RU2520401C2 - Method of increasing stealthiness of radio-frequency radiating means in pseudorandom operational frequency readjustment radio link - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: invention relates to radio communication and particularly to methods of increasing stealthiness of radio-frequency radiating means operating with a pseudorandom operational frequency readjustment signal. The transmitting end divides an input signal into information units presented in binary form; a reflected signal arises when a signal is emitted into space at the frequency position f_j of the pseudorandom operational frequency readjustment cycle when an airborne radio reconnaissance means enters the lobe of the beam pattern of the antenna of the radio-frequency radiating means, said signal also propagating towards the antenna of the radio-frequency radiating means. After the radio-frequency radiating means emits the radio signal on said pseudorandom operational frequency readjustment cycle, the frequency of the emitted radio signal f_j changes to f_k. The frequency of the previous pseudorandom operational frequency readjustment cycle f_j for transmission is freed, while simultaneously turning on a receiver tuned to f_j, and analysing presence of a reflected signal. If a reflected signal is present, the radio-frequency radiating means turns off its transmitter for the time during which the airborne radio reconnaissance means flies through lobe of the beam pattern of the antenna.

EFFECT: higher stealthiness of radio-frequency radiating means operating with pseudorandom operational frequency readjustment signals.

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Description

FIELD OF THE INVENTION

The invention relates to radio communications, and in particular to the transmission of information by radio signals with pseudo-random tuning of the operating frequency (MFC).

The proposed method can be used in radio links with frequency hopping, especially in satellite radio links, the radio reconnaissance and information interception of which is mainly carried out from flight-lifting radio reconnaissance means, patrolling in a given area of space.

State of the art

a) Description of analogues

A known method of transmitting discrete information in a radio line with pseudo-random tuning of the operating frequency (see Gorshkov V.V., Kuksin O.V., Rubtsov S.A., Sukhov A.V. Military communication systems with pseudorandom tuning of the working frequency. Foreign electronics 3 , 1986, pp. 3-13), consisting in the fact that packets are generated from the information signal from the information signal, which modulate the sequentially emitted carrier frequencies, at the receiving end of the radio link, the radio signal is received, converted to an intermediate frequency, demodulated and transmitted to terminal equipment.

The disadvantage of this method is the low secrecy of the radio-emitting means, due to the fact that when the flight-lifting radio reconnaissance means fall into the petals of the directional diagram of the antenna of the radio-emitting means, it is possible to intercept information, direction finding and identification of the radio-emitting means.

There is also a method of transmitting discrete information in a radio line with a pseudo-random tuning of the operating frequency (see RF patent No. 2228575 class. H04B 1/713, publ. In 2004). The known method consists in the fact that at the transmitting end the input signal is divided into blocks formed in the form of binary vectors, n-bit long in accordance with the number of used frequency channels p = 2 ⁿ , the formation of two binary vectors of the pseudo-random sequence by simultaneously collecting information from different bits of the shift register, while the length of each binary vector of the pseudo-random sequence is chosen equal to the length of the binary vector of the input signal block, encoding of the binary vector and the input signal block by modulo adding its two bits with the bits of the first binary vector of the pseudo-random sequence, rearranging the transmitter to frequencies in accordance with the codes that form the second binary vectors of the pseudo-random sequence, modulating the frequency of the transmitter and subsequently emitting the signal into space, receiving the signal at the receiving end of the radio link simultaneously at all frequencies, converting the signal to an intermediate frequency, amplifying, demodulating and generating a binary vector and demodulated signals, forming, similarly to the transmitting side of two binary vectors of a pseudo-random sequence, decoding a signal by modulo adding two first binary vectors of a pseudo-random sequence with bits of a binary vector of demodulated signals and supplying a signal to a terminal device, according to the invention, the transmitter frequency is modulated by an error-correcting code , and the tuning of the transmitter is carried out simultaneously at several frequencies, while the first frequency chosen for the frequency channel, the number of which corresponds to the code of the second binary vector of the pseudo-random sequence, and all other frequency channels are selected by sequential search in accordance with the value "1" in the corresponding bit of the encoded binary vector of the input signal block, and on the receiving side after demodulation of the signals in the frequency channels form a binary vector, the bits of which take the value "1" in the presence of a signal in the corresponding frequency channels, the numbers of which follow the frequency anal, which is determined by the code of the second pseudo-random sequence of binary vector. The listed set of essential features provides high noise immunity of the communication, since the transmitter emits simultaneously at different frequencies, the number of which and the difference between them can have different values at each frequency jump. Such signal generation with a pseudo-random tuning of the operating frequency and energy suppression during active intrusions makes it difficult to detect them, since the signal emitted by the transmitter is expanded by means of direct modulation of the carrier frequencies by a noise-resistant code with a large base. In this case, the energy distribution of the signal is carried out in a large frequency band, which increases the energy, structural and informational secrecy of the signals. In such conditions, the jammer is forced to either distribute the limited jamming power over the entire space of the radio signal, thereby creating a small spectral density of the jamming power, or to use all the available jamming transmitter power in a small subspace, leaving the remaining part of the radio signal space free from interference. As a result, the noise immunity of a radio communication system with pseudo-random tuning of the operating frequency under conditions of active intrusions is increased.

