RU2804059C1 - Method for noise-free transmission of discrete signals based on single-sideband modulation - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: invention is intended for use in noise-immune radio communication systems when they operate in channels with a random phase change. The technical result of the proposed method is to increase the noise immunity of receiving a single-sideband modulation radio signal by compensating for a random phase shift of the radio signal during demodulation. This technical result is achieved due to the fact that the phase shift introduced by the radio channel is calculated from the pilot signal, which is a harmonic oscillation at the carrier frequency of the single-sideband modulation radio signal. Then, on the receiving side, before synchronous detection, the initial and channel values of phase shifts are added to the phase of the reference oscillation of the synchronous detector. Due to this, a random change in the phase of the radio signal is eliminated, which ensures an increase in the noise immunity of its reception.

EFFECT: increased noise immunity of receiving a single-sideband modulation radio signal.

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Description

The invention relates to the field of radio engineering and is intended for use in noise-resistant radio communication systems when they operate in channels with random phase changes.

The “Method for transmitting and receiving discrete signals based on single-sideband modulation” is known (RF Patent No. 2763520, IPC H04L 27/32, published 12/30/2021. Bulletin No. 1).

In the known method, discrete signals are transmitted on the basis of permutation modulation, and the subcarriers of the discrete permutation modulation signal are formed in the spectrum of an noise-resistant analog single-sideband modulation signal. Transmission of information bits is carried out over the upper side frequency band, onto which a single-sideband modulation masking signal is superimposed over the lower side frequency band, formed on the basis of orthogonal phase-shift keyed frequency subcarriers.

The disadvantage of this known method is the low noise immunity of receiving single-sideband modulation radio signals in channels with random changes in the phase of the radio signal.

Known is the “Method of generating single-sideband modulation radio signals using Barker codes” (RF Patent No. 2749877 “Method of generating structurally covert, noise-resistant single-sideband modulation radio signals using Barker codes. IPC N04V 17/30, publ. 06/18/2021, Bulletin No. 17) .

In the analogue method, radio pulses are generated based on direct and inverse wavelet functions of arbitrary order and a single-sideband modulation radio signal is generated. Based on the results of assessing the state of the radio channel, during the comparison of the initial test sequence formed in the single-sideband modulation spectrum with the accepted test sequence, a timely change of the operating frequency is made.

The disadvantage of this known method, like the previous analogue, is the low noise immunity of receiving a single-sideband modulation radio signal in channels with random changes in the phase of the radio signal.

The closest in technical essence to the proposed method is “Method for noise-free transmission of discrete signals based on single-sideband modulation” (RF Patent No. 2784030, IPC N04V 10/54, published November 23, 2022. Bulletin No. 33).

In the prototype method, a code with a constant weight is selected to encode the subcarriers of the generated radio signal in such a way that the bit depth of the code corresponds to the number of subcarriers available for transmission, and the bit stream is divided into information blocks in accordance with the number of available code combinations that determine its alphabet. Each information block is assigned its own unique combination of code elements, signals are generated in the form of amplitude-keyed oscillations for the duration of each transmitted symbol only on those subcarriers to which the information units correspond, after which additive addition of the generated signals is carried out on all subcarriers. The resulting frequency-shift keyed signal is demodulated at subcarrier frequencies as independent frequency-spaced amplitude-shift keyed oscillations. On the transmitting and receiving sides, the values of frequency and phase shifts are set, for which the frequency range from zero to two kilohertz and the phase change range from zero to three hundred and sixty degrees are divided into nine equal intervals, each of which is assigned a numerical value that determines the corresponding nominal frequency or phase shift and a numerical value equal to the sum of the initial boundary value of the interval and the value that determines its length. For each information block, a random binary sequence of ten elements is formed, on the basis of which the first and second random numbers are obtained, and the first random number is obtained as a result of converting all elements of the generated binary random sequence into a decimal number, from the first element of which a second random number is obtained, taking respectively, the value of zero or one. The range of values of the first random number is divided into nine integer uniform intervals, each of which is sequentially assigned the values of frequency and phase shifts. The value of the radiation frequency is determined, for which the value of the frequency shift corresponding to the value of the first random number is added to the nominal operating frequency, if the second random number is equal to one, if the random number is equal to zero, then the frequency shift is subtracted. On the transmitting side, at an intermediate frequency, the resulting frequency-shift keyed signal is formed, on the basis of which a single-sideband modulation radio signal is formed at the emission frequency, and the carrier phase of the single-sideband modulation signal is chosen equal to the phase shift corresponding to the value of the first random number. They emit a radio signal towards the correspondent. At the receiving side, a radio signal is received at the emission frequency, the single-sideband modulation radio signal is demodulated to an intermediate frequency, and the carrier phase of the single-sideband modulation signal is taken equal to the value of the phase shift corresponding to the value of the first random number, then the resulting frequency-shift keyed signal is demodulated.

