JP5473386B2 - Radar equipment - Google Patents

Description

  The present invention relates to a radar apparatus, and more particularly to improvement of target detection performance and interference suppression performance.

  In a radar apparatus, it is important to detect and capture a target as far away as possible. As a typical ranging method of radar, a pulse compression method and an FMCW (Frequency Modulated Continuous Wave) method are known (for example, refer to Non-Patent Document 1 below). These are based on the principle of measuring distance by time delay and frequency, respectively.

  The pulse compression method is excellent in clutter suppression performance and interference suppression performance, but there is a problem that the scale of the signal processing system becomes large when high-speed correlation processing computation is required and high distance resolution is required. The FMCW system is a system that can obtain a high distance resolution by relatively low-speed signal processing, and is widely used in radar devices that require cost reduction. However, the FMCW system has a transmission / reception isolation problem because the transmission wave is CW, and there is an unnecessary wave (clutter) problem from an unnecessary reflector at a short distance with small propagation loss.

  As a method for improving the target detection performance, it is most effective and efficient to increase the irradiation power to the target. Therefore, it is desirable to perform control so that a peak gain is obtained in the target direction for the transmission beam or reception beam of the antenna.

  In the actual environment, multipath due to reflection and scattering by surrounding objects (structures, terrain) occurs, but it is spatially suppressed using the difference in arrival angle or using the difference in Doppler frequency. There is a countermeasure technique such as suppression by filtering processing.

Takashi Yoshida, “Revised Radar Technology”, Corona, 1996.

  By the way, in ranging by a radar apparatus, for a target flying at a low altitude, there is almost no spatial angular difference between the direct wave and multipath from the target, and there is almost no difference in Doppler frequency. Under such an environment, a decrease in received electric field level due to multipath fading depending on the propagation path environment is inevitable. In particular, the above-described prior art based on a single frequency cannot be essentially handled. Furthermore, since the phase relationship between the direct wave and the reflected wave (multipath) also depends on the distance to the target, the detection performance is significantly deteriorated in a specific region.

  In addition, since interference waves that interfere with detection are unavoidable for radar and are a factor that greatly degrades radar performance, it is necessary to take countermeasures simultaneously.

  An object of the present invention is to solve such a problem, and to provide a radar apparatus with improved target detection performance and interference suppression performance. In this radar apparatus, a subcarrier is arranged in a band having good propagation path characteristics including a multipath, and a detection distance is efficiently increased by using a multicarrier transmission wave in which energy is concentrated there. Furthermore, it is possible to simultaneously detect and suppress interference waves by using a band not used for transmission.

  The present invention is a radar apparatus for detecting a target by a reflected wave received by a receiving antenna of a multicarrier transmitting wave from a transmitting antenna, wherein the subcarrier arrangement transmitted from the transmitting antenna is a known multicarrier transmitting wave. Transmission wave control that sets the subcarrier arrangement of multicarrier transmission waves within the band to be observed based on the result of analyzing propagation path characteristics from the reflected wave received by the receiving antenna or based on a preset reference subcarrier arrangement Means, and a transmission waveform generating means for generating a multicarrier transmission waveform in which subcarriers are arranged by the number and position according to the subcarrier arrangement set by the transmission wave control means and transmitting from the transmission antenna, and the transmission waveform Reflected wave received by the receiving antenna with respect to the transmitted wave generated and transmitted by the generating means The received signal is demultiplexed for each subcarrier band, and further, according to the setting in the transmission wave control means, a signal in a band in which no subcarrier is arranged in the multicarrier transmission waveform and a signal in a band in which the subcarrier is arranged In the case of detecting the interference wave in the interference detection means for detecting the interference wave based on the signal of the band that does not arrange the discriminated subcarrier, the discrimination / discrimination means for discrimination, Interference removing means for suppressing interference waves with respect to a signal in a band in which subcarriers discriminated according to the detection result are arranged, and target detecting means for detecting a target using a signal obtained from the interference removing means, A radar apparatus is provided.

  According to the present invention, it is possible to provide a radar apparatus that uses a multicarrier signal as a transmission wave and has improved target detection performance and interference suppression performance.

It is a block diagram of the radar apparatus by Embodiment 1 of this invention. It is a figure which shows the various signals in the radar apparatus by this invention. It is a figure which shows the specific structural example of one duplexer of the radar apparatus by this invention. It is an operation | movement flow which shows an example of operation | movement of the radar apparatus by Embodiment 1 of this invention. It is an operation | movement flow which shows another example of operation | movement of the radar apparatus by Embodiment 1 of this invention. It is a block diagram of the radar apparatus by Embodiment 2 of this invention. It is the figure which showed some examples of the subcarrier arrangement | positioning used as a reference | standard with the radar apparatus by this invention. It is an operation | movement flow which shows an example of operation | movement of the radar apparatus by Embodiment 2 of this invention.

