Radar system and method for synchronizing plurality of radars

Abstract

Realized is a radar system and a method for synchronizing a plurality of radars whereby position estimation accuracy can be improved. The present invention includes: a first radar (11a) that transmits and receives radio waves in a first synchronization signal (SNC1) cycle and combines transmission waves and reflected waves of the transmission waves to acquire a first IF signal (IF1); a second radar (11b) that transmits and receives radio waves in a second synchronization signal (SNC2) cycle and combines transmission waves and reflected waves of the transmission waves to acquire a second IF signal (IF2); a processing unit that estimates an angle and a distance to a target on the basis of the first IF signal (IF1) and the second IF signal (IF2); and a synchronization compensation unit (15) that suppresses synchronization deviation between the first synchronization signal (SNC1) and the second synchronization signal (SNC2).

Description

Radar system and method for synchronizing multiple radars

[0001] The present invention relates to a radar system and a method for synchronizing multiple radars.

[0002] Conventionally, techniques for estimating the distance and direction to a target with high accuracy using multiple radars (RADAR: Radio Detection And Ranging) have been disclosed (e.g., Non-Patent Document 1 and Non-Patent Document 2). In a radar system using multiple radars, it is necessary to synchronize the transmission and reception timing between the radars.

[0003] A. Correas-Serrano et al., “Performance Analysis and Design of a Distributed Radar Network for Automotive Application,” doi: 10.23919 / IRS54158.2022.9904987.M. Gottinger et al., “Coherent Signal Processing for Loosely Coupled Bistatic Radar,” doi: 10.1109 / TAES.2021.3050650.

[0004] As described above, in a radar system using multiple radars, the transmission and reception timing needs to be synchronized between the radars. However, differences in the lengths of signal propagation paths such as coaxial lines, wiring on a circuit board, and wiring inside an IC can cause skew, resulting in a discrepancy in the transmission and reception timing and potentially reducing the accuracy of position estimation.

[0005] The present disclosure has been made in view of the above, and aims to provide a radar system and a method for synchronizing multiple radars that can improve position estimation accuracy.

[0006] A radar system according to one aspect of the present disclosure includes a first radar that transmits and receives radio waves at a period of a first synchronization signal and acquires a first IF signal by combining the transmitted waves with reflected waves of the transmitted waves; a second radar that transmits and receives radio waves at a period of a second synchronization signal and acquires a second IF signal by combining the transmitted waves with reflected waves of the transmitted waves; a processing unit that estimates a distance and an angle to a target based on the first IF signal and the second IF signal; and a synchronization compensation unit that suppresses synchronization misalignment between the first synchronization signal and the second synchronization signal.

[0007] This suppresses misalignment between the first synchronization signal provided to the first radar and the second synchronization signal provided to the second radar, thereby improving the accuracy of position estimation in the subsequent processing stages.

[0008] A synchronization method for multiple radars according to one aspect of the present disclosure is a synchronization method for multiple radars in a radar system including: a first radar that transmits and receives radio waves at a period of a first synchronization signal and acquires a first IF signal by combining the transmitted waves with reflected waves of the transmitted waves; and a second radar that transmits and receives radio waves at a period of a second synchronization signal and acquires a second IF signal by combining the transmitted waves with reflected waves of the transmitted waves, the synchronization method including: a first step of calculating a delay time difference between the first synchronization signal and the second synchronization signal based on a difference value between the frequency of the first IF signal and the frequency of the second IF signal; a second step of setting a first delay amount and a second delay amount according to the delay time difference; and a third step of delaying the first synchronization signal according to the first delay amount and delaying the second synchronization signal according to the second delay amount.

[0009] This suppresses misalignment between the first synchronization signal provided to the first radar and the second synchronization signal provided to the second radar, thereby improving the accuracy of position estimation in the subsequent processing stages.

[0010] According to the present disclosure, it is possible to realize a radar system and a method for synchronizing multiple radars that can improve the accuracy of position estimation.

