無線感測網路之有限誤差線上查詢處理

Bounded-Error Online Query Process in Wireless Sensor Network

蔡瑞華(Jui-Hua Tsai)

指導教授 ： 吳文中

共同指導教授 ： 張瑞益(Ray-I Chang)

國立臺灣大學/工學院/工程科學及海洋工程學研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.02839

摘要

在無線感測網路 (Wireless Sensor Network)中，由於無法提供節點穩定的電源，電量往往是無線感測網路的一大限制。因此無線感測網路的研究中，如何減少節點耗電、延長系統壽命是非常重要課題。無線裝置的無線模組傳輸一個位元的耗電量相當於微控制單元 (Micro Controller Unit, MCU)執行 1051行指令的耗電量 [1]，根據先前的研究，在某些應用中，傳輸資料甚至消耗總體電量的90% [2]，因此減少資料傳輸能大幅減少耗電，有效延長系統壽命。
在無線感測網路中，由於硬體技術等限制，測量所得資料往往與實際物理量有所差異 [3]，所以實際應用上，使用者會規範一個有限誤差範圍，避免誤差過大。如：美國冷凍協會的溫度量標準方法容許誤差為攝氏0.5度 [4]。本文依據無線感測網路特有的有限誤差需求，提出支援資料有限誤差的查詢處理，透過有限誤差壓縮技術大幅減少資料傳輸的耗電，兼顧省電及控制資料誤差兩點需求。
本文以無線電表感測網路的資料為例，說明有限誤差查詢處理的潛在應用，以SQL查詢處理架構為基礎，透過有限誤差減少感測網路耗電。根據本文的實驗，在不同的查詢指令下耗電狀態有不同幅度的改善，在本文的實驗顯示有限誤差線上查詢處理比傳統無失真的線上查詢方法減少15.78 % 至75.7 %的耗電，查詢過濾器也比過去傳統的傳輸方式減少87.9 % 的耗電。

關鍵字

無線感測網路 ； 有限誤差 ； 查詢處理 ； 線上查詢 ； 能源效率

並列摘要

In wireless sensor networks (WSNs), due to the limitation of battery power, reducing power waste to prolong the system lifetime is an important issue. The power of transmitting one bit datum is nearly the power of computing 1051 lines of codes [1]. According to previous research [2], in certain scenario wireless devices might spent up to 90 percent of power in communication cost. Hence reducing communication cost can save battery power and prolong system lifetime.
In real wireless sensor networks, it is impossible to transform physical phenomena to data without data errors [3]. Hence limited data errors is allowed in wireless sensor networks. For example, ASHRAE (American Society of Heating, Refrigerating, and Air-Condition Engineers) tolerates 0.5°C temperature bounded-error [4]. In this thesis, we propose bounded-error query (BEQ) process based on the special bounded-error feature of wireless sensor network. Different from other query process, our method not only satisfies the requirement of the limitation of data errors, but also reduces communication cost.
At the end of this thesis, we use wireless wattmeter sensor networks to demonstrate one of the potential applications of bounded-error query (BEQ) process. In our evaluation, BEQ reduction ratio of communication cost varies from query results. In our evaluation, our method reduces up to 15.78 % to 75.7 % of the communication cost, compared with traditional online query process that uses lossless compression. Query filter also saves 87.9 percent of communication cost.

並列關鍵字

Wireless Sensor Networks ； Bounded-Error ； Query Processing ； On-Line Query ； Power Efficient

參考文獻

[11] 林哲論, "有限誤差霍夫曼編碼在無線感測網路的資料壓縮應用," 臺灣大學工程科學及海洋工程學研究所學位論文, pp. 1-57, 2014.

[3] " R. P. David Freedman, Roger Purves, Statistics: Norton & Company, 1998. ."

[1] Y. Liang and W. Peng, "Minimizing energy consumptions in wireless sensor networks via two-modal transmission," ACM SIGCOMM Computer Communication Review, vol. 40, pp. 12-18, 2010.

[2] J. M. Rabaey, M. J. Ammer, J. L. da Silva, D. Patel, and S. Roundy, "PicoRadio supports ad hoc ultra-low power wireless networking," Computer, vol. 33, pp. 42-48, 2000.

[5] E. Balestrieri, P. Daponte, and S. Rapuano, "A state of the art on ADC error compensation methods," IEEE transactions on instrumentation and measurement, vol. 54, pp. 1388-1394, 2005.