Communications: electrical – Selective – Interrogation response
Utility Patent
1998-04-23
2001-01-02
Horabik, Michael (Department: 2735)
Communications: electrical
Selective
Interrogation response
C340S010300, C340S010400, C340S010410, C340S572800, C340S541000
Utility Patent
active
06169474
ABSTRACT:
TECHNICAL FIELD
The invention relates to wireless communication systems. More particularly, the invention relates to backscatter communication systems.
BACKGROUND OF THE INVENTION
Backscatter communication systems are known in the art. In a backscatter system, one transponder, such as an interrogator, sends out a command to a remote communications device. After the interrogator transmits the command, and is expecting a response, the interrogator switches to a CW mode (continuous wave mode). In the continuous wave mode, the interrogator does not transmit any information. Instead, the interrogator just transmits radiation at a certain frequency. In other words, the signal transmitted by the interrogator is not modulated. After a remote communications device receives a command from the interrogator, the remote communications device processes the command. The remote communications device of the backscatter system modulates the continuous wave by switching between absorbing RF radiation and reflecting RF radiation. For example, the remote communications device alternately reflects or does not reflect the signal from the interrogator to send its reply. Two halves of a dipole antenna can be either shorted together or isolated from each other to modulate the continuous wave.
One example of a backscatter system is described in commonly assigned U.S. patent application Ser. No. 08/705,043, filed Aug. 29, 1996, and incorporated herein by reference. Another example of a backscatter system is described in U.S. Pat. No. 5,649,296 to MacLellan et al. which is also incorporated herein by reference.
In backscatter systems, the power level of the command sent by the interrogator is the same as the power level of the continuous wave sent by the interrogator.
One application for backscatter communications is in wireless electronic identification systems, such as those including radio frequency identification devices. Of course, other applications for backscatter communications exist as well. Most presently available radio frequency identification devices utilize a magnetic coupling system. An identification device is usually provided with a unique identification code in order to distinguish between a number of different devices. Typically, the devices are entirely passive (have no power supply), which results in a small and portable package. However, such identification systems are only capable of operation over a relatively short range, limited by the size of a magnetic field used to supply power to the devices and to communicate with the devices.
Another wireless electronic identification system utilizes a large, board level, active transponder device affixed to an object to be monitored which receives a signal from an interrogator. The device receives the signal, then generates and transmits a responsive signal. The interrogation signal and the responsive signal are typically radio-frequency (RF) signals produced by an RF transmitter circuit. Because active devices have their own power sources, and do not need to be in close proximity to an interrogator or reader to receive power via magnetic coupling. Therefore, active transponder devices tend to be more suitable for applications requiring tracking of something that may not be in close proximity to an interrogator, such as a railway car.
SUMMARY OF THE INVENTION
The invention provides an interrogator for a backscatter system which allows the power level of a command or forward link to be set at a value different from the power level of a continuous wave for the return signal.
One aspect of the invention provides a method of communications in a backscatter system. The method comprises transmitting a command at a first power level; and transmitting a continuous wave for a backscatter reply. The continuous wave is transmitted at a second power level different from the first power level. In one embodiment, the second power level is higher than the first power level.
Another aspect of the invention provides a method of communications in a backscatter system including an interrogator and including a wireless communications device having an integrated circuit having a processor, and a memory, a receiver, and a backscatter modulator coupled to the processor. The method comprises transmitting a command from the interrogator to the wireless communications device at a first power level; and transmitting a continuous wave from the interrogator to the wireless communications device for modulation by the backscatter modulator at a second power level. Transmitting the command and transmitting the continuous wave comprises independently controlling the first power level and second power level.
Another aspect of the invention provides a backscatter system interrogator. The interrogator comprises a transmitter configured to transmit a command at a first power level and to transmit a continuous wave for a backscatter reply. The transmitter is configured to transmit the continuous wave at a second power level different from the first power level.
Another aspect of the invention provides a system comprising a wireless communications device including an integrated circuit having a processor, and a memory, a receiver, and a backscatter modulator coupled to the processor. The system further comprises an interrogator configured to transmit a command to the wireless communications device at a first power level and subsequently transmit a continuous wave to the wireless communications device for modulation by the backscatter modulator at a second power level. The first power level and second power level are independently controllable. The interrogator includes a controllable attenuator configured to control at least one of the first and second power levels.
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Greeff Roy
Ovard David
Asongwed Anthony A.
Horabik Michael
Micro)n Technology, Inc.
Wells, St. John, Roberts Gregory & Matkin P.S.
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