JP2017219483A - Radar system and radar signal processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce impact of time error due to a separate arrangement and output a precise position.SOLUTION: A radar system has t (Nt≥1) pieces of transmitters and Nr (Nr≥1, Nt+Nr≥4) pieces of receivers. The transmitter modulates and transmits at least one continuous wave or one pulse-modulated signal of upsweep or downsweep having a frequency sweep gradient by using transmission information including position, transmission frequency, and transmission time, as a modulation signal. The receiver receives direct waves from the transmitter or reflected waves from a target, selects a start time in which an FFT output becomes a maximum, extracts transmission information by demodulating after integrating as necessary, synchronizes a received local signal with the received signal on the basis of the transmission information, further corrects the received local signal, observes a beat frequency by FFT processing, measuring distance of the target and, as necessary, speed and angle, and calculates a three-dimensional position (x,y,z) of the target.SELECTED DRAWING: Figure 1

Description

  The present embodiment relates to a multistatic radar system and a radar signal processing method thereof.

  Recently, in the radar system, a multi-static method has been developed in which one or more transmission / reception radar devices or reception radar devices are arranged apart from the transmission / reception radar device, and the target position is detected based on the observation results of each radar device. Has been. However, in this type of radar system, if the time synchronization between the separated radar devices is insufficient or the distance accuracy is insufficient, the error of the observation position becomes large. In addition, when observing the beat frequency of a continuous wave such as FMCW (Frequency Modulated Continuous Wave), if the center frequency shifts, the accuracy of the beat frequency becomes insufficient, and the distance measurement / speed measurement accuracy also decreases. End up. In the case of a receiving device with a small aperture, it is difficult to obtain sufficient angle measurement accuracy. Further, when the transmitting device is out of line of sight, direct waves cannot be received, and synchronized multi-static operation cannot be performed.

JP 2010-271115 A

FMCW system (up-chirp and down-chirp), Yoshida, "Revised radar technology", IEICE, pp.274-275 (1996) FMICW (FRED E. Nathanson, 'RADAR DESIGN PRINCIPLES second edition), Scitech, pp452-454 (1999) Phase monopulse (phase comparison monopulse) system, Yoshida, 'Revised radar technology', IEICE, pp.262-264 (1996) Taylor distribution, Yoshida, 'Revised radar technology', IEICE, pp.134-135 (1996) MIMO processing, JIAN LI, PETER STOICA, ‘MIMO RADAR SIGNAL PROCESSING’, WILEY, pp.1-5 (2009) BPSK, QPSK, Nishimura, 'Communication system design by digital signal processing, CQ Publisher, pp.222-226 (2006)

  As described above, in the conventional multistatic radar system, the beat frequency cannot be observed accurately due to the influence of the time synchronization deviation or the center frequency deviation between the radar devices, and the target three-dimensional position is calculated. Above, the distance accuracy and the speed accuracy are insufficient, and the small receiving device has a problem that the angle measurement accuracy is low.

  The present embodiment has been made in view of the above-described problems, and reduces the influence of time synchronization shift and center frequency shift between the transmission apparatus and the reception apparatus, improves the beat frequency observation accuracy, and achieves target 3D or 2 An object of the present invention is to provide a radar system and a radar signal processing method thereof that can obtain sufficient distance accuracy and velocity accuracy for calculating a dimensional position, and can obtain high angle measurement accuracy even with a small receiving device.

  In order to solve the above problems, the radar system according to the present embodiment includes t (Nt ≧ 1) transmission devices and Nr (Nr ≧ 1, Nt + Nr ≧ 4 or 3) reception devices. . In the transmission apparatus, transmission information including position, transmission frequency, and transmission time is used as a modulation signal, and at least one continuous wave or pulse-modulated signal having a frequency sweep gradient is modulated and transmitted. In the receiving device, a direct wave from the transmitting device or a reflected wave reflected from the target is received, and a start time at which the FFT output is maximized is selected by changing a plurality of FFT (Fast Fourier Transform) start times. Is integrated and demodulated to extract transmission information, and based on the transmission information, the received local signal is synchronized with the received signal. Further, the received local signal is corrected, and the FFT processing is performed to obtain the beat frequency. , Measure the target distance, and perform speed measurement and angle measurement as necessary, and calculate the intersection point from the distance of three or more pairs of transmission and reception and the angle measurement value of the receiver. A dimensional position (x, y, z) or a two-dimensional position (x, y) is calculated.

