Radar device and signal processing method for radar device

Abstract

To provide a radar device and a signal processing method for the radar device, capable of accurately detecting a distance to a target existing in a nearby region.SOLUTION: A radar device receives a reflection wave from a target 2 to generate a distance spectrum from the reflection wave, and when a plurality of peak points exceeding a predetermined threshold value exist in a nearby region within a predetermined distance range and a distance between the adjacent two peak points is fixed in the distance spectrum, a determination unit 19 outputs a determination result that the target 2 exists in the nearby region within the predetermined distance range, and a distance detection unit 18 detects the distance between the adjacent two peak points in the distance spectrum as a distance to the target 2 on the basis of the determination result.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a radar device for detecting a distance to a target and a signal processing method for the radar device. [Background technology]

[0002] Some radar devices, which transmit waves toward a target and receive reflected waves from the target to detect the distance to the target, are equipped with a sensitivity time control (STC) function. The STC function attenuates the signal strength of the reflected wave according to the distance to the target based on the basic principle that the signal strength of the reflected wave from the target is inversely proportional to the fourth power of the distance to the target. In radar devices, this STC function attenuates signals such as reflected waves (ground clutter) from the ground near the antenna, thereby suppressing signal saturation in the receiving system.

[0003] In the invention disclosed in Patent Document 1, the STC function is realized by using a high-pass filter (HPF). Fig. 4 shows a schematic configuration of an FMCW (Frequency Modulation Continuous Wave) radar device 10 described in Patent Document 1. The FMCW radar device 10 includes a transmitting antenna 101, a receiving antenna 102, an oscillator 103, a mixer 104, an HPF 105, an A / D conversion unit 106, a fast Fourier transform (FFT) unit 107, and a distance detection unit 108.

[0004] An oscillator 103 transmits a transmission wave, for example a frequency-modulated triangular wave, from a transmitting antenna 101, and a receiving antenna 102 receives a reflected wave, which is a transmission wave reflected by a target. A mixer 104 mixes the transmission wave and the reflected wave to generate a beat signal, and an HPF 105 attenuates the beat signal according to the distance to the target (the frequency of the beat signal). An A / D conversion unit 106 converts the attenuated beat signal into a digital signal, an FFT unit 107 performs a fast Fourier transform in the distance direction on the beat signal converted into a digital signal to generate a distance spectrum, and a distance detection unit 108 detects the distance to the target based on the distance spectrum. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 07-055925 Summary of the Invention [Problem to be solved by the invention]

[0006] As mentioned above, the use of a high-pass filter can suppress signal saturation in the receiving system, but depending on the filter characteristics of the high-pass filter, the signal strength due to multiple reflections between the target and the target may be greater than the signal strength of the reflected wave from a target located very close to the target, resulting in the generation of a false image (also called a virtual image), making it impossible to properly detect the target. Also, when the distance to the target is very close, the spectrum of the reflected wave from the target may be buried in the spectrum of the radio wave that leaks directly from the transmitting antenna to the receiving antenna, making it impossible to detect.

[0007] For example, Fig. 5(a) to (c) show distance spectra generated by the FFT unit 107 of the FMCW radar device 10. The distance spectrum in Fig. 5(c) is an example of an ideal distance spectrum in which the intensity of the signal T of the reflected wave from the target is greater than the signal intensity of the multiple reflections, and the distance of this peak point is usually detected as the distance to the target. On the other hand, in the distance spectrum in Fig. 5(a), the signal T of the target located 1 m from the FMCW radar device 10 is suppressed by the filter characteristics of the HPF 105, and the intensity of the false signal F generated at a position about 2 m from the FMCW radar device 10 is greater than the signal T of the target, resulting in erroneous detection. Also, in the distance spectrum in Fig. 5(b), the signal T of the target located 1 m from the FMCW radar device 10 is buried by the spectrum A of the radio wave that leaks directly from the transmitting antenna to the receiving antenna, and cannot be detected.

[0008] SUMMARY OF THE PRESENT EMBODIMENTS An object of the present invention is to provide a radar device and a signal processing method for a radar device that are capable of detecting the distance to a nearby target with high accuracy. [Means for solving the problem]

[0009] In order to solve the above problem, the invention described in claim 1 is a radar device comprising: a transmission / reception means for transmitting a transmission wave toward a target and receiving a reflected wave from the target; a signal processing means for generating a distance spectrum from the reflected wave; a determination unit for outputting a determination result that the target is present in a nearby region within a predetermined distance range when the distance spectrum contains a plurality of peak points exceeding a predetermined threshold value in a nearby region within the predetermined distance range and the distance between two adjacent peak points among the plurality of peak points is constant; and a distance detection unit for detecting the distance between the two adjacent peak points in the distance spectrum as the distance to the target based on the determination result.

