86 research outputs found
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
Seasonal Variation of Surface Radio Refractivity and Water Vapour Density for 48 Stations in Nigeria
The monthly and seasonal variation of surface
refractivity and water vapour density were studied using thirtynine
years meteorological data for forty-eight stations in Nigeria.
The factors which influence the transmission of radio signals
operating within the troposphere are water vapour and
refractivity. The results show that the surface refractivity and
water vapour density generally have higher values during the
rainy season than dry season at all station studied. Furthermore
the results show that the value of surface refractivity and water
vapour density varies from about 263 N-units and 3 g/m3 in arid
region of Nigeria (North East) to about 393 N-units and 23 g/m3
in the coastal area of Nigeria (South West) respectively. For
optimal performance of terrestrial radio link across Nigeria it is
required to account for the variability of these parameters for
optimal systems design
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
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%
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
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
Analysis and comparison of tropospheric scintillation prediction models at Covenant University
Knowledge of tropospheric scintillation is an important phenomenon in the design of
satellite communication system. One year (January 2015-December 2015) scintillation data
extracted from Astra 2E/2F/2G Satellite link measurement installed at Covenant University,
Ota (Lat: 6.7 oN, Long: 3.23 oE) southwest Nigeria, at an elevation angle of 59.9o and a
frequency of 12.245 GHz was used in this study. The analysis and the result were compared
with some reputable scintillation prediction models so as to obtain best performance model for
Ota region. From the result, it was discovered that the Karasawa model gives the lowest
percentage error rate for both fade and enhancement of about 0.57% at 0.1 percentage of time
and 6.93% at 0.01 percentage of time respectively and therefore was best found fit for the
prediction of propagation impairment for the region. However, the model should be tested
further using higher frequency band such as Ka and V bands to confirm the accuracy of the
model. The information provided in this study will help in fade margin for antenna sizing and
performance needed for satellite communication link in the region
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
Freeze-thaw Resistance of an Alluvial Soil Stabilized with EcoSand and Asbestos-free Fiber Powder
Stabilization of poor soils subjected to large daily temperature variations requires careful selection of suitable stabilizer for improvement of such soils. This study investigated the freeze-thaw resistance of an alluvial soil stabilized with EcoSand and asbestos-free fiber powder (AFP). Physical and mechanical properties of the soil were determined. The soil sample was stabilized with 5 variants of equal mixtures of the EcoSand and AFP in proportions of 2, 4, 6, 8 and 10%, with 1% sodium silicate and 1% fly ash, by weight of the soil. UCS tests were conducted before and after three freeze-thaw cycles, while keeping the sample at 0ºC for 8 hours and later at 30ºC for 8 hours for each cycle. It was found that the 8% EcoSand + AFP with 1% sodium silicate and 1% fly ash content provided an optimized increase of the freeze-thaw resistance of the soil. The use of a mixture of EcoSand and AFP as a soil stabilizer for regions of the world experiencing large temperature variation has the potential to improve the resistance of sand to freezing and thawing
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
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