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Fense Technology, Changsha 410073, China; weichen@nudt.edu.cn (W.C.); wangwp@nudt.edu.cn (W.W.); qchang@telin.ugent.be (Q.C.); houhongtao@nudt.edu.cn (H.H.) * Correspondence: liqunnudt@163.com; Tel.: +86-731-8457-3558 Academic Editor: Gonzalo Pajares Martinsanz Received: 24 January 2016; Accepted: 16 March 2016; Published: 19 MarchAbstract: Indoor positioning based on existing Wi-Fi fingerprints i