[0011] FIG. 1 is a block diagram showing a schematic configuration of a radar system according to an embodiment. FIG. 2 is a timing chart of the radar system. FIG. 3 is a block diagram showing an example configuration of a control unit according to a comparative example. FIG. 4 is a conceptual diagram showing a delay of a synchronization signal in the comparative example. FIG. 5 is a block diagram showing an example configuration of a synchronization signal control unit of a radar system according to an embodiment. FIG. 6 is a flowchart showing an example of distance estimation processing using the AF method. FIG. 7 is a diagram showing time-series data up to sampling point N. FIG. 8 is a diagram showing an example of a distance estimation result using the AF method. FIG. 9 is a diagram showing a specific example of a lookup table. FIG. 10 is a conceptual diagram showing an example correction of a synchronization signal in the embodiment. FIG. 11 is a block diagram showing an example of an additional configuration of a control unit according to a modified example of the embodiment.

[0012] A radar system and a method for synchronizing multiple radars according to an embodiment will be described in detail below with reference to the drawings. However, the present disclosure is not limited to the embodiment.

[0013] 1 is a block diagram showing a schematic configuration of a radar system according to an embodiment. The radar system 1 according to the embodiment includes a first radar 11 a, a second radar 11 b, a processing unit 12, and a control unit 13.

[0014] In the configuration of the radar system 1 according to the embodiment, the first radar 11a and the second radar 11b are, for example, FMCW (Frequency Modulated Continuous Wave) or FCM (Fast Chirp Modulation) radars each having multiple transmitting antennas and receiving antennas and capable of acquiring distance information and angle information of an observation target. Since FMCW and FCM radars are well known, detailed descriptions thereof may be omitted. The present disclosure is widely applicable to sensors capable of estimating distance and angle from the time difference between a transmitted signal and a received signal using electromagnetic waves (including light) or sound waves.

[0015] The first radar 11a emits a transmission wave Tx1 toward the target 100, receives a reflected wave Rx1 of the transmission wave Tx1, and acquires a first IF signal IF1.

[0016] The second radar 11b emits a transmission wave Tx2 toward the target 100, receives a reflected wave Rx2 of the transmission wave Tx2, and acquires a second IF signal IF2.

[0017] The processing unit 12 estimates and outputs the distance and angle to the target 100 based on the first IF signal IF1 acquired by the first radar 11a and the second IF signal IF2 acquired by the second radar 11b. The present disclosure is not limited to the specific content of the processing by the processing unit 12.

[0018] The control unit 13 is a component that controls the first radar 11a, the second radar 11b, and the processing unit 12 based on control commands from outside. Before describing the configuration and operation of the control unit 13 according to the embodiment, the basic operation of the radar system of the present disclosure will be described. Figure 2 is a timing chart of the radar system. Figure 2 illustrates signals when the first radar 11a and the second radar 11b are FMCW radars.

[0019] The first radar 11a generates a transmission wave Tx1 based on a first synchronization signal SNC1 supplied from the control unit 13. Specifically, the first radar 11a transmits a chirp signal that is linearly frequency-modulated in a band BW from frequency f1 to frequency f2 with a period of Tchirp, a predetermined number of times with a period of Tframe of the first synchronization signal SNC1. In FIG. 2, the transmission wave Tx1 is indicated by a solid line.

[0020] The first radar 11a receives a reflected wave Rx2 reflected by the target 100. In Fig. 2, the reflected wave Rx1 is indicated by a dashed line. The first radar 11a then generates a first IF signal IF1 by combining the transmitted wave Tx1 and the reflected wave Rx1.

[0021] The second radar 11b generates a transmission wave Tx2 based on a second synchronization signal SNC2 supplied from the control unit 13. Specifically, the second radar 11b transmits a chirp signal that is linearly frequency-modulated in a band BW from frequency f1 to frequency f2 with a period of Tchirp, a predetermined number of times with a period of Tframe of the second synchronization signal SNC2. In FIG. 2, the transmission wave Tx2 is indicated by a solid line.

