U.S. patent number RE41,471 [Application Number 11/862,121] was granted by the patent office on 2010-08-03 for method of addressing messages and communications system.
This patent grant is currently assigned to Round Rock Research, LLC. Invention is credited to Clifton W. Wood, Jr..
United States Patent |
RE41,471 |
Wood, Jr. |
August 3, 2010 |
Method of Addressing Messages and Communications System
Abstract
A method of establishing wireless communications between an
interrogator and individual ones of multiple wireless
identification devices, the method .[.comprising utilizing a tree
search method to attempt to identify individual ones of the
multiple wireless identification devices so as to be able to
perform communications, without collision, between the interrogator
and individual ones of the multiple wireless identification
devices, a search tree being defined for the tree search method,
the tree having multiple nodes respectively representing subgroups
of the multiple wireless identification devices, wherein the
interrogator transmits a command at a node, requesting that devices
within the subgroup represented by the node respond, wherein the
interrogator determines if a collision occurs in response to the
command and, if not, repeats the command at the same node. An
interrogator configured to transmit a command at a node, requesting
that devices within the subgroup represented by the node respond,
the interrogator further being configured to determine if a
collision occurs in response to the command and, if not, to repeat
the command at the same node.]. .Iadd.includes: transmitting by an
interrogator a first signal including a first set of bits, the
interrogator to identify a first subgroup of a group of possible
random numbers; communicating by each of one or more RFID devices a
first response if the one or more RFID devices has generated a
random number that is included in the first subgroup; receiving by
the interrogator one or more received responses from respective
ones of the one or more RFID devices; and responsive to receiving
one of the one or more received responses without a collision,
retransmitting by the interrogator at least the first
signal.Iaddend..
Inventors: |
Wood, Jr.; Clifton W. (Tulsa,
OK) |
Assignee: |
Round Rock Research, LLC (Mount
Kisco, NY)
|
Family
ID: |
21829591 |
Appl.
No.: |
11/862,121 |
Filed: |
September 26, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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10652573 |
Aug 28, 2003 |
|
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|
09026050 |
Feb 19, 1998 |
6061344 |
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Reissue of: |
09556235 |
Apr 24, 2000 |
06282186 |
Aug 28, 2001 |
|
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Current U.S.
Class: |
370/346 |
Current CPC
Class: |
H04L
41/0893 (20130101); H04W 4/00 (20130101); H04L
41/12 (20130101) |
Current International
Class: |
H04L
1/00 (20060101) |
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Primary Examiner: Patel; Ajit
Attorney, Agent or Firm: Gazdzinski & Associates, PC
Parent Case Text
.Iadd.RELATED REISSUE APPLICATIONS .Iaddend.
.Iadd.More than one reissue application has been filed for the
reissue of U.S. Pat. No. 6,282,186. The reissue applications are
the initial reissue application Ser. No. 10/652,573 filed Aug. 28,
2003, a continuation reissue application Ser. No. 11/862,130, filed
Sep. 26, 2007, a continuation reissue application Ser. No.
11/862,124, filed Sep. 26, 2007, and the present continuation
reissue application..Iaddend.
CROSS REFERENCE TO RELATED APPLICATION
This is a .[.Continuation.]. .Iadd.continuation application of a
reissue application Ser. No. 10/652,573, filed Aug. 28, 2003, which
is a reissue application of U.S. patent application Ser. No.
09/556,235, now U.S. Pat. No. 6,282,186, which is a continuation
application .Iaddend.of U.S. patent application Ser. No.
09/026,050, filed Feb. 19, 1998, now U.S. Pat. No. 6,061,344 and
titled "Method of Addressing Messages and Communications System".
Claims
What is claimed is:
.[.1. A method of establishing wireless communications between an
interrogator and wireless identification devices, the method
comprising utilizing a tree search technique to establish
communications, without collision, between the interrogator and
individual ones of the multiple wireless identification devices,
the method including using a search tree having multiple nodes
respectively representing subgroups of the multiple wireless
identification devices, the method further comprising, for a node,
transmitting a command, using the interrogator, requesting that
devices within the subgroup represented by the node respond,
determining with the interrogator if a collision occurred in
response to the command and, if not, repeating the command at the
same node..].
