| 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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