1 is a block diagram showing a configuration of a radar system according to a first embodiment. The wave form diagram for demonstrating the time synchronization of the radar system which concerns on 1st Embodiment. The wave form diagram which shows the signal waveform of the up sweep-down sweep used by the time synchronization of the radar system which concerns on 1st Embodiment. FIG. 4 is a waveform diagram for explaining local control processing of the radar system according to the first embodiment. The wave form diagram which shows the sweep waveform for long distances in the radar system which concerns on 1st Embodiment. The figure which shows a mode that the distance measurement in the case of the radar system which concerns on 1st Embodiment in case there are three transmitters and one receiver. The figure which shows a mode that the target position is calculated in the radar system which concerns on 1st Embodiment. The block diagram which shows the structure of the radar system which concerns on 2nd Embodiment. 9 is a flowchart showing a flow of distance measurement / speed measurement processing by MRAV of the radar system according to the second embodiment. The figure which shows the transmission signal waveform of the radar system which concerns on 2nd Embodiment. The figure for demonstrating the beat frequency calculation process of the radar system which concerns on 2nd Embodiment. The figure for demonstrating the phase monopulse observation process of the radar system which concerns on 2nd Embodiment. The figure for demonstrating the process which calculates | requires an error voltage from a phase monopulse in the radar system which concerns on 2nd Embodiment. The figure for demonstrating the process in the case of 4 sweeps in the radar system which concerns on 2nd Embodiment. The block diagram which shows the structure of the radar system which concerns on 3rd Embodiment. The figure which shows the concept for implement | achieving the isolation ensuring between transmitters in the radar system which concerns on 3rd Embodiment. The block diagram which shows the structure of the radar system which concerns on 4th Embodiment. The block diagram which shows the specific structure of the MIMO process part of the radar system which concerns on 4th Embodiment. The conceptual diagram which shows a mode that the virtual array opening is formed in the radar system which concerns on 4th Embodiment. The figure which shows the general example of the antenna coordinate system of transmission and reception in the radar system which concerns on 4th Embodiment. The block diagram which shows the structure of the radar system which concerns on 5th Embodiment. The block diagram which shows the structure of the radar system which concerns on 6th Embodiment. The block diagram which shows the structure of the radar system which concerns on 7th Embodiment.

  Hereinafter, embodiments will be described with reference to the drawings. In the description of each embodiment, the same portions are denoted by the same reference numerals, and redundant description is omitted.

(First embodiment)
The radar system according to the first embodiment will be described with reference to FIGS. This radar system includes N transmitting apparatuses 11 to 1N illustrated in FIG. 1A and one receiving apparatus 2 illustrated in FIG. The transmission apparatus 1i (i is any one of 1 to N) includes a transmission antenna 1i1 and a transmitter 1i2, and each transmitter 1i2 includes a transmission unit 1i21 and a transmission modulation unit 1i22. The receiving device 2 includes a receiving antenna 21, a receiver 22, and a signal processor 23. The receiver 22 includes a receiving unit 221, a local control unit 222, and a timing control unit 223. The signal processor 23 includes a Σ-system AD conversion unit 231, an FFT (Fast Fourier Transform) weight unit 232, an FFT processing unit 233, a CFAR processing unit 234, a distance measurement / speed measurement processing unit 235, an angle measurement unit 236, and Δ A system AD conversion unit 237, an FFT weight unit 238, and an FFT processing unit 239 are provided, and a demodulation unit 23A and a control signal generation unit 23B are further provided.

  In the transmission device 1i, the antenna 1i1 is a phased array antenna formed by arranging a plurality of antenna elements to form a large aperture array, and transmits a transmission signal of a specific frequency repeatedly supplied from the transmitter 1i2 in a specified direction. In the receiving device 2, the antenna 21 is a phased array antenna in which a plurality of antenna elements are arranged to form a large aperture array as in the transmission system, and receives a reflected wave of a transmission wave transmitted from the transmitting device 1i. . In the receiver 22, the reception unit 221 performs phase control on the signals respectively received by the plurality of antenna elements of the antenna 21 according to the beam control instruction and combines them, thereby forming a reception beam in an arbitrary direction and generating a reception signal. Acquire and frequency convert to baseband. The reception signal obtained in this way is sent to the signal processor 23.

  The signal processor 23 distributes the received signal to the Σ beam system and the Δ beam system. The received signal input to the Σ beam system is converted into a digital signal by an AD (Analog-Digital) conversion unit 231, multiplied by a weight as FFT preprocessing by an FFT (Fast Fourier Transformation) weight unit 232, and an FFT processing unit After being subjected to FFT processing at 233 and converted to a Σ beam signal in the frequency domain, detection of cells (time samples) exceeding a predetermined threshold is executed by the CFAR processing unit 234. Subsequently, the distance measurement / speed measurement processing unit 235 performs distance measurement / speed measurement calculation on the CFAR detection cell, and the calculation result is sent to the angle measurement unit 236.

  On the other hand, the received signal input to the Δ beam system is converted into a digital signal by the AD conversion unit 237, multiplied by a weight as FFT preprocessing by the FFT weight unit 238, and FFT processed by the FFT processing unit 239 to be frequency domain. Is then sent to the angle measuring unit 236. The angle measuring unit 236 measures the angle in the target direction from the result of the distance measurement / speed measurement calculation of the Σ beam and the Δ beam signal.

