Short wave weak signal detection method based on array distributed acquisition

Abstract

The invention provides a short-wave weak signal detection method based on array distributed acquisition, and relates to the technical field of short-wave communication reconnaissance, and the method comprises the steps: receiving a short-wave signal through employing M antennas which are separated at a preset interval in space, and obtaining M paths of synchronous parallel signal data; setting two time dislocation sliding detectors, segmenting the M paths of synchronous parallel data by using the sliding detectors, and carrying out signal combination on each segment of signal according to a maximum signal-to-noise ratio principle to obtain a first signal and a second signal; respectively performing signal synchronization sequence correlation detection on the first signal and the second signal, and respectively recording correlation peak moments when correlation peak values are greater than a threshold value th as a first peak value and a second peak value; and synthesizing the detection results of the two paths of signals, and outputting a final detection result. The method can effectively cope with the multipath fading phenomenon caused by ionosphere channel time variation, significantly improves the weak signal detection capability, has both accuracy and timeliness, and can be used in an array distributed acquisition short wave system.

Description

Technical Field

[0001] The invention belongs to the technical field of shortwave communication reconnaissance, and in particular relates to a shortwave weak signal detection method based on array distributed acquisition. Background Art

[0002] At present, array distributed acquisition is also called multi-antenna diversity technology. It uses multiple antennas to receive signals in a certain airspace, which can improve the quality of signal reception in complex electromagnetic environments. It also has the advantages of anti-fading and flexible deployment, and can better guarantee signal reception. Compared with traditional array signal processing methods, diversity reception has the advantages of flexible array element deployment, diverse antenna selection, and good airspace complementarity.

[0003] After using multiple antennas to synchronously collect the target signal, there are two signal merging schemes: a synthesis scheme based on synchronous demodulation and a synthesis scheme based on signal waveform. The former requires each antenna to perform carrier tracking and symbol synchronization separately, complete the synthesis while demodulating the signal, and require the single-channel signal signal-to-noise ratio to reach the synchronization threshold; the latter synthesizes the original signal of each antenna. In order to ensure the correlation, the signal needs to be delayed compensated, frequency compensated and phase adjusted before synthesis. Considering the detection scenario of weak signals in complex fading channels, the synthesis scheme based on signal waveform is more applicable. In practical applications, signal synthesis can be combined using different criteria and methods, mainly including maximum ratio combining (MRC), equal gain combining (EGC), selective combining (SC) and switching combining. Among them, maximum ratio combining has the best combining gain, but it has high requirements on signal stability and is difficult to cope with the signal fading fluctuation scenario caused by the time-varying ionospheric channel.

[0004] Therefore, how to provide a shortwave weak signal detection method based on array distributed acquisition has become a technical problem that urgently needs to be solved in this field. Summary of the invention

[0005] The purpose of the present invention is to provide a shortwave weak signal detection method based on array distributed acquisition, comprising:

[0006] Step S1: using M antennas spaced apart by a preset distance in space to receive shortwave signals, and obtaining M channels of synchronous parallel signal data, where M≥2;

[0007] Step S2: setting two time-shifted sliding detectors, a first sliding detector D1 and a second sliding detector D2, wherein the durations of the first sliding detector D1 and the second sliding detector are both T, and their starting times are shifted by T / 2;

[0008] Step S3: Use the sliding detector D1 to segment the M channels of synchronous parallel data, and merge each segment of the signal according to the maximum signal-to-noise ratio principle to obtain a synthesized first signal S1;

[0009] Step S4: using the sliding detector D2, segmenting the M channels of synchronous parallel data, and merging each segment of the signal according to the maximum signal-to-noise ratio principle to obtain a synthesized second signal S2;

[0010] Step S5: Perform signal synchronization sequence correlation detection on the first signal S1 and the second signal S2 respectively, and record the time when the correlation peak value is greater than the threshold value th as the first peak value T d1 and the second peak T d2 ;

[0011] Step S6: Detection results T of the two signals d1 、T d2 Perform synthesis and output T d The final test result.

[0012] Optionally, in step S1, the preset spacing is greater than 3 times the signal wavelength.

[0013] Optionally, in step S2, the duration T is 2 times or more longer than the duration of the synchronization sequence of the signal.

[0014] Optionally, a synchronization sequence detection method is used for detection, and a reference sequence Q can be obtained after the signal synchronization sequence is modulated, as follows:

[0015] Q=[q1,q2,…,q n ]

[0016] q n Take the value of the nth signal sample.

