Radar system and radar signal processing method

Abstract

To achieve long time FFT with a small processing scale even in long time integration.SOLUTION: According to an embodiment, a radar system receives a reflected wave of a single pulse transmitted from a transmission system or a N(N≥1) hit pulse signal, and extracts a target signal from the received signal. The radar system uses a signal having Ns(Ns≥2) cells on a slow-time axis and Nf(Nf≥1) cells on a fast-time axis to divide the slow-time axis of the received signal into Ms(Ms≥2) for every Ls(Ls≥1) cell, and performs first FFT processing Ms times on the slow-time axis for each division unit to acquire Doppler cells (ls=1-Ls), performs Ms points of second FFT processing for every Doppler cell for each division unit, and performs long time integration of a signal in which processing results are arranged for each of the original Doppler cells (ls=1-Ls) to detect a target.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present embodiment relates to a radar system and a radar signal processing method. [Background technology]

[0002] In conventional radar systems, when there are a large number of integration hits or when performing long-term integration with a long PRI (Pulse Repetition Interval) and CPI (Coherent Pulse Interval), the number of points in a single FFT (Fast Fourier Transform) becomes too large, making it impossible to implement the FFT. Furthermore, in the case of long-term observations, there is the issue of integration loss occurring due to range walk and Doppler walk.

[0003] On the other hand, there is a method of maximizing an integral series (speed / acceleration correction) as a long-term integration process (see Patent Document 1). This method maximizes an integral series by searching for speed and acceleration, but in the case of long-term integration, it is necessary to process a long-term FFT over the entire search range, which increases the overall processing scale. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5025403 [Non-patent literature]

[0005] [Non-Patent Document 1] Range Compression, Ouchi, 'Fundamentals of Synthetic Aperture Radar for Remote Sensing', Tokyo Denki University Press, pp.131-149(2003) [Non-patent document 2] CFAR (Constant False Alarm Rate), Yoshida, 'Revised Radar Technology', Institute of Electronics, Information and Communication Engineers, pp.87-89 (1996) [Non-patent document 3] FFT, Hino, 'Spectral Analysis', Asakura Shoten, pp.193-198(1977) [Non-patent document 4] DBF (Digital Beam Forming), Yoshida, 'Revised Radar Technology', Institute of Electronics, Information and Communication Engineers, pp.289-291 (1996) [Non-Patent Document 5] MIMO(Multi-Input Multi-Output), JIAN LI, PETER STOICA, 'MIMO RADAR SIGNAL PROCESSING', WILEY, pp.1-5(2009) Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, conventional radar systems have a method for maximizing an integral sequence by searching for velocity and acceleration. However, in the case of long-term integration, it is necessary to process a long-term FFT over the entire search range, which poses a problem of increasing the overall processing scale.

[0007] An object of this embodiment is to provide a radar system and a radar signal processing method that can achieve a small processing scale even during long-term integration and can reduce integration losses due to range walk and Doppler walk. [Means for solving the problem]

[0008] To solve the above problems, a radar system according to an embodiment receives a reflected wave of a single pulse or a modulated pulse signal with N (N≧1) hits transmitted from a transmission system and extracts a target signal from the received signal. The radar system includes a first FFT processing unit, a second FFT processing unit, and a detection unit. The first FFT processing unit uses a signal with Ns (N≧2) cells on the slow-time axis and Nf (N≧1) cells on the fast-time axis, divides the slow-time axis of the received signal into Ms (M≧2) divisions of Ls (L≧1) cells, and performs a first FFT process Ms times on the slow-time axis for each division unit to obtain Doppler cells (l=1 to Ls). The second FFT processing unit performs a second FFT process of Ms points for each Doppler cell for each division unit. The detection unit detects targets by long-term integration of the signal processed by the second FFT processing unit, which has been arranged for each original Doppler cell (l=1 to Ls).

[0009] In other words, a long-term FFT can be realized by FFT processing with a small number of points (data length) using a two-stage FFT.

[0010] A radar system according to an embodiment receives a reflected wave of a single pulse or a modulated pulse signal with N (N≧1) hits transmitted from a transmission system and extracts a target signal from the received signal. The radar system includes a first FFT processing means, a second FFT processing means, and a detection means. The first FFT processing means sequentially inputs a signal having Ls (Ls≧1) cells on the slow-time axis and Nf (Nf≧1) cells on the fast-time axis as division units, and performs a first FFT process on each unit on the slow-time axis to obtain Doppler cells (ls=1 to Ls). The second FFT processing means performs a second FFT process of Ms points for each Doppler cell using Ms (Ms≧2) division units that have already been processed. The detection means detects targets by long-term integration of the signals processed by the second FFT processing means, which are arranged for each original Doppler cell (ls=1 to Ls).

[0011] That is, by performing the first FFT process on the division units that are input sequentially and the second FFT process using a plurality of division units that have already been processed, it is possible to reduce the processing scale and realize FFT processing that takes a long time.

