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The location accuracy of an RFID system (that is, its ability to locate an object in space) would depend on the type of RFID system to which you are referring. Generally speaking, most passive HF and UHF RFID systems do not provide location accuracy—they tell you that a tag has been read by a specific reader. Since you would know the location of the reader by its unique ID (say, dock door 1), you would know the tag was in the read zone of that reader (that is, the tagged item came through dock door 1).
There are some passive UHF real-time location systems (RTLSs) that can tell you the location of a tag in 3D space. These are typically accurate to within a one-meter cube. These passive systems might cover 10 square meters each, so you would need multiple readers to cover 50 square meters.
Active RFID-based RTLSs have tags that use a battery to broadcast a signal. Readers around a defined area triangulate on that signal and pinpoint its location. Because the tag is sending out a signal, like a cell phone, the tags can be read from much further away—1,000 meters or more. You can cover a large area with fewer readers than a passive RTLS, but the tags cost more. The location accuracy of an active RTLS is usually within 3 meters.
An ultra-wideband RTLS is able to achieve greater location accuracy over long distances by using different frequencies to mitigate something called multipath, where signals bounce off surfaces and reach the reader at different times, making it hard to calculate distance precisely. A UWB system can locate a tagged object to within 10 centimeters. You can set the tags to emit signals in microseconds to record movement.
As for the last part of your question, I do not know how much energy is required. Readers are typically plugged in and do not measure how much energy they are using (at least, not to my knowledge).
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