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WO2001065481A1 - Systeme d'etiquette radio et procede servant a eviter les interferences entre les etiquettes - Google Patents

Systeme d'etiquette radio et procede servant a eviter les interferences entre les etiquettes Download PDF

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Publication number
WO2001065481A1
WO2001065481A1 PCT/US2000/005773 US0005773W WO0165481A1 WO 2001065481 A1 WO2001065481 A1 WO 2001065481A1 US 0005773 W US0005773 W US 0005773W WO 0165481 A1 WO0165481 A1 WO 0165481A1
Authority
WO
WIPO (PCT)
Prior art keywords
tag
tag transceiver
transceiver
radio frequency
signal
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/US2000/005773
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English (en)
Inventor
Wayne E. Steeves
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Axcess Inc
Original Assignee
Axcess Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Axcess Inc filed Critical Axcess Inc
Priority to PCT/US2000/005773 priority Critical patent/WO2001065481A1/fr
Priority to AU2000237263A priority patent/AU2000237263A1/en
Publication of WO2001065481A1 publication Critical patent/WO2001065481A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K19/00—Record carriers for use with machines and with at least a part designed to carry digital markings
    • G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
    • G06K19/067—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components
    • G06K19/07—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips
    • G06K19/0723—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
    • G06K7/0008—General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer

Definitions

  • This invention relates generally to radio frequency identification (RFID) systems and methods, and specifically to systems and methods for two way communication among radio tags and readers using techniques that reduce interference among a number of radio tags .
  • RFID radio frequency identification
  • Radio receivers and transmitters have been used for many years to identify personnel and objects m such environments.
  • many systems are known for attaching radio tags to items, such as automobiles, so that when automobiles equipped with radio tags enter a certain area, such as a toll booth area, the automobiles are automatically identified and the appropriate tolls are deducted from corresponding accounts, thereby obviating the need for drivers to stop and make payment at toll booths.
  • Innumerable other applications for such radio tag systems have been identified, m areas ranging from inventory control to facility security to sporting event timing.
  • known systems typically provide an RFID "reader" for each lane of traffic.
  • readers intentionally have a small effective coverage area to prevent signals from multiple vehicles from interfering with one another. Otherwise, multiple tags transmitting simultaneously from two or more vehicles might cause signal interference with one another, thereby impeding the reception of valid data at a reader.
  • multiple-read systems are known for reducing the deleterious effects of collisions among multiple tag signals, none is sufficiently robust to effectively provide a multiple-read system that uses a single reader to cover an area where a large number of radio tag-equipped vehicles are entering at the same
  • a data transmission system (100) includes a reader transceiver
  • the reader transmits an activation signal to the tag.
  • the tag selectively transmits a response signal to the reader at a specific time determined by a detected level of communications channel activity.
  • the specific time for transmitting the response signal is determined by the tag according to a randomized time slot selection seeded by a pre-transmission listening period to determine the amount of RF traffic.
  • the reader transmits a request signal and the tag selectively transmits a response signal based on predetermined characteristics of the request signal .
  • the tag operates m a low-power standby state until reception of the activation signal causes the tag to operate m an active state.
  • a method of transmitting data includes transmitting, by a reader transceiver, an activation signal to a radio tag; and transmitting, by the radio tag, a response signal to the reader at a specified time, the specified time being determined responsive to an activity level of a communications channel.
  • Further aspects of the invention utilize a two way communications protocol which includes tag acknowledgment to take advantage of stopping near field tags from transmitting repetitively so that far field tags can transmit m accordance with the invention without interference from the stronger signal of the near field tags .
  • a simple modified superregenerative circuit is utilized wherein the quench frequency is varied to control current draw and tag sensitivity to activation signals.
  • FIG. 1 is a block diagram of a system for data transmission, m accordance with the present invention.
  • Figure 2 is a clock diagram of a radio tag, m accordance with the present invention.
  • Figure 3 is a flow chart illustrating processing, m accordance with the present invention.
  • Figure 4 is a clock diagram of a superregenerative micropower receiver circuit m accordance with the present invention.
  • Figure 5 is a diagram of superregenerative receiver quench frequency oscillator outputs m accordance with the present invention.
  • Figure 6 is a diagram of the components of each reader 101-103 m accordance with the present invention.
  • FIG. 1 there is shown a system 100 m accordance with the present invention.
  • the operation of the system 100 is illustrated by discussion of the component parts illustrated m Figure 1.
  • three readers 101 - 103 each with respective antennas 111 - 113, communicate with radio tags 151 - 155.
  • computer 110 connected to readers 101 - 103 directs the transmission of signals from readers 101 - 103 to tags 151 - 155 and processes data received by readers 101 - 103.
  • Readers 101 - 103 communicate with computer 110 via a media independent control network such as LonWorks ® (a registered trademark of Echelon, Inc.) .
  • LonWorks ® a registered trademark of Echelon, Inc.
  • Computer 110 contains applications level software that commands the readers to interrogate m accordance with the desired application of the present invention. Each reader 101-103 is individually addressed by computer 110 using industry standard control network protocols or, m the case of an RF interconnection scheme, the collision avoidance techniques of the present invention are utilized. In a preferred embodiment, computer 110 is connected to readers 101-103 using conventional industry standard physical connections, e . g. , under the industry standard EIA232 or EIA485 protocols. The application software running on computer 110 communicates via the physical connections using conventional ASCII command syntax. For example, m a preferred embodiment commands issued by computer 110 to readers 101-103 take therefrom of a packet m C language syntax, such as:
  • system 100 uses improved techniques for avoiding collisions among tag signals, for detecting such collisions, and for reconstructing data packets affected by such collisions.
  • a tag e . g . , 151
  • a reader e . g. , 101
  • the reader sends a request for information, m essence polling any activated tags within range.
  • a receiving tag determines whether the requested information is relevant to that tag. If not, the tag returns to its quiescent stand-by state. If the request is relevant, the tag transmits the requested information to the reader as detailed herein. Referring now also to Figure 2, a tag, e .
