Transmit Diversity for Backscatter RFID
Chenming Zhou (Disney Research Pittsburgh)
Azhar Hasan (Georgia Institute of Technology)
Joshua Griffin (Disney Research Pittsburgh)
The experimental setup used to measure backscatter transmit diversity with monostatic readers at 5.8 GHz. The four reader patch antennas are located on the table and the tag was moved over a grid using the 2D linear positioner.
Measurements showing the difference in power delivered to the RF tag with and without transmit diversity applied. The tag was moved along the X Path and Y Path shown by the dashed yellow lines (see the figure to the left).
The read range of passive, backscatter radio frequency (RF) tags is limited by the power delivered to the RF tag’s integrated circuit. This project seeks to increase the power delivered to passive backscatter RF tags using transmit diversity – a method that uses multiple antennas and channel knowledge to deliver power to the tag. By adjusting the phase of the signal transmitted from each reader antenna to cancel the phase delay of the channel, the signals from each antenna add constructively at the RF tag; hence, the power delivered to the RF tag is maximized. This technology can improve the read range and reliability for radio frequency RF tags in applications with time-varying channels — e.g., backscatter sensors operating near moving people or where radio frequency identification (RFID) tags cannot be confined to a portal.
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