The disadvantage of this method is the low secrecy of the radio-emitting means, since the flight-lifting radio reconnaissance means, falling into the petals of the directional diagram of the antenna, is able to detect a signal, determine the location and type of radio-emitting means.

b) a description of the closest analogue (prototype)

The closest in technical essence to the claimed invention (prototype) is a method of transmitting discrete information in a radio line with hopping restructuring of the working part (see RF patent No. 2290758 class. H04B 7/00 publ. In 2006), which consists in the fact that for To increase noise immunity and ensure informational and structural secrecy of the transmitted message during information transfer, the binary informational sequence is converted to decimal numbers defining a pseudo-random sequence code (PSP) and the carrier frequency of the transmitter, which sequentially takes on different values. At the reception with the help of frequency filtering, the channel through which the transmission was performed is selected, the maximum value of the peak of the autocorrelation function is determined, from which the PSP code is determined, from which a decimal number is obtained by successive inverse transformations, which is converted to binary form corresponding to the transmitted information.

The disadvantage of this method is also the low secrecy of the radio-emitting means, since it does not eliminate the possibility of intercepting information, direction-finding and identification of the radio-emitting means.

Disclosure of the invention (its essence)

a) technical result, the achievement of which the invention is directed

The aim of the present invention is to develop a method for increasing the secrecy of a radio-emitting means in a radio line with pseudo-random tuning of the operating frequency by turning off the transmitter of the radio-emitting means while the flight-lifting radio reconnaissance means are in the lobes of the directional diagram of the antenna of the radio-emitting means.

b) a set of essential features

This goal is achieved by the fact that in the known method of transmitting and receiving discrete information in a radio line with pseudo-random tuning of the operating frequencies, which consists in the fact that to increase the noise immunity and ensure informational and structural secrecy of the transmitted message when transmitting information, the binary information sequence is converted to decimal numbers, determining the pseudo-random sequence code (PSP) and the carrier frequency of the transmitter, which sequentially receives times s values. At the reception, with the help of frequency filtering, the channel through which the transmission was performed is selected, the maximum value of the peak of the autocorrelation function is determined, by which the SRP code is determined, from which a decimal number is obtained by successive inverse transformations, which is converted into binary form corresponding to the transmitted information.