  • microcontroller 2C1 includes a microcontroller 2C1, an PF transmitter 202, an RF receiver 203, and an antenna 204.
  • microcontroller 201 is implemented using a conventional model MC143120 microcontroller chip available from Motorola, Inc. (m alternative embodiments other microcontrollers, such as a model COP842 microcontroller chip from National Semiconductor, Inc., may be used)
  • RF transmitter 202 is implemented using a conventional transmitter circuit such as model NT315TX available from Advanced Systems Group International
  • antenna 204 is implemented using a conventional antenna with conventional switching circuitry allowing use of antenna 204 with both transmitter 202 and receiver 203. It should be recognized that other components could be used in alternate embodiments.
  • RF receiver 203 is, m a preferred embodiment, implemented by a modified super-regenerative receiver circuit whereby the quench frequency is varied to provide quiescent operation with a current draw m a quiescent stand-by state of less than 2 microamps, further described below.
  • power control functions of superregenerative receiver permit some of the elements of receiver 203 to be completely shut down to save tag power while operating m a quiescent state.
  • Conventional superregenerative receiver designs include a front end amplification stage, a local oscillator operating at the center frequency, a quench frequency oscillator operating with a duty cycle of at least 10 times the data rate, and a detector circuit.
  • the modified design of the present invention includes the amplification stage 401, the local oscillator 402, and quench frequency source 403, and a detector stage 404 as m conventional designs.
  • Conventional designs utilize typical forward-biased transistor stages configured as amplifiers.
  • the present invention utilizes tne same method of amplification except that forward biasing is provided by the quench frequency such that power draw is limited to 50% of the normal 100% biasing techniques due to the 50% duty cycle of the quench.
  • Amplifier power 401 is limited to leakage currents only (generally less than 500 nanoamps) when the quench frequency is shut down.
  • the local oscillator (LO) m conventional designs s controlled by the quench frequency such that t is turned off prior to achieving stable oscillation. In this way the RF is sampled as the LO is able to achieve stable oscillation significantly faster in the presence of an RF signal than without an RF signal.
  • the detector circuit simply filters out the quench and LO frequencies (low pass filters) leaving the pulse created by the increased size of the RF envelope with RF present . Since the LO 402 is also turned on and off by the quench frequency, power can also be controlled m the same way as the front end amplifier 401 biasing described above.
  • a Surface Acoustic Wave (SAW) Delay Line 408 (m a preferred embodiment model no. SL1011 from RF Monolithics, and m alternate embodiments any of the SLXXXX series of devices or equivalents) provides stability to the LO frequency and inserts the proper timing for signal reception 400, amplification 401 and quench 403 sampling of the LO 402.
  • the quench frequency oscillator 403 actually consists of two separate oscillators that operate in one of two modes and that are referred to as quench oscillator full power mode 405 and quench oscillator low power mode 406.
  • the oscillator 403 In low power quiescent mode, the oscillator 403 outputs a quench signal as m Figure 5.
  • a duty cycle of 1 to 5% over a period of 10ms provides sufficient time for reception of a 20 to 30ms activation signal and reduces total circuit draw by as much as 99%.
  • the high pulse consists of a 30 to 500khz 50% duty cycle trapezoidal pulse train for normal quenching of the LO 402.
  • microcontroller 407 turns off the low duty cycle oscillator 406 such that the 50% 30 to 500khz normal quench frequency is maintained for normal data retrieval .
  • the detector circuit 404 is a micropower diode/comparator arrangement although other more efficient types of detectors can be implemented m alternate embodiments as long as the power requirement is 1 microamp or less to minimize the total circuit power requirement.
  • the detector circuit 404 illustrated Figure 4 is typical of superregenerative and other receiver designs, with low power consumption being achieved through use of conventional low power componentry, e . g. , m a preferred embodiment a model MAX417 dual op-amp device from Maxim (not shown) .
  • detector circuit 404 operates as follows: The output of quench frequency oscillator 403 as integrated with the local oscillator 402 is first passed through a low pass filter (not shown) and applied to the first op amp of the Maxim device to amplify the resulting signal sufficiently to be applied to the second op amp of the Maxim device, which is configured as a comparator creating a data pulse from detector circuit 404 when triggered. This data pulse is then applied to microcontroller 407 to indicate that quench frequency oscillator 403 should be placed m full power mode 405 by setting quench oscillator low power mode 406 to a stable high output state.
  • Microcontroller 201 is conventionally programmed to provide the logic for the functionality described herein, and is coupled to receiver 203 to provide receiver sensitivity and power control via the quench oscillator 403.
  • Tag 151 is normally a low-power quiescent stand-by state which tag 151 monitors the RF environment for an activation signal from a reader, e . g. , 101.
  • a reader initiates 301 a request for tag data by transmitting such an activation signal, followed by a request for data.
  • the activation signal is received 302 by all tags within range of the transmitting reader, and causes each such tag to change from quiescent stand-by state to an active state. Once m active state, the tags evaluate 303 the request sent by the reader.
  • the activation signal is a modulated waveform with a preamble and a unique reader ID number.
