在5G發展中，有三個主要的應用情境，分別為 eMBB、uRLLC 以及 mMTC，各自場景有不同的要求/技術需要克服。其中，uRLLC (ultra-Reliable and Low Latency Communications) 的情境強調超高可靠性以及低延遲的應用，而車聯網 (V2X) 便是此情境下主要應用之一。

車聯網的一項重要應用為透過車輛間通訊將緊急特殊訊息以多躍 (multi-hop) 方式通知後方車輛，使其能及早回應，以提高用路安全及效率。此應用主要是透過廣播方式進行訊息傳遞，但廣播有幾個基本的特性/問題需要克服: 第一，廣播由於沒有特定的目的地，一般訊息接收者不會回傳ACK 給傳送者，故其通訊可靠性無法確認；第二，由於緊急訊息是以廣播且多躍方式傳輸，若無適當機制，將產生不必要的轉傳，不只浪費通道資源，並將引發嚴重碰撞問題，形成所謂的「廣播風暴」(Broadcast storm)。因此，如何設計廣播協定來確保低延遲及高可靠性，並將緊急訊息傳遠是主要研究議題。

在本論文中，我們模擬比較了幾種廣播抑制(Broadcast suppression)協定(包括先透過特殊Black-burst訊號選出指定的轉傳者)的可靠性、延遲即傳輸距離等性能表現後，發現減少轉傳者雖然能夠降低廣播過程中的碰撞機率，但可能會損失系統可靠度，如何調整轉傳者是重要設計問題。因此，本論文提出一整合廣播抑制技術，包含加入backoff 的機制與透過side-acknowledge的方式確保不損害系統可靠度下，訊息能順利傳遞。由模擬結果得知，和其他已知方法比較，本論文所提技術在延遲沒有明顯增加下，可靠度能夠大幅提升。

In the development of 5G, there are three main application scenarios, namely eMBB, uRLLC and mMTC, and each scenario has different difficulties to overcome. Among them, the uRLLC (ultra-Reliable and Low Latency Communications) scenario emphasizes ultra-high reliability and low latency applications, where V2X is one of the main applications in this scenario.

“Emergency message Alert” is one of important application in V2X. This application is to notify the subsequently vehicles the alert message primarily in broadcast and multi-hop manner. However, the “Broadcast storm” problem is an important issue that need to be overcome in broadcast process. If there is no proper mechanism to determine whether to forward the message, it will cause unnecessary transmission and serious collision. Thus, how to design a broadcast protocol to ensure low latency and high reliability and make the messages be delivered far is the main research topic.

In this thesis, we simulated and compared the reliability, latency and communication range between several broadcast suppression protocols (p-persistence, weighted p-persistence, slot1/p-persistence and BPAP). And we think the way to select the forwarding node is an important design issue. Therefore, this thesis proposes an integrated broadcast suppression technology, including the mechanism of backoff and through side-acknowledge method to ensure that the message can be transmitted smoothly without compromising the reliability of the system. The simulation results show that the reliability can be greatly improved without a significant increase in latency compared with other known methods.

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