[0022] The second radar 11b receives a reflected wave Rx2 reflected by the target 100. In Fig. 2, the reflected wave Rx2 is indicated by a dashed line. The second radar 11b then generates a second IF signal IF2 by combining the transmitted wave Tx2 and the reflected wave Rx2.

[0023] Fig. 3 is a block diagram illustrating an example of the configuration of a control unit according to a comparative example, and Fig. 4 is a conceptual diagram illustrating a delay of a synchronization signal in the comparative example.

[0024] In the configuration according to the comparative example, the control unit 130 includes a synchronization signal generation unit 14. The synchronization signal generation unit 14 generates a synchronization signal SNC.

[0025] The synchronization signal SNC generated by the synchronization signal generator 14 is delayed by signal propagation paths such as coaxial cables, wiring on a circuit board, and wiring within an IC. Specifically, the synchronization signal SNC arrives at the first radar 11a as a first synchronization signal SNC1 delayed by a delay time Δt1. The synchronization signal SNC arrives at the second radar 11b as a second synchronization signal SNC2 delayed by a delay time Δt2. As a result, as shown in FIG. 4 , a delay time difference Δt (= Δt1 - Δt2) occurs between the first synchronization signal SNC1 and the second synchronization signal SNC2, causing a synchronization error between the first synchronization signal SNC1 provided to the first radar 11a and the second synchronization signal SNC2 provided to the second radar 11b, thereby reducing the accuracy of position estimation in the downstream processing unit 12.

[0026] The configuration and synchronization method of this embodiment, which can improve the accuracy of position estimation in a radar system having multiple radars, will be described below.

[0027] 5 is a block diagram showing an example of the configuration of a synchronization signal control unit of a radar system according to the embodiment. In the configuration according to the embodiment, the control unit 13 includes a synchronization compensation unit 15 in addition to a synchronization signal generation unit 14.

[0028] The synchronization compensation unit 15 includes a delay time difference calculation unit 151, a delay amount setting unit 152, a first delay circuit 153a, and a second delay circuit 153b.

[0029] The delay time difference calculation unit 151 calculates the delay time difference Δt between the first IF signal IF1 and the second IF signal IF2. The delay time difference Δt between the first IF signal IF1 and the second IF signal IF2 is expressed by the following equation (1): In the following equation (1), Fif1 represents the frequency of the first IF signal IF1, and Fif2 represents the frequency of the second IF signal IF2.

[0030]

[0031] The frequency Fif1 is the frequency at which the power is maximum in the spectrum after Range-FFT processing of the first IF signal IF1. The frequency Fif2 is the frequency at which the power is maximum in the spectrum after Range-FFT processing of the second IF signal IF2. The Range-FFT processing may be performed by the first radar 11a and the second radar 11b, or may be performed by the synchronization compensation unit 15.

[0032] Furthermore, the process for deriving the frequencies Fif1 and Fif2 is not limited to FFT processing, and may be, for example, processing using an annihilating filter (AF) method (hereinafter also referred to as the "AF method"). By using the AF method, it is possible to significantly speed up the processing (for example, about 25 times faster) compared to an aspect in which FFT processing is performed at a T frame period.

[0033] A specific example of speeding up distance estimation processing using the AF method will be described below: Fig. 6 is a flowchart showing an example of distance estimation processing using the AF method.

[0034] First, data x(n) (n is a natural number from 1 to N, and N is the data length) is acquired in a time series (at each sampling point) (step S100), and a convolution matrix C shown in the following equation (2) is generated (step S200). The data x(n) represents the time series data of the IF signal acquired by the radar. FIG. 7 is a diagram showing the time series data up to sampling point N. In the following equation (2), L represents the number of estimated spectra.

[0035]

[0036] Next, a filter h(z) used in the AF method is generated using the convolution matrix C shown in the above equation (2) (step S300). The filter coefficient H of H(z) is found by a minimization problem shown in the following equation (3). The optimization problem applied here is just an example, and other methods may also be used.

[0037]

[0038] Next, using the following equation (4), the zero point z of the filter h(z) configured with the coefficient H is calculated. ｌ is calculated (step S400), where L is the estimated number of spectra.