  The output of the CFAR processing unit 234 is sent to the demodulation unit 23A, and the transmission information such as the transmission position, transmission time, and transmission frequency is demodulated from the received signal. The control signal generation unit 23B generates a control signal for the output timing and reception timing of the local signal based on the demodulation result, and sends the control signal to the local control unit 222 and the timing control unit 223 of the receiver 22, respectively.

  In the radar system according to the present embodiment, the transmitter and the receiver are separated from each other. Therefore, the present embodiment provides a method for adjusting time synchronization between apparatuses with high accuracy.

  First, time synchronization will be described with reference to FIG. Note that the signal waveform is described as a continuous waveform of up sweep-down sweep as shown in FIG. 3, but the present invention can be applied to the case of only up sweep or only down sweep. In this embodiment, FMCW (Frequency Modulated Continuous Wave, see Non-Patent Document 1) that calculates distance and speed based on the beat frequency, or FMICW that is pulse-modulated (Frequency Modulated Interrupted Continuous Wave, see Non-Patent Document 2). This method is assumed.

  First, as shown in FIG. 2A, the transmission device 11 uses a frequency range in which no target exists on the beat frequency axis, and uses a bit code (quantization) that represents information such as a transmission position, a transmission time, and a transmission frequency. 2 (b), a time domain amplitude modulation waveform is generated by inverse FFT processing as shown in FIG. 2 (b), and the amplitude modulation waveform is used by the transmission modulator 1122 as shown in FIG. 2 (c). Amplify the FMCW sweep signal or pulse modulated FMICW sweep signal. The modulated signal generated here is power amplified by the transmission unit 1121 and transmitted from the transmission antenna 111. The transmission antenna 111 is assumed to be an antenna having wide-angle directivity. However, when the target direction is within a limited range, the transmission antenna 111 may have transmission directivity that covers that direction.

Here, the modulation signal is formulated as follows. When the target maximum distance and maximum speed are set on the beat frequency axis, the maximum value of the beat frequency can be calculated.

  In the transmission apparatus, the maximum value of the beat frequency is set to a frequency having a margin equal to or larger than the modulation code width shown in FIG. 2A, and includes transmission information such as a transmission position, a transmission center frequency, and a transmission time. Radar transmission wave is generated. In the receiving apparatus, if the reflected signal from the target by the radar transmission wave is observed, the modulation code of the transmission information is superimposed on the reflected signal at the beat frequency depending on the position and speed of the target. be able to. This method has a great merit that a communication line for transmitting necessary information can be minimized. For example, the center frequency that is expected to change from moment to moment can be superimposed on the target signal in real time.

  The modulation code is, for example, a code quantized by transmission information, and arranged with amplitudes corresponding to 0 and 1 on the frequency axis. When this modulated signal is subjected to inverse FFT, an amplitude / phase waveform for the modulated signal including information on the sweep time is obtained. Using this modulation signal waveform, the frequency sweep signal is modulated to obtain a modulation signal. The carrier signal having the center frequency fc is modulated by this modulated signal to obtain a transmission waveform.

  As another example of the modulated signal, the amplitude may be constant and the phase may be changed (BPSK, QPSK) by (0, π) or the like to perform inverse FFT (see Non-Patent Document 6).

  In the receiving device 2, as a method for adjusting the time synchronization, there is a method of adjusting using GPS (Global Positioning System) reception information and time information indicated by an atomic clock, but a time error occurs. For this reason, in this embodiment, transmission information such as a transmission position, a transmission time, and a transmission frequency superimposed on the carrier is demodulated from the radar wave reception signal shown in FIG. 2D as shown in FIG. This is a technique for performing extraction processing using the extracted data.

  In this method, there are a case where a direct wave from a transmission source can be received and a case where transmission and reception are out of line of sight and are received as a target reflected wave. In order to extract transmission information, it is necessary to receive at a high SN. Therefore, the modulated signal shown in FIG. 3A is demodulated by time synchronization control as shown in FIG. 3B. Therefore, the synchronized Δtsel is selected according to the maximum value of the target signal after FFT in each case shown in FIG. Based on this selected Δtsel, transmission information when received is demodulated by the demodulator 23A. As this method, it is possible to demodulate by using a predetermined threshold and setting 1 above for exceeding and 0 for not exceeding. In the case of phase modulation such as BPSK or QPSK, the phase of the FFT output of a signal exceeding a predetermined threshold is detected and demodulated.

  As described above, the transmission information can be demodulated, and the ranging / speed measurement described below can be performed using the beat signal of FIG. 2 (e) including the transmission information. At this time, since the beat frequency has a width corresponding to the modulation code, when pairing up and down sweeps, for example, only the first beat frequency in the modulation code width may be used.

