ABSTRACT

Telecommunication market is driven by the increasing need of the end users for multimedia services which require high data rates. Within the fixed satellite service, frequency bandwidths wide enough to carry such high data rates are to be found in Ka band (26 - 40 GHz), and Q/V bands (33 - 50 GHz)/(40 - 75 GHz). However, at Ka band and above, transmitted signals can be severely affected by tropospheric attenuation for substantial percentages of time, resulting in the degradation of the quality and of the availability of communication services. Fade Mitigation Techniques (FMTs) must be used to counteract these severe propagation impairments. The significance ofthis work cannot be over emphasized it will give engineering designers and International Telecommunication union (ITU) insight to the effects of rain attenuation in the tropics and better mitigation techniques. Also it will serve as a pre-design tool for microwave engineers. In this thesis we explored the use of two ofthe most promising techniques, known as Site diversity and Adaptive Transmission power control (ATPC), these two techniques do not change the basic signal format nor require large bandwidth. Some of our accomplishments include, but are not limited to: a methodology to describe rain attenuation conditions for multiple users in large geographical areas, sighting of three site stations located at distances between 42 and 64kms as site diversity stations, comparing data measured by NIMET with ITU-R and Hodge models to determine which of the data is more reliable for the South East tropical region. Comparison of performance between transmission using site diversity and transmission without site diversity. Finding out the impact of distance, frequency, elevation angle and azimuth of the earth station on the site diversity gain. In addition we tried using adaptive power control to complement the site diversity; we considered transmission with adaptive power control and without adaptive power control. Similarly, a simulation on site diversity was carried out using three earth stations. Likewise, similar simulation was carried out for adaptive power control using Ziegler-Nichols technique for proportional integral derivative (PID) power control. In the course ofthis study we found out that the site diversity gain depends on the separation between the two sites, the frequency, the elevation angle and the azimuth of the propagation path with respect to the baseline between the two or more sites. On the other hand the improvement factor depends on the distance between the stations, angle of elevation and the azimuth of the earth stations. There is an indication that at higher frequencies the diversity gain decreases. On the adaptive power control: the normal received signal level declines due to the rain attenuation. It was also demonstrated that the received signal level reduces as the rainfall rate continues to increase. The received signal level with PID power control as a countermeasure shows that these effects can be well compensated, regardless of rainfall rate variations. In conclusion, this two mitigation techniques are to complement each other for better effectiveness and improved efficiency as well as improved availability.