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Wireless mobile relay communication system with two sections operating over short term fading channel in the presence of co-channel interference subjected to small scale fading has been considered. Desired signal experiences Nakagami-m fading and co- channel interference experiences Rician fading. Desired signal at output of the second section has Nakagami-m*Nakagami-m distribution. The signal-to-interference ratio of product of two Nakagami-m random variables and Rician random variable has been presented. In this paper, closed form expresions for moments of signal- to-interference ratio of considered system are calculated. The influence of Nakagami-m short term fading severity parameter and Rician κ factor on presence is analysed and discussed. Mobile relay communication system with two sections can lead to a more reliable and efficient transmission, which is of great importance in the risky environments. Key words: Nakagami-m fading, Rician fading, moment, mobile relay communications system

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In this paper, using simulation in the software OptiSystem 7.4, the FSO (Free Space Optical) system operating at wavelengths of 850 nm, 1315 nm and 1550 nm was observed. The influence of different levels of atmospheric turbulence and link distance on the signal transmission quality was investigated. The Q factor and BER (Bit Error Rate) were used as a measure of quality. The changes of the Q factor depending on the observed system parameters are graphically shown. Eye diagrams and signal spectrum are also given. The analysis of the results shows how the quality of the received signal changes due to different atmospheric phenomena at certain distances from the transmitter.

Kratak sadržaj: U radu je prikazan uređaj za magnetni monitoring stanja asinhronih motora sa kaveznim rotorom, razvijen u Institutu Nikola Tesla, Beograd. Uređaj je zasnovan na merenju rasutog magnetnog fluksa i spektralnoj analizi signala. Senzor rasutog magnetnog fluksa je vazdušna prstenasta zavojnica različitih prečnika koja se postavlja osno simetrično na poklopac kućišta motora. Elektromotorna sila na krajevima zavojnice, nastala kao posledica promene slabog magnetnog polja, je niske magnitude. Nakon neophodnih pojačanja i prilagođenja, signal se u akvizicionom delu digitalizuje i memoriše. Pogodnim algoritmima se vrši obrada signala, prvenstveno FFT analiza. Dobijeni rezultati se dalje analiziraju prema karakterističnim frekvencijama za date karakteristike motora, njegovog opterećenja i stanja. U radu su date neke karakteristične analize spektra signala rasutog magnetnog fluksa koje su deo dijagnostike stanja motora.