USO0RE41531E
(19) United States (12) Reissued Patent
(10) Patent Number: US RE41,531 E (45) Date of Reissued Patent: *Aug. 17, 2010
Wood, Jr. (54)
COMMUNICATIONS SYSTEMS FOR RADIO
FREQUENCY IDENTIFICATION (RFID) (75) Inventor: Clifton W. Wood, Jr., Tulsa, OK (US) (73) Assignee: Round Rock Research, LLC, Mount
Kisco, NY (U S) (*)
Notice:
This patent is subject to a terminal dis claimer.
(Continued) Primary ExamineriBrian D Nguyen (74) Attorney, Agent, or FirmiGaZdZinski & Associates,
(57)
Sep. 21, 2007
ABSTRACT
A [method of] system for establishing Wireless communica tions between an interrogator and individual ones of mul
Related US. Patent Documents
tiple Wireless identi?cation devices[, the method comprising
Reissue of:
(64) Patent No.: Issued:
utilizing a tree search method to establish communications
6,307,847
without collision between the interrogator and individual
Oct. 23, 2001
Appl. No.:
09/617,390
Filed:
Jul. 17, 2000
ones of the multiple Wireless identi?cation devices, a search
tree being de?ned for the tree search method, the tree having
multiple levels respectively representing subgroups of the multiple Wireless identi?cation devices, the method further
US. Applications: (63)
Continuation of application No. 10/693,697, ?led on Oct. 23, 2003, which is a continuation of application No. 09/026,
(51)
Int. Cl. H04W 4/00
043, ?led on Feb. 19, 1998, now Pat. No. 6,118,789.
(52) (58)
“13.56 MHZ ISM Band Class 1 Radio Frequency Identi?ca
tion Tag Interface Speci?cation: Recommended Standard,” Technical Report, Feb. 1, 2003.
PC
(21) Appl.No.: 11/859,364 (22) Filed:
OTHER PUBLICATIONS
AutoilD Center, Massachusetts Institute of Technology,
comprising starting the tree search at a selectable level of the search tree. A communications system comprising an interrogator, and a plurality of Wireless identi?cation devices con?gured to communicate with the interrogator in a wire
less fashion, the respective Wireless identi?cation devices having a unique identi?cation number, the interro gator being
(2006.01)
con?gured to employ a tree search technique to determine the unique identi?cation numbers of the different Wireless
US. Cl. ....................... .. 370/329; 370/346; 370/347 Field of Classi?cation Search ................ .. 370/329,
identi?cation devices so as to be able to establish communi
370/346, 347, 462, 408, 230, 437, 441, 442, 370/449, 458, 463, 342, 345, 348 See application ?le for complete search history. (56)
References Cited U.S. PATENT DOCUMENTS
cations between the interrogator and individual ones of the
multiple Wireless identi?cation devices without collision by multiple wireless identi?cation devices attempting to respond to the interrogator at the same time, wherein the interrogator is con?gured to start the tree search at a select able level of the searched tree.] The interrogator transmits a
?rst request comprising a bit string comprising aplurality of bitsfor use in selecting one or more wireless identification
devices to participate in a slotted anticollision algorithm. 4,075,632 A
2/1978 Baldwin et al.
Wireless identi?cation devices in a ?eld of the interrogator use the bit string to determine whether or not they are
(Continued)
selected for participation. Those wireless identi?cation
FOREIGN PATENT DOCUMENTS
devices that are selected for participation respond to the interrogator in a slot with a certain probability in accor
EP
779520
9/1997
dance with the slotted anticollision algorithm.
(Continued)
41 Claims, 3 Drawing Sheets
16 \ RFID
CIRCUITRY INTERROGA TOR
26/
14L
I POWER SOURCE
18/
US RE41,531 E Page 2
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473/1/1/,Jun. 26,2003. Wolf, Jack Keil, “Principles of Group Testing and an Appli cation to the Design and Analysis of MultiiAccess Proto
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Finkenzeller, Klaus, “Radio Frequency Identi?cationiThe Authors Homepage of the RFID Handbook,” located at
http://WWW.r?d*handbook.com, accessed Feb. 22, 2007. Smart Active Labels Consortium, organization homepage located at hIIPZ//WWW.Sal%.OI‘g, accessed Feb. 22, 2007. Symbol Technologies, Inc., “Understanding Gen 2: What It Is, HoW You Will Bene?t and Criteria for Vendor Assess ment,” White paper, Jan. 2006.
Wright, Jim, “Trends and Innovations in RF Indenti?cation,” Sun Microsystems Inc. presentation, Mar. 2005. Wood, Jr., Clifton W., U.S. Reissue Appl. No. 10/693,697, ?led Oct. 23, 2003.
Wood, Jr., Clifton W., U.S. Reissue Appl. No. 11/865,580, ?led Oct. 1, 2007.
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InterfacesiPart 3: Physical Layer, Anti Collision System
?led Oct. 1, 2007.
and Protocol Values at 13.56 MHZ MODE 4,” ISO/IEC
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18000i3i4, Mar. 1, 2001. ISO/IEC, “Automatic Identi?cationiRadio Frequency Identi?cation for Item ManagementiCommunications and InterfacesiPart 3: Physical Layer, Anti£ollision and Pro tocol Values at 13.56 MHZ MODE 1,” ISO/IEC 180004341, Mar. 1, 2001.
ISO/IEC, “Identi?cation Cards4Contactless Integrated Cir cuit(s) CardsiProXimity CardsiPar‘t 1: Physical Charac teristics,” ISO/IEC FCD 1444341, 1997. ISO/IEC, “Identi?cation Cards4Contactless Integrated Cir
cuit(s) CardsiProximity CardsiPar‘t 2: Radio Frequency Power and Signal Interface,” ISO/IEC FCD 1444342, Mar. 26, 1999. ISO/IEC, “Identi?cation Cards4Contactless Integrated Cir cuit(s) CardsiProximity CardsiPart 3: Initiation and Anti collision,” ISO/IEC FDIS 1444343:2000(E), Jul. 13, 2000. ISO/IEC, “Identi?cation Cards4Contactless Integrated Cir cuit(s) CardsiProximity CardsiPar‘t 4: Transmission Pro tocol,” ISO/IEC FDIS 1444344:2000(E), Jul. 13, 2000. ISO/IEC, “Identi?cation Cards4Contactless Integrated Cir
cuit(s) CardsiVicinity CardsiPart 1: Physical Character istics,” ISO/IEC FDIS 1569341:2000(E), May 19, 2000. ISO/IEC, “Identi?cation Cards4Contactless Integrated Cir cuit(s) CardsiVicinity CardsiPar‘t 2: Interface and Initial ization,” ISO/IEC FDIS 1569342:2000(E), Feb. 3, 2000. ISO/IEC, “Identi?cation Cards4Contactless Integrated Cir cuit(s) CardsiVicinity CardsiPar‘t 3: Anticollision and Transmission Protocol,” ISO/IEC CD 1569343:1999(E), Nov. 17, 1999.
ISO/IEC, “Information Technology AIDC Techniquesi
573, ?led Aug. 28, 2008. Wood, Jr., Clifton W., U.S. Reissue Appl. No. 11/862,121, ?led Sep. 26, 2007. Wood, Jr., Clifton W., U.S. Reissue Appl. No. 11/862,124, ?led Sep. 26, 2007. Wood, Jr., Clifton W., U.S. Reissue Appl. No. 11/862,130, ?led Sep. 21, 2007. International Application No. PCT/US08/50630, Written Opinion, Jun. 27, 2008. International Application No. PCT/US08/50630, Intema tional Search Report, Jun. 27, 2008. Tuttle, John R., US. Appl. No. 11/755,073 entitled “Meth ods and Systems of Receiving Data Payload of RFID Tags,” ?led May 30, 2007. International Application No. PCT/US99/02288, Written Opinion, Jan. 27, 2000. Wood, Jr., Clifton W., U.S. Reissue Appl. No. 10/693,696, ?led Oct. 23, 2003.
International Application No. PCT/US99/02288, Intema tional Search Report, Aug. 3, 1999. Wood, Jr., Clifton W., U.S. Reissue Appl. No. 11/859,360, ?led Sep. 21, 2007. Wood, Jr., Clifton W., U.S. Reissue Appl. No. 12/541,882, ?led Aug. 14, 2009. Wood, Jr., Clifton W., U.S. Reissue Appl. No. 12/493,542, ?led Jun. 29, 2009.
