定位(Localization)在無線感測網路(WSNs)中是一項很重要的議題。然而，即使每個感測器(Sensor)均配有GPS，其定位亦有誤差且耗費硬體成本。近年來已有許多相關研究提出以Mobile Anchor(MA)定位，在每個感測器不需額外硬體成本的前提下，透過發送Beacon message以及MA的移動性，來提供感測器大致的位置資訊。然而，其所提供的位置精準度並無法區別感測器之間的相對位置，間接影響現存之繞徑協定(Location Aware Routing; LAR)及物件追蹤等應用之效能。本論文除了位置精準度外，亦著重於鄰近感測器間的位置區別度，我們利用MA所廣播的Beacon及Tone兩種訊號，以分散式的方法提供每個感測器位置資訊並區別鄰近感測器間之相對位置。實驗結果顯示，本論文所提出的定位技術確實可區別感測器與鄰居間的相對位置關係，並大量改善現存之LAR及物件追蹤協定的效能。 Location information is of utmost importance for most applications in wireless sensor networks (WSNs). A number of bounding-box mechanisms have been proposed based on a mobile anchor which periodically broadcasts its location information to help nodes estimate their location using the bounding-box constraints. However, the bounding-box location information can not distinguish the relative locations between neighboring sensors, hence leading to a poor performance for some applications such as location-aware routing. This paper proposes a Differentiating Relative Locations (DRL) mechanism which adopts tones and beacons techniques aiming at distinguishing the relative locations between any two adjacent nodes. With the order of entering and existing tone transmission range, each sensor is able to identify its relative location relation with each of its neighbor. In addition, a path planning mechanism is proposed to guarantee that all sensors can identify their relative locations with their neighbors while the energy consumption of the mobile anchor can be reduced. Theoretical analysis is developed for determining the duration ratio of broadcasting tone and silence so that the mobile anchor can further achieve energy conservation during executing the proposed DRL mechanism. Experimental study reveals that the proposed DRL mechanism effectively distinguishes relative locations between any two adjacent nodes and hence improves the performance of upper layer applications in WSNs.
