0029] The acquisition block 110 acquires the received signal from the communication unit 31. The acquisition block 110 also performs frame detection on the acquired received signal.

[0030] The Doppler estimation block 120 estimates the Doppler shift amount Δf of the radio wave W that occurs according to the relative speed between the communication devices 20 and 30, from the acquired received signal. For example, the Doppler estimation block 120 estimates the Doppler shift amount Δf based on the phase change of the reference signal.

[0031] The Doppler correction block 130 corrects the received signal by canceling the Doppler shift component from the received signal.

[0032] The object estimation block 140 estimates the state of object T based on the received signal. The state of object T is target information (object information) including, for example, the distance to object T, the relative velocity to object T, and the relative angle of object T. The object estimation block 140 obtains the above target information as information correlated with the received signal by performing a discrete Fourier transform on the received signal.

[0033] Object correction block 150 corrects the estimated target information. Specifically, object correction block 150 corrects the relative velocity within the target information. Object correction block 150 calculates the Doppler velocity correlated with the Doppler shift estimated by Doppler estimation block 120, and corrects the relative velocity by adding this Doppler velocity to the estimated relative velocity.

[0034] The demodulation block 160 demodulates the data from the received signal based on the channel estimation result. The demodulation block 160 outputs the demodulated data.

[0035] The object detection method, which detects objects through the combined action of these blocks 110, 120, 130, 140, 150, and 160, is executed according to the object detection flow shown in Figure 5. This object detection flow is executed repeatedly while the communication device 30 is running. In this object detection flow, each "S" represents multiple steps executed by multiple instructions included in the object detection program.

[0036] First, in S10, the acquisition block 110 acquires the received signal, which is the radio wave W received by the communication unit 31 that has been converted.

[0037] Next, in S20, the acquisition block 110 performs frame detection on the received signal. Specifically, the acquisition block 110 extracts a specific signal pattern that was inserted during transmission. Then, based on this signal pattern, the acquisition block 110 identifies the starting point of frame FR.

[0038] Then, in S30, the Doppler estimation block 120 estimates the Doppler shift amount Δf of the radio wave W that occurs according to the relative speed between the communication devices 20 and 30. For example, the Doppler estimation block 120 estimates the Doppler shift amount Δf based on the phase change of the reference signal Sr. The Doppler estimation block 120 compares the set phase of the reference signal Sr, which is stored in advance in the memory 321, with the received phase, which is the phase of the reference signal Sr that is actually received. The Doppler estimation block 120 estimates the Doppler shift amount Δf by converting the amount of phase change from the set phase of the received phase into a frequency change.

[0039] Furthermore, if multiple symbols of the reference signal Sr are generated in a single frame FR as in this embodiment, the Doppler estimation block 120 may integrate the phase change amounts calculated for each symbol by taking an average or the like. Alternatively, the Doppler estimation block 120 may adopt the phase change amount of a specific symbol as a representative value.

[0040] Next, in S40, the Doppler correction block 130 performs Doppler shift correction. Specifically, the Doppler correction block 130 cancels a component (phase component) corresponding to the Doppler shift amount Δf in the received signal.

[0041] Here, the received signal r before correction x The corrected received signal r after canceling the phase component from (μ) xc (μ) can be defined by the following equation (1). Note that in equation (1), f s μ represents the sampling frequency. μ is the index of each symbol, and is an integer greater than or equal to zero and less than or equal to the number of waveform samples minus 1.

number

[0042] In the subsequent S50, the object estimation block 140 receives the corrected received signal r xc Channel estimation is performed based on (μ). In channel estimation, object estimation block 140 uses the corrected received signal rxc In (μ), the phase change from the time of transmission is calculated for at least the symbols of the reference signal Sr. The object estimation block 140 only needs to calculate the phase change from the set phase for each symbol of the reference signal Sr. Then, in S60, the object estimation block 140 defines the phase change for each symbol of the reference signal Sr as a propagation matrix, which is a matrix of time and frequency.

[0043] Next, in S70, the object estimation block 140 performs a 3D-DFT (Discrete Fourier Transform) on the propagation matrix. Specifically, the object estimation block 140 performs a 1D-DFT on the propagation matrix in the time domain, and then a 1D-IDFT (Inverse Discrete Fourier Transform) on it in the frequency domain to generate a two-dimensional spectrum of velocity and distance. Then, the object correction block 150 performs another 1D-DFT on the two-dimensional spectrum for each antenna to obtain a three-dimensional spectrum of distance, velocity, and angle.

