Investigation of OFDM Signal Reception Noise Immunity in Memory Channels
Students Name: Lonevskyi Nazar Andriiovych
Qualification Level: magister
Speciality: System Administration of Telecommunications Networks
Institute: Institute of Telecommunications, Radioelectronics and Electronic Engineering
Mode of Study: full
Academic Year: 2023-2024 н.р.
Language of Defence: ukrainian
Abstract: Modern communication systems provide users with a very wide range of services, and the expansion of this range requires an increase in the throughput and improvement of the system’s resistance to interference through the introduction of new technologies for the formation and processing of signals that carry messages. The main factor that prevents this in cellular communication channels is the energy dissipation of the transmitted signal in time (channel memory), frequency and space [1-3]. Adequate consideration of the time scattering in the channel requires special methods of signal formation at the transmission and the use of optimal signal processing algorithms at the reception. Among the modern technologies used in cellular communication networks, we should highlight the technology of orthogonal frequency division multiplexing (OFDM), which has become widespread in the creation of LTE cellular communication networks [4-5]. Every year and with each new communication standard, the frequency band is becoming wider, but there are limitations to this. Therefore, systems that combine several frequency channels into one are becoming more and more relevant. From a financial perspective, it is better to use a certain radio frequency spectrum more efficiently instead of expanding it. This can be done through the use of OFDM and MIMO technologies. The effect of channel memory on the signal is a rather large obstacle to the transmission of discrete messages over a communication channel. Thus, the study of the interference immunity of OFDM signal reception in a channel with memory is relevant. The first section analyses the properties of a wireless communication channel. The phenomenon of multipath signal propagation is considered. Fading and its impact on the communication channel are discussed, and the differences between fast and slow fading are shown. The second section shows how an OFDM group signal is formed on the transmitting side. MIMO technology, which is used in conjunction with OFDM, is considered. The process of demodulation on the receiving side of the OFDM signal is described. The third section discusses the basic principles of noise-resistant coding when transmitting a signal over channels with memory and fast fading. The algorithms for demodulation of OFDM signal in a memory channel are described. An improved OFDM system design to combat fast fading in memory channels is presented. The fourth section presents the results of modelling communication systems in a channel with memory and fast fading, and provides graphs of the noise immunity of these systems. The modelling and analysis of the obtained results of the OFDM system in assessing the impulse response of the channel with memory is carried out. The model of the MIMO-OFDM system is considered and the noise immunity graphs obtained as a result of modelling such a system for a channel with memory are presented. In the fifth section, an economic assessment of the creation of a software product for modern communication systems is carried out. Based on the calculations, the economic feasibility of such a project is proved.