JP6716352B2 - Radar system and radar signal processing method thereof - Google Patents

Description

The present embodiment relates to a multi-static radar system and a radar signal processing method thereof.

Recently, in a radar system, a multi-static method has been developed in which one or more transmission/reception radar devices or reception radar devices are spaced apart from each other along with transmission/reception radar devices, and the target position is detected by the observation result of each radar device. Has been done. However, in this type of radar system, when the time synchronization between the separated radar devices is insufficient or the distance accuracy is insufficient, the error of the observation position becomes large. Further, when observing the beat frequency of a continuous wave such as FMCW (Frequency Modulated Continuous Wave), if the center frequency is deviated, the beat frequency becomes inaccurate and the ranging/speed measuring accuracy also deteriorates. Will end up. Further, in the case of a receiving device having a small aperture, it is difficult to obtain sufficient angle measurement accuracy. Further, when the transmitter is out of the line of sight, the direct wave cannot be received, and the synchronized multi-static operation cannot be performed.

JP, 2010-271115, A

FMCW method (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) method, Yoshida,'Revised radar technology', IEICE, pp.262-264 (1996) Taylor Distribution, Yoshida,'Revised Radar Technology', The Institute of Electronics, Information and Communication Engineers, 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 multi-static radar system, the beat frequency cannot be accurately observed due to the time synchronization deviation between the radar devices and the deviation of the center frequency, and the target three-dimensional position is calculated. In the above, there is a problem that the distance accuracy and the speed accuracy are insufficient, and the angle measuring accuracy is low in a small receiving device.

The present embodiment has been made in view of the above problems, and reduces the effects of time synchronization deviation and center frequency deviation between the transmission device and the reception device, improves the accuracy of beat frequency observation, and achieves the target three-dimensional or two-dimensional measurement. An object of the present invention is to provide a radar system and a radar signal processing method thereof, which can obtain sufficient distance accuracy and speed 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 Nt (Nt≧1) transmitters and Nr (Nr≧1, Nt+Nr≧4 or 3) receivers. .. The transmission device modulates and transmits at least one up-sweep or down-sweep continuous wave or pulse-modulated signal having a frequency sweep gradient, using transmission information including position, transmission frequency, and transmission time as a modulation signal. The receiving device receives a direct wave from the transmitting device or a reflected wave reflected from a target, and selects a start time at which the FFT output becomes maximum by changing a plurality of FFT (Fast Fourier Transform) start times, , And then demodulates to extract transmission information, synchronizes the received local signal with the received signal based on the transmitted information, further corrects the received local signal, and performs the beat frequency by the FFT processing. The target three-dimensional position (x, y) is calculated by observing the target and measuring the distance and angle of the target, and calculating the intersection point from the distance of three or more pairs of transmission and reception and the angle measurement value of the receiving device. , Z) or a two-dimensional position (x, y) is calculated.

The block diagram which shows the structure of the radar system which concerns on 1st Embodiment. FIG. 3 is a waveform diagram for explaining time synchronization of the radar system according to the first embodiment. FIG. 3 is a waveform diagram showing an up-sweep-down-sweep signal waveform used in time synchronization of the radar system according to the first embodiment. FIG. 3 is a waveform chart for explaining local control processing of the radar system according to the first embodiment. FIG. 3 is a waveform diagram showing a long-distance sweep waveform in the radar system according to the first embodiment. The figure which shows a mode that distance measurement is carried out in the radar system which concerns on 1st Embodiment when there are three transmitters and one receiver. The figure which shows a mode that a 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 the flow of processing of distance measurement/speed measurement 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 isolation isolation 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 concrete structure of the MIMO processing part of the radar system which concerns on 4th Embodiment. The conceptual diagram which shows a mode that a virtual array aperture 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 parts will be denoted by the same reference numerals, and overlapping description will be omitted.

