摘要
在過去兩年裡、實驗室的兩位學長──許立正、廖培凱先後對中華衛星一號的通道特性和通道模擬做過一些相關研究。在兩位學長的努力下，中華衛星一號的直播實驗模擬程式得以建構完成，這包括了雨衰減的評估、雜訊功率的計算、錯誤保護碼的功效分析……等等。可是、當我們仔細地檢查兩位學長所提出來的模型時，我們發現還有一些地方可以改善來讓這個模擬程式更接近真實情況；如何改善舊有的模型便是這本論文的主題。

第一、地面站的高速調變器──CM701提供了一套保護機制來保護傳輸資料，這套保護機制是由里德-所羅門碼(Reed-Solomon Code)和旋積碼(Convolutional Code)串連而成，其中里德-所羅門碼的編碼率(coding rate)決定於輸入資料傳輸率，然而舊的模型並沒有考慮這一點；另外、舊的型模使用硬性決策旋積碼(hard-convolutional code)，而CM701其實是使用效率較高的軟性決策旋積碼(soft-convolutional code)。第二、對低軌道衛星如中華衛星一號而言，正確地描述衛星與地面站之間的相對運動是很重要的，在新修正的模型中我們採用了正確的軌道資料，使得修正後的模型更為可信。第三、一般認為雨衰減的特性在Ka頻帶裡是區域性的，因此在使用雨衰減模型時，配合台南當地的氣候參數相信是有幫助的。第四、在舊的模型裡，地面接收站的效應並沒有被考慮在內；在地面接收站裡，包含纜線在內的每一項連接設備都有雜訊效應，也因此會影嚮整個系統的表現。

在這本論文裡，我們會詳細介紹如何基於上述的四項因子來改善舊有模型，我們相信透過這樣的修正會讓模擬程式更接近實際情況；最後、我們會描述一個完整的模擬過程，並且基於模擬的結果給予一些建議。

Abstract
In the past two years, two members of our lab, Le-Gen Shi and Pei-Kai Liau, have successively made some researches on channel characteristics and channel simulations of ROCSAT-1. Thanks to Shi and Liau, the prototypes of simulation model including rain loss evaluation, noise power calculation, and analysis of FEC performance etc., are established. However, when examining the proposed simulation model, we found that some efforts can be made to make the model closer to the reality. The refinement to the old model is the objective of this thesis.

First of all, the high rate modem of ground terminal, CM701, provides a protection scheme comprising of Reed-Solomon code and soft-convolutional code to protect the input sequence. The coding rate of Reed-Solomon code depends on the input data rate (symbol per second), but the old model does not take this into account. Besides, the old model adopted a less-efficient hard-convolutional codec. Second, since ROCSAT-1 is a LEO satellite, an accurate description of relative motion between ROCSAT-1 and the ground terminal is very important. The modified model uses real orbit data and is hence believed to be more authentic. Third, it is believed presently that the characteristics of rain attenuation in Ka-band are regional. Therefore, a rain model with input parameters in accordance with Tainan’s weather conditions is helpful. Fourth, the old simulation model does not consider the effect of receiving system. In the receiving system, each cascading device including cables induces noise and hence affects the overall performance.

In this thesis, how to improve the old model based on aforementioned items is introduced in detail. Finally, we present the simulation process and give some suggestions from the simulation results.

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