A non-coherent and coherent accumulation joint processing method based on an external radiation source non-cooperative radar

Abstract

The application provides a non-coherent and coherent accumulation joint processing method based on an external radiation source radar, which firstly uses non-coherent accumulation on the scattered echo after pulse compression to obtain a relative time-of-arrival coarse estimation, and then performs coherent accumulation after range selection according to the actual engineering requirements. In order to reduce the operation amount, the segmented coherent accumulation is used to obtain the accurate echo relative time-of-arrival information of each pulse. According to the obtained time-of-arrival information, the echo is guided to perform multi-pulse FFT, the echo signal is detected and the echo time difference from the direct wave is extracted after the signal-to-noise ratio is improved. The joint processing method provided by the application improves the scattered echo time-of-arrival detection accuracy from the direct wave under the condition of low operation amount, accurately realizes the extraction of the time difference between the direct wave and the scattered echo, realizes the scattered echo time-of-arrival information monitoring accuracy, and has feasibility and great use value in engineering application.

Description

Technical Field

[0001] This invention belongs to the field of signal processing for non-cooperative radar with external radiation sources, and particularly relates to a method for joint processing of non-coherent and coherent accumulation based on non-cooperative radar with external radiation sources, which can realize the arrival time estimation of the radar-reflected echo relative to the direct wave. Background Technology

[0002] External radiation source radar, also known as passive radar, is a bistatic radar that can perform covert detection by receiving forward and lateral scattered echoes from targets. This type of radar features separate transmit and receive components and does not emit its own signals, giving it advantages such as strong anti-stealth capabilities, strong anti-jamming ability, and being environmentally friendly with no electromagnetic pollution, making it a focus of attention in the last decade. External radiation source radar typically selects non-cooperative radar signals or broadcast signals as radiation sources; however, due to the uncontrolled nature of its transmitted signals, obtaining high-purity scattered echoes has become an important research direction.

[0003] Receivers based on external radiation source radar typically employ two types of channels: a direct wave channel for receiving the direct wave signal from the external radiation source and a scattered echo channel for receiving the echo signal scattered by the target. The receiver uses the arrival information of the direct wave and the scattered echo to guide the time-domain alignment of the scattered echo channel and perform signal correlation processing, thereby completing accumulation detection. Time synchronization is crucial for external radiation source radar operations; its core is obtaining absolute time by combining the arrival times of the direct wave and the scattered echo. The direct wave signal directly indicates when the external radiation source emitted the signal, while the absolute time can be obtained by comparing the arrival time of the scattered echo with that of the direct wave. Time synchronization avoids problems caused by time errors in the system's inter-pulse coherence accumulation. Furthermore, the time difference between the echo and direct wave signals, combined with prior information about the radiation source's location, can be used to calculate the target's position.

[0004] However, echo information contains multipath signals, clutter, and noise. Complex electromagnetic environments can affect the detection of the arrival time of scattered echoes, causing offsets in the time-domain alignment of the echo signals and thus introducing errors in target localization. Therefore, signal processing typically involves accumulating multiple pulse echo signals, effectively increasing the echo signal reception time to achieve high gain. Accumulation methods are divided into non-coherent and coherent accumulation. Non-coherent accumulation does not require target phase information, while coherent accumulation includes both amplitude and phase information. Therefore, inter-pulse accumulation methods can be used to perform non-coherent and coherent accumulation on a certain number of pulse echo signals, thereby accurately extracting the relative arrival time of the echo to the direct wave. This provides more accurate time guidance for subsequent scattered echo signal processing, improving the accuracy of subsequent target information calculations. Summary of the Invention

[0005] To address the issue of time-of-arrival (TOA) deviation between echoes and the direct wave, this invention employs a joint detection method combining non-coherent and coherent accumulation. First, non-coherent accumulation is used to obtain a coarse estimate of the TOA. Then, coherent accumulation is used to find the maximum value, yielding precise TOA information for each echo pulse relative to the direct wave. This method accurately obtains TOA information and uses it to guide multi-pulse FFT of the echoes, thereby improving the signal-to-noise ratio and detecting and extracting the time difference between the echoes and the direct wave.

[0006] The specific technical solution of this invention is as follows:

[0007] A method for joint processing of noncoherent and coherent accumulation based on external radiation source radar, the specific steps of which include:

[0008] Step 1: Based on the pulse signal echo points, analyze the external radiation source radar received over a period of time. n Each echo signal undergoes pulse compression, where:

[0009] The external radiation source radar is specifically described as follows: there is a radar external radiation source on the ground that transmits linear frequency modulated pulse signals, and it is assumed that the radar external radiation source is turned on and working, and at the same time, our external radiation source receiver is also turned on and working, and at this time there is a maneuvering target in the air.