(First embodiment)
A radar system according to the first embodiment will be described with reference to FIGS. 1 to 7. This radar system includes N transmitters 11 to 1N shown in FIG. 1A and one receiver 2 shown in FIG. 1B. Each of the transmitters 1i (i is one of 1 to N) includes a transmission antenna 1i1 and a transmitter 1i2, and each transmitter 1i2 includes a transmitter 1i21 and a transmission modulator 1i22. The receiving device 2 includes a receiving antenna 21, a receiver 22, and a signal processor 23. The receiver 22 includes a receiver 221, a local controller 222, and a timing controller 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. The system includes an AD conversion unit 237, an FFT weight unit 238, and an FFT processing unit 239, and further includes a demodulation unit 23A and a control signal generation unit 23B.

In the transmitter 1i, the antenna 1i1 is a phased array antenna formed by arranging a plurality of antenna elements to form a large aperture array, and sends out a transmission signal of a specific frequency repeatedly supplied from the transmitter 1i2 in a designated direction. In the receiving device 2, the antenna 21 is a phased array antenna formed by arranging a plurality of antenna elements to form a large aperture array similarly to the transmitting system, and receives the reflected wave of the transmitting wave transmitted from the transmitting device 1i. .. In the receiver 22, in the receiver 221, the signals respectively received by the plurality of antenna elements of the antenna 21 are subjected to phase control in accordance with a beam control instruction and are combined to form a reception beam in an arbitrary direction to generate a reception signal. Obtain and frequency convert to baseband. The received signal thus obtained 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 then an FFT processing unit. After being FFT processed by 233 and converted into a Σ beam signal in the frequency domain, a CFAR processing unit 234 detects a cell (time sample) exceeding a predetermined threshold. Subsequently, the distance measurement/speed measurement processing unit 235 performs distance measurement/speed measurement calculation for 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 weights as FFT preprocessing by the FFT weight unit 238, and FFT processed by the FFT processing unit 239 to perform frequency domain processing. After being converted into the Δ beam signal of, the beam is sent to the angle measuring unit 236. The angle measuring unit 236 measures the angle in the target direction from the distance measurement/speed measurement calculation result 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 demodulates the transmission information such as the transmission position, the transmission time and the transmission frequency from the received signal. The control signal generation unit 23B generates control signals for the output timing and the reception timing of the local signal based on the demodulation result, and sends the control signals to the local control unit 222 and the timing control unit 223 of the receiver 22, respectively.

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

First, the time synchronization will be described with reference to FIG. As the signal waveform, a continuous waveform of upsweep-downsweep as shown in FIG. 3 will be described, but it is applicable to only upsweep or downsweep. Further, in the present embodiment, an FMCW (Frequency Modulated Continuous Wave, see Non-Patent Document 1) that calculates a distance and a velocity based on a beat frequency, or a pulse-modulated FMICW (Frequency Modulated Interrupted Continuous Wave, see Non-Patent Document 2). The method is assumed.

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

The formula of the modulated signal is as follows. By setting the target maximum distance and maximum velocity on the beat frequency axis, the maximum value of the beat frequency can be calculated.

In the transmitter, 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 the transmission information such as the transmission position, the transmission center frequency, and the transmission time is included. Generate a radar transmission wave. In the receiving device, when the reflected signal from the target due to the radar transmitted wave is observed, since the modulation code of the transmitted information is superimposed on the beat frequency depending on the target position and velocity in the reflected signal, the transmitted information is demodulated to obtain the transmitted information. be able to. This method has a great advantage that the number of communication lines for transmitting necessary information can be minimized. For example, the center frequency, which is expected to change moment by moment, can be superimposed on the target signal in real time.

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

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

As a method for time synchronization adjustment in the receiving device 2, there is a method of making adjustment using reception information of GPS (Global Positioning System) and time information indicated by an atomic clock, but a time error occurs. Therefore, in the present embodiment, the transmission information such as the transmission position, the transmission time, the transmission frequency, etc. superimposed on the carrier is demodulated from the reception signal of the radar wave shown in FIG. 2(d) as shown in FIG. 2(e). It is a method of performing reception processing using the extracted data.

