Locating Targets in RFID System in a Sensing Covered Anchor-Free Network

In an RFID system, the RFID readers consume huge energy and are considerably expensive in practical applications. To minimize the total number of readers with guaranteed surveillance such that the position of each tag can be uniquely determined is a challenge. This paper considers a simple but practically useful model of anchor-free network of RFID readers where each tag falls within the sensing zone of at least two readers. To maintain the quality of service in the real applications, a practical condition, the communication range is at least twice its sensing range, is considered. Under this condition, a characterization of a network is proved. An efficient algorithm for recognizing such a network is then developed without any initial position information of the readers. Using these readers as the references, an algorithm is designed for finding the exact positions of the tags in distributed manner. Unlike the existing techniques, it requires no external references for tag tracking. The proposed technique finds at most two possible positions (in some cases, unique position), out of which one is correct, for each tag.