Non-coherent and coherent accumulation combined processing method based on external radiation source non-cooperative radar

Abstract

The invention provides a non-coherent and coherent accumulation combined processing method based on an external radiation source radar, and the method comprises the steps: firstly carrying out the non-coherent accumulation of scattered echoes after pulse compression, obtaining a relative arrival time rough estimation value, carrying out the range selection through combining with the actual demands of a project, and then carrying out the coherent accumulation. In order to reduce the operand, accurate echo relative arrival time information of each pulse is obtained through segmented coherent accumulation traversal, according to the obtained time information, the echo is guided to carry out multi-pulse FFT, after the signal-to-noise ratio is improved, echo signal detection is carried out, and the time difference between the echo and the direct wave is extracted. According to the combined processing method provided by the invention, the detection accuracy of the arrival time of the scattering echo relative to the direct wave is improved under the condition of relatively low operand, the extraction of the time difference of the direct wave and the scattering echo is relatively accurately realized, and the information monitoring accuracy of the arrival time of the scattering echo relative to the direct wave is realized; the method has feasibility and great use value in engineering application.

Description

Technical Field

[0001] The present invention belongs to the field of exo-radiation source non-cooperative radar signal processing, and in particular relates to a non-cooperative and coherent accumulation joint processing method based on exo-radiation source non-cooperative radar, which can realize the estimation of the arrival time of the non-cooperative exo-radiation source radar scattered echo relative to the direct wave. Background Art

[0002] Exo-radiation radar, also known as passive radar, is a dual-base radar that can detect targets covertly by receiving forward and side scattered echoes. This type of radar has separate transmitters and receivers and does not transmit signals itself, which makes it have strong anti-stealth, strong anti-interference capabilities, green and environmentally friendly, and no electromagnetic pollution. It has attracted much attention in the past decade. Exo-radiation radar usually chooses non-cooperative radar signals, broadcast signals, etc. as radiation sources, but due to the problem that its transmitted signals are uncontrolled, obtaining high-purity scattered echoes has become an important research direction.

[0003] The receiving device based on the external radiation source radar body usually sets two types of channels, one is the direct wave channel, which is used to receive the direct wave signal of the external radiation source, and the other is the scattered echo channel, which is used to receive the echo signal scattered by the target. The receiving device guides the time domain alignment of the scattered echo channel and performs signal correlation processing through the arrival information of the direct wave and the scattered echo, and then completes the accumulation detection. Time synchronization is the focus of the work of the external radiation source radar. The core is to obtain the absolute time by combining the direct wave and the scattered echo. The direct wave signal can directly obtain when the external radiation source is emitted, and the absolute time can be obtained by the arrival time of the scattered echo relative to the direct wave. Time synchronization can avoid the problem of coherent accumulation between system pulses caused by time error. At the same time, the time difference between the echo signal and the direct wave signal can also be used in combination with the prior information of the radiation source position to complete the solution of the target position.

[0004] However, the echo information contains multipath signals, clutter and noise, etc. The complex electromagnetic environment will affect the detection of the arrival time of the scattered echo, causing an offset when aligning the echo signal in the time domain, thereby causing errors in the positioning of the target. Therefore, in signal processing, multiple pulse echo signals are generally accumulated, which is equivalent to increasing the receiving time of the echo signal to obtain high gain. The accumulation method is divided into non-coherent and coherent accumulation. Non-coherent accumulation does not require the use of target phase information, while coherent accumulation contains both amplitude and phase information. Therefore, the inter-pulse accumulation method of the echo can be used to perform non-coherent and coherent accumulation on a certain number of pulse echo signals, so that the arrival time point of the echo relative to the direct wave can be more accurately extracted, providing more accurate time guidance for the subsequent scattered echo signal processing, thereby improving the accuracy of the subsequent target information solution. Summary of the invention

[0005] In order to solve the problem that the echo arrival time detection relative to the direct wave will be offset, the present invention uses the method of joint detection of non-coherent and coherent accumulation, first uses non-coherent accumulation to obtain a rough estimate of the arrival time, and then uses coherent accumulation to find the maximum value to obtain the accurate relative direct wave arrival time information of each echo pulse. This method can accurately obtain the arrival time information, and use the arrival time information to guide the echo to perform multi-pulse FFT, thereby improving the signal-to-noise ratio, and detecting and extracting the time difference between the echo and the direct wave.

