一個基於Wi-Fi的節能車輛定位與車速評估演算法

Abstract

近年來，由於智慧型行動裝置逐漸開始普及。這些裝置配備有GPS、Wi-Fi、感測器等等，再加上其高度的行動力，於是出現了“以行動裝置當成移動式感測器”的構想，其高度的移動力和彈性是以往固定式感測器所沒有的特性。然而，行動裝置有個缺點，其電源供應非常有限。行動裝置上的GPS雖然定位準確度高，但是耗電量也很大，無法長時間運作，因此降低了它的可用性。相較之下，Wi-Fi的耗電量則比較小，在續航力的考量下，使用Wi-Fi雖然喪失了一些準確度，卻可以讓裝置運作更長的時間。本篇論文提出了一個適用於戶外環境且Wi-Fi普及的地區、以Wi-Fi訊號強度與距離之對數常態機率分配模型為基礎的節能車輛定位與車速評估演算法，以已知的Wi-Fi熱點的位置進行模擬實驗。實驗結果顯示，本方法可比GPS平均省下35%的電力，但平均定位誤差會達18公尺，車速估計平均誤差為25%。

In recent years, smart devices become so prevalent and ubiquitous. Many of these devices are equipped with GPS, Wi-Fi, and other sensors. With their high mobility, the idea of “mobile devices as probes” has been attracting more and more attention. Mobility and flexibility offered by smart mobile devices are what traditional fixed sensors lack. However, mobile devices’ power supply is quite limited. Though GPS is accurate, its high power consumption somewhat limits its accessibility and sustainability. In contrast, Wi-Fi is less power-hungry, but at the same time, less accurate. For the sake of sustainability, by adopting Wi-Fi as an alternative to GPS, longer operation is attainable at the cost of losing some degree of accuracy. In this thesis, a Wi-Fi-based algorithm based on log-normal probability distribution of distances with respect to received signal strength is proposed. It is suitable for outdoor environment where Wi-Fi APs are abundant. Simulations are conducted over known AP locations, and results show that the proposed algorithm can save, on average, as much as 35% more battery power than GPS does; average localization error is about 18 meters, and average velocity estimation error is about 25%.