[0010] At time t, the linear frequency modulated pulse signal of the radar external radiation source is:

[0011]

[0012] Where t is the fast time, A is the signal amplitude, T is the pulse width, and f c It is the carrier frequency, k = B / T is the frequency modulation slope, and B is the signal bandwidth.

[0013] At time t, the scattered echo signal of the nth pulse signal received by the external radiation source receiver is expressed as:

[0014]

[0015] Where Δt n Let A be the relative direct wave delay of the nth echo pulse. For targets with slowly changing radar cross-sections in the air, A is considered to be constant within one pulse time.

[0016] The carrier frequency result is obtained by extracting the direct wave data of each echo pulse, and the scattered echo signal S is then guided. r (t) After digital down-conversion, the echo data is obtained, and the frequency-converted echo data is pulse-compressed and saved.

[0017] The pulse compression itself is a matched filtering of the signal, and the impulse response of the matched filter is h(t) = s. *(-t), then the echo signal s r (t) The output of the filtering system is:

[0018]

[0019] in Represented as convolution, s o (t) represents the pulse compression result, where u is the transformed value of t.

[0020] The non-coherent and coherent accumulation are processed in the fast-slow time domain and defined according to n consecutively received pulses. Each segment is defined as a single pulse, with the time within a single pulse segment being the fast time and the time between pulse segments being the slow time. The pulse-compressed signal S is represented by the horizontal axis as fast time and the vertical axis as slow time. c (t) is represented as:

[0021]

[0022] Step 2: Perform non-coherent accumulation on the pulse-compressed echo signal to find a coarse estimate of the relative arrival time of the maximum echo pulse. in:

[0023] The non-coherent accumulation of the pulse-compressed echo signal is called envelope superposition, which involves adding the n slow time values ​​corresponding to the fast time point, expressed as:

[0024]

[0025] After envelope superposition, a coarse estimate of the relative arrival time of the maximum echo pulse is found. That is, the x-coordinate of the maximum value after non-coherent accumulation, where the x-coordinate of the maximum value is the maximum value after non-coherent accumulation at each fast time point. Represented as:

[0026]

[0027] Step 3: Roughly estimate the arrival time based on engineering experience using relative arrival time. The time interval for each pulse signal is selected as the reference. The part is coherently accumulated. When When, the selected interval is when At that time, t max To maximize the sampling duration, the selected interval is: in:

[0028] In actual testing, the interval selected based on engineering experience has an error of 2 to 3 sampling time intervals when detecting the relative arrival time of each pulse. Therefore, it is necessary to select the pulse signal centered on the coarse time estimate. The interval is the range S of subsequent coherent accumulation. j (t) is:

[0029]

[0030] Where, Δt s The sampling time unit is p. Generally, in engineering experience, p is an integer and p = 2 to 3.

[0031] The rough estimated time point satisfies At that time, the selected coherent accumulation range S j (t) is:

[0032]

[0033] The rough estimated time point satisfies At that time, t max The selected coherent accumulation time range S is the maximum sampling duration. j (t) is:

[0034]

[0035] Step 4: First, traverse the previous... pulse Coherent accumulation is performed over a time interval to find the maximum value of the coherent accumulation and mark the echo relative arrival time t of each pulse corresponding to the maximum value. n After traversing again pulse Coherent accumulation is performed over a time period to find the maximum value of the coherent accumulation and mark the relative arrival time t of the echo of each pulse corresponding to the maximum value. n ,in:

[0036] The coherent accumulation is a step-by-step coherent accumulation, which reduces the amount of computation by splitting the pulse signal within a selected range;

[0037] The received n pulses are divided into two parts, and the precise relative arrival times of the n pulses are found in a relatively short time. The two data matrices after grouping are represented as follows: Wherein S jl (t) is:

[0038]

[0039] The S jr (t) is

[0040]

[0041] The S jl (t) represents the previous The data required for coherent accumulation of each pulse, the S jr (t) corresponds to Data accumulated by pulse coherence.

[0042] For the S jl (t) Coherent accumulation is performed, meaning that only one sampling time point is taken for each pulse echo for coherent accumulation. After traversing each time point, the values ​​of each group of FFTs are obtained, and the fast time point corresponding to each pulse with the maximum value is taken, which is the first time point found after coherent accumulation. The precise relative arrival time of each pulse is expressed as:

[0043]

[0044] For the S jr (t) is coherently accumulated to obtain the result. The precise relative arrival time of each pulse is expressed as:

[0045]

[0046] The step-by-step coherent accumulation identifies the cell containing the relative arrival time of the echo. This cell is then marked, and the time stamps of the two marked parts are merged to obtain a set of relative arrival time matrices for the echo pulses. The precise relative arrival time values ​​obtained after the step-by-step coherent accumulation are:

[0047]

[0048] The precise relative arrival time can guide the scattered echo for subsequent signal processing of the target.