  In the present invention, a multicarrier signal is used as a transmission wave, a transmission waveform is adaptively controlled according to propagation path characteristics, and processing is performed on the reception signal using the waveform information. A radar device with improved interference suppression performance is provided. Embodiments of the radar apparatus of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a block diagram of a radar apparatus according to Embodiment 1 of the present invention. In FIG. 1, the radar apparatus includes a receiving antenna 10 that is an array antenna including K element antennas 11 to 13 and K demultiplexers 21 to 23 that are individual components provided for the respective element antennas. The wave unit 20, the interference removal unit 30, the signal synthesis unit 40, the target detection unit 50, the interference detection unit 60, and further includes a transmission antenna 70, a transmission waveform generation unit 80, and a determination unit 90.

  Although FIG. 1 shows the receiving antenna 10 and the transmitting antenna 70 separately, the present invention is not limited to this. A configuration in which the element antennas 11 to 13 are shared by the reception antenna 10 and the transmission antenna 70 is also possible. Further, although the transmission antenna 70 is a single element, it is of course possible to adopt an array antenna configuration. In an actual apparatus, various devices and circuits for converting the frequency of the received high-frequency signal into baseband digital data are necessary. However, illustration and description thereof are omitted. Similarly, in the transmission system, each functional block for converting a digital signal into a high-frequency signal is omitted. The components shown in FIG. 1 are limited to the main functions in the present invention.

  In this embodiment, an active radar system is assumed in which a radar device transmits a signal itself to detect a reflected wave from a target. Therefore, it is utilized that the transmission wave can be generated arbitrarily to some extent. More specifically, a transmission waveform using a band suitable for target detection is generated according to the propagation path characteristics during operation. In order to take advantage of this characteristic, a multicarrier signal is applied.

  The reception antenna 10, the demultiplexing unit 20, the transmission antenna 70, the transmission waveform generation unit 80, and the determination unit 90 constitute a transmission wave control unit, and the transmission antenna 70 and the transmission waveform generation unit 80 constitute a transmission waveform generation unit. The demultiplexing unit 20 constitutes a demultiplexing / discrimination unit, the interference detection unit 60 constitutes an interference detection unit, the signal synthesis unit 40 constitutes an interference removal unit, and the target detection unit 50 constitutes a target detection unit. .

  Next, a detailed operation will be described. First, regarding a transmission procedure, a training signal is transmitted as a pre-process before a highly accurate target detection process for grasping propagation path characteristics. FIG. 2 shows various signals in the radar apparatus according to the present invention. FIG. 2 (a) shows an example of a training signal. The horizontal axis represents frequency, and each line represents the level (amplitude) of the subcarrier 100. In this way, the subcarriers are uniformly arranged in the band. The carrier interval is arbitrary, but if it is an OFDM (Orthogonal Frequency Division Multiplexing) signal, the interval satisfies the orthogonal relationship. Moreover, although it is desirable that the bandwidth is as wide as possible, in practice, this is a trade-off between the feasibility and performance of the transceiver.

  First, this training signal is emitted, and the reception antenna 10 receives a group of reflected waves from the target. The demultiplexer 20 shown in FIG. 1 separates the received signals of the respective element antennas into subcarriers by demultiplexers 21 to 23. The signal demultiplexed in units of subcarriers is sent to the determination unit 90 by the demultiplexing unit 20. As a result, multicarrier signals as shown in FIG. 2B are input to the determination unit 90 as the number of elements as received signals.

  The duplexers 21 to 23 have the same configuration, for example, and FIG. 3 shows a specific configuration example of one duplexer. The example in case a transmission waveform is an OFDM signal is shown. The output signal from the element antenna 11 is rearranged in units of N by the serial / parallel converter 24. The N signal groups are separated into subcarriers by an FFT (Fast Fourier Transform) unit 25. Here, N represents the number of subcarriers (or FFT size). Thereafter, all subcarriers are output to determination section 90. The discrimination circuit 26 discriminates each subcarrier signal into an output signal (M) to the interference removal unit 30 and an output signal (L) to the interference detection unit 60 based on information from the determination unit 90. . That is, the relationship of N ≧ M + L is established.