In this method, there are cases where the direct wave from the transmission source can be received, and cases where the transmission and reception are out of sight and received as the target reflected wave. Since it is necessary to receive at a high SN in order to extract the transmission information, the modulated signal shown in FIG. 3(a) is demodulated by time synchronization control as shown in FIG. 3(b). The start time Δt of the sweep frequency is changed by Nt, and the synchronized Δtsel is selected according to the maximum value of the target signal after FFT in each case shown in FIG. According to the selected Δtsel, the transmission information when received is demodulated by the demodulation unit 23A. As a method of this, demodulation can be performed by using a predetermined threshold and setting 1 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 that exceeds a predetermined threshold is detected and demodulated.

As described above, the transmission information can be demodulated, and the distance measurement/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 the up sweep and the down sweep, for example, only the first beat frequency in the modulation code width may be used.

However, when a plurality of targets are close to each other, it is possible that they cannot be separated by superimposing them. As a countermeasure, there is a method of alternately transmitting a radar wave containing transmission information and a radar wave not containing transmission information. For example, the unit for integrating a plurality of up-sweeps (down-sweeps) is one burst, and the presence or 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 by only down sweep or up sweep, there is transmission information in up sweep (down sweep) and no transmission information in down sweep (up sweep). There is also a method of repeating. On the receiving side, the presence/absence of transmission information can be distinguished by whether or not demodulation is possible. In the following description of distance measurement/velocity measurement, a method of using pairing of an up-chirp signal and a down-chirp signal will be described regardless of the presence or absence of transmission information of radar waves. If the transmission time of the transmission source can be acquired, the control signal generation unit 23B generates a control signal, and the timing control unit 223 adjusts the timing of the local signal with respect to the reception signal 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 the transmission information, and the beat frequency of the local signal whose time timing and frequency are adjusted. Then, the AD converter 231 converts the obtained signal into a digital signal.

The FFT weighting unit 232 multiplies the input signal by the FFT weight, the FFT processing unit 233 converts the input signal into a frequency domain signal to extract a beat frequency, and the CFAR processing unit 234 extracts a signal that exceeds a predetermined threshold. The distance is detected, and the distance/speed calculation unit 235 performs distance/speed calculation. As this method, there is an FMCW method (see Non-Patent Document 1) that uses pairing of down sweep and up sweep signals.

This is formalized. An up-sweep signal and a down-sweep signal are extracted from the received signal and converted into a signal on the beat frequency axis. A frequency having an extreme value in amplitude is extracted from the result of FFT of an up-series signal and a down-series signal using the signal on the frequency axis. This relational expression is shown below.

On the other hand, the frequency fr according to the distance and the Doppler frequency fd according to the target speed are given by the following equation.

When the formula (3) is expanded with R and V and the formula (2) is substituted, the following formula 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 according to the target distance. Therefore, in order to observe the beat frequency by using the difference from the local signal of the receiving 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, it is necessary for the local signal to sweep both up-sweep (down-sweep) and down-sweep (up-sweep) at the same time.

Further, regarding the angle measurement, in the system of FIG. 1, the angle is determined by the monopulse angle measurement (see Non-Patent Document 3) using Δ(ΔAZ, ΔEL) and the component of the same beat frequency as the detected Σ. It can be calculated and output.

Here, assuming that the number of transmitting devices is three as shown in FIG. 6, the same process is performed for the receiving devices, so that the transmitting devices Tx1 to Rx, the transmitting devices Tx2 to Rx, and the transmitting device Tx3. R1, R2, and R3 can be obtained as the respective distances from the receiver to the receiving device Rx.

Using this distance, the target position (x, y, z) is calculated as shown in FIG. This method is the intersection of the sphere of R1 and the ellipsoid of R2 and R3. Among them, an intersection point is calculated with a target existing area within a predetermined range centered on a three-dimensional position in the AZ angle and EL angle directions observed by the reception radar device. If the solution cannot be calculated, the points in the target existing area are divided into (x, y, z) grid points, and the point (x, y, z) at which the value of the following formula is the minimum is calculated for each point. To do.

If the receiving device has a transmitting/receiving function, the number of transmitting devices may be two, and the midpoint of the intersection line can be output as a target three-dimensional observation position in the same manner.