  However, when multiple targets are close to each other, there may be a case where they cannot be separated and overlapped. As a countermeasure, there is a method of alternately transmitting a radar wave including transmission information and a radar wave not including transmission information. For example, the unit of integrating a plurality of up sweeps (down sweeps) is set as one burst, and the presence / absence of transmission information is alternately repeated in burst units. Further, as shown in the second embodiment, when distance measurement / speed measurement can be performed only by the down sweep or the up sweep, the up sweep (down sweep) has transmission information, and the down sweep (up sweep) has no transmission information. There is also a method to repeat as. On the receiving side, the presence or absence of transmission information can be distinguished by whether or not demodulation is possible. In the following description of distance measurement / speed measurement, a method using pairing of an up-chirp signal and a down-chirp signal regardless of the presence / absence of radar wave transmission information will be described. If the transmission time of the transmission source can be acquired, a control signal is generated by the control signal generator 23B, and the timing of the local signal with respect to the received signal is adjusted by the timing controller 223 as shown in FIGS. 4 (a) and 4 (b). . In addition, since the transmission information includes the transmission frequency of the transmission source, the local control unit 222 adjusts the frequency of the local signal based on this transmission information, and the beat frequency using the local signal that adjusts the time timing and frequency of the local signal. And converted into a digital signal by the AD conversion unit 231.

  The input signal is multiplied by the FFT weight in the FFT weight unit 232 and then converted into a frequency domain signal by the FFT processing unit 233 to extract the beat frequency, and the CFAR processing unit 234 outputs a signal exceeding a predetermined threshold. Then, the distance measurement / speed measurement calculation unit 235 performs distance measurement / speed measurement calculation. As this method, there is an FMCW method (see Non-Patent Document 1) that uses pairing of a down sweep and an up sweep signal.

This is formulated. An up sweep signal and a down sweep signal are extracted from the received signal and converted to a signal on the beat frequency axis. Using this frequency axis signal, a frequency having an extreme value is extracted from the result of FFT of the up-sequence and down-sequence signals. This relational expression is shown below.

On the other hand, the frequency fr depending on the distance and the Doppler frequency fd depending on the target speed are as follows.

When the expression (3) is expanded with R and V and the expression (2) is substituted, the following expression is obtained.

  However, when the target is at a long distance, a signal for one sweep of up sweep (down sweep) is received with a delay in accordance with the target distance. Therefore, in order to observe the beat frequency using the difference from the local signal of the reception system, it is necessary to extend the local signal as shown in FIG. 5B with respect to the transmission signal of FIG. . That is, even during the transmission down sweep (up sweep) time, the local signal needs to sweep both the up sweep (down sweep) and the down sweep (up sweep) at the same time.

  As for angle measurement, in the system of FIG. 1, using Δ (ΔAZ, ΔEL), the component of the same beat frequency as the detected Σ is used, and the angle is measured by monopulse angle measurement (see Non-Patent Document 3) or the like. Calculation output is possible.

  Here, if there are three transmission devices as shown in FIG. 6, the same processing is performed on the reception device, so that the transmission device Tx1 to the reception device Rx, the transmission device Tx2 to the reception device Rx, and the transmission device Tx3 R1, R2, and R3 can be obtained as the respective distances from to the receiving device Rx.

Using this distance, a target position (x, y, z) is calculated as shown in FIG. This method is the intersection of the spherical surface of R1 and the elliptical spherical surfaces of R2 and R3. Among them, an intersection in the predetermined range is calculated with a three-dimensional position in the AZ angle and EL angle directions observed by the receiving radar device as a center. If it cannot be calculated by the solution, the points in the target existence area are divided into (x, y, z) grid points, and the point (x, y, z) where the value of the following expression is the minimum is calculated at each point. To do.

  If the receiving device has a transmission / reception function, two transmitting devices are sufficient, and the midpoint of the intersection line can be output as a target three-dimensional observation position by the same method.

  For example, in the case of one transmission device, if there are three reception devices, R1 to R3 can be obtained in the same manner, so that a three-dimensional position can be determined by the same method.

  Further, in the case of a plurality of transmission apparatuses, a radar with a low target SN may be included, and if a three-dimensional position is calculated as it is, a position error may increase. As a countermeasure, a predetermined threshold may be provided for the SN value, and the position may be calculated using values of the transmission device to the reception device that are equal to or higher than the threshold.

  In the above description, the case where the target three-dimensional position is output has been described. However, in the case where the target two-dimensional position (x, y) is output, the number of transmission devices + reception devices is two transmission devices + One or more receiving devices, or one transmitting device + two or more receiving devices may be used.

  As described above, in the present embodiment, transmission information such as position, transmission frequency, transmission time, etc. is provided in Nt (Nt ≧ 1) transmission devices and Nr (Nr ≧ 1, Nt + Nr ≧ 4) reception devices. As a modulation signal, at least one continuous wave or pulse-modulated signal (such as FMCW or FMICW) of up sweep or down sweep having a frequency sweep gradient is modulated and transmitted. In the receiving device, the direct wave from the transmitting device or the received wave reflected from the target is selected as the start time that maximizes the FFT output when the FFT start time is changed in a plurality of ways, and is integrated as necessary. The transmission information is demodulated and extracted, the received local signal is synchronized with the received signal based on the transmitted information, the received local signal is corrected, the beat frequency is observed by FFT processing, and the observed beat frequency The target three-dimensional position is calculated by measuring the target distance (speed measurement and angle measurement if necessary) and calculating the intersection point from the distance R of three or more pairs of transmission and reception and the angle measurement value of the receiving device. (X, y, z) can be calculated (reception local correction and position calculation by communication).