[0044] In the subsequent S80, the object estimation block 140 extracts the peak of object T from the three-dimensional spectrum. This allows the object estimation block 140 to identify the position of the peak on the spectrum and obtain the corresponding target information for object T. Specifically, the object estimation block 140 obtains distance, velocity, and angle information for object T.

[0045] Then, in S90, the object correction block 150 performs velocity correction, which corrects the velocity information obtained by peak extraction in correlation with the Doppler shift amount Δf. Specifically, the object estimation block 140 synthesizes the relative velocity portion between communication devices 20 and 30, which was lost from the peak velocity information due to the Doppler shift correction, into the velocity information.

[0046] Regarding the relative speed lost due to Doppler shift correction, as shown in the velocity spectrum of FIG. 6, the noise level in the spectrum is reduced by Doppler shift correction. This is because the error in channel estimation caused by Doppler shift is suppressed. On the other hand, since the Doppler shift is caused by the relative speed between the communication devices 20 and 30, canceling the Doppler shift amount Δf causes the peak position on the velocity spectrum indicating the object T to move by the relative speed between the communication devices 20 and 30 from its original position. Therefore, the velocity v of the object T obtained at the time of S80 d is velocity information that does not include the relative speed between the communication devices 20 and 30. The object correction block 150 adds the relative speed between the communication devices 20 and 30 based on the estimated Doppler shift amount Δf to the velocity v d before correction, thereby correcting the velocity v d of the object T. The relative speed corresponds to the "correlation speed".

[0047] The corrected velocity v d obtained by synthesizing the relative speed to the velocity v before correction is defined by the following formula (2). In formula (2), c is the speed of light, and f dc is the center frequency of the radio wave W. The object correction block 150 calculates the corrected velocity v c based on the relationship of formula (2). dc

Equation

[0048] In the subsequent S100, the object correction block 150 outputs target information including the corrected velocity information. For example, the object estimation block 150 outputs the target information to other in-vehicle ECUs (Electronic Control Units) via the in-vehicle network. The in-vehicle ECU executes various processes related to the running control of the vehicle 3 based on the acquired target information. Examples of the processes based on the target information include, for example, running trajectory generation processing, collision avoidance processing, warning processing, etc.

[0049] ​Furthermore, this flow branches from S40 to S110. In S110, the demodulation block 160 demodulates the original data from the data signal Sd. For example, the demodulation block 160 performs channel estimation by calculating the phase change amount for the symbols of the data signal Sd through interpolation based on the phase change amount of the reference signal Sr. Then, the demodulation block 160 demodulates the data based on this channel estimation result. In the subsequent S120, the demodulation block 160 outputs the demodulated data to the vehicle ECU or the like, which is the target of the data output.

[0050] According to the first embodiment described above, the received signal can be corrected by estimating the Doppler shift and removing it from the received signal. Furthermore, the velocity of the object can be corrected in correlation with the Doppler shift. Therefore, while removing the Doppler shift component, which can be a source of noise, from the received signal, the velocity corresponding to the Doppler shift lost during the removal process can be corrected. Consequently, detection accuracy can be improved.

[0051] Furthermore, according to the first embodiment, the Doppler shift can be estimated based on the phase change of a reference signal whose phase is known. This makes it possible to estimate the Doppler shift using a reference signal transmitted in communication.

[0052] Furthermore, according to the first embodiment, the velocity is corrected by adding a relative velocity correlated with the Doppler shift to the velocity before correction.

[0053] (Second embodiment) The second embodiment is a modification of the first embodiment.

[0054] In the second embodiment, the communication device 20, acting as a transmitter, transmits its own location information and speed information as transmitter information.

[0055] The object detection flow of the second embodiment will be explained with reference to Figure 5. In this flow, the Doppler estimation block 120 in S30 estimates the Doppler shift amount Δf from the position information and velocity information of the communication device 20 and the position information and velocity information of the communication device 30. For example, the Doppler estimation block 120 can acquire the position information and velocity information of the communication device 20 itself transmitted from the communication device 20 via the communication unit 31. Alternatively, the Doppler estimation block 120 can acquire the position information and velocity information of the communication device 30 itself from a locator and vehicle speed sensor mounted on the vehicle 3. The Doppler estimation block 120 estimates the Doppler shift amount Δf based on the calculated relative velocity.

[0056] According to the second embodiment described above, the Doppler shift amount Δf is estimated based on the position information and velocity information acquired for each of the communication devices 20 and 30. Therefore, the Doppler shift amount Δf can be estimated by a simplified process that does not require calculation of phase changes of the reference signal, etc. Consequently, the processing load in Doppler shift estimation can be reduced.

[0057] (Third embodiment) As shown in Figure 7, the third embodiment is a modified version of the first embodiment.

