Anti-detection-sorting radar pulse signal hiding method based on artificial noise

Abstract

The invention provides a novel radar pulse signal hiding method based on artificial noise, which is resistant to detection and sorting. Before a signal is transmitted, the direction characteristics of a channel are fully utilized, artificial noise designed according to the direction characteristics of the channel is ingeniously superposed on a radar pulse waveform to be transmitted, and the superposed artificial noise does not disturb the radar pulse waveform transmitted by the own side. And finally, compromise optimization of the own detection performance and the third-party pulse detection probability can be realized by controlling the power ratio of the artificial noise to the own radar pulse signal, the detection probability of a third-party receiver to the radar signal is effectively reduced, and the anti-detection performance is realized. By designing and optimizing randomly overlapped parameters of time domain artificial noise and radar signals, parameters such as PRI, pulse width, TOA and the like of the radar signals can be accurately hidden, so that a reconnaissance receiver is disturbed to form a correct pulse description word PDW, and the anti-sorting and waveform hiding capabilities of the radar pulse signals are realized at the lowest cost-effectiveness ratio.

Description

Technical Field

[0001] The present invention relates to radar signal processing technology, in particular to concealment, anti-detection and anti-sorting technology of radar pulse waveform. Background Art

[0002] The main task of electronic reconnaissance is to obtain the carrier frequency, arrival direction, pulse width, arrival time and pulse amplitude of the target radar pulse signal. It is very important to ensure the concealment of the key parameters of the radar pulse signal. At present, the existing technology mainly controls the energy and other parameters of the transmitted pulse waveform to achieve anti-interception and concealment of the radar pulse signal, which will lead to a decrease in the detection performance of the party. Artificial noise is a secure transmission method used in the field of wireless communications. It mixes pre-coded noise signals that are orthogonal to the receiving channel into the transmitted signal, while ensuring that it does not affect the receiving performance of the receiver in the target direction, while interfering with eavesdropping users in the non-target direction. In electronic reconnaissance and counter-reconnaissance, the radar pulse waveform also needs to be concealed and counter-reconnaissance. However, there is currently no technology that fully utilizes the directional characteristics of the channel to conceal, resist detection and anti-sorting solutions for radar pulse waveforms.

[0003] At present, the research on radar signal anti-interception technology is mainly focused on modulated radar signal, and the carrier frequency energy is studied to achieve this performance. The anti-detection technology at the baseband end is still in a blank stage. For radar signal anti-sorting technology, the current research is to add an interference pulse to the radar pulse signal for simple splicing. This does not conceal the TOA and PRI parameters of the radar pulse signal, but only conceals the PW parameter of the radar signal. Summary of the invention

[0004] The technical problem to be solved by the present invention is to propose a radar pulse signal anti-detection sorting waveform concealment scheme which utilizes the directional characteristics of a channel to reduce the detection probability of a third-party receiver for the radar pulse signal.

[0005] The technical solution adopted by the present invention to solve the above technical problems is a method for transmitting radar pulse signals based on artificial noise and resistant to detection and sorting, comprising the steps of:

[0006] The radar pulse signal transmitter determines that the power proportion of the signal is α1 and the power proportion of the artificial noise is α2;

[0007] The radar pulse signal transmitter generates a first noise n which is sent synchronously with the radar pulse signal. AN1 (t), the second noise n is generated by pseudo-random code control AN2 (t) and the third noise n AN3 (t); the second noise n AN2 (t) is used to randomly mask the leading edge of the radar pulse waveform, the third noise n AN3(t) is used to randomly cover the trailing edge of the radar pulse waveform; the first noise n AN1 (t), the second noise n AN2 (t) and the third noise n AN3 (t) obeys Gaussian distribution, and the second noise n AN2 (t) and the third noise n AN3 (t) is equal to the power of the first noise n AN1 The power of (t) is less than the second noise n AN2 (t) and the third noise n AN3 (t) power;

[0008] The radar pulse signal transmitter is based on the first noise n AN1 (t), the second noise n AN2 (t) and the third noise n AN3 (t) Complete artificial noise n AN Generation of (t): n AN (t) = b r [n AN1 (t)+n AN2 (t)+n AN3 (t)]; where t is the time variable, b r is the AN precoding matrix, and the legal channel H between the radar pulse signal transmitter and the radar pulse signal receiver B Orthogonal, satisfying H B b r =0;

[0009] The radar pulse signal transmitter adds artificial noise n to the radar pulse signal to be sent according to the power ratio α1 and α2 of the signal and the artificial noise. AN (t) and then sent to the radar pulse signal receiver.