USPTO Transaction History of US. Appl. No. 09/026,043, ?led Feb. 19, 1998, entitled “Method of Addressing Mes
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US RE41,531 E Page 4
Select Radio Frequency identi?cation Devices in Accor
USPTO Transaction History of US. Appl. No. 10/693,697, ?led Oct. 23, 2003, entitled “Method of Addressing Mes sages, Methods of Establishing Wireless Communications, and Communications System.” USPTO Transaction History of US. Appl. No. 11/143,395, ?led Jun. 1, 2005, entitled “Method of Addressing Messages and Communications System.” USPTO Transaction History of US. Appl. No. 11/270,204, ?led Nov. 8, 2005, entitled “Method of Addressing Mes sages and Communications System.” USPTO Transaction History of US. Appl. No. 11/416,846, ?led May 2, 2006, entitled “Method of Addressing Messages and Communications System.” USPTO Transaction History of US. Appl. No. 11/855,855, ?led Sep. 14, 2007, entitled “Method of Addressing Mes sages and Communications System.” USPTO Transaction History of US. Appl. No. 11/855,860, ?led Sep. 14, 2007, entitled “Method of Addressing Mes sages and Communications System.” USPTO Transaction History of US. Appl. No. 11/859,360, ?led Sep. 21, 2007, entitled “Method of Addressing Mes sages and Communications System.” USPTO Transaction History of US. Appl. No. 11/862,121, ?led Sep. 26, 2007, entitled “Method of Addressing Mes sages and Communications System.” USPTO Transaction History of US. Appl. No. 11/862,124, ?led Sep. 26, 2007, entitled “Method of Addressing Mes sages and Communications System.” USPTO Transaction History of US. Appl. No. 11/862,130, ?led Sep. 26, 2007, entitled “Method of Addressing Mes sages and Communications System.” USPTO Transaction History of US. Appl. No. 11/865,580, ?led Oct. 1, 2007, entitled “Method of Addressing Mes sages, Methods of Establishing Wirelsee Communications, and Communications System.” USPTO Transaction History of US. Appl. No. 11/865,584, ?led Oct. 1, 2007, entitled “Method of Addressing Mes sages, Methods of Establishing Wirelsee Communications, and Communications System.”
dance with an Arbitration Scheme.”
* cited by examiner
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6,307,847. USPTO Transaction History of US. Appl. No. 09/773,461, ?led Jan. 31, 2001, entitled “Method of Addressing Mes sages, Methods of Establishing Wireless Communications, and
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7,315,522. USPTO Transaction History of US. Appl. No. 10/652,573, ?led Aug. 28, 2003, entitled “Method of Addressing Mes sages and Communications System.” USPTO Transaction History of US. Appl. No. 10/693,696, ?led Oct. 23, 2003, entitled “Method and Apparatus to
US. Patent
Aug. 17, 2010
Sheet 3 0f3
US RE41,531 E
US RE41,531 E 1
2
COMMUNICATIONS SYSTEMS FOR RADIO
duced 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
FREQUENCY IDENTIFICATION (RFID)
magnetic coupling. Therefore, active transponder devices
Matter enclosed in heavy brackets [ ] appears in the original patent but forms no part of this reissue speci?ca tion; matter printed in italics indicates the additions made by reissue.
tend to be more suitable for applications requiring tracking of a tagged device that may not be in close proximity to an
interro gator. For example, active transponder devices tend to be more suitable for inventory control or tracking. Electronic identi?cation systems can also be used for remote payment. For example, when a radio frequency iden ti?cation device passes an interrogator at a toll booth, the toll booth can determine the identity of the radio frequency iden ti?cation device, and thus of the owner of the device, and
CROSS REFERENCE TO RELATED APPLICATION
[This] More than one reissue has been ?led for the resis sue ofU.S. Pat. No. 6,307,847. The reissue applications are
the initial reissue application Ser. No. 10/693, 696, ?led Oct.
debit an account held by the owner for payment of toll or can receive a credit card number against which the toll can be
23, 2003, a continuation reissue application Ser. No. 11/859,
360, ?eld Sep. 21, 2007, the present continuation resissue application Ser. No. 11/859,364, ?led Sep. 21, 2007, and a
charged. Similarly, remote payment is possible for a variety of other goods or services. A communication system typically includes two tran sponders: a commander station or interrogator, and a
continuation reissue application Ser. No. 12/493,542, ?led Jun. 29, 2009. The present application is a continuation
application of U.S. patent application Ser. No. 10/693,696, ?led Oct. 23, 2003, which is a reissue application of U.S.
Pat. No. 6,307,847 having U.S. patent application Ser. No. 09/617,390, ?led Jul. 17, 2000, which is a [Continuation] continuation application of U.S. patent application Ser. No. 09/026,043, ?led Feb. 19, 1998, and titled “Method of Addressing Messages and Communications System”, now U.S. Pat. No. 6,118,789, each ofwhich is incorporated by
20
responder station or transponder device which replies to the
interrogator. If the interrogator has prior knowledge of the identi?ca 25
tion number of a device which the interrogator is looking for, it can specify that a response is requested only from the device with that identi?cation number. Sometimes, such information is not available. For example, there are occa
sions where the interrogator is attempting to determine
reference. TECHNICAL FIELD
30
device requesting a reply, there is a possibility that multiple
This invention relates to communications protocols and to
transponder devices will attempt to respond simultaneously,
digital data communications. Still more particularly, the invention relates to data communications protocols in medi
causing a collision, and thus causing an erroneous message
to be received by the interrogator. For example, if the inter
ums such as radio communication or the like. The invention
also relates to radio frequency identi?cation devices for
35
inventory control, object monitoring, determining the
rogator sends out a command requesting that all devices within a communications range identity themselves, and
gets a large number of simultaneously replies, the interroga
existence, location or movement of objects, or for remote
automated payment. BACKGROUND OF THE INVENTION
which of multiple devices are within communication range. When the interrogator sends a message to a transponder
40
tor may not be able to interpret any of these replies. Thus, arbitration schemes are employed to permit communications free of collision. In one arbitration scheme or system, described in com
Communications protocols are used in various applica tions. For example, communications protocols can be used in electronic identi?cation systems. As large numbers of
objects are moved in inventory, product manufacturing, and merchandising operations, there is a continuous challenge to accurately monitor the location and ?ow of objects. Additionally, there is a continuing goal to interrogate the
monly assigned U.S. Pat. Nos. 5,627,544; 5,583,850; 5,500, 45
responding devices to select a random number from a known range and use it as that device’s arbitration number. By
location of objects in an inexpensive an streamlined manner.
One way of tracking objects is with an electronic identi?ca
tion system. One presently available electronic identi?cation system
650; and 5,365,551, all to Snodgrass et a1. and all incorpo rated herein by reference, the interrogator sends a command causing each device of a potentially large number of
50
transmitting requests for identi?cation to various subsets of the full range of arbitration numbers, and checking for an error-free response, the interrogator determines the arbitra tion number of every responder station capable of communi cating at the same time. Therefore, the interrogator is able to
utilizes a magnetic coupling system. In some cases, an iden
conduct subsequent uninterrupted communication with
ti?cation device may be provided with a unique identi?ca tion code in order to distinguish between a number of differ
devices, one at a time, by addressing only one device. 55
ent devices. Typically, the devices are entirely passive (have
Another arbitration scheme is referred to as the Aloha or
no power supply), which results in a small and portable
slotted Aloha scheme. This scheme is discussed in various references relating to communications, such as Digital Com
package. However, such identi?cation systems are only capable of operation over a relatively short range, limited by
munications: Fundamentals and Applications, Bernard
the size of a magnetic ?eld used to supply power to the devices and to communicate with the devices. Another wireless electronic identi?cation system utilizes a large active transponder device a?ixed 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 respon sive signal are typically radio-frequency (RF) signals pro
Sklar, published January 1988 by Prentice Hall. In this type 60
of scheme, a device will respond to an interrogator using one
of many time domain slots selected randomly by the device. A problem with the Aloha scheme is that if there are many devices, or potentially many devices in the ?eld (i.e. in com
munications range, capable of responding) then there must 65
be many available slots or many collisions will occur. Hav
ing many available slots slows down replies. If the magni tude of the number of devices in a ?eld is unknown, then
US RE41,531 E 3
4
many slots are needed. This results in the system slowing
FIG. 2 is a front view of a housing, in the form of a badge or card, supporting the circuit of FIG. 1 according to one embodiment the invention. FIG. 3 is a front view of a housing supporting the circuit of FIG. 1 according to another embodiment of the invention. FIG. 4 is a diagram illustrating a tree splitting sort method
down signi?cantly because the reply time equals the number of slots multiplied by the time period required for one reply. An electronic identi?cation system which can be used as a
radio frequency identi?cation device, arbitration schemes, and various applications for such devices are described in
detail in commonly assigned US. patent application Ser. No. 08/705,043, ?led Aug. 29, 1996, [and] now US. Pat. No. 6,130, 602, which is incorporated herein by reference.
for establishing communication with a radio frequency iden ti?cation device in a ?eld of a plurality of such devices. FIG. 5. is a diagram illustrating a modi?ed tree splitting sort method for establishing communication with a radio frequency identi?cation device in a ?eld of a plurality of such devices.
SUMMARY OF THE INVENTION The invention provides a wireless identi?cation device
con?gured to provide a signal to identify the device in response to an interrogation signal. One aspect of the invention provides a method of estab lishing wireless communications between an interrogator and individual ones of multiple wireless identi?cation devices. The method comprises utiliZing a tree search method to establish communications without collision between the interrogator and individual ones of the multiple wireless identi?cation devices. A search tree is de?ned for the tree search method. The tree has multiple levels respec
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
This disclosure of the invention is submitted in further ance of the constitutional purposes of the US. Patent Laws
“to promote the progress of science and useful arts” (Article 20
FIG. 1 illustrates a wireless identi?cation device 12 in accordance with one embodiment of the invention. In the
tively representing subgroups of the multiple wireless iden ti?cation devices. The method further comprising starting the tree search at a selectable level of the search tree. In one
aspect of the invention, the method further comprises deter mining the maximum possible number of wireless identi? cation devices that could communicate with the interrogator,
25
groups is considered level Zero, and lower levels are num
less or radio frequency transmission and reception by the circuitry 16. In the illustrated embodiment, the RFID cir cuitry is de?ned by an integrated circuit as described in the 30
embodiments are possible. A power source or supply 18 is
connected to the integrated circuit 16 to supply power to the integrated circuit 16. In one embodiment, the power source 35
40
single metal layer integrated circuit including the receiver,
an antenna 28, as well as dedicated transmitting and receiv 45
Generally, the interrogator 26 transmits an interrogation
receives the incoming interrogation signal via its antenna 14.
