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• DEVELOPMENT OF ADAPTIVE OFDM-BASED COMMUNICATION SYSTEM FOR TROPOSPHERE AND RADIO RELAY CHANNEL

  P.V. Luferchik, А.А. Komarov, P.V. Shtro, А.N. Konev

  2022-11-01

  Abstract ▼

  It is known that inter-symbol interference may occur during data transmission in radio relay
  and tropospheric communication systems. The presence of multipath propagation, frequencyselective
  fading and extreme instability in the tropospheric and radio relay channel significantlyreduces the energy efficiency of the communication system. The aim of the work was to increase
  the efficiency of using the channel for radio relay and tropospheric communication by using
  OFDM (orthogonal frequency-division multiplexing) signals in the system using adaptive coding
  and modulation. In the course of execution, the modulator and demodulator models of the OFDM
  signal are implemented. When using various signal code structures in various reception/
  transmission conditions, it is possible to achieve optimal use of the frequency and energy
  resources, to create systems that adapt to the conditions of signal propagation. To implement this
  mechanism, a service field was introduced into the transmitted service data, which contains information
  about the code rate used, the modulation type, and the interleaving depth. This approach
  allows optimizing the use of energy and frequency resources. Together with the use of channel
  quality estimation algorithms, it becomes possible to dynamically change the signal-code structure
  when the reception conditions change. By adjusting the interleaving depth, it is possible to optimize
  the S/N threshold or the amount of information delay in the channel, depending on the system
  requirements. The use of adaptive choice of code rate and modulation will allow more efficient use
  of the channel resource with a constant change in its state. The obtained results will significantly
  increase the energy efficiency of the OFDM system, lead to stable communication in nonstationary
  channels and increase the throughput.

• DEVELOPMENT OF ENERGY EFFICIENT COMMUNICATION SYSTEM IN THE TROPOSPHERE RADIO CHANNEL BASED ON OFDM SIGNALS

  P.V. Luferchik, P.V. Shtro, А.N. Konev, А.А. Komarov

  2022-11-01

  Abstract ▼

  It is known that inter-symbol interference may occur during data transmission in radio relay
  and tropospheric communication systems. The presence of multipath propagation and frequencyselective
  fading in the tropospheric, radio relay channel significantly reduces the energy efficiency
  of the communication system as a whole. The aim of the work was to increase the efficiency of
  using the channel for radio relay and tropospheric communication by using OFDM (orthogonal
  frequency-division multiplexing using the methods of reducing the peak factor of the OFDM signal
  and increasing the linearity of the transmission path. To evaluate digital predistortion algorithms
  in the Matlab/Simulink environment, a model was developed for the LMS, NLMS, RLS, RPEM
  methods and a power amplifier model with real characteristics. Based on the results of modeling
  algorithms, RLS was chosen. In addition, in this work, a modified version of the adaptation algorithm
  based on the recursive least squares method (RLSm) was developed. The main result of the
  modification is: a decrease in the number of arithmetic operations per iteration (more than
  5 times), an increase in the stability of adaptation algorithms, due to the introduction of regularization
  methods, a decrease in the convergence time, due to the introduction of an exponential dependence.
  Various algorithms for reducing the peak factor of an OFDM signal were investigated,
  the best result was achieved by combining Tone reservation (TR) and Active constellation extension
  (ACE). Simulation in the Matlab/Simulink environment showed that the combination of TR
  and ACE algorithms reduces the peak factor of OFDM signals by ~5dB for BPSK data stream and
  ~4.5dB for 8-PSK, QAM-16, QAM-64, QAM-128 and QAM- 256. To increase the linearity of the
  transmission path, the RLSm digital pre-distortion algorithm was selected and upgraded, it made
  it possible to reduce the magnitude of the error vector modulus (EVM) by 13.5dB, and also increase
  the modulation/error ratio (MER) by 13.6dB.

• INVESTIGATION OF THE INTERFERENCE BACKGROUND AT THE INPUT OF THE RECEIVER OF THE NEAR-FIELD MAGNETIC COMMUNICATION SYSTEM IN URBAN CONDITIONS

  А. N. Konev, А.А. Komarov, P.V. Luferchik, P.V. Shtro

  2023-02-17

  Abstract ▼

  Near-field magnetic communication (NFMC) has unique characteristics, such as secrecy,
  communication channel security, the ability to pass a signal through the vast majority of obstacles
  without significant attenuation. NFMC can be used in such use cases where traditional radio is
  impossible. One of the tasks in which the use of NFMC is relevant is to provide reliable wireless communication for rescuers, firefighters, employees of the Ministry of Emergency Situations when
  performing their professional activities in the conditions of blockages caused by various destructions
  of urban buildings. It should be noted that under such conditions, the conductivity of building
  materials and soil can affect the propagation of not only electric, but also magnetic fields. The fact
  is that due to the conductivity of such materials, when using radio coupling, eddy currents arise in
  the materials, which leads to the appearance of a secondary magnetic field that is in antiphase.
  The system under consideration is not subject to the effects described above. This article presents
  the results of experimental studies aimed at studying the interference environment in the NFMC
  channel. Field experiments were carried out to measure the interference environment. Based on
  the data obtained, it was concluded that the use of NFMC systems in urban environments is a rather
  difficult task due to the nature of the interference propagating in the channel of this type of
  communication. The effective use of NFMC requires the development of receiving devices that
  provide sufficiently strong filtering of signals outside the selected band. Narrow band and high
  order filtering is key priority of observed communication system.