Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1999-08-11
2001-07-24
Vo, Don N. (Department: 2734)
Pulse or digital communications
Spread spectrum
Direct sequence
Reexamination Certificate
active
06266362
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to data communication with low power radio frequency (RF) transceivers, specifically to data communication between RF identification (RFID) tags and an operator (interrogator) and, more particularly, to using spread spectrum techniques to simplify the tag receiver design, reduce tag cost, increase the range and reduce interference on the RF communication channel.
2. State of the Art
An RFID tag is a small radio transceiver that can be attached to a movable article to help keep track of its whereabouts and status. A small, lightweight, inexpensive tag is desirable. To miniaturize the tag, the size of the circuitry is reduced by using an integrated circuit (IC) design. The simpler the circuit, the smaller the resulting IC becomes, thereby reducing the cost.
Operational environment factors can disrupt the reliability of these weak communication links. Reflective and refractive properties of the environment introduce possible multipath errors, and outside RF sources introduce interference in the received signal.
SUMMARY OF THE INVENTION
The principal object of this invention is to provide a method by which an RFID tag can communicate more information over much greater distances through harsher RF environments than previously available, while reducing the size and cost of the tag IC.
The secondary objects of this invention are to provide: simple AM reception by the receiver circuit without having to use complex synchronization schemes, external frequency references such as quartz crystals and complex circuits like Costas loops;
interrogator transmission power to be less than or equal to 1 Watt, allowing unlicensed operation within FCC guidelines;
extension of the range from interrogator to RFID tag;
limitation of eavesdropping of signals by outside parties; and
selective addressing of particular tags or communicating with more than one tag simultaneously in any given transmission.
These and other objects are achieved by modulating a spectrally spread carrier with a pulse code waveform representing information pertaining to the article to which the tag is attached.
One advantage of using a spread spectrum modulated signal is the enhanced interference rejection obtained during the demodulation process. The effect is a signal to noise gain over traditional narrow band broadcasting techniques.
Using spread spectrum techniques gives good range with relatively little complexity on the tag. The high complexity is contained in the interrogator design.
Other advantages are: selectively addressing a particular receiver, pulse code multiplexing allowing addressing of a plurality of receivers in any given transmission, broadcast transmissions with low density power spectra for signal hiding, message encryption to discourage eavesdroppers, and high resolution ranging between transmitter and receiver.
Although this invention was specifically designed for RFID tag communication, there are applications for it in hand-held walkie-talkies, pagers, mobile phones, cordless telephones, cordless microphones and musical instruments, cordless computer network communication links, and intercoms.
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Hoyt Eugene P.
Springett James C.
Tuttle John R.
Micro)n Technology, Inc.
TraskBritt
Vo Don N.
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