在無線感測器網路(Wireless Sensor Networks)中，定位相關應用已經成為重要的議題並廣泛地被提出討論。對於這些應用而言，測距定位法面臨無線訊號傳遞的不規則性以及額外硬體裝置花費的挑戰，而無測距定位法不需要利用收到的訊號強度來估量距離，因此需要的硬體裝置簡單且花費少。若在不需求得太精確估計位置的前提下，無測距定位法較適用於無線感測器網路，而現存的無測距定位法有些計算太複雜，有些不夠精確。為了改進之前的定位方法，我們提出無線感測器網路中分散式之無測距定位法(Distributed Range-Free Localization Scheme)。我們假設只有一些感測器可以利用全球定位系統(Global Position System)獲得位置資訊，而其他感測器可藉由蒐集已定位感測器的位置資訊來估算自己的位置。首先我們先找出初始估計位置，再利用比較遠的已定位感測器與初始估計位置間的相對位置來修正初始估計位置。在模擬結果中可看出分散式之無測距定位法較其他定位法可獲得較精確的估計位置。 Location-related applications have become essential issues and have been widely proposed in wireless sensor networks (WSNs). For those applications, radio propagation irregularity and the cost of the additional devices on sensor nodes make range-based localization schemes in WSNs very challenging. Instead, range-free localization schemes don’t have to utilize received signal strength to estimate distances and only needs simple and costless hardware. Thus, range-free localization schemes are more suitable for WSNs if only coarse accuracy is required. However,existing range-free localization schemes are either too costly or not accurate enough. To improve previous works, we present DRLS, a fully distributed range-free localization scheme for WSNs. We assume that only a few sensor nodes, called anchors, can get their locations by Global Positioning System (GPS) and the remaining nodes need to estimate their own locations by gathering the nearby neighboring information. We first find the coarse estimative locations of the nodes. Furthermore, we derive a refinement method to correct the coarse estimative locations according to the relative position of the farther anchor and the coarse estimative locations. We show that our DRLS scheme performs well when random node placement is considered. Besides, our scheme is superior to previous range-free localization schemes via extensive simulations under a variety anchor densities. Simulation results show that the proposed algorithm achieves better accuracy of estimative locations.