[0017] Optionally, a reference sequence Q is used to perform point-by-point sliding window detection on M synchronous parallel signal data, and the signal sequence is:

[0018] S(k)=[s k ,s k+p ,s k+2p ,…,s k+(n-1)p ]

[0019] Where k is the sliding starting point, and p is the oversampling rate;

[0020] Calculate the Pearson correlation coefficient between Q and S(k) point by point, and we can get:

[0021]

[0022] Set the threshold th, when the correlation coefficient r xyWhen the maximum value V is greater than th, it is considered that the signal is detected; the larger V is, the better the detection effect is;

[0023] Pearson correlation coefficient, also known as Pearson correlation coefficient, is a statistical indicator that measures the degree of linear correlation between two variables;

[0024] Use multiple antenna array elements distributed in space to receive signals. The M branch signals are r1(t), r2(t), …, r M (t), the combined signal is:

[0025]

[0026] Among them, a k is the weighted coefficient of the kth branch signal, which needs to be normalized, that is,

[0027] The instantaneous signal-to-noise ratio of each branch signal of M is γ i And the average signal-to-noise ratio Γ:

[0028]

[0029] Among them, E s is the unit signal energy; α i is the signal amplitude of the i-th channel; N0 is the average noise power; E() means finding the expected value.

[0030] Optionally, the maximum ratio combining method is used to combine the signals so that the signal-to-noise ratio of the output signal is maximized, and the branch weighting coefficient a is k It is directly proportional to the envelope and inversely proportional to the noise power;

[0031] Among them, the weight coefficient of the kth branch can be expressed as a k =γ k / N k , where γ k represents the envelope of the kth branch, N k represents the noise power of the kth branch, so the signal envelope γ output under maximum ratio combining can be obtained R for:

[0032]

[0033] If the signal received by each branch is expressed as: Then the weighting coefficient can also be expressed as: Among them, A k represents the amplitude of the received signal, represents the phase of the received signal, e is the base of the natural logarithm, and j is the imaginary unit. m Represents the sum of the signal-to-noise ratios of each branch:

[0034]

[0035] In the Rayleigh distribution, the square of the envelope is subject to the chi-squared distribution with 2 degrees of freedom. 2 distribution, from which we can conclude that γ m The probability distribution function of is:

[0036]

[0037] Apply this formula to γ m Taking the derivative, we can get the probability density function as:

[0038]

[0039] The average signal-to-noise ratio of the sum of the signal-to-noise ratios of each branch after merging is:

[0040]

[0041] In the maximum ratio combining mode, the average signal-to-noise ratio is proportional to the number of diversity branches M. Therefore, it can be concluded that the diversity gain under maximum ratio combining is:

[0042]

[0043] It can be seen that maximum ratio combining can achieve the optimal gain.

[0044] Optionally, it is ensured that the signal does not change during the merging period.

[0045] Optionally, in step S6, two results satisfying the time difference ≤ Ta are merged, and the result with the larger correlation peak is retained.

[0046] Optionally, in step S1, 128 antenna arrays are used to synchronously collect signal data.

[0047] Optionally, the aperture of the antenna array is greater than 1 km.

[0048] It can be seen from the above scheme that the embodiment of the present invention provides a shortwave weak signal detection method based on array distributed acquisition, which has the following beneficial effects:

[0049] The present invention adopts multi-antenna spatial separation diversity reception to address the different fading characteristics of shortwave multipath fading signals in space; according to the signal protocol characteristics, two offset sliding detectors with a duration of 2 times or more of the signal synchronization sequence are set, and multi-channel signals are merged according to the maximum ratio principle; the two synthetic signals are respectively subjected to correlation detection and result synthesis to obtain the detection result. This method can effectively deal with the multipath fading phenomenon caused by the time-varying ionospheric channel, significantly improve the weak signal detection capability, and has both accuracy and timeliness, and can be used in array distributed acquisition shortwave systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 A schematic diagram of a shortwave weak signal detection method based on array distributed acquisition provided according to an embodiment

[0051] Figure 2 A schematic diagram of the principle of a shortwave weak signal detection method based on array distributed acquisition provided according to an embodiment;

[0052] Figure 3 A schematic diagram of the M110A signal frame structure in a shortwave weak signal detection method based on array distributed acquisition provided according to an embodiment;

[0053] Figure 4 A schematic diagram of a sliding detector in a shortwave weak signal detection method based on array distributed acquisition provided according to an embodiment;

[0054] Figure 5 A schematic diagram of the implementation principle of maximum ratio combining in a shortwave weak signal detection method based on array distributed acquisition provided according to an embodiment;

[0055] Figure 6(a)-Figure 6(c) This is a diagram showing the effect of M110A signal detection of a shortwave weak signal detection method based on array distributed acquisition provided according to an embodiment. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] like Figure 2The figure shows a design principle diagram of a shortwave weak signal detection method based on array distributed acquisition of the present invention. The main application scenario of the method of the present invention is shortwave communication signal reconnaissance. After completing the multi-channel synchronous acquisition of the signal, firstly, two time-staggered sliding detectors are constructed according to the signal specific protocol. After data segmentation, maximum ratio merging, and signal detection, the results of the two sliding detectors are integrated and the signal detection result is output.