  • Modulation is pulse width using conventional continuous wave (CW) , i.e., unmodulated, signal at the center frequency to which the RF receiver 203 is tuned.
  • CW continuous wave
  • a reader transmits a request that is directed to a single tag, to a subset of tags, or to any tag within range as directed by computer 110. Based on the nature of the request, each active tag makes a determination 304 as to whether the request is relevant to that tag. If not, the tag returns 306 to quiescent stand-by state.
  • the tag assembles 305 a packet of data, including a tag identification number and, depending on the nature of the request from the reader, other relevant information. For example, one application the request may be for all tags corresponding to fresh food crates to identify themselves and to transmit their pre-programmed expiration dates. If the requested data are voluminous, a preferred embodiment the data are formed into several packets for individual transmission. In practice it is found that fewer collisions occur by transmitting several smaller packets than one large packet .
  • the tag receiver e . g . , 203, monitors 307 the RF traffic on the transmission channel to determine whether many other tags are responding.
  • the tag Based on the amount of other traffic, or noise, the RF environment, the tag calculates 308 time slot availability for transmission of its data.
  • the time slot availability includes a random component and is determined based upon packet size and the level of RF traffic being generated by other tags.
  • the preprogrammed data rate and the amount of RF traffic determines the time the tag will spend determining slot availability.
  • the duration of a time slot is determined by dividing the tag data packet size by the fixed data rate of the tag. In a preferred embodiment, a data rate of 20k bits per second is employed with a packet size of 200 bits, making the time slots (i.e., cycle duration) equal to 200/20000, or 10 ms .
  • the maximum packet size for each tag is 200 bits and is pre-programmed at the time of manufacture. Packet size for a particular transmission is determined by the data being requested by the interrogation command sent by the reader, e.g., 101.
  • Each tag is programmed to transmit during a fixed number of active cycles (two in a preferred embodiment) , followed by a fixed number of passive cycles during wnich the tag does not transmit (ten a preferred embodiment) .
  • the tag redundantly transmits the exact same packet during each of the two active cycles.
  • the tag is silent for a randomized number of passive cycles.
  • the random number is less than or equal to the fixed number of passive cycles .
  • Each reader transmits back acknowledgments using this same scheme.
  • one complete transmission from a tag would include a first random passive portion of, say, 7 cycles; a first fixed active portion of one cycle; a second random passive portion of, say, 4 cycles; a second fixed active portion of one cycle; and a final fixed passive portion of 10 cycles.
  • a tag that is preparing to transmit will listen for a pattern of two active cycles from another transmitting tag (the transmitting tag being uniquely identified by the ID number it transmits on each active cycle) , and will synchronize with such transmitting tag based on the second active cycle transmission (after which that tag is certain to be silent for ten cycles) .
  • the tag attempting to commence transmission listens for RF activity from other tags during the final fixed passive 10-cycle period of the tag to which it has synchronized and, based on the amount of detected RF activity, determines whether to (l) transmit its signal during the next fixed passive 10-cycle period which it detects, or (n) wait for a longer period of time to allow the RF environment to quiet down. In practice, it is found that the likelihood of simultaneous transmissions from multiple tags is significantly reduced by this technique.
  • each tag attempting transmission can then determine how many of the ten passive cycles, i . e . , available time slots, are being used by other tags. For instance, if the tag detects RF activity during eight of the ten passive cycles, that indicates a very crowded RF environment. In such event, the tag may determine not to initiate transmission, since it is highly probable that such transmission would take place at the same time as transmission from another tag and might therefore not be properly received by a reader, e . g. , 101.
  • the tag will continue to identify a series of two active cycles from some transmitting tag and determine the relative RF activity during the following 10 passive cycles until the amount of activity has reached some threshold value where transmission by the listening tag would have a sufficient possibility of successful transmission.
  • this threshold is based on no RF activity being detected for at least five of the ten passive cycles. Also a preferred embodiment, the threshold is based not on a single 10-cycle period but on a rolling average of several such periods.
  • the tag wishing to transmit begins transmission of its message during one of the cycles of an ensuing ten passive cycle period, choosing at random one of the particular ten cycles for commencement of transmission. As previously described, the tag then waits a random number of passive cycles (m the preferred embodiment between one and ten) before its second active cycle, and then is silent for a fixed duration of ten more cycles.
  • the tag randomly selects 309 time slots for transmission and waits 310 for that selected time slot.
  • the tag transmits 311 a packet of data (using the two active cycles described above) and checks 312 for an acknowledgment signal from the reader indicating that the data packet was received.