Upon receiving the signal 27, the device 12 responds by 50
generating and transmitting a responsive signal or reply 29. The responsive signal 29 typically includes information that uniquely identi?es, or labels the particular device 12 that is transmitting, so as to identify any object or person with which the device 12 is associated.
55
embodiment includes an active transponder, instead of a
Although only one device 12 is shown in FIG. 1, typically there will be multiple devices 12 that correspond with the interrogator 26, and the particular devices 12 that are in com
munication with the interrogator 26 will typically change
and therefore has a much greater range. 60
over time. In the illustrated embodiment in FIG. 1, there is no communication between multiple devices 12. Instead, the
devices 12 respectively communicate with the interrogator 26. Multiple devices 12 can be used in the same ?eld of an
Preferred embodiments of the invention are described
interrogator 26 (i.e., within communications range of an
below with reference to the following accompanying draw
ings. rogator and a radio frequency identi?cation device embody ing the invention.
circuit 16. signal or command 27 via the antenna 28. The device 12
transponder which relies on magnetic coupling for power,
FIG. 1 is a high level circuit schematic showing an inter
[and], now US. Pat. No. 6,289,209, which is incorporated
ing circuitry, similar to that implemented on the integrated
the transmitter, and the microprocessor. The device of this
BRIEF DESCRIPTION OF THE DRAWINGS
plary integrator is described in commonly assigned US. patent application Ser. No. 08/907,689, ?led Aug. 8, 1997 herein by reference. Preferably, the interrogator 26 includes
without collision by multiple wireless identi?cation devices attempting to respond to the interrogator at the same time. The interrogator is con?gured to start the tree search at a selectable level of the search tree. One aspect of the invention provides a radio frequency identi?cation device comprising an integrated circuit includ ing a receiver, a transmitter, and a microprocessor. In one embodiment, the integrated circuit is a monolithic single die
18 comprises a battery. The device 12 transmits and receives radio frequency communications to and from an interrogator 26. An exem
bers of the different wireless identi?cation so as to be able to
establish communications between the interro gator and indi vidual ones of the multiple wireless identi?cation devices
above-incorporated patent application Ser. No. 08/705,043, ?led Aug. 29, 1996, now US. Pat. No. 6,130,602. Other
bered consecutively. Another aspect of the invention provides a communica tions system comprising an interrogator, and a plurality of wireless identi?cation devices con?gured to communicate with the interrogator in a wireless fashion. The respective wireless identi?cation devices have a unique identi?cation number. The interrogator is con?gured to employ a tree search technique to determine the unique identi?cation num
illustrated embodiment, the wireless identi?cation device is a radio frequency data communication device 12, and includes RFID circuitry 16. The device 12 further includes at least one antenna 14 connected to the circuitry 16 for wire
and selecting a level of the search tree based on the deter
mined maximum possible number of wireless identi?cation devices that could communicate with the interrogator. In another aspect of the invention, the method further com prises starting the tree search at a level determined by taking the base two logarithm of the determined maximum possible number, wherein the level of the tree containing all sub
1, Section 8).
interro gator 26). 65
The radio frequency data communication device 12 can be
included in any appropriate housing or packaging. Various methods of manufacturing housings are described in com
US RE41,531 E 5
6
monly assigned U.S. patent application Ser. No. 08/ 800,037,
potential for a large number of transmitting devices 12 and
?led Feb. 13, 1997, [and] now US. Pat. No. 5,988,510, which is incorporated herein by reference.
there is a need for the interrogator 26 to work in a changing environment, where different devices 12 are swapped in and
FIG. 2 shows but one embodiment in the form of a card or
out frequently (e.g., as inventory is added or removed). In such systems, the inventors have determined that the use of random access methods work effectively for contention
badge 19 including a housing 11 of plastic or other suitable material supporting the device 12 and the power supply 18. In one embodiment, the front face of the badge has visual identi?cation features such as graphics, text, information
resolution (i.e., for dealing with collisions between devices 12 attempting to respond to the interrogator 26 at the same
time).
found on identi?cation or credit cards, etc.
RFID systems have some characteristics that are different
FIG. 3 illustrates but one alternative housing supporting the device 12. More particularly, FIG. 3 shows a miniature housing 20 encasing the device 12 and power supply 18 to de?ne a tag which can be supported by an object (e. g., hung from an object, af?xed to an object, etc.). Although two par ticular types of housings have been disclosed, the device 12 can be included in any appropriate housing. If the power supply 18 is a battery, the battery can take any
suitable form. Preferably, the battery type will be selected depending on weight, size, and life requirements for a par ticular application. In one embodiment, the battery 18 is a thin pro?le button-type cell forming a small, thin energy cell more commonly utilized in watches and small electronic devices requiring a thin pro?le. A conventional button-type cell has a pair of electrodes, an anode formed by one face and a cathode formed by an opposite face. In an alternative embodiment, the power source 18 comprises a series con
20
lifetime of a device 12 can often be measured in terms of 25
nected pair of button type cells. Instead of using a battery,
and is con?gured to provide a responsive signal to the inter
30
FIG. 4 illustrates one arbitration scheme that can be
employed for communication between the interrogator and 35
By transmitting requests for identi?cation to various subsets 40
heard simultaneously by all devices 12 within range. If the interrogator 26 sends out a command requesting that all devices 12 within range identify themselves, and gets a
large number of simultaneous replies, the interrogator 26
45
may not be able to interrupt any of these replies. Therefore, arbitration schemes are provided. If the interrogator 26 has prior knowledge of the identi?
from a known range and use it as that device’s arbitration
devices 12. The receiving devices 12 evaluate the following 55
equation: (AMASK & AVALUE)==(AMASK & RV) wherein “&” is a bitwise AND function, and wherein “==” is an equality function. If the equation evaluates to “1”
(TRUE), then the device 12 will reply. If the equation evalu 60
access communication system. The distance between the
interrogator 26 and devices 12 within the ?eld is typically
fairly short (e.g., several meters), so packet transmission time is determined primarily by packet size and baud rate. Propagation delays are negligible. In such systems, there is a
number of responding devices to select a random number
number. The interrogator sends an arbitration value (AVALUE) and an arbitration mask (AMASK) to a set of
ti?cation numbers are now known by the interrogator 26.
Therefore, the interrogator 26 must identify all devices 12 in the ?eld (within communication range) such as by determin ing the identi?cation numbers of the devices 12 in the ?eld. After this is accomplished, point-to-point communication can proceed as desired by the interrogator 26. Generally speaking, RFID systems are a type of multi
12. Three variables are used: an arbitration value (AVALUE), an arbitration mask (AMASK), and a random value ID (RV).
(IdentifyCmnd) causing each device of a potentially large 50
from the device 12 with that identi?cation number. To target a command at a speci?c device 12, (i.e., to initiate point-on point communication), the interrogator 26 must send a num ber identifying a speci?c device 12 along with the command. At start-up, or in a new or changing environment, these iden
of the full range of arbitration numbers, and checking for an error-free response, the interrogator 26 determines the arbi tration number of every responder station capable of com municating at the same time. Therefore, the interrogator 26 is able to conduct subsequent uninterrupted communication with devices 12, one at a time, by addressing only one device
The interrogator sends an Identify command
cation number of a device 12 which the interrogator 26 is
looking for, it can specify that a response is requested only
devices 12. Generally, the interrogator 26 sends a command causing each device 12 of a potentially large number of responding devices 12 to select a random number from a known range and use it as that device’s arbitration number.
large quantities of items. The interrogator 26 communicates with the devices 12 via an electromagnetic link, such as via an RF link (e.g., at microwave frequencies, in one embodiment), so all transmissions by the interrogator 26 are
sumed by the devices 12 during the process. This is in con trast to the measure of throughout and packet delay in other
types of multiaccess systems.
rogator 26 by radio frequency. More particularly, the cir cuitry 16 includes a transmitter, a receiver, and memory such as is described in Us. patent application Ser. No. 08/705, 043, now US. Pat. No. 6,130,602. Radio frequency identi?cation has emerged as a viable and affordable alternative to tagging or labeling small to
number of transmissions before battery power is lost. Therefore, one of the most important measures of system performance in RFID arbitration is total time required to arbitrate a set of devices 12. Another measure is power con
any suitable power source can be employed.
The circuitry 16 further includes a backscatter transmitter
from other communications systems. For example, one char acteristic of the illustrated RFID systems is that the devices 12 never communicate without being prompted by the inter rogator 26. This is in contrast to typical multiaccess systems where the transmitting units operate more independently. In addition, contention for the communication medium is short lived as compared to the ongoing nature of the problem in other multiaccess systems. For example, in a RFID system, after the devices 12 have been identi?ed, the interrogator can communicate with them in a point-to-point fashion. Thus, arbitration in a RFID system is a transient rather than steady state phenomenon. Further, the capability of a device 12 is limited by practical restriction on size, power, and cost. The
65
ates to “0” (FALSE), then the device 12 will not reply. By performing this in a structured manner, with the number of bits in the arbitration mask being increased by one each time, eventually a device 12 will respond with no collisions.