.[.2. A method in accordance with claim 1 and further comprising,
if a collision occurred in response to the first mentioned command,
sending a command at a different node, using the
interrogator..].
.[.3. A method in accordance with claim 1 wherein when a subgroup
contains both a device that is within communications range of the
interrogator, and a device that is not within communications range
of the interrogator, the device that is not within communications
range of the interrogator does not respond to the command..].
.[.4. A method in accordance with claim 1 wherein when a subgroup
contains both a device that is within communications range of the
interrogator, and a device that is not within communications range
of the interrogator, the device that is within communications range
of the interrogator responds to the command..].
.[.5. A method in accordance with claim 1 wherein a device in a
subgroup changes between being within communications range of the
interrogator and not being within interrogators range, over
time..].
.[.6. A method in accordance with claim 1 wherein the wireless
identification 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 a
selected one or more of a number of communications devices, the
method comprising: establishing for respective devices unique
identification numbers; causing the devices to select random
values, wherein respective devices choose random values
independently of random values selected by the other devices;
transmitting a communication, from the interrogator, requesting
devices having random values within a first specified group of
random values to respond; receiving the communication at multiple
devices, devices receiving the communication respectively
determining if the random value chosen by the device falls within
the first specified group and, if so, sending a reply to the
interrogator; and determining using the interrogator if a collision
occurred between devices that sent a reply and, if so, creating a
second specified group smaller than the first specified group; and,
if not, again transmitting a communication requesting devices
having random values within the first specified group of random
values to respond..].
.[.8. A method of addressing messages from an interrogator to a
selected one or more of a number of communications devices in
accordance with claim 7 wherein sending a reply to the interrogator
comprises transmitting the unique identification number of the
device sending the reply..].
.[.9. A method in accordance with claim 7 wherein one of the first
and second specified groups contains both a device that is within
communications range of the interrogator, and a device that is not
within communications range of the interrogator, and wherein the
device that is not within communications range of the interrogator
does not respond to the interrogator..].
.[.10. A method of addressing messages from an interrogator to a
selected one or more of a number of communications devices in
accordance with claim 7 wherein, after receiving a reply without
collision from a device, the interrogator sends a communication
individually addressed to that device..].
.[.11. A method of addressing messages from a transponder to a
selected one or more of a number of communications devices, the
method comprising: establishing unique identification numbers for
respective devices; causing the devices to select random values,
wherein respective devices choose random values independently of
random values selected by the other devices; transmitting a
communication from the transponder requesting devices having random
values within a specified group of a plurality of possible groups
of random values to respond, the plurality of possible groups being
organized in a binary tree defined by a plurality of nodes at
respective levels, the specified group being defined as being at
one of the nodes; receiving the communication at multiple devices,
devices receiving the communication respectively determining if the
random value chosen by the device falls within the specified group
and, if so, sending a reply to the transponder; and, if not, not
sending a reply; and determining using the transponder if a
collision occurred between devices that sent a reply and, if so,
creating a new, smaller, specified group by descending in the tree;
and, if not, transmitting a communication at the same node..].
.[.12. A method of addressing messages from a transponder to a
selected one or more of a number of communications devices in
accordance with claim 11 wherein establishing unique identification
numbers for respective devices comprises establishing a
predetermined number of bits to be used for the unique
identification numbers..].
.[.13. A method of addressing messages from a transponder to a
selected one or more of a number of communications devices in
accordance with claim 12 and further including establishing a
predetermined number of bits to be used for the random
values..].