[0049] The step-by-step coherent accumulation is processed in units of pulses, so a result will be output within one pulse cycle in each loop.

[0050] When each pulse is aligned with a relative time point for coherent accumulation, its corresponding accumulated amplitude will be higher than that of other unaligned time points. Therefore, by traversing each time point within the range of values ​​for coherent accumulation, the relative arrival time of each pulse can be obtained, providing a more accurate reference for subsequent signal processing.

[0051] Step 5: Use the already marked pulse echoes to correspond to the relative arrival time t n The echo is guided to undergo multi-pulse FFT. After the signal-to-noise ratio is improved, the echo signal is detected and the time difference between the echo and the direct wave is extracted.

[0052] The FFT is Fast Fourier Transform.

[0053] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0054] This invention addresses the problem of relative arrival time offset detection of scattered echoes. It utilizes a combined non-coherent and coherent accumulation processing method, and combines it with practical engineering needs, performing non-coherent accumulation followed by segmented coherent accumulation to achieve accurate detection of the relative arrival time information of scattered echoes and direct waves. This method is feasible and has significant practical value in engineering applications. Attached Figure Description

[0055] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0056] Figure 1 A schematic flowchart of a phase coherent accumulation processing method based on an external radiation source radar provided by the present invention;

[0057] Figure 2 This is a schematic diagram of pulse sampling point coherent accumulation in a coherent accumulation processing method based on an external radiation source radar provided in a specific implementation method of the present invention;

[0058] Figure 3 This is a comparison diagram of time-scale simulation in the simulation experiment of this invention;

[0059] Figure 4 In the simulation experiment provided by the embodiments of the present invention, the signal-to-noise ratio is -10dB to 10dB and the root mean square error of the number of time scale offsets.

[0060] Figure 5 In the embodiments provided by the present invention, the signal-to-noise ratio is -30dB to 10dB, and the root mean square error of the number of time scale offsets is used.

[0061] Figure 6 The image shows a magnified view of the root mean square error of the number of timescale offsets with a signal-to-noise ratio of -30dB to 10dB in the embodiments provided by the present invention. Detailed Implementation

[0062] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0063] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0064] This invention provides a method for joint processing of noncoherent and coherent accumulation based on external radiation source radar, such as... Figure 1 As shown, the specific steps of the joint processing method include:

[0065] Step 1: Based on the pulse signal echo points, analyze the external radiation source radar received over a period of time. n Each echo signal is pulse-compressed;

[0066] Step 2: Perform non-coherent accumulation on the pulse-compressed echo signal to find a coarse estimate of the relative arrival time of the maximum echo pulse.

[0067] Step 3: Roughly estimate arrival time based on engineering experience. The time interval for each pulse signal is selected as the reference. The parts are accumulated through coherent interaction.

[0068] when When, the selected interval is when At that time, t max To maximize the sampling duration, the selected interval is:

[0069] The Δt s The sampling time unit is p; generally, in engineering experience, p is an integer and p = 2 to 3.

[0070] Step 4: First, traverse the previous... pulse Coherent accumulation is performed over a time interval to find the maximum value of the coherent accumulation and mark the echo relative arrival time t of each pulse corresponding to the maximum value. n After traversing again pulse Coherent accumulation is performed over a time period to find the maximum value of the coherent accumulation and mark the relative arrival time t of the echo of each pulse corresponding to the maximum value. n ;

[0071] Step 5: Use the already marked pulse echoes to correspond to the relative arrival time t n The echo is guided to undergo multi-pulse FFT. After the signal-to-noise ratio is improved, the echo signal is detected and the time difference between the echo and the direct wave is extracted.

[0072] The FFT is Fast Fourier Transform.

[0073] A specific embodiment of the noncoherent and coherent accumulation joint processing method based on external radiation source radar in this example is as follows:

[0074] The simulation conditions for this embodiment of the invention are as follows:

[0075] The experiment of this invention includes one non-cooperative external radiation source, one non-cooperative receiver, and one moving target.