Thus, a binary search tree methodology is employed. An example using actual numbers will now be provided using only four bits, for simplicity, reference being made to FIG. 4. In one embodiment, sixteen bits are used for AVALUE and AMASK. Other numbers of bits can also be
US RE41,531 E 7
8
employed depending, for example, on the number of devices
device 12 with the random value of 1010. There is no
12 expected to be encountered in a particular application, on desired cost points. etc. Assume, for this example, that there are two devices 12 in the ?eld, one with a random value (RV) of 1100 (binary), and another with a random value (RV) of 1010 (binary). The
collision, and the interrogator 26 can determine the identity (e.g., an identi?cation number) for the device 12 that does
respond. By recursion, what is meant is that a function makes a call to itself. In other words, the function calls itself within the body of the function. After the called function returns, de-recursion takes place and execution continues at the place just after the function call; i.e. at the beginning of the state ment after the function call.
interrogator is trying to establish communications without collisions being caused by the two devices 12 attempting to communicate at the same time.
The interrogator sets AVALUE to 0000 (or “don’t care” for all bits, as indicated by the character “X” in FIG. 4) and AMASK to 0000. The interrogator transmits a command to
all devices 12 requesting that they identify themselves. Each of the devices 12 evaluate (AMASK & AVALUE)== (AMASK & RV) using the random value RV that the respec
For instance, consider a function that has four statements (numbered 1,2,3,4 ) in it, and the second statement is a recur
tive devices 12 selected. If the equation evaluates to “1”
ment. The ?rst time through the loop (iteration 1) the func
(TRUE), then the device 12 will reply. If the equation evalu
tion executes the statement 2 and (because it is a recursive call) calls itself causing iteration 2 to occur. When iteration 2
sive call. Assume that the fourth statement is a return state
ates to “0” (FALSE), then the device 12 will not reply. In the ?rst level of the illustrated tree, AMASK is 0000 and any thing bitwise ANDed with all zeros results in all zeros, so both the devices 12 in the ?eld respond, and there is a colli
gets to statement 2, it calls itself making iteration 3. During execution in iteration 3 of statement 1, assume that the func tion does a return. The information that was saved on the
sion.
Next, the interrogator set AMASK to 0001 and AVALUE to 0000 and transmits an identify command. Both devices 12 in the ?eld have a zero for their least signi?cant bit, and
stack from iteration 2 is loaded and the function resumes
execution at statement 3 (in iteration 2), followed by the 25
(AMASK & AVALUE)==(AMASK & RV) will be true for both devices 12. For the device 12 with a random value of
1100, the left side of the equation is evaluated as follows
(0001 & 0000)==0000. The right side is evaluated as (0001 & 1100)=0000. The left side equals the right side, so the equation is true for the device 12 with the random value of 1100. For the device 12 with a random value of 1010, the left side of the equation is evaluated as (0001 & 0000)=0000. The right side is evaluated as (0001 & 1010)=0000. The left side equals the right side, so the equation is true for the device 12 with the random value of 1010. Because the equa tion is true for both devices 12 in the ?eld, both devices 12 in the ?eld respond, and there is another collision. Recursively, the interrogator next sets AMASK to 0011
30
35
execution of statement 4 which is also a return statement. Since there are no more statements in the function, the func
tion de-recurses to iteration 1. Iteration 1, has previously recursively called itself in statement 2. Therefore, it now executes statement 3 (in iteration 1 ). Following that it executes a return at statement 4. Recursion is known in the art.
Consider the following code which can be used to imple ment operation of the method shown in FIG. 4 and described above.
Arbitrate(AMASK, AVALUE) 40
with AVALUE still at 0000 and transmits an Identity com
collision=IdentifyCmnd(AMAS K,AVALUE)
mand. (AMASK & AVALUE)==(AMASK & RV) is evalu
if (collision) then
ated for both devices 12. For the device 12 with a random
value of 1100, the left side of the equation is evaluated as follows (0011 & 0000)=0000. The right side is evaluated as
/* recursive call for left side */
Arbitrate((AMASK>>1)+1, AVALUE) 45
(0011 & 1100)=0000. The left side equals the right side, so the equation is true for the device 12 with the random value of 1100, so this device 12 responds. For the device 12 with a random value of 1010, the left side of the equation is evalu ated as (0011 & 0000)=0010. The right side is evaluated as
} /* endif */ }/* return */
50
(0011 & 1010)=0000. The left side does not equal the right side, so the equation is false for the device 12 with the ran dom value of 1010, and this device 12 does not respond. Therefore, there is no collision, and the interrogator can determine the identity (e. g., an identi?cation number) for the device 12 that does respond. De-recursion takes place, and the device 12 to the right for
55
recursive call, AMASK=(AMASK=(AMASK<<1)+1. So for the ?rst recursive call, the value of AMASK is 0000+
0010+1=0011. For the third recursive call, AMASK=
(0011<<1)+1=0110+1=0111. 60
command and evaluates the equation (AMASK & AVALUE)==(AMASK & RV). The left side of the equation is evaluated as (0011 & 0010)=0010. The right side of the equation is evaluated as (0011 & 1010)=0010. The right side equals the left side, so the equation is true for the device 12
The symbol “<<” represents a bitwise left shift. “<<” means shift left by one place. Thus, 0001<<1 would be 0010. Note, however, that AMASK is originally called with a value of zero, and 0000<<1 is still 0000. Therefore, for the ?rst
0001=0001. For the second call, AMASK=(0001<<)+1=
the same AMASK level are accessed when AVALUE is set at
0010, andAMASK is set to 0011. The device 12 with the random value of 1010 receives a
/* recursive call for right side */
Arbitrate((AMASK>>1)+1, AVALUE+(AMASK+1))
65
The routine generates values for AMASK and AVALUE to be used by the interrogator in an identify command “Iden tifyCmnd.” Note that the routine calls itself if there is a collision. De-recursion occurs when there is no collision. AVALUE and AMASK would have values such as the fol
with the random value of 1010. Because there are no other
lowing assuming collisions take place all the way down to
devices 12 in the substrate, a good reply is returned by the
the bottom of the tree.
US RE41,531 E 9
10
AVALUE
AMASK
0000 0000 0000 0000 0000 1000 0100 0100 1100
0000 0001 0011 0111 1111* 1111* 0111 1111* 1111*
5
10
Thls seguentfe Of AM‘ittSK’ AV‘IAILIIIJE bmagy numbeiis 15
assumes t at t ere are _CO 1519115 a
t e _Way
own to t e
bottom of the tree, at which point the ldent1fy command sent
6
0000 0001 0001 0011 0011 0011 0011 0111 0111
Rows in the table for which the interrogator is successful
in receiving a reply without collision are marked with the
26 starts the tree search at a selectable level of the search 20 tree. The search tree has a plurality of nodes 51, 52, 53, 54
Wlth the Symb01 ' Now that lithe _Ide1_mfy command was successful at, for example, the th1rd line 1n the table then the interrogator would Stop gOing down that branCh Of the tree hhd Start dOVt’h anOther, 50 the seqhehee WOhld he as ShOWh 1h the fonerhg table
0000 0000 0001 0000 0010 0001 0011 0000 0100
FIG. 5 illustrates an embodiment wherein the interrogator
ermga or 15 51:1:
Gees u m ween/32% a rep y W_1t out CO fSIOn are mar e
AMASK
Symh 01 wk”
by the ntltterrogatai lst {2111211113, 51123615153111 5.05112“ not 6011151011 occufrsl' _ OWS 11,1 _ e a e tor W, he
AVALUE
etc. at respective levels. The size of subgroups of random values decrease in Size by half With each node descended The upper bound of the number of devices 12 in the ?eld (the
maximum possible number of devices that could communi 25 cate with the interrogator) is determined, and the tree search method is started at a level 32, 34, 36, 38, or 40 in the tree depending on the determined upper bound. In one
AVALUE 0000 0000
AMASK 0000 0001*
0000
0011
0010
0011
embodiment, the maximum number of devices 12 poten tially capable of responding to the interro gator is determined 30 manually and input into the interrogator 26 via an input device such as a keyboard, graphical user interface, mouse, or other interface. The level of the search tree on which to . . start the tree search 1s selected based on the determ1ned
maximum possible number of wireless identi?cation devices 35 that could communicate with the interrogator. This method is referred to as a splitting method. It works The tree search is started at a level determined by taking
by splitting groups of colliding devices 12 into subsets that
the base two logarithm of the determined maximum possible
are resolved in turn. The splitting method can also be viewed 1111111her- MOTe Partiehlar1}” the tree seareh is Started at a level as a type of tree search. Each split moves the method one 40 deterhhhed by taklhg the base tWO legahthm Ofthe Pewer Of
level deeper in the tree
two' nearest the determined maximum possible number of
_ E1ther depth-?rst or breadth-?rst traversals of the tree can
deV1ces 12. The level of the tree containing all subgroups of random values is considered level zero (see FIG 5), and
he employedpepth hrSt traversals are_ Perfenhed by uSihg
lower levels are numbered 1, 2, 3, 4, etc. consecutively.
recurslon, as 1s employed in the code listed above.t Breadth- 45 By determining the upper hound of the number of devices ?rst traversals are accompllshed by us1ng a queue instead of 12 in the ?eld, and Starting the tree search at an appropriate Fecursmn' The fOHOng 15 an example Of cede for perform' level, the number of collisions is reduced, the battery life of mg a breadth'?rSt traversal
Arbitrat@(AMASK, AVALUE) Fem
)
(EMASKTAVAPEYUE) = dequeuet) collision=ldentifyCrnnd(AMASK,AVALUE)
the devices 12 is increased, and arbitration time is reduced. For example, for the search tree shown in FIG. 5, if it is 50 known that there are seven devices 12 in the ?eld, starting at node 51 (level 0 ) results in a collision. Starting at level 1 (nodes 52 and 53 ) also results in a collision. The same is true for nodes 54, 55, 56, and 57 in level 2. If there are seven devices 12 in the ?eld, the nearest power of two to seven is 55 the level at Wthll the tree search should be started. Log2
if (collision) th?n
8=3, so the tree search should be started at level 3 if there are
TEMP = AMASKH
seven deV1ces 12 in the ?eld.
