RU2228575C2 - Method for digital data transfer in pseudorandom operating frequency tuned link - Google Patents

Abstract

FIELD: electrical communications and computer engineering. SUBSTANCE: proposed method and device are designed for data transfer in computer network over radio link incorporating provision for tuning pseudorandom operating frequency. On sending end of radio link input signal is divided into blocks produced in the form of n-bit binary vectors in compliance with number of p = 2ⁿ, frequency channels used; two pseudorandom-sequence binary vectors are generated by simultaneously and concurrently taking data off different places of shift register; in the process length of each pseudorandom-sequence binary vector is chosen to equal that of binary vector of input-signal block; binary vector of input signal block is coded by modulo two addition of its bits to those of first pseudorandom-sequence binary vector; transmitter is tuned to desired frequencies in compliance with codes generated in the form of second pseudorandom-sequence binary vector, transmitter frequency is modulated followed by signal radiation into space. On receiving end of radio link signal is received simultaneously at all frequencies, converted to intermediate frequency, amplified, and demodulated; binary vector of demodulated signals is generated; two pseudorandom-sequence binary vectors are produced in same manner as on sending end; signal is decoded by modulo two addition of two bits of first pseudorandom-sequence binary vector to bits of demodulated-signal binary vector, and signal is supplied to terminal device; transmitter frequencies are modulated by noiseimmune code and transmitter tuning is effected to several frequencies simultaneously; in the process first frequency is chosen for frequency channel whose number corresponds to code of second pseudorandom-sequence binary vector and all other frequencies are selected by sequential search in compliance with symbol 1 meaning in respective bit of coded binary vector of input signal; on receiving end of radio link binary vector whose bits acquire 1 meaning is generated upon demodulation of signals in presence of signal in respective frequency channels whose numbers follow that of frequency channel found by code of second pseudorandom-sequence binary vector. EFFECT: enhanced noise immunity and security of communications. 1 cl, 2 dwg

Description

The invention relates to the field of radio communications and computer technology, and more particularly to the field of methods and devices for transmitting information in a computer network via a radio link with pseudo-random tuning of the operating frequency.

Known methods for transmitting discrete information in a radio line with pseudo-random tuning of the operating frequency (see, for example, [1] p. 19-35, patent application 99123808/09, 10.11.1999 [2]).

In known methods, the transmission of discrete information is carried out by expanding the spectrum of the signals due to the pseudo-random tuning of the operating frequency.

The closest in technical essence to the claimed method is the method described in application 99123808/09, 10.11.1999. The method includes, at the transmitting end of the radio link, dividing the input signal into blocks formed as binary vectors of n-bit length in accordance with the number of used frequency channels p = 2 ⁿ , generating two binary vectors of the pseudo-random sequence by simultaneously collecting information from different bits of the shift register, 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 of the block the input signal by modulo adding its two bits with the bits of the first binary vector of the pseudorandom sequence, sequentially tuning the transmitter into frequencies in accordance with the codes that form the second binary vectors of the pseudorandom sequence, modulating the frequency of the transmitter and then emitting the signal into space, receiving the signal by the receiving end of the radio link simultaneously at all frequencies, the selection according to the code of the second binary vector of the pseudo-random sequence of that frequency of the channel through which the signal was transmitted, the signal was converted to an intermediate frequency, amplification, demodulation, and the formation of a binary vector of demodulated signals, the formation of the pseudorandom sequence in the same way as on the transmitting side of two binary vectors, the decoding of the signal by modulo addition of two bits of the binary signal vector arising in frequency channel with bits of the first binary vector of a pseudo-random sequence and the signal to the terminal device.

However, the prototype method has a drawback. Despite the fact that the carrier frequency of the transmitter is tuned in accordance with a pseudo-random sequence code, the communication system is not sufficiently noise-protected during active intrusions. Since the signal is emitted at one frequency at a certain point in time, it is opened by the enemy’s reconnaissance, which allows him to optimally distribute the limited interference power over the entire space of the radio signal.

The invention is aimed at improving the noise immunity (stealth and noise immunity) of communication.