[0076] Assume the radiation source emits a linear frequency modulated pulse signal with a repetition period of 120 μs and a bandwidth of 2 MHz, and remains continuously operational. A non-cooperative receiver is constantly in reconnaissance mode, with one channel dedicated to receiving the direct wave signal and multiple channels receiving the target's scattered signals. When eight pulses are received, assume the original timescale has a positive and negative offset of 5 units, and take p = 2. Subsequently, a combined non-coherent and coherent accumulation method is used to estimate the true timescale of the eight pulses. First, the precise relative timescales of the first four pulses are estimated, and then the precise relative timescales of the last four pulses are estimated. The relative timescales of the two sets of detected pulses are merged to obtain the timescale matrix of the pulse train. During coherent accumulation, only one sampling time point is taken from each pulse echo for coherent accumulation, as illustrated in the diagram below. Figure 2 As shown.

[0077] When the signal-to-noise ratio is set to -10dB, the unaligned time scales, the time scales after non-coherent accumulation, and the time scales after non-coherent accumulation of 8 pulses are compared to compare the accumulation effect of the time scales under various conditions. For example... Figure 3 As shown.

[0078] Simulation results analysis of the embodiments of the present invention:

[0079] Figure 3 It is a comparison chart of the non-aligned timescale of coherent accumulation of 8 pulse sampling points, and the timescale after non-coherent accumulation and the timescale after non-coherent coherent accumulation. Figure 4 This refers to the root mean square error of the number of scale offsets when the signal-to-noise ratio is -10dB to 10dB. Figure 5 This refers to the root mean square error of the number of scale offsets when the signal-to-noise ratio is -30dB to 10dB. Figure 6 yes Figure 5 Enlarged view of part of the image.

[0080] Simulation results show that the combined non-coherent and coherent processing method described in this invention can effectively improve the accuracy of direct wave arrival time extraction. Figure 3The results show that, at a signal-to-noise ratio of -10dB, the method described in this invention exhibits a significant coherent accumulation effect compared to directly received timescales and timescales accumulated without coherence. Furthermore, it can effectively locate the arrival time of each pulse. Figure 4 The results show that when the signal-to-noise ratio (SNR) is -10dB, the timescale extraction method described in this invention can improve the mean square error of the timescale offset to about 0.5 offset units. However, the mean square error of the simple non-coherent accumulation timescale extraction is 1.2 offset units. In comparison, the improved method significantly improves the timescale extraction accuracy. When the SNR is between -30dB and 10dB, simulations are performed again under the same conditions. Figure 6 It can be seen that when the signal-to-noise ratio (SNR) exceeds 18 dB, the number of time marker offsets increases as the SNR decreases, leading to inaccurate measurement. This is because the SNR improvement from coherent accumulation of eight pulses is eight times that of a single pulse. Therefore, after coherent accumulation, multi-pulse accumulation provides better time marker localization than single-pulse accumulation. However, when the accumulation effect does not exceed the current SNR, this method can only achieve the desired effect by increasing the number of accumulated pulses.

[0081] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention based on the above disclosure without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for joint processing of noncoherent and coherent accumulation based on external radiation source radar, characterized in that, The processing method can detect the accurate arrival time information of radar echoes from external radiation sources relative to direct waves. Specific steps include: Step 1: Based on the pulse signal echo points, analyze the external radiation source radar received over a period of time. Each echo signal is pulse-compressed; Step 2: Perform non-coherent accumulation on the pulse-compressed echo signal to find a coarse estimate of the relative arrival time of the maximum echo pulse. ; Step 3: Based on engineering experience, make a rough estimate of the relative arrival time. The time interval for each pulse signal is selected as the reference. Partial coherent accumulation; when When, the selected interval is To determine the maximum sampling duration, the selected interval is... ; The The unit of measurement is the sampling time; in engineering experience, ; Step 4: First, traverse the previous... pulse Coherent accumulation is performed over a time interval to find the maximum value of the coherent accumulation, and the echo relative arrival time of each pulse corresponding to the maximum value is marked. ; Iterate again pulse Coherent accumulation is performed over a time period to find the maximum value of the coherent accumulation, and the relative arrival time of the echo of each pulse corresponding to the maximum value is marked. ; Step 5: Use the already marked pulse echoes to correspond to the relative arrival time The echo is guided to undergo multi-pulse FFT. After the signal-to-noise ratio is improved, the echo signal is detected and the time difference between the echo and the direct wave is extracted. The FFT is Fast Fourier Transform.

2. The method for joint processing of noncoherent and coherent accumulation based on external radiation source radar according to claim 1, characterized in that, Step 1: The external radiation source radar specifically refers to: a ground-based external radiation source emitting a linear frequency modulated (LFM) pulse signal, and assuming this external radiation source is powered on and operational, and our external radiation source receiver is also powered on, while a maneuvering target exists in the air; at time t, the LFM pulse signal of the external radiation source is: Where t is the fast time, A is the signal amplitude, and T is the pulse width. It is the carrier frequency. Where B is the frequency modulation slope and B is the signal bandwidth; at time t, the scattered echo signal of the nth pulse signal received by the external radiation source receiver is expressed as: in Given the relative direct wave time delay of the nth echo pulse, for a target with a slowly changing radar cross section in the air, it is assumed that within one pulse time...