.[.14. A method of addressing messages from an interrogator to a
selected one or more of a number of RFID devices, the method
comprising: establishing for respective devices unique
identification numbers; causing the devices to select random
values, wherein respective devices choose random values
independently of random values selected by the other devices;
transmitting a command using the interrogator requesting devices
having random values within a specified group of a plurality of
possible groups of random values to respond, the specified group
being equal to or less than the entire set of random values, the
plurality of possible groups being organized in a binary tree
defined by a plurality of nodes at respective levels; receiving the
command at multiple RFID devices, RFID devices receiving the
command respectively determining if their chosen random values fall
within the specified group and, only if so, sending a reply to the
interrogator, wherein sending a reply to the interrogator comprises
transmitting the unique identification number of the device sending
the reply; determining using the interrogator if a collision
occurred between devices that sent a reply and, if so, creating a
new, smaller, specified group using a different level of the tree,
the interrogator transmitting a command requesting devices having
random values within the new specified group of random values to
respond; and, if not, the interrogator re-transmitting a command
requesting devices having random values within the first mentioned
specified group of random values to respond; and if a reply without
collision is received from a device, the interrogator subsequently
sending a command individually addressed to that device..].
.[.15. A method of addressing messages from an interrogator to a
selected one or more of a number of RFID devices in accordance with
claim 14 wherein the first mentioned specified group contains both
a device that is within communications range of the interrogator,
and a device that is not within communications range of the
interrogator, and wherein the device that is not within
communications range of the interrogator does not respond to the
transmitting of the command or the re-transmitting of the
command..].
.[.16. A method of addressing messages from an interrogator to a
selected one or more of a number of RFID devices in accordance with
claim 14 wherein the first mentioned specified group contains both
a device that is within communications range of the interrogator,
and a device that is not within communications range of the
interrogator, and wherein the device that is within communications
range of the interrogator responds to the transmitting of the
command and the re-transmitting of the command..].
.[.17. A method of addressing messages from an interrogator to a
selected one or more of a number of RFID devices in accordance with
claim 14 wherein a device in the first mentioned specified group is
capable of changing between being within communications range of
the interrogator and not being within communications range of the
interrogator over time..].
.[.18. A method of addressing messages from an interrogator to a
selected one or more of a number of RFID devices in accordance with
claim 14 wherein the devices respectively comprise an integrated
circuit including a receiver, a modulator, and a microprocessor in
communication with the receiver and modulator..].
.[.19. A method of addressing messages from an interrogator to a
selected one or more of a number of RFID devices in accordance with
claim 14 and further comprising, after the interrogator transmits a
command requesting devices having random values within the new
specified group of random values to respond; devices receiving the
command respectively determining if their chosen random values fall
within the new smaller specified group and, if so, sending a reply
to the interrogator..].
.[.20. A method of addressing messages from an interrogator to a
selected one or more of a number of RFID devices in accordance with
claim 19 and further comprising, after the interrogator transmits a
command requesting devices having random values within the new
specified group of random values to respond; determining if a
collision occurred between devices that sent a reply and, if so,
creating a new specified group and repeating the transmitting of
the command requesting devices having random values within a
specified group of random values to respond using different
specified groups until all of the devices capable of communicating
with the interrogator are identified..].
.[.21. A communications system comprising an interrogator, and a
plurality of wireless identification devices configured to
communicate with the interrogator using RF, the interrogator being
configured to employ tree searching to attempt to identify
individual ones of the multiple wireless identification devices, so
as to be able to perform communications without collision between
the interrogator and individual ones of the multiple wireless
identification devices, the interrogator being configured to follow
a search tree, the tree having multiple nodes respectively
representing subgroups of the multiple wireless identification
devices, the interrogator being configured to transmit a command at
a node, requesting that devices within the subgroup represented by
the node respond, the interrogator further being configured to
determine if a collision occurs in response to the command and, if
not, to repeat the command at the same node..].
.[.22. A communications system in accordance with claim 21 wherein
the interrogator is configured to send a command at a different
node if a collision occurs in response to the first mentioned
command..].
.[.23. A communications system in accordance with claim 21 wherein
a subgroup contains both a device that is within communications
range of the interrogator, and a device that is not within
communications range of the interrogator..].
.[.24. A communications system in accordance with claim 21 wherein
a subgroup contains both a device that is within communications
range of the interrogator, and a device that is not within
communications range of the interrogator, and wherein the device
that is within communications range of the interrogator responds to
the command..].
