JP7770931B2 - Radar system and radar signal processing method - Google Patents

Description

This embodiment relates to a radar system and a radar signal processing method.

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, with long-term observations, there is the issue of integration loss due to range walk and Doppler walk.

On the other hand, one long-term integration process is the integral series maximization (speed/acceleration correction) method (see Patent Document 1). This method maximizes the integral series using a speed and acceleration search method, 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.

Patent No. 5025403

Range Compression, Ouchi, 'Fundamentals of Synthetic Aperture Radar for Remote Sensing', Tokyo Denki University Press, pp.131-149(2003) CFAR (Constant False Alarm Rate), Yoshida, 'Revised Radar Technology', Institute of Electronics, Information and Communication Engineers, pp.87-89(1996) FFT, Hino, 'Spectral Analysis', Asakura Publishing, pp.193-198 (1977) DBF (Digital Beam Forming), Yoshida, 'Revised Radar Technology', Institute of Electronics, Information and Communication Engineers, pp.289-291 (1996) MIMO (Multi-Input Multi-Output), JIAN LI, PETER STOICA, ‘MIMO RADAR SIGNAL PROCESSING’, WILEY, pp.1-5(2009)

As mentioned above, conventional radar systems have a method for maximizing integral sequences by searching for velocity and acceleration, but in the case of long-term integration, a long-term FFT must be processed across the entire search range, which poses a problem of increasing the overall processing scale.

The objective of this embodiment is to provide a radar system and radar signal processing method that can achieve long-term integration with a small processing scale and reduce integration loss due to range walk and Doppler walk.

To solve the above problems, a radar system according to an embodiment receives a reflected wave of a single pulse or modulated pulse signal with N (N≧1) hits transmitted from a transmission system and extracts a target signal from the received signal. It comprises a first FFT processing means, a second FFT processing means, and a detection means. The first FFT processing means 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) 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 (ls = 1 to Ls). The second FFT processing means performs a second FFT process of Ms points for each Doppler cell in the division unit. The detection means detects the target by long-term integration of the signal processed by the second FFT processing means, which has been arranged for each original Doppler cell (ls = 1 to Ls).

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

The radar system according to the embodiment receives reflected waves of a single pulse or modulated pulse signal with N (N≧1) hits transmitted from a transmission system and extracts a target signal from the received signal. It comprises a first FFT processing means, a second FFT processing means, and a detection means. The first FFT processing means sequentially inputs a signal with Ls (Ls≧1) cells on the slow-time axis and Nf (Nf≧1) cells on the fast-time axis as division units, and performs first FFT processing on each unit on the slow-time axis to obtain Doppler cells (ls = 1 to Ls). The second FFT processing means performs second FFT processing 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).

In other words, by performing a first FFT process on sequentially input division units and a second FFT process using multiple division units that have already been processed, the processing scale can be reduced and long-term FFT processing can be achieved.

Furthermore, the radar system according to the embodiment 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. First, a signal having N (N≧1) cells on the slow-time axis and N (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. After that, the range frequency is divided into M (M≧1) parts, and the slow-time axis is divided into M (M≧1) parts. Of the N×N regions remaining, the M×M divided signals are zero-padded on the fast-time axis and not zero-padded on the slow-time axis. The fast-time axis is range-compressed, and the FFT-processed M×M signal on the slow-time axis is amplitude-integrated, and provisional detection is performed to extract P (P≧1) range cells R and Doppler cells F. Next, 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 for the Ms points of slow-time axis data, centered on the provisionally detected Pt cells, using the velocity (sv ways) and acceleration (sa ways) in a predetermined search range and the range cell bias (sb ways). The range shift amount is set by 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 by rearranging the results on the slow-time axis, and then a 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 results of the second FFT on the slow-time axis at Ms points are replaced with Doppler cells (ls = 1 to Ls).The Doppler cells (ls = 1 to Ls) are then detected using range-Doppler data repeated for each provisional detection Pt.

In other words, by narrowing the range frequency axis and limiting the slow-time axis, 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 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.