This is achieved by the fact that in the known method of transmitting discrete information in a radio line with pseudo-random tuning of the operating frequency, which consists in dividing the input signal into blocks formed in the form of binary vectors with a length of n-bits in accordance with the number of frequency channels used p = 2 ⁿ , forming two binary vectors of a pseudo-random sequence by simultaneously simultaneously taking information from different bits of the shift register, with the length of each binary vector of the pseudo-random sequence the springs are chosen equal to the length of the binary vector of the input signal block, the coding of the binary vector of the input signal block by modulo addition of its two bits with the bits of the first binary vector of the pseudo-random sequence, the tuning of the transmitter to frequencies in accordance with the codes that form the second binary vectors of the pseudo-random sequence, modulation of the frequency of the transmitter and the subsequent radiation of the signal into space, receiving a signal at the receiving end of the radio line simultaneously at all frequencies, pre generating a signal at an intermediate frequency, amplifying, demodulating and generating a binary vector of demodulated signals, generating, similarly to the transmitting side, two binary vectors of a pseudo-random sequence, decoding the signal by modulo adding two first binary vectors of a pseudo-random sequence with bits of the binary vector of demodulated signals and signal delivery to the terminal device, according to the invention, the transmitter frequency is modulated by an error-correcting code and the transmitter is tuned simultaneously to several frequencies, with the first frequency being selected for the frequency channel whose number 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 block of the input signal, and on the receiving side after demodulation of the signals in the frequency channels form a binary vector whose bits take significant e "1" when a signal in the respective frequency channels, whose numbers follow the frequency channel, which is determined by the code of the second pseudo-random sequence of binary vector.

In the totality of the features of the claimed method, a binary vector is understood to mean a signal in the form of a sequence of zero and single bits corresponding to the representation of a number (symbol) in a binary calculus.

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 pseudo-random tuning of the operating frequency and energy suppression during active intrusions makes it difficult to reconnoiter, 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, and then due to an abrupt change in the operating frequencies of the transmitter. In this case, the energy distribution of the signal is carried out in a large frequency band, which ensures 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 use the entire 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 possibility of technical implementation of the claimed method is illustrated as follows.

If the number of frequency channels used is 2 ^k , then the length of the binary vector of the input signal block is chosen equal to k bits. For example, for 16 frequency channels used, the length of the binary vector of the input signal block should be 4 bits.

The formation of a pseudo-random sequence of maximum length containing 2 ⁿ -1 characters can be achieved by using a linear shift register with n digits, the feedback of which is determined by the form of the selected primitive polynomial of degree n. Finding primitive polynomials of degree n is described in [3] on pages 74-75.

The formation of each binary vector of a pseudo-random sequence of length k bits can be accomplished by taking information from k different bits of the shift register, the numbers of which can be determined by the value of the entered security key K (initial filling of the bits of the shift register). For example, by defining a parent element

l ₀ ≡ K (mod q), if l ₀ <2, then l ₀ = 2,

and calculating the number of the discharge register shift according to the formula

l ₁ = l ₀ , l _i ≡ l ₀ l _i-1 (mod q), i = 1, k,

where the value of q is selected from primes for the shift register having 256 bits q = 257, and for the shift register having 128 bits q = 127. In this case, by raising to the power of the generating number l ₀ , we will pass from one element of the field Fq to another. Moreover, as shown in [3] p. 44, if l ₀ is an element of order m, then all elements l ₀ l $\genfrac{}{}{0ex}{}{\text{2}}{\text{0}}$ l $\genfrac{}{}{0ex}{}{\text{3}}{\text{0}}$ , ..., l $\genfrac{}{}{0ex}{}{\text{m-1}}{\text{0}}$ will be different.

In accordance with the second binary vector of the pseudo-random sequence (for example, 1000), the code K ₁ for tuning the transmitter to the first carrier frequency will correspond to the 8-frequency channel, since in the binary number system 1000 corresponds to the number 8.

The coding of the input signal block can be accomplished by modulo adding two characters of the first binary vector of the pseudo-random sequence (for example, 0011), with the symbols of the binary vector of the block of the input signal (for example, 0111)

K ₂ = 0100.

In accordance with the generated codes K ₁ and K _{2, the} transmitter will emit a signal simultaneously on the 8- and 11-frequency carrier channels, since the 9th channel will correspond to the zero bit of the K ₂ code, the 10th bit will correspond to the first bit of the K ₂ code The 11th channel will correspond to the second category of the K ₂ code, and the 12th channel will correspond to the third category of the K ₂ code.

The symbols of binary vectors of a pseudo-random sequence are calculated on the receiving side, one of which is used to determine the channel numbers in which the appearance of the encoded signal is possible. For our example, in accordance with the pseudo-random sequence code (1000⇒ 8), the appearance of signals should be expected in the 9th, 10th, 11th, 12th channels. Since the signal appeared in the 11th channel, they form the binary vector K ₂ = 0100. The decoding of the generated signal is carried out by adding modulo two bits of the codes K ₂ (0100) with the bits of the first binary vector of the pseudorandom sequence (0011). The resulting number (0111⇒ 7) is fed to the terminal device.