[0010] The invention described in claim 2 is a signal processing method for a radar device that transmits a transmission wave toward a target, receives a reflected wave from the target, and detects a distance to the target, characterized in that a distance spectrum is generated from the reflected wave, and if a plurality of peak points exceeding a predetermined threshold are present in a nearby region within a predetermined distance range in the distance spectrum, and the distance between two adjacent peak points among the plurality of peak points is constant, a judgment result is output that the target is present in a nearby region within the predetermined distance range, and the distance between the two adjacent peak points in the distance spectrum is detected as the distance to the target based on the judgment result. Effect of the Invention

[0011] According to the inventions described in claims 1 and 2, when a target is present in a nearby area within a predetermined distance range, the distance between two adjacent peak points in the distance spectrum is detected as the distance to the target, making it possible to detect the distance to the target with high accuracy. [Brief description of the drawings]

[0012] [Figure 1] 1 is a block diagram showing a schematic configuration of an FMCW radar device according to an embodiment of the present invention; [Diagram 2] 2A is a graph showing a distance spectrum generated by the FFT unit shown in FIG. 1 when a target is present in the nearby region, and FIG. 2B is an enlarged view of part P in FIG. [Diagram 3] 4 is a flowchart showing a procedure for distance detection by the FMCW radar device shown in FIG. [Figure 4] FIG. 1 is a block diagram showing a schematic configuration of a conventional FMCW radar device. [Diagram 5] 5A to 5C are graphs showing examples of distance spectra generated by the FFT unit shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the present invention will be described based on the illustrated embodiment.

[0014] 1 is a block diagram showing a schematic configuration of an FMCW radar device 1 according to an embodiment of the present invention. The FMCW radar device 1 is mounted on a moving object such as a ship or a vehicle.

[0015] The FMCW radar device (radar device) 1 includes a transmitting antenna (transmitting / receiving means) 11, a receiving antenna (transmitting / receiving means) 12, an oscillator (transmitting / receiving means) 13, a mixer (signal processing means) 14, an HPF (signal processing means) 15, an A / D conversion unit (signal processing means) 16, an FFT unit (signal processing means) 17, a judgment unit 19, and a distance detection unit 18.

[0016] The oscillator 13 transmits a transmission wave, for example a frequency-modulated triangular wave, from the transmission antenna 11. The receiving antenna 12 receives a reflected wave, which is the transmission wave reflected by the target 2.

[0017] The mixer 14 mixes the transmitted wave and the reflected wave to generate a beat signal. The HPF 15 removes and attenuates the low-frequency components of the beat signal according to the distance to the target 2 (the frequency of the beat signal).

[0018] The filter characteristics of the HPF 15 can be formulated, and are not limited to a specific characteristic or type as long as they attenuate the beat signal according to the distance to the target 2 (the frequency of the beat signal). For example, a filter in which the cutoff frequency can be switched among a plurality of types according to predetermined conditions can also be applied.

[0019] The A / D conversion unit 16 converts the attenuated beat signal into a digital signal. At this time, since the beat signal has been attenuated by the HPF 15, the beat signal is not saturated in the A / D conversion unit 16.

[0020] The FFT unit 17 performs a fast Fourier transform in the distance direction on the beat signal converted into a digital signal to generate a distance spectrum. That is, the FFT unit 17 generates a distance spectrum of the beat signal attenuated by the HPF 15.

[0021] When the target 2 is present in a nearby region within a predetermined distance range, the distance spectrum generated by the FFT unit 17 may suppress the signal T of the target 2, depending on the filter characteristics of the HPF 15, as shown in the graph of Fig. 5(a), and the strength of the false signal F generated at a position about 2 m from the FMCW radar device 1 may be greater than the signal T of the target 2. Also, as shown in the graph of Fig. 5(b), the signal T of the target 2 may be buried by the spectrum A of the radio wave that has leaked directly from the transmitting antenna to the receiving antenna.

[0022] When the distance spectrum generated by the FFT unit 17 has multiple peak points exceeding a predetermined threshold in a neighborhood area within a predetermined distance range, and the distance between two adjacent peak points among the multiple peak points is constant, the determination unit 19 outputs a determination result that "the target 2 is present in the neighborhood area within the predetermined distance range." On the other hand, when the neighborhood area within the predetermined distance range does not have multiple peak points exceeding the predetermined threshold, or when the neighborhood area within the predetermined distance range has multiple peak points exceeding the predetermined threshold but the distance between two adjacent peak points among the multiple peak points is not constant, the determination unit 19 outputs a determination result that "the target 2 is not present in the neighborhood area within the predetermined distance range." Here, the number of peak points needs to be three or more in order to compare the distance between the peak points. In addition, an example of a case where the distance between two adjacent peak points among the multiple peak points is not constant is the spectrum of radio waves reflected from an obstacle.

[0023] Fig. 2 shows a distance spectrum generated by the FFT unit 17 of the FMCW radar device 1 according to this embodiment. In this distance spectrum, as shown in Fig. 2(a), there are five peak points exceeding the threshold thr in a neighborhood region P within a predetermined distance range. Moreover, as shown in Fig. 2(b), among these five peak points, the distances D1 to D4 between two adjacent peak points are constant (D1 = D2 = D3 = D4). In such a case, the determination unit 19 outputs a determination result that "the target 2 is present in the neighborhood region P within the predetermined distance range."

