由於近年來網路技術的進步與發達，運用電子通訊技術的電子產品已逐漸地佔領人們的生活。整個世界可用“無所不在的通訊”來形容。無線網路通訊也成為了目前重要的議題。在西元1997年IEEE為無線網路制定了標準是為802.11。802.11標準經由不斷的補充與調整，發展出了主要用於車用電子的無線通通訊標準802.11p。用以符合智慧型運輸系統的相關應用。
車載行動通訊網路(Vehicular Ad hoc Network. VANET)也在網路技術的熱潮日益成熟。與傳統的行動隨意網路(Mobile Ad hoc Network, MANET)相比，車用隨意網路當中的移動節點為車輛，其移動速度可為移動隨意網路節點的好幾倍。因此即時的判斷封包的傳輸有效路徑，則為一個重要議題。車載網路的另一個特點為車輛節點的移動較可預期，對於車輛來說，其移動路徑大多侷限於道路上，因此有許多針對車載網路的特性設計的路由協定(Routing Protocol)因應而生。
車載網路受控存取協定(Controlled Vehicular Internet Access, CVIA)即是一種針對車載網路所設計的路由協定。此協定的設計是為了要避免在高速公路中車間通訊中的隱藏節點問題(Hidden node)及不必要的RTS/CTS，並可為道路上每一段的區段帶來相等的資料吞吐量。其運作原理是將道路分割為彼此交錯的主動區段(Active segment)與非主動區段(Inactive Segment)。位在主動區段的車輛會把欲傳送之封包收集至其中的一車輛接著會將封包傳送給鄰近的非主動區段。當時間進入新的時槽(Time slot)時，系統將會互換主動區段與非主動區段。封包藉由此機制不斷的往前傳遞。
然而在車輛密度較低的區域，會有很高的機率出現無車輛存在的區段，在此協定之下將會造成封包無法繼續往前傳遞，我們稱之為通訊空洞(Communication hole)。在原始的CVIA協定之下，在此種狀況車輛只能繼續攜帶封包並繼續向前並等待網路拓樸的改變。所造成的封包延遲，對於即時性封包是很嚴重的問題。
因此在本篇論文主要研究的目的，在於針對再低車輛密度的道路出現通訊空洞提出解決方案。原始想法是增強傳輸功率，使封包能到及位於通訊空洞另一方的車輛。然而直接加強傳輸功率反而會破壞CVIA的傳輸機制及其優點。我們分析了CVIA在活躍時段的步驟，選擇在車輛在計算選擇出蒐集區域封包的車輛時做出增強傳輸功率的傳送。而判斷前方區段是否為通訊空洞的方法為利用向前傳輸時的交握(Handahake)成功與否，並且利用。根據我們的模擬結果證明，使用我們修改過後的機制不僅可以確實的解決通訊空洞的問題，車輛仍然可以在在沒有通訊空洞的環境做正常的傳輸。使CVIA的傳輸更加可靠且其應用更符合於現實狀況。

In recent years, the development of network technologies has greatly changed human being’s living habits, and the abundant network services are also getting more and more close to human lives. With the maturity and popularization of network technologies, the network applications have developed from household electronic products to products for mobile vehicles. In such an evolution, several vehicular network standards and drafts have been released, like 802.11p that is extended from 802.11.
Due to the research and development, Vehicular Ad hoc Network (VANET) is becoming well-known and matured. Different from Mobile Ad hoc Network(MANET), all the mobile node for VANET are vehicles. Mobility of the VANET node is much more than node of MANET. So it is an important issue to find an effective route for data transmission. And predictable node is also one of the VANET feature. According to above, many corresponding routing protocols are researched for VANET.
Controlled Vehicular Internet Access (CVIA) is one of the routing protocols designed for VANET. This protocol not only pursuit for hidden node avoidance and fairness providing to all the segments, but also remove unnecessary RTS/CTS handshake. CVIA divide a strait road into many segments. It set segment as Inactive segment and Active segment in interleaving way. For each active segment, one of the vehicles of the segment is responsible for gathering all of the packets in the local segment and forwarding to next segment. As enter a new time slot, inactive segments turn into active segment and active segment will turn into inactive segment.
But in low density of vehicles environment, there has high probability for non-vehicle segment causing the transmission link broken called “communication hole”. In this case, vehicle only can queue the packet and wait for topology changing in CVIA protocol. Delay of the packet cause a critical problem for real-time packet.
This paper presents a CVIA based scheme that solves the hole problem but maintains the advantage of CVIA protocol. The simulation results reveal that our proposed scheme can enhance vehicular transmission power conditionally and suit the non-hole environment as well. The improvement of this scheme makes the real vehicular network environment by CVIA protocol much more reachable.

