Zigbee無線感測網路用於居家照護之設計與探討

Studies and Design of a Zigbee Wireless Sensor Network for Home Health Care

楊朝翔(Chao-Hsiang Yang)

指導教授 ： 婁世亮

中原大學/工學院/醫學工程研究所/碩士(2007年)

https://doi.org/10.6840/CYCU.2007.00658

摘要

本課題的目標為建構無線感測網路平台，探討其於居家照護應用之可行性。平台的建構是以Zigbee為基礎的無線感測網路，含五組無線感測節點之設計製作以做為擷取感測訊號之用，藉iZAP堆疊平台整合無線感測網路，應用在遠距居家照護系統。無線感測網路通訊效能是本課題的探討重點，測試項目包含資料收集中心的最大頻寬、障礙物對於通訊效能的影響與無線感測網路拓樸的傳輸限制。
無線感測網路的頻寬與距離範圍測試的探討結果顯示，資料收集中心的通訊頻寬上限為400 bytes/秒，最遠通訊距離為10 公尺。木門障礙對於Zigbee的通訊影響測試結果指出，在通訊路徑與木門成900角時，具有最佳通訊效能，且可穩定傳輸的最遠距離為3公尺；鋼筋混泥土之轉角障礙對於Zigbee通訊影響的測試結果是，穩定通訊地最遠距離可達4公尺。樹狀式無線感測網路是藉由Router節點協助轉傳封包，因此在同一樹枝線上的Router節點數將影響其通訊效能，這方面的結果顯示與預測相同，也就是傳輸路徑有越多的Router節點，則通訊效能越低；又，當路徑改變時，Router節點因重新搜尋新路徑需得花費時間，其時若資訊充塞，訊息遺失將不可豁免。在星狀式多點傳輸的模式下，因感測節點競爭通訊權，獲權者才可進行資料傳送；實驗結果顯示，當其中一節點連續傳送訊息且速率高於100 bytes/秒之時，其他節點因無法取得通訊權，將有訊息資料遺失之虞。
以現今Zigbee科技發展階段而言，將之運用於高速連續式生理訊號的通訊，其限制性較大，但若將Zigbee 做為傳遞訊息式生理訊號的工具，可行性則較高。

關鍵字

Zigbee ； 生理訊號 ； 無線感測網路 ； 居家照護系統

並列摘要

The purpose of this course is to study the feasibility of a wireless sensor network technology for the use of tele-home care. A wireless sensor network test-bed including five sensor nodes was first developed. Each node was an integration of a Zigbee wireless module and a sensing unit. To become a functional communication unit, an iZAP stack software package was used to program the Zigbee module. The sensing unit is responsible for acquiring two types of signals: vital physiology signs and indoor health risk factors. The test-bed was examined by a series of studies. The study results are as follows.
For a node-to-node transmission study, in a distance of 10-meter the bandwidth was up to 400 bytes/second. In a concrete corner barrier study, the transmission distance was reduced to 4 meters. This was down to 3 meters when the node-to-node transmission study was carried out in a setup that a 4.7-cm thick wood-door was between the two nodes. For a tree-topology study, we noticed when the number of node in a branch increases, the transmission bandwidth decreases. Furthermore, while the transmission path changes, searching new pathways takes place and usually the action takes time. This may jam the data traffic at the searching node and potentially end up missing data. Another commonly known topology is star mode, which a group of satellite nodes solely communicate with a specified central node. Its communication protocol is based on the right of transmission granted by the central node. On this mode, the satellite sensor nodes compete for the right and only one of them is granted at a time. For a right-granted node continuously sending data, it likely ties up all transmission time. Thus those un-granted nodes are going to lose data owe to keep-coming data. According to our study result, the use of the star-topology was subjected to a restriction. Only a single satellite node allowed transmitted data continuously and the transmission rate was limited at 100 bytes/second. Under such a circumstance, other satellite nodes periodically sending short messages to the central node was permitted.
In conclusion, today’s Zigbee technology both in hardware and software has a plenty of room for improvement. In its current stage, applications requiring high transmission throughput such as transmitting waveform physiological signals are not feasible. On the other hand, one may find its usefulness in the applications of transmitting short messages such as heart rate and body temperature.

並列關鍵字

Zigbee ； Tele-home care ； Wireless sensor network ； Physiological signals

參考文獻

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