[0039]

[0040] Then, using the following equation (5), the zero point z ｌ The corresponding frequency bin is found by the following equation. Note that in the FFT processing, it is expressed as an integer, but in the AF method, it is expressed as a real number. Here, since the number of estimated spectra is L, L line spectra are output. For simplicity, it is assumed that l=0 is the maximum amplitude, and r ｂｉｎ (0) is set as the output bin (step S500).

[0041]

[0042] 8 is a diagram showing an example of a distance estimation result by the AF method. In FIG. 8, the horizontal axis shows the distance (Range), which is calculated using the above formula (5). ｂｉｎ The horizontal axis of FIG. 8, which shows the estimation results by the AF method, is the calculation result of the above formula (5), r ｂｉｎ (0) may also be used.

[0043] The delay amount setting unit 152 executes a loop filter (LF) process to derive the delay amount Δtf.

[0044] 5, A denotes the loop gain in the loop filter (LF) processing. The delay amount setting unit 152 multiplies the delay time difference Δt calculated by the delay time difference calculation unit 151 by a predetermined loop gain A. This makes it possible to stabilize the feedback loop and reduce errors.

[0045] The delay amount Δtf is expressed by the following equation (6): In the following equation (6), LF represents a filter function in discrete time, and if there is a phase margin in the feedback loop, it may be a simple LPF (Low Pass Filter) such as an FIR (Finite Impulse Response). As a result, the delay amount Δtf after loop filter (LF) processing becomes a discrete value in which high-frequency components have been smoothed.

[0046]

[0047] The delay amount setting unit 152 uses a first lookup table LUT1 to derive a first delay amount Dt1 corresponding to the delay amount Δtf after loop filter (LF) processing. The delay amount setting unit 152 also uses a second lookup table LUT2 to derive a second delay amount Dt2 corresponding to the delay amount Δtf after loop filter (LF) processing. FIG. 9 is a diagram showing a specific example of a lookup table. The solid line in FIG. 9 indicates the first delay amount Dt1 obtained using the first lookup table LUT1. The dashed line in FIG. 9 indicates the second delay amount Dt2 obtained using the second lookup table LUT2.

[0048] The first delay amount Dt1 and the second delay amount Dt2 may be numerical values ​​indicating analog real time or may be discrete values ​​in digital processing. When the first delay amount Dt1 and the second delay amount Dt2 are expressed as real time, the relationship with the delay time difference Δt is expressed by the following equation (7).

[0049]

[0050] The first delay circuit 153a applies a first delay amount Dt1 to the synchronization signal SNC to generate the first synchronization signal SNC1. Specifically, the first delay circuit 153a delays the first synchronization signal SNC1 according to the first delay amount Dt1. As a result, the delay time of the first synchronization signal SNC1 relative to the synchronization signal SNC is the sum of the delay time Δt1 and the real time corresponding to the first delay amount Dt1.

[0051] The second delay circuit 153b applies a second delay Dt2 to the synchronization signal SNC to generate a second synchronization signal SNC2. Specifically, the second delay circuit 153b delays the second synchronization signal SNC2 according to the second delay Dt2. As a result, the delay time of the second synchronization signal SNC2 relative to the synchronization signal SNC is the sum of the delay time Δt2 and the real time corresponding to the second delay Dt2.

[0052] Fig. 10 is a conceptual diagram showing an example of correction of synchronization signals in the embodiment. The dashed-dotted lines in Fig. 10 represent the first synchronization signal SNC1 and the second synchronization signal SNC2 of the comparative example shown in Fig. 4. When the first delay amount Dt1 and the second delay amount Dt2 are expressed as real time, the relationship between the delay time of the first synchronization signal SNC1 relative to the synchronization signal SNC and the delay time of the second synchronization signal SNC2 relative to the synchronization signal SNC can be expressed by the following equation (8).

[0053]

[0054] This reduces the delay time difference between the first synchronization signal SNC1 and the second synchronization signal SNC2, thereby reducing the synchronization error between the first synchronization signal SNC1 provided to the first radar 11a and the second synchronization signal SNC2 provided to the second radar 11b, thereby improving the accuracy of position estimation in the downstream processing unit 12.