  As a result of the above configuration, radar wave transmission information is detected with high SN (signal-to-noise power ratio) using integration by continuous wave, and the received local signal is controlled using that information, and the distance etc. by beat frequency By observing, the position of the three-dimensional target can be observed.

  In the present embodiment, the local signals of up (down) sweep and down (up) sweep are extended so as to receive a target signal from a long distance. In other words, even in the case of a reflected signal from a long distance, the beat frequency can be observed because the time-extended local signal is used.

(Second Embodiment) (Position output by MRAV)
In the first embodiment, the method for calculating the distance and speed using FMCW has been described. In the present embodiment, a method using an MRAV (Measurement Range after Measurement Velocity) method (see Patent Document 1) will be described. The system is shown in FIG. The difference from the first embodiment shown in FIG. 1 is that an MRAV processing unit 23C is used in place of the distance measurement / speed measurement processing unit 235.

  FIG. 9 shows distance measurement / speed measurement processing in the receiving apparatus employing the MRAV processing unit 23C. In the present embodiment, for example, a triangular sweep as shown in FIG. 5 is used as a transmission signal waveform. However, for simplicity, only a down sweep (same as an up sweep) is extracted as shown in FIG. Will be described. In the case of the triangular sweep, processing is performed for each of the down sweep and the up sweep, and the average value of the distance and speed and the distance and speed of the higher SN are output. For simplicity, the case where two sweeps are generated in one cycle will be described, but the same applies to the case where n (n ≧ 2) times.

(1) A signal to be swept (hereinafter referred to as “sweep 1”) transmitted first in one cycle is received, and a sample sequence of sweep 1 is subjected to FFT processing to obtain a phase monopulse signal in the frequency domain (step ST1).
(2) A threshold is detected from the FFT result of sweep 1 (step ST2).
(3) The beat frequency fp having the peak signal is extracted and stored based on the threshold (step ST3).
(4) The presence of the next sweep is determined (step ST4). Here, sweep 2 transmitted after time T12 from sweep 1 is specified (step ST5), and the processes of steps ST1 to ST4 are executed.
(5) Using the beat frequencies fp of the sweeps 1 and 2, the target speed V = (R2-R1) / T12 is calculated (step ST6), and the relative distances R1 and R2 are calculated (step ST7). The target information obtained in this way is stored (step ST8), and the processes of steps ST6 to ST8 are executed for all target objects in the measurement cycle (steps ST9 and ST10).

Here, the relative distance R is as follows.

Using the beat frequency fp and the speed V calculated in step ST6, the distance R and the speed V can be calculated by the following simultaneous equations.

  The above method is called MRAV (Measurement Range after Measurement Velocity) method (refer to Patent Document 1) because the distance is calculated after calculating the speed based on the beat frequency.

  At this time, there is a method for improving the observation accuracy of the beat frequency. In particular, when the beat frequency is within the same bank between sweeps, such as when the target speed is low, the target beat frequency that moves within the same bank as shown in FIGS. It is necessary to calculate. As a countermeasure, as shown in FIG. 12, a phase monopulse (see Non-Patent Document 2) used on the angle axis is used on the frequency axis, and the frequency in the bank is observed with high accuracy. The procedure is shown below.

(1a) Frequency axis monopulse
Using the extracted target frequency Σ (f) and Δ (f), an error voltage ε of the following equation is calculated. The error voltage ε corresponds to the target observation frequency as shown in FIG. 13B in the phase monopulses Σ and Δ shown in FIG.

  (2a) The reference value ε0 of the error voltage ε calculated using the frequency characteristics of Σ and Δ stored in advance is tabulated (corresponding relationship between ε0 and the frequency f), and using the reference table, A highly accurate frequency fp is extracted from the observed value ε.

  (3a) Using this frequency fp, the distance and speed are calculated by the procedures (1) to (5) of the second embodiment.

  In addition, about weighting, in addition to -1 or 1, you may multiply weights, such as a tailor weight (refer nonpatent literature 4), in order to reduce a side lobe.

  Although the above processing has been described for the case of two sweeps, it may generally be a case of multiple sweeps. As an example, the case of four sweeps is shown in FIGS. When calculating the speed from the gradient of the beat frequency at four points with respect to the sweep time, linear fitting or the like may be used.

  In addition, the monopulse calculation of the angle axis is performed on the cell detected by the CFAR processing unit 234 using the Σ signal. Further, the angle measuring unit 237 performs angle measurement using Σ and Δ of the beam output, and calculates the Az angle and the EL angle.

  As described above, in the present embodiment, the MRAV method using continuous waves is adopted as the distance measurement / speed measurement method, and therefore, the three-dimensional position of a plurality of targets, etc. without using pairing by up sweep and down sweep. Can be output.

