Investigation of Low Clouds Attenuation on Earth Space Path for some West-Africa Stations

The study investigate the contribution of low clouds, to signal fade rate, at Ka band in the satellite communication links on earth-space path(s) to NigComSat 2, from three tropical locations in West Africa. Extracted cloud cover statistical data such as average cloud amount, average base height, and frequency of occurrence, were used to obtain the monthly variations and seasonal variations for Lagos (6.55o, 3.35o), Bouake (7.73o, -5.07o) and Bamako (12.53o, -7.95o). Cloud attenuation statistics were computed for each of the three stations for their respective uplink and downlink. The uplink and downlink attenuation ranges between about 0.2 to 1.6 dB and 0.1 to 0.8 dB respectively for Lagos; for Bouake between 0.005 to 0.035 dB and 0.003 to 0.016 dB respectively; finally, for Bamako between about 0.2 to 2 dB and about 0.1 to 1 dB respectively. The stations downlink attenuation sets of values are generally about twice their corresponding uplink attenuation values

ATMOSPHERIC GASES ATTENUATION IN WEST AFRICA

Atmospheric gases variations were evaluated to have major effect on Ku-band and above at 0.01 % unavailability of an average year on both uplink and down link. The International Telecommunication Union Radio Propagation Recommendation (ITU-RP 676, 2012) data bank was used for the computation of gaseous attenuation for West Africa. Monthly and yearly mean of temperature, pressure and relative humidity were used as input parameters obtained from ITU-R study group 3 data base. The results presented on contour map show that total atmospheric absorption signal fade attenuation values at C, Ku, Ka and V bands is between 0.015 to 0.09 dB, 0.04 to 0.9 dB, 0.04 to 1.4 dB and 0.2 to 3.2 dB respectively for both uplink and downlink frequencies. Generally, consistent signal absorption due to Oxygen and water vapour are higher in the western region than southern part of West Africa

Tropospheric Scintillation and its Impact on Earth- Space Satellite Communication in Nigeria

The study investigates the impact of tropospheric scintillation on fixed satellite communication link on earth-space path for frequencies between 10 and 50 GHz for 37 stations in Nigeria. Elevation angles of 5º, 55º which are typical look angles for links over the Atlantic Ocean region and Indian Ocean region, look angles to the Nigeria Communication Satellite was also considered. Meteorological climatic data retrieve from satellite such as; profiles of temperature, pressure, and relative humidity, were validated with the available ground data in Nigeria. These data were reprocessed to derive radio propagation input parameters, such as; water vapour density integrated water vapour content and radio refractivity. Secondly, the International Telecommunication Union Propagation model (ITU-P 618, 2009) was used to estimate tropospheric scintillation for time unavailability between 0.01 to 10% in an average year. The result shows that scintillation fade depth is between 4.0 to 19.0 dB and 0.2 to 1.3 dB at 5º and 55º elevation angles respectively. For links to NigComsat scintillation fade depth is between 0.05 to 1.26 dB for all the 37-locations. The results will help in designing, planning and quick integration and expansion of satellite telecommunication services in the six regions of Nigeria

Analysis of non-rainy attenuation on earth-space path in Ota, Southwest Nigeria

Propagation effects due to atmospheric gases and tropospheric scintillation requires accurate modelling in the design of satellite communication systems. The combination of the two attenuation phenomena was observed within the period of August 2014 to December 2015. The result of this paper presents the on-going observation and data analysis of non-rainy attenuation on earth-space path in Ota, Southwest Nigeria. Results of clear-sky attenuation vary between 0 dBm and 4.85 dBm in January and February 2015 respectively. While a value of 4.23 dBm and 4.75 dBm were observed in October 2014 and 2015 respectively. The results will be useful for satellite communication system design and will be submitted to ITU-R Study group 3 Databank

Earth-Space Rain Attenuation Prediction: Its Impact at Ku, Ka and V-band Over Some Equatorial Stations

Attenuation due to rain predictive models have been used to calculate the impact of rainfall on satellite communication for six stations in Malaysia. The impact of rainfall is very important for designing a modern satellite system for heavy rainfall climatic regions like Malaysia, with large annual rainfall accumulation exceeding 3000 mm and rainfall rate exceeding 150 mm/h at Ku (12/14 GHz), Ka (20/30 GHz) and V (40/50 GHz) bands. The present result shows that the avalibility of link for 99.99% at the three bands for uplink and downlink to Malaysian Communication Satellite (MEASAT-3a) is not practicable. The results suggest link availability of 99.9% for Ku-uplink and Ka downlink, while 99% for Ka uplink and 99% for V band uplink and downlink due to high annual rainfall rates for most of the stations. The overall result shows that the impact of heavy rainfall on satellite communication will be more severe in the Eastern part than the Western of Malaysia

Proposed Model for the Estimation of Rain Attenuation: At Ku-Band at Ota, a Tropical Location