[0058] The object detection flow of the third embodiment will be described with reference to Figure 7. This flow proceeds to S21 after the frame detection process in S20. In S21, the Doppler estimation block 120 analyzes the uncorrected received signal r x Channel estimation based on (μ) is performed. Next, in S22, the Doppler estimation block 120 defines the phase change amount of the reference signal symbols as a propagation matrix, which is a matrix of time and frequency. Then, in S23, the Doppler estimation block 120 performs 3D-DFT processing on the propagation matrix.

[0059] In the subsequent S24, the Doppler estimation block 120 extracts the peak corresponding to the direct signal, which is the radio wave W directly received from the transmitter, the communication device 20. For example, since the direct signal has a shorter propagation distance than the reflected signal, the Doppler estimation block 120 can extract the peak with the shortest distance in the distance spectrum as the peak corresponding to the direct signal. The peak corresponding to the direct signal represents the peak corresponding to the communication device 20. In other words, by extracting this peak, the Doppler estimation block 120 obtains the distance, relative velocity, and relative angle of the communication device 20.

[0060] In S30, which follows S24, the Doppler estimation block 120 estimates the Doppler shift amount Δf based on the relative speed of the communication device 20 obtained in processing S21 to S24.

[0061] According to the third embodiment described above, the relative speed of the communication device 20 is estimated based on the direct signal received by the receiver from the radio wave W transmitted from the communication device 20. Therefore, the Doppler shift amount Δf is estimated from this relative speed. Thus, it is possible to estimate the relative speed, and consequently the Doppler shift amount Δf, with high accuracy using a direct signal with relatively high intensity.

[0062] (Fourth embodiment) As shown in Figure 8, the fourth embodiment is a modification of the first embodiment.

[0063] The object detection flow of the fourth embodiment will be described with reference to Figure 8. This flow proceeds to S25 after the frame detection process in S20. In S25, the Doppler estimation block 120 determines whether or not a direct wave Wd from the communication device 20 has arrived.

[0064] Specifically, the Doppler estimation block 120 determines the presence or absence of a direct wave Wd based on the correlation between the distance between communication device 20 and communication device 30 and the strength of the received signal. For example, the Doppler estimation block 120 determines that a direct wave Wd is present if the signal strength of the received signal reaches the arrival strength range, which is the range expected when a direct wave Wd arrives. Here, the arrival strength range is defined as the range in which the signal strength is equal to or exceeds a threshold. The threshold defining the arrival strength range is defined as a value that decreases as the distance between communication device 20 and communication device 30 increases. For example, since the signal strength of a direct wave Wd is generally inversely proportional to the square of the distance, the threshold is also defined as a function inversely proportional to the square of the distance.

[0065] The distance between communication device 20 and communication device 30 may be obtained by transmitting position information from communication device 20, or by other means. Alternatively, the distance between communication device 20 and communication device 30 may be obtained from the peak of communication device 20 in the DFT distance spectrum obtained in the previous frame FR.

[0066] If it is determined that the direct wave Wd is arriving, this flow proceeds to S30. On the other hand, if it is determined that the direct wave Wd is not arriving, this flow skips S30 and S40 and proceeds to S50. In other words, the estimation and correction process of the Doppler shift amount Δf is performed when it is determined that the direct wave Wd is arriving, and is canceled when the direct wave Wd has not arrived.

[0067] Furthermore, in this embodiment, after S80, the flow proceeds to S85. In S85, it is determined whether or not a direct wave Wd is arriving, similar to S25. If it is determined that a direct wave Wd is arriving, the flow proceeds to S90. On the other hand, if it is determined that a direct wave Wd is not arriving, the flow skips S90 and proceeds to S100. In other words, the velocity correction process for object T is performed when it is determined that a direct wave Wd is arriving, and is canceled if a direct wave Wd has not yet arrived.

[0068] According to the fourth embodiment described above, if it is determined that the direct wave Wd has not arrived, the Doppler shift correction is skipped. Therefore, noise can be reduced by performing the Doppler shift correction only when the direct wave Wd, which is likely to be a major source of noise, has arrived. Furthermore, if the direct wave Wd has not arrived and the noise is likely to be relatively small, the computational load can be reduced by canceling the Doppler shift correction.

[0069] Furthermore, according to the fourth embodiment, the presence or absence of a direct wave Wd is determined based on the relationship between the distance between the communication device 20 and the communication device 30 and the strength of the received signal. Therefore, the presence or absence of a direct wave Wd can be determined with greater accuracy.