  The determination unit 90 determines whether or not the reception level of each subcarrier is higher than a preset threshold based on a preset threshold (101 in FIG. 2B), and sets a predetermined reception level. Determine a satisfactory band. Based on this determination information, the transmission waveform generation unit 80 generates an optimized transmission signal in which subcarriers are arranged at optimal positions according to propagation path characteristics as shown in FIG. 2C as a transmission multicarrier signal. Here, reference numeral 102 in FIG. 2C denotes a subcarrier in a band used for transmission waveform generation, and 103 denotes a subcarrier in a band not used. In this way, energy can be concentrated and transmitted to a signal in a band with good propagation path characteristics.

  Note that the above threshold determination may be executed by selecting an output from a certain duplexer in the demultiplexing unit 20, or may be performed for each output from a plurality of demultiplexers. It may be determined automatically. Alternatively, the determination may be made using a signal after combining the outputs of a plurality or all of the duplexers. Regarding the weighting factor (weight) required for this synthesis, the excitation distribution for forming a search beam (fixed beam pattern) to be used in a so-called normal operation state where interference waves and multipaths do not matter (Amplitude, phase) can be applied.

  Next, a procedure for detecting a target is shown. The transmission signal generated as described above is emitted from the transmission antenna 70 and received by the element antennas 11 to 13 of the reception antenna 10. Up to this point, it is the same as the pre-processing using the training signal. The received signal is subsequently input to the demultiplexing unit 20 and is frequency-separated in units of subcarriers in the demultiplexers 21 to 23, respectively, but based on the subcarrier arrangement information obtained from the determination unit 90, the band used The subcarrier signal (102 in FIG. 2 (c)) is output to the interference removing unit 30, and the subcarrier signal (103 in FIG. 2 (c)) in the unused band is output to the interference detecting unit 60. Is done.

  First, the interference detection unit 60 checks for the presence or absence of interference waves that cause interference. The subcarrier signal input to the interference detection unit 60 corresponds to a band in which no subcarrier is arranged in the transmission waveform generation unit 80, that is, not used for a transmission wave. Therefore, the presence / absence of an interference wave can be identified only by determining the reception level of the input subcarrier signal. Since a plurality of subcarrier signals are obtained for each element antenna, it is possible to easily improve the identification accuracy by averaging these reception levels.

  In this way, when the interference detection unit 60 detects the presence of an interference wave, the interference removal unit 30 performs processing to remove the interference wave component from the received signal. Since the subcarrier signal including only the interference wave has already been demultiplexed for each element antenna, the interference canceling unit calculates the weighting factor that forms a null (point with low reception sensitivity) in the interference wave direction using these signals. By applying (weighting) each signal at 30, interference waves can be removed.

  A plurality of subcarrier signals from which interference wave components have been removed are output to the signal synthesis unit 40. Here, the subcarriers having the same frequency arrangement are combined to further improve the SNR (Signal-to-Noise Ratio) and improve the target detection performance. Since the interference wave component has already been removed, it is sufficient to operate as so-called maximum ratio combining diversity in which in-phase combining is performed with a weight corresponding to the amplitude of each output.

  In the signal synthesizer 40, when the receiving antenna 10 is composed of one element antenna, for example, a primary storage memory or the like (not shown) is provided, and a plurality of sub-cells are received by a plurality of times of reception with the same element antenna. Carrier signals may be combined, and when the receiving antenna 10 is an array antenna including a plurality of element antennas 11 to 13, a plurality of sub-signals each received by the plurality of element antennas 11 to 13 are received. Carrier signals may be combined. Further, when the receiving antenna is composed of one element antenna, the signal combining unit 40 may be omitted.

  In this way, when the signal with the interference wave removed and the SNR improved is output to the target detection unit 50, and the presence / absence of the target is detected by detecting the time change of the level (amplitude) of the output signal. The information such as the target distance, direction, and moving speed is calculated by radar signal processing.

  An example of an operation flow relating to the above-described contents is shown in FIG. The operation of FIG. 4 will be described. First, in order to measure the propagation path characteristics, for example, the transmission waveform generation unit 80 in accordance with a command signal from the determination unit 90 uniformly subdivides the use band as shown in FIG. A training signal, which is a transmission waveform in which carriers are arranged, is generated and transmitted from the transmission antenna 70 (step S1). On the receiving side, the received signal received by the receiving antenna 10 is demultiplexed in subcarrier units by the demultiplexing unit 20 (step S2), and after the frequency characteristics can be observed, it is sent to the determination unit 90. The determination unit 90 selects a subcarrier having a high reception level through determination processing with a preset threshold value (step S3).

