隨著無線多媒體網際網路應用的日益頻繁，地面微波通訊的應用 上日趨重要，由於頻譜之擁擠，世界各國均傾向採用Ka(26~40GHz) 波段。不過此一波段信號在地表大氣通道傳播時，容易受到自然環境 因素影響，其中又以降雨和植被遮蔽造成的信號衰減情況最為嚴重， 所以本文將針對降雨和植被遮蔽的效應進行討論。 在降雨效應部分，本文利用實際架設的Ka 波段地面鏈路來量測 降雨效應所造成的信號衰減，並且統計由中央氣象局所提供的中壢地 區及台灣北、中、南三區的十數年逐時降雨分佈，並與國際上常用的 ITU-R 與Crane 模式作比較後，發現兩者皆有明顯高估之情形，所以 本文基於本地實驗結果，嘗試修正ITU-R 與Crane 模式的係數，以符 合中壢地區真實的降雨分佈與降雨衰減；另外由於中央氣象局提供的 資料為逐時資料，但在通訊上使用逐分資料較為恰當，所以發展了逐 時與逐分資料的轉換，經由轉換中壢地區十數年的逐時資料為逐分資 料後，我們建議中壢地區降雨分佈的R0.01 值為71mm/hr。 在植被遮蔽效應部分，分別針對各主要樹種(混和、闊葉、針葉 林)進行量測信號穿透的衰減與機率分佈，實驗結果發現其有效衰減 ii 分別為7.24dB/m、9.67dB/m 與1.51dB/m；而在機率分佈上，三種主 要樹種皆偏向於Gamma 分佈。 Because there are more and more applied in the wireless internet multimedia application. It is more important in the terrestrial microwave communication. But, because the crowded of the spectrum, many people tend to choice the Ka-band(26-40GHz) for the application. But this band is easily to be influenced by the environment, when it transferred in the atmosphere. Which the most obvious is the attenuation by the rain or the vegetations. In this article, we will discuss some effect of the rain and the vegetations. In the rain effect. We build up a Ka-band terrestrial link to measure the signal attenuation by rain. We also made the statistics distribution of the hourly rain rate in Jung-Li, Taipei, Taichung, and Kaoshung(data offered by CWB). Compared with the most used ITU-R and Crane model, we find that both them are overestimate. So we try to modify the coefficients in the ITU-R and Crane model to match the local experiment. The other side, the data offered by CWB are hourly data, but it is more appropriate to use minutely data in communication analysis. We also develop a conversion model to convert the hourly data to minutely data. After we convert 10 years data in Jung-Li, we suggest that the R0.01 value in Jung-Li should be 71mm/hr. In the vegetations effect. We measure the attenuation and made the probability distribution pass through the mixed, deciduous, and coniferous trees. We find the effective attenuation rate is 7.24dB/m in mixed trees, 9.67dB/m in deciduous trees, 1.51dB/m in coniferous trees. We also find the probability distribution is most fitted to Gamma distribution in all three types of trees.