Using the above method, even long-term integration can be achieved with a small processing scale, and losses due to range walk and Doppler walk can be reduced.

FIG. 1 is a block diagram showing the configuration of a transmission system and a reception system of a radar system according to a first embodiment. FIG. 2 is a flowchart showing the flow of processing in 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 according to the first embodiment. 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. 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. FIG. 6 is a flowchart showing the flow of processing in the reception system of the second embodiment. FIG. 7 is a diagram showing the state in the case of a transmission fan beam and multiple beams by reception DBF in the second embodiment. 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. 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. FIG. 10A is a flowchart showing the flow of processing in the reception system of the third embodiment. FIG. 10B is a flowchart showing the flow of processing in the reception system of the third embodiment. FIG. 11 is a diagram illustrating the processing state of the reception system of the third embodiment. FIG. 12 is a diagram showing the narrowband range compression process used in the third embodiment. FIG. 13 is a diagram showing the state of the time-division FFT processing used in the third embodiment. FIG. 14 is a diagram showing the wideband range compression process used in the third embodiment. FIG. 15A is a diagram showing the range walk and Doppler walk correction processing used in the third embodiment. FIG. 15B is a diagram showing the range walk and Doppler walk correction processing used in the third embodiment. FIG. 16 is a flowchart showing the flow of the countermeasure process for the occurrence of erroneous detection in the third embodiment. FIG. 17 is a diagram showing the process of preventing the occurrence of erroneous detection shown in FIG.

The following describes the embodiments with reference to the drawings.

(First embodiment)
The first embodiment will be described with reference to FIGS. 1 to 5. FIG.

Figure 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 the transmission system, and (b) is a block diagram showing the configuration of the reception system.

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.

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

In the above radar system, the transmission system and reception system may be integrated, or may be installed in separate locations.

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

First, the signal reflected by a target or the like from N (N≧2) hits of transmitted 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 N (N≧2) hits of transmitted 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 PRIs.

In FIG. 2, first, received data is input and divided along the slow-time axis to form divided CPIs. The CPIs are sequentially pulse-compressed in division units, and then FFT processing (first FFT) is performed on the slow-time axis. The FFT results for 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 to identify the target, and distance, velocity, and angle measurements are performed and output as target information (28, step S23).

In the above configuration, we will explain the two-stage FFT (first FFT and second FFT) used in the radar system of this embodiment.

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 may make it impossible to implement. As a countermeasure to this, we consider dividing the slow-time axis, as shown in the flowchart in Figure 2.

The two-stage FFT process will be explained with reference to Figure 3. In Figure 3, (a) shows the CPI division, (b) shows the first-stage Doppler axis by the first FFT, (c) shows the rearrangement by CPI division unit on the first-stage Doppler axis, and (d) shows the second-stage Doppler axis by the second FFT.

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

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

When the results of this FFT are arranged by bank for the first FFT shown in Figure 4(a), the second FFT produces results identical to those of the FFT for the entire slow-time axis, as shown in Figure 4(b). This is shown in Figure 5. In Figure 5, (a) shows how tentatively 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 tentatively detected cell 1 is obtained from the processing results of the second FFT for Ms points on the Doppler (Ns = 1Ls x Ms bank) axis - range Nf cell axis.

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

Second Embodiment
Next, a second embodiment will be described with reference to Figures 6 to 8. Figure 6 is a flowchart showing the processing flow of the receiving system of the second embodiment, Figure 7 is a diagram showing the case of a transmit fan beam and a multi-beam by receive DBF in the second embodiment, and Figure 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 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 Figure 1, so a description thereof will be omitted.

Figure 6 differs from the flowchart shown in Figure 2 in that the CPI division change loop in steps S15 and S16 has been removed. Instead, after the CFAR detection process in step S23, it is determined whether observation has ended (step S24), and CPI division input continues until observation has ended (step S25).

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 cell is replaced with a Doppler cell for the second FFT process (step S18). Since the results of the first FFT process are the number of range cells multiplied by the number of Doppler cells, each cell is processed separately (steps S19 to S22). This allows for high-resolution Doppler cell signals to be obtained, allowing targets to be detected using CFAR or similar techniques (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.

