Transmit diversity for passive backscatter RFID

摘要

Techniques are presented for adaptively increasing power delivered to an RF tag. In one embodiment, a tag reader uses multiple transmit antennas to increase the power delivered to an RF tag without increasing the transmission power. The tag reader may perform transmit diversity (or a related antenna diversity schema) to ensure that transmitted signals from the multiple transmit antennas constructively interfere at the location of the RF tag. The tag reader may transmit a pilot signal and measure a phase associated with a received signal from the RF tag. The tag reader may then use the phase to determine a phase shift for each of the plurality of antennas. The phase shift may then be applied to any subsequent signals transmitted by the antennas to ensure that the signals interfere at the RF tag's location.

主权项

1. A method of delivering power to an RF tag, comprising:
transmitting a pilot signal from a first antenna, the first antenna selected from a plurality of antennas coupled to an RF tag reader; measuring a first phase of a modulated signal received from the RF tag, wherein the modulated signal is emitted by the RF tag in response to the pilot signal; determining a phase shift by identifying, based on the first phase of the modulated signal, a phase delay of a forward link in a backscatter channel corresponding to the first antenna of the plurality of antennas; and phase shifting a first signal transmitted by at least one of the plurality of antennas based on the phase shift, wherein the phase shift is selected to cause interference between the first signal and at least a second signal transmitted from a different antenna of the plurality of the antennas at a location of the RF tag.