[0010] The present invention makes full use of the directional characteristics of the channel, and while transmitting the radar pulse waveform, cleverly superimposes artificial noise designed based on the directional characteristics of the channel on the third-party radar pulse signal, and the superimposed artificial noise does not cause any disturbance to the radar pulse waveform transmitted by the own party. By controlling the power ratio of the artificial noise and the own radar pulse signal, the detection probability of the radar pulse signal by the third-party receiver is controlled to achieve anti-detection performance. By randomly overlapping the artificial noise with the radar pulse, the present invention can conceal the arrival time TOA, pulse repetition period PRI and pulse width PW of the radar pulse signal, thereby disrupting the reconnaissance receiver to form the correct pulse description word PDW. By adjusting the power ratio of the artificial noise and the radar signal, the radar signal anti-detection technology at the baseband end can be realized.

[0011] The beneficial effect of the present invention is that the artificial noise superimposed while transmitting the radar pulse waveform does not disturb the radar pulse waveform transmitted by the party, but causes the third-party receiver to form an erroneous pulse description word PDW, thereby realizing the anti-sorting capability of the radar pulse signal with the lowest cost-effectiveness. By controlling the power ratio α2 / α1 of the artificial noise and the radar pulse signal of the party, the compromise optimization of the detection performance of the party and the detection probability of the third party can be realized, thereby realizing the anti-detection performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 System model: The third party Eve detects and sorts radar pulse signals;

[0013] Figure 2 Receive waveform for Eve: anti-sorting type based on artificial noise;

[0014] Figure 3 The waveform received by Bob: not affected;

[0015] Figure 4 Schematic diagram of the effect of the power ratio of artificial noise and radar signal on the detection probability;

[0016] Figure 5 This is the result diagram of 1-4 order CDIF radar sorting;

[0017] Figure 6 This is a schematic diagram of the pulse width error rate at the Eve end. DETAILED DESCRIPTION

[0018] System model such as Figure 1 As shown in the figure, Alice is the radar pulse signal transmitter, Bob is the legal radar receiver, Alice and Bob are sending and receiving radar pulses, Bob receives and extracts the pulse signal transmitted by Alice, performs parameter estimation and detection, and can further extract the internal information of the pulse in some scenarios, such as the interrogation / response signal of the secondary radar. At this time, a third party Eve is eavesdropping on the radar pulse process in the non-target direction. Eve will intercept the radar pulse signal, and then detect and sort it. Assume that the legal channel between Alice and Bob is H B , the reconnaissance channel between Alice and Eve is H E In order to achieve anti-detection and anti-sorting of radar pulse signals, Alice adds artificial noise AN in the form of precoding designed by the present invention to the radar pulse signal and ensures that Bob is not interfered by the artificial noise AN. B With the eavesdropping channel H ETo ensure that it does not affect Bob and interfere with the detection and sorting of radar pulse signals by third parties, the precoding of artificial noise is designed to be orthogonal to Bob’s channel.

[0019] The radar waveform x(t) sent by Alice is expressed as:

[0020]

[0021] Among them, P t is the total transmission power, α1, α2 are the power ratios of the signal and artificial noise, defined as the ratio of the total transmission power, α1+α2=1. s(t) is the radar pulse signal, n AN (t) is the artificial noise designed by the present invention and obeys Gaussian distribution, b t is the beamforming matrix of the radar transmitter and t is the time variable.

[0022] Bob channel matrix H B and Eve channel matrix H E The expression is:

[0023]

[0024] in, T is the transpose of the matrix, h bt is θ bt Directional channel vector in far-field space; h br is θ br Directional channel vector in far-field space; h et is θ et Directional channel vector in far-field space; h er is θ er Channel vector in directional far-field space;

[0025] N A ,N B ,N E The total number of array elements of Alice, Bob, and Eve, n A ,n B ,n E They are the array element number variables of Alice, Bob, and Eve, and their value ranges are 1 to N. A ,1~N B ,1~N E ;

[0026] θ bt is the outgoing signal beam angle from the transmitter Alice to the receiver Bob, θ br is the incident signal beam angle from the transmitter Alice to the receiver Bob, θ etThe outgoing signal beam angle from the transmitter Alice to the third party Eve, θ er The beam angle of the incident signal from the transmitter Alice to the third party Eve;

[0027] Δφ bt is the position of each element of Alice phased array antenna at θ bt Phase difference in direction, Δφ br is the position of each element of Bob phased array antenna at θ bt Phase difference in direction, Δφ et is the position of each element of Alice phased array antenna at θ et Phase difference in direction, Δφ er is the position of each element of Bob phased array antenna at θ er Phase difference in direction. Δφ bt The expression is:

[0028]

[0029] Where d is the phased array element spacing, λ is the RF signal wavelength, Δφ br ,Δφ et ,Δφ er Similarly, the expression of the artificial noise to be added is:

[0030] n AN (t) = b r [n AN1 (t)+n AN2 (t)+n AN3 (t)];

[0031] Among them, b r is the AN precoding matrix, and the target channel H B Orthogonal, satisfying H B b r = 0. AN1 (t) is artificial noise 1, which is sent synchronously with the radar pulse signal, n AN2 (t),n AN3 (t) is artificial noise 2 and artificial noise 3, which are controlled by pseudo-random code; n AN2 (t) is used to randomly mask the leading edge of the radar pulse waveform, n AN3 (t) is used to randomly mask the trailing edge of the radar pulse waveform, n AN1 (t), n AN2 (t), n AN3 (t) all obey Gaussian distribution, and the power relationship of the three parts of noise is P AN2 =P AN3 >P AN1 , and P AN2 +P AN3 +PAN1 =P AN .

[0032] After transmission through the channel, the target receiver Bob receives the signal r b (t) is:

[0033]

[0034] Among them, b br is the array steering vector at Bob’s receiver, and n(t) is the additive white Gaussian noise AWGN in the channel.

[0035] Due to H B b r =0, therefore, And b t is the radar transmitter beamforming matrix that can be combined with the channel vector h et Offset, that is The Bob signal is not disturbed by injected artificial noise.

[0036] The signal Eve receives is:

[0037]

[0038] Among them, b er is the array guide vector of the third-party Eve, h et b r ≠0, the third party cannot eliminate the influence of artificial noise AN, and the radar pulse signal received by Eve is seriously interfered by artificial noise, which will interfere with the detection and sorting of radar pulse signals by the third party Eve, thereby realizing the signal waveform concealment and anti-detection sorting of radar pulse signals.

[0039] The detection method for radar signals is mainly based on a binary detection model, which is as follows:

[0040]

[0041] Where 0≤t≤T, T is the detection time length, s(t) is the radar signal, n(t) is the artificial noise, and n(t)~N(0,σ 2 ), N(0,σ 2 ) means the mean is 0 and the variance is σ 2 Gaussian distribution. Eve samples x(t) in time T and can obtain N observations x1(t), x2(t), ..., x N (t), when Eve receiver receives the signal, according to the Neyman-Pearson criterion, that is, maintaining the false alarm probability P FThe optimal detection threshold V is obtained by the following integration method when the noise power is known. T , greater than the detection threshold V T is recognized as a valid signal, which is less than the detection threshold V T Identification of as noise:

[0042]

[0043] V T For the decision mechanism in the radar system according to P F The best decision threshold is obtained, p(G|H0) is the probability density function of the statistic G under the original hypothesis of noise-free condition H0, N0 is the noise power spectrum density, E S is the signal energy, and Φ is the complementary cumulative distribution function of the standard normal distribution.

[0044] By adjusting the power ratio of artificial noise and radar signal α2 / α1, E is affected by α2 / α1. S The ratio of N0 to N0 can accurately control the detection probability P of the radar signal after it is intercepted by a third-party receiver. D . The relationship is as follows:

[0045]

[0046] Eve's radar sorting is mainly achieved by separating the overlapping signals of multiple radar radiation sources, and further obtaining parameters such as pulse repetition period PRI and pulse width PW through the identified arrival time TOA. It is necessary to adopt sorting algorithms such as cumulative difference histogram CDIF and sequence difference histogram SDIF.

[0047] Without using this method, the TOA of the radar pulse signal sorted by Eve is periodic, and it is easier to obtain TOA, so the radar sorting success rate is higher. This patent conceals and randomizes the parameters of the radar signal such as TOA and PW by randomly overlapping artificial noise and radar signals in the time domain. In this way, it is difficult for traditional radar sorting algorithms to obtain the parameters of the radar signal because the parameters of the radar signal after random aliasing in the time domain have been randomized, such as Figure 2 shown.