[0058] like Figure 1 As shown, the present application provides a shortwave weak signal detection method based on array distributed acquisition, comprising:

[0059] Step S1: using M antennas spaced apart by a preset distance in space to receive shortwave signals, and obtaining M channels of synchronous parallel signal data, where M≥2;

[0060] Preferably, the M antennas are consistent, and using the M antennas to receive shortwave specific protocol signals meets the requirement of synchronous acquisition;

[0061] Wherein, the preset spacing is greater than 3 times of the signal wavelength.

[0062] M110A is a representative signal in shortwave digital communication. It uses 8PSK modulation, a symbol rate of 2400, and a data rate that can be selected between 75 and 2400 bps according to transmission needs. The synchronization preamble of M110A consists of multiple synchronization sequences of 200ms in length, which are repeated 3 times and 24 times in the case of short interleaving and long interleaving, respectively. Each synchronization sequence contains 480 symbols, of which the first 288 symbols are fixed, and the following symbols contain the waveform parameter information of the signal. The part after the synchronization preamble is the data segment, and the duration of each data segment is the same as the synchronization preamble. Figure 3 This is a schematic diagram of the M110A signal frame structure.

[0063] Step S2: Set up two time-shifted sliding detectors, a first sliding detector D1 and a second sliding detector D2. The durations of the first sliding detector D1 and the second sliding detector are both T, and their starting times are shifted by T / 2. The duration T is greater than or equal to 2 times the duration of the synchronization sequence of the signal.

[0064] Step S3: Use the sliding detector D1 to segment the M channels of synchronous parallel data, and merge each segment of the signal according to the maximum signal-to-noise ratio principle to obtain a synthesized first signal S1;

[0065] Step S4: using the sliding detector D2, segmenting the M channels of synchronous parallel data, and merging each segment of the signal according to the maximum signal-to-noise ratio principle to obtain a synthesized second signal S2;

[0066] Step S5: Perform signal synchronization sequence correlation detection on the first signal S1 and the second signal S2 respectively, and record the time when the correlation peak value is greater than the threshold value th as the first peak value T d1 and the second peak T d2 ;

[0067] Step S6: Detection results T of the two signals d1 、T d2 Perform synthesis, where the two results that satisfy the time difference ≤ Ta are merged, retain the result with the largest correlation peak, and output T d The final test result.

[0068] The synchronous sequence detection method is used for detection. After the signal synchronization sequence is modulated, the reference sequence Q can be obtained, as follows:

[0069] Q=[aq1,q2,…,q n ];

[0070] q n Take the value of the nth signal sample.

[0071] Use the reference sequence Q to perform point-by-point sliding window detection on the M-channel synchronous parallel signal data. The signal sequence is:

[0072] S(k)=[s k ,s k+p ,s k+2p ,…,s k+(n-1)p ]

[0073] Where k is the sliding starting point, and p is the oversampling rate;

[0074] Calculate the Pearson correlation coefficient between Q and S(k) point by point, and we can get:

[0075]

[0076] Set the threshold th, when the correlation coefficient r xy When the maximum value V is greater than th, it is considered that the signal is detected; the larger V is, the better the detection effect is;

[0077] Pearson correlation coefficient, also known as Pearson correlation coefficient, is a statistical indicator that measures the degree of linear correlation between two variables;

[0078] Use multiple antenna array elements distributed in space to receive signals. The M branch signals are r1(t), r2(t), …, r M (t), the combined signal is:

[0079]

[0080] Among them, a k is the weighted coefficient of the kth branch signal, which needs to be normalized, that is,

[0081] The instantaneous signal-to-noise ratio of each branch signal of M is γ i And the average signal-to-noise ratio Γ:

[0082]

[0083] Among them, E s is the unit signal energy; α i is the signal amplitude of the i-th channel; N0 is the average noise power; E() means finding the expected value.

[0084] The maximum ratio combining method is used to combine the signals so that the signal-to-noise ratio of the output signal is maximized. The branch weighting coefficient a k It is proportional to the envelope and inversely proportional to the noise power. Maximum ratio combining is the optimal combining method. The weighting coefficient of this method is adjusted according to certain rules to maximize the signal-to-noise ratio of the output signal. The branch weighting coefficient is proportional to the envelope and inversely proportional to the noise power. The basic principle is as follows: Figure 5 shown.