[0055] 11 is a block diagram illustrating an example of an additional configuration of a control unit according to a modification of the embodiment. In the example shown in FIG. 11, the processing in the downstream processing unit 12 is stopped (UNLOCK=1) according to the delay time difference Δt calculated by the delay time difference calculation unit 151 of the synchronization compensation unit 15.

[0056] Specifically, when the absolute value |Δt| of the delay time difference Δt calculated by the delay time difference calculation unit 151 of the synchronization compensation unit 15 exceeds a predetermined value ε, the processing control unit 16 stops processing in the downstream processing unit 12 (UNLOCK=1). Note that the predetermined value ε is a value determined by the maximum target distance error allowable in the radar system 1 of the present disclosure, and is a parameter that can be changed arbitrarily. For example, this predetermined value ε is expressed by the following equation (9), where ΔR is the maximum target distance error and C is the speed of light.

[0057] ε=ΔR / C...(9)

[0058] This makes it possible to suppress the output of unreliable data, and also reduces power consumption by eliminating the position estimation in the processing unit 12 at the subsequent stage.

[0059] The above-described embodiments are intended to facilitate understanding of the present disclosure and are not intended to limit the present disclosure. The present disclosure may be modified or improved without departing from the spirit thereof, and equivalents thereof are also included in the present disclosure.

[0060] The present disclosure can have the following configurations as described above or instead of the above.

[0061] (1) A radar system according to one aspect of the present disclosure includes a first radar that transmits and receives radio waves at a period of a first synchronization signal and acquires a first IF signal by combining the transmitted waves with reflected waves of the transmitted waves; a second radar that transmits and receives radio waves at a period of a second synchronization signal and acquires a second IF signal by combining the transmitted waves with reflected waves of the transmitted waves; a processing unit that estimates a distance and an angle to a target based on the first IF signal and the second IF signal; and a synchronization compensation unit that suppresses synchronization misalignment between the first synchronization signal and the second synchronization signal.

[0062] This suppresses misalignment between the first synchronization signal provided to the first radar and the second synchronization signal provided to the second radar, thereby improving the accuracy of position estimation in the subsequent processing stages.

[0063] (2) In the radar system of (1) above, the synchronization compensation unit includes a delay time difference calculation unit that calculates a delay time difference between the first synchronization signal and the second synchronization signal based on a difference value between the frequency of the first IF signal and the frequency of the second IF signal, a delay amount setting unit that sets a first delay amount and a second delay amount according to the delay time difference, a first delay circuit that delays the first synchronization signal according to the first delay amount, and a second delay circuit that delays the second synchronization signal according to the second delay amount.

[0064] (3) In the radar system of (2) above, the delay amount setting unit includes a loop filter that smooths high-frequency components of a value obtained by multiplying the delay time difference by a predetermined gain, a first lookup table in which the first delay amount is set according to the output of the loop filter, and a second lookup table in which the second delay amount is set according to the output of the loop filter.

[0065] (4) The radar system of (2) or (3) above further comprises a processing control unit that stops the processing in the processing unit when the delay time difference exceeds a predetermined value.

[0066] This configuration can suppress the output of unreliable data, and can also reduce power consumption by eliminating the position estimation in the subsequent processing section.

[0067] (5) A synchronization method for multiple radars according to one aspect of the present disclosure is a synchronization method for multiple radars in a radar system including: a first radar that transmits and receives radio waves at a period of a first synchronization signal and acquires a first IF signal by combining the transmitted waves with reflected waves of the transmitted waves; and a second radar that transmits and receives radio waves at a period of a second synchronization signal and acquires a second IF signal by combining the transmitted waves with reflected waves of the transmitted waves, the synchronization method including: a first step of calculating a delay time difference between the first synchronization signal and the second synchronization signal based on a difference value between the frequency of the first IF signal and the frequency of the second IF signal; a second step of setting a first delay amount and a second delay amount according to the delay time difference; and a third step of delaying the first synchronization signal according to the first delay amount and delaying the second synchronization signal according to the second delay amount.