The disadvantage of the known prototype method is the low noise immunity of receiving a single-sideband modulation radio signal in channels with random changes in the phase of the radio signal.

The objective of the invention is to create a method that provides increased noise immunity for receiving single-sideband modulation radio signals in channels with random changes in the phase of the radio signal, in particular in short-wave radio communication channels.

The technical result of the proposed method is to increase the noise immunity of single-sideband modulation radio signal reception by compensating for the random phase shift of the radio signal during the demodulation process.

The technical result is achieved by the fact that in the method of noise-resistant transmission of discrete signals based on single-sideband modulation, which consists in choosing a code with a constant weight for encoding the subcarriers of the generated radio signal in such a way that the bit width of the code corresponds to the number of subcarriers available for transmission, breaking the bit stream into information blocks in accordance with the number of available code combinations that determine its alphabet, assign each information block its own unique combination of code elements, generate signals in the form of amplitude-keyed oscillations for the duration of each transmitted symbol only on those subcarriers to which the information units correspond, and then carry out additive addition of the generated signals on all subcarriers, demodulate the resulting frequency-keyed signal on subcarrier frequencies as independent frequency-spaced amplitude-shift keyed oscillations, set the values of frequency and phase shifts on the transmitting and receiving sides, for which the frequency range is from zero to two kilohertz and the range phase changes from zero to three hundred and sixty degrees are divided into nine equal intervals, each of which is assigned a numerical value that determines the corresponding nominal frequency or phase shift, and a numerical value equal to the sum of the initial boundary value of the interval and the value that determines its length, and for each information block, a random binary sequence of ten elements is formed, on the basis of which the first and second random numbers are obtained, and the first random number is obtained as a result of converting all elements of the generated binary random sequence into a decimal number, from the first element of which a second random number is obtained, taking the corresponding value zero or one, divide the range of values of the first random number into nine integer uniform intervals, each of which is sequentially assigned the values of frequency and phase shifts, determine the value of the radiation frequency, for which the value of the frequency shift corresponding to the value of the first random number is added to the nominal operating frequency, if the second random number is equal to one, if the random number is equal to zero, then the frequency shift is subtracted, the resulting frequency-keyed signal is formed on the transmitting side at the intermediate frequency, on the basis of which a single-sideband modulation radio signal is formed at the emission frequency, and the carrier phase of the single-sideband modulation signal is chosen equal to the initial phase shift corresponding to the value of the first random number, a radio signal is emitted towards the correspondent, a radio signal is received at the receiving side at the emission frequency, the single-sideband modulation radio signal is demodulated to an intermediate frequency, and the carrier phase of the single-sideband modulation signal is taken equal to the value of the phase shift corresponding to the value of the first random number , then demodulation of the resulting frequency-keyed signal is carried out, according to the invention , on the receiving side, before the technical demodulation procedure, the frequency of the received radio signal is converted from the operating frequency to the first intermediate frequency, at which a highly stable first reference harmonic oscillation is formed with an initial phase shift and unit amplitude, then to The pilot signal of the received single-sideband modulation radio signal is allocated to the first intermediate frequency, the amplitude of the selected pilot signal is limited and it is fed to the mixer, where the selected pilot signal with limited amplitude is multiplied by the first reference harmonic oscillation, the channel phase shift is measured, and then the received radio signal is converted single-sideband modulation from the first intermediate frequency to the second intermediate frequency, at which its synchronous detection is carried out at the intermediate frequency, and the values of the original and channel phase shifts are previously added to the phase of the reference oscillation during synchronous detection by means of a controlled phase shifter.

Thanks to a new set of essential features, the inventive method compensates for random changes in the phase of a radio signal received in a radio channel (channel phase shift) during its demodulation based on synchronous detection.