[0006] The specific technical solutions of the present invention are as follows:

[0007] A non-coherent and coherent accumulation joint processing method based on external radiation source radar, the specific steps include:

[0008] Step 1: Based on the pulse signal echo characteristics, the external radiation source radar received within a period of time n The echo signal is pulse compressed, where:

[0009] The external radiation source radar is specifically: there is a radar external radiation source on the ground that transmits a linear frequency modulation pulse signal, and it is assumed that the radar external radiation source is turned on and working, and 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 modulation 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, f c 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 A is the relative delay of the nth echo pulse to the direct wave. For targets with slowly changing radar scattering cross sections in the air, A is considered to be a constant within one pulse time.

[0016] Extract the direct wave data of each echo pulse to obtain the carrier frequency result, and guide the scattered echo signal S r (t) After digital down-conversion, echo data is obtained, and the converted echo data is pulse compressed and then stored.

[0017] The pulse compression itself is to achieve the 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 through the filtering system is:

[0018]

[0019] in Represented as convolution, s o (t) is the pulse compression result, and 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 the n pulses received continuously. Each segment is defined as a single pulse, the time within the single pulse segment is the fast time, and the time between pulse segments is the slow time. With the fast time as the horizontal axis and the slow time as the vertical axis, the pulse compressed signal S c (t) is expressed as:

[0021]

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

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

[0024]

[0025] After envelope superposition, find the rough estimate of the maximum relative arrival time of the echo pulse That is, the horizontal coordinate of the maximum value after non-coherent accumulation, the horizontal coordinate of the maximum value is the maximum value after non-coherent accumulation at each fast time point. It is expressed as:

[0026]

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

[0028] In actual detection, 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. It is necessary to select the pulse signal based on the rough estimated time value. The interval is the subsequent coherent accumulation range S j (t) is:

[0029]

[0030] Among them, Δt s is the sampling time unit. Generally, in engineering experience, p is an integer and p=2~3.

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

[0032]

[0033] The rough estimated time point satisfies When t max is the maximum sampling time, and the selected coherent integration time range S j (t) is:

[0034]

[0035] Step 4: First traverse the front Pulse The coherent accumulation is performed in the time interval, the maximum value of the coherent accumulation is found and the relative arrival time t of each pulse echo corresponding to the maximum value is marked. n , after traversing again Pulse The coherent accumulation is performed in the time period, the maximum value of the coherent accumulation is found and the relative arrival time t of each pulse echo corresponding to the maximum value is marked. n ,in:

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

[0037] The received n pulses are divided into two parts, and the precise relative arrival time of the n pulses is found in a faster time. The two-part data matrix after grouping is expressed as Among them, S jl (t) is:

[0038]

[0039] The S jr (t) is

[0040]

[0041] The S jl (t) represents the front The pulses are used to perform coherent accumulation of the data required. jr (t) After corresponding The data accumulated by each pulse is coherent.

[0042] For the S jl (t) is coherently integrated, that is, each pulse echo only takes one sampling time point for coherent integration. After traversing each time point, the value of each group of FFT is obtained, and the fast time point corresponding to each pulse in the maximum value is taken, which is the previous value found after coherent integration. The precise relative arrival time of each pulse is expressed as:

[0043]

[0044] For the S jr (t) performs coherent accumulation and obtains The precise relative arrival time of each pulse is expressed as:

[0045]

[0046] The step-by-step coherent accumulation can find the unit where the echo relative arrival time is located, mark the unit, merge the marked time scales of the two parts, and obtain a relative arrival time matrix of a group of echo pulses. The accurate relative arrival time value obtained after the step-by-step coherent accumulation is:

[0047]

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

[0049] The unit of the step-by-step coherent accumulation is processed in pulses, so a result will be output within a pulse cycle each time;