Further, for example, if there are three receiving devices in the case of one transmitting device, R1 to R3 can be obtained in the same manner, so that the three-dimensional position can be determined by the same method.

Further, in the case of a plurality of transmitters, a radar having a low target SN may be included, and if the three-dimensional position is calculated as it is, a position error may increase. For this measure, a predetermined threshold may be provided for the SN value, and the position may be calculated using the values of the transmitting device to the receiving device that are equal to or higher than the threshold.

In addition, the above has described the case of outputting the target three-dimensional position, but when outputting the target two-dimensional position (x, y), the number of transmitters+receivers is two transmitters+ It may be one or more receiving devices or one transmitting device+two receiving devices.

As described above, in the present embodiment, in Nt (Nt≧1) transmitters and Nr (Nr≧1, Nt+Nr≧4) receivers, transmission information such as position, transmission frequency, and transmission time is transmitted. Is used as a modulation signal to modulate and transmit at least one continuous wave or pulse-modulated signal (FMCW or FMICW) of up sweep or down sweep having a frequency sweep gradient. 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 start time of the FFT is changed in multiple ways, and after integration if necessary. , Demodulate and extract transmission information, synchronize the received local signal with the received signal based on the transmission information, further correct the received local signal, observe the beat frequency by FFT processing, and observe the observed beat frequency The target distance measurement (speed measurement and angle measurement if necessary) is performed, and the intersection point is calculated from the distance R of three or more pairs of transmission and reception and the angle measurement value of the reception device, thereby obtaining the three-dimensional position of the target. It is possible to calculate (x, y, z) (receive local correction and position calculation by communication).

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

Further, in this 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. That is, even in the case of a reflected signal from a long distance, since the time-extended local signal is used, the beat frequency can be observed.

(Second embodiment) (position output by MRAV)
In the first embodiment, the method of calculating the distance and the velocity using the 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 instead of the distance measurement/speed measurement processing unit 235.

FIG. 9 shows a measurement process of distance measurement/speed measurement in the receiving device adopting the MRAV processing unit 23C. In the present embodiment, the transmission signal waveform is, for example, a triangular sweep as shown in FIG. 5, but here, for simplification, as shown in FIG. 10, when only down sweep (the same applies to up sweep) is extracted. Will be described. In the case of the triangular sweep, each of the down sweep and the up sweep is processed, and the average value of the distance and the speed thereof and the distance and the speed of the higher SN are output. Further, for simplification, the case of generating the sweep twice in one cycle will be described, but the same applies to the case of n (n≧2) times.

(1) Receive a signal to be swept (firstly referred to as sweep 1) transmitted first in one cycle, perform FFT processing on the sample sequence of sweep 1, and obtain a phase monopulse signal in the frequency domain (step ST1).
(2) The threshold is detected from the FFT result of sweep 1 (step ST2).
(3) The beat frequency fp having a peak signal is extracted and stored based on the threshold (step ST3).
(4) The presence of the next sweep is judged (step ST4). Here, the sweep 2 transmitted after the time T12 from the sweep 1 is designated (step ST5), and the processes of the 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 thus obtained is stored (step ST8), and the processes of steps ST6 to ST8 are executed for all target objects in the measurement cycle (steps ST9, ST10).

Here, the relative distance R is given by the following equation.

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

The above method is called an MRAV (Measurement Range after measurement Velocity) method (see Patent Document 1) because the distance is calculated after the velocity is calculated by the beat frequency.

At this time, there is a method for improving the accuracy of beat frequency observation. In particular, when the beat frequency is in 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. 11A and 11B is accurately measured. Need to calculate. As a countermeasure against this, as shown in FIG. 12, a phase monopulse used in the angle axis (see Non-Patent Document 2) is used in the frequency axis to observe the frequency in the bank with high accuracy. The procedure is shown below.

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

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

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

Regarding weighting, in addition to -1 or 1, weights such as a tailor weight (see Non-Patent Document 4) may be multiplied in order to reduce side lobes.

