Range Extension and Multiple Access in Modulated Backscatter Systems
First Claim
1. An RFID communication system comprising an RFID reader in communication with a plurality of RFID tags having an integrated circuit and a memory unit, the memory unit storing tag data representing the RFID tag identification, each RFID tag having a spreading sequence associated with the tag, the RFID tags responding to an RF signal from the RFID reader with a spread spectrum modulated backscatter signal including the tag data mixed with the spreading sequence, the RFID tag providing the spread spectrum modulated backscatter signal having a signal to noise ratio higher that a corresponding backscatter signal without the spreading sequence, the RFID reader receiving and correlating the spread spectrum modulated backscatter signal against expected spreading sequences to identify the corresponding RFID tag at a distance greater than for an RFID tag sending the corresponding backscatter signal without the spreading sequence.
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Accused Products
Abstract
One or more readers transmit radio frequency (RF) beacons to be electronically reflected by tags. Data transmitted via modulated backscatter from radio frequency identification (RFID) tags is encoded so as to permit reliable demodulation of simultaneous transmissions from multiple tags. This includes the use of spreading sequences as in direct sequence spread spectrum, where the spreading sequences may be a function of the tag ID, or may be randomly chosen. Backscattered signals from multiple tags may be detected using well-known receiver techniques for code division multiple access (CDMA) systems. Readers may be equipped with transmit and/or receive antenna arrays. A receive antenna array permits a reader to estimate directions of arrival for received signals, as well as to enhance range by performing receive beamforming.
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Citations
12 Claims
- 1. An RFID communication system comprising an RFID reader in communication with a plurality of RFID tags having an integrated circuit and a memory unit, the memory unit storing tag data representing the RFID tag identification, each RFID tag having a spreading sequence associated with the tag, the RFID tags responding to an RF signal from the RFID reader with a spread spectrum modulated backscatter signal including the tag data mixed with the spreading sequence, the RFID tag providing the spread spectrum modulated backscatter signal having a signal to noise ratio higher that a corresponding backscatter signal without the spreading sequence, the RFID reader receiving and correlating the spread spectrum modulated backscatter signal against expected spreading sequences to identify the corresponding RFID tag at a distance greater than for an RFID tag sending the corresponding backscatter signal without the spreading sequence.
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7. A method for RFD communication, comprising:
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transmitting an RF signal from an RFID reader to a RFID tag; mixing a RFID tag identification data with a spreading sequence to produce a resultant output; reflecting the RF signal from the RFID tag to the RFID reader as a spread spectrum modulated backscatter signal modulated with the resultant output and having a signal to noise ratio higher than a backscatter signal modulated without the spreading sequence; reading the spread spectrum modulated backscatter signal at the RFID reader, the RFID reader having a first receive antenna; and correlating the spread spectrum modulated backscatter signal against expected spreading sequences to identify the corresponding RFID tag that provided the spread spectrum modulated backscatter signal, even with the spread spectrum modulated backscatter signal being reflected at a power too low to be read by the RFID reader when absent the spreading sequence. - View Dependent Claims (8, 9, 10, 11)
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12. A CDMA communication system comprising an RFID reader in communication with a plurality of RFID tags having an integrated circuit and a memory unit, the memory unit storing tag data representing the RFID tag identification, each RFID tag having a spreading sequence associated with the tag, the RFID tags responding to an RF signal from the RFID reader with a CDMA signal including the tag data mixed with the spreading sequence, the RFID tag providing the CDMA signal having a signal to noise ratio higher that a corresponding backscatter signal without the spreading sequence, the RFID reader receiving and correlating the CDMA signal against expected spreading sequences to identify the corresponding RFID tag at a distance greater than for an RFID tag sending the corresponding backscatter signal without the spreading sequence.
Specification