RU2692081C1 - Short-wave radio communication system using frequency-shift keyed signals transmitted in pseudorandom operating frequency tuning mode - Google Patents

Abstract

FIELD: wireless communications.

SUBSTANCE: invention relates to radio communication and can be used to transmit discrete messages over short-wave communication channels in conditions of action of deliberate additive interference. Short-wave radio communication system employs frequency-shift keyed signals transmitted by frequency-time coding, providing protection from selective fading, unintentional and deliberate noise concentrated on the spectrum. Frequencies of frequency-time matrices of all subchannels are uniformly spaced apart by a quasi-random law within the entire pass band of the communication channel, and signal is transmitted in pseudo-random frequency tuning mode. Values of symbols which correspond to separate pulses transmitted by frequency-time coding are determined by leading edges of said pulses, which provides protection against intentional targeted interference, which at quasi-random frequencies always appear after transmitted information pulses and in this case can not affect correct reception of transmitted message.

EFFECT: technical result consists in improvement of reliability of transmitting messages over radio communication channels in conditions of creation of intentional additive interference by the opponent.

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Description

The invention relates to the field of radio and is designed to increase the secrecy of the transmission of discrete messages over short-wave radio channels and to increase the noise immunity of radio communication systems to intentional additive interference created by the opposing party.

In order to counteract the direction finding and suppression of transmitted signals by the opposing side, the communication systems use the method of pseudo-random frequency tuning (PFC) [Prokis J. Digital communications. - M .: Radio and communication, 2000. p. 628-639; Sklar Bernard. Digital communication. - M .: Publishing House "Williams", 2003. p. 752-759; Makarenko S.I., Ivanov M.S., Popov S.A. Interference immunity to pseudo-random frequency tuning systems Monograph. - SPb .: Own publishing house, 2013. - 166 p. and etc.]. A disadvantage of the known communication systems with a pseudo-random frequency tuning is that by increasing protection against intentional interference by frequency tuning, these systems usually use signal manipulation types that are poorly protected from the effects of selective fading and unintentional additive interference.

Known adopted for the prototype, a method of transmitting information over a short-wave communication channel using frequency-manipulated signals, which has high protection against selective signal fading, station and impulse noise [Patent No. 2519011 "Method of transmitting information over a short-wave communication channel using frequency-manipulated signals ”Published: 06/10/2014 Bull. No. 16]. In the prototype, the frequency-spaced transmission of discrete messages determines the algorithm for generating, detecting and decoding radio signals manipulated in amplitude and frequency, taking into account frequency-time matrices corresponding to a multi-element symbol sequentially transmitted by radio pulses over frequency-spaced subchannels, the number of which corresponds to the number of 2 ⁿ time positions on the duration of one character. It is considered that all subchannels are located at certain frequencies in the bandwidth of one common communication channel, for example, in the bandwidth of a single-band telephone channel, which is equal to 3,100 Hz. Obviously, in this case, the messages transmitted on one working frequency have specific features that allow the opposing party to easily identify this type of signals and create both targeted and barrage interference that will counteract the transmission of these messages. Thus, this method is not protected from the effects of intentional interference, since the many subchannels along which the message is transmitted are arranged in a certain order in a limited frequency band, which allows the opposing side to relatively easily detect the signals emitted by the transmitter and suppress them, creating intentional interference.

The objective of the invention is to increase the reliability of the correct reception of the message in the communication channels, in terms of the intentional additive interference created by the opposing party.

The technical result of the invention is to increase the coefficient of good operation of radio communication channels exposed to intentional additive interference, by using MN-multiple separated in the entire bandwidth of the communication channel according to the quasi-random frequency law AM signals with multiposition time-frequency coding.