[0050] When each pulse is aligned with the relative time point for coherent accumulation, its corresponding accumulation amplitude will be higher than other non-aligned time points. Therefore, by traversing each time point within the value range 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 marked pulse echo to correspond to the relative arrival time t n , guide the echo to perform multi-pulse FFT, and after the signal-to-noise ratio is improved, perform echo signal detection and extract the time difference between the echo and the direct wave;

[0052] The FFT is fast Fourier transform.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] The present invention aims to solve the problem of detection offset of scattered echo relative to arrival time point, utilizes a combined processing method of non-coherent and coherent accumulation, and combines it with actual engineering needs to perform non-coherent accumulation first and then segmented coherent accumulation, so as to achieve the correctness of detection of scattered echo relative to direct wave arrival time information, which is feasible and has great use value in engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0056] Figure 1 A schematic flow chart of a coherent integration processing method based on external radiation source radar provided by the present invention;

[0057] Figure 2 A schematic diagram of coherent accumulation of pulse sampling points 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 It is a time scale simulation comparison diagram in the simulation experiment of the present invention;

[0059] Figure 4 In the simulation experiment of the embodiment provided by the present invention, the signal-to-noise ratio is -10dB to 10dB, and the root mean square error of the time-scale offset is obtained;

[0060] Figure 5 In the embodiment provided by the present invention, the signal-to-noise ratio is -30dB to 10dB, and the root mean square error of the time-scale offset is;

[0061] Figure 6 This is an enlarged diagram of the root mean square error of the time scale offset number when the signal-to-noise ratio is -30dB to 10dB in the embodiment provided by the present invention. DETAILED DESCRIPTION

[0062] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways 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 illustrations of the basic concept of the present invention, and thus the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0064] The embodiment of the present invention provides a non-coherent and coherent accumulation joint processing method based on external radiation source radar, such as Figure 1 As shown, the joint processing method specifically comprises the following steps:

[0065] Step 1: Based on the pulse signal echo characteristics, the external radiation source radar received within a period of time n The echo signal is pulse compressed;

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

[0067] Step 3: Roughly estimate the arrival time based on engineering experience The time interval of each pulse signal is selected as The parts are coherently accumulated.

[0068] when When , the selected interval is when When t max is the maximum sampling duration, the selected interval is

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

[0070] Step 4: First traverse the front Pulse The coherent accumulation is performed in the time interval, the maximum value of the coherent accumulation is found and the relative arrival time t of each pulse echo corresponding to the maximum value is marked. n , after traversing again Pulse The coherent accumulation is performed in the time period, the maximum value of the coherent accumulation is found and the relative arrival time t of each pulse echo corresponding to the maximum value is marked. n ;

[0071] Step 5: Use the marked pulse echo to correspond to the relative arrival time t n , guide the echo to perform multi-pulse FFT, and after the signal-to-noise ratio is improved, perform echo signal detection and extract the time difference between the echo and the direct wave;

[0072] The FFT is fast Fourier transform.

[0073] A specific embodiment of a non-coherent and coherent accumulation joint processing method based on an external radiation source radar in this embodiment is as follows:

[0074] The simulation conditions of the embodiment of the present invention are:

[0075] In the experiment of the present invention, there is a non-cooperative external radiation source, a non-cooperative receiver and a moving target.

[0076] Assume that the radiation source emits a linear frequency modulated pulse signal with a pulse repetition period of 120μs, a bandwidth of 2MHz, and is always in operation. The non-cooperative receiver is always in reconnaissance mode, and one channel is dedicated to receiving direct wave signals, and multiple channels receive target scattered signals. When 8 pulses are received, it is assumed that the original time scale has a total of 5 units of positive and negative offsets, and p=2. Subsequently, the joint processing method of non-coherent and coherent accumulation is used to estimate the true time scale of the 8 pulses. First, the first 4 pulses are estimated to obtain the precise relative time scale of the first 4 pulses, and then the last 4 pulses are estimated to obtain the precise relative time scale of the last 4 pulses. The relative time scales of the two groups of pulses after detection are merged to obtain the time scale matrix of the pulse train. When coherent accumulation is performed, each pulse echo only takes one sampling time point for coherent accumulation. The schematic diagram is shown in FIG. Figure 2 shown.