[0085] Among them, the weight coefficient of the kth branch can be expressed as a k =γ k / N k , where γ k represents the envelope of the kth branch, N k represents the noise power of the kth branch, so the signal envelope γ output under maximum ratio combining can be obtained R for:

[0086]

[0087] If the signal received by each branch is expressed as: Then the weighting coefficient can also be expressed as: Among them, A k represents the amplitude of the received signal, represents the phase of the received signal, e is the base of the natural logarithm, and j is the imaginary unit. m Represents the sum of the signal-to-noise ratios of each branch:

[0088]

[0089] In the Rayleigh distribution, the square of the envelope is subject to the chi-squared distribution with 2 degrees of freedom. 2 distribution, from which we can conclude that γ m The probability distribution function of is:

[0090]

[0091] Apply this formula to γ m Taking the derivative, we can get the probability density function as:

[0092]

[0093] The average signal-to-noise ratio of the sum of the signal-to-noise ratios of each branch after merging is:

[0094]

[0095] In the maximum ratio combining mode, the average signal-to-noise ratio is proportional to the number M of diversity branches.

[0096] Therefore, the diversity gain under maximum ratio combining can be obtained as:

[0097]

[0098] It can be seen that maximum ratio combining can achieve optimal gain, but this combining method has high requirements on signal stability and needs to ensure that the signal does not change during the combining period. However, the actual shortwave communication channel is easily affected by the time-varying effect of the ionosphere, resulting in severe attenuation and fluctuation of the received signal, and does not have a fixed signal-to-noise ratio. If you want to improve the combining effect, you must reduce the combining time. However, reducing the time may cause adjacent combined sections to be discontinuous and the related detection peak to decrease.

[0099] The present invention fully considers the time-varying characteristics of the ionospheric channel, shortens the merging time as much as possible, and adopts two time-staggered sliding detectors for parallel detection in order to avoid signal discontinuity. Figure 4 This is a schematic diagram of the sliding detector in an embodiment of the present invention. The time length of the two detectors is T, and the two are offset by T / 2. The time length of T can be set to twice the time length of the signal synchronization sequence. Such sliding detection can ensure that the synchronization sequence of the signal appears completely in at least one detector window, thereby realizing short-time maximum ratio combining and correlation detection and obtaining the optimal detection effect.

[0100] In addition, in some specific embodiments, the processing effect of the above method on the actual M110A detection is shown in Figure 6. In the test sample, 128 antennas are used for synchronous acquisition, the antenna array aperture is greater than 1km, and the antenna system includes cages, dipoles, etc. Figure 6 (a) shows the peak values ​​after 128 single-channel correlation detection. Due to the different reception conditions of long-distance skywave signals at various points in the airspace, the detected correlation peaks are different, most of which are distributed between 0.2 and 0.4, and the largest correlation peak is 0.57. Using the above method for detection, Figure 6 (b) is the correlation detection result of the sliding detector D1, with the maximum correlation peak of 0.79; Figure 6 (c) is the correlation detection result of the sliding detector D2, with the maximum correlation peak of 0.83. Both are significantly better than the highest single-channel detection correlation peak, proving that the signal detection capability is greatly improved after being processed by the sliding detector of the present invention.

[0101] The method proposed in the present invention is also effective for other shortwave specific protocol signals, such as M110B, 3G-ALE, etc. In the description of this specification, specific features or characteristics may be combined in any one or more embodiments or examples in a suitable manner.

[0102] In summary, the present invention adopts multi-antenna spatial separation diversity reception to address the different fading characteristics of shortwave multipath fading signals in space; according to the signal protocol characteristics, two offset sliding detectors with a duration of 2 times or more of the signal synchronization sequence are set, and multi-channel signals are merged according to the maximum ratio principle; the two synthetic signals are respectively subjected to correlation detection and result synthesis to obtain the detection result. This method can effectively deal with the multipath fading phenomenon caused by the time-varying ionospheric channel, significantly improve the weak signal detection capability, and has both accuracy and timeliness, and can be used in array distributed acquisition shortwave systems.