NEWiAMASK= (AMASK>>1)+1
AVALUE and AMASK would have values such as the
e1141116116(NEWiAMASK,AVALUE) enqueudNEWiAMASK’ AVALUE+TEMP) } /* endif */
following assuming collisions take place from level 3 all the 60 way down to the bottom of the tree.
endwhile
}/* return */
The symbol “!=” means not equal to. AVALUE and 65 AMASK would have values such as those indicated in the
following table for such code.
AVALUE
AMASK
0000 0000
0111 1111*
US RE41,531 E 12 sions because only messages transmitted in the same slot can interfere with one another. The retransmission mode of the pure Aloha scheme is modi?ed for slotted Aloha such that if
-continued AVALUE
AMASK
1000 0100 0100 1100
1111* 0111 1111* 1111*
a negative acknowledgment occurs, the device retransmits after a random delay of an integer number of slot times.
Aloha methods are described in [a] commonly assigned patent application [naming Clifton W. Wood, Jr. as an
inventor, US. patent application] Ser. No. 09/026,248, ?led Feb. 19, 1998, [titled “Method of Addressing Messages and
Communications System,” ?led concurrently herewith, and],
Rows in the table for which the interrogator is successful in receiving a reply without collision are marked with the
now US. Pat. No. 6,275,476, which is incorporated herein by reference.
symbol “*”. In operation, the interrogator transmits a command requesting devices 12 having random values RV within a speci?ed group of random values to respond, the speci?ed group being chosen in response to the determined maximum number. Devices 12 receiving the command respectively determine if their chosen random values fall within the speci?ed group and, if so, send a reply to the interrogator. The interrogator determines if a collision occurred between
In one alternative embodiment, an Aloha method (such as 15
20
devices that sent a reply and, if so, creates a new, smaller,
speci?ed group, descending in the tree, as described above in connection with FIG. 4. Another arbitration method that can be employed is referred to as the “Aloha” method. In the Aloha method, every time a device 12 is involved in a collision, it waits a
25
30
35
receive either an acknowledgment or a negative acknowl edgment within a certain amount of time, the user “times out” and retransmits the message. There is a scheme known as slotted Aloha which improves
40
are constant. Messages are required to be sent in a slot time
the beginning of a time slot. This reduces the rate of colli
unique identi?cation numbers are unknown. Level skipping reduces the number of collisions, both reducing arbitration time and conserving battery life on a set of devices 12. In
one embodiment, every other level is skipped. In alternative embodiments, more than one level is skipped each time. The trade off that must be considered in determining how many (if any) levels to skip with each decent down the tree is as follows. Skipping levels reduces the number of collisions,
reduction in collisions. However, skipping levels results in longer search times because the number of queries (Identify commands) increases. The more levels that are skipped, the longer the search times. Skipping just one level has an
almost negligible effect on search time, but drastically 45
reduces the number of collisions. If more than one level is
skipped, search time increases substantially. Skipping every other level drastically reduces the number of collisions and saves battery power without signi?cantly increasing the
number of queries. 50
Level skipping methods are described in a commonly
assigned patent application 09/026,045 naming Clifton W. Wood, Jr. and Don Hush as inventors, titled “Method of
Addressing Messages, Method of Establishing Wireless 55
Communications, and Communications Systems,” ?led con currently herewith, now U.S. Pat. No. 6,072,801, and incor
porated herein by reference. In one alternative embodiment, a level skipping method is combined with determining the upper bound on a set of devices and starting at a level in the tree depending on the 60
the Aloha scheme by requiring a small amount of coordina tion among stations. In the slotted Aloha scheme, a sequence of coordination pulses is broadcast to all stations (devices). As is the case with the pure Aloha scheme, packet lengths
between synchronization pulses, and can be started only at
by multiple devices 12 responding, reduces the number of subsequent collisions without adding signi?cantly to the
(skipping more than one level) further reduces the number of collisions. The more levels that are skipped, the greater the
When a negative acknowledgment is received, the messages are retransmitted by the colliding users after a random delay. If the colliding users attempted to retransmit without the random delay, they would collide again. If the user does not
26 do so within a randomly selected time slot of a number of
thus saving battery power in the devices 12. Skipping deeper
ent users will sometimes overlap in time (collide), causing reception errors in the data in each of the contending mes sages. The errors are detected by the receiver, and the receiver sends a negative acknowledgment to the users.
by combining an Aloha method with the method shown and described in connection with FIG. 5. For example, in one embodiment, devices 12 sending a reply to the interrogator
number of no replies. In real-time systems, it is desirable to have quick arbitration sessions on a set of devices 12 whose
University of Hawaii. In 1971, the University of Hawaii began operation of a system named Aloha. A communication satellite was used to interconnect several university comput ers by use of a random access protocol. The system operates as follows. Users or devices transmit at any time they desire. After transmitting, a user listens for an acknowledgment from the receiver or interrogator. Transmissions from differ
the upper bound on a set of devices and staring at a level in the tree depending on the determined upper bound, such as
slots. In another embodiment, levels of the search tree are skipped. Skipping levels in the tree, after a collision caused
random period of time before retransmitting. This method can be improved by dividing time into equally sized slots and forcing transmissions to be aligned with one of these slots. This is referred to as “slotted Aloha.” In operation, the interrogator asks all devices 12 in the ?eld to transmit their identi?cation numbers in the next time slot. If the response is garbled, the interrogator informs the devices 12 that a colli sion has occurred, and the slotted Aloha scheme is put into action. This means that each device 12 in the ?eld responds within an arbitrary slot determined by a randomly selected value. In other words, in each successive time slot, the devices 12 decide to transmit their identi?cation number with a certain probability. The Aloha method is based on a system operated by the
the method described in the commonly assigned patent application mentioned above) is combined with determining
65
determined upper bound, such as by combining a level skip ping method with the method shown and described in con nection with FIG. 5. In yet another alternative embodiment, both a level skip ping method and an Aloha method (as described in the com
monly assigned applications described above) are combined with the method shown and described in connection with FIG. 5.
US RE41,531 E 14
13 In compliance with the statue, the invention has been
establishing a second predetermined number of bits to be used for random values; causing the devices to select random values, wherein
described in language more or less speci?c as to structural
and methodical features. It is to be understood, however, that the invention is not limited to the speci?c features shown and described, since the means herein disclosed comprise pre ferred forms of putting the invention into effect. The inven tion is, therefore, claimed in any of its forms or modi?ca tions within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of
respective devices choose random values indepen dently of random values selected by the other devices; determining the maximum number of devices potentially capable of responding to the interrogator; transmitting a command from the interrogator requesting devices having random values within a speci?ed group of random values to respond, by using a subset of the
equivalents. What is claimed is:
second predetermined number of bits, the speci?ed
[1. A method of establishing wireless communications
group being chosen in response to the determined
between an interrogator and individual ones of multiple wireless identi?cation devices, the wireless identi?cation
maximum number; receiving the command at multiple devices, devices receiving the command respectively determining if the
devices having respective identi?cation numbers and being addressable by specifying identi?cation numbers with any one of multiple possible degrees of precision, the method comprising utilizing a tree search in an arbitration scheme to determine a degree of precision necessary to establish one on-one communications between the interrogator and indi vidual ones of the multiple wireless identi?cation devices, a search tree being de?ned for the tree search method, the tree
20
new, smaller, speci?ed group.] [8. A method of addressing messages from an interrogator
having multiple selectable levels respectively representing
to a selected one or more of a number of communications
subgroups of the multiple wireless identi?cation devices, the level at which a tree search starts being variable the method
random value chosen by the device falls within the speci?ed group and, if so, sending a reply to the inter rogator; and determining using the interrogator if a collision occurred between devices that sent a reply and, if so, creating a
25
further comprising starting the tree search at any selectable
level of the search tree.]
devices in accordance with claim 7 wherein sending a reply
to the interrogator comprises transmitting the unique identi ?cation number of the device sending the reply.]