第一章 緒論 - 1 -
1.1 前言 - 1 -
1.2 動機與目的 - 2 -
1.3 論文章節架構 - 4 -
第二章 背景知識與相關研究 - 6 -
2.1 行動隨意無線網路(MANET) - 8 -
2.2 車載行動通訊網路(VANET) - 11 -
2.3 行動隨意網路與車載行動通訊網路之比較 - 14 -
2.4 車載行動通訊網路之網路架構 - 18 -
2.4.1 車輛對車輛通訊 (V2V Communications) - 19 -
2.4.2 車輛對基地台通訊 (V2I Communications) - 21 -
2.4.3 混合型通訊 (Hybrid of V2V and V2I) - 23 -
第三章 車載網路受控存取協定之介紹 - 25 -
3.1 名詞定義 - 26 -
3.2 運作流程 - 28 -
第四章 基於車載網路受控存取協定的增強型功率控制傳輸機制 - 34 -
4.1 增強型功率控制傳輸機制概述 - 34 -
4.2 系統模型 - 36 -
4.3 增強型功率控制傳輸 - 38 -
4.4 基於車輛密度的時間調變機制 - 40 -
第五章 模擬與分析 - 47 -
5.1 實驗一 - 47 -
5.2 實驗二 - 53 -
第六章 結論與未來展望 - 57 -
參考文獻 - 59 -
圖目錄
圖 2.1智慧型運輸系統架構 - 7 -
圖 2.2基礎架構模式(Infrastructure Mode) - 8 -
圖 2.3隨意網路模式(Ad Hoc Mode) - 9 -
圖 2.4車間通訊架構(CALM)之網路分層[7] - 14 -
圖 2.5 DSRC頻寬分配圖[2] - 18 -
圖 2.6車輛對車輛通訊(V2V) - 19 -
圖 2.7車輛對基地台通訊(V2I) - 22 -
圖 2.8混合型通訊(V2V and V2I) - 23 -
圖 3.1 CVIA協定的循環週期 - 28 -
圖 3.2路由車輛選擇階段 - 29 -
圖 3.3區內封包序列傳送階段 - 31 -
圖 3.4局部區域封包收集階段 - 32 -
圖 3.5區間封包序列傳送階段 - 32 -
圖 4.1通訊空洞 - 35 -
圖 4.2道路場景 - 37 -
圖 4.3車輛傳輸干擾 - 38 -
圖 4.4 EPCT傳輸運作流程 - 39 -
圖 4.5 CVIA傳輸運作流程 - 39 -
圖 4.6通訊空洞出現機率 - 43 -
圖 4.7增強型傳輸使用率 - 45 -
圖 5.1模擬場景 - 47 -
圖 5.2 CVIA抖動與時間關係圖 - 50 -
圖 5.3 EPCT抖動與時間關係圖 - 51 -
圖 5.4 RSU封包接收與時間關係圖 - 52 -
圖 5.5 封包到達率與車輛密度關係圖 - 53 -
圖 5.6 End-to-end delay與車輛密度關係圖 - 55 -
圖 5.7 Throughput與車輛密度關係圖 - 56 -

表目錄
表 2.1 MANET與VANET特性比較表 - 15 -
表 4.1公式係數表 - 44 -
表 5.1模擬參數表 - 49 -

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