[0012] Furthermore, the radar system according to the embodiment receives the reflected wave of a single pulse or a modulated pulse signal with N (N≧1) hits transmitted from a transmission system and extracts a target signal from the received signal. First, a signal with Ns (N≧1) cells on the slow-time axis and Nf (N≧1) cells on the fast-time axis is used, and an FFT is performed on the fast-time axis to generate a range frequency axis. The range frequency is then divided into Mf (M≧1) parts, and the slow-time axis is divided into Ms (Ms≧1) parts. Of the Mf×Ms divided signals, signals with zero padding on the fast-time axis and no zero padding on the slow-time axis are used within the remaining Nf×Ns regions. The fast-time axis is range compressed, and the FFT-processed Mf×Ms signal on the slow-time axis is amplitude integrated, and provisional detection is performed to extract Pt (Pt≧1) range cells Rt and Doppler cells Ft. Next, the range is compressed using the signal of the entire range frequency band, and the slow-time axis is divided into Ms divisions, and then each division unit is multiplied by Ms times. 1st FFT Then, for each Doppler cell (ls = 1 to Ls) in each division unit, an integral series (sv × sa × sb) along the slow-time axis is set using the velocity (sv pattern) and acceleration (sa pattern) of a specified search range and the range cell bias (sb pattern) for the Pt provisionally detected cells centered on the data on the slow-time axis at Ms points. The range shift amount is set using the phase gradient of the range frequency axis so that each integral series becomes the Rt cell on the range axis, and range walk correction is performed. After rearranging on the slow-time axis, the Ms-point integral series (before the slow-time axis FFT) with the maximum value of the sv × sa × sb results obtained by performing a second FFT (Ms points) on the slow-time axis is selected, and the results of the second FFT on the slow-time axis at Ms points are replaced with the Doppler cells (ls = 1 to Ls). Next, the Doppler cells (ls=1 to Ls) are detected using range-Doppler data repeated for each provisional detection Pt.

[0013] In other words, by narrowing the range frequency axis and limiting the slow-time axis, the range resolution and Doppler resolution are limited, reducing the effects of range walk and Doppler walk, and then tentative detection is performed using CFAR. Using wideband high-resolution range data and high-resolution Doppler data from a two-stage FFT, the search range for tentative detection is limited to reduce the processing scale, and the range walk (range cell shift due to velocity) and Doppler walk (Doppler cell shift due to acceleration) are corrected, allowing targets to be detected with high range resolution and high Doppler resolution.

[0014] By using the above method, even when integration is performed for a long time, it is possible to realize it with a small processing scale and also to reduce losses due to range walk and Doppler walk. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a block diagram showing the configuration of a transmission system and a reception system of a radar system according to the first embodiment. [Figure 2] FIG. 2 is a flowchart showing the flow of processing in the reception system of the first embodiment. [Figure 3] FIG. 3 is a diagram for explaining the division unit two-stage FFT processing on the slow-time axis according to the first embodiment. [Figure 4] FIG. 4 is a diagram showing how the results of the two-stage FFT processing of the first embodiment are arranged for each bank of the first FFT. [Figure 5] FIG. 5 is a diagram showing a comparison between the first FFT processing result and the second FFT processing result for the entire slow-time axis in the first embodiment. [Figure 6] FIG. 6 is a flowchart showing the flow of processing of the reception system of the second embodiment. [Figure 7] FIG. 7 is a diagram showing the state in the case of a transmission fan beam and multiple beams by a reception DBF in the second embodiment. [Figure 8]FIG. 8 is a diagram showing how the FFT range is slid in units of observation frames to perform long-term integration in the second embodiment. [Figure 9] FIG. 9 is a block diagram showing the configuration of a transmission system and a reception system of a radar system according to the third embodiment. [Figure 10A] FIG. 10A is a flowchart showing the flow of processing in the reception system of the third embodiment. [Figure 10B] FIG. 10B is a flowchart showing the flow of processing in the reception system of the third embodiment. [Figure 11] FIG. 11 is a diagram illustrating the processing state of the reception system of the third embodiment. [Figure 12] FIG. 12 is a diagram showing the narrowband range compression process used in the third embodiment. [Figure 13] FIG. 13 is a diagram showing the state of the time-division FFT processing used in the third embodiment. [Figure 14] FIG. 14 is a diagram showing the wideband range compression process used in the third embodiment. [Figure 15A] FIG. 15A is a diagram showing the range walk and Doppler walk correction processing used in the third embodiment. [Figure 15B] FIG. 15B is a diagram showing the range walk and Doppler walk correction processing used in the third embodiment. [Figure 16] FIG. 16 is a flowchart showing the flow of the erroneous detection occurrence countermeasure process in the third embodiment. [Figure 17] FIG. 17 is a diagram showing the process of preventing the occurrence of erroneous detection shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments will be described with reference to the drawings.

[0017] (First embodiment) The first embodiment will be described with reference to FIGS.

[0018] FIG. 1 is a block diagram showing the configuration of a radar system according to the first embodiment, where (a) is a block diagram showing the configuration of a transmission system, and (b) is a block diagram showing the configuration of a reception system.

[0019] In the transmission system shown in Figure 1(a), a signal generator 11 generates a transmission seed signal, a modulator 12 modulates and multiplexes transmission information onto the transmission seed signal, a frequency converter 13 converts the modulated signal into a high-frequency signal, a pulse modulator 14 pulse-modulates the high-frequency signal to generate a transmission pulse train, and a transmission antenna 15 transmits N (N≧2) hit pulses.

