ZigBee無線樹狀感測網路之初始化及通訊問題研究

Abstract

無線感測網路相關的研究議題得到許多研究單位及學者的關注，近年來ZigBee 通 訊協定被視為最適用於感測網路的通訊協定，本計畫將研究以ZigBee 樹狀網路為基礎 之無線感測網路相關通訊協定，本計畫目標主要包含三個面向：(1) ZigBee 無線感測網 路生成之研究，(2) ZigBee 樹狀網路資料傳遞排程，(3) ZigBee 基礎之長鏈狀網路研究。 在第一個研究主題中，我們研究ZigBee 感測網路的生成問題，在ZigBee 規範中， 一個節點加入到一個網路的條件為：該節點能找到一個父節點能夠給予該節點一ZigBee 網路位址，父節點們可利用ZigBee 所定義之分散式位址分配法來指定位址給子節點們， 這一個位址指定方法相當簡單但是卻限制了一個節點最多可容忍之子節點個數以及整 體網路的深度，我們觀察到如果使用ZigBee 所定義之網路生成方式，會使得網路位址 的使用率偏低，進而造成節點無法連上網路，因此在本計畫中，我們提出適用於ZigBe 之網路生成方法，我們的目標是為能夠使得網路上的節點能夠自動組態並且形成一個可 通訊之網路。 在第二個研究主題中，我們研究ZigBee 樹狀網路封包排程，在許多無線感測網路 的應用中，網路上的節點被要求回報資料給一個資料收集伺服器，早先所提出之資料回 報流排程方式皆著重於要節省網路節點電量消耗與降低回報延遲，但是該些方法皆不能 適用於ZigBee 網路。在考量ZigBee 的特性下，本計畫將探討該如何排程節點的信標訊 框，並將提出信標排程演算法，目標為針對資料流之特性來排定網路節點之運作時間， 以達到省電之目的。除了考量回報性的資料流外，我們亦會討論廣播性的資料流之封包 排程。 在第三個研究主題中，我們探討一特殊網路—長鏈狀網路，在這一網路中節點們被 部署為數個長條狀拓樸，這些長條狀拓樸們連接成一個網路，並且覆蓋整個想要涵蓋之 範圍，這一網路看似為一個特例型態網路，但是我們觀察到該網路型態是相當常見於許 多無線感測網路之應用中。本計畫探討該如何將ZigBee 協定用於此一特殊但卻常見之 樹狀拓樸中。我們預計將從網路層協定來切入討論，我們發現原有ZigBee 定義之位址 指定方式與路由方式並不適用於此長鏈狀網路，因此我們的目標為提出簡單又有效之適 用於長鏈狀網路之位址指派方法以及路由通訊協定。 上述三個研究方向除了理論方面的探討外，本計畫實做出所設計之演算法，並且探 討理論與實務經驗上之差別，我們期許本計畫能夠理論與實務兼顧，並且為ZigBee 樹 狀網路尖端研究。

Recently, a lot of research works have been dedicated to the wireless sensor networks (WSNs) field. ZigBee is a commnunication standard which is considered to be suitable for WSNs. In this project, we discuss initialization and communication protocols for ZigBee tree-based WSNs. This project contains three research topics including 1) formation of a ZigBee-based WSN, 2) scheduling for ZigBee tree-based networks considering data flows, and 3) ZigBee-based long thin networks. In the first research topic, we discuss the ZigBee network formation problem. In ZigBee, a device is said to join a network if it can obtain a network address from a parent device. Devices calculate addresses for their child devices by a distributed address assignment scheme. This assignment is easy to implement, but it restricts the number of children of a device and the depth of the network. We observe that if one uses the random formation policy specified in ZigBee, the utilization of the address pool may be very low. Those devices that can not receive network addresses will be isolated from the network and become orphan nodes. In this project, we propose network formation strategies to relieve the orphan problem. In the second topic, we discuss how to schedule beacons in ZigBee tree-based networks. Convergecast is a fundamental operation in wireless sensor networks. Existing convergecast solutions have focused on reducing latency and energy consumption. However, a good design should be compliant to standards, in addition to considering these factors. Based on this observation, we define a minimum delay beacon scheduling problem for quick convergecast in ZigBee tree-based wireless sensor networks. We will design beacon scheduling algorithms, which are compliant with the low power design of ZigBee and are able to achieve quick convergecast. In the last topic, we discuss a new concept of long-thin (LT) topology for WSNs, where a network may have a number of linear paths of nodes as backbones connecting to each other. These backbones are to extend the network to the intended coverage areas. A LT WSN only seems to be a special case of numerous WSN topologies. However, we observe, from real deployment experiments, that such a topology is quite general in many applications and deployments. We show that the address assignment and thus the routing scheme defined in the original ZigBee specification may work poorly, if not fail, in a LT topology. We plan to propose simple, yet efficient, address assignment and routing schemes for a LT WSN. In this project, we will not only do researches, but also implement our designed algorithms. We will also discuss the disfferences between simulations and prototyping experiences. We consider that we can be pioneers in the field of ZigBee tree-based WSNs.