COMPARATIVE STUDY OF BISTATIC INTERSYSTEM INTERFERENCE LOCATIONS

Abstract

Very many prediction models have been used in recent times to estimate transmission loss arising from Bisastic scattering of terrestrial microwave signals into the receiver of Earth-space communication systems operating at the frequency. Among the models, Capsoni Simplified 3-D EXponential rain CELL (EXCELL) model has yielded the most satisfactory results for interference prediction in all rainfall climate regions. In the model, the horizontal structure of rain is the same in all region, hence only the measured cumulative distribution of point rainfall rates in the region of interest is required. This study is based on this model. It uses as input measured cumulative distribution of rainfall rates from three locations in Africa, Ile-lfe (Nigeria), Nairobi (Kenya) and Douala (Cameroon) to estimate bistatic intersystem interference (transmission loss) due to hydrometeor scattering of signals from terrestrial microwave system into the receiving terminal of a ground Earth-space communication system. Two elevation angles, 230 and 550, which are the prominent satellite look angles in Nigeria are considered. The transmission loss statistics computed for varying distances from the terrestrial System (TS) antenna to the common volume (CV) formed by the intersection of the antenna beams, varying antenna gains and varying percentage unavailabilities. Frequencies ranging from 4 to 35 GHz and two path length configurations short (≤50km) and long (> 50km) are considered; Results obtained showed that transmission loss increases with increasing TS to CV distance, implying decreasing possibility of severe interference in the sastelite system. The Variation of Transmission loss with increasing TS antenna gain shows that transmission increases with decreasing time unavailability (exceedance probability). The study also shows that for a given fade depth, the higher TS antenna gain, the higher is the probability of the ground satellite receiver picking severe interference from the terrestrial microwave network, Further, comparing the results in Kenya and Cameroon with Nigeria; it was observed that variation of transmission loss with TS to CV distance is lower by 1.3% in Kenya, while it is higher by 1.4% in Cameroon for 0.01%-time unavailability. Therefore, in Cameroon, the satellite ground receiver system is more likely receive higher interference from a microwave transmitting system Operating at the same frequency. Evaluation of the effective transmission loss in these regions also show the possibility of complete signal outage due to rain attenuation in Cameroon compared to other locations, no matter the amount interference received from the microwave system. This is because of the higher rainfall intensity find accumulated water in Cameroon.