[2. A method in accordance with claim 1 and further com
[9. A method of addressing messages from an interrogator
prising determining the maximum possible number of wire
to a selected one or more of a number of communications
less identi?cation devices that could communicate with the interrogator, and selecting a level of the search tree based on
30
devices in accordance with claim 7 wherein sending a reply
to the interrogator comprises transmitting the random value
the determined maximum possible number of wireless iden ti?cation devices that could communicate with the interroga
of the device sending the reply.]
tor.]
tor to a selected one or more of a number of communications
[10. A method of addressing messages from an interroga devices in accordance with claim 7 wherein sending a reply
[3. A method in accordance with claim 2 and further com prising starting the tree search at a level determined by tak ing the base two logarithm of the determined maximum pos sible number, wherein the level of the tree containing all subgroups is considered level zero, and lower levels are
35
numbered consecutively.]
40 tor to a selected one or more of a number of communications
[4. A method in accordance with claim 2 and further com prising starting the tree search at a level determined by tak ing the base two logarithm of the determined maximum pos sible number, wherein the level of the tree containing all subgroups is considered level zero, and lower levels are numbered consecutively, and wherein the maximum number of devices in a subgroup in one level is half of the maximum number of devices in the next higher level [5. A method in accordance with claim 2 and further com prising starting the tree search at a level determined by tak ing the base two logarithm of the power of two nearest the
determined maximum possible number, wherein the level of the tree containing all subgroups is considered level zero, and lower levels are numbered consecutively, and wherein the maximum number of devices in subgroup in one level is half of the maximum number of devices in the next higher
devices in accordance with claim 7 wherein, after receiving a reply without collision from a device, the interrogator sends a command individually addressed to that device.] [12. A method of addressing messages from an interroga 45 tor to a selected one or more of a number of communications
devices, the method comprising: causing the devices to select random values for use as
50
multiple possible degrees of precision; 55
number of bits;
of a plurality of possible groups of random values to
respond, the speci?ed group being less than the entire set of random values, the plurality of possible groups being organized in a binary tree de?ned by a plurality 60
of nodes at respective levels, wherein the size of groups of random values decrease in size by half with each node descended, wherein the speci?ed group is below a node on the tree selected based on the maximum num
ber of devices capable of communicating with the inter
to a selected one or more of a number of communications
devices, the method comprising: establishing for respective devices unique identi?cation numbers respectively having a ?rst predetermined
arbitration numbers, wherein respective devices choose random values independently of random values selected by the other devices, the devices being addres sable by specifying arbitration numbers with any one of transmitting a command from the interrogator requesting devices having random values within a speci?ed group
level.]
[6. A method in accordance with claim 1 wherein the wireless identi?cation device comprises an integrated circuit including a receiver, a modulator, and a microprocessor in communication with the receiver and modulator] [7. A method of addressing messages from an interrogator
to the interrogator comprises transmitting both the random value of the device sending the reply and the unique identi? cation number of the device sending the reply.] [11. A method of addressing messages from an interroga
65
rogator; receiving the command at multiple devices, devices receiving the command respectively determining if the random value chosen by the device falls within the
US RE41,531 E 15
16 [18. A method of addressing messages from an interroga
speci?ed group and, if so, sending a reply to the inter rogator; and, if not, not sending a reply; and determining using the interrogator if a collision occurred
tor to a selected one or more of a number of RFID devices in
accordance with claim 16 wherein selecting the level of the tree comprises taking the base two logarithm of the deter mined maximum possible number, wherein a level of the tree containing all subgroups is considered level zero, and lower levels are numbered consecutively.] [19. A method of addressing messages from an interroga
between devices that sent a reply and, if so, creating a
new, smaller, speci?ed group by descending in the
tree.] [13. A method of addressing messages from an interroga tor to a selected one or more of a number of communications
tor to a selected one or more of a number of RFID devices in
devices in accordance with claim 12 and further including establishing a predetermined number of bits to be used for
accordance with claim 16 wherein selecting the level of the tree comprises taking the base two logarithm of the deter mined maximum possible number, wherein a level of the tree containing all subgroups is considered level zero, and
the random values] [14. A method of addressing messages from an interroga tor to a selected one or more of a number of communications
mined number of bits to be used for the random values com
lower levels are numbered consecutively, and wherein the maximum number of devices in a subgroup in one level is
prises an integer multiple of eight.]
half of the maximum number of devices in the next higher
devices in accordance with claim 13 wherein the predeter
level.]
[15. A method of addressing messages from an interroga
[20. A method of addressing messages from an interroga
tor to a selected one or more of a number of communications
devices in accordance with claim 13 wherein devices send ing a reply to the interrogator do so within a randomly selected time slot of a number of slots
tor to a selected one or more of a number of RFID devices in 20
accordance with claim 16 wherein selecting the level of the tree comprises taking the base two logarithm of the power of two nearest the determined maximum possible number, wherein the level of the tree containing all subgroups is con
25
consecutively, and wherein the maximum number of devices
[16. A method of addressing messages from an interroga tor to a selected one or more of a number of RFID devices,
sidered level zero, and lower levels are numbered
the method comprising: establishing for respective devices a predetermined num ber of bits to be used for random values, the predeter mined number being a multiple of sixteen; causing the devices to select random values, wherein
respective devices choose random values indepen dently of random values selected by the other devices; transmitting a command from the interrogator requesting devices having random values within a speci?ed group of a plurality of possible groups of random values to respond, the speci?ed group being equal to or less than the entire set of random values, the plurality of possible groups being organized in a binary tree de?ned by a
in a subgroup in one level is half of the maximum number of
devices in the next higher level [21. A method of addressing messages from an interroga tor to a selected one or more of a number of RFID devices in 30
modulator, and a microprocessor in communication with the
receiver and modulator] [22. A method of addressing messages from an interroga 35 tor to a selected one or more of a number of RFID devices in
accordance with claim 16 and further comprising, after the
interrogator transmits a command requesting devices having
plurality of nodes at respective levels, wherein the
random values within the new speci?ed group of random
maximum size of groups of random values decrease in
size by half with each node descended, wherein the speci?ed group is below a node on a level of the tree selected based on the maximum number of devices
values to respond, determining, using devices receiving the 40
random value chosen by the device falls within the speci?ed group and, only if so, sending a reply to the interro gator, wherein sending a reply to the interro gator comprises transmitting both the random value of the
smaller speci?ed group and, if so, sending a reply to the
[23. A method of addressing messages from an interroga tor to a selected one or more of a number of RFID devices in 45
interrogator transmits a command requesting devices having
50
55
transmitting, the interrogator transmitting a command requesting devices having random values within the new speci?ed group of random values to respond; and if a reply without collision is received from a device, the
speci?ed group and repeating the transmitting of the com mand requesting devices having random values within a speci?ed group of random values to respond using different speci?ed groups until all of the devices within communica tions range are identi?ed.] [24. A communications system comprising an interrogator, and a plurality of wireless identi?cation devices con?gured to communicate with the interrogator in a wire less fashion, the wireless identi?cation devices having
respective identi?cation numbers, the interrogator being 60
interrogator subsequently sending a command indi vidually addressed to that device.] [17. A method of addressing messages from an interroga
con?gured to employ a tree search in a search tree having
multiple selectable levels, to determine the identi?cation numbers of the different wireless identi?cation devices with suf?cient precision so as to be able to establish one-on-one
tor to a selected one or more of a number of RFID devices in
accordance with claim 16 and further comprising determin ing the maximum possible number of wireless identi?cation devices that could communicate with the interrogator]
accordance with claim 22 and further comprising, after the random values within the new speci?ed group of random values to respond, determining if a collision occurred between devices that sent a reply and, if so, creating a new
device sending the reply and the unique identi?cation number of the device sending the reply; using the interrogator to determine if a collision occurred between devices that sent a reply and, if so, creating a new, smaller, speci?ed group using a level of the tree different from the level used in the interrogator
command, if their chosen random values fall within the new
interrogator]
known to be capable of communicating with the inter
rogator; receiving the command at multiple devices, devices receiving the command respectively determining if the
accordance with claim 16 wherein the wireless identi?cation device comprises an integrated circuit including a receiver, a
65
communications between the interrogator and individual ones of the multiple wireless identi?cation devices, wherein the interrogator is con?gured to start the tree search at any
selectable level of the search tree.]
US RE41,531 E 17
18
[25. A communications system in accordance with claim
[31. A system in accordance with claim 30 wherein the random values respectively have a predetermined number of
24 wherein the tree search is a binary tree search.]
[26. A communications system in accordance with claim
bits.]
24 wherein the wireless identi?cation device comprises an integrated circuit including a receiver, a modulator, and a
[32. A system in accordance with claim 30 wherein respective devices are con?gured to store unique identi?ca tion numbers of a predetermined number of bits [33. A system in accordance with claim 30 wherein respective devices are con?gured to store unique identi?ca tion numbers of sixteen bits
microprocessor in communication with the receiver and
modulator.]