[0077] When the signal-to-noise ratio is set to -10dB, the non-aligned time scale, the time scale after non-coherent accumulation and the time scale after non-coherent accumulation of 8 pulses are compared to compare the accumulation effect of the time scale in various cases. Figure 3 shown.

[0078] Analysis of simulation results of the embodiment of the present invention:

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

[0080] From the simulation test results, the non-coherent and coherent joint processing method described in the present invention can effectively improve the accuracy of direct wave arrival time extraction. Figure 3The results show that when the signal-to-noise ratio is -10 dB, the method of the present invention has an obvious coherent accumulation effect compared with the time stamp of direct reception and the time stamp after non-coherent accumulation. And it can effectively find the arrival time point of each pulse. Figure 4 The results show that when the signal-to-noise ratio is -10dB, the time-scale extraction method of the method of the present invention can improve the average offset mean square error of the time-scale to about 0.5 offset units, but the mean square error of the simple non-coherent accumulation time-scale extraction is 1.2 offset units. In comparison, the improved method has greatly improved the time-scale extraction accuracy. When the signal-to-noise ratio is -30dB to 10dB, the same situation is simulated again. Figure 6 It can be seen that when the signal-to-noise ratio exceeds 18dB, the number of time-scale offsets will increase as the signal-to-noise ratio decreases, making the measurement accuracy inaccurate. This is because the improvement in the signal-to-noise ratio when coherently accumulating 8 pulses can reach 8 times that of a single pulse. Therefore, after the traversal search of the coherent accumulation, the accumulation effect of multiple pulses can better locate the time scale compared to the accumulation effect of a single pulse. However, when its accumulation effect does not exceed the current signal-to-noise ratio, this method can only achieve the desired effect by increasing the number of accumulated pulses.

[0081] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention using the above disclosed contents without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the contents of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A non-coherent and coherent accumulation joint processing method based on external radiation source radar, characterized in that: The processing method can detect the accurate arrival time information of the external radiation source radar echo relative to the direct wave, and the specific steps include: Step 1: Based on the pulse signal echo characteristics, the external radiation source radar received within a period of time n The echo signal is pulse compressed; Step 2: Perform non-coherent accumulation on the echo signal after pulse compression to find the rough estimate of the maximum relative arrival time of the echo pulse. Step 3: Make a rough estimate of the relative arrival time based on engineering experience The time interval of each pulse signal is selected as The part is coherently accumulated; when When , the selected interval is when When t max is the maximum sampling duration, the selected interval is The Δt s is the sampling time unit; generally, in engineering experience, p is an integer and p=2~3; Step 4: First traverse the front Pulse The coherent integration is performed over the time interval to find the maximum value of the coherent integration and mark the relative arrival time t of each pulse echo corresponding to the maximum value. n ; After traversing again Pulse The coherent accumulation is performed in the time period, the maximum value of the coherent accumulation is found, and the relative arrival time t of the echo of each pulse corresponding to the maximum value is marked. n ; Step 5: Use the marked pulse echo to correspond to the relative arrival time t n , guide the echo to perform multi-pulse FFT, and after the signal-to-noise ratio is improved, perform echo signal detection and extract the time difference between the echo and the direct wave; The FFT is fast Fourier transform.

2. The non-coherent and coherent accumulation joint processing method based on external radiation source radar according to claim 1 is characterized in that: The external radiation source radar described in step 1 is specifically: there is a radar external radiation source on the ground that transmits a linear frequency modulation pulse signal, 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; At time t, the linear frequency modulation pulse signal of the radar external radiation source is: Where t is the fast time, A is the signal amplitude, T is the pulse width, f c is the carrier frequency, k = B / T 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: Where Δt n A is the relative delay of the nth echo pulse to the direct wave. For targets with slowly changing radar scattering cross sections in the air, A is considered to be a constant within one pulse time.