This technical result is achieved by the fact that in the method of transmitting information over a short-wave communication channel using frequency-manipulated signals with a large frequency deviation, the fact that signals at subcarrier frequencies are received as independent frequency-separated amplitude-manipulated oscillations with an estimate of the quality of received signals and decide on the value of the received symbol, which depends on the location of the leading edge of the received pulses on the subcarrier frequencies and the According to the quasi-random law of subcarriers, the number of frequencies separated along the axis in the entire communication channel bandwidth is equal to the number NM, on the subcarriers corresponding to the transmitted symbol, to ensure the minimum peak signal of the radio signal, the transmission is performed sequentially in time at one of the NM frequencies, radiating radio pulses of duration , N times shorter than the duration of one character of the transmitted message, while the time of radiation and the frequency of radiation of a radio pulse depend on the value of the transmitted n-th element (n = ln ₂ (M⋅N)) symbol, and a decision about the received symbol value, taking into account endure received pulses quality estimates for each subcarrier frequency diversity criterion of the time ratio of the first maximum value of the reference power level for a given frequency received both along the time axis and along the frequency axis to the normalized (for example, using AGC) power level of additive interference at this frequency.

Currently known shortwave radio receivers, which provide multi-channel reception of signals simultaneously in the entire frequency band of the KB band [Patent No. 65329 "High-speed multichannel receiving device KB band" H04L 27/34. Publ. 07/27/2007 Patent number 90634. "Multichannel radio receiver". Publ. January 10, 2010]. This allows the frequency-manipulated signals transmitted in accordance with the method described in Patent No. 2519011 to separate along the frequency axis over very long distances within the entire frequency band of the used radio wave range (from the lowest applicable to the maximum applicable frequency) [Kalinin A.I. , Cherenkova E.L. The propagation of radio waves and the work of radio lines. - M .: Communication, 1971. S. 300-311. Fig. 8.11]. From Figure 8.11 of the indicated source, it follows that the bandwidth of the KB communication channel may exceed the bandwidth equal to ΔF = 4-6 MHz. In this case, if the number of subchannels is equal to N, and the number of frequencies of the frequency-time matrix in each subchannel is equal to M, then the average distance between the frequencies of the emitted signals will be equal to Δf = ΔF / (N⋅M). If, for example, N = 8 and M = 16 (a 7-element code combination is transmitted by one pulse), then the number of frequencies over which the message will be transmitted will be 128 and the average distance between frequencies will be 31.250 ÷ 46.875 kHz. In this case, the frequency assignment of all N frequency-time matrices should be made by a quasi-random method using random number generators (pseudo-noise sequence generators) that operate synchronously at the transmitting and receiving ends of the radio link. [Bernard Sklar Digital communication. - M .: Publishing House "Williams", 2003. Fig. 12.11] The specific value of the frequency F _ij is determined as follows:

F _ij (n) = f _min + [ΔF⋅R _ij (n)],

where F _jj (n) is the value of the j-th frequency of the time-frequency matrix of the i-th subchannel;

f _min - the value of the lowest applicable frequency;

ΔF is the bandwidth of the communication channel;

R _ij (n) is a quasi-random number received from a random number generator when determining the j-th frequency for the i-th subchannel when transmitting the n-th symbol;

[⋅] is the operation of rounding the number in square brackets to the nearest integer.

The transmitter of frequency-manipulated signals in this case will operate in frequency hopping mode, taking into account the quasi-random placement of subchannels along the frequency axis and the values of quasi-randomly spaced frequencies in the time-frequency matrices of transmitted symbols.