[27. A system comprising:
an interro gator;
a number of communications devices capable of wireless
[34. A system comprising:
communications with the interrogator;
an interrogator con?gured to communicate to a selected
means for establishing a predetermined number of bits to
one or more of a number of RFID devices;
be used as random numbers, and for causing respective devices to select random numbers respectively having the predetermined number of bits;
a plurality of RFID devices, respective devices being con ?gured to store unique identi?cation numbers respec
means for inputting a predetermined number indicative of
tively having a ?rst predetermined number of bits,
the maximum number of devices possibly capable of
respective devices being further con?gured to store a second predetermined number of bits to be used for
communicating with the receiver;
random values, respective devices being con?gured to
means for causing the interrogator to transmit a command
requesting devices having random values within a speci?ed group of random values to respond, the speci ?ed group being chosen in response to the inputted pre
select random values independently of random values 20
determined number; means for causing devices receiving the command to determine if their chosen random values fall within the speci?ed group and, if so, send a reply to the interroga tor; and means for causing the interrogator to determine if a colli sion occurred between devices that sent a reply and, if so, create a new, smaller, speci?ed group.] [28. A system in accordance with claim 27 wherein send
command requesting a response from devices having random values within a speci?ed group of a plurality of
possible groups or random values, the speci?ed group being less than or equal to the entire set of random
values, the plurality of possible groups being organized in a binary tree de?ned by a plurality of nodes at 30
ing a reply to the interrogator comprises transmitting the random value of the device sending the reply.] [29. A system in accordance with claim 27 wherein the interrogator further includes means for, after receiving a reply without collision from a device, sending a command
mum number of devices known to be capable of com 35
[30. A system comprising:
sable by specifying random values with differing levels of precision; the interrogator being con?gured to transmit a command requesting devices having random values within a speci?ed group of a plurality of possible groups of ran dom values to respond, the speci?ed group being less than the entire set of random values, the plurality of possible groups being organized in a binary tree de?ned by a plurality of nodes at respective levels, wherein the size of groups of random values decrease in size by half with each node descended, wherein the speci?ed group
40
45
50
in the tree.]
sion occurred between devices that sent a reply and, if so, create a new, smaller, speci?ed group using a level of the tree different from the level used in previously
having random values within the new speci?ed group of random values to respond; and the interrogator being con?gured to send a command indi vidually addressed to a device after communicating with a device without a collision.]
[35. A system in accordance with claim 34 wherein the
interrogator is con?gured to input and store the predeter 55
mined number] [36. A system in accordance with claim 34 wherein the devices are con?gured to respectively determine if their cho sen random values fall within a speci?ed group and, if so,
mined maximum number of devices capable of com
respectively determine if their chosen random values fall within the speci?ed group and, if so, send a reply to the interrogator; and, if not, not send a reply; and the interrogator being con?gured to determine if a colli sion occurred between devices that sent a reply and, if so, create a new, smaller, speci?ed group by descending
within the speci?ed group and, only if so, send a reply to the interrogator, wherein sending a reply to the inter rogator comprises transmitting both the random value of the device sending the reply and the unique identi? cation number of the device sending the reply; the interrogator being con?gured to determine if a colli
transmitting an identify command, the interrogator transmitting an identify command requesting devices
is below a node on the tree selected based on a predeter
municating with the interrogator; devices receiving the command being con?gured to
municating with the interrogator; devices receiving the command respectively being con?g ured to determine if their chosen random values fall
an interrogator con?gured to communicate to a selected one or more of a number of communications devices;
respective levels, wherein the maximum size of groups of random values decrease in size by half with each node descended, wherein the speci?ed group is below a node on a level of the tree selected based on the maxi
individually addressed to that device.]
a plurality of communications devices; the devices being con?gured to select random values, wherein respective devices choose random values inde pendently of random values selected by the other devices, different sized groups of devices being addres
selected by the other devices; the interrogator being con?gured to transmit an identify
send a reply, upon receiving respective identify commands] 60
[37. A system in accordance with claim 34 wherein the interrogator is con?gured to determine if a collision occurred between devices that sent a reply in response to
respective identify commands and, if so, create further new
speci?ed groups and repeat the transmitting of the identify 65
command requesting devices having random values within a speci?ed group of random values to respond using different speci?ed groups until all responding devices are identi?ed.]
US RE41,531 E 19
20
38. A system, comprising: an interrogator comprising:
the transmitter is to communicate the one or more
identifiers in a time slot with a certain probability. 45. The system ofclaim 44, wherein the one or more iden
one or more antennas,
tifiers comprise a sixteen bit random number and the inter rogator is configured to send an acknowledge command to the RFID device the interrogator receives the random
a transmitter and a receiver coupled to the one or more
antennas, and a controller coupled to the transmitter and the receiver, the controller to cause the transmitter to transmit,
number without a collision error.
via the one or more antennas, an initial command to
46. The system ofclaim 44, wherein the RFID device is further configured to communicate an identification code to the interrogator to identi?) a person with whom the RFID device is associated.
select one or more radio frequency identification
(RFID) devicesfrom among a potential plurality of RFID devices that are within communications range,
the initial command specifying a bit string having
47. The system of claim 44, wherein the interrogator is further configured to individually address the RFID device
multiple bits; and the one or more RFID devices, each respective device of
using an access command, wherein the access command
the one or more RFID devices including:
includes a random number to be included in the one or more
memory to store a respective identification code, a receiver to receive the initial command from the
identifiers. 48. The system ofclaim 44, wherein the one or more iden
interrogator,
tifiers comprise both a random number dynamically gener ated by the RFID device and a static number programmed
a circuit to compare the bit string specified in the initial
command against corresponding bits stored in the respective device to determine whether the respective device is a member of a population of RFID devices selected according to the initial command, and if‘the respective device is a member of the population, pick a respective random value from a range of values to determine a respective slot, and
into the RFID device. 49. The system of claim 44, wherein the transmitter is to
further communicate theplurality ofbits, along with the one or more identifiers, to the interrogator in accordance with 25
a transmitter to communicate a respective reply, includ
a communication field of an interrogator, the RFID
ing at least a portion of an identifier of the respective device, to the interrogator in accordance with the
respective slot. 39. The system of claim 38, wherein the interrogator is
the slotted anticollision algorithm. 50. A system, comprising: a radio frequency identification (RFID) device disposed in
device including: a receiver to receive a first command from the interro 30
configured to send an acknowledge command in response to
the interrogator receiving the respective reply from the
gator after the RFID device is disposed in the field and before the interrogator transmits any other command, thefirst command specifying a bit string comprising two or more bits,
respective device and in response to the interrogator deter
a circuit to, in response to the first command, use the bit
mining the respective reply to be collision-free; and the respective reply includes the bit string. 40. The system of claim 3 8, wherein the respective device
string to determine the RFID device is selectedfor participation in a slotted anticollision algorithm, and
is to communicate a respective identification code to identify a person with whom the respective device is associated.
a transmitter to communicate one or more responses to
4]. The system ofclaim 38, wherein the interrogator is to
the interrogator in accordance with the slotted anti 40
further access the respective device individually by sending the identifier to the respective device after receiving the identifier from the respective device. 42. The system ofclaim 38, wherein the interrogator is to indicate the range ofvalues. 43. The system ofclaim 38, wherein the identifier com prises a random number generated by the respective device, and the random number is sixteen bits in length. 44. A system comprising:
lision algorithm, wherein the one or more responses
45
include at least a portion ofafirst identifier and at least a portion of a second identifier stored in the RFID device.
5]. The system of claim 50, wherein the first identifier comprises a random number dynamically generated by the RFID device for the interrogator to use to individually address the RFID device, and the second identifier is a static number stored in the RFID device. 52. The system of claim 5], wherein the receiver is to further receive from the interrogator an indication of a num ber ofslots?om which the RFID device is to randomly select
an interrogator having a transmitter to send an initial command to select one or more radiofrequency identi
fication (RFID) devices, the initial command specifying a bit string having multiple bits; and an RFID device comprising: a device memory to store aplurality ofbits, a receiver to receive the initial command, a circuit to, in response to the initial command, deter
collision algorithm if‘the RFID device is determined to be selectedfor participation in the slotted anticol
a slot in which to communicate the one or more responses in
mine whether the RFID device is selected via a com
accordance with the slotted anticollision algorithm. 53. The system of claim 5], wherein the receiver is to further receive from the interrogator an indication of a change in a number of slots in accordance with the slotted
parison between the bit string and the plurality of
anticollision algorithm.
bits stored in the memory and, if‘the RFID device is
54. The system ofclaim 5], wherein the RFID device is configured for use in a wireless payment application and further comprises memory storing an identification code to identify a person to be chargedfor payment. 55. The system ofclaim 5], wherein the random number is sixteen bits long and the transmitter is to communicate the
determined to be selected, communicate a response
in accordance with a slotted anticollision algorithm, and a transmitter to communicate one or more identifiers of
the RFID device to the interrogator in accordance with the slotted anticollision algorithm, wherein in
accordance with the slotted anticollision algorithm
55
bit string back to the interrogator with the one or more responses.
US RE41,531 E 21
22
56. The system ofclaim 5], wherein the RFID device is con?gured to pick a random value from a range of values
a second RFID device to
store a second set of bits,
and to communicate the one or more responses with aprob
receive the ?rst signal and determine ifthe second
ability corresponding to the random value in accordance with the slotted anticollision algorithm, wherein the ?rst command is to indicate the range ofvalues. 57. The system of claim 56, wherein the receiver is to
device is selected by the interrogator, including com paring so, the bit string with the second set ofbits, and
ofa change in the range ofvalues.
pick a second random integerfrom a variable range of random integers and associate the second ran dom integer with a second time slot in accordance
58. The system ofclaim 5], wherein the transmitter is to communicate the bit string back to the interrogator with the
modulate the RF?eld to communicate a second iden
further receive a second command comprising an indication
with the anticollision algorithm, and
ti?cation code of the second RFID device during
one or more responses.
the second time slot.