[0024] In this embodiment, the vicinity region P is set to within about 4 m from the FMCW radar device 1, but is not limited to this and may be set appropriately. Also, in this embodiment, the threshold value thr is set to about 70 dB, but is not limited to this and may be set appropriately.

[0025] The distance detection unit 18 detects the distance to the target 2 based on the determination result output by the determination unit 19. Specifically, when the determination result by the determination unit 19 is that "the target 2 is present in a nearby area within a predetermined distance range", the distance detection unit 18 detects the distance between two adjacent peak points in the distance spectrum as the distance to the target 2. This is based on the fact that multiple reflections occurring between the target 2 appear for each distance between the radar device 1 and the target 2. For example, in the example shown in FIG. 2, the distances D1 to D4 between two adjacent peak points are detected as the distance to the target 2.

[0026] On the other hand, if the determination result by the determination unit 19 is that "the target 2 does not exist in the nearby area within the predetermined distance range," the distance detection unit 18 determines the signal with the strongest signal strength in the distance spectrum to be the target 2, as in the conventional case, and detects the distance of that signal as the distance to the target 2. For example, in the example shown in FIG. 5(c), the distance of the signal T is detected as the distance to the target 2.

[0027] In this way, in the FMCW radar device 1 of this embodiment, the distance detection unit 18 can switch the algorithm for distance detection depending on the judgment result output by the judgment unit 19, making it possible to detect with high accuracy not only the distance to a target 2 located nearby, but also the distance to a target 2 located far away.

[0028] Next, the operation of distance detection in this embodiment will be described with reference to the flow chart of FIG.

[0029] First, the FFT unit 17 generates a distance spectrum (step S1). Next, the determination unit 19 determines whether or not, in this distance spectrum, (1) there are multiple peak points exceeding a predetermined threshold in a nearby region within a predetermined distance range, and (2) the distance between two adjacent peak points among the multiple peak points is constant. If both (1) and (2) are "yes," the determination unit 19 outputs a determination result that "the target 2 is present in a nearby region within a predetermined distance range" (step S2), and based on this determination result, the distance detection unit 18 detects the distance between the two adjacent peak points in the distance spectrum as the distance to the target 2 (step S3). On the other hand, if both (1) and (2) are "no," the judgment unit 19 outputs a judgment result that "the target 2 is not present in a nearby area within a specified distance range" (step S4), and based on this judgment result, the distance detection unit 18 detects the distance of the signal with the greatest signal strength in the distance spectrum as the distance to the target 2 (step S5).

[0030] As described above, according to the FMCW radar device 1 of this embodiment, when the target 2 is present in a nearby area within a predetermined distance range, the distance between two adjacent peak points in the distance spectrum is detected as the distance to the target 2, thereby avoiding problems such as erroneous detection due to the filter characteristics of the high-pass filter and inability to detect due to radio waves leaking in, and making it possible to detect the distance to the target 2 with high accuracy.

[0031] Although the embodiments of the present invention have been described above, the specific configuration is not limited to the above embodiments, and even if there are design changes within the scope of the present invention, the present invention is included. For example, in the above embodiments, the present invention has been described using an FMCW radar as an example, but the present invention can also be applied to a pulse radar. In addition, the present invention has been described using a radar device that uses a high-pass filter for the STC function as an example, but the present invention can also be applied to a radar device that does not use a high-pass filter or a radar device that does not have an STC function.

[0032] 1 FMCW radar device (radar device) 11 Transmitting antenna (transmitting / receiving means) 12 Receiving antenna (transmitting / receiving means) 13 Oscillator (transmitting / receiving means) 14 Mixer (signal processing means) 15 High-pass filter (signal processing means) 16 A / D conversion unit (signal processing means) 17 Fast Fourier transform section (signal processing means) 18 Distance detection unit 19 Judgment section 2 Target

Claims

1. a transmitting / receiving means for transmitting a transmission wave toward a target and receiving a reflected wave from the target; A signal processing means for generating a distance spectrum from the reflected wave; a determination unit that outputs a determination result that the target is present in a nearby region within a predetermined distance range when a plurality of peak points exceeding a predetermined threshold are present in the distance spectrum and a distance between two adjacent peak points among the plurality of peak points is constant; and a distance detection unit that detects a distance between the two adjacent peak points in the distance spectrum as a distance to the target based on the determination result; A radar device comprising:

2. 1. A signal processing method for a radar device that transmits a transmission wave toward a target and receives a reflected wave from the target to detect a distance to the target, comprising: generating a distance spectrum from the reflected wave; outputting a determination result that the target is present in a nearby region within a predetermined distance range when a plurality of peak points exceeding a predetermined threshold value are present in the distance spectrum in a nearby region within a predetermined distance range and a distance between two adjacent peak points among the plurality of peak points is constant; Detecting a distance between the two adjacent peak points in the distance spectrum as a distance to the target based on the determination result; 2. A signal processing method for a radar device comprising:

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