The proposed method can be implemented using devices represented by the flowchart in figure 1, where:

block 1 - signal source;

block 2 - the first shift register;

block 3 - encoding device;

block 4 - frequency synthesizer;

block 5 - modulator;

block 6 - transmitter;

block 7 - the receiver;

block 8 - the second shift register;

block 9 - decoding device;

block 10 - terminal device

and the block diagram of figure 2, where blocks 11-16 are bits 1-6 of the shift register, and block 17 is an adder modulo two.

For simplicity, the description of the operation of the device will use small numbers. We assume that the shift register has 6 bits (the protection key length is 6 bits), and the number of frequency channels used is 16, then a 4-bit binary vector can be used to transmit one block of the input signal.

To determine the structure of the shift register, a primitive polynomial of the sixth degree is chosen, for example

λ ⁶ + λ ⁵ +1.

For the selected primitive polynomial, the block diagram of the feedback shift register will have the form shown in FIG. 2. 6-bit security key generated using a random number generator

<λ ₆ , λ ₅ , λ ₄ , λ ₃ , λ ₂ , λ ₁ >

where λ ₁ = 0, λ ₂ = 0, λ ₃ = 0, λ ₄ = 1, λ ₅ = 1, λ ₆ = 1 - enters the shift register and is used for the initial filling of the bits of the shift register. Binary symbols from the 5th and 6th bits of the shift register arrive at the input of the adder 17 modulo two in each clock cycle, and from the output of the adder modulo two the symbol ε = λ ₅ ⊕ λ ₆ goes to the input of the first bit of the shift register (block 11). In this case, the state of the discharges for each cycle during the operation of the shift register is determined by the expression

, λ ₁=ε .λ _i = λ _i-1 for

, λ ₁ = ε.

If the characters are removed from the sixth digit λ ₆ , then the binary pseudorandom sequence of the maximum period will have the form

{1110000010000110001010011110100011100100101101110110

011010101111}.

Note that during the period of this sequence, any nonzero set of six characters 0 and 1 occurs only once.

If we take binary numbers from the 1st, 2nd, 3rd and 4th digits of the shift register (blocks 11, 12, 13, 14) at each step of its operation and with the set <λ ₁ , λ ₂ , λ ₃ , λ ₄ > we will match binary vector (number) x = λ ₁ + 2λ ₂ +2 ² λ $\genfrac{}{}{0ex}{}{}{\text{3}}$ , + 2 ³ λ $\genfrac{}{}{0ex}{}{}{\text{4}}$ , then the sequence of binary numbers during the operation of the register can be considered as a sequence of characters x (0, 1, 2, ..., 15} in the form

x = {8, 0, 0, 1, 2, 4, 8, 0, 1, 3, 6, 12, 8, 1, 2, 5, 10, 4, 9, 3, 7, 15, 14, 13 , 10, 4, 8, 1, 3, 7, 14, 12, 9, 2, 4, 9, 2, 5, 11, 6, 13, 11, 7, 14, 13, 11, 6, 12, 9 , 3, 6, 13, 10, 5, 10, 5, 11, 7, 15, 15, 15, 14, 12, ...}.

If we take binary numbers simultaneously from the 1st, 2nd, 5th, 6th digits of the shift register (blocks 11, 12, 15, 16) at each step of its operation with the set <λ ₆ , λ ₅ , λ ₂ , λ ₁ >, we will compare the number in the form y = λ ₆ + 2λ ₅ +2 ² λ $\genfrac{}{}{0ex}{}{}{\text{2}}$ + 2 ³ λ $\genfrac{}{}{0ex}{}{}{\text{1}}$ , then the sequence of binary numbers during the operation of the shift register can be considered as a sequence of characters y {0,1,2, ..., 15} in the form

y = {3, 3, 1, 8, 4, 0, 0, 2, 9, 12, 4, 0, 2, 11, 5, 8, 4, 2, 9, 14, 13, 12, 6, 11 , 7, 3, 1, 10, 13, 12, 4, 2, 11, 7, 1, 8, 6, 9, 12, 6, 9, 14, 15, 5, 10, 15, 7, 1, 10 , 15, 5, 8, 6, 11, 5, 10, 13, 14, 13, 14, 15, 7, 3, ...}.

An analysis of the generated sequences x and y shows that in the interval corresponding to the period equal to 63 clock cycles of the shift register, each of the symbols {1, 2, ... 15} occurs exactly four times. The symbol corresponding to zero occurs exactly three times in both sequences, while the sequences x and y cannot be obtained from each other as a result of a cyclic shift. In sequences x and y, there are no hidden periodicities and the statistical uniformity of the symbols used is ensured.

The generated pseudo-random sequences of symbols x and y in the form of binary vectors are sent to the encoding device 3, where codes K ₁ and K ₂ are generated for tuning the transmitter to the corresponding carrier frequencies.