[0070] (Fifth embodiment) As shown in Figures 9 and 10, the fifth embodiment is a modification of the first embodiment.

[0071] In this embodiment, the number of times the reference signal Sr is transmitted in one frame FR is relatively small. For example, the communication device 20, acting as a transmitter, sets the time width of one frame FR to be smaller than in the first embodiment, and consequently sets the number of times the reference signal Sr is transmitted to be smaller as well. In the example shown in Figure 9, the communication device 20 transmits the reference signal once per frame FR.

[0072] In this case, the communication device 30, acting as a receiver, stores the received signals for multiple frames FR and performs sensing. That is, in this embodiment, the sensing period is longer than the transmission period of frame FR.

[0073] The object detection flow of the fifth embodiment will be described with reference to Figure 10. This flow proceeds from step S20 to S26. In S26, the Doppler estimation block 120 determines whether the estimation of the Doppler shift amount Δf has been completed for the current sensing period. In other words, the Doppler estimation block 120 determines whether the received frame FR is the first frame FR in the current sensing period.

[0074] If it is determined that the estimation of the Doppler shift amount Δf is incomplete, this flow proceeds to S30 to perform the estimation of the Doppler shift amount Δf. On the other hand, if it is determined that the estimation of the Doppler shift amount Δf is complete, this flow skips S30 and proceeds to S40.

[0075] If S30 is executed, the Doppler correction block 130 in S40 corrects the received signal using the Doppler shift amount Δf estimated in the preceding S30, similar to the first embodiment. On the other hand, if S30 is skipped, the Doppler correction block 130 in S40 corrects the received signal using the Doppler shift amount Δf estimated in past frames FR. In other words, the Doppler correction block 130 corrects the received signal by assuming that the Doppler shift amount Δf is constant within the sensing period.

[0076] Furthermore, the object detection flow of this embodiment proceeds to S51 after processing in S50. In S51, the object estimation block 140 determines whether or not it has acquired the number of frames FR required for sensing. The number of frames FR required for sensing is predetermined to be, for example, a number sufficient to ensure the accuracy of the relative velocity acquired in a later stage of processing. If it is determined that the number of frames FR required for sensing has not been acquired, the flow returns to S10. On the other hand, if it is determined that the number of frames FR required for sensing has been acquired, the flow proceeds to S60.

[0077] In S60 of this embodiment, the object estimation block 140 generates a propagation matrix from multiple frames FR within the sensing period. That is, the object estimation block 140 considers a composite frame, obtained by arranging each frame FR in time series, as a single frame, and generates a propagation matrix from this composite frame. In the subsequent processing of S70, S80, and S90, the propagation matrix generated from this composite frame is used to perform target information detection and velocity correction.

[0078] According to the fifth embodiment described above, target information can be detected from a propagation matrix obtained by synthesizing multiple frames FR. Therefore, even when using wireless communication standards such as Wi-Fi, where one frame FR is relatively short, object T can be detected.

[0079] (Other embodiments) Although several embodiments have been described above, this disclosure is not intended to be limited to those embodiments, and can be applied to various embodiments and combinations without departing from the spirit of this disclosure.

[0080] In a modified example, the object detection system 1 may be configured to implement multiple methods for estimating the Doppler shift. For example, the Doppler estimation block 120 may be configured to select information to be used for estimating the Doppler shift amount Δf from among the phase change of the reference signal, the position and velocity information of the transmitter and receiver, and the peak of the transmitter.

[0081] In a modified example, the object detection system 1 may have the communication device 20 function as a receiver and the communication device 30 as a transmitter. In this case, the functional block that executes the object detection flow is constructed in the control unit 22 on the communication device 20 side.

[0082] In the modified example, both communication devices 20 and 30 may be mounted on the mobile device, or only the communication device 20 may be mounted on the mobile device.

[0083] In the modified example, the mobile body on which at least one of the communication devices 20 and 30 is mounted may be something other than the vehicle 3. For example, the mobile body may be an autonomous mobile robot, an aircraft, a train, or a ship. Alternatively, the mobile body may be a mobile device that can be carried by a person, such as a smartphone or a wearable device.

[0084] In the modified example, the communication devices 20 and 30 may transmit and receive data using a modulation scheme other than OFDM.