59. The system ofclaim 50, wherein the RFID device is con?gured to receive a signalfrom the interrogator, after the interrogator sends the ?rst command to the RFID device and
code includes a ?rst random number generated by the ?rst
before the RFID device communicates the one or more
RFID device; and the second identi?cation code includes a
responses to the interrogator, wherein the signal indicates
second random number generated by the second RFID
66. The system ofclaim 65, wherein the?rst identi?cation
the RFID device when to communicate the identifier to the
interrogator. 60. The system ofclaim 50, wherein the RFID device com
device. 20
municates the one or more responses via modulating an
radio frequency
?eld provided by the interrogator.
6]. The system ofclaim 50, wherein the transmitter is to communicate the bit string back to the interrogator with the
slot and, in response thereto, to send a ?rst acknowledge
signal to acknowledge the ?rst RFID device; and the interro 25
one or more responses.
62. The system ofclaim 50, wherein the RFID device is con?gured for use in a wireless payment system andfurther comprises memory storing an identi?cation code to identify a person to be chargedfor payment. 63. The system ofclaim 50, wherein the RFID device is
67. The system of claim 66, wherein the interrogator is con?gured to receive the ?rst random number from the ?rst RFID device during a period of time associated with the ?rst
gator is con?gured to receive the second random number
from the second RFID device during a period oftime associ ated with the second slot and, in response thereto, to send a
second acknowledge signal to acknowledge the second RFID device. 30
con?gured to randomly pick an integer from a number of
68. The system of claim 66, wherein after receiving the ?rst random number and the?rst identi?cation codefrom the
integers and to communicate the one or more responses in a
?rst RFID device, the interrogator is to send a command that
?rst slot with a probability corresponding to the randomly picked integer in accordance with the slotted anticollision
includes the ?rst random number to individually identify the ?rst RFID device. 69. The system of claim 68, wherein the interrogator is con?gured to receive a ?rst identi?er from the ?rst RFID
algorithm, wherein the?rst command is to indicate the num
ber of integers. 64. The system of claim 63, wherein the receiver is to further receive from the interrogator a second command, the second command to indicate a different number of integers
second RFID device to identify a person with whom the sec
for the RFID device to use in accordance with the slotted
ond RFID device is associated.
device to identi?) a person with whom the ?rst RFID device is associated and to receive a second identi?er from the
anticollision algorithm.
70. The system of claim 69, wherein the interrogator is con?gured to send a second signal after sending the ?rst signal; and wherein the ?rst RFID device is con?gured to
65. A system comprising: an interrogator including:
communicate the ?rst identi?cation code in response to
at?eld, least one a plurality antenna of to provide radio frequency a radio frequency identi?cation
receiving the second signal.
(RFID) devices to modulate the RF ?eld to transmit responses to the interrogator;
a transmitter to send a ?rst signal after the plurality of RFID devices are disposed in the?eld and before any of the plurality of RFID devices transmit responses to the interrogator, the ?rst signal including a bit
50
string comprising multiple bits; and a receiver to receive responses to the ?rst signal in accordance with a slotted anticollision algorithm;
wherein the plurality ofRFID devices include:
7]. The system of claim 65, wherein the interrogator is con?gured to send a ?rst acknowledge signal to acknowl edge the ?rst RFID device and a second acknowledge signal to acknowledge the second RFID device. 72. A system comprising: an interrogator including: an antenna to provide a radio frequency
?eld to
interrogate;
55 a
transmitter to send an initial command to identi?)
a ?rst RFID device con?gured to store a ?rst set of bits,
radio frequency identi?cation (RFID) devices dis
receive the ?rst signal and determine the ?rst RFID device is selected by the interrogator, including com paring the bit string with the?rst set ofbits, and ifso, pick a?rst random integerfrom a variable range of random integers and associate the ?rst random
posed in the ?eld, the initial command to be sent after the RFID devices are disposed in the ?eld and before any of the RFID devices communicate any responses to the interrogator, the initial command to
integer with a ?rst time slot in accordance with the
select one or more of the RFID devices to participate
anticollision algorithm, and modulate the RF?eld to communicate a ?rst identi?
include a?rst specifying a plurality ofbit values to in a slotted anticollision algorithm; and a receiver to receive responses to the initial command
cation code ofthe?rst RFID device during the?rst
in accordance with the slotted anticollision algo
time slot; and
rithm; and
US RE41,531 E 24
23
75. The system of claim 74, wherein the first identifier comprises a random number generated by the RFID device;
an RFID device disposed in the RF ?eld of the interrogator, the RFID device comprising: a receiver to wirelessly receive the initial command; a random number generator to randomly select an inte
and the second identifier comprises a static code pro grammed into the RFID device. 76. The system ofclaim 72, wherein the RFID device is to compare the plurality ofbit values to at least a portion ofa
ger value from a range of integer values in accor
dance with the slotted anticollision algorithm, the range to be adjustable and to be indicated to the
number stored in the RFID device to determine whether the
RFID device by the interrogator; and
plurality of bit values receivedfrom the interrogator identify
a transmitter to modulate the RFfield to communicate a one or more responses to the interrogator based at
least in part on whether the plurality of bit values
the RFID device for response, wherein the one or more responses to the interrogator are to include the number as a
received from the interrogator identify the RFID
second identifier from the RFID device; and wherein the
device for response, wherein the one or more responses are to include a first identifier and are to
interrogator is configured to send a subsequent command specifically addressed to the RFID device using the identi
be communicated in accordance with the randomly selected integer value in accordance with the slotted
15
77. The system ofclaim 76, wherein the RFID device is to
anticollision algorithm.
communicate the one or more responses in a first slot in
accordance with the slotted anticollision algorithm with a
73. The system ofclaim 72, wherein the RFID device is configured to communicate at least a portion of an identifi cation code to the interrogator, wherein the identification code identifies a person with whom the RFID device is asso
ciated.
fier.
first probability corresponding to the integer value. 20
78. The system of claim 72, wherein the range is to be indicated to the RFID device by the initial command, and a di?‘erent range is to be indicated to the RFID device by a
74. The system of claim 72, wherein the one or more subsequent command, wherein the subsequent command includes afield re-speci?ing the plurality of bit values to responses are to further include a second identifier to be communicated in accordance with the randomly selected 25 select one or more ofthe RFID devices.
integer value in accordance with the slotted anticollision
algorithm.
*
*
*
*
*
USO0RE41531C1
(12) EX PARTE REEXAMINATION CERTIFICATE (10248th) United States Patent (10) Number: US RE41,531 C1 Wood, Jr. (54)
(45) Certi?cate Issued:
COMMUNICATIONS SYSTEMS FOR RADIO
(51)
FREQUENCY IDENTIFICATION (REID) _
(75)
Inventor'
(52)
Chm“ W' W°°d’ Jr" Tum: OK (Us)
(58) Field Of ClaSSi?cation seardl
Kisco, NY (U S)
None See application ?le for complete search history.
Reexamination Request: No. 90/012,114, Jan. 30, 2012
(56)
(*)
Issued: Appl. No.: Filed:
Aug. 17, 2010 11/859,364 Sep. 21, 2007
Notice:
This patent is subject to a terminal dis claimer.
Primary Examiner * Michael J. Yigdall
(57)
Related U.S. Patent Documents
ABSTRACT
A system for establishing Wireless communications between
Reissue of:
(64) Patent No.: Issued:
(63)
References Cited
To vieW the complete listing of prior art documents cited during the proceeding for Reexamination Control Number 90/012,114, please refer to the USPTO’S public Patent Application Information Retrieval (PAIR) system under the Display References tab.
Reexamination Certi?cate for:
Re. 41,531
(2009.01)
U.S. Cl.
USPC .......................... .. 370/329; 370/345; 370/347
(73) Assignee: Round Rock Research, LLC, Mt.
Patent No.:
Int. Cl.
H04W4/00
_
*Aug. 8, 2014
an interrogator and individual ones of multiple Wireless iden ti?cation devices The interrogator transmits a ?rst request comprising a bit String comprising a plurality of bits for use in
6,307,847 Oct. 23, 2001
Appl. No.:
09/617,390
Filed:
Jul. 17, 2000
selecting one or more Wireless identi?cation devices to par
Related U.S. Application Data
ticipate in a Slotted anticollision algorithm. Wireless identi ?cation devices in a ?eld of the interrogator use the bit String
Continuation of application No. 10/693,697, ?led on Oct. 23, 2003, nOW Pat. No. Re. 42,344, Which is an
application for the reissue of Pat. No. 6,307,847, Which is a continuation of application No. 09/026,043, ?led on Feb. 19, 1998, nOW Pat. No. 6,118,789.
to determine Whether or not they are selected for participa tion. Those Wireless identi?cation devices that are selected
for participation respond to the interrogator in a Slot With a certain probability in accordance With the Slotted anticolli
sion algorithm.
27
16\ RFID
28
141/?
IN TERROGA TOR
29
26 /
C/RCU/TRY l POWER SOURCE
18/