(Third Embodiment) Transmission Isolation In this embodiment, in order to ensure isolation between transmissions, the transmission device 1i1 and the reception device 2 are configured as shown in FIGS. 15 (a) and 15 (b), respectively. This is a method of changing the frequency band of each of the plurality of transmission devices (Nt ≧ 2) for each transmission device.

  That is, as shown in FIG. 16A, the radar system according to the present embodiment changes the sweep frequency band between the transmission devices 1i by the transmission modulation unit 1i22. On the other hand, in order to receive the signal from each transmitting device 1i, the receiving device 2 sequentially receives signals in sweeps corresponding to Nr sweeps in the local control unit 222a as shown in FIG. 16B. To do. When receiving Nr channels are provided, parallel processing is performed, and when only one channel is provided, it is necessary to switch to receive in time series.

  Since the receiver 22 and the AD conversion unit 231 receive only a signal having a predetermined bandwidth according to the beat frequency, signals from the transmission device 1i having different sweep signal bands are not in the case where the transmission and reception sweep bands do not match. Is not received, it is possible to ensure isolation between the transmitting devices.

  As described above, in the present embodiment, in the case of a plurality of transmission apparatuses (Nr ≧ 2), the frequency band of the sweep signal is changed for each transmission apparatus, and the observation is performed while sequentially changing the sweep band of the local frequency. By doing so, it is possible to ensure the isolation of the transmission signal of the transmission apparatus and to observe with a reduced false target.

(Fourth Embodiment) MIMO (Multiple-Input Multiple-Output)
In the present embodiment, when the reception aperture area is small, MIMO (see Non-Patent Document 5) is used to increase the aperture area of the transmission / reception virtual array and improve the angular resolution.

  17 and 18 show the system, FIG. 19 shows an example of the real aperture and the virtual array aperture, and FIG. 20 shows a general example of the transmission and reception antenna coordinate systems. The figure shows an example in which transmission and reception are included in the same antenna aperture, but at least the multistatic transmission and reception may have different configurations.

  In FIG. 17A, the transmitting apparatus 1i uses an antenna 1i1a as an N-element array antenna. In FIG. 17B, the receiving device 2 uses an antenna 21a as an M-element array antenna, and between the AD conversion units 231 and 237 and the FFT weight units 232 and 238 of the signal processor 23, the configuration shown in FIG. A MIMO processing unit 23D shown in FIG. As shown in FIG. 18, the MIMO processing unit 23D includes a virtual array conversion unit 23D1 and a beam forming unit 23D2.

  That is, in MIMO, the N-element transmission apparatus 1i performs transmission modulation with different modulation schemes in order to achieve isolation. In the receiving device 2, the antenna 21 a is used as an array antenna, and signals received by each element (M element) of the array antenna are frequency-converted by the receiving unit 221 of the receiver 22, respectively, and then the AD converter 231 of the signal processor 23 is used. A digital signal corresponding to M elements is obtained by converting into a digital signal. Then, in the virtual array conversion unit 23D1 of the MIMO processing unit 23D, the digital signals for M elements are used to demodulate with reference signals that match the transmission modulation for N elements to obtain N × M signals.

This is formulated below. When the signals of the transmitting antenna (N transmitting devices) and the receiving antenna (array of M elements) are respectively expressed as A and B, the following equations are obtained.

From this, each element becomes the following equation.

Next, when each transmitting / receiving element signal is expressed by a matrix element, the following equation is obtained.

  Each signal (an · bm) of this virtual array is equivalent to the presence of a virtual array element at the position where the position vector of the array of the transmitting device and the array of the receiving device is combined, and the aperture can be virtually enlarged. it can.

The transmission / reception beam output is given by the following equation by adding a weight for side lobe reduction and a weight for side lobe reduction to the elements of equation (13) after beam formation.

  Thus, for example, when M = 1 and N = 4, the large aperture antenna is configured as the virtual array aperture for transmission and reception as shown in FIG. 19B for the real aperture shown in FIG. And the angular resolution can be improved.

  As described above, in the present embodiment, a plurality of transmission devices are arranged so as to be separated from each other by the reception aperture, and the reception device side performs observation and transmission / reception MIMO processing by using a MIMO virtual array. The angle can be measured after the aperture of the virtual array is enlarged, and the angle accuracy can be improved.

(Fifth Embodiment) Non-Line-of-Sight Reflection Device When the receiving device is out of line of sight from the transmission device, the receiving device cannot receive a direct wave, and therefore, a reflected wave from the target is used as the communication means. However, when the reflected wave from the target is small, the SN (signal-to-noise power ratio) is low and cannot be demodulated, and transmission information cannot be obtained. In this embodiment, the countermeasure is described.

  As a countermeasure against this, as shown in FIG. 21, a reflection device 1001 to 100P such as a reflection sphere is disposed within the line-of-sight from the transmission device and the reception device. In order to be placed within the line of sight, it is generally necessary to raise the altitude. Various methods are conceivable as the method, such as mounting a balloon-like reflector on the transmission source device.