Let us explain the achieved technical result. In the prototype method, an increase in structural secrecy is carried out, and, consequently, noise immunity (noise immunity) (see, for example, Borisov V. I., Zinchuk V. M., Limarev A. E. Noise immunity of radio communication systems by expanding the spectrum of signals by the method of pseudo-random restructuring of the working frequencies // edited by V. I. Borisov; 2nd edition, revised and supplemented - M.: RadioSoft, 2008. - 512 pp.). In this case, technically, a pseudo-random initial phase shift of the single-sideband modulation radio signal is additionally carried out during its formation. The condition for correct demodulation of the radio signal thus generated is the equality of the phase shifts of the synthesized and received radio signals.

However, in a random phase shift radio channel, a random (channel) phase shift will be added to the phase of the original phase shift radio signal.

As a result, the radio signal on the receiving side will be demodulated with phase distortions (see, for example, M.V. Verzunov “Single-sideband modulation in radio communications.” - M., Voenizdat, 1972 - 296 p.). In addition, taking into account the coding based on phase shifts used in the prototype method, the values of phase shifts on the transmitting and receiving sides will differ, which will ensure a significant reduction in noise immunity (noise immunity) of reception.

In the proposed method, the random phase shift introduced by the radio channel is calculated from the pilot signal, which is a harmonic oscillation at the carrier frequency of the single-sideband modulation radio signal. Then, on the receiving side, before synchronous detection, the initial and channel values of the phase shifts are added to the phase of the reference oscillation of the synchronous detector. This demodulation method eliminates random changes in the phase of the radio signal, which increases the noise immunity of its reception.

The claimed method is illustrated by drawings, which show:

Fig. 1 – phase shifts in transmission and reception (example);

Fig. 2 – block diagram of the algorithm for implementing the proposed method;

Fig. 3 – simulation results.

The implementation of the proposed method of noise-free transmission of discrete signals based on single-sideband modulation involves the following technical operations.

1. Select a code with a constant weight to encode the subcarriers of the generated radio signal in such a way that the bit depth of the code corresponds to the number of subcarriers available for transmission.

2. The bit stream is divided into information blocks in accordance with the number of available code combinations that determine its alphabet, and each information block is assigned its own unique combination of code elements.

3. Signals are generated in the form of amplitude-keyed oscillations for the duration of each transmitted symbol only on those subcarriers to which information units correspond, after which additive addition of the generated signals on all subcarriers is carried out.

4. On the transmitting and receiving sides, the values of frequency and phase shifts are set, for which the frequency range from zero to two kilohertz and the phase change range from zero to three hundred and sixty degrees are divided into nine equal intervals (see Fig. 1), each of which fix a numerical value that determines the corresponding nominal frequency or phase shift, and a numerical value equal to the sum of the initial boundary value of the interval and the value that determines its length.

5. On the transmitting and receiving sides, for each information block, a random binary sequence of ten elements is formed, on the basis of which the first and second random numbers are obtained, and the first random number is obtained as a result of converting all elements of the generated binary random sequence into a decimal number, according to the first element which produces a second random number that takes the value of zero or one, respectively.

6. On the transmitting and receiving sides, the range of values of the first random number is divided into nine integer uniform intervals, each of which is sequentially assigned the values of frequency and phase shifts.

7. Determine the value of the radiation frequency, for which the value of the frequency shift corresponding to the value of the first random number is added to the nominal operating frequency, if the second random number is equal to one, if the random number is equal to zero, then the frequency shift is subtracted.

8. On the transmitting side, at an intermediate frequency, the resulting frequency-shift keyed signal is formed, on the basis of which a single-sideband modulation radio signal is formed at the emission frequency, and the carrier phase of the single-sideband modulation signal is chosen equal to the phase shift corresponding to the value of the first random number.

9. They emit a radio signal towards the correspondent.

10. On the receiving side, a radio signal is received at the radiation frequency.

The operations according to claim 1 – claim 10 are identical to similar procedures of the prototype method.

11. On the receiving side, before the technical demodulation procedure, the frequency of the received radio signal is converted ( $$S_{\text{OM}}(f_{\text{slave}})$$ ) from operating frequency ( $$f_{\text{slave}}$$ ) to the first intermediate frequency ( $$f_{\text{IF1}}$$ ), on which a highly stable first reference harmonic oscillation is formed ( $$u_{\text{OG1}}$$ ) with the initial phase shift ( $$\Delta {\phi }_{\text{ref}}$$ ) and unit amplitude (see Fig. 2 block T1).