The above processing has been described with respect to the case of two sweeps, but generally, the case of multiple sweeps may also be used. As an example, the case of 4 sweeps is shown in FIGS. When calculating the velocity from the gradient of the beat frequency at four points with respect to the sweep time, linear fitting or the like may be used.

Further, the angular axis monopulse calculation is performed on the cell detected by the CFAR processing unit 234 using the Σ signal. Further, in the angle measuring unit 237, the angle is measured using Σ and Δ of the beam output, and the Az angle and the EL angle are calculated.

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

(Third Embodiment) Transmission Isolation In the present 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. , The frequency band of the sweep signal of each of the plurality of transmitters (Nt≧2) is changed for each transmitter.

That is, in the radar system according to the present embodiment, as shown in FIG. 16A, in each transmitter 1i, the transmission modulator 1i22 changes the sweep frequency band from each other. On the other hand, in the receiver 2, in order to receive the signal from each transmitter 1i, as shown in FIG. 16B, the local control unit 222a sequentially receives Nr sweeps corresponding to sweeps and detects signals. To do. If the receiving system has Nr channels, parallel processing is performed, and if there is only one channel, it is necessary to switch and 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 different from each other except when the transmission and reception sweep bands do not match. Is not received, isolation between transmitters can be secured.

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

(Fourth Embodiment) MIMO (Multiple-Input Multiple-Output)
In the present embodiment, when the receiving aperture area is small, MIMO (see Non-Patent Document 5) is used to increase the aperture area of the virtual transmit/receive array to 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 antenna coordinate system for transmission and reception. Although the figure shows an example in which transmission and reception are included in the same antenna aperture, at least transmission and reception for multi-static may have different configurations.

In FIG. 17A, the transmitter 1i uses the antenna 1i1a as an N-element array antenna. Further, in FIG. 17B, the receiving device 2 uses the antenna 21a as an M element array antenna, and is arranged between the AD conversion units 231 and 237 and the FFT weight units 232 and 238 of the signal processor 23 as shown in FIG. The MIMO processing unit 23D shown is arranged. As shown in FIG. 18, this 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 using different modulation schemes for isolation and transmission. In the receiving device 2, the antenna 21a is used as an array antenna, and the signals received by the respective elements (M elements) of the array antenna are frequency-converted by the receiving unit 221 of the receiver 22, respectively, and then by the AD conversion unit 231 of the signal processor 23. It is converted into a digital signal to obtain a digital signal for M elements. Then, in the virtual array converter 23D1 of the MIMO processor 23D, the digital signals for M elements are used to demodulate with reference signals that match the transmission modulation for N elements, respectively, 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 represented by A and B, respectively, the following equations are obtained.

From this, each element becomes the following equation.

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

Each signal (an·bm) of this virtual array is equivalent to a virtual array element being present at the position where the position vector of the array of the transmitter and the position vector of the array of the receiver are combined, and it is possible to enlarge the aperture virtually. it can.

The transmit/receive beam output is given by the following equation by multiplying the element of equation (13) by the side lobe reduction weight and the side lobe reduction weight by beam forming and adding them.

Thus, for example, in the case of M=1 and N=4, the large aperture antenna should be configured as a virtual array aperture for transmission and reception with respect to the real aperture shown in FIG. 19A as shown in FIG. 19B. The angular resolution can be improved.

As described above, in the present embodiment, a plurality of transmitters are arranged at a distance of about the reception aperture, and the receivers perform observation using a virtual array of MIMO to perform transmission/reception MIMO processing. It is possible to measure the angle after enlarging the aperture of the virtual array by, and improve the angle accuracy.

(Fifth Embodiment) Non-Line-of-Sight Reflecting Device When the receiving device is out of the line-of-sight from the transmitting device, the receiving device cannot directly receive the wave, and therefore the 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 demodulation cannot be performed, so that transmission information cannot be obtained. In this embodiment, the countermeasure will be described.

As a countermeasure against this, as shown in FIG. 21, a reflecting device 1001 to 100P such as a reflecting sphere is arranged within the line of sight from the transmitting device and the receiving device. Generally, it is necessary to raise the altitude in order to place it in the line of sight. As the method, various methods such as mounting a balloon-shaped reflector on the device of the transmission source can be considered.