[0103] The above are preferred embodiments of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A shortwave weak signal detection method based on array distributed acquisition, characterized in that: include: Step S1: using M antennas spaced apart by a preset distance in space to receive shortwave signals, and obtaining M channels of synchronous parallel signal data, where M≥2; Step S2: setting two time-shifted sliding detectors, a first sliding detector D1 and a second sliding detector D2, wherein the durations of the first sliding detector D1 and the second sliding detector are both T, and their starting times are shifted by T / 2; Step S3: Use the sliding detector D1 to segment the M channels of synchronous parallel data, and merge each segment of the signal according to the maximum signal-to-noise ratio principle to obtain a synthesized first signal S1; Step S4: using the sliding detector D2, segmenting the M channels of synchronous parallel data, and merging each segment of the signal according to the maximum signal-to-noise ratio principle to obtain a synthesized second signal S2; Step S5: Perform signal synchronization sequence correlation detection on the first signal S1 and the second signal S2 respectively, and record the time when the correlation peak value is greater than the threshold value th as the first peak value T d1 and the second peak T d2 ; Step S6: Detection results T of the two signals d1 、T d2 Perform synthesis and output T d The final test result.

2. The shortwave weak signal detection method based on array distributed acquisition according to claim 1 is characterized in that: In step S1, the preset spacing is greater than 3 times the signal wavelength.

3. The shortwave weak signal detection method based on array distributed acquisition according to claim 2 is characterized in that: In step S2, the duration T is greater than or equal to 2 times the duration of the synchronization sequence of the signal.

4. The shortwave weak signal detection method based on array distributed acquisition according to claim 3 is characterized in that: The synchronous sequence detection method is used for detection. After the signal synchronization sequence is modulated, the reference sequence Q can be obtained, as follows: Q=[aq1,q2,…,q n ] q n Take the value of the nth signal sample.

5. The shortwave weak signal detection method based on array distributed acquisition according to claim 4 is characterized in that: Use the reference sequence Q to perform point-by-point sliding window detection on the M-channel synchronous parallel signal data. The signal sequence is: S(k)=[s k ,s k+p ,s k+2p ,…,s k+(n-1)p ] Where k is the sliding starting point, and p is the oversampling rate; Calculate the Pearson correlation coefficient between Q and S(k) point by point, and we can get: Set the threshold th, when the correlation coefficient r xy When the maximum value V is greater than th, it is considered that the signal is detected; the larger V is, the better the detection effect is; Use multiple antenna array elements distributed in space to receive signals. The M branch signals are r1(t), r2(t), …, r M (t), the combined signal is: Among them, a k is the weighted coefficient of the kth branch signal, which needs to be normalized, that is, The instantaneous signal-to-noise ratio of each branch signal of M is γ i And the average signal-to-noise ratio Γ: Among them, E s is the unit signal energy; α i is the signal amplitude of the i-th channel; N0 is the average noise power; E() means finding the expected value.

6. The shortwave weak signal detection method based on array distributed acquisition according to claim 5 is characterized in that: The maximum ratio combining method is used to combine the signals so that the signal-to-noise ratio of the output signal is maximized. The branch weighting coefficient a k It is directly proportional to the envelope and inversely proportional to the noise power; Among them, the weight coefficient of the kth branch can be expressed as a k =γ k / N k , where γ k represents the envelope of the kth branch, N k represents the noise power of the kth branch, so the signal envelope γ output under maximum ratio combining can be obtained R for: If the signal received by each branch is expressed as: Then the weighting coefficient can also be expressed as: Among them, A k represents the amplitude of the received signal, represents the phase of the received signal, e is the base of the natural logarithm, and j is the imaginary unit; In the maximum ratio combining mode, γ m Represents the sum of the signal-to-noise ratios of each branch: In the Rayleigh distribution, the square of the envelope is subject to the chi-squared distribution with 2 degrees of freedom. 2 distribution, from which we can conclude that γ m The probability distribution function of is: Apply this formula to γ m Taking the derivative, we can get the probability density function as: The average signal-to-noise ratio of the sum of the signal-to-noise ratios of each branch after merging is: In the maximum ratio combining mode, the average signal-to-noise ratio is proportional to the number of diversity branches M; Therefore, the diversity gain under maximum ratio combining can be obtained as: It can be seen that maximum ratio combining can achieve the optimal gain.

7. The shortwave weak signal detection method based on array distributed acquisition according to claim 6 is characterized in that: It is necessary to ensure that the signal does not change during the consolidation period.

8. The shortwave weak signal detection method based on array distributed acquisition according to claim 7 is characterized in that: In step S6, two results satisfying the time difference ≤ Ta are merged, and the result with the larger correlation peak is retained.

9. The shortwave weak signal detection method based on array distributed acquisition according to claim 8 is characterized in that: In step S1, 128 antenna arrays are used to synchronously collect signal data.

10. The shortwave weak signal detection method based on array distributed acquisition according to claim 9 is characterized in that: The aperture of the antenna array is greater than 1 km.

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