Influence of the quality of functioning of the automatic gain control device on the noise immunity of reception of signal digital communication lines and correction of intersymbol distortions

The purpose of the research  is a theoretical assessment of the potential noise  immunity of quadrature amplitude modulation signals  in digital communication  lines under  the condition of imperfect parameters of the automatic gain control device.  
Methods. The research methods are based on the theory of potential noise immunity of multi-position digital signals, the fundamentals of quasi-optimal reception, and methods of mathematical modeling of signals. It is assumed that the synthesizer of heterodyne oscillations of the carrier and clock synchronization devices  in  the radio receiving system function ideally, i.e. the phases of the output oscillation of the heterodyne oscillation synthesizer and the output oscil- lation of the carrier recovery device are zero, there is no instability in the clock pulse repetition period, and the frequency response of the channel corresponds to the Nyquist condition. 
Results. Complex analytical models have been developed that allow estimating the potential noise immunity of multi- position QAM signals reception taking into account the influence of static and dynamic error factors in the operation of the automatic gain control device. It has been shown that the requirements for the accuracy of setting the signal level at the  input of  the decision device of the radio  receiving system become more stringent with  increasing modulation multiplicity. Thus, the results of mathematical modeling have shown that for the QAM-16, QAM-64, QAM-256 and QAM- 1024 modulation types, the static error in setting the signal level at the input of the decision device should be no more than 0,27, 0,12, 0,054 and 0,027 dB, respectively. The specified values, as shown by the calculations and the obtained theoretical dependencies, allow obtaining acceptable values of the equivalent energy loss level, which does not exceed 0,3 dB. 
Conclusion. It is shown that the development and design of adaptive correctors of intersymbol distortions is a very relevant direction for increasing the noise immunity of radio receiving systems, allowing to compensate for the imper- fection of the characteristics of various structural and functional elements of multi-position digital signal demodulators, including the automatic gain control device. In correctors of complex signal demodulators, the most appropriate criterion is  the minimum mean square error. The lowest  level of the square error  in the range of low signal-to-noise ratios  is provided by an algorithm  that  is a combination of a modified start-stop algorithm and a  two-mode algorithm  with a constant modulus. 

1. Makarov S.B., Zavyalov S.V., Ovsyannikova A.S. Optimization of the shape of signals with quadrature amplitude modulation using the criterion of a given rate of decay of the level of out-of-band emissions. Computing, Telecommunications and Control = Proceedings of Russian Universities. Radio Electronics. 2022;25(4):6–22. (In Russ.) https://doi.org/10.32603/1993-8985-2022-25-4-6-22

2. Ershov I.A., Danishevsky N.S. Methodology for calculating the automatic gain control system in amplifiers of receiving devices. Computing, Telecommunications and Control. 2022;15(3):22–37. (In Russ.) https://doi.org/10.18721/JCSTCS.15302

3. Alyoshintsev A.V. Optimization of the structure of a multi-frequency modem. T-Comm: Telekommunikatsii i transport = T-Comm: Telecommunications and Transport. 2021;15(6):10–19. (In Russ.)

4. Belov A.D., Polushin P.A. Methods of "soft" and "hard" correction to combat intersymbol distortions of digital signals. Proektirovanie i tekhnologiya elektronnykh sredstv = Design and Technology of Electronic Means. 2020;(1):33–37. (In Russ.)

5. Polushin P.A., Arkhipov N.A., Shalina V.V. Efficiency of "physical" and "logical" correction of intersymbol distortions of digital signals. Radio-tekhnicheskie i telekommunikatsionnye sistemy = Radio Engineering and Telecommunication Systems. 2023;(2):21–28. (In Russ.) https://doi.org/10.24412/2221-2574-2023-2-21-28

6. Lobov E.M., Alaa A. Review of existing methods for correcting intersymbol distortions of radio signals in digital communication systems using machine learning. Telekommunikatsii i informatsionnye tekhnologii = Telecommunications and Information Technologies. 2023;10(1):109–119. (In Russ.)

7. Polushin P.A., Arkhipov N.A., Shalina V.V. Modification of the coding method in the fight against intersymbol distortions of digital signals with QPSK modulation. Radiotekhnicheskie i telekommunikatsionnye sistemy = Radio Engineering and Telecommunication Systems. 2023;(1):33–40. (In Russ.) https://doi.org/10.24412/2221-2574-2023-1-33-40

8. Sharamet A.V., Azarov I.S. Features of the receiving path in a multi-channel radar station with temporary automatic gain control. Tsifrovaya obrabotka signalov = Digital Signal Processing. 2023;(3):47–51. (In Russ.)