.[.25. A communications system in accordance with claim 21 wherein
a device in a subgroup is movable relative to the interrogator so
as to be capable of changing between being within communications
range of the interrogator and not being within communications
range..].
.[.26. A communications system in accordance with claim 21 wherein
the wireless identification device comprises an integrated circuit
including a receiver, a modulator, and a microprocessor in
communication with the receiver and modulator..].
.[.27. A system comprising: an interrogator; a number of
communications devices capable of wireless communications with the
interrogator; means for establishing for respective devices unique
identification numbers respectively having the first predetermined
number of bits; means for causing the devices to select random
values, wherein respective devices choose random values
independently of random values selected by the other devices; means
for causing the interrogator to transmit a command requesting
devices having random values within a specified group of random
values to respond; means for causing devices receiving the command
to determine if their chosen random values fall within the
specified group and, if so, to send a reply to the interrogator;
and means for causing the interrogator to determine if a collision
occurred between devices that sent a reply and, if so, to create a
new, smaller, specified group; and, if not, transmit a command
requesting devices having random values within the same specified
group of random values to respond..].
.[.28. A system in accordance with claim 27 wherein sending a reply
to the interrogator comprises transmitting the unique
identification number of the device sending the reply..].
.[.29. A system in accordance with claim 27 wherein a specified
group contains both a device that is within communications range of
the interrogator, and a device that is not within communications
range of the interrogator..].
.[.30. 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 individually
addressed to that device..].
.[.31. A system comprising: an interrogator configured to
communicate to a selected one or more of a number of communications
devices; and a plurality of communications devices; the devices
being configured to select random values, wherein respective
devices choose random values independently of random values
selected by the other devices; the interrogator being configured to
transmit a command requesting devices having random values within a
specified group of a plurality of possible groups of random values
to respond, the specified group being less than the entire set of
random values, the plurality of possible groups being organized in
a binary tree defined by a plurality of nodes at respective levels,
the specified group being defined as being at one of the nodes;
devices receiving the command being configured to respectively
determine if their chosen random values fall within the specified
group and, only if so, send a reply to the interrogator, wherein
sending a reply to the interrogator comprises transmitting the
unique identification number of the device sending the reply; the
interrogator being configured to determine if a collision occurred
between devices that sent a reply and, if so, create a new,
smaller, specified group using a different level of the tree, the
interrogator being configured to transmit a command requesting
devices having random values within the new specified group of
random values to respond; and, if not, the interrogator being
configured to re-transmit a command requesting devices having
random values within the first mentioned specified group of random
values to respond..].
.[.32. A system in accordance with claim 31 wherein the first
mentioned specified group contains both a device that is within
communications range of the interrogator, and a device that is not
within communications range of the interrogator..].
.[.33. A system in accordance with claim 31 wherein a device in the
first mentioned specified group is capable of changing between
being within communications range of the interrogator and not being
within communications range of the interrogator over time..].
.[.34. A system in accordance with claim 31 wherein the respective
devices comprise an integrated circuit including a receiver, a
modulator, and a microprocessor in communication with the receiver
and modulator..].
.[.35. A system comprising: an interrogator configured to
communicate to a selected one or more of a number of RFID devices;
a plurality of RFID devices, respective devices being configured to
store a unique identification number, respective devices being
further configured to store a random value; the interrogator being
configured to transmit a command requesting devices having random
values within a specified group of a plurality of possible groups
of random values to respond, the plurality of possible groups being
organized in a binary tree defined by a plurality of nodes at
respective levels, the specified group being defined as being at
one of the nodes; devices receiving the command respectively being
configured to determine if their chosen random values fall within
the specified group and, if so, send a reply to the interrogator;
and, if not, not send a reply; and the interrogator being
configured to determine if a collision occurred between devices
that sent a reply and, if so, to create a new, smaller, specified
group by descending in the tree; and, if not, to transmit a command
at the same node..].
.[.36. A system in accordance with claim 35 wherein the unique
identification numbers for respective devices are stored in digital
form and respectively comprise a predetermined number of
bits..].