In the above processing system, the radar system according to this embodiment forms a transmit fan beam in the observation space, and forms multiple beams for reception using DBF (Digital Beam Forming) (see Non-Patent Document 4), or forms transmit and receive multiple beams using MIMO (Multiple Input Multiple Output) (see Non-Patent Document 5). In this case, transmit and receive beams can be formed continuously in the observation space, enabling long-term integration. Figure 7(a) shows a top view, and (b) shows a side view, showing the formation of a transmit fan beam and receive multiple beams using DBF.

By the way, if the observation space is observed continuously rather than time-shared, even if the receiving beam width is wide and angle measurement accuracy is low, the angle measurement accuracy can be improved due to 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).

In order to shorten the search frame time for the entire observation space while maintaining a high signal-to-noise ratio during continuous observation, it is necessary to integrate over a long period of time by sliding the FFT processing range in observation frame units, as shown in Figure 8. When doing this, data from the same time period is integrated multiple times, resulting in an increase in the processing scale.

To address this issue, the aforementioned two-stage FFT is used as a countermeasure to the increased processing scale. In other words, the entire frame time is divided, and the results of the first FFT processing are slid for each division unit to perform the second FFT processing. Specifically, as shown in Figure 8, for the dsth (ds = 1 to Ds) observation frame, the first FFT processing is performed for Ls points in the dsth division unit, and the second FFT processing is performed for Ms (Ms ≥ 1) points.

The following is a comparison of the amount of calculation per observation frame between this two-stage FFT method and the standard all-point FFT method. Here, we use the fact that the amount of calculation for an FFT of N-point data is proportional to Nlog2N (see Non-Patent Document 3).

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 high data rate (short frame time) processing.

As described above, the radar system according to this embodiment processes received signals by sequentially inputting signals with Ls (Ls ≥ 1) cells on the slow-time axis and Nf (Nf ≥ 1) cells on the fast-time axis as division units, performing a first FFT process on each unit on the slow-time axis, and then using Ms (Ms ≥ 2) division units that have already been processed, performing a second FFT process on Ms points for each Doppler cell. Targets are then detected using the results arranged for each original Doppler cell (ls = 1 to Ls). In other words, by performing the first FFT process on the division units that are input sequentially and the second FFT process using multiple division units that have already been processed, the processing scale can be reduced, enabling long-term FFT processing.

(Third embodiment)
Next, a third embodiment will be described. In the first and second embodiments, long-term integration processing using a two-stage FFT was 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.

Figure 9 is a block diagram showing the configuration of a radar system according to the third embodiment, where (a) is a block diagram showing the configuration of the transmission system and (b) is a block diagram showing the configuration of the reception system. The transmission system shown in Figure 9(a) is the same as the transmission system of the first and second embodiments shown in Figure 1(a). The reception system shown in Figure 9(b) differs from the reception system of the first and second embodiments shown in Figure 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, slow-time axis divider 30, slow-time axis FFT processor 31, and tentative detector 32, and a target determination system that uses a wideband range compressor 33, range walk/Doppler walk corrector 34, slow-time two-stage FFT processor 35, and CFAR detector 36.

The long-term integration method used in this embodiment will be described. For each pulse transmitted at a PRI (Pulse Repetition Interval), data is acquired in range cell units within the PRI. This acquired data is used to perform long-term integration processing. With 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 will reduce the target SN (signal-to-noise ratio). As a countermeasure, we consider reducing the range resolution and Doppler resolution and performing provisional detection.

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 to 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.

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 using a band-limited narrow band (29), the slow-time axis (the N-hit PRI axis) is divided (30), FFT processing is performed on the divided slow-time axis (31), and reflection points are tentatively detected using CFAR or similar (32). The narrow band signal is used to reduce range resolution and suppress the effects of range walk, and the slow-time axis is divided to reduce 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 amplitude integration of the processing results for each division unit prevents this reduction in signal-to-noise ratio and allows tentative detection.

