TDMA 應用於802.11無線區域網路監控平臺之建立

Abstract

近年來由於無線通信與感測器技術的進步，加快了智慧型監控系統的開發。但對於監控系統中，前端監控裝置如何將資料傳送到後端的監控中心，則少有相關技術著墨。有鑑於此，本論文提出以802.11無線標準為基礎的分時多工無線監控傳輸協定(Time Division Wireless Monitoring Transmission Protocol, TDWMTP)，搭配分時多工(Time Division Multiple Access, TDMA)傳輸方式，以應用於智慧型監控系統上。在無線通訊中，802.11的技術與應用已相當成熟，適用於數十到數百公尺的短距通訊，並具有設備成本較低的優勢。但是802.11所採用載波偵測多重存取與碰撞避免(Carrie Sense Multiple Access/Collision Avoidance, CSMA/CA)的傳輸方式，無法提供低延遲的傳輸與保證傳輸品質，因此利用搭配TDMA機制來改善此缺失。此分時多工無線監控傳輸系統為多個無線節點所組成，並以隨意網路(Ad-Hoc Network)的架構來呈現。當系統開始運作時，TDWMTP使用一種非基於IEEE 802.11規範的連結方式，稱為鄰近節點搜尋協定(Neighbor Discovery Protocol, NDP)，來取得系統中所有節點的資訊。另外，針對TDMA的時槽規劃與管理，此系統以中控型管理方式來運作。系統中會有一個控制節點用來分配每個節點的時槽，並使用點對點(Hop by Hop)傳播方式讓系統中所有的節點與控制節點的時間達到同步。在資料收集上，每個節點則透過多點傳輸(Multi-Hop)方式將資料傳送至遠端監控中心。在最終相關實驗結果中，證實在多個無線節點環境下，每一個網路節點可以連結其它節點與取得鄰居相關資訊並形成一個通訊網路；亦驗證TDMA傳輸機制可快速同步所有節點，讓每個節點成功的將擷取的監控資料傳回到後端監控中心。

In recent years, the development of intelligent surveillance system has been accelerated due to the advances in the wireless communication and the sensor technology. However, for transmitting the data from the monitoring device to the monitoring center, studies in related technologies are seldom discussed.The purpose of this study is to propose a time division wireless monitoring transmission protocol (TDWMTP), based on IEEE 802.11 standard with the transmission method of TDMA (Time Division Multiple Access), to apply to the intelligent surveillance system.In wireless communication, the technology and application of 802.11 has been developed quite mature. With the advantages in low cost in equipment, it is suitable to be used in short range communication within tens or hundreds of meters. However CSMA/CA(Carrie Sense Multiple Access/Collision Avoidance), the method adopted by 802.11, is unable to offer low latency transmission and guarantee the quality of transmission. Therefore, TDWMTP uses TDMA to improve the shortcoming.Time division wireless monitoring transmission system is composed by multiple wireless nodes, and operates in Ad-Hoc mode. When the system starts to run, TDWMTP uses a link way not based on IEEE802.11 standard which is called NDP (Neighbor Discovery Protocol) to get all of the nodes information in the system. Besides, for the plan and management of the time slot of TDMA, the system operates via central control management. There is one controlled node in the system which is used to assign the time slot for each node and the system uses hop by hop to synchronize all of the nodes time with the controlled nodes'. In the data collection, each node sends the data to the remote monitoring center through multi-hop packet transmission.Finally, the experiments confirmed under the environment with multiple wireless nodes, each network node was able to connect to other node for obtaining related information from neighbors and formed a communication network. This study also verified that TDMA transmission mechanism could synchronize all of the nodes quickly to make each node sending the captured data to the remote monitoring center successfully.