| Summary: | 碩士 === 國立高雄第一科技大學 === 電腦與通訊工程所 === 97 === In wireless communications, the atmosphere is used as a transmission medium. However, this free open medium varies frequently due to atmospheric anomalies. Recently, many technical papers have been reported the factors such as the meteorological conditions and reflectivity or refractivity in the effects of the performance of the radio system.
In this thesis we measure the signals received from a 265 kilometers line-of-sight over sea microwave radio link operating at 4 GHz. The data collection period is about 7 months. Our analytical results show that about 67.56 percent of transmission outage is related to the tidal variance, 62.16 percent correlated with the humidity and pressure, and 59.45 percent with the refractive index and temperature.
In long distance over sea propagation microwave links, severe fading occurs frequently, which often substantially impair the quality or reliability of the transmission system. The space diversity scheme has been used to deal with this problem.
In general, two methods are used in diversity schemes. The first one is to combine the two received signals by the phase combiner, and the other is to select the larger amplitude of the two received signals. The first method has been used prevalently for a long time. Although it obtained a combining gain, the combining signal amplitudes could be possibly pulled back with a long delay times between different paths. Hence even both signal magnitudes are strong, the effect of combing are limited. In order to solve this problem, we propose a second method to deal this problem by selecting largest amplitude. Our result shows that the improvement of the system availability is better than the first method, noticeably as the availability is below 99.95%.
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