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| Acceleration sensing ring laser gyroscope |
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| Vibrators vibratory gyroscopes a method of detecting a turning angular rate and a linear accelerometer |
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| Method and apparatus for tracking objects and people |
| OF THE PREFERRED EMBODIMENTS Referring now to the drawings wherein like reference numerals ... |
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| Time slot arrangements for local area network systems |
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| Sequence synchronization |
| We claim: 1. Apparatus for transmitting a data sequence from a transmitter to a receiver, including ... |
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| Mobile terminal having power saving mode that monitors specified numbers of filler messages |
| The foregoing and other problems are overcome and the objects of the invention are realized by ... |
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| Receiver for receiving a spectrum dispersion signal |
| The subject to be solved by the present invention is to suspend despreading code generating means ... |
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QPSK modulated backscatter system
| Details |
Inventors: MacLellan, John Austin; Shober, R. Anthony; Vannucci, Giovanni; Wright, Gregory Alan;
Assignee: Lucent Technologies Inc. (Murray Hill, NJ)
Primary Examiner: Trost; William G.
Assistant Examiner: Tran; Congvan
Attorney, Agent or Firm: Malvon; Christopher N., Lager; Irena
In accordance with the present invention, a duplex radio communication system comprises an Interrogator which generates a radio signal to at least one remote Tag. The remote Tag receives the radio signal. The Tag then generates a subcarrier signal, and using Quadrature Phase Shift Keying (QPSK), modulates an information signal onto the subcarrier. A Backscatter Modulator, using this modulated subcarrier, modulates the reflection of the radio signal, the reflected signal being a reflected modulated signal. The Interrogator receives and demodulates the reflected modulated signal to obtain the information signal. In one embodiment, demodulation utilizes a homodyne detector. In another embodiment, the Interrogator modulates an information signal onto the radio signal, transmits that modulated radio signal to the Tag, and the Tag demodulates that modulated radio signal to recover the information signal. In another embodiment, higher order phase modulations are used to modulate an information signal onto the subcarrier. |
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DETAILED DESCRIPTION One class of RFID applications involves using RFID technology to read information from a Tag affixed to a container or pallet.
In this application, the container is moved across the reading field of an Interrogator.
The reading field is defined as that volume of space within which a successful communication can take place.
While the Tag is in the reading field, the Interrogator and Tag must complete their information exchange before the Tag moves out of the field.
Since the Tag is moving through the reading field, the RFID system has only a limited amount of time to successfully complete the transaction.
With reference to FIG.
1, there is shown an overall block diagram of an illustrative RFID system useful for describing the application of the present invention.
An Application Processor 101 communicates over Local Area Network (LAN) 102 to a plurality of Interrogators 103-14104.
The Interrogators may then each communicate with one or more of the Tags 105-107.
For example, the Interrogator 103 receives an information signal, typically from an Application Processor 101.
The Interrogator 103 takes this information signal and Processor 200 (FIG.
2) properly formats a downlink message (Information Signal 200a) to be sent to the Tag.
The information signal (200a) includes information such as information specifying which Tag is to respond (each Tag may have fixed or programmed identification number), instructions for the Tag's processor to execute or other information to be used and/or stored by the Tag's processor.
With joint reference to FIGS.
1 and 2, Radio Signal Source 201 generates a radio signal, the Modulator 202 modulates the Information Signal 200a onto the radio signal, and the Transmitter 203 sends this modulated signal via Antenna 204, illustratively using amplitude modulation, to a Tag.
Amplitude modulation is a common choice since the Tag can demodulate such a signal with a single, inexpensive nonlinear device (such as a diode).
In the Tag 105 (see FIG.
3), the Antenna 301 (frequently a loop or patch antenna) receives the modulated signal
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Communications 