  As described above, in the present embodiment, the direct wave from the transmission device is transmitted to the reception device via the reflection device arranged at a high level within the line-of-sight, so that the transmission device is viewed from the reception device. Even when it is out of line of sight, it is possible to observe a reflected wave by a reflection device, obtain transmission information with a high SN, and control a local signal using it, thereby observing a beat frequency with a high SN. And the radar observation accuracy can be improved.

(Sixth embodiment) Non-line-of-sight data link In the fifth embodiment, a method of using a reflected wave from a target as a countermeasure to prevent direct reception when the receiving device is out of sight from the transmission source has been described. . In this embodiment, another countermeasure will be described.

  As a countermeasure, as shown in FIG. 22 (a), a transmission device 1i is used as a transmission / reception device 1ia, a data link is formed between them by transmission waves, and transmission information is shared between the transmission / reception devices 1ia. The receiving apparatus is the same as that of the first embodiment as shown in FIG.

  Specifically, the transmission / reception device 3i (i is 1 to N) is configured by the shared antenna 3i1, the transmission device 3i2, and the reception device 3i3, the transmission device 3i2 is configured by the transmission unit 3i21 and the transmission modulation unit 3i22, and the reception device 3i3 includes a reception unit 3i31, an AD conversion unit 3i32, an FFT weight unit 3i33, an FFT processing unit 3i34, a CFAR processing unit 3i35, a demodulation unit 3i36, a time synchronization control unit 3i37, and a modulation signal generation unit 3i38.

  In the transmission / reception device 3i configured as described above, the demodulation unit 3i36 of the reception device 3i3 receives the transmission wave of the other transmission / reception device, demodulates the transmission information, and transmits it to the other transmission / reception device together with its own transmission information. Then, the modulation signal generation unit 3i32 generates a modulation signal and transmits it to the transmission modulation unit 3i22.

  The receiving device 2 receives and demodulates the transmission wave from the line-of-sight transmission / reception device, and controls the local signal using the transmission information. Thereby, since the position, transmission time, transmission frequency, etc. of a transmission / reception apparatus can be recognized even if it is out of sight, the target three-dimensional position can be observed.

  As described above, in the present embodiment, a data link is formed by a radar communication wave between transmission / reception devices, transmission information is shared by the transmission / reception devices, and a transmission wave from a line-of-sight transmission / reception device from the reception device is received by the reception device. And demodulating, and controlling the local signal using the transmission information. That is, even when a certain transmission / reception device is out of line of sight with respect to the reception device, a transmission / reception device capable of observing direct waves can relay and transmit, obtain transmission information at a high SN, and use it to transmit a local signal. By controlling, the beat frequency can be observed with a high SN, and the radar observation accuracy can be improved.

(Seventh Embodiment) Center Frequency Correction In the first embodiment, the method of correcting the center frequency using transmission information has been described. In the present embodiment, a technique for increasing the accuracy of the center frequency in a receivable situation will be described.

  The system is shown in FIGS. 23 (a) and (b). As shown in FIG. 23 (b), the feature of this embodiment is that, in the receiving apparatus 2, the beat frequency signal is acquired from the output of the distance measurement / speed measurement processing unit 236, and the center frequency is calculated from the modulated carrier wave signal. And a center frequency calculation unit 23E that combines the two. The transmission / reception signal waveform in this case is an FMCW sweep in which both up sweep and down sweep are continuously transmitted / received.

The beat frequency in the case of FMCW (see Non-Patent Document 1) or FMICW (see Non-Patent Document 2) can be expressed by the following equation when the target beat frequency signals of up sweep and down sweep are associated by pairing.

The procedure for calculating the error frequency Δferr in this equation is as follows.
Procedure 1) Velocity V is calculated by MRAV method.
Procedure 2) If V is substituted into equation (15) and added, the term of distance R can be deleted. Therefore, Δferr is calculated by the following equation.

Then, using this Δferr calculated by the center frequency calculation unit 23E as a correction value, the local signal is controlled or corrected by subtracting Δferr from the right side of the beat frequency in the equation (15), and the distance and speed are corrected by the MRAV method. Is calculated.

  In addition, it is necessary to extract a frequency pair (fbd and fbu or fb1 and fb2) by pairing the target signal between sweeps of up and down sweeps, or sweeps of different slopes. There is a method of pairing those whose values are within a predetermined width using an amplitude value, a measured angle value, or the like.

  As described above, in the present embodiment, the difference between the center frequencies of the transmission device and the reception device is calculated and corrected from the received signal using the MRAV technique. That is, it is possible to observe the shift of the center frequency between the transmission device and the reception device from the received signal and observe the beat frequency without the information on the center frequency in the transmission information.

  According to the above configuration, even if an error occurs in the Doppler frequency due to the deviation of the local center frequency of each radar device, the error in the Doppler frequency can be calibrated, thereby the target speed based on the error in the Doppler frequency. Detection error can be reduced.