[0048] The artificial noise of the present invention can have the above two designs. Among them, for Eve, artificial noise 1 and radar pulse signal are sent synchronously. Artificial noise 2 and artificial noise 3 are randomly overlapped with the radar pulse signal to cover up the parameters such as TOA, PW and PRI of the radar pulse signal. The degree of random overlap is controlled by the pseudo-random code PN. The power P of artificial noise 2 AN2 and the power P of the artificial noise 3 AN3 equal, artificial noise 1 is used to cover the radar pulse waveform, and the power of artificial noise 1 PAN1 The power of artificial noise 2 and artificial noise 3 should be greater than the power of the radar pulse signal. At the same time, the peak power of artificial noise 2 and artificial noise 3 should be equal to the peak power of artificial noise 1 superimposed with the radar pulse waveform, so that the PRI and PW information can be concealed. For Bob, since the artificial noise is orthogonal to Bob's channel, Bob is not affected by the artificial noise, so Bob can receive the radar pulse signal completely. Figure 3 shown.

[0049] Example

[0050] S1: The radar pulse signal is superimposed with a synchronous artificial noise 1 sent at the same time, and then a pseudo-random code PN is generated to control the overlap degree δ1, δ2 of artificial noise 2 and artificial noise 3 with the radar pulse signal. Then artificial noise 2 and artificial noise 3 are superimposed on the radar pulse signal. At this time, each radar pulse is randomly overlapped with artificial noise 2 and artificial noise 3, and the peak power of artificial noise 2 is consistent with that of artificial noise 3, both of which are greater than the power of the radar pulse signal. Then the artificial noise AN is multiplied by the precoding matrix b that is orthogonal to the target channel. r , which is used to interfere with the third party Eve while leaving the legitimate end Bob unaffected. Finally, the radar pulse signal with artificial noise superimposed on the baseband end is sent out. The specific relationship is shown below.

[0051]

[0052] Among them, δ1 and δ2 are the frontier masking noise n AN2 (t) and the trailing edge masking noise n AN3 (t) The degree of overlap with the radar pulse signal, and δ1,δ2∈(0,N], N is the length of the radar pulse waveform, and δ1 and δ2 are independent of each other.

[0053] S2: Eve performs matched filtering on the received radar signal, and then uses the Neyman-Pearson criterion to calculate the false alarm probability P according to the preset false alarm probability P. F Determine the detection threshold V T , through V T Radar signal detection decision. Assuming that Eve receiver knows the power of artificial noise, the optimal detection threshold V is obtained in the worst case. T :

[0054]

[0055] At this time, the Eve receiver has a certain probability of detecting the radar pulse signal, and then by controlling the power ratio α2 / α1 when the artificial noise and radar signal are sent, the detection probability P of the third-party receiver for the intercepted radar pulse signal can be accurately controlled. DDown to the set safety limit:

[0056]

[0057] S3: Eve radar receiver uses CDIF sorting algorithm to sort the received signal, obtains the arrival time TOA of the received signal by detecting the rising edge, and further calculates the TOA difference of each level:

[0058] TOA'=TOA k+c -TOA k ,k=1,2,...,n;

[0059] Among them, TOA' is the difference of TOA at each level, TOA k is the kth TOA value, c is the level, and n is the total number of TOAs.

[0060] By comparing the TOA difference frequency of each order with the threshold, T threshold , taking the value exceeding the threshold as PRI, thus obtaining the PRI parameter of the radar signal, and then further obtaining the pulse width PW by detecting the rising edge and falling edge. threshold Settings:

[0061] T threshold =α×T / τ;

[0062] Where α is a constant related to the pulse loss rate, and its value range is (0,1]. T represents the observation time, and τ represents the arrival time difference of the pulse, which is the horizontal axis variable of the cumulative difference histogram.

[0063] By injecting random overlap of artificial noise and radar pulse signal in the time domain, since the artificial noise randomly overlaps with each radar pulse, the degree of overlap is expressed as δ, δ k is the degree of overlap at the kth TOA, and the TOA difference at each level is:

[0064] TOA'=(TOA k+c -δ k+c )-(TOA k -δ k ),k=1,2,...,n;

[0065] Therefore, it can be seen from the above formula that the injected AN can disturb the estimation of TOA by Eve sorting system, making Eve's estimation of TOA random, thus realizing the anti-sorting of radar signals, making it difficult for the sorting system to obtain the correct parameters such as PRI and PW.

[0066] like Figure 4As shown in the figure, the full-time AN ​​is to transmit the AN signal in the full time period. Except for the pulse signal transmission period, all the power of the transmitter is used to transmit the AN signal. The transmission period AN only transmits the AN signal when the radar pulse signal is transmitted, and does not transmit the AN signal in other periods. Therefore, the transmission period AN saves more power than the full-time AN. It can be seen that as the noise-to-signal power ratio increases, the detection probability of both methods gradually decreases, but because the transmission period AN saves more power, for the same power ratio, its detection probability is lower than that of the full-time AN.

