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An electronic leash is the pairing (“leashing”) of one or more wireless devices to a host device that allows the user to find misplaced or out-of-sight objects by activating the host device such that the “leashed” object identifies itself. The system is identical in concept to a key pager, but offers multiple codes that allow a single user-operated device to send codes to a large number of objects. Leash systems generally also offer a form of distance measurement that raises an alarm if the leashed object travels more than a selected distance from the operator. == Modes of operation == The concept may be implemented by various vendors in different ways. A code transmission in conjunction with a distance measurement raises an alarm as soon as a predetermined distance between the paired devices is exceeded. Receivers may be born by the owner of an object, whereas the other transmitting item gets attached to the object for virtually leashing it to the owner. The transmission distance is adjusted to the intention of keeping the leashed object in contiguity to the bearers body or workdesk or mobile workplace environment, that is a distance usually as short as the visually controlled ambience, i.e. no more than about five metres. There are four different concepts available for implementing the required distance to raise the alarm: * conventional RSSI concept as defined by the WLAN IEEE 802.11 and Bluetooth IEEE 802.15.1 standards * transmission power variation without breaking connection * transmission power variation provoking breaking connection * transmission power polarisation segregating direct and indirect path signalling The four options make use of various physical phenomena and thus offer a variety of signal processing to overcome * multipath propagation, * crinked and direct paths * multipath fading and * excess reach of nearby colliding transmitters * higher populations of transmitters. Two factor concept fails if both items get lost at the same time without raising alarm or one of the batteries is below operational stage or one item is simply inactive. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Electronic leash」の詳細全文を読む スポンサード リンク
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