A Frequency Hopping Parameter Modification Protection Method Based on Cooperative Reconnaissance

Abstract

The present invention belongs to the field of frequency-hopping communication protection, and particularly relates to a frequency-hopping parameter modification protection method based on cooperative reconnaissance. The protecting party obtains the pulse duration parameter of the frequency-hopping radio of the communicating party through cooperative reconnaissance; while detecting the frequency-hopping communication signal, time synchronization and signal forwarding are carried out to ensure that a processed signal with a random length is immediately transmitted after the end of the frequency-hopping communication pulse as a protection signal, thereby destroying the single-transmitter working rule that only one hop pulse exists at the same moment in the frequency-hopping signal and the rule that the pulse duration of most frequency-hopping signals is fixed; for the reconnaissance party, within the same moment, there is an overlap in the time domain between two adjacent frequency-hopping pulses, and the pulse durations are inconsistent, so the reconnaissance system will not recognize it as a frequency-hopping signal but will recognize it as a discontinuous signal at different frequency points, destroying the signal detection link in the frequency-hopping reconnaissance process and reducing or even invalidating the reconnaissance effectiveness of the reconnaissance system for the frequency-hopping signal.

Description

Technical Field

[0001] The present invention belongs to the field of electronic countermeasures, and particularly relates to a frequency-hopping parameter modification protection method based on cooperative reconnaissance. Background Art

[0002] Frequency-hopping communication is one of the most commonly used spread-spectrum communication methods. Its working principle refers to a communication method in which the carrier frequencies of the transmitting and receiving parties' transmitted signals change discretely according to a predetermined rule, that is, the carrier frequencies used in communication are randomly hopped under the control of a pseudo-random change code. In terms of the implementation method of communication technology, frequency-hopping communication is a communication method using a code sequence for multi-frequency frequency shift keying, and is also a communication system with code-controlled carrier frequency hopping. Due to its strong anti-jamming ability, low interception probability, and good suppression effect on frequency-selective fading, frequency-hopping communication is widely used in military communications, such as short-wave and ultra-short-wave radio stations using frequency-hopping technology, and at the same time it has rapidly penetrated into civilian communications, such as mobile communications, data transmission, computer wireless data transmission, wireless local area networks, etc.

[0003] Radio reconnaissance is an important application field of radio and electronic science and technology. Its basic tasks are to search, intercept, parameter estimate, locate, analyze and identify radio signals with radio electronic equipment. In the field of military communication countermeasures, radio reconnaissance occupies a very important position, mainly used for electronic support measures and intelligence reconnaissance in electronic warfare, while frequency-hopping communication reconnaissance is specifically used for the reconnaissance of frequency-hopping communication, usually including three major tasks: detection of frequency-hopping signals, parameter estimation, and signal sorting.

[0004] Electronic jamming refers to the radio wave disturbance measures taken to make the enemy's electronic equipment and systems lose or reduce their effectiveness. It is an integral part of electronic countermeasures. The purpose is to weaken or destroy the enemy's ability to use various electronic equipment and systems to perform battlefield reconnaissance, combat command, communication liaison, and weapon control and guidance, and create favorable conditions for concealing one's own intentions and improving the survival ability of one's own aircraft and ships. Due to the wide use of frequency-hopping communication in military communications, frequency-hopping communication jamming has also become an important part of electronic jamming. Frequency-hopping communication jamming mainly uses the information such as the signal parameters, positions, and threat levels of frequency-hopping radio stations obtained by frequency-hopping reconnaissance to actively emit various interference signals to weaken or destroy the normal communication of the enemy's frequency-hopping radio stations.

[0005] Electronic protection refers to the measures and actions taken to prevent the enemy from intercepting and using the electromagnetic signals emitted by one's own electronic information equipment. Electronic protection can make it difficult for the enemy's reconnaissance system to obtain valuable information and make it difficult for the interference system to obtain the reconnaissance information required for effective interference and destruction. The current protection technologies can be divided into the following four methods:

[0006] 1) Spread spectrum communication technologies that broaden the frequency domain of effective information to obtain frequency domain protection performance. Currently, the spread spectrum communication technologies adopted include direct sequence spread spectrum (DSSS) technology, frequency hopping communication technology; and mixed frequency spread spectrum technology that combines direct sequence spread spectrum and frequency hopping technology;

[0007] 2) Time domain protection technologies such as time hopping communication technology that changes the dwell time of the signal at the transmitting frequency point, and adaptive power adjustment technology that adaptively adjusts the transmitting power according to the electromagnetic environment;

[0008] 3) Smart antenna technology (space domain protection technology) that adaptively adjusts the antenna pattern, has high gain in the signal direction, and has notch characteristics in the interference direction;

[0009] 4) Error correction coding technology that changes the encoding and decoding algorithms in real time by learning the characteristics of the channel.