  • a check 312 is made to see whether there are additional packets to transmit, which case processing returns to 307 to enable such transmission as described above. If the acknowledgment signal is not received, processing returns to 310 so that the current packet may be retransmitted at the next available time slot. After all of the packets have ceen successfully transmitted, processing returns to 306 and the tag is put back the quiescent low-power standby state .
  • system 100 can tolerate slight overlaps of transmissions causing interference at the beginning or end of a data packet transmission.
  • a number of hashing bits are installed at the beginning and end of each packet to verify data is received accurately and to possibly allow m some embodiments for data reconstruction m the event an overlap occurs.
  • the first and last bits generally have a 2 to 5 times greater pulse width than a normal bit and transmission overlap will then usually only impact the first several bits.
  • the hashing bits allow the reader unit to substitute bits until the hashing bit agrees with the input.
  • Final error checking occurs using other more conventional error correction techniques, including CRC error coding.
  • CRC error coding is employed so that intermittent lost or invalid bits due to noise or collision m the transmission channel that were reconstructed can be re-ve ⁇ fled.
  • the most robust signal transmission techniques are applied to the tag ID number, so that even if other data transmitted by the tag are lost, computer 110 can recognize that a particular tag was trying to send data and another request for transmission by only that tag may be made from one of the readers when the RF activity quiets down.
  • use of these techniques provides effective data transmission with as low as 7 dbm differentiation between colliding signals. Since an acknowledged signal is not retransmitted, the stronger tags the near field (i.e., those closer to the reader) complete their transmissions quickly, leaving a quieter RF environment for more distant tags m the far field to respond. By eliminating the strongest signals early on, and randomizing the time slot selection for weaker signals, it is found that a large number of tags may be detected m a relatively short time period and with relatively small bandwidth requirements.
  • Each reader 101-103 operates both individually and m concert with the other readers 101-103 and computer 110.
  • Each reader 101-103 is assigned a unique ID number by the applications software or as burned at time of manufacture.
  • the tag activation/wakeup signal consists of a short pulse with this reader ID number. In a preferred embodiment, such pulse will be, on the order of 8 ms in duration, but the duration will depend on the number of bits required to uniquely specify the reader ID number and may be longer than 8 ms if a large number of readers, each with a unique ID number, are used.
  • transmission of the reader ID number is followed by tag-specific polling information.
  • the tags, e . g. , 151, as part of the transmission packet will also transmit back this reader ID number as confirmation that it is responding to a particular reader case the signal is received by some other adjacent reader unit.
  • an adjacent reader unit receives data intended for another reader
  • the data is m one embodiment retained
  • an acknowledgment issued to the tag and the other reader contacted to verify the tag information is received.
  • the activating reader then acknowledges receipt of the tag data to the receiving reader and either rejects the data or maintains it for later disposition to the computer 110.
  • the protocol described herein provides a very effective mechanism for reducing RF traffic and allows far field tags to respond separately without being forced to wait for available far field time slots. In addition, repetitive attempts are significantly reduced, thus saving bandwidth.
  • each reader e . g. , 101
  • each reader consists of a miniature network and of itself essentially providing a means for parallel processing of different or even similar tasks.
  • Reader to reader communications are performed using a specific processor that is directly connected to other readers via any type of conventional connection (e.g., RF, power line, twisted pair cabling, or other type of media) and routes pertinent information to the appropriate internal reader process, e . g . , valid receipt of a far field tag from a poll request is routed to the reader receiver processor.
  • any type of conventional connection e.g., RF, power line, twisted pair cabling, or other type of media
  • reader 101 includes a reader network processor 601, an RF receiver with processor 602, an RF transmitter with processor 603, a memory/data storage component with processor 604, a power supply and regulation circuitry 605, and an I/O & relay controller module with processor 606.
  • Each component of the reader is configured to operate independently of the other, so each component or module can be subtracted or added m multiples and other such modules can be added to provide additional capabilities.
  • each module includes a microcontroller 608, a functional circuit 610 providing the specific function of the module, and a media access circuit 609 providing communication with the other components of reader 101.
  • each module of each available reader can be shared with other readers, either to save cost or to provide fault tolerance to the network.
  • the computer 101 communicates with the reader network via a serial, wiegand reader communications module 611 or, m an alternate embodiment, another industry standard I/O port.
  • the physical connection is directly from the computer 110 to the communications module 611 installed withm an individual reader or m an alternative embodiment as a standalone module connected to the reader network.
  • Power supply/battery module 607 and battery backup 608 provide alternate power sources m applications where such are deemed desirable.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Artificial Intelligence (AREA)
  • Computer Vision & Pattern Recognition (AREA)
  • Near-Field Transmission Systems (AREA)