[0068] This suppresses misalignment between the first synchronization signal provided to the first radar and the second synchronization signal provided to the second radar, thereby improving the accuracy of position estimation in the subsequent processing stages.

[0069] (6) In the method for synchronizing multiple radars described in (5) above, the second step includes a step of smoothing high-frequency components of a value obtained by multiplying the delay time difference by a predetermined gain, and a step of setting the first delay amount and the second delay amount according to the output of the loop filter.

[0070] (7) In the method for synchronizing multiple radars described in (5) or (6) above, the frequencies of the first IF signal and the second IF signal are derived using an AF (Annihilating Filter) method.

[0071] This configuration can significantly speed up the processing compared to a mode in which FFT processing is performed at the synchronization signal period.

[0072] The present disclosure makes it possible to realize a radar system and a method for synchronizing multiple radars that can improve the accuracy of position estimation.

[0073] REFERENCE SIGNS LIST 1 radar system 11a first radar 11b second radar 12 processing unit 13 control unit 14 synchronization signal generation unit 15 synchronization compensation unit 16 processing control unit 100 target 130 control unit 151 delay time difference calculation unit 152 delay amount setting unit 153a first delay circuit 153b second delay circuit LF loop filter LUT1 first lookup table LUT2 second lookup table

Claims

1. A radar system comprising: a first radar that transmits and receives radio waves at a period of a first synchronization signal and obtains a first IF signal by combining the transmitted wave with a reflected wave of the transmitted wave; a second radar that transmits and receives radio waves at a period of a second synchronization signal and obtains a second IF signal by combining the transmitted wave with a reflected wave of the transmitted wave; a processing unit that estimates a distance and angle to a target based on the first IF signal and the second IF signal; and a synchronization compensation unit that suppresses synchronization deviation between the first synchronization signal and the second synchronization signal.

2. A radar system as described in claim 1, wherein the synchronization compensation unit comprises: a delay time difference calculation unit that calculates a delay time difference between the first synchronization signal and the second synchronization signal based on a difference value between the frequency of the first IF signal and the frequency of the second IF signal; a delay amount setting unit that sets a first delay amount and a second delay amount according to the delay time difference; a first delay circuit that delays the first synchronization signal according to the first delay amount; and a second delay circuit that delays the second synchronization signal according to the second delay amount.

3. A radar system as claimed in claim 2, wherein the delay amount setting unit includes: a loop filter that smooths high frequency components of a value obtained by multiplying the delay time difference by a predetermined gain; a first lookup table in which the first delay amount corresponding to the output of the loop filter is set; and a second lookup table in which the second delay amount corresponding to the output of the loop filter is set.

4. A radar system according to claim 2 or 3, further comprising a processing control unit that stops processing in the processing unit when the delay time difference exceeds a predetermined value.

5. A method for synchronizing multiple radars in a radar system including: a first radar that transmits and receives radio waves at a period of a first synchronization signal, and obtains a first IF signal by combining the transmitted wave with a reflected wave of the transmitted wave; and a second radar that transmits and receives radio waves at a period of a second synchronization signal, and obtains a second IF signal by combining the transmitted wave with a reflected wave of the transmitted wave, the method comprising: a first step of calculating a delay time difference between the first synchronization signal and the second synchronization signal based on a difference value between the frequency of the first IF signal and the frequency of the second IF signal; a second step of setting a first delay amount and a second delay amount according to the delay time difference; and a third step of delaying the first synchronization signal according to the first delay amount, and delaying the second synchronization signal according to the second delay amount.

6. A method for synchronizing multiple radars as described in claim 5, wherein the second step includes the steps of: smoothing, using a loop filter, high-frequency components of a value obtained by multiplying the delay time difference by a predetermined gain; and setting the first delay amount and the second delay amount according to an output of the loop filter.

7. A method for synchronizing multiple radars according to claim 5 or 6, comprising deriving the frequencies of the first IF signal and the second IF signal using an AF (Annihilating Filter) method.

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