[0010] The communication protection technologies listed above mainly focus on changing the communication system, and anti-interference and anti-interception technologies are adopted when designing the communication system. It is difficult to directly transform the already maturely used communication system. Summary of the Invention

[0011] Aiming at the problem of frequency hopping communication protection, the present invention proposes a frequency hopping parameter modification protection method based on cooperative reconnaissance. The protection means adopted by the present invention is to use an independent communication protection device to actively protect the frequency hopping communication system to reduce the probability of the communication system being intercepted and the risk of being detected. At present, there is no foreign report on this aspect of research, and domestic research has just started.

[0012] The technical solution adopted by the present invention is as follows:

[0013] Most frequency hopping communication radios adopt a fixed hopping speed and a fixed pulse duration during transmission. The protection party obtains the pulse duration parameter of the communication party's frequency hopping radio through cooperative reconnaissance; while receiving the frequency hopping communication signal, time synchronization and signal forwarding are carried out to ensure that a processed signal with a random length is immediately transmitted after the end of the frequency hopping communication pulse as a protection signal, destroying the single transmitter working rule that only one hop pulse exists at the same moment in the frequency hopping signal, and the rule that the pulse duration of most frequency hopping signals is fixed; the frequency hopping communication signal and the protection signal enter the reconnaissance party's receiver at the same time. For the reconnaissance party, within the same moment, there is an overlap in the time domain between two adjacent frequency hopping pulses, and the pulse durations are inconsistent. Therefore, the reconnaissance system will not recognize it as a frequency hopping signal, but will recognize it as a discontinuous signal at different frequency points, destroying the signal detection link in the frequency hopping reconnaissance process, and reducing the reconnaissance efficiency of the reconnaissance system for the frequency hopping signal or even making it ineffective. Specifically, it includes:

[0014] The frequency hopping protection equipment is placed near the frequency hopping radio station so that the azimuth difference between the two in the reconnaissance system is smaller than the spatial resolution, that is, the frequency hopping signal and the frequency hopping protection signal cannot be directly separated from the spatial domain;

[0015] The frequency hopping protection party obtains the pulse duration of the protected frequency hopping radio station through cooperative reconnaissance and synchronize time with the protected equipment;

[0016] Calculate the time parameters required for protection, including: Frequency hopping protection parties cooperate to obtain frequency hopping radio stations To protective equipment distance, calculate the signal transmission time from the frequency hopping radio to the protection device , obtain enemy reconnaissance equipment Or the direction and distance of the key protection area, and calculate the signal transmission time from the frequency hopping radio to the reconnaissance equipment and the signal transmission time from the protection equipment to the reconnaissance equipment , get the total time of signal processing and transmission for:

[0017]

[0018] Total signal processing and transmission time Contains the protection equipment frequency hopping pulse storage time , the processing time required for the protective equipment to be stored and launched In order to protect each frequency hopping pulse, the total time of signal processing and transmission cannot be greater than the duration of a pulse, that is:

[0019]

[0020] Thus we get for:

[0021]

[0022] Random emission time Intercept the frequency hopping pulse after storage processing;

[0023] Receive frequency hopping pulse signal, according to the calculated maximum storage time of frequency hopping pulse Store frequency hopping pulses, randomly intercept part of the length of the stored frequency hopping pulses as protection signals for transmission, and randomly transmit within a certain time range , the transmission power of the protection signal is consistent with the transmission power of the frequency hopping communication station.

[0024] Furthermore, when the distance between the frequency hopping radio station A and the protection device C is much smaller than the distance between the frequency hopping radio station A and the reconnaissance device B, , Simplified to:

[0025]

[0026] Random emission time Intercepted from the stored and processed frequency-hopping pulse, the maximum emission time is:

[0027]

[0028] Then Simplified to:

[0029]

[0030] Obtain the position of the storage start time in the duration of a received frequency-hopping pulse as: , and the position of the storage end time in the duration of a received frequency-hopping pulse as: .

[0031] The present invention has the following beneficial effects:

[0032] The protection signal in the present invention is the retransmission signal of the frequency-hopping signal, which is consistent with the frequency-hopping signal parameters and is difficult to distinguish by the reconnaissance party.