.[.37. A system in accordance with claim 35 wherein the random
values for respective devices are stored in digital form and
respectively comprise a predetermined number of bits..].
.[.38. A system in accordance with claim 35 wherein the
interrogator is configured to determine if a collision occurred
between devices that sent a reply in response to respective
Identify commands and, if so, to create further new specified
groups and repeat the transmitting of the command requesting
devices having random values within a specified group of random
values to respond using different specified groups until all
responding devices capable of responding are identified..].
.Iadd.39. A method for performing radio frequency communications,
the method comprising: transmitting by an interrogator a first
signal, the first signal including a first set of bits to identify
a first subgroup of a group of possible random numbers; receiving
by one or more RFID devices the first signal; communicating by each
of the one or more RFID devices a first response if the one or more
RFID devices has generated a random number that is included in the
first subgroup; receiving by the interrogator one or more received
responses, the one or more received responses being received from
respective ones of the one or more RFID devices; and responsive to
receiving one of the one or more received responses without a
collision, retransmitting by the interrogator at least the first
signal..Iaddend.
.Iadd.40. The method of claim 39, wherein the first signal includes
a selection indicator, the selection indicator identifying one or
more RFID devices, the communicating by each of the one or more
RFID devices only being performed if the selection indicator
corresponds to one or more selection bits stored on each respective
RFID device..Iaddend.
.Iadd.41. The method of claim 39, further comprising setting, by
the one or more RFID devices communicating the first response, an
inventoried flag to a first state to indicate that each respective
RFID device has responded to the interrogator..Iaddend.
.Iadd.42. The method of claim 39, further comprising transmitting
by the interrogator a wake-up signal, the wake-up signal causing an
RFID device to transition out of a sleep state..Iaddend.
.Iadd.43. The method of claim 39, wherein the one of the one or
more received responses without a collision is received from a
first RFID device, and further comprising the interrogator
transmitting a command to silence the first RFID
device..Iaddend.
.Iadd.44. The method of claim 39, wherein the one of the one or
more received responses without a collision is received from a
first RFID device and includes at least one random number generated
by the first RFID device, and further comprising transmitting by
the interrogator at least one additional command to the first RFID
device, the first RFID device being identified in the at least one
additional command by an identifier including the at least one
random number..Iaddend.
.Iadd.45. The method of claim 39, further comprising transmitting
by the interrogator a wake up signal..Iaddend.
.Iadd.46. The method of claim 39, further comprising responsive to
a collision occurring in the receiving by the interrogator one or
more received responses, transmitting by the interrogator a second
signal, the second signal including a second set of bits to
identify a second subgroup of the group of possible random numbers,
wherein the second subgroup is a subgroup of the first subgroup,
the second set of bits includes the first set of bits plus one or
more additional bits, and the second signal includes the first
signal..Iaddend.
.Iadd.47. The method of claim 46, wherein the second subgroup is
determined at least in part by skipping one or more levels of a
search tree..Iaddend.
.Iadd.48. The method of claim 46, wherein the second set of bits
includes the first set of bits plus two or more of the additional
bits..Iaddend.
.Iadd.49. The method of claim 39, wherein the first subgroup is
based at least in part on a maximum number of possible random
numbers..Iaddend.
.Iadd.50. A system for performing radio frequency communications,
the system comprising: a first radio frequency identification
(RFID) device configured to generate a random number and to
communicate a response, including at least a portion of the random
number, upon receiving a request that includes an indication of a
subset of possible random numbers if the first RFID device
determines that the subset includes the random number generated by
the first RFID device; an antenna positioned in a first region; and
an interrogator coupled to the antenna, the interrogator configured
to transmit a signal comprising a portion of an identifier and to
receive a reply to the signal from a target RFID device that has
generated a random number having a portion equal to the portion of
the identifier, the interrogator further configured to re-transmit
the signal, including at least the portion of the identifier, if
the reply is received without a collision..Iaddend.
.Iadd.51. The system of claim 50, wherein the request includes a
selection indicator, the selection indicator identifying one or
more RFID devices, the first RFID device being configured to
communicate the response only if the selection indicator
corresponds to one or more selection bits stored on the first RFID
tag..Iaddend.
