摘要
物聯網(Internet of Things; IoT)的發展越來越受到重視，逐漸改變人們生活習慣，未來也會有更多裝置設備連上網路。無線感測網路(wireless sensor network; WSN)是由多個感測節點裝置組成，經由無線傳輸方式來傳輸資料，其特點包括短距離傳輸、低成本、低功耗、頻寬要求低與裝置精簡。它可應用在不同的領域，例如: 農業、遠距離醫療照護、智慧電網、環境監測與工業自動化等。
IEEE 802.15.4標準為無線感測網路的一種規範。標準中提供超碼框(superframe)結構傳輸資料，其中分成活動週期與非活動週期，長度分別由超碼框級數與訊標級數決定，但此兩參數不能因應網路負載做調整，可能降低產能、功耗增加或延遲變高。標準中定義裝置在競爭訪問週期間，使用載波檢測多重存取與碰撞避免(carrier sense multiple access with collision avoidance; CSMA/CA)機制來傳輸資料，但此機制的傳輸參數對所有訊框設定一致，無法滿足不同優先權訊框的傳輸需求。在免競爭週期間，裝置不必與其他裝置競爭傳輸通道，而是被分配到固定時間點傳送，稱為保證時槽(guaranteed time slots; GTSs)，可提供即時性資料傳輸應用，但如果沒有考慮資料大小做分配，可能造成頻寬浪費問題。
目前有許多改善標準的方法，提供不同無線感測網路應用達到需求，但這些方法只注重一兩項服務品質(quality of service; QoS)的改善，少有考慮多個需求。因此本論文提出以優先權為基礎的動態調整超碼框機制結合保證時槽分配(PDSGTS)。模擬結果顯示，PDSGTS機制與IEEE 802.15.4標準相比，可以有效提升有效產能並降低傳輸延遲。

關鍵字: IEEE 802.15.4、無線感測網路、超碼框調整、CSMA/CA

Abstract
The development of the Internet of Things (IoT) has received increasing attention and gradually changes people's living habits. In the future, there will be more devices connected to the Internet. Wireless sensor network (WSN) is consisted of several sensor devices and transmits data through wireless transmission. It is characterized by its short distance transmission, low cost, low power consumption, low bandwidth requirements, and has a small device size. It can be applied in different fields such as: agriculture, telemedicine care, smart grid, environmental monitoring and industrial automation etc.
The IEEE 802.15.4 standard is a specification for wireless sensing networks. The standard provides superframe structure to transmit data. It is divided into active period and inactive period, and the length is determined by superframe order and beacon order. However, these two parameters cannot be adjusted by considering the network traffic load, which may reduce the throughput, increase power consumption or add a delay. In the standard, the device uses the carrier sense multiple access with collision avoidance (CSMA/CA) mechanism to transmit data during the contention access period. Nevertheless, the transmission parameters of this mechanism are the same for all frames and cannot meet the transmission requirements of different priority frames. In the contention free period, the device does not have to compete with other devices for transmission channels. Instead, it is assigned to a specific time to do, known as guaranteed time slots (GTSs). It can provide for the transmission of real-time data, yet not consider the size of the data assignment may cause the problem of bandwidth waste.
At present, there are many methods to improve the standard and provide different wireless sensor network applications to meet the requirements. But these methods only focus on one or two issues for quality of service (QoS), and with few considerations on multiple requirements. Therefore, this thesis proposes a priority based scheme to dynamic superframe adjustment with guaranteed time slot(PDSGTS). Simulation results show that compared with the IEEE 802.15.4 standard, the PDSGTS mechanism can effectively increase the goodput and reduce the transmission delay.

Keywords: IEEE 802.15.4, wireless sensor network, Superframe adjust, CSMA/CA

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