ESTIMATION OF FADE DEPTH AND OUTAGE PROBABILITY DUE TO MULTIPATH PROPAGATION OF RADIO SIGNALS OVER SOUTHWESTERN NIGERIA

Abstract

The variation of point refractivity gradient with time of the day as well as seasons of the year provide information on the occurrence of multipath fading which often cause reduction in signal strength. For optimum services, it is of much importance to investigate the conditions experienced along the propagation path of a radiowaves in the troposphere. This study was carried out using six (6) years (January 2013 – December 2018) reanalysis data of parameters: Temperature, Pressure and Humidity obtained from the archive of the National European Centre for Medium Range Weather Forecast (ECMWF) over some locations in the southwestern part of Nigeria (Osogbo, Lagos, Akure Abeokuta, Ado-Ekiti and Ibadan). The data was employed to estimate the radio refractivity, point refractivity gradient, geoclimatic factor (K) at different intervals of time and the percentage of time that a certain fade depth A (dB) is exceeded in the average worst month. The percentage of time for the fade depth to occur (P w ) was deduced and the results shows that the diurnal variation of point refractivity gradient have their minimum values at 12 hr local time in all locations. The seasonal variation of the point refractivity gradient shows that high values of point refractivity gradient were observed in the dry season, which are well observed at the peak of dry season (January and December) in the region considered except for Lagos which is observed at early and late hours (00 hr and 18 hr). The fade probability for the worst month was highest in Lagos with a value of about 6.5% and the least value was recorded in Ado-Ekiti of about 2.7%. The values of the Geoclimatic factor K, shows a clear inverse relationship with point refractivity gradient and it indicated that the geoclimatic factor which represent geographical and climatic conditions in multipath fading distribution varies with the month, season and year.