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

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.