[0085] In modified examples, the object detection system 1 may consist of a transmitter and receiver that do not have communication functions. Alternatively, the object detection system 1 may perform sensing functions with communication devices 20 and 30 that have communication functions, while temporarily suspending the communication functions. In these cases, the object detection flow omits the steps performed by the demodulation block 160. In this case, the transmitter only needs to transmit a radio wave W consisting only of a reference signal Sr and not a data signal Sd, for example. [Explanation of Symbols]

[0086] 1: Object detection system, 3: Vehicle (moving object), 20: Communication device (transmitter), 30: Communication device (receiver), 321: Memory (storage medium), 322: Processor, FR: Frame, Δf: Doppler shift amount, Sr: Reference signal, T: Object, W: Radio wave, Wd: Direct wave

Claims

1. An object detection system comprising a transmitter (20) that transmits radio waves (W) and a receiver (30) that receives the radio waves, at least one of which is mounted on a mobile body (3), for detecting an object (T) that has reflected the radio waves, The aforementioned receiver is The receiving signal is acquired by receiving the aforementioned radio waves, To estimate the amount of Doppler shift (Δf) of the radio waves that occurs according to the relative speed between the transmitter and the receiver, The estimated Doppler shift component is removed from the received signal to correct the received signal, From the corrected received signal, the velocity of the object that reflected the radio waves is estimated, The estimated velocity is corrected in correlation with the Doppler shift amount, An object detection system having a processor (322) configured to perform the following.

2. To acquire the aforementioned received signal, This includes acquiring a reference signal (Sr) with a predetermined phase during transmission as the received signal, Estimating the Doppler shift amount is The object detection system according to claim 1, comprising estimating the amount of Doppler shift based on the phase change of the received reference signal.

3. The aforementioned processor, Each of the aforementioned transmitter and receiver is further configured to acquire position information and speed information. Estimating the Doppler shift amount is The object detection system according to claim 1, comprising estimating the Doppler shift amount based on the acquired position information and velocity information.

4. To acquire the aforementioned received signal, This includes acquiring a direct signal, which is the received signal that is directly received by the receiver from the radio waves transmitted from the transmitter. Estimating the velocity of the aforementioned object is This includes estimating the relative speed of the transmitter in accordance with the direct signal, Estimating the Doppler shift amount is The object detection system according to claim 1, comprising estimating the amount of Doppler shift from the estimated relative velocity.

5. Correcting the aforementioned speed means The object detection system according to claim 1, further comprising correcting the velocity by adding a correlation velocity correlated with the Doppler shift amount.

6. To acquire the aforementioned received signal, This includes estimating whether or not the direct wave (Wd), which is the radio wave transmitted from the transmitter and arriving directly at the receiver, has been received by the receiver. Estimating the Doppler shift amount is The object detection system according to claim 1, further comprising stopping the estimation of the Doppler shift amount when it is estimated that the direct wave has not been received.

7. To acquire the aforementioned received signal, The object detection system according to claim 6, which includes estimating whether or not the direct wave has been received based on the relationship between the distance between the transmitter and the receiver and the intensity of the received signal.

8. The aforementioned processor, It is further configured to generate a propagation matrix by arranging the phase change amounts of multiple frames (FRs) from the time of transmission in a time series, Estimating the Doppler shift amount is The object detection system according to claim 1, comprising estimating the Doppler shift amount based on one of the multiple frames.

9. The object detection system according to claim 1, wherein the radio waves are modulated using an orthogonal frequency division multiplexing scheme.

10. The transmitter transmits the radio waves containing the transmission data. The processor of the receiver is The object detection system according to claim 1, further configured to demodulate the transmitted data from the received signal.

11. An object detection device having a processor (322), receiving radio waves from a transmitter (20) that transmits radio waves, and detecting an object (T) that has reflected the radio waves, The aforementioned processor, The receiving signal is acquired by receiving the aforementioned radio waves, To estimate the amount of Doppler shift (Δf) of the radio waves that occurs according to the relative speed between the transmitter and the radio waves, The estimated Doppler shift component is removed from the received signal to correct the received signal, From the corrected received signal, the velocity of the object that reflected the radio waves is estimated, The estimated velocity is corrected in correlation with the Doppler shift amount, An object detection device configured to perform the following actions.

12. An object detection system (1) comprising a transmitter (20) that transmits radio waves and a receiver (30) that receives the radio waves, at least one of which is mounted on a mobile body (3), includes an object detection program stored in a storage medium (321) and containing instructions to be executed by a processor (322) in order to detect an object (T) that has reflected the radio waves, The receiving signal is acquired by receiving the aforementioned radio waves, To estimate the amount of Doppler shift (Δf) of the radio waves that occurs according to the relative speed between the transmitter and the receiver, The estimated Doppler shift component is removed from the received signal to correct the received signal, From the corrected received signal, the velocity of the object that reflected the radio waves is estimated, The estimated velocity is corrected in correlation with the Doppler shift amount, An object detection program that includes the instruction to execute the aforementioned command.

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