[0020] 1(b), a reflected wave of a pulse signal transmitted from transmitting antenna 15 is received by receiving antenna 21, the received signal is frequency-converted to baseband by frequency converter 22, and converted to a digital signal by AD converter 23 to obtain a received signal. Next, the received signal undergoes range compression by range compressor 24, CPI division of the slow-time axis by slow-time axis divider 25, first FFT processing on the slow-time axis by slow-time axis first FFT processor 26, and second FFT processing on the slow-time axis by slow-time axis second FFT processor 27. Observed values ​​are detected by CFAR (Constant False Alarm Rate, see Non-Patent Document 2) detector 28 to identify the target, and distance, speed, and angle measurements are performed and output as target information.

[0021] In the above radar system, the transmission system and the reception system may be integrated or may be installed at separate locations.

[0022] In the radar system configured as described above, the processing operation after the reception system acquires received data will be described with reference to Fig. 2 to Fig. 5. Here, Fig. 2 is a flowchart showing the processing flow of the reception system of the first embodiment, Fig. 3 is a diagram for explaining the division unit two-stage FFT processing on the slow-time axis of the first embodiment, Fig. 4 is a diagram showing how the two-stage FFT processing results of the first embodiment are arranged for each bank of the first FFT, and Fig. 5 is a diagram showing a comparison of the first FFT processing results and the second FFT processing results on the entire slow-time axis in the first embodiment.

[0023] First, the signal reflected by a target or the like from the N (N≧2) hits of transmission pulses transmitted from the transmission system shown in Figure 1(a) is received by the receiving antenna 21, frequency converted to baseband by the frequency converter 2, and converted to a digital signal by the AD converter 23, thereby obtaining the received data. In this way, the received data obtained by receiving the N (N≧2) hits of transmission pulses is called CPI (Coherent Pulse Interval) data based on PRI (Pulse Repetition Interval) data. This CPI data is two-dimensional data with a fast-time axis for each range cell and a slow-time axis between the PRIs.

[0024] 2, first, received data is input and divided on the slow-time axis to form divided CPIs, and the CPIs are sequentially pulse-compressed in division units. Then, FFT processing (first FFT) is performed on the slow-time axis, and the FFT processing results of the divided CPIs are saved (24-26, steps S11-S16). When the first FFT processing for all divided CPIs is completed in step S15, slow-time axis FFT processing (second FFT) is sequentially performed on the Doppler cells (27, steps S17-S20). Similarly, slow-time axis FFT processing (second FFT) is sequentially performed on the range cells (27, steps S21-S22). Observation values ​​are detected using CFAR detection, and targets are identified. Then, distance, velocity, and angle measurements are performed, and output as target information (28, step S23).

[0025] In the above configuration, the two-stage FFT (first FFT and second FFT) employed in the radar system of this embodiment will be described.

[0026] First, when performing slow-time axis FFT processing, if the FFT is performed for a long time, the number of FFT points (data length) increases, which increases the processing scale (see Non-Patent Document 3), and it may become impossible to implement. As a countermeasure to this, we consider dividing the slow-time axis as shown in the flowchart in Figure 2.

[0027] The two-stage FFT process will be described with reference to Fig. 3. In Fig. 3, (a) shows the state of CPI division, (b) shows the state of the one-stage Doppler axis by the first FFT, (c) shows the state of rearrangement in CPI division units on the one-stage Doppler axis, and (d) shows the state of the two-stage Doppler axis by the second FFT.

[0028] The above two-stage FFT can be formulated as follows:

[0029]

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[0030]

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[0031] Next, as shown in FIG. 3(d), a second FFT is performed on the slow-time axis for each division unit.

[0032]

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[0033] When the results of this FFT processing are arranged for each bank of the first FFT shown in Figure 4(a), the second FFT obtains the same results as the FFT of the entire slow-time axis, as shown in Figure 4(b). This is shown in Figure 5. In Figure 5, (a) shows how tentative detected cell 1 is obtained from the processing results of first FFTs #1 to #Ms (data length Ls) on the Doppler (Ls bank) axis-range Nf cell axis obtained from Ms divided CPIs, and (b) shows how tentative detected cell 1 is obtained from the processing results of the second FFT of Ms points on the Doppler (Ns = 1Ls × Ms bank) axis-range Nf cell axis.

[0034] As described above, the radar system according to this embodiment receives the reflected wave of a single pulse or modulated N (N≧2) pulse signal transmitted from the transmission system, and uses a signal with Ns (N≧2) cells on the slow-time axis and Nf (N≧1) cells on the fast-time axis for the received signal. The slow-time axis is divided into Ms (M≧2) divisions, each with Ls (L≧1) cells, and a first FFT process is performed Ms times on the slow-time axis for each division. Next, a second FFT process is performed Ms points for each Doppler cell in each division, and the results are arranged for each of the original Doppler cells (ls=1 to Ls) to detect targets. In this way, a long-term FFT can be achieved by performing FFT process with a small number of points (data length) using a two-stage FFT.

