Communications: directive radio wave systems and devices (e.g. – Radar transponder system
Reexamination Certificate
2000-05-12
2001-12-11
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Radar transponder system
C342S044000, C342S050000, C342S051000, C340S007300, C340S010330, C340S010420
Reexamination Certificate
active
06329944
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
(Not Applicable)
BACKGROUND OF THE INVENTION
The present invention generally relates to radio frequency communications and more particularly to a radio frequency communication protocol between an interrogator and a tag.
Radio frequency (RF) tags are used for tracking of ground-based inventory by an overhead vehicle such as an aircraft or satellite. Upon interrogation by the radar of the aircraft or satellite, the radar responsive tag will transmit. a unique identifier. The unique identifier provides information about the tag. As such, RF tags are used to control inventory of assets on land and sea.
Typically, the RF tags are interrogated at unscheduled times. Accordingly, the RF tag must be turned on continuously to listen for the interrogator's signal. However, the tag's power consumption limits the tag's battery life to only a few hours when continuously listening for the interrogator. This deficiency is amplified by the fact that interrogation times are irregular and scheduling is impractical and/or impossible. The prior art RF tags typically remain in a state of readiness for interrogation thereby leading to a substantial amount of power consumption.
Prior art RF tags that allow unscheduled communications with an interrogator have limited signal processing and can only operate at short ranges. However, the limited signal processing ability of these prior art RF tags limits the tags to the processing of very strong signals. Weak and noisy signals are not useable with the prior art RF tag. This results in a limited operating range from as little as 1 meter to at most 100 meters for the prior art RF tag.
The present invention addresses the above-mentioned deficiencies in the prior art RF tags by providing a RF tag communications protocol between an interrogator and the RF tag. The communications protocol of the present invention provides a method whereby power consumption within the RF tag is adjusted thereby providing a power savings within the RF tag and extending the battery lifetime thereof. Additionally, the RF communications protocol of the present invention provides a method whereby the RF tag will respond only to an interrogator that is within a prescribed range. The RF communications protocol of the present invention provides a method of communication between an RF tag and an interrogator that is power efficient.
BRIEF SUMMARY OF THE INVENTION
A method of communicating to a RF tag having a low power mode and a scan mode with a radar and an interrogator. The method comprises the steps of alternating the RF tag between the low power mode and the scan mode and then transmitting a wake-up call to the RF tag with the radar. Next, the wake-up call is received from the radar by the RF tag when the RF tag is in the scan mode. Once the wake-up call has been received, the radar will transmit a downlink message to the RF tag. Upon receipt of the downlink message, the RF tag will send an uplink message to the radar. After the uplink message has been sent to the radar, the RF tag will return to the low power mode. By alternating the RF tag between the low power mode and the scan mode, the power consumption of the RF tag is greatly reduced thereby increasing the battery life thereof.
Typically, the RF tag is alternated between the low powered mode for 977 milliseconds and the scan mode for 23 milliseconds. The uplink message will not be sent to the radar until a prescribed period of time has passed. Typically, the prescribed period of time is specified in the downlink message received by the RF tag. Similarly, the RF tag will be returned to the low power mode after a prescribed period of time in order to conserve power. Typically, the prescribed period of time is about four hours.
In the preferred embodiment, a wake-up call is modulated with a linear frequency modulation. The radar will transmit the wake-up call in a left beam, a center beam, and a right beam. The pulse width of the left beam is 20 &mgr;s, the pulse width of the center beam is 30 &mgr;s, and the pulse width of the right beam is 40 &mgr;s. In the preferred embodiment, the downlink message and the uplink message are transmitted when the radar transmits a wake-up call in the center beam. In this respect, the RF tag will receive and transmit information to the radar when the beam from the radar is aligned with the RF tag.
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Bendor Giora A.
Decker Martin J.
Lee Henry E.
Richardson David L.
Stratmoen Scott A.
Anderson Terry J.
Hoch, Jr. Karl J.
Northrop Grumman Corporation
Sotomayor John B.
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