Meanwhile, the digital signal from the AD converter 23 undergoes wideband range compression using the transmitted chirp band (33), and then range walk and Doppler walk correction is performed based on the provisionally detected reflection point to replace the slow-time axis signal passing through the provisionally detected point (34). Then, slow-time axis two-stage FFT processing is performed (35), and the target is detected using CFAR or similar to obtain target information (36).

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

As shown in Figure 10A, the radar system of this embodiment transmits and receives wideband pulse signals (step S31), and then performs an FFT on the fast-time axis using the CPI (Coherent Pulse Interval) signals (fast-time and slow-time signals, Figure 11(a)) from the AD converter 23 to convert them to the range-frequency axis (step S32, Figure 11(b)). Using these signals, the signals on the range-frequency axis and slow-time axis are divided into Mf and Ms, respectively, to obtain Mf x Ms signals (steps S33 and S34, Figure 11(c)). On the range-frequency axis, signals other than the divided signals are zero-padded. On the slow-time axis, on the other hand, zero-padding is not performed to reduce the number of FFT points. For each of these Mf x Ms signals, pulse compression is performed on the fast-time axis (step S35) and FFT is performed on the slow-time axis (step S36), resulting in low-resolution signals on the range and Doppler axes. Furthermore, the Mf x Ms signals are amplitude integrated (steps S37-S41), and tentative detection points are determined using CFAR or similar methods (step S42, Figure 11(d)).

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

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

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

If this is band-limited, the following equations are obtained (FIG. 12(c1) and (FIG. 12(c2)).

Conjugate multiplication of the band-limited signal and the reference signal results in the following equations (FIG. 12(d1) and (FIG. 12(d2)).

To place it on the time axis, this s can be inverse Fourier transformed as shown in the following equation (FIG. 12(e1) and (FIG. 12(e2)).

The above results are amplitude integrated to extract tentatively detected cells (FIG. 12(f)).

This allows the range cell resolution of narrowband range compression and wideband range compression to be the same, and cells provisionally detected using narrowband range compression can be directly used with wideband range compression.

Next, we will formulate the time-division FFT processing with reference to Figure 13. Figure 13 is a diagram showing the time-division FFT processing used in the third embodiment.

First, the input signal (Figure 13(a)) is expressed as follows:

Here, when the slow-time axis is divided by band limiting (FIG. 13(b)) and FFT processing is performed on the slow-time axis, the following equation is obtained (FIG. 13(c)).

Using the range-Doppler signal (fastd x slowd) in equation (13), amplitude integration is performed to improve the signal-to-noise ratio (Figure 13(d)), and then provisional detection is performed using CFAR or similar, and range cells are extracted to obtain range cell Rt (t = 1 to Pt: Pt is the provisional detection number).

The processing after the provisional detection will be described with reference to FIG. 10B and FIG.
In 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 steps S45 to S48 are repeated. If the predetermined velocity number is exceeded, a determination is made as to whether a predetermined acceleration has been reached (step S50). If not, the acceleration is changed (step S51), and steps S45 to S50 are repeated. If the predetermined acceleration has been reached, a determination is made as to 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 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).

Figure 14 shows 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 ( Figure 14 (a1)) and the reference signal ( Figure 14 (a2)), an FFT is performed on the fast-time axis ( Figure 14 (b1) ( Figure 14 (b2))), and complex conjugate multiplication of both is performed ( Figure 14 (c)). The process at this time is as follows:

To plot it on the time axis, s can be inverse Fourier transformed as shown in the following equation (FIG. 14(d)).

Next, range walk and Doppler walk correction will be explained using Figures 15A and 15B. Figures 15A and 15B are diagrams showing the range walk and Doppler walk correction processes used in the third embodiment.

First, a signal divided along the slow-time axis is generated as a unit of correction, and the first FFT processing is performed along the slow-time axis for each divided signal (Figure 15A (a)).

Next, using the velocity (sv) and acceleration (sa) of a predetermined search range and the range cell bias (sb), centered on the provisionally detected Rt cell, an integral series (sv × sa × sb) is set along the divided slow-time axis slowd (Figure 15A (b)).