[0035] (Second embodiment) Next, a second embodiment will be described with reference to Figs. 6 to 8. Fig. 6 is a flowchart showing the processing flow of the receiving system of the second embodiment, Fig. 7 is a diagram showing the case of a transmit fan beam and a multi-beam by receive DBF in the second embodiment, and Fig. 8 is a diagram showing the case of long-term integration by sliding the FFT range in observation frame units in the second embodiment. In the first embodiment, two-stage FFT processing was described. In this embodiment, specific processing performed using this two-stage FFT processing is proposed. Note that the system configuration of the transmitting system and receiving system is the same as that in Fig. 1, so a description thereof will be omitted.

[0036] The difference between the flowchart in FIG. 6 and that in FIG. 2 is that the CPI split change loop in steps S15 and S16 is omitted, and instead, after the detection process using CFAR in step S23, it is determined whether the observation has ended (step S24), and the CPI split input continues until the observation has ended (step S25).

[0037] As described above, in the radar system according to this embodiment, each time a divided CPI signal is sequentially input, the divided CPI signal is pulse compressed, a first FFT process is performed on the slow-time axis, and the results are saved for each divided CPI (steps S11 to S14). Next, using the saved CPI results, a second FFT process is performed on the slow-time axis (step S17). The first FFT Doppler cells are replaced with Doppler cells for the second FFT process (step S18). Since there are results of the first FFT process equal to the number of range cells multiplied by the number of Doppler cells, each cell is processed (steps S19 to S22). This allows signals from high-resolution Doppler cells to be obtained, and targets are detected using CFAR or the like (step S23). By performing this process for each sequentially input divided CPI (steps S24 and S25), observation values ​​can be output at a high data rate for each divided CPI.

[0038] In the above processing system, the radar system according to this embodiment forms a transmission fan beam in the observation space, and forms multiple beams for reception using DBF (Digital Beam Forming) (see Non-Patent Document 4), or when forming transmission and reception multiple beams using MIMO (Multiple Input Multiple Output) (see Non-Patent Document 5), transmission and reception beams can be formed continuously in the observation space, enabling long-term integration. The top view in Figure 7(a) and the side view in Figure 7(b) show how transmission fan beam formation and reception multibeam formation are performed using DBF.

[0039] Incidentally, if the observation space is observed continuously rather than in a time-sharing manner, even if the receiving beam width is wide and angle measurement accuracy is low, the angle measurement accuracy can be improved by the averaging effect of increasing the number of observations. To achieve this, it is effective to shorten the search frame time (improve the search rate).

[0040] In order to shorten the search frame time for the entire observation space while ensuring a high SN (signal-to-noise power) in continuous observations, it is necessary to perform long-term integration by sliding the FFT processing range in observation frame units, as shown in Figure 8. When this is done, data from the same time period will be integrated multiple times, which increases the processing scale.

[0041] Therefore, as a countermeasure against the increase in the processing scale, the above-mentioned two-stage FFT, that is, dividing the entire frame time and performing the second FFT processing by sliding the results of the first FFT processing for each division unit, is performed. Specifically, as shown in Fig. 8, in the ds-th (ds = 1 to Ds) observation frame, the first FFT processing of Ls points in the division unit ds and the second FFT processing of Ms (Ms ≥ 1) points are performed.

[0042] The amount of calculation per observation frame for this two-stage FFT method and the normal all-point FFT method is compared as follows: Here, we use the fact that the amount of calculation for FFT of N-point data is proportional to Nlog2N (see Non-Patent Document 3).

[0043]

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[0044]

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[0045] For ease of understanding, if we quantify the case where md=16, mdiv=1024, and rngcell=1000, in the case of FFT processing of all points, 16·1024·log2(16·1024)·1000=229376000 On the other hand, in the case of the two-stage FFT processing method, 1024·log2(1024)+16·log2(16)·1024·1000=65546240 The ratio in this case is 65546240 / 229376000=0.29, so the amount of calculation can be significantly reduced by using the two-stage FFT method. As a result, using the two-stage FFT improves the SN (signal-to-noise ratio) through long integration times, and enables processing at high data rates (short frame times).

[0046] As described above, in the radar system according to this embodiment, a signal having Ls (Ls≧1) cells on the slow-time axis and Nf (Nf≧1) cells on the fast-time axis is sequentially input as division units for signal processing of a received signal, and a first FFT process is performed on each unit on the slow-time axis. Next, using Ms (Ms≧2) division units that have already been processed, a second FFT process is performed on Ms points for each Doppler cell, and the results are arranged for each of the original Doppler cells (ls=1 to Ls). In other words, by performing the first FFT process on the division units that are sequentially input and the second FFT process using multiple division units that have already been processed, it is possible to reduce the processing scale and realize FFT processing that takes a long time.

[0047] (Third embodiment) Next, a third embodiment will be described. In the first and second embodiments, long-term integration processing using a two-stage FFT has been described. In this embodiment, a method for performing highly efficient integration processing by correcting range walk and Doppler walk using a two-stage FFT will be described with reference to Figs. 9 to 17.