[0033] The present invention acts on the signal detection stage in frequency-hopping reconnaissance and can effectively reduce or even prevent the reconnaissance equipment from reconnaissance of its own frequency-hopping communication;

[0034] The protection signal in the present invention does not intersect with the frequency-hopping communication signal in the time-frequency domain and has little influence on its own communication;

[0035] In the present invention, there is no need to redesign the signal, and only the frequency-hopping signal needs to be received, stored, processed and retransmitted. The method is simple and the effect is good;

[0036] The transmission power required for the protection signal in the present invention is of the same order of magnitude as that of the frequency-hopping radio station and is easily achieved in actual equipment. Description of the drawings

[0037] Figure 1 is the flowchart of frequency-hopping parameter modification protection based on cooperative reconnaissance;

[0038] Figure 2 is the schematic diagram of frequency-hopping parameter modification protection based on cooperative reconnaissance;

[0039] Figure 3 is the schematic diagram of the protection signal retransmission process of frequency-hopping parameter modification based on cooperative reconnaissance;

[0040] Figure 4 is the time-frequency diagram of signal interception of 1 frequency-hopping radio station;

[0041] Figure 5 Time-frequency diagram of FH radio signal detection after adding protection signal Specific implementation mode

[0042] Refer to Figure 1 . The present invention specifically includes the following steps:

[0043] (1) Arrange the FH protection device near the FH radio so that the azimuth difference between the two in the reconnaissance system is less than the spatial resolution, that is, the FH signal and the FH protection signal cannot be directly separated from the airspace.

[0044] (2) The FH protection party obtains the pulse duration of the protected FH radio through cooperative reconnaissance , and synchronizes the time with the protected device.

[0045] (3) Calculate the time of each protection process.

[0046] For a single-antenna protection device, the protection device not only needs to transmit the protection signal, but also needs to receive and store the FH radio signal. Therefore, in order to perform protection processing on each FH pulse, the reception, storage, and processing of the FH pulse should be carried out sequentially, and the processed FH pulse should be intercepted as the protection signal for transmission.

[0047] Refer to Figure 3 . The FH protection party cooperates to obtain the distance from the FH radio to the protection device , calculate the signal transmission time from the FH radio to the protection device , obtain the approximate azimuth and distance of the enemy reconnaissance device or the key protection area through other channels, and calculate the signal transmission time from the FH radio to the reconnaissance device and the signal transmission time from the protection device to the reconnaissance device . Then the total time of signal processing and transmission is:

[0048] (1)

[0049] When the distance between the FH radio A and the protection device C is much smaller than the distance between the FH radio A and the reconnaissance device B, , formula (1) can be simplified as:

[0050] (2)

[0051] Signal processing time Specifically includes the FH pulse storage time of the protection device , the processing time required for the protection device to store and transmit , random transmission time , in order to be able to protect each frequency-hopping pulse, the total time of one signal processing and transmission cannot be greater than one pulse duration, that is:

[0052] (3)

[0053] Substitute Equation (2) into Equation (3) to obtain:

[0054] (5)

[0055] Also, the random transmission time is intercepted from the frequency-hopping pulse after storage and processing, so the maximum transmission time that can be achieved is:

[0056] (6)

[0057] From Equations (5) and (6), we obtain:

[0058] (7)

[0059] (4) Receive the frequency-hopping pulse signal and store the frequency-hopping pulse according to the maximum storage time of the frequency-hopping pulse calculated in (3) The position of the storage start time in one receiving frequency-hopping pulse duration is: , and the position of the storage end time in one receiving frequency-hopping pulse duration is: .

[0060] (5) After simply processing the stored frequency-hopping pulse, randomly intercept a part of the length as the protection signal for transmission. The random transmission time range , and the position of the transmission start time in one receiving frequency-hopping pulse duration is: . To prevent the reconnaissance equipment from distinguishing the frequency-hopping radio signal from the protection signal in the energy domain, the transmission power of the protection signal is the same as that of the frequency-hopping communication radio.

[0061] (6) If starting from (2), not only obtain the pulse duration of the protected frequency-hopping radio , and then store one frequency-hopping pulse, then in (4), the protection device can no longer receive the frequency-hopping radio signal, and only needs to intercept and process the transmission of a random length from the stored frequency-hopping pulse as the protection signal.

[0062] In a practical simulation example: Design 1 frequency-hopping radio in the range of 12 - 16 MHz as the frequency-hopping reconnaissance target object, with a radio power of 20 w, a hopping speed of 1000 hops / s, a pulse duration of 1000 us, and 64 hopping frequency points. The distance between the frequency-hopping radio and the frequency-hopping reconnaissance equipment is 200 km. The protection device adopts a single-antenna transmission working mode, and the signal processing time 。

[0063] The working process of the present invention is as follows:

[0064] (1) Arrange the frequency hopping protection device within a 3 km area near the frequency hopping radio.

