在 TinyOS 上實現 TDMA 機制

Abstract

現今無線感測網路在各種領域都有相當廣泛的應用，TinyOS 是無線感測網路中相當常見的作業系統。由於此系統的底層為CSMA-CA 機制，所以當網路流量擁擠時，封包彼此干擾或是碰撞情形亦相對嚴重，在封包重新傳送的過程，意味著感測器額外電池電力消耗。在本篇論文中，我們將嘗試將TDMA 機制加到TinyOS 作業系統中，硬體方面則選用Micaz。在TDMA 系統中，每顆感測器都將在其擁有的時間區段內傳輸資料，如此將可避免因為封包干擾或碰撞而導致的封包重新傳送。實作元件分別為系統時間同步、感測器時間區段分配、低耗電機制。同時，當感測器進入省電模式時，其無線模組界面亦會關閉，藉此達到省電效果。最後，在實驗中亦可以驗證系統時間同步有相當的準確度與穩定性，這對維持TDMA 運作的穩定性來說是相當重要的因素。

Wireless sensor network (WSN) is widespread in several different application fields now. In WSN, TinyOS is the most popular operating system. TinyOS adopts CSMA-CA mechanism in its MAC layer. When the network with heavy traffic loads, packets collision and interference will be more serious. When packets collision happened, sensor nodes will do packets retransmission and consume additional power. In this thesis, we try to implement TDMA mechanism in TinsOS with platform Micaz. TDMA mechanism can resolve the problem of packets collision because each sensor node has its time slot and data will be transmitted in the assigned time slot. We implement the components include time synchronization, slot assignment algorithm and power saving mechanism. When a sensor node enters power saving mode, program process will also disable radio interface for power saving. Time synchronization one of the important factor for TDMA mechanism and experiment result shows our time synchronization algorithm can work over many hours with accuracy and stability.