[0048] FIG. 9 is a block diagram showing the configuration of a radar system according to a third embodiment, where (a) is a block diagram showing the configuration of a transmission system and (b) is a block diagram showing the configuration of a reception system. The transmission system shown in FIG. 9(a) is the same as the transmission system of the first and second embodiments shown in FIG. 1(a). The reception system shown in FIG. 9(b) differs from the reception system of the first and second embodiments shown in FIG. 1(b) in that it uses a signal processing configuration using a long-time integration method after the AD converter 23. That is, the third embodiment includes a target tentative detection processing system that processes received data obtained by the AD converter 23 using a narrowband range compressor 29, a slow-time axis divider 30, a slow-time axis FFT processor 31, and a tentative detector 32, and a target determination system that includes a wideband range compressor 33, a range walk / Doppler walk corrector 34, a slow-time two-stage FFT processor 35, and a CFAR detector 36.

[0049] The long-term integration method used in this embodiment will be described. Data is acquired in range cell units within a Pulse Repetition Interval (PRI) for each pulse transmitted at PRI intervals. This acquired data is used for long-term integration processing. In the case of long-term integration, the range cells and Doppler cells move relative to the slow-time axis due to the target's speed and acceleration, so high-resolution range compression and slow-time axis FFT reduce the target SN (signal-to-noise ratio). As a countermeasure, we consider reducing the range resolution and Doppler resolution and performing provisional detection.

[0050] In the radar system according to this embodiment, in the transmission system, a transmission seed signal is generated by a signal generator 11, a modulated signal is generated by a modulator 12, this is converted into a high-frequency signal by a frequency converter 13, pulse-modulated by a pulse modulator 14, and N (N≧2) hit pulses are transmitted from a transmission antenna 15.

[0051] In the receiving system, the signal received by the receiving antenna 21 is frequency-converted by the frequency converter 22, converted to a digital signal by the AD converter 23, and output as a received signal. Next, if the received signal is a range-compressed signal (see Non-Patent Document 1), the range is compressed in a band-limited narrow band (29), the slow-time axis (the PRI axis with N hits) is divided (30), FFT processing is performed on the divided slow-time axis (31), and reflection points are tentatively detected using CFAR or the like (32). The narrow band signal is used to reduce the range resolution and suppress the effects of range walk, and the slow-time axis is divided to reduce the Doppler resolution and suppress the effects of Doppler walk. Note that dividing the range frequency band and dividing the slow-time axis reduces the signal-to-noise ratio, so the processing results for each division are amplitude-integrated to prevent this reduction in signal-to-noise ratio and perform tentative detection.

[0052] Meanwhile, the digital signal from the AD converter 23 is wideband range compressed using the transmitted chirp band (33), and then range walk and Doppler walk corrections are made based on the provisionally detected reflection point, replacing it with the slow-time axis signal passing through the provisionally detected point (34). After that, a slow-time axis two-stage FFT process is performed (35), and the target is detected using CFAR or the like to obtain target information (36).

[0053] In the above configuration, the processing of the reception system of this embodiment will be described with reference to Fig. 10A, Fig. 10B, and Fig. 11. Fig. 10A and Fig. 10B are flowcharts showing the flow of processing of the reception system of the third embodiment. Fig. 11 is a diagram showing the state of processing of the reception system of the third embodiment.

[0054] In the radar system of this embodiment, as shown in Fig. 10A, a wideband pulse signal is transmitted and received (step S31), and an FFT is performed on the fast-time axis using CPI (Coherent Pulse Interval) signals (fast-time and slow-time signals, Fig. 11(a)) from the AD converter 23, converting them to the range-frequency axis (step S32, Fig. 11(b)). Using these signals, the signals on the range-frequency axis and the slow-time axis are divided into Mf and Ms, respectively, to obtain Mf x Ms signals (steps S33 and S34, Fig. 11(c)). On the range-frequency axis, signals other than the divided signals are zero-padded. On the other hand, on the slow-time axis, zero-padding is not performed to reduce the number of FFT points. For each of these Mf×Ms signals, pulse compression is performed on the fast-time axis (step S35) and FFT is performed on the slow-time axis (step S36), to obtain low-resolution signals on the range axis and Doppler axis. Further, the Mf×Ms signals are amplitude integrated (steps S37 to S41), and a tentative detection point is determined using CFAR or the like (step S42, FIG. 11(d)).

[0055] Let us formulate this part. For ease of understanding, we will explain range compression and slow-time axis FFT separately. In practice, the processing is performed in the order of range compression followed by slow-time axis FFT, or vice versa.

[0056] First, narrowband range compression will be described with reference to Fig. 12 (see Non-Patent Document 1). Fig. 12 is a diagram showing the narrowband range compression process used in the third embodiment. Range compression is a correlation process between an input signal and a range compression signal, and can be formulated as follows when performed in the frequency domain:

[0057] First, when the input signal (Fig. 12(a1)) and the reference signal (Fig. 12(a2)) are subjected to FFT on the fast-time axis, the following equations (Fig. 12(b1) and (Fig. 12(b2)) are obtained.

[0058]

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[0059]

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[0060]

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[0061]

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[0064] As a result, the resolution of the range cells in narrowband range compression and wideband range compression can be made the same, and cells provisionally detected in narrowband range compression can be directly used in wideband range compression.