Similarly, on the receiving side, the symbols x, y are generated in block 8 to determine the numbers of frequency channels in which to expect the appearance of signals and to decode the received signals.

In this case, due to the modulation of the carrier frequencies of the transmitter by an error-correcting code (for example, Barker) with a large base, the energy secrecy of the emitted signals is provided, and the radiation of the signal at two or more frequencies simultaneously increases the structural secrecy of the emitted signals and the noise immunity of the communication.

Since when working with the shift register, it is possible to skip those cycles of its operation for which the symbols of the generated binary vectors of the pseudorandom sequence coincide in all or several selected bits, the statistical uniformity of the frequency channels used is provided when transmitting constant characters of the source text and the use of statistical methods of cryptanalysis for opening is excluded pseudo-random sequence.

If the frequency channel corresponding to the code of the second binary vector of the pseudo-random sequence is used only for the case of checking the encoded block of the input signal for parity, then it is possible to detect and correct errors in the decoded message, which increases the noise immunity of the communication.

If the code for tuning the transmitter to the first carrier frequency is generated by modulo adding two bits of the second binary vector of the pseudorandom sequence with the bits of the encoded binary vector of the input signal block, then on the receiving side it is possible to filter the false signals by generating an additional binary vector by adding module two bits of the second binary vector of the pseudo-random sequence with bits of the binary vector corresponding to the ordinal frequency channel number for the first frequency of the transmitter and comparing the resulting additional binary vector with binary vector demodulated signals.

If the frequency channel corresponding to the code of the second binary vector of the pseudo-random sequence is not used, then in this case the structural secrecy of the emitted signals is increased and the opening of the codes of the pseudo-random sequences is difficult.

The implementation of the proposed method does not cause difficulties, since all the blocks and nodes included in the device that implements the method are well known and widely described in the technical literature.

Sources of information

1. V.I. Borisov, V.M. Zinchuk, A.E. Limarev, N.P. Mukhin, V.I. Shestopalov. Interference immunity of radio communication systems with the expansion of the spectrum of signals by the method of pseudo-random tuning of the operating frequency. M .: Radio and communications, 2000.

2. A method of transmitting discrete information in a radio line with pseudo-random tuning of the operating frequency and a device for its implementation. Application for invention 99123808/09, 10.11.1999, IPC 7 Н 04 В 1/713.

3. B.N. Voronkov, V.I. Stupid. Toolkit for the development of information security tools in computer networks. Voronezh: Voronezh State University, 2000.

Claims (4)

1. A method for transmitting discrete information in a radio line with a pseudo-random tuning of the operating frequency, including at the transmitting end dividing the input signal into blocks formed as binary vectors of length n bits in accordance with the number of frequency channels used, p = 2 ⁿ , forming two binary vectors of the pseudorandom sequence by simultaneously collecting information from different bits of the shift register, the length of each binary vector of the pseudo-random sequence being chosen equal to the length of the binary vector of the block of the input signal, the coding of the binary vector of the block of the input signal by modulating its two bits with the bits of the first binary vector of the pseudo-random sequence, tuning the transmitter to frequencies in accordance with the codes that form the second binary vector of the pseudo-random sequence, modulating the frequency of the transmitter and subsequent radiation of the signal into space, receiving a signal at the receiving end of the radio link simultaneously at all frequencies, converting the signal to intermediate frequency, amplification, demodulation and generation of a binary vector of demodulated signals, generating, similarly to the transmitting side of two binary vectors of a pseudo-random sequence, decoding the signal by modulo adding two bits of the first binary vector of the pseudo-random sequence with bits of the binary vector of the demodulated signal and applying the signal to terminal device, characterized in that the transmitter frequencies are modulated by an error-correcting code, and by tuning The transmitter is carried out simultaneously at several frequencies, with the first frequency being selected for the frequency channel whose number 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 of the symbol "1" in the corresponding bit of the encoded binary vector of the block input signal, and at the receiving end of the radio line after demodulating the signals in the frequency channels form a binary vector, the bits of which take value "1" in the presence of a signal in the corresponding frequency channels, the numbers of which follow the frequency channel, which is determined by the code of the second binary vector of the pseudo-random sequence. 2. The method according to claim 1, characterized in that the frequency channel corresponding to the code of the second binary vector of the pseudo-random sequence on the transmitting side is used only to provide an even number of simultaneously used carrier frequencies, and on the receiving side it is used to check the encoded binary vector of the input signal block for parity. 3. The method according to claim 1, characterized in that the frequency channel corresponding to the code of the second binary vector of the pseudo-random sequence is not used when transmitting and receiving messages. 4. The method according to any one of claims 1 to 3, characterized in that those clock cycles of the shift register are skipped for which the generated binary vectors of pseudorandom sequences coincide.

Images