When the flight-lifting radio reconnaissance means is located in the petals of the directional diagram of the antenna of the radio-emitting means, a reflected signal appears, propagating, including, towards the antenna of the radio-emitting means. At the end of the emission of the radio signal at this frequency hopping frequency, the frequency of the emitted radio signal changes from f _j to f _k . The frequency f _{j is} freed up, which makes it possible to tune the detector of the reflected signal to the frequency f _j . When a reflected signal is detected, the radio-emitting means turns off its transmitter and stops emitting the radio signal during the flight by the flight-lifting means of the petals of the directional diagram of its antenna.

c) a causal relationship between the signs and the technical result

The listed set of essential features provides high secrecy of the radio-emitting means operating with a frequency hopping signal, with high noise immunity of the connection, since the transmitter sequentially emits a radio signal at several frequencies, the number of which and the frequency intervals between which have different values. Such a signal generation with pseudo-random tuning of the operating frequency makes it possible to detect the reflected signal arising from the flight-lifting radio reconnaissance means located in the lobes of the directional diagram of the antenna of the radio-emitting means. The reflected signal is detected by a special detector. Since the antenna is a reversible device, the signal to the detector can come from the same antenna that emits a radio signal into space. When a reflected signal is detected, the radio emitting means turns off the transmitter and stops emitting the radio signal. In such conditions, the flight-lifting radio reconnaissance means cannot detect the information signal and, therefore, intercept, direction-finding and identification of the radio-emitting means. As a result, the secrecy of the radio-emitting means with pseudo-random tuning of the operating frequency is increased.

Brief Description of the Drawings

The claimed method is illustrated by drawings, which show:

figure 1 - illustration of the necessary conditions for radio reconnaissance of the radiating means - finding the flight-lifting means of radio reconnaissance in the petals of the directional diagram of the antenna of the radio emitting means;

figure 2 - structure of the radio signal with frequency hopping;

figure 3 is a frequency-time diagram of the emitted radio signal with frequency hopping and the signal reflected from the flight-lifting means of intelligence.

The implementation of the invention

The possibility of technical implementation of the claimed method is illustrated as follows.

A necessary condition for the interception of information, direction finding and identification of radio emitting means is to find the flight-lifting radio reconnaissance means in the petals of the directional diagram of the antenna of the radio emitting means (Fig. 1). When the radio-emitting means is operating on radiation, a radio signal reflected from the flight-lifting means of radio reconnaissance arises, propagating, among other things, towards the antenna of the radio-emitting means.

It is known that the antenna is a reversible device [4]. Thus, the radiating antenna of the radio-emitting means can be used to receive the reflected signal and apply this signal to the detector input.

The frequency hopping signal is shown in FIG. 2. It is characterized by the following parameters:

1) n is the number of frequency positions (nominal frequencies of carrier frequencies) of the RF signal with frequency hopping;

2) T _{î pos} - the duration of the radio signal from the frequency _hopping at one frequency position;

3) Δf _jk is the frequency interval between the denominations of the jth and kth frequency positions, Δf _jk = | f _j -f _k |.

The frequency-time diagram of the emitted radio signal with frequency hopping and the signal reflected from the flight-lifting means of intelligence, at the input of the detector is shown in Fig.3. The thickened line shows the time of emission of the radio signal at the frequency position. At the reception, the time of the presence of the reflected signal at a given frequency position will be delayed (shifted to large values along the frequency axis) relative to the emitted signal by

$${\tau }_{{}^{‵}e}=2D_{PP}/c,\left(\mathrm{one}\right)$$

where D _Рl - the distance between the radio-emitting means and the flight-lifting means of radio reconnaissance, m (see _figure 1); c = 3 · 10 ⁸ m / s is the speed of light.

In Fig. 1, two defining events are indicated: A - the end of the radiation of the radio-emitting means at a given frequency hopping position, B - the end of the reception of the reflected signal. The moments of occurrence of these events are indicated by t (A) and t (B), respectively. Since after the occurrence of event A, the frequency of the emitted radio signal changes by Δf = | f (t ₂ ) -f (t ₁ ) |, the frequency of the previous frequency hopping clock frequency f (t ₁ ) is freed. After event A, it becomes possible to turn on the receiver tuned to f (t ₁ ) and analyze the presence of the reflected signal. Upon detecting the presence of a reflected signal, the detector gives a command to turn off the transmitter of the radio-emitting means.