[0065] Next, the time-division FFT processing will be formulated with reference to Fig. 13. Fig. 13 is a diagram showing the state of the time-division FFT processing used in the third embodiment.

[0066] First, the input signal (FIG. 13(a)) is expressed by the following equation.

[0067]

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[0069] Using the range-Doppler signal of fastd × slowd in equation (13), amplitude integration is performed to improve the SN ratio (Fig. 13(d)), and then provisional detection is performed using CFAR or the like, and range cells are extracted to obtain range cells Rt (t = 1 to Pt: Pt is the provisional detection number).

[0070] The processing after the provisional detection will be described with reference to FIG. 10B and FIG. 10B, after the provisional detection, the fast-time axis is subjected to wideband range compression (step S43), the slow-time axis is divided and a first FFT process is performed (step S44), the range and Doppler integral sequences are corrected using the integral sequence search method (step S45), a second FFT process is performed on the slow-time axis (step S46), and the results are saved (step S47). At this point, the velocity number is determined (step S48). If the predetermined velocity number is not reached, the velocity is changed (step S49), and the processes of steps S45 to S48 are repeated. If the predetermined velocity number is exceeded, it is determined whether the predetermined acceleration has been reached (step S50). If not, the acceleration is changed (step S51), and the processes of steps S45 to S50 are repeated. If the predetermined acceleration has been reached, it is determined whether the range bias adjustment has been completed (step S52). If the adjustment has not been completed, the range bias is changed (step S53), and the processes of steps S45 to S52 are repeated. If range bias adjustment is complete, the maximum sequence is extracted from the second FFT processing result (step S54), the maximum sequence is replaced (step S55), and it is determined whether the number of provisional detections has reached the maximum value (step S56). If not, the number of provisional detections is changed and the processing of steps S45 to S56 is repeated. If the number of provisional detections has reached the maximum value, FFT processing on the slow-time axis is performed (step S458), and the target cell is detected using CFAR or the like (step S59).

[0071] Fig. 14 is a diagram showing the wideband range compression process used in the third embodiment. That is, after tentative detection, wideband range compression is performed on the fast-time axis using the original input signal (Fig. 14(a1)) and the reference signal (Fig. 14(a2)), and an FFT is performed on the fast-time axis (Fig. 14(b1) and (Fig. 14(b2))), and complex conjugate multiplication of both signals is performed (Fig. 14(c)). The process at this time is as follows:

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[0076] Next, range walk and Doppler walk correction will be described with reference to Figures 15A and 15B, which are diagrams showing the range walk and Doppler walk correction processing used in the third embodiment.

[0077] First, signals divided on the slow-time axis are generated as units to be corrected, and a first FFT process is performed on the slow-time axis for each divided signal (FIG. 15A(a)).

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[0080] Each integrated sequence is range-walk corrected to form an Rt cell on the range axis, and then rearranged on the slow-time axis (slowd). This range-walk correction involves shifting the sequence on the range-frequency axis (Fig. 15A(c)), which will be described later. This sequence is subjected to an FFT on all slow-time axes, and the integrated sequence at Ms points (before the second FFT on the slow-time axis) with the largest maximum value of the sv × sa × sb results is selected (Fig. 15B(d)). The results of the slow-time axis FFT on Ms points are then replaced with Doppler cells (ls = 1 to Ls) (Fig. 15B(e)). This process is repeated for each provisional detection Pt, and the range-Doppler data is used for detection using CFAR or other methods (Fig. 15B(f)).

[0081]

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[0082] Through the above processing, the search range is limited by tentative detection to reduce the processing scale, and then range walk correction and Doppler walk correction are performed, allowing processing with a high SN ratio, so targets can be detected while suppressing false detections.

[0083] The range walk and Doppler walk correction methods have been described above. Here, we will describe a method for performing range walk correction on the range frequency axis. To perform range walk and Doppler walk correction for each candidate integral sequence (sv × sa × sb ways) for each target Pt, it is necessary to correct the range axis shift for each cell on the slow-time axis, as shown in FIG. 15A(c). In this case, if the shift amount is determined on a range cell basis, a quantization error occurs in the shift amount, degrading the Doppler axis side lobes when performing FFT processing on the slow-time axis and reducing the signal-to-noise ratio (SN), resulting in false detection. In this embodiment, we will describe a solution to this problem.

[0084] FIG. 16 is a waveform diagram showing the flow of the countermeasure process for preventing the occurrence of erroneous detection in the third embodiment, and FIG. 17 is a diagram showing the state of the countermeasure process for preventing the occurrence of erroneous detection shown in FIG.

[0085] In Fig. 16, the range-compressed slow-time axis data is input (step S61), and is subjected to FFT processing on the fast-time axis to convert it to the range frequency-slow-time axis (step S62). Next, the range shift amount is calculated for each integration series (sv x sa x sb combinations) and for each cell on the slow-time axis (step S63, Fig. 17(a)). Furthermore, the phase gradient corresponding to the range shift amount is calculated for each cell on the slow-time axis using the following equation (step S64, Fig. 17(b)).