  Note that the present embodiment is not limited to the above-described embodiment as it is, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

11 to 1N: transmitting device, 1i1 ... transmitting antenna, 1i2 ... transmitter, 1i21 ... transmitting unit, 1i22, 1i22a ... transmitting modulating unit,
DESCRIPTION OF SYMBOLS 2 ... Receiving device, 21, 21a ... Reception antenna, 22 ... Receiver, 221 ... Reception part, 222, 222a ... Local control part, 223 ... Timing control part, 23 ... Signal processor, 231 ... AD conversion part, 232 ... FFT weight unit, 233... FFT processing unit, 234... CFAR processing unit, 235... Ranging / speed measurement processing unit, 236 .. Angle measurement unit, 237... AD conversion unit, 238. , 23A ... demodulator, 23B ... control signal generator, 23C ... MRAV processor, 23D ... MIMO processor, 23D1 ... virtual array converter, 23D2 ... beam former, 23E ... center frequency calculator,
31-3N: Transmission / reception device, 3i1 ... Transmit / receive antenna, 3i2 ... Transmission device, 3i21 ... Transmission unit, 3i22 ... Transmission modulation unit, 3i3 ... Reception device, 3i31 ... Reception unit, 3i32 ... AD conversion unit, 3i33 ... FFT weight 3i34 ... FFT processor, 3i35 ... CFAR processor, 3i36 ... demodulator, 3i37 ... time synchronization controller, 3i38 ... modulation signal generator,
1001 to 100P: Reflector.

Claims (9)

In a radar system comprising t (Nt ≧ 1) transmitters and Nr (Nr ≧ 1, Nt + Nr ≧ 4 or 3) receivers,
In the transmitter, the transmission information including position, transmission frequency, and transmission time is used as a modulation signal, and at least one continuous wave or pulse-modulated signal of up sweep or down sweep having a frequency sweep gradient is modulated and transmitted.
In the receiving device, a direct wave from the transmitting device or a reflected wave reflected from the target is received, and a start time at which the FFT output is maximized is selected by changing a plurality of FFT (Fast Fourier Transform) start times. And then demodulating and extracting transmission information, synchronizing the reception local signal with the received signal based on the transmission information, correcting the reception local signal, and calculating the beat frequency by the FFT processing. Observe, measure the target distance, and measure the speed and angle as necessary, and calculate the intersection from the distance of the transmission and reception or two or more pairs and the angle measurement value of the receiver, so that the target three-dimensional A radar system that calculates a position (x, y, z) or a two-dimensional position (x, y).   2. The radar system according to claim 1, wherein the receiving device extends a reception local signal corresponding to an up sweep or down sweep and a down sweep or up sweep on the transmission device side to a length for receiving a target signal from a predetermined distance or more. .   The radar system according to claim 1, wherein MRAV (Measurement Range After Measurement Velocity) is used as the distance measurement / speed measurement technique.   2. The radar system according to claim 1, wherein when a plurality of the transmission devices are provided, the signal of the sweep is set to a different frequency band for each of the transmission devices.   The radar system according to claim 1, wherein the transmission device is separated by a reception aperture, and the reception device observes using a virtual array based on MIMO (Multiple-Input Multiple-Output).   Furthermore, a reflection device that reflects the direct wave from the transmission device in a predetermined direction is provided, and the direct wave from the transmission device is transmitted to another reception device via the reflection device that is disposed at a high altitude within the line of sight. The radar system according to claim 1.   When a plurality of the transmission devices are provided, a data link by a radar communication wave is formed between the transmission devices to share transmission information between the transmission devices, and the reception device receives a transmission wave from a line-of-sight transmission device. The radar system according to claim 1, wherein the local signal is controlled using the transmission information.   The radar system according to claim 1, wherein the receiving device calculates and corrects a difference in center frequency between the transmitting device and the device itself using an MRAV technique from the received signal. used in radar systems comprising t (Nt ≧ 1) transmitters and Nr (Nr ≧ 1, Nt + Nr ≧ 4 or 3) receivers,
In the transmitter, the transmission information including position, transmission frequency, and transmission time is used as a modulation signal, and at least one continuous wave or pulse-modulated signal of up sweep or down sweep having a frequency sweep gradient is modulated and transmitted.
In the receiving device, a direct wave from the transmitting device or a reflected wave reflected from the target is received, and a start time at which the FFT output is maximized is selected by changing a plurality of FFT (Fast Fourier Transform) start times. And then demodulating and extracting transmission information, synchronizing the reception local signal with the received signal based on the transmission information, correcting the reception local signal, and calculating the beat frequency by the FFT processing. Observe, measure the target distance, and measure the speed and angle as necessary, and calculate the intersection from the distance of the transmission and reception or two or more pairs and the angle measurement value of the receiver, so that the target three-dimensional A radar signal processing method of a radar system for calculating a position (x, y, z) or a two-dimensional position (x, y).

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