The duration of the transmitter shutdown (the termination of the operation of the emitting means for radiation) is selected based on the compromise between the requirement of secrecy of the radio line and the quality of the transmission of traffic. So, for telephone traffic it is advisable to set the transmitter off time to 0.2 s, which according to [5] does not affect the quality of the conversation.

After the radiation of the radio-emitting means is resumed, the presence of the reflected signal, etc., is analyzed again, which allows the radio-emitting means to be practically stopped to operate while the flight-lifting radio reconnaissance means are in the lobes of the directional diagram of the antenna of the radio-emitting means.

An example of calculating the duration of the analyzed reflected signal.

At D _PP = 60 km, which corresponds to the maximum range along the main lobe of the directional diagram of the antenna of the radio-emitting means with its elevation angle β = 10 ° (see Fig. 1) to the flight-lifting radio reconnaissance means patrolling at an altitude of H _Рl = 10 km , according to the expression (1), τ _и = 0.4 ms.

An example of calculating the power of the reflected signal at the detector input.

The effectiveness of the detection methods is characterized by an energy signal-to-noise ratio h ² , at which predetermined probability values of the correct P _D and false P _F detection of the reflected signal are provided. With optimal reception of a signal with a random initial phase and amplitude, these values are related by the expression [4]

. $$h^2=\frac{\lg P_F}{\lg P_D}-\mathrm{one}$$

.

, где П₁ - плотность потока мощности прямой волны в точке расположения летно-подъемного средства радиоразведки; П₂ - плотность потока мощности волны, отраженной от летно-подъемного средства радиоразведки, у приемной антенны обнаружителя; D_PP - дальность от радиоизлучающего средства до летно-подъемного средства радиоразведки.Reflective properties of aerial survey equipment characterized by effective scattering area $$\sigma =\mathrm{four}\pi D_{PP}^2{\ddot{I}}_2/{\ddot{I}}_{\mathrm{one}}$$

where P ₁ is the direct wave power flux density at the location of the flight-lifting radio reconnaissance means; P ₂ - the power flux density of the wave reflected from the flight-lifting means of radio reconnaissance at the receiving antenna of the detector; D _PP - the distance from the radio-emitting means to the flight-lifting means of radio reconnaissance.

The initial calculation data:

the distance from the radio-emitting means to the flight-lifting means of radio reconnaissance D _Рl = 60 êì;

effective scattering area of the flight-lifting radio reconnaissance means σ = 2ì ² ;

electromagnetic wavelength λ = 5 cm;

signal power at the output of the transmitter of the radio-emitting means R _prd = 65 W;

the gain of the antenna of the radio-emitting means G = 34 dB; the noise temperature of the antenna of the radio-emitting means G _sh = 100K;

noise temperature of the receiving path of the detector of the reflected signal T _{W a} = 70 K;

the duration of the reflected pulse is τè = 0.4 ms.

The calculation of the probability of correct detection of the reflected signal is carried out according to the known method [4]:

1. The spectral density of the noise power at the input of the receiving path is calculated

N ₀ = k (T _sha + T _sprat ),

where k is the Boltzmann constant, k = 1.38 ּ 10 ^-23 W · deg / Hz; T _{W a} - noise temperature of the antenna; T _{w pr} - the noise temperature of the receiver.

2. The power of the received reflected signal is determined

. $$R_{PR}=\frac{R_{PRd}{G}^2{\lambda }^2{\sigma }_{LP\mathrm{FROM}}}{{(\mathrm{four}\pi )}^3{D}_{PP}^2}$$

.

3. The value is found

$$h^2=\frac{P_{\text{ð}}÷{\tau }_{{}^{‵}e}}{N_0}$$

where P _{ð ÷} is the real sensitivity of the reflected signal detector.

4. The probability of correct detection of the reflected signal is calculated

. $$\lg P_D=\frac{\lg P_F^{*}}{h^2+\mathrm{one}}$$

.

Calculations show that for the indicated initial data at P _D = 0.85 and P _F = 0.1, the real sensitivity of the reflected signal detector should be R _RF = -155 dB, which is technically feasible.