Abstract

Système de transmission de données comprenant un émetteur-récepteur lecteur et un ou plusieurs émetteurs-récepteurs d'étiquettes. Le lecteur transmet un signal d'activation à une étiquette. L'étiquette transmet, de façon sélective, un signal de réponse au lecteur à un moment spécifique déterminé par un niveau détecté d'activité de voix de communication. Le détecteur fonctionne dans un état de veille basse puissance jusqu'au moment de réception du signal d'activation, puis fonctionne ensuite dans un état actif. L'invention concerne, de plus, une technique servant à maintenir un état de puissance extrêmement basse pour l'étiquette en mode de repos, tout en conférant une totale sensibilité à des signaux d'activation émis par le lecteur. Les émetteurs-récepteurs lecteurs présentent une architecture modulaire, chaque module fonctionnant de façon indépendante, et, cependant, en concert avec les autres. Ces modules sont interconnectés selon une technique indépendante du support et peuvent entrer en interaction à distance avec d'autres modules.
PCT/US2000/005773 2000-03-01 2000-03-01 Systeme d'etiquette radio et procede servant a eviter les interferences entre les etiquettes Ceased WO2001065481A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
PCT/US2000/005773 WO2001065481A1 (fr) 2000-03-01 2000-03-01 Systeme d'etiquette radio et procede servant a eviter les interferences entre les etiquettes
AU2000237263A AU2000237263A1 (en) 2000-03-01 2000-03-01 Radio tag system and method with tag interference avoidance

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/US2000/005773 WO2001065481A1 (fr) 2000-03-01 2000-03-01 Systeme d'etiquette radio et procede servant a eviter les interferences entre les etiquettes

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005029698A2 (fr) 2003-09-15 2005-03-31 Rf Saw Components, Incorporated Procede de discrimination d'etiquettes d'identification a ondes acoustiques de surface
WO2008026988A1 (fr) * 2006-09-01 2008-03-06 Leptonradio Ab Dispositif pour un fonctionnement sans fil et procédé d'actionnement du dispositif
WO2008015613A3 (fr) * 2006-08-03 2008-06-05 Kimberly Clark Co Système d'antenne intelligente pour lire des étiquettes de données
US7752089B2 (en) 2007-03-02 2010-07-06 The Curators Of The University Of Missouri Adaptive inventory management system
US8143996B2 (en) 2007-01-08 2012-03-27 The Curators Of The University Of Missouri Decentralized radio frequency identification system

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4471345A (en) * 1982-03-05 1984-09-11 Sensormatic Electronics Corporation Randomized tag to portal communication system
US5541928A (en) * 1993-11-02 1996-07-30 Nippondenso Co., Ltd. Communication system which establishes communication sessions based on unit ID codes to avoid transmission conflicts
US5754541A (en) * 1994-06-20 1998-05-19 Nokia Telecommunications Oy Data transmission method, base station, and subscriber terminal
US5774459A (en) * 1993-05-12 1998-06-30 Gemplus Card International Method of managing the transmission of messages from a set of transmitters to a single receiver on a single channel

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4471345A (en) * 1982-03-05 1984-09-11 Sensormatic Electronics Corporation Randomized tag to portal communication system
US5774459A (en) * 1993-05-12 1998-06-30 Gemplus Card International Method of managing the transmission of messages from a set of transmitters to a single receiver on a single channel
US5541928A (en) * 1993-11-02 1996-07-30 Nippondenso Co., Ltd. Communication system which establishes communication sessions based on unit ID codes to avoid transmission conflicts
US5754541A (en) * 1994-06-20 1998-05-19 Nokia Telecommunications Oy Data transmission method, base station, and subscriber terminal

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005029698A2 (fr) 2003-09-15 2005-03-31 Rf Saw Components, Incorporated Procede de discrimination d'etiquettes d'identification a ondes acoustiques de surface
EP1665526A4 (fr) * 2003-09-15 2008-09-10 Rf Saw Components Inc Procede de discrimination d'etiquettes d'identification a ondes acoustiques de surface
WO2008015613A3 (fr) * 2006-08-03 2008-06-05 Kimberly Clark Co Système d'antenne intelligente pour lire des étiquettes de données
WO2008026988A1 (fr) * 2006-09-01 2008-03-06 Leptonradio Ab Dispositif pour un fonctionnement sans fil et procédé d'actionnement du dispositif
US8368514B2 (en) 2006-09-01 2013-02-05 Leptonradio Ab Device for wireless operation and method for operating the device
US8143996B2 (en) 2007-01-08 2012-03-27 The Curators Of The University Of Missouri Decentralized radio frequency identification system
US7752089B2 (en) 2007-03-02 2010-07-06 The Curators Of The University Of Missouri Adaptive inventory management system

Also Published As

Publication number Publication date
AU2000237263A1 (en) 2001-09-12

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