[0065] (2) The frequency hopping protection party obtains the pulse duration of the protected frequency hopping radio through cooperative reconnaissance and synchronizes the time with the protected device.

[0066] (3) Calculate the time of each protection process.

[0067] Since the distance between the frequency hopping radio A and the protection device C is much smaller than the distance between the frequency hopping radio A and the reconnaissance device B, the signal emission timing of the protection can be directly calculated using Equation (2). The frequency hopping protection party cooperatively obtains the distance from the frequency hopping radio to the protection device is 3 km, and the signal transmission time from the frequency hopping radio to the protection device is calculated , given , the signal processing time , from Equation (7), the frequency hopping pulse storage time , the maximum emission duration .

[0068] (4) Receive the frequency hopping pulse signal and store the frequency hopping pulse according to the maximum storage time of the frequency hopping pulse calculated in (3) . The position of the storage start time in a received frequency hopping pulse duration is: , and the position of the storage end time in a received frequency hopping pulse duration is: .

[0069] (5) After simply processing the stored frequency hopping pulses, randomly intercept a part of the length as the protection signal for emission. The random emission time range , and the position of the emission start time in a received frequency hopping pulse duration is: . Adjust the emission power to be the same as the communication radio power, which is 20 w.

[0070] The spectrogram of the received signal based on the short-time Fourier transform is as Figure 4 shown, from which one frequency hopping radio signal can be clearly seen. Taking this frequency hopping radio as the protected object, emit the frequency hopping parameter-modified protection signal based on cooperative reconnaissance. Its spectrogram of the received signal based on the short-time Fourier transform is as Figure 5 shown. Comparing Figure 4 with Figure 5 , it can be found that Figure 2The length of the original frequency-hopping pulse signal has changed, and all the frequency-hopping pulse lengths are different.

[0071] Protection effect:

[0072] Before the protection signal is applied, when using the reconnaissance simulation program for frequency-hopping reconnaissance, parameters such as the hopping period, hopping time, and frequency-hopping frequency points can be accurately obtained. After the protection signal is applied, when using the reconnaissance simulation program for frequency-hopping reconnaissance, under 1000 Monte Carlo simulations, the correct hopping period and hopping time cannot be obtained, and the correct rate of the hopping frequency is only 1.68%. The simulation analysis results prove that the present invention can effectively reduce the reconnaissance effect of the frequency-hopping reconnaissance equipment on the frequency-hopping communication radio station, and confirm the effectiveness of the frequency-hopping parameter modification protection method based on cooperative reconnaissance proposed by the present invention.

Claims

1. A method for protecting frequency hopping parameters by modifying based on cooperative reconnaissance, characterized in that Including: Arrange the frequency-hopping protection device near the frequency-hopping radio so that the azimuth difference between the two in the reconnaissance system is less than the spatial resolution, that is, the frequency-hopping signal and the frequency-hopping protection signal cannot be directly separated from the airspace; The frequency hopping protection party obtains the pulse duration of the protected frequency hopping radio through the means of cooperative reconnaissance , and synchronizes the time with the protected device; Calculate the time parameters required for protection, including: obtaining the frequency-hopping radio through cooperation in frequency-hopping protection to the protection device distance, calculate the signal transmission time from the frequency-hopping radio to the protection device , obtain the azimuth and distance of the enemy reconnaissance device or the key protection area, and calculate the signal transmission time from the frequency-hopping radio to the reconnaissance device and the signal transmission time from the protection device to the reconnaissance device , obtain the total time for signal processing and transmission which is: ， Total time for signal processing and transmission Including the storage time of the hopping pulse of the protection device , the processing time required for the protection device to store and transmit , in order to be able to protect each hopping pulse, the total time for one signal processing and transmission shall not be greater than one pulse duration, that is: ， Thus, it is: ， Random emission time Intercepted from the frequency-hopping pulse after storage processing; Receive a frequency-hopping pulse signal and store the frequency-hopping pulse according to the calculated maximum storage time of the frequency-hopping pulse Randomly intercept a part of the length as a protection signal for transmission according to the stored frequency-hopping pulse, and the random transmission time range , and the transmission power of the protection signal is the same as that of the frequency-hopping communication radio station.

2. A frequency hopping parameter modification protection method based on cooperative reconnaissance according to claim 1, characterized in that When the distance between the frequency-hopping radio A and the protection device C is much smaller than the distance between the frequency-hopping radio A and the reconnaissance device B, , Simplified to: ， Random emission time Intercepted from the frequency-hopping pulse after storage processing, the maximum emission time is: ， Then It is simplified to: ， The position of the stored start time in a received frequency-hopping pulse duration is: , and the position of the stored end time in a received frequency-hopping pulse duration is: .

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