Date of Award
Master of Science
Electrical and Computer Engineering
Wireless communications systems of all types must deliver reliable connections to the end users to be accepted by the public. The reliability of these systems is composed of two aspects. The first aspect is the reliability of the actual hardware and software composing the device and is completely under the control of the designers of the equipment. The second aspect of reliability or availability is the wireless propagation link connecting the users. This link is very difficult to model exactly and is composed of a fixed propagation loss plus random elements of propagation loss.This thesis focuses on the propagation links associated with satellite communications systems (Satcom). The fixed portion of the link loss in this case is the "spreading loss" or free space loss which occurs due to the large distance between the user and the satellite. The random portion of the link loss in these systems is due to many things such as rain, absorption, shadowing, multipath and cross polarization effects. However the major element associated with fades in Satcom systems is rain and the fades associated with rain. Rain becomes an even more dominate term in the situation as higher frequencies are used to obtain the increases in bandwidths required to accommodate the increases in use. Rain fades on the satellite links are modeled as random processes whose parameters are given in RECOMMENDATION ITU-R P.837-5 of the International Telecommunications Union (ITU). Over the years this recommendation has been revised and the current revision is 837-5 as indicated above. However, the data used to develop these models has always come from the European Centre for Medium-range Weather Forecasts based upon data measured at approximately 100 stations around the world. Since 1998 satellite sensory data is available for the tropics which directly measures rain data in this area. The Tropical Rainfall Measuring Mission (TRMM) is a join satellite project involving the USA and Japan. As a result of the availability of TRMM data it is possible to improve the statistical rain rate models for the tropical regions of the world. Recently a number of researchers (T.V, Omotosho, C.O. Oluwafemi, C Prabhakara et all) have begun to use TRMM data to improve the rain rate and rain fade estimates. The ITU has also begun to study using TRMM data in their recommendations. In this thesis the TRMM data is used to construct a rain rate and rain fade models for the Indian sub-continent as well as other parts of the tropics. This model is compared to the predictions based upon the ITU 837-5 models and substantial differences are found in the heavy rain fall areas. India is currently building a satellite (GSAT-4) to measure rain fades at 20/30 GHz and it is hoped that these results can be used to compare with the measured GSAT-4 data when it is available.
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