As described above, in the present embodiment, the direct wave from the transmitting device is transmitted to the receiving device via the reflecting device disposed at a high line-of-sight position. Even in the case of non-line-of-sight, the reflected wave by the reflection device can be observed, the transmission information can be obtained with a high SN, and the local signal can be controlled using the transmitted information, whereby the beat frequency can be observed with a high SN. Therefore, 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 has been described as a measure to prevent direct reception when the receiving device is out-of-line from the transmission source. .. In this embodiment, another measure will be described.

As a countermeasure against this, as shown in FIG. 22A, the transmission device 1i is used as a transmission/reception device 1ia, and a data link is formed by a transmission wave between them, and the transmission information is shared by each transmission/reception device 1ia. The receiving device is the same as that of the first embodiment, as shown in FIG.

Specifically, the transmitter/receiver 3i (i is 1 to N) is configured by the transmission/reception shared antenna 3i1, the transmitter 3i2, and the receiver 3i3, and the transmitter 3i2 is configured by the transmitter 3i21 and the transmission modulator 3i22. 3i3 includes a receiving unit 3i31, an AD converting unit 3i32, an FFT weighting unit 3i33, an FFT processing unit 3i34, a CFAR processing unit 3i35, a demodulating unit 3i36, a time synchronization control unit 3i37, and a modulation signal generating unit 3i38.

In the transmission/reception device 3i having the above-described configuration, 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 the transmission information 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 transmitted wave from the line-of-sight transmitting/receiving device, and controls the local signal using the transmitted information. As a result, the position of the transmitter/receiver, the transmission time, the transmission frequency, and the like can be recognized even outside the line of sight, so that 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 transmitting and receiving devices, transmission information is shared by each transmitting and receiving device, and a transmitting wave from the transmitting and receiving device within line-of-sight of the receiving device is received by the receiving device. Then, the local signal is controlled by using the transmitted information. That is, even when a certain transmitter/receiver is out of the line of sight of the receiver, the transmitter/receiver capable of observing direct waves can relay and transmit it, obtain transmission information with a high SN, and use it to transmit a local signal. By controlling, the beat frequency can be observed with high SN, and radar observation accuracy can be improved.

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

The system is shown in FIGS. 23(a) and 23(b). A feature of this embodiment is that, as shown in FIG. 23B, in the receiving device 2, a beat frequency signal is captured from the output of the distance measurement/speed measurement processing unit 236, and the center frequency is changed from the modulated carrier signal. And a center frequency calculation unit 23E for reading and reading and matching. The transmission/reception signal waveform in this case is the case of FMCW sweep in which both up sweep and down sweep are continuously transmitted and 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 for 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) The velocity V is calculated by the MRAV method.
Step 2) The term of the distance R can be deleted by substituting V into the equation (15) and adding it. 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 Δferr is subtracted from the right side of the beat frequency in equation (15) to correct, and the MRAV method is used to correct the distance and speed. To calculate.

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

As described above, in the present embodiment, the difference between the center frequencies of the transmitter and the receiver is calculated and corrected from the received signal by using the MRAV method. That is, it is possible to observe the deviation of the center frequencies of the transmitter and the receiver from the received signal and observe the beat frequency without the information of 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, it is possible to calibrate the error in the Doppler frequency with each other. The detection error of can be reduced.

It should be noted that the present embodiment is not limited to the above-described embodiment as it is, and constituent elements can be modified and embodied in a range not departing from the gist of the invention at an implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, the constituent elements of different embodiments may be combined appropriately.

