由於衛星通訊的快速成長與較低頻帶的擁擠，越來越多的商業應用將頻帶提升到較高的Ka頻段。為了發展太空研究及其相關應用，台灣第一顆科學衛星，中華衛星一號，已於1999年 1月27日發射升空。對於低軌道中華衛星一號來說，有兩個重要的問題我們必須了解。一個是低軌道衛星的特性而另一個就是Ka頻段的通道特性。對於低軌道衛星來說，當系統在低仰角時不僅受到較大的路徑衰減還會受到大量的對流層衰減，例如：降雨衰減、對流層閃爍效應、雲的衰減、大氣的吸收…等等，尤其是Ka頻段。為了精確的計算訊號在Ka頻段傳播所受到的衰減，我們建立了一個結合傳播影響和衛星軌道追蹤的模擬系統。 我們使用了two-site diversity和robust coding system來改善系統的效能。模擬的結果顯示出我們可以有較長的有效鍊結時間和較少的錯誤位元機率。藉著我們對低軌道衛星、ka頻段通道和改善系統效能的研究，我們可以對中華衛星一號通訊實驗籌載系統的特性有進一步的了解。最後，我們對於將來的實驗提出了一些可行的規劃。 Because of the rapid growth of satellite services and congestion of lower frequencies bands, more and more commercial applications are being promoted for Ka-Band. In order to develop the emerging technology of space research and related applications, the first scientific satellite of Taiwan, ROCSAT-1, which has been launched on 1/27/1999. However for the direct broadcast experiment of digital TV signals, there are two important problems which we must understand at first. One is the characteristic of LEO satellite and the other is the characteristic of Ka-Band channel. For LEO satellites, systems at low elevation angle suffer not only large free space loss but also great tropospheric losses, such as rain attenuation, tropospheric scintillation, cloud attenuation, gas absorption, and so on, especially in Ka-Band channel. An evaluation of procedure that combines overall propagation impairments and the tracking of LEO ROCSAT-1 is built for our simulation system. For having the better performance, a combined scheme of two-site diversity and robust coding system is used. The simulation results show that we can have longer available link time and less bit error probability by using this technique. By the analysis of LEO satellites, Ka-Band channel and improved methods of system performance, we will have more understanding on the characteristics of ROCSAT-1 ECP system. Finally, we present an effective plan for the future experiment.