9. Dovbnja V.G., Koptev D.S. Influence of the quality of heterodyne operation on the noise immunity of reception of signals with quadrature amplitude modulation. Radiotekhnika = Radio Engineering. 2020;84(9):40–48. (In Russ.) https://doi.org/10.18127/j00338486-202009(17)-03

10. Dovbnya V.G., Koptev D.S. Main directions of increasing the noise immunity of radio receiving systems based on spatio-temporal processing of complex signals in the antenna device. Izvestiya Yugo-Zapadnogo gosudarstvennogo universiteta. Seriya: Upravlenie, vychislitel'naya tekhnika, informatika. Meditsinskoe priborostroenie = Proceedings of the Southwest State University. Series: Control, Computer Engineering, Information Science. Medical Instruments Engineering. 2020;10(1):36–50. (In Russ.)

11. Dovbnya V.G., Koptev D.S., Herman Floresmilo L.R., Podkhaldin G.I. Evaluation of the value of equivalent energy losses due to the quality of frequency synthesis functioning in digital communication systems with quasi-coherent reception of signals with quadrature amplitude keypad. T-Comm. 2023;17(5):58–63. https://doi.org/10.36724/2072-8735-2023-17-5-58-63

12. Bobrovsky V.I., Latypova S.S. Modification of a signal design with thirty-two-position quadrature amplitude keying. Tekhnika sredstv svyazi = Communication Equipment. 2018;(4):36–47. (In Russ.)

13. Dovbnja V.G., Gulamov A.A., Babanin I.G., Koptev D.S. Evaluation of noise immunity of wireless digital communication systems exposed to interference via side reception channels. Izvestiya Yugo-Zapadnogo gosudarstvennogo universiteta. Seriya: Upravlenie, vychislitel'naya tekhnika, informatika. Meditsinskoe priborostroenie = Proceedings of the Southwest State University. Series: Control, Computer Engineering, Information Science. Medical Instruments Engineering. 2018;8(3):35–40. (In Russ.)

14. Savishchenko N.V., Issa A., Ishimov A.S., Popov E.A. Calculation of the error probability in a channel with general κ-μ fading and additive white Gaussian noise. Radiotekhnika = Radio Engineering. 2023:87(3):109–121. (In Russ.) https://doi.org/10.18127/j00338486-202303-11

15. Sannikov V.G., Volchkov V.P. Increasing the noise immunity of a modem with optimal finite signals that do not cause intersymbol interference in a linear communication channel. Telekommunikatsii i informatsionnye tekhnologii = Telecommunications and Information Technologies. 2019;6(2):19–28. (In Russ.)

16. Adzhemov A.S., Kudryashova A.Yu. Study of minimizing the probability of errors arising from four-fold discrete modulation methods. SVCh-tekhnika i telekommunikatsionnye tekhnologii = Microwave Engineering and Telecommunication Technologies. 2022;(4):31–33. (In Russ.)

17. Degtyarev A.N., Koneva S.A. Minimizing the error probability in weighted reception of a message with two-position pulse-code manipulation under conditions of intersymbol interference. Zhurnal radioelektroniki = Journal of Radio Electronics. 2024;(6). (In Russ.) https://doi.org/10.30898/1684-1719.2024.6.1

18. Flaksman A.G., Sorokin I.S., Kokarev A.O. Minimizing the bit error probability in a multi-stage relay MIMO system. Trudy uchebnykh zavedenii svyazi = Proceedings of Educational Institutions of Communication. 2020;6(4):36–44. (In Russ.) https://doi.org/10.31854/1813-324X-2020-6-4-36-44

19. Kudryavtsev A.A., Shestakov O.V. Asymptotic behavior of the loss function in the method of multiplicative scaling of wavelet coefficients of the signal function. Vestnik Moskovskogo universiteta. Seriya 15: Vychislitel'naya matematika i kibernetika = Bulletin of Moscow University. Series 15: Computational Mathematics and Cybernetics. 2017;(1):16–19. (In Russ.)

20. Zhirnov A.I., Orlov E.V., Egrushev V.E., et al. Analysis of methods for combating intersymbol distortions in digital tropospheric communication lines. Innovatsii. Nauka. Obrazovanie = Innovations. Science. Education. 2021;(42):874–879. (In Russ.)

21. Atakishchev O.I., Ryumshin K.Yu., Amelenkov A.A., Zhuravlev A.P. Features of the implementation of a block signal demodulator with quadrature-amplitude modulation. Izvestiya Instituta inzhenernoi fiziki = Bulletin of the Institute of Engineering Physics. 2021;(4):16–19. (In Russ.)

22. Bazarov T.O., Senko M.A., Samodelkin L.A., et al. A system of digital signal processing algorithms for coherent optical communications. Zhurnal tekhnicheskoi fiziki = Journal of Technical Physics. 2024;94(6):894–912. (In Russ.) https://doi.org/10.61011/JTF.2024.06.58131.3-24

23. Kochubey R.I., Bychkovsky M.M., Zaykin N.N., et al. Principles of signal generation with orthogonal frequency multiplexing. Izvestiya Tul'skogo gosudarstvennogo universiteta. Tekhnicheskie nauki = Proceedings of Tula State University. Technical Sciences. 2024;(1):134–141. (In Russ.) https://doi.org/10.24412/2071-6168-2024-1-134-135