The frequency conversion operation is known and is implemented, for example, in superheterodyne radio receivers of the R-160P, R-170P series.

The procedure for generating highly stable oscillations is known, is based on the use of highly stable reference oscillators, and is implemented in frequency synthesizers, for example, radio receivers of the R-160P, R-170P series. A distinctive feature of this operation is the addition of the initial phase shift to the phase of the generated oscillation. It is advisable to carry out this operation based on the use of controlled phase shifters, the technical implementation of which see, for example, (RF Patent No. 2738316 “Controlled Phase Shifter”. IPC N03L 7/08, published 12/11/2020. Bulletin No. 35).

The choice of intermediate frequency ratings is known and is described, for example, in (S.V. Dvornikov et al. Radio receivers. Textbook - St. Petersburg. VAS, 2016), implemented in radio receivers of the R-160P, R-170P series.

The formation of a unit amplitude is based on the use of broadband limiter circuits with amplification and narrowband limitation, see, for example, (S.V. Dvornikov and others. Radio receiving devices. Textbook - St. Petersburg. VAS, 2016) or (RF Patent No. 2233542 “Adaptive wideband amplifier-limiter-narrow-band amplifier". IPC N04V 1/10, publ. 06.18.2021, Bulletin No. 17).

12. At the first intermediate frequency, a pilot signal is isolated ( $$u_{\text{PS}}$$ ) of the received single-sideband modulation radio signal, the amplitude of the selected pilot signal is limited and it is fed to the mixer (see Fig. 2, block T2).

The operation of isolating harmonic oscillations is based on the use of quartz bandpass frequency filters. The requirements for bandpass frequency filters are known and are given, for example, in (S.V. Dvornikov et al. Radio receiving devices. Textbook - St. Petersburg. VAS, 2016) or in (M.V. Verzunov “Single-sideband modulation in radio communications.” – M., Voenizdat, 1972 – 296 p.).

13. Multiply the allocated pilot signal ( $$u_{\text{PS}}$$ ) with a limited amplitude for the first reference harmonic oscillation (see Fig.2 block T3).

This operation can be performed using a nonlinear electronic element, for example, a diode operating in a nonlinear mode. Another option for performing this operation is the use of digital microprocessor devices and performing multiplication operations based on digital signal processing, see, for example, (A.I. Solonina, D.A. Ulakhovich, etc. Fundamentals of digital signal processing. Textbook. - St. Petersburg BHV-Petersburg, 2005). The selection procedures and technical implementation of the use of microprocessor devices are given, for example, in (RF Patent No. 2273099 “Radio link with program tuning of the operating frequency.” IPC N04V 15/00, published 03.27.2006. Bulletin No. 9).

14. Measure the channel phase shift ( $$\Delta {\phi }_{\text{kan}}$$ ).

As a result of multiplying a pilot signal with a limited amplitude and the value of the first intermediate frequency by the first reference harmonic oscillation at the first intermediate frequency (see paragraph 13), harmonic oscillations will be obtained:

- at double (total) first intermediate frequency ( $$u_{\text{2ПЧ1}}^{+}$$ )

- low (difference, close to zero) frequency ( $$u_0^{-}$$ ).

Next, it is necessary to isolate the harmonic oscillation at a low (difference) frequency. Why is it advisable to use a low-pass filter with a bandwidth of several tens of hertz.

The operations described above in this paragraph, in combination with the operations given in paragraph 13, are implemented, for example, using a frequency converter consisting of a nonlinear element (for example, a diode) and a low-pass filter with a bandwidth of up to tens of hertz. Frequency converter circuits are known and are implemented, for example, in superheterodyne radio receivers of the R-160P, R-170P series.

Another option for performing this operation is to use digital microprocessor devices and perform multiplication and filtering operations based on digital signal processing, see, for example, (A.I. Solonina, D.A. Ulakhovich, etc. Fundamentals of digital signal processing. Textbook. – St. Petersburg, BHV-Petersburg, 2005).

The operation of calculating the channel phase shift is based on calculating the arc cosine function of the selected component at low frequency and can be performed on the basis of digital microprocessor devices (see Fig. 2 block T4).

15. The received single-sideband modulation radio signal is converted from the first intermediate frequency to the second intermediate frequency ( $$f_{\text{IF2}}$$ ), at which its synchronous detection is carried out at an intermediate frequency, and to the phase of the reference oscillation ( $$u_{\text{OG2}}$$ ) during synchronous detection, the values of the initial ( $$\Delta {\phi }_{\text{ref}}$$ ) and channel ( $$\Delta {\phi }_{\text{kan}}$$ ) phase shifts (see Fig.2 block T5).