  In step S3, the propagation path characteristics may not be good overall, or the received signal of the selected element antenna may be deteriorated. When it is difficult to select a subcarrier as described above, the determination unit 90 returns to the procedure of transmitting the training signal in step S1 again to improve. It is also possible to complete subcarrier selection at an early stage by lowering the threshold and re-determining before resending the training signal.

  When the subcarrier arrangement to be used in the determination unit 90 is determined in this way (step S4), the determination unit 90 generates a waveform optimized according to the propagation path characteristics based on the determined subcarrier arrangement in the transmission waveform generation unit 80, Transmission for target detection is performed from the transmission antenna 70 (step S5). On the receiving side, the reflected wave from the target is received by the receiving antenna 10 and demultiplexed by the demultiplexing unit 20 (step S6), and the above-described processing, that is, the interference detection unit 60 and the interference removal unit 30 detect and remove the interference wave. (Step S7) Further, after the target signal component is synthesized by the signal synthesis unit 40 (Step S8), the target detection unit 50 executes target detection processing (Step S9). At this time, since the signal received by each element antenna is already in a high reception level due to the optimization of the transmission waveform, it is possible to expect higher accuracy of each process in the subsequent stage. The above series of processing is operated while being repeated periodically or at a necessary timing.

  FIG. 5 shows another example of the operation flow. In the flow of FIG. 4, a threshold is introduced when the determination unit 90 selects a subcarrier having a high reception level, but an operation in which a processing delay due to retransmission of a training signal or the like is not allowed is also assumed. Therefore, when importance is attached to responsiveness, it is assumed that the number M of subcarriers to be used is not set in step S3a but the number M of subcarriers to be used is set in advance, and the M reception subcarriers having the highest reception level are selected. The other steps are the same as in FIG. By doing so, since the training signal is transmitted only once (retransmission is prohibited), the processing delay until target detection can be improved.

  Through the processing as described above, the radar apparatus according to the present invention generates a transmission waveform according to the propagation path characteristics and uses the information on the reception side to increase the target detection distance even in a multipath fading environment. On the other hand, it is possible to realize detection and removal of interference waves that interfere with distance measurement.

Embodiment 2. FIG.
FIG. 6 is a block diagram of a radar apparatus according to Embodiment 2 of the present invention. The same or corresponding parts as those in the above embodiment are denoted by the same reference numerals and the description thereof is omitted. In FIG. 6, an arbitrary arrangement control unit 95 has a function of arbitrarily controlling the subcarrier arrangement. In the first embodiment, in order to generate a transmission waveform, propagation path characteristics are accurately grasped in advance by transmission and reception processing of a training signal. On the other hand, in the second embodiment, the subcarrier arrangement is controlled by the transmission side alone.

  The arbitrary arrangement control unit 95 constitutes a transmission wave control unit.

  Propagation path characteristics change from moment to moment depending on the surrounding conditions and movement of the observation target, so it is necessary to follow them, and it may be necessary to increase the processing speed. Since there are many relatively static (fixed) environments other than the target that is a moving object, it is possible to predict the propagation path characteristics to some extent in advance. Therefore, a technique for generating a transmission waveform based on a deterministic reference based on a prediction model on the transmission side is effective for increasing the processing speed. As a standard to be used, some examples of subcarrier arrangement are shown in FIG. Since the band in which the reception level decreases due to frequency selectivity is considered to be a part of the observation band 150, in FIG. 7A, subcarriers are concentrated in a predetermined band set (predicted) in advance. In addition, there is a method of increasing the probability of receiving subcarriers in a good band as much as possible with a small number of transmissions by arranging them randomly as shown in FIG. 7B. On the other hand, as shown in FIG. 7C, there is a method in which the interference wave can be detected by reducing the probability that the target cannot be detected as much as possible by arranging it uniformly in the observation band. It is also possible to improve by combining these arrangements.

  FIG. 8 shows an example of the operation flow of this embodiment. The arbitrary arrangement control unit 95 sets the subcarrier arrangement based on any of the above deterministic criteria (step S4a), and generates a waveform optimized according to the propagation path characteristics based on the subcarrier arrangement set in the transmission waveform generation unit 80. Thus, transmission for target detection is performed from the transmission antenna 70 (step S5a). Other steps are the same as those in FIGS. This can be simplified by omitting the prior propagation path estimation process.