For the formation of a targeted interference to the opposing side, time is needed to detect the signal at a given frequency and tune the transmitter that forms a targeted interference to a given frequency. If the EW facilities of the opposing side are in close proximity to the transmitter of the useful signal, the response time to the formation of a targeted interference with modern high-operational radio countermeasures can be, taking into account the time delays in the filtering elements of the radio’s receiving and transmitting paths, only a few milliseconds and targeted interference will come to the point of reception of the signal practically with this signal. In all subchannels, amplitude detection of received signals is carried out and a decision is made on the results of detection (taking into account the time difference between the signals emitted at individual frequencies due to the coding method described in the prototype). Purposeful interference generated by the opposing side, in this case, in each subchannel will always be delayed by a certain time interval relative to the time of arrival at the point of reception of the information radio pulse, which makes it possible to make the right decision on the first front of the appearance of the information signal in the subchannels. This kind of decision-making method corresponds to the discovery in the communication channel of the “PRESS” packages when transmitting messages by the method of relative amplitude telegraphy [Petrovich NT Transfer of discrete information in channels with phase shift keying. - M .: Soviet radio, 1965. S. 72]. The algorithm for demodulating signals by the proposed method can, for example, be implemented as follows: in “sliding windows” along the time axis, at intervals of the duration of an elementary premise, determine the difference of energy values accumulated over the time interval of the “sliding window” at the given moment and accumulated over the same time interval previous point in time. If this difference exceeds a predetermined threshold, then decide on the detection of a signal. The greater the difference in energy values accumulated in the “sliding windows”, the greater the power of the received signal. In this case, the ratio of the maximum recorded value of the energy difference in the “sliding windows” to the interference energy accumulated over the same time interval can serve as an estimate of the quality of the received signal. The moment of decision making in one or another subchannel indicates the information content of the given pulse signal. This type of signal demodulator can be called “differential”, because its algorithm is based on determining the difference in energy levels that correspond to the neighboring time points for receiving signals at the corresponding frequency, i.e. in fact, an estimate is made of the derivative of the energy accumulated in a “sliding window” by the finite difference ratio method [EA Volkov. Numerical methods.- M .: Nauka, 1987. S. 47-50].

It must be borne in mind that in short-wave communication channels, as a rule, there is multipath. In this case, the interference of the rays. The difference of the rays in this case can reach values of 5-6 ms [LM Fink Theory of the transfer of discrete messages. - M .: Soviet Radio, 1070. S. 504]. The accuracy of the estimate of the location of the front of the received pulse in this case, depending on the value of the phases in the interfering rays, can be 3 times the difference in the path of the rays [Khmelnitsky, EA Evaluation of the actual noise immunity of receiving signals in the KB range. - M .: Communication, 1975. S. 153, Fig. 5.2]. Considering the above, to avoid ambiguous results when receiving messages in the FH mode, it is necessary that the duration of single elements is many times greater than the possible path difference in the HF communication channel, for example, would be at least 20 ms. In this case, the information transmission rate of the message will be approximately 20 bit / s with an 8-position time-frequency matrix (for example, 8 time positions and 1 subcarrier frequency in a time-frequency matrix) and 50 bit / s with a 256-position time-frequency a matrix (for example, 8 time positions and 32 frequency subcarriers in a time-frequency matrix).

Since decisions about transmitted information are made on the first fronts of received radio pulses, and signals always precede targeted interference from the opposing side, messages transmitted by the proposed radio communication system cannot in principle be suppressed by targeted interference generated by the opposing side. Moreover, in the case of creating a signal-like interference, it will not only interfere with the reception of information, but, on the contrary, will increase the energy accumulated in the “sliding window” at the moments of reception of the useful signal and thereby increase the noise immunity of the communication system to unintentional additive interference. As for barrage jamming, their appearance is possible only in the case when the opposing party knows the algorithm of the work of the frequency hopping system, which is practically excluded. Thus, the proposed system of short-wave radio communication using frequency-manipulated signals transmitted in the mode of pseudo-random tuning of the operating frequency is indifferent to the means of radio suppression of the opposing side.

Let us explain the above for the case when N = 4 and M = 4 (16-position frequency-time matrix, when a 4-element combination is transmitted in one pulse in one subchannel). FIG. 1. shows the points in time and frequency of transmission of all possible 4-element combinations. Frequencies F _ij correspond to the i-th subchannel and j-th frequency of the time-frequency matrix of the i-th subchannel. If the signal is emitted, for example, in the first time interval of the transmitted symbol at frequency F ₄₄ , this means that a combination of four elements 1101 is transmitted. The same combination is transmitted at the next time point at frequency F _14. During the third time interval, this combination elements transmitted at a frequency of F ₂₄ , and during the fourth time interval, respectively, at a frequency of F ₃₄ .