3. The method for joint processing of noncoherent and coherent accumulation based on external radiation source radar according to claim 2, characterized in that, The carrier frequency result is obtained by extracting the direct wave data of each echo pulse, and the scattered echo signal is then guided. After performing digital down-conversion, the echo data is obtained. The frequency-converted echo data is then pulse-compressed and saved. The pulse compression itself is a form of matched filtering of the signal, which affects the impulse response of the matched filter. The echo signal output through the filtering system is: ,in Represented as convolution, This is represented as the result of pulse compression. yes The transformed value.

4. The method for joint processing of noncoherent and coherent accumulation based on external radiation source radar according to claim 1, characterized in that, The non-coherent and coherent accumulation are processed in the fast-slow time domain and defined according to n consecutively received pulses; each segment is defined as a single pulse, the time within a single pulse segment is the fast time, and the time between pulse segments is the slow time; with the horizontal axis representing fast time and the vertical axis representing slow time, the pulse-compressed signal... Represented as: 。 5. The method for joint processing of noncoherent and coherent accumulation based on external radiation source radar according to claim 1, characterized in that, Step 2 involves non-coherent accumulation of the pulse-compressed echo signal, which is envelope superposition, i.e., adding the n slow time values ​​corresponding to the fast time points, expressed as: After envelope superposition, a coarse estimate of the relative arrival time of the maximum echo pulse is found. That is, the x-coordinate of the maximum value after non-coherent accumulation, where the x-coordinate of the maximum value is the maximum value after non-coherent accumulation at each fast time point. Represented as: .

6. The method for joint processing of noncoherent and coherent accumulation based on external radiation source radar according to claim 1, characterized in that, In step 3, the interval selected based on engineering experience has an error of 2-3 sampling time intervals in actual detection of the relative arrival time of each pulse. Therefore, it is necessary to select the pulse signal centered on the coarse time estimate. The interval is the range of subsequent coherent accumulation. for: in, The sampling time unit is used in engineering experience. ; Roughly estimated time point meets At that time, the selected coherent accumulation range for: Roughly estimated time point meets hour, The selected coherent accumulation time range is the maximum sampling duration. for: 。 7. The method for joint processing of noncoherent and coherent accumulation based on external radiation source radar according to claim 1, characterized in that, The coherent accumulation described in step 4 is a step-by-step coherent accumulation, which reduces the amount of computation by splitting the pulse signal within the selected range; The received n pulses are divided into two parts, and the precise relative arrival times of the n pulses are found in a relatively short time; the two data matrices after grouping are represented as follows. , wherein for: The for: .

8. The method for joint processing of noncoherent and coherent accumulation based on external radiation source radar according to claim 7, characterized in that, The Indicated as before The data required for coherent accumulation of each pulse, the aforementioned After corresponding Data accumulated by pulse coherence; Regarding the Coherent accumulation is performed, meaning that only one sampling time point is taken for each pulse echo for coherent accumulation; after traversing each time point, the values ​​of each group of FFTs are obtained, and the fast time point corresponding to each pulse with the maximum value is taken, which is the first pulse found after coherent accumulation. The precise relative arrival time of each pulse is expressed as: Regarding the Perform coherent accumulation to obtain the result. The precise relative arrival time of each pulse is expressed as: 。 9. The method for joint processing of noncoherent and coherent accumulation based on external radiation source radar according to claim 7, characterized in that, The step-by-step coherent accumulation identifies the cell containing the relative arrival time of the echo. This cell is then marked, and the time stamps of the two marked parts are merged to obtain a set of relative arrival time matrices for the echo pulses. The precise relative arrival time values ​​obtained after the step-by-step coherent accumulation are: The precise relative arrival time can guide the scattered echo for subsequent signal processing of the target.

10. The method for joint processing of noncoherent and coherent accumulation based on external radiation source radar according to claim 7, characterized in that, The step-by-step coherent accumulation is processed in units of pulses, so one result is output within each pulse cycle. When each pulse is aligned with a relative time point for coherent accumulation, its corresponding accumulation amplitude will be higher than that of other unaligned time points. Therefore, by traversing each time point within the range of values ​​for coherent accumulation, the relative arrival time of each pulse can be obtained, providing a more accurate reference for subsequent signal processing.

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