  By such processing, the feedback processing between transmission and reception regarding the training signal can be omitted in the second embodiment as compared with the first embodiment. This enables high-speed processing, and does not require signal output from the demultiplexing unit 20 to the arbitrary arrangement control unit 95, so that the apparatus can be reduced in size and power consumption can be reduced.

In each of the above-described embodiments, the configuration using the training signal has been described. However, it is of course possible to regularly observe the propagation path characteristics using the transmission wave during normal operation.
In each of the above embodiments, the configuration in which the subcarrier arrangement is always controlled has been described. However, it is desirable to perform detection processing using as wide a band as possible from the viewpoint of resolution. Therefore, in an environment where there is no interfering interference wave or an environment where multipath is not a problem, it is of course possible to operate subcarriers all over the observation band.
In the second embodiment, although the effect of shortening the time (speeding up the processing) is reduced, a plurality of transmission pulses are transmitted by changing the subcarrier arrangement in various ways to obtain a reception signal with good characteristics. It is also possible to increase the probability of being received.

  DESCRIPTION OF SYMBOLS 10 Reception antenna, 11-13 element antenna, 20 demultiplexing part, 21-23 demultiplexer, 24 serial-parallel conversion part, 25 FFT part, 26 discrimination circuit, 30 interference removal part, 40 signal synthesis part, 50 target detection part , 60 interference detection unit, 70 transmission antenna, 80 transmission waveform generation unit, 90 determination unit, 95 arbitrary arrangement control unit.

Claims (9)

A radar device that detects a target by a reflected wave received by a receiving antenna of a multicarrier transmission wave from a transmitting antenna,
Observation target based on a result of analyzing propagation path characteristics from a reflected wave received by the receiving antenna of a multicarrier transmission wave having a known subcarrier arrangement transmitted from the transmission antenna, or a preset reference subcarrier arrangement Transmission wave control means for setting the subcarrier arrangement of the multicarrier transmission wave in the band
Transmission waveform generation means for generating a multi-carrier transmission waveform in which subcarriers are arranged in the position and number according to the subcarrier arrangement set by the transmission wave control means and transmitting from the transmission antenna;
The reception signal of the reflected wave received by the receiving antenna with respect to the transmission wave generated and transmitted by the transmission waveform generation means is demultiplexed for each subcarrier band, and further, the multicarrier transmission is performed according to the setting of the transmission wave control means Demultiplexing / discriminating means for discriminating between a signal in a band in which no subcarriers are arranged in the waveform and a signal in a band in which subcarriers are arranged;
Interference detecting means for detecting an interference wave based on a signal in a band in which the discriminated subcarrier is not arranged;
When the interference detection unit detects an interference wave, an interference removal unit that suppresses the interference wave with respect to a signal in a band in which subcarriers discriminated according to the detection result are arranged;
Target detection means for detecting a target using a signal obtained from the interference cancellation means;
A radar apparatus comprising: Signal synthesis means for synthesizing a target signal component using a plurality of output signals from the interference cancellation means;
The radar apparatus according to claim 1, wherein the target detection unit detects a target using a signal obtained from the signal synthesis unit.   The transmission wave control means causes the transmission waveform generation means to generate and transmit a transmission waveform training signal in which subcarriers are arranged in all of the observation band as a transmission wave having a known subcarrier arrangement, and propagates from the received signal. The radar apparatus according to claim 1 or 2, wherein a subcarrier arrangement of a multicarrier transmission wave in which subcarriers are arranged in a band having good road characteristics is set.   The radar apparatus according to claim 3, wherein the transmission wave control unit arranges and sets subcarriers in each band having a reception level larger than a preset threshold value.   4. The radar apparatus according to claim 3, wherein the transmission wave control means arranges and sets subcarriers in a predetermined number of bands in descending order of reception level.   The transmission wave control means is characterized in that a predetermined reference subcarrier arrangement is a predetermined number of subcarriers concentrated in a part of the band to be observed. Item 3. The radar device according to item 1 or 2.   3. The transmission wave control means according to claim 1, wherein a predetermined reference subcarrier arrangement is a predetermined number of subcarriers randomly arranged in the observation target band. The radar device described in 1.   3. The transmission wave control means according to claim 1, wherein a predetermined reference subcarrier arrangement is a predetermined number of subcarriers arranged uniformly in the band to be observed. The radar device described in 1. 9. The device according to claim 1, wherein the receiving antenna has an array antenna configuration in which a plurality of element antennas are provided, and a target is detected from a reflected wave received by each element antenna. 10. Radar device.

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