FIG. 2 shows the oscillogram of the voltage at the input of the demodulator of one of the subchannels at the frequency on which the signal is transmitted in the event that the opposing party manages to form a targeted (signal-like) interference. From the oscillogram it is seen that the signal element appears somewhat earlier than the targeted interference and on its leading edge, which contains information about the transmitted message, the targeted interference in no way affects the state.

FIG. 3 shows a block diagram of one of the possible options for implementing a “differential” amplitude demodulator. In the block diagram indicated:

1 - demodulator input;

2 - filter of the main signal selection (FOS);

3 - automatic gain control unit (AGC);

4 - amplitude detector;

5 - low pass filter (LPF);

6.1 and 6.2 - delay lines;

7 - voltage quadrants;

8 - adders;

9 - subtractor of the oscillation energies accumulated in the delay lines;

10 - solver;

11 - AGC input for control signals from cyclic synchronizer

12 - output to assess the quality of the received signal;

13 - demodulator output for the decision made on the value of the received symbol.

The bandwidth of the FOS is consistent with the width of the spectrum of the pulse signal. AGC blocks in subchannels at all frequencies are controlled by signals from cyclic synchronizers and operate only at time intervals that precede the first time positions of the possible appearance of radio pulses on all time-frequency matrices of subchannels. The gains of paths obtained using the AGC are maintained throughout all time intervals of the frequency-time matrices of the subchannels. From the output of the amplitude detector, a low-frequency oscillation filtered by means of a low-pass filter enters two series-connected delay lines with taps. Quadraters, which, in turn, are connected to the corresponding adders, ensuring the accumulation of signal energy at specified time intervals in “sliding windows”, whose time intervals correspond to the lengths of the delay lines, are included in the taps of both delay lines. From the outputs of the voltage adders go to the subtractor, after which there is a device for analyzing and making decisions, determining the moment of appearance of the leading edge of the received pulse and evaluating the quality of the received signal by the level of the voltage difference at the output of the subtractor. If we assume that the noise level normalized by AGC, estimated in the second adder, is equal to “one”, then the voltage at the output of the subtractor that characterizes the difference between the accumulated energies in the adders will be equal to the power ratio H ² = [“signal + interference” - “interference”] / “Disturbance”, which characterizes the quality of the message character reception. The algorithm of the “differential” amplitude demodulator, the block diagram of which is shown in FIG. 3, is easily implemented in the software version on the processor.

FIG. 4 shows the waveforms of the signal at the input of the amplitude demodulator (a), at the output of the low-pass filter of the amplitude detector (b), at the output of adders (c) and at the output of the subtractor (d). In the waveform of FIG. 4 (d) shows the threshold U ₀ , the excess of which corresponds to the decision on the location on the time axis of the moment of the decision to detect the pulse signal and, therefore, on the value of the received symbol. This point in time may differ slightly from the point in time when the leading edge of the pulse is found. It is important that the time to to not go beyond the limits of the time interval to which the received radio pulse corresponds. The quality assessment of a received radio pulse may vary over time. At the moment of making a decision about the detection of a pulse, it can be significantly lower compared to that finally adopted due to an increase in the voltage at the output of the subtractor as the signal energy accumulates in the adder during the reception time of the entire radio pulse.

Claims (1)

The system of shortwave radio communication using frequency-manipulated signals transmitted in the pseudo-random frequency tuning mode, when each message symbol is transmitted to ensure the minimum peak factor sequentially in time on one of the (M⋅N) frequencies of subchannel frequency-time matrices, while radio pulses of duration N times less than the duration of one character of the transmitted message, and the emission time and the emission frequency of each radio pulse in each subchannel depend on the value before n-Vai element (n = ln ₂ (M⋅N)) symbol, and a decision about the value of the received symbol shall be made taking into account the received pulses quality assessments in each frequency-spaced subchannel, wherein the time-frequency matrices of the frequency subchannels for each of the next the transmitted symbol is assigned synchronously on the transmitting and receiving side of the radio link according to a quasi-random law within the entire bandwidth of the communication channel, and the information value of the symbol determines the location of the leading edge of the pulse transmitted go at a given frequency.

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