3. The non-coherent and coherent accumulation joint processing method based on external radiation source radar according to claim 2 is characterized in that: Extract the direct wave data of each echo pulse to obtain the carrier frequency result, and guide the scattered echo signal S r (t) performing digital down-conversion to obtain echo data, and performing pulse compression on the converted echo data and then saving it; The pulse compression itself is to achieve the 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 through the filtering system is: in Represented as convolution, s o (t) is the pulse compression result, and u is the transformed value of t.

4. The non-coherent and coherent accumulation joint processing method based on external radiation source radar according to claim 1 is characterized in that: The non-coherent and coherent accumulation are processed in the fast-slow time domain and defined according to the n pulses received continuously; each segment is defined as a single pulse, the time within the single pulse segment is the fast time, and the time between pulse segments is the slow time; according to the fast time as the horizontal axis and the slow time as the vertical axis, the pulse compressed signal S c (t) is expressed as:

5. The non-coherent and coherent accumulation joint processing method based on external radiation source radar according to claim 1 is characterized in that: In step 2, the echo signal after pulse compression is non-coherently accumulated as envelope superposition, that is, n slow time values ​​corresponding to the fast time point are added, which is expressed as: After envelope superposition, find the rough estimate of the maximum relative arrival time of the echo pulse That is, the horizontal coordinate of the maximum value after non-coherent accumulation, the horizontal coordinate of the maximum value is the maximum value after non-coherent accumulation at each fast time point. It is expressed as:

6. The non-coherent and coherent accumulation joint processing method based on external radiation source radar according to claim 1 is characterized in that: In actual detection, the interval selected based on engineering experience in step 3 has an error of 2 to 3 sampling time intervals when detecting the relative arrival time of each pulse. It is necessary to select the pulse signal based on the rough estimated time value. The interval is the subsequent coherent accumulation range S j (t) is: Among them, Δt s is the sampling time unit. Generally, in engineering experience, p is an integer and p=2~3; The rough estimated time point satisfies When the coherent accumulation range S is selected j (t) is: The rough estimated time point satisfies When t max is the maximum sampling time, and the selected coherent integration time range S j (t) is:

7. The non-coherent and coherent accumulation joint processing method based on external radiation source radar according to claim 1 is characterized in that: The coherent accumulation in step 4 is a step-by-step coherent accumulation, which reduces the amount of calculation by splitting the pulse signal within the selected range; The received n pulses are divided into two parts, and the precise relative arrival time of the n pulses is found in a faster time; the two-part data matrix after grouping is expressed as The S jl (t) is: The S jr (t) is:

8. The non-coherent and coherent accumulation joint processing method based on external radiation source radar according to claim 7 is characterized in that: The S jl (t) represents the front The pulses are used to perform coherent accumulation of the data required. jr (t) After corresponding The data accumulated by each pulse coherently; For the S jl (t) is coherently accumulated, that is, only one sampling time point is taken for each pulse echo for coherent accumulation; after traversing each time point, the value of each group of FFT is obtained, and the fast time point corresponding to each pulse in the maximum value is taken as the previous one found after coherent accumulation. The precise relative arrival time of each pulse is expressed as: For the S jr (t) performs coherent accumulation and obtains The precise relative arrival time of each pulse is expressed as:

9. The non-coherent and coherent accumulation joint processing method based on external radiation source radar according to claim 7 is characterized in that: The step-by-step coherent accumulation can find the unit where the echo relative arrival time is located, mark the unit, merge the marked time scales of the two parts, and obtain a relative arrival time matrix of a group of echo pulses. The accurate relative arrival time value obtained after the step-by-step coherent accumulation is: The precise relative arrival time can guide the scattered echoes for subsequent signal processing on the target.

10. The non-coherent and coherent accumulation joint processing method based on external radiation source radar according to claim 7 is characterized in that: The unit of the step-by-step coherent accumulation is processed in pulses, so a result will be output within a pulse cycle each time; When each pulse is aligned with the relative time point for coherent accumulation, its corresponding accumulation amplitude will be higher than other non-aligned time points. Therefore, by traversing each time point within the value range 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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