Each integral series 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 on the range-frequency axis (Figure 15A(c)), which will be described later. This series is subjected to an FFT on all slow-time axes, and the Ms-point integral series (before the second FFT on the slow-time axis) with the largest value of the sv × sa × sb results is selected (Figure 15B(d)). The results of the slow-time axis FFT processing on the Ms points are replaced with Doppler cells (ls = 1 to Ls) (Figure 15B(e)). This process is repeated for each provisional detection Pt, and the range-Doppler data is used for detection using CFAR, etc. (Figure 15B(f)).

The above processing limits the search range through tentative detection, reducing the processing scale, and then performs range walk and Doppler walk corrections, allowing processing with a high S/N ratio, enabling targets to be detected while suppressing false detections.

The methods for range walk and Doppler walk correction 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 series (sv x sa x 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 Figure 15A (c). In this case, if the shift amount is determined on a range cell basis, quantization errors will occur in the shift amount, degrading the Doppler axis side lobes when performing FFT processing on the slow-time axis and reducing the SN (signal-to-noise ratio), resulting in false detections. This embodiment describes a solution to this problem.

Figure 16 is a waveform diagram showing the flow of the false detection countermeasure processing in the third embodiment, and Figure 17 is a diagram showing the false detection countermeasure processing shown in Figure 16.

In Figure 16, the range-compressed slow-time axis data is input (step S61), and FFT processing is performed 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, Figure 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, Figure 17(b)).

Using repeated range-Doppler data, cells are detected by CFAR or the like.

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

This result is repeated for each integral series (sv × sa × sb ways) and the integral series that maximizes the result of the second FFT processing on the slow-time axis is extracted, thereby obtaining the range walk and Doppler walk correction results (Figure 17(c)).

Note that while the embodiments have been described as systems that transmit and receive radar waves, the present invention can also be applied to passive radars that use transmission sources from other systems (including communications, etc.).

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, an FFT is performed on the fast-time axis to convert it to the range frequency axis, and then the range frequency is divided into Mf (Mf ≧ 1) parts and the slow-time axis is divided into Ms (Ms ≧ 1) parts. The Mf × Ms divided signals are then used from the remaining Nf × Ns regions, with the fast-time axis being zero-filled and the slow-time not being zero-filled. 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 using CFAR to extract Pt (Pt ≧ 1) range cells Rt and Doppler cells Ft. Next, the range is compressed using signals of the entire range frequency band, and the slow-time axis is divided into Ms divisions, and then a second FFT process is performed Ms times on each division unit. For each Doppler cell (ls = 1 to Ls) of each division unit, an integral series (sv x sa x sb) is set along the slow-time axis using the velocity (sv ways) and acceleration (sa ways) of a predetermined search range and the bias of the range cell (sb ways) for each provisionally detected Pt cells as the center for the slow-time axis data of Ms points. Range walk correction is performed 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 then the series is rearranged on the slow-time axis. After that, a second FFT process (Ms point) is performed on the slow-time axis. The Ms point integrated series (before slow-time axis FFT processing) with the largest value of the sv x sa x sb results is selected, and the result of the second FFT process on the slow-time axis at the Ms point is replaced with a Doppler cell (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.

In other words, range resolution and Doppler resolution are limited by narrowing the range frequency axis and limiting the slow-time axis, 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 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.

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 of the components shown in the embodiments. Furthermore, components from different embodiments may be appropriately combined.

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 (6)

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 long-term integration of signals obtained by arranging the processing results of said second FFT processing means for each original Doppler cell (ls = 1 to Ls). 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 long-term integration of signals obtained by arranging the processing results of said second FFT processing means for each original Doppler cell (ls = 1 to Ls). 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. 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;
A radar signal processing method for detecting a target by integrating the signals obtained by arranging the results of the second FFT processing for each original Doppler cell (ls = 1 to Ls) for a long period of time. 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;
A radar signal processing method for detecting a target by integrating the signals obtained by arranging the results of the second FFT processing for each original Doppler cell (ls = 1 to Ls) for a long period of time. 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.