This study proposes a model for calculating rain attenuation on earth-space path carried out in Covenant University, Ota, Nigeria, a tropical location. The beacon signals from a geostationary satellite - ASTRA 28°E (2E/2F/2G) was monitored, recorded and analysed using a spectrum analyzer operating at frequencies of 12.245 GHz. Rain rates at the station of the antenna receivers were also logged and analysed. The rainfall rate cumulative distributions and the resultant rain attenuation are obtained and presented. The results obtained showed that the cumulative distribution of the measured rainfall rate is not in agreement with ITU-R prediction. Rainfall rate at 0.001 %, 0.01 %, 0.1 % and 1 % were fed into the existing Simple Attenuation Model (SAM) and corresponding rain attenuation were obtained. The measured rain attenuation from the beacon signal was compared with sixteen existing rain attenuation models in literature only SAM model was closed to the measured result at the location. SAM model overestimated and underestimated the rain attenuation for this location at some percentage of time. Hence, a modified SAM model is proposed using newly obtained specific attenuation coefficients. The proposed modified model is found to be close to the measured rain attenuation

Four Year Cloud Attenuation Study in a Tropical Station

The paper present four year results of Cloud attenuation measurements carried out at Covenant University, Ota, Nigeria. The links operate at frequency of 12.245 GHz and the cumulative distribution function for monthly Cloud attenuation have been estimated from the 4-year measured spectrum analyser data. The result of the visually measured Cloud and Satellite Cloud cover data are presented. The monthly variability shows that the highest cloud attenuation at the station occur in August, reaching a maximum of 3.96 dB for 0.01% of time; which corresponding to an average cloud cover of 89.86% and 75.36% by ground and satellite data respectively of which Nimbostratus (Ns) is average of 29.1%. The lowest cloud attenuation at the station occur in September, with a value of 2.5 dB for 0.01% of time; corresponding to an average cloud cover of 90.3% and 77.26% by ground and satellite data respectively, of which Nimbostratus (Ns) is average of 28.9%

Total Attenuation of Satellite Signal on Earth‐Space Link in West Africa

The study examines the consequence of total attenuation impairments on fixed satellite communication link on earth‐space path in West Africa for 0.01 % unavailability of an average year. The International Telecommunication Union Radio Propagation Recommendation (ITU‐RP 618, 2012) procedure and study group 3 data bank base was used for the computation of total attenuation for seventeen (17) West Africa countries for both uplink and downlink frequencies. The results reveal lowest value at C‐band which gradually increases at Ku and Ka bands while the highest values of total attenuation are experienced at v‐ band for all the locations. Both uplink and downlink results at v‐bands show constantly that total attenuation is more severe (more than 100 dB) in countries like Togo (139.64 dB), Liberia (138.55 dB), Ghana (138.20 dB), Benin (134.19 dB), Ivory Coast (132.75 dB), and Nigeria (122.42 dB). It should be noted that all stations are in the tropical region of West Africa where rainfall is very high and therefore will experience more signal loss due to the presence of rain, cloud, oxygen, and water vapor even in clear‐sky or none rainy conditions. The overall results will be helpful for system planning and better performance of satellite communication link in West Africa region

Impact of Tropospheric Scintillation Models on Earth-Space Path in Southwest, Nigeria

signals being attenuated by rain, cloud, gas and tropospheric scintillation. This paper present the impact of tropospheric scintillation on earth-space path in southwest, Nigeria at 12.245 GHz. Twenty-four months of scintillation data from ASTRA 2E/2F/2G on latitude 6.7° N and longitude 3.23° E for two years (2015-2016) were statistically analysed and compare with four existing models. The result reveals that under non-rainy atmosphere, ITU-R model gave the lowest percentage error of about 1.07%, followed closely by Karasawa model with 1.67%. The work also shows that ITU-R is the best fit model of tropospheric scintillation fade for the study area at 1% of time. A modified ITU- R scintillation fade model was also proposed for the tropical region of Ota and its environs

STUDY OF OXYGEN AND WATER VAPOUR ATTENUATION IN WEST AFRICA

Atmospheric gases such as Oxygen and water vapour attenuation has become a major concern on earth-space path at higher frequencies both uplink and down link at 0.01% unavailability of an average year. Moreover, few studies of non-rainy attenuation have been reported and the statistical analysis is still not clear most especially in West Africa. The meteorological data used in this study is obtained from Atmospheric Infrared Sounder (AIRS) satellites between 2002 and 2009, while the International Telecommunication Union Radio Propagation Recommendation (ITU-RP 676) model is used to validate and estimate gaseous attenuation for West Africa. The results show on contour map that total atmospheric absorption signal fade attenuation values at C band is between 0.015 to 0.09 dB, Ku band is 0.04 to 0.9 dB, Ka band is 0.04 to 1.4 dB and V band is 0.2 to 3.2 dB respectively for both uplink and downlink frequencies. The results also show consistent increase in attenuation due to gases are higher in the western region than in the southern part of West Africa