Abstract: Aspects and features of this disclosure include operating an RFID reader to identify targeted tags and background tags from among a population of RFID tags. The background tags are then monitored by reading the background tags at a background rate and the targeted tags are tracked by reading the targeted tags at an enhanced rate. The enhanced rate is significantly greater than the background rate. The tags from a large population can be segregated into the two subpopulations based on read measurements stored in a tag database. A tag may become “targeted” by moving towards or appearing near a portal of interest. Tag detection, and therefore an alarm message or some other desired result, can be provided quickly due to the higher, enhanced read rate being applied to the targeted tags.

Abstract: Aspects and features of this disclosure include a radio frequency identification (RFID) antenna multiplexer. An RFID reader and an RFID system using the RFID antenna multiplexer are also disclosed. The multiplexer includes multiple output ports. Each of at least some of the output ports is connectable to an antenna or another device. In some aspects, a logic circuit in the multiplexer is configured to cause a radio frequency (RF) switch to select an output port from the multiple output ports to connect to the input port based upon a reduction in RF power at the input port. In some aspects, the multiplexer includes an energy harvester connected to the input port to harvest signal energy from the RFID reader and a storage device connected to the energy harvester to store the signal energy and supply power to the multiplexer using the signal energy.

Abstract: Aspects and features of this disclosure include a radio frequency identification (RFID) antenna multiplexer. An RFID reader and an RFID system using the RFID antenna multiplexer are also disclosed. The multiplexer includes multiple output ports. Each of at least some of the output ports is connectable to an antenna or another device. In some aspects, a logic circuit in the multiplexer is configured to cause a radio frequency (RF) switch to select an output port from the multiple output ports to connect to the input port based upon a reduction in RF power at the input port. In some aspects, the multiplexer includes an energy harvester connected to the input port to harvest signal energy from the RFID reader and a storage device connected to the energy harvester to store the signal energy and supply power to the multiplexer using the signal energy.

Abstract: An RF system using amplitude modulation (AM) with orthogonal offset is disclosed. The orthogonal offset generator can shift the AM signal trajectory away from the origin while maintaining the time domain requirements for an RFID signal, such as waveform edge rise and fall times. In some embodiments stored waveforms incorporating the controlled orthogonal offset are used to synthesize a sequence of symbols. The stored waveforms may also include nonlinear and/or linear predistortion to reduce computational complexity. The waveforms can be represented in Cartesian coordinates for use in a direct conversion transmitter or polar coordinates for use in a polar modulation transmitter. An RFID system can also include a receiver to receive incoming RFID signals.