11 to 1N... Transmitting device, 1i1... Transmitting antenna, 1i2... Transmitter, 1i21... Transmitting unit, 1i22, 1i22a... Transmitting modulating unit,
2... Receiving device 21, 21a... Receiving antenna, 22... Receiver, 221,... Receiving part, 222, 222a... Local control part, 223... Timing control part, 23... Signal processor, 231,... AD converting part, 232... FFT weight section, 233... FFT processing section, 234... CFAR processing section, 235... Distance measuring/speed measurement processing section, 236... Angle measuring section, 237... AD conversion section, 238... FFT weight section, 239... FFT processing section , 23A... Demodulation section, 23B... Control signal generation section, 23C... MRAV processing section, 23D... MIMO processing section, 23D1... Virtual array conversion section, 23D2... Beam forming section, 23E... Center frequency calculation section,
31-3N...Transceiver, 3i1...Transmission/reception shared antenna, 3i2...Transmitter, 3i21...Transmitter, 3i22...Transmission modulator, 3i3...Receiver, 3i31...Receiver, 3i32...AD converter, 3i33...FFT weight Section, 3i34... FFT processing section, 3i35... CFAR processing section, 3i36... demodulation section, 3i37... time synchronization control section, 3i38... modulated signal generation section,
1001-100P... Reflector.

Claims (9)

In a radar system comprising Nt (Nt≧1) transmitters and Nr (Nr≧1, Nt+Nr≧4 or 3) receivers,
In the transmission device, 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 upsweep or downsweep having a frequency sweep gradient is modulated and transmitted,
The receiving device receives a direct wave from the transmitting device or a reflected wave reflected from a target, and selects a start time at which the FFT output becomes maximum by changing a plurality of FFT (Fast Fourier Transform) start times, , And then demodulates the transmission information, synchronizes the received local signal with the received signal based on the transmission information, further corrects the received local signal, and determines the beat frequency by the FFT processing. By observing and measuring the distance and angle of the target, and calculating the intersection from the distance of three or more pairs of transmission and reception and the angle measurement value of the receiving device, the three-dimensional position (x, y, z) or a radar system that calculates a two-dimensional position (x, y). The radar system according to claim 1, wherein the receiving device extends an up sweep or a down sweep and a received local signal corresponding to the down sweep or the up sweep on the transmitting device side to a length for receiving a target signal from a predetermined distance or more. .. The radar system according to claim 1 , wherein the receiving device further measures a target speed, and MRAV (Measurement Range After measurement Velocity) is used as the distance measuring/ speed measuring method. The radar system according to claim 1, wherein, when a plurality of the transmitters are provided, the signals of the sweep are set to different frequency bands for each transmitter. The radar system according to claim 1 , wherein when a plurality of the receivers are provided, the transmitters are separated by a reception aperture and the receivers observe using a virtual array by MIMO (Multiple-Input Multiple-Output). .. Furthermore, a direct wave from the transmitting device is reflected in a predetermined direction, and the direct wave from the transmitting device is transmitted to another receiving device via the reflecting device arranged at a high altitude in the line of sight. The radar system according to claim 1, wherein: When a plurality of the transmitters are provided, a data link by a radar communication wave is formed between the transmitters so that the transmitters share the transmission information including the position, the transmission frequency, and the transmission time, and the receivers. Then, the radar system according to claim 1, wherein a transmission wave from a line-of-sight transmission device is received and demodulated, and a local signal is controlled using the transmission information. The radar system according to claim 1, wherein the receiving device calculates and corrects the difference between the center frequencies of the transmitting device and the own device by using the MRAV method from the received signal. Used in a radar system including Nt (Nt≧1) transmitters and Nr (Nr≧1, Nt+Nr≧4 or 3) receivers,
In the transmission device, 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 upsweep or downsweep having a frequency sweep gradient is modulated and transmitted,
The receiving device receives a direct wave from the transmitting device or a reflected wave reflected from a target, and selects a start time at which the FFT output becomes maximum by changing a plurality of FFT (Fast Fourier Transform) start times, , And then demodulates the transmission information, synchronizes the received local signal with the received signal based on the transmission information, further corrects the received local signal, and determines the beat frequency by the FFT processing. By observing and measuring the distance and angle of the target, and calculating the intersection from the distance of three or more pairs of transmission and reception and the angle measurement value of the receiving device, the three-dimensional position (x, y, z) or a radar signal processing method of a radar system for calculating a two-dimensional position (x, y).

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