The frequency conversion operation is well-known and is implemented in paragraph 11, as well as in superheterodyne radio receivers of the R-160P, R-170P series.

The operation of synchronous detection is similar to the prototype method, with the exception of the use of a reference (harmonic) oscillation for synchronous detection, to the phase of which the values of the original and channel phase shifts are added.

The procedure for adding phase shifts to the phase of the reference oscillation is similar to step 11, which proposes the use of controlled phase shifters.

16. The frequency-shift keyed signal is demodulated.

This operation is similar to the prototype method and is based on receiving the resulting frequency-shift keyed signal at subcarrier frequencies as independent frequency-spaced amplitude-shift keyed oscillations.

The results of the simulation (see Fig. 3) in the MatLAB environment for receiving single-sideband modulation signals in a channel with a random phase change based on the developed method (taking into account $$\Delta {\phi }_{\text{kan}}$$ ) confirmed a decrease in the symbol probability of error ( P _{error s} ) (up to 7 dB) of signal reception compared to the prototype (without taking into account $$\Delta {\phi }_{\text{kan}}$$ ), which indicates that the objective of the invention has been achieved.

Claims (1)

A method for noise-free transmission of discrete signals based on single-sideband modulation, which consists in choosing a code with a constant weight for encoding the subcarriers of the generated radio signal in such a way that the bit width of the code corresponds to the number of subcarriers available for transmission, breaking the bit stream into information blocks in accordance with the number of available combinations code that defines its alphabet, assign each information block its own unique combination of code elements, generate signals in the form of amplitude-manipulated oscillations for the duration of each transmitted symbol only on those subcarriers to which the information units correspond, after which they perform additive addition of the generated signals on all subcarriers, demodulate the resulting frequency-keyed signal at subcarrier frequencies as independent frequency-spaced amplitude-shift keyed oscillations, and set the values of frequency and phase shifts on the transmitting and receiving sides, for which the frequency range is from zero to two kilohertz and the phase change range is from zero to three hundred sixty degrees is divided into nine equal intervals, each of which is assigned a numerical value that determines the corresponding nominal frequency or phase shift, and a numerical value equal to the sum of the initial boundary value of the interval and the value that determines its length, and for each information block a random binary sequence is formed of ten elements, on the basis of which the first and second random numbers are obtained, and the first random number is obtained as a result of converting into a decimal number all elements of the generated binary random sequence, from the first element of which the second random number is obtained, taking the value zero or one, respectively, the range is divided values of the first random number into nine integer uniform intervals, each of which is sequentially assigned the values of frequency and phase shifts, the value of the radiation frequency is determined, for which the value of the frequency shift corresponding to the value of the first random number is added to the nominal operating frequency, if the second random number is equal to one , if the random number is zero, then the frequency shift is subtracted, the resulting frequency-keyed signal is formed on the transmitting side at the intermediate frequency, on the basis of which a single-sideband modulation radio signal is formed at the emission frequency, and the carrier phase of the single-sideband modulation signal is chosen equal to the original phase shift corresponding to the value first random number, emit a radio signal towards the correspondent, receive a radio signal at the emission frequency on the receiving side, demodulate the single-sideband modulation radio signal to an intermediate frequency, and the carrier phase of the single-sideband modulation signal is taken equal to the value of the phase shift corresponding to the value of the first random number, then demodulate the resulting frequency - a manipulated signal, characterized in that on the receiving side, before the technical demodulation procedure, the frequency of the received radio signal is converted from the operating frequency to the first intermediate frequency, at which a highly stable first reference harmonic oscillation is formed with an initial phase shift and a unit amplitude, then at the first intermediate frequency the pilot signal of the received single-sideband modulation radio signal, the amplitude of the selected pilot signal is limited and fed to the mixer, where the selected pilot signal with limited amplitude is multiplied by the first reference harmonic oscillation, the channel phase shift is measured, then the received single-sideband modulation radio signal is converted from the first intermediate frequency to the second intermediate frequency, at which its synchronous detection is carried out at the intermediate frequency, and the values of the initial and channel phase shifts are first added to the phase of the reference oscillation during synchronous detection by means of a controlled phase shifter.