| 摘要 |
An apparatus ( 10, 240, 300 ) includes a signpost ( 11, 241 - 256, 322, 612, 623, 626 - 628, 652, 661, 682, 686, 703 ) which transmits signpost signals ( 24 ) that are received by a tag ( 12, 271 - 275, 301 - 316, 395 - 397, 616 - 618, 641 - 643, 653, 656 - 657, 662 - 664, 679, 708, 711 ). The tag in turn transmits radio frequency beacon signals ( 72 ) which are received by a reader ( 13, 261, 319, 521 - 530 ). The tag can vary the duration of the beacon signals, for example in dependence on whether it is currently receiving a signpost signal. Further, the tag can dynamically vary the transmission rate and/or transmission power of the beacon signals, for example following receipt of a signpost signal. Varying these parameters can facilitate compliance with governmental regulations.
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