An example of calculating the power of the reflected signal at the detector input.

As a result of calculating the power of the reflected signal at the detector input, it was determined that for P _ïðä = 18 dB (65 W), it is necessary to have a detector with R _RF = -155 dB.

The dynamic range of the transistor low-noise amplifier, which determines the total dynamic range of the detector, is at least K _ä ≥70 dB [6]. This means that the signal from the transmitter of the radio-emitting means at the input of the low-noise amplifier of the detector must be attenuated by P _ïðä -P _Ðx -K _ä = 18 + 155-70 = 103 äÁ by the tunable band-pass detector filter.

It is known that the quality factor of a filter is defined as [6]

, $$Q=\frac{f}{\Delta f_{\ddot{I}\ddot{I}}}$$

,

where f is the center frequency of the filter settings; Δf _ÏÏ is the filter bandwidth.

. Фильтр с такой добротностью может быть реализован, например, на связанных полосковых линиях [6].When the signal is emitted in the range of 6 GHz, which corresponds to λ = 5 cm, and the mismatch between the frequency positions of the signal with frequency hopping Δf = f (t ₂ ) -f (t ₁ ) = 10 Hz, the quality factor of the tunable filter will be equal to $$Q=\frac{f_{\ddot{I}\dot{a}\text{ð}}}{2\Delta f}=\frac{6\tilde{A}\tilde{A}\ddot{o}}{\mathrm{twenty}{}^{‵}I\tilde{A}\ddot{o}}$$

. A filter with such a quality factor can be implemented, for example, on connected strip lines [6].

Information sources

1. Gorshkov VV, Kuksin OV, Rubtsov S.A., Sukhov A.V. Military communications systems with pseudo-random tuning of the operating frequency. Foreign electronics 3, 1986, p. 3-13.

2. A method of transmitting discrete information in a radio line with a pseudo-random tuning of the operating frequency. RF patent No. 2228575 cl. H04B 1/713, publ. in 2004

3. A method of transmitting discrete information in a radio link with hopping the operating frequency. RF patent No. 2290758 cl. H04B 7/00, publ. in 2006

4. Theoretical foundations of radar: a textbook for universities. / Ed. V.E.Dulevich. - M .: Owls. Radio, 1978.

5. Kantor L.Ya., Minashin V.P., Timofeev V.V. Satellite Broadcasting - M.: Radio and Communications, 1981, 169 pp.

6. Volkov L.N., Nemirovsky M.S., Shinakov Yu.S. Digital radio communication systems: basic methods and characteristics: Textbook. Allowance. - M.: Eco-Trends, 2005.

Claims (1)

A method for increasing the secrecy of a radio-emitting means in a radio frequency hopper radio frequency transmission system, which consists in converting the binary information sequence into decimal numbers defining a pseudo-random sequence code (PSP) and the carrier frequency of the transmitter in order to increase the noise immunity and ensure informational and structural secrecy of the transmitted message which sequentially takes on different meanings; at the reception with the help of frequency filtering, the channel through which the transmission was performed is selected, the maximum value of the peak of the autocorrelation function is determined, by which the SRP code is determined, from which a decimal number is obtained by successive inverse transformations, which is converted to binary form corresponding to the transmitted information, characterized in that the signal emitted in space frequency location f _j hopping cycle at the time of entering aircraft lifting means radio intelligence in the diagram on the pitch systematic way the antenna radio-emitting means arises a reflected signal propagating, including and in the direction of the radio emitting antenna means; after the end of the radiation by the radio-emitting means of the radio signal at this frequency hopping frequency, the frequency of the emitted radio signal f _j changes by f _k ; the frequency of the previous frequency hopping cycle f _j for transmission is freed, at the same time the receiver tuned to f _{j is} turned on, and the presence of the reflected signal is analyzed; in the presence of a reflected signal, the radio-emitting means turns off its transmitter for the duration of the flight by the flight-lifting means of radio reconnaissance of the lobe of the directional diagram of its antenna.

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