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Enhanced uplink modulated backscatter system
| Details |
Inventors: MacLellan, John Austin; Shober, R. Anthony; Vannucci, Giovanni;
Assignee: Lucent Technologies Inc. (Murray Hill, NJ)
Primary Examiner: Cuchlinski, Jr.; William A.
Assistant Examiner: Beaulieu; Y.
Attorney, Agent or Firm:
A Time Division Multiple Access (TDMA) duplex radio communication system uses an Interrogator to generate a first radio signal by modulating a first information signal onto a radio carrier signal which is sent to at least one remote Tag of the system. The remote Tag receives and modulates a second information signal onto a second radio carrier signal to form a second modulated signal which is transmitted, in a time-slotted manner, back to the Interrogator. The remote Tag selects, or is instructed, how many times it should repetitively transmit the second modulated signal; and selects, or is instructed, over how many of the time slots following receipt of the first radio signal the remote Tag should repetitively transmit the second modulated signal. Other embodiments use Modulated Backscatter to transmit the second modulated signal, and use homodyne detection to demodulate the second modulated signal. A Frequency Division Multiple Access (FDMA) duplex radio communication system embodiment utilizes multiple subcarrier frequencies and another embodiment combines the FDMA and the TDMA methods. A Code Division Multiple Access (CDMA) embodiment utilizes multiple spreading codes and another embodiment combines the CDMA and the TDMA methods. |
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DETAILED DESCRIPTION RFID system applications differ greatly in the data rate requirements for the Downlink (Interrogator to Tag) and the Uplink (Tag to Interrogator) directions; they also differ greatly in other parameters, such as the number of Tags that may be located in the reading field.
For example, one class of applications involves using RFID technology to read information from a Tag affixed to a container or pallet.
In this application, the container is moved (by being pulled by a small truck) across the reading field of an Interrogator.
The reading field is defined as that volume of space within which a successful transaction can take place.
Since the Tag is moving through the reading field, the RFID system has only a limited amount of time to successfully complete the transaction In this application, the Tag could be moving as fast as 10 meters/second through the reading field.
The reading field would consist of a roughly conical volume, extending 5 meters away from the Interrogator, and the cone having an angle of roughly 60 degrees total spread (30 degrees to either side of a direct path from the Interrogator to a point immediately in front of the Interrogator).
Given this situation, the RFID communications with each Tag must be completed in less than about 0.
2 seconds.
Also, in this application, generally only a few (1-2) Tags are in the reading field at the same time.
Another application example is to use RFID flags to track sacks of mail in a post office.
In this example, the sacks of mail would be placed inside a large bin or container, and the bin moved through the reading field at a relatively low speed (perhaps 1-2 meters/second at most).
However, this application may have up to 50 or more Tags in the reading field simultaneously.
In other applications, RFID Tags may be attached to every item on the shelves of supermarkets, and these RFID Tags interrogated as the shopping cart is passed under (or through) an Interrogator reading field.
In this application, far beyond 50 Tags may need to be in the reading field
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Cell Phones 
