臺灣博碩士論文加值系統

使用低軌道的小衛星網路系統能夠提供許多非即時性的服務應用，包括資料的收集、分頁服務或者是電子郵件的轉送等。由於這類型的衛星網路系統成本低廉、部署簡易，逐漸成為許許多多成本較昂貴的網路系統的替代方案。
本論文中考慮到了在低軌道的小衛星網路系統上，當有眾多地面站要同時在同一廣播頻道上傳送資料給單一小衛星時，決定哪個地面站能夠存取頻道資源的協定，是由資料鏈結層中的子層所負責的。我們稱此子層為媒介存取控制子層。眾所皆知的存取協定中—純粹式ALOHA和時槽式ALOHA—能夠應用在衛星網路系統傳輸資料上。
衛星網路系統中，在地球和衛星之間有很長的資料傳遞延遲。雖然這兩個存取協定能夠應用在衛星網路系統上，然而，系統的效能依舊無法滿足現有應用，主要原因是封包碰撞而造成的封包的重傳而降低了整體系統的效能。因此，本論文提議了一個另類的存取協定，目的是為了改善傳統存取協定的效能。此協定我們命名為使用競爭存取區間之隨機接取協定。
在我們提議的協定中，我們將通訊過程期間分成兩個部份，一個是資料傳送期間，另一個是地面站競爭存取頻道資源期間。因此，在資料傳送期間，我們會把頻道資源都給同一個地面站，再利用一種抑制的機制來抑制其他欲傳送資料的地面站，盡量避免新的連結請求和目前的正在傳送的封包產生了碰撞。而在地面站競爭存取頻道資源期間，會決定下一個能夠傳送資料的地面站。
藉由模擬這個低軌道的小衛星網路系統，我們發現這個協定確實比兩個傳統的協定效能還要好。若能提供適當的成本，這個協定會提供很強健的產能效益。所以我們相信我們所提議的協定非常適合在科學上做遠端資料的收集，例如：利用衛星資料收集分析與探勘海水鹽度變化以建構災害預警系統。

The store-and-forward system using little low earth orbital satellites can provide non-real-time communication services such as data collection, paging, e-mail, etc. It is a solid alternative to various applications because of its low cost and simple deployment.
In this thesis, we consider the collision problem in the data link control sublayer of the store-and-forward system. The sublayer is called the medium access control (MAC) sublayer. The well-known access protocols such as Pure-ALOHA and Slotted-ALOHA have found their applications in this problem. However, these conventional protocols are not optimized to handle long propagation delay characterizing the satellite network. Hence, to improve time and throughput efficiency of the conventional protocols, a novel protocol is proposed in this thesis. The novel protocol is called the Multiple Access Control with Rush Period (MAC/RP) protocol.
In MAC/RP protocol, the communications are divided into two periods, the transmission and rush periods. Conceptually, contentions are resolved during the rush periods while uninterrupted transmissions are ensured in the transmission period.
Through simulations, we found that this protocol provides strong throughput performance with moderate cost increase. We believe it will be best used in remote scientific data collection such as oceanic salinity.

ACKNOWLEDGEMENTS i
中文摘要 ii
ABSTRACT iv
TABLE OF CONTENTS v
LIST OF FIGURES vii
LIST OF TABLES viii
LIST OF ABBREVIATIONS ix
CHAPTER 1 INTRODUCTION 1
1.1 The History of Satellite Communications 1
1.2 Remote Data Collection 1
1.2.1 Overview of Little Low Earth Orbital Satellites 2
1.2.2 The Architecture of Store-and-Forward Systems 2
1.3 Motivation 4
1.4 Thesis Organization 4
CHAPTER 2 LITTLE LOW EARTH ORBITAL SATELLITES 5
2.1 Satellite Communication Systems 5
2.2 Satellite Orbits 6
2.3 Advantages of LEO Satellites 8
2.4 Little LEO Satellites 8
CHAPTER 3 EXISTING WORKS 11
3.1 Overview 11
3.2 Pure-ALOHA 11
3.2.1 The Pure-ALOHA Scheme 11
3.2.2 Frame Collision in Pure-ALOHA 13
3.2.3 Channel Utilization in Pure-ALOHA 14
3.3 Slotted-ALOHA 16
3.3.1 The Slotted-ALOHA Scheme 16
3.3.2 Frame Collision in Slotted-ALOHA 16
3.3.3 Channel Utilization in Slotted-ALOHA 17
3.4 Adaptive-ALOHA 19
3.4.1 The Adaptive-ALOHA Scheme 19
3.4.2 Remarks 20
3.5 Adaptive-Polling and Slotted-ALOHA (AP-SALOHA) 21
3.5.1 The AP-SALOHA Scheme 21
3.5.2 Remarks 22
CHAPTER 4 MULTIPLE ACCESS CONTROL WITH RUSH PERIOD (MAC/RP) PROTOCOL 23
4.1 The MAC/RP Scheme 23
4.2 Suppression Situations 27
4.3 Binary Exponential Backoff Algorithm 29
4.4 State Diagram 30
4.5 MAC Sublayer Issues 32
4.6 Frame Format of MAC/RP Protocol 33
CHAPTER 5 NUMERICAL RESULTS AND DISCUSSION 35
5.1 Simulation Model and Parameters 35
5.2 Performance Comparisons 36
5.3 Relationships among Performance Parameters and Rush Period 39
5.4 MAC/RP Protocol Issues 41
CHAPTER 6 COLNCLUSIONS AND FUTURE WORK 42
6.1 Conclusions 42
6.2 Future Works 43
BIBLIOGRAPHY 44

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