[0086]

number

[0087]

number

[0088] The range frequency axis is corrected by the phase gradient for each cell on the slow-time axis (step S65), and the range frequency axis is subjected to inverse FFT to obtain a range compressed slow-time axis signal (step S66).

[0089]

number

[0090] In the embodiment, a system that transmits and receives radar waves has been described, but the present invention can also be applied to a passive radar that uses a transmission source of another system (including communications, etc.).

[0091] As described above, in this embodiment, the signal processing of the received signal uses a signal with Ns (Ns≧1) cells on the slow-time axis and Nf (Nf≧1) cells on the fast-time axis, first performs FFT on the fast-time axis to convert it to the range frequency axis, then divides the range frequency into Mf (Mf≧1) and divides the slow-time axis into Ms (Ms≧1), and uses the Mf×Ms divided signals from the remaining Nf×Ns regions with zero padding on the fast-time axis and not zero padding on the slow-time, range compression is performed on the fast-time axis, and amplitude integration of the FFT processed Mf×Ms signal on the slow-time axis is performed, and provisional detection is performed using CFAR to extract Pt (Pt≧1) range cells Rt and Doppler cells Ft. Next, the range is compressed using signals from the entire range frequency band, and the slow-time axis is divided into Ms divisions, after which the second FFT process is performed Ms times for each division unit. For each Doppler cell (ls = 1 to Ls) in each division unit, an integral series (sv × sa × sb) is set along the slow-time axis using the velocity (sv) and acceleration (sa) of a predetermined search range and the bias of the range cell (sb) centered on the provisionally detected Pt cells for the slow-time axis data of Ms points. The range walk is corrected by setting the range shift amount using the phase gradient of the range frequency axis so that the integrated series becomes the Rt cell on the range axis, and after rearranging on the slow-time axis, the second FFT processing (Ms points) on the slow-time axis is performed. The Ms-point integrated series (before slow-time axis FFT processing) with the largest value of the sv × sa × sb results is selected, and the results of the second FFT processing on the slow-time axis at Ms points are replaced with Doppler cells (ls = 1 to Ls). This process is repeated for each provisionally detected Pt, and the range-Doppler data is used to detect targets using CFAR, etc.

[0092] That is, by narrowing the range frequency axis and limiting the slow-time axis, the range resolution and Doppler resolution are limited, reducing the effects of range walk and Doppler walk, and then tentative detection is performed using CFAR. Then, using wideband high-resolution range data and high-resolution Doppler data obtained by two-stage FFT, the search range for tentative detection is limited to reduce the processing scale, and range walk (range cell shift due to velocity) and Doppler walk (Doppler cell shift due to acceleration) are corrected. This allows targets to be detected with high range resolution and high Doppler resolution.

[0093] The present invention is not limited to the above-described embodiments, and the components can be modified and embodied in practice without departing from the spirit of the invention. Furthermore, various inventions can be created by appropriately combining multiple components disclosed in the above-described embodiments. For example, some components may be omitted from all the components shown in the embodiments. Furthermore, components from different embodiments may be appropriately combined. [Explanation of symbols]

[0094] 11... signal generator, 12... modulator, 13... frequency converter, 14... pulse modulator, 15... transmitting antenna, 21... receiving antenna, 22... frequency converter, 23... AD converter, 24... range compressor, 25... slow-time axis divider, 26... slow-time axis first FFT processor, 27... slow-time axis second FFT processor, 28... CFAR detector, 29...narrowband range compressor, 30...slow-time axis divider, 31...slow-time axis FFT processor, 32...temporary detector, 33...wideband range compressor, 34...range walk / Doppler walk corrector, 35...slow-time two-stage FFT processor, 36...CFAR detector.

Claims

1. A radar system that receives a reflected wave of a single pulse or a modulated pulse signal of N (N≧1) hits transmitted from a transmission system and extracts a target signal from the received signal, a first FFT processing means for dividing the slow-time axis of the received signal into M (M ≧ 2) segments of L (L ≧ 1) cells each, and performing a first FFT process M times on the slow-time axis for each segment to obtain Doppler cells (L = 1 to L); a second FFT processing means for performing a second FFT process of Ms points for each Doppler cell in the division unit; a detection means for detecting a target by integrating the signals obtained by arranging the processing results of the second FFT processing means for each original Doppler cell (ls = 1 to Ls) for a long period of time; A radar system comprising:

2. A radar system that receives a reflected wave of a single pulse or a modulated pulse signal of N (N≧1) hits transmitted from a transmission system and extracts a target signal from the received signal, a first FFT processing means for sequentially inputting a signal having Ls (Ls≧1) cells on the slow-time axis and Nf (Nf≧1) cells on the fast-time axis as division units, and performing a first FFT process on each unit on the slow-time axis to obtain Doppler cells (ls=1 to Ls); a second FFT processing means for performing a second FFT process of M points for each Doppler cell using M division units (M≧2) that have already been processed; a detection means for detecting a target by integrating the signals obtained by arranging the processing results of the second FFT processing means for each original Doppler cell (ls = 1 to Ls) for a long period of time; A radar system comprising:

3. A radar system that receives a reflected wave of a single pulse or a modulated pulse signal of N (N≧1) hits transmitted from a transmission system and extracts a target signal from the received signal, a means for using a signal having Ns (Ns≧1) cells on the slow-time axis and Nf (Nf≧1) cells on the fast-time axis to perform FFT on the fast-time axis to create a range frequency axis, then dividing the range frequency into Mf (Mf≧1) and dividing the slow-time axis into Ms (Ms≧1), and using the Mf×Ms divided signals in the remaining Nf×Ns regions with zero padding on the fast-time axis and not zero padding on the slow-time axis, range compressing the fast-time axis and amplitude integrating the FFT processed Mf×Ms signal on the slow-time axis, and provisionally detecting and extracting Pt (Pt≧1) range cells Rt and Doppler cells Ft; Range compression is performed using signals from the entire range frequency band, and the slow-time axis is divided into Ms divisions, and then a first FFT is performed Ms times on each division unit. For each Doppler cell (ls = 1 to Ls) in each division unit, an integral series (sv x sa x sb) is set along the slow-time axis using the velocity (sv patterns) and acceleration (sa patterns) of a predetermined search range and the bias of the range cell (sb patterns) for each provisionally detected Pt cells as the center, and each integral a means for performing range walk correction by setting the range shift amount by the phase gradient of the range frequency axis so that the series becomes an Rt cell on the range axis, rearranging the results on the slow-time axis, and then performing a second FFT (Ms points) on the slow-time axis to select an integrated series at Ms points (before the slow-time axis FFT) that has the largest maximum value of sv x sa x sb results, and replacing the results of the second FFT on the slow-time axis at Ms points with a Doppler cell (ls = 1 to Ls); and means for detecting said Doppler cells (ls = 1 to Ls) using range-Doppler data repeated for each provisional detection Pt.

4. A radar signal processing method for receiving a reflected wave of a single pulse or a modulated pulse signal of N (N≧1) hits transmitted from a transmission system, and extracting a target signal from the received signal, comprising: Using a signal having Ns (Ns≧2) cells on the slow-time axis and Nf (Nf≧1) cells on the fast-time axis, the slow-time axis of the received signal is divided into Ms (Ms≧2) cells, each of which is Ls (Ls≧1), and a first FFT process is performed Ms times on the slow-time axis for each division unit to obtain Doppler cells (ls=1 to Ls); performing a second FFT process of M points for each Doppler cell in the division unit; The processing result of the second FFT processing is arranged for each original Doppler cell (ls = 1 to Ls), and the signal is integrated for a long time to detect the target. Radar signal processing method.

5. A radar signal processing method for receiving a reflected wave of a single pulse or a modulated pulse signal of N (N≧1) hits transmitted from a transmission system, and extracting a target signal from the received signal, comprising: A signal having Ls (Ls ≥ 1) cells on the slow-time axis and Nf (Nf ≥ 1) cells on the fast-time axis is input sequentially as a division unit, and a first FFT process is performed on the slow-time axis for each unit to obtain Doppler cells (ls = 1 to Ls); performing a second FFT process of M points for each Doppler cell using M division units (M≧2) that have already been processed; The processing result of the second FFT processing is arranged for each original Doppler cell (ls = 1 to Ls), and the signal is integrated for a long time to detect the target. Radar signal processing method.

6. A radar signal processing method for receiving a reflected wave of a single pulse or a modulated pulse signal of N (N≧1) hits transmitted from a transmission system, and extracting a target signal from the received signal, comprising: Using a signal with Ns (Ns ≥ 1) cells on the slow-time axis and Nf (Nf ≥ 1) cells on the fast-time axis, FFT is performed on the fast-time axis to create a range frequency axis, then the range frequency is divided into Mf (Mf ≥ 1) and the slow-time axis is divided into Ms (Ms ≥ 1). Of the Mf x Ms divided signals, zero-padded signals are used for the fast-time axis and non-zero-padded signals for the slow-time in the remaining Nf x Ns regions. The fast-time axis is range compressed, and the FFT-processed Mf x Ms signal is amplitude integrated for the slow-time axis, and provisional detection is performed to extract Pt (Pt ≥ 1) range cells Rt and Doppler cells Ft. Range compression is performed using signals from the entire range frequency band, and the slow-time axis is divided into Ms divisions, after which a first FFT is performed Ms times on each division unit. For each Doppler cell (ls = 1 to Ls) in each division unit, an integral series (sv x sa x sb) is set along the slow-time axis using the velocity (sv patterns) and acceleration (sa patterns) of a predetermined search range and the range cell bias (sb patterns) for each of the Pt provisionally detected cells in the slow-time axis data at Ms points. The range shift amount is set by the phase gradient of the range frequency axis so that the integral series becomes the Rt cell on the range axis, and range walk correction is performed by rearranging on the slow-time axis, and then the second FFT (Ms points) is performed on the slow-time axis. The Ms point integral series (before the slow-time axis FFT) with the largest value of the sv × sa × sb results is selected, and the result of the second FFT on the slow-time axis at the Ms point is replaced with a Doppler cell (ls = 1 to Ls). A radar signal processing method for detecting the Doppler cells (ls = 1 to Ls) using range-Doppler data obtained by repeating the Doppler cells for each provisional detection Pt.

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