[0067] like Figure 5 As shown in the figure, the yellow line is the detection threshold. The PRI of the real radar pulse signal received by Bob is 1000us, and the corresponding 1st order TOA difference to 4th order TOA difference are 1000us, 2000us, 3000us, and 1000us respectively. It can be seen that for Bob, the 1st to 4th order differences detected by the CDIF sorting system are all correct and all exceed the threshold, corresponding to the blue line in the figure, so the correct PRI can be extracted. For Eve, due to the influence of artificial noise, the TOA differences of each order received by Eve have been randomized, because each radar pulse randomly overlaps with the artificial noise, so for each order of CDIF, Eve gets multiple TOA differences, and the corresponding CDIF histograms of each order are multiple random values, corresponding to the red line, and the threshold is not exceeded after the 2nd order CDIF histogram, so the sorting system cannot get the real PRI.

[0068] from Figure 6 It can be seen that as the power ratio of random artificial noise to radar signal α2 / α1 increases, the pulse width error rate gradually increases, which interferes with the sorting system's recognition of PW parameters.

Claims

1. A radar pulse signal concealment method based on artificial noise emission and resistant to detection and sorting, characterized in that: Includes steps: The radar pulse signal transmitter determines that the power proportion of the signal is α1 and the power proportion of the artificial noise is α2; The radar pulse signal transmitter generates a first noise n which is sent synchronously with the radar pulse signal. AN1 (t), the second noise n is generated by pseudo-random code control AN2 (t) and the third noise n AN3 (t); the second noise n AN2 (t) is used to randomly mask the leading edge of the radar pulse waveform, the third noise n AN3 (t) is used to randomly cover the trailing edge of the radar pulse waveform; the first noise n AN1 (t), the second noise n AN2 (t) and the third noise n AN3 (t) obeys Gaussian distribution, and the second noise n AN2 (t) and the third noise n AN3 (t) is equal to the power of the first noise n AN1 The power of (t) is less than the second noise n AN2 (t) and the third noise n AN3 (t) power; The radar pulse signal transmitter is based on the first noise n AN1 (t), the second noise n AN2 (t) and the third noise n AN3 (t) Complete artificial noise n AN Generation of (t): n AN (t) = b r [n AN1 (t)+n AN2 (t)+n AN3 (t)]; where t is the time variable, b r is the AN precoding matrix, and the legal channel H between the radar pulse signal transmitter and the radar pulse signal receiver B Orthogonal, satisfying H B b r =0; The radar pulse signal transmitter adds artificial noise n to the radar pulse signal to be sent according to the power ratio α1 and α2 of the signal and the artificial noise. AN (t) and then the final transmission signal is obtained, and the final transmission signal is transmitted to the radar pulse signal receiver.

2. The method according to claim 1, characterized in that: The radar pulse signal transmitter adds artificial noise n to the radar pulse signal to be sent according to the power ratio α1 and α2 of the signal and the artificial noise. AN The final transmitted signal obtained after (t) is: Among them, P t is the total transmission power, α1 is the ratio of the signal to the total transmission power, α2 is the ratio of the artificial noise to the total transmission power, α1+α2=1; s(t) is the radar pulse signal to be sent, b t is the beamforming matrix of the radar transmitter.

3. The method according to claim 2, characterized in that: The radar pulse signal transmitter controls the detection probability P of the radar signal after being intercepted by a third-party receiver by adjusting the power ratio of artificial noise and radar signal α2 / α1. D .

4. The method according to claim 3, characterized in that: The detection probability P of the radar signal after being intercepted by a third-party receiver D The calculation method is: Where Φ is the complementary cumulative distribution function of the standard normal distribution, N0 is the noise power spectral density, E S is the signal energy, V T The decision threshold of the radar system; E S The ratio of N0 to N0 is controlled by α2 / α1.

5. The method according to claim 4, characterized in that: Radar system decision threshold V T According to the Neyman-Pearson criterion, when determining the false alarm probability P F After calculation, we get:

6. The method according to claim 5, characterized in that By adding artificial noise n AN (t) is randomly overlapped with the radar pulse signal to be sent in the time domain to hide the arrival time TOA, pulse repetition period PRI and pulse width PW of the radar pulse signal to be sent.

7. The method according to claim 6, characterized in that The arrival time difference TOA' of each level obtained by the third party receiving the transmitted signal is: TOA'=(TOA k+c -δ k+c )-(TOA k -δ k ),k=1,2,...,n; Among them, TOA' is the TOA difference of level c, TOA k is the kth TOA value, c is the level, n is the total number of TOAs, δ k is the degree of overlap at the kth TOA.

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