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Tham khảo tài liệu 'advances in measurement systems part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 196 Advances in Measurement Systems basic on-off pulse-keying protocol has been implemented in order to enable the communication of the master with multiple slaves. The second approach uses commercial ZigBee radio interface devices and is based on the RTT measurement of communication packets. The main feature is the introduction of a selfcalibration method aiming at removing the bias introduced by the latencies of the fixed-position nodes. Detailed descriptions of the architectures as well as experimental test results are presented in this chapter together with a comparison and discussion of the advantages and disadvantages of each approach. 2. State of the art in the field of indoor positioning Indoor positioning is the object of a considerable research interest. Accurate geolocation in fact represents an enabling technology for indoor location-aware sensor networks Gezici et al. 2005 Wymeersch et al. 2009 . Some of the real-life applications for research in this field are related to the industry and logistic areas e.g. for efficient asset tracking Fontana 2004 . Another application area of interest is the location and tracking of emergency personnel and incident first responders Rantakokko et al. 2007 . In this context both ad-hoc systems and architectures based on pre-existing communication infrastructures have been developed in the literature. Comprehensive surveys of the fundamental positioning strategies as well as the main research and commercial systems in the indoor positioning area can be found in Pahlavan et al. 2002 Liu et al. 2007 . In the following subsections some aspects of the state of the art are presented related to the research activity described in the rest of this chapter. 2.1 UWB indoor positioning In the specific field of UWB systems for indoor positioning there is also a large number of research activities. In fact such systems are considered good candidates for accurate ranging mainly due to their fine time resolution which is a .
