http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
Fade dynamics modelling for earth-satellite links at Ku-Band in tropical region
International Islamic University Malaysia
Kulliyyah of Engineering, International Islamic University Malaysia
Effects of the earth's atmosphere on radio wave propagation are concerned in the design and performance of satellite communication systems. Frequencies above 10 GHz are currently employed in modern satellite systems with higher bandwidth for very large channel capacities requirements. However, the operation of high frequencies is vulnerable to atmosphere and highly sensitive to tropospheric changes. Signal at Ku-band and above is severely attenuated by rain and performance degraded seriously in tropical regions. In order to design and operate a modern satellite system in tropics, suitable rain fade mitigation techniques must be adopted to meet satisfying availability and Quality of Service. The dynamic characteristics of rain fade such as fade slope, fade and interfade durations and scintillation are important parameters to design rain fade mitigation techniques for highly reliable Ku-band services and severe rain fade period. Several prediction models were proposed by ITU-R and other researchers to estimate dynamic characteristics of rain such as fade slope, fade duration, interfade duration and scintillations. All of these were developed based on measurements done in non-tropical regions. Hence it is an urgent need to verify all models and propose more suitable models for tropical region. Characteristics of dynamics behaviour and scintillation are determined and proposed the model based on measurement. One year received signal levels at Ku-band from MEASAT3 were collected concurrently with rain intensity data in Kuala Lumpur, Malaysia. Measured fade slope, fade duration and scintillation are compared with those predicted by available prediction models. Prediction models are unable to fit with measured data for almost all of the cases. Standard deviation of measured fade slope is found nonlinear while it is proposed as linear by ITU-R model for all attenuation levels. A modification of ITU-R fade slope model is proposed for tropics. Short fade duration is less than 30s mainly caused by scintillation and long duration is exceeded 30s caused by rain. Based on measured fade duration statistic, Cheffena-Ayama model has similar trend to measured data comparing to other prediction models. Cheffena-Ayama model is modified and propose for Malaysian tropical climate. Measured scintillation amplitudes and intensities are found higher during rains than non-rains. Scintillation statistics in dry season is found higher than wet season due to meteorological conditions. Probability density function of scintillation intensity (standard deviation) agrees with Generalized extreme value (GEV). Based on measured data, none of prediction models can predict scintillation amplitude accurately. Since prediction models proposed for fade slope, fade duration and scintillation were developed based on elevation angle below 50˚, they are unable to predict the measured data statistics accurately. Therefore, empirically developed fade slope and fade duration models are proposed and will be valid for similar tropical climates and high elevation angles. These findings can be utilized for planning and designing fade mitigation techniques to overcome severe rain effects on earth-to-satellite microwave links operating at Ku-band in tropical regions.
Thesis (Ph.D)--International Islamic University Malaysia, 2013.
Includes bibliographical references (leaves 169-177).