.Iadd.52. The system of claim 50, wherein the first RFID device is
further configured to set an inventoried flag to a first state to
indicate that the first RFID device has responded to the at least
one interrogator..Iaddend.
.Iadd.53. The system of claim 50, wherein the first RFID device is
further configured to communicate the response after receiving a
wake-up signal..Iaddend.
.Iadd.54. The system of claim 50, wherein the first RFID device is
further configured to communicate a response at a time slot
corresponding to a random number generated by the first RFID
device..Iaddend.
.Iadd.55. The system of claim 50, wherein the interrogator is
further configured to transmit a sleep command upon receiving the
reply without a collision..Iaddend.
.Iadd.56. The system of claim 50, wherein the interrogator is
further configured to transmit a larger portion of the identifier
if the reply is received with a collision..Iaddend.
.Iadd.57. The system of claim 56, wherein a difference between the
portion of the identifier and the larger portion of the identifier
is two or more bits..Iaddend.
.Iadd.58. An interrogator comprising: one or more antennas; a
receiver communicatively coupled to at least one of the one or more
antennas to receive one or more messages from one or more radio
frequency identification (RFID) devices; a transmitter
communicatively coupled to at least one of the one or more antennas
to transmit one or more messages; and a control unit
communicatively coupled to the transmitter and the receiver, the
control unit configured to implement an algorithm to detect at
least a single RFID device in a field of the interrogator,
including re-transmitting a first signal responsive to receipt of a
first response from the one or more RFID devices without a
collision, the first signal including a first set of bits of at
least a first portion of possible random numbers that may be
generated by the one or more RFID devices, and the first response
including at least a second portion of a random number generated by
the one or more RFID devices..Iaddend.
.Iadd.59. The interrogator of claim 58, wherein the first signal
includes a selection indicator, the selection indicator
corresponding to one or more selection bits stored on the one or
more RFID devices..Iaddend.
.Iadd.60. The interrogator of claim 58, wherein the control unit is
further configured to transmit a command to silence the one or more
RFID devices from which the first response was received without a
collision, and the control unit is further configured to indicate a
number of time slots from which at least a first RFID device is to
randomly select a time slot in which to communicate a random value
generated by the first RFID device..Iaddend.
.Iadd.61. The interrogator of claim 58, wherein the control unit is
further configured to define a second set of bits of at least a
second portion, greater than the first portion, of possible random
numbers responsive to a collision detected in the receipt of the
first response from the one or more RFID devices..Iaddend.
.Iadd.62. The interrogator of claim 61, wherein the control unit is
further configured to define the second set of bits to be at least
two bits greater than the first portion..Iaddend.
.Iadd.63. The interrogator of claim 58, wherein the possible random
numbers define a binary search tree, the first set of bits define a
level in the search tree, and the control unit is further
configured to skip one or more intermediate levels in the binary
search tree to implement the algorithm..Iaddend.
.Iadd.64. The interrogator of claim 58, wherein the control unit is
further configured to transmit a wake-up signal, indicate a number
of time slots, and receive a random value from a first RFID device
in a time slot randomly determined by the first RFID device from
among the number of time slots..Iaddend.
.Iadd.65. A method comprising: providing an interrogator to
generate an RF field and to initiate the implementation of an
algorithm to detect at least a single target RFID device out of
potentially multiple target RFID devices in the RF field, the
algorithm including: defining a first subgroup of possible random
numbers that may be generated by the target device, the first
subgroup being defined by a first set of bits common to the first
subgroup; transmitting a signal comprising at least the first set
of bits to identify the first subgroup of possible random numbers
and requesting the target device to respond if the target device
has generated a random number included in the subgroup; receiving a
response from the target device if the target device has generated
the random number included in the subgroup; if no collision is
detected in the receiving of the response from the target device,
determining, from the response, the random number generated by the
target device and retransmitting the signal; and if a collision is
detected in the receiving of the response from the target device,
defining a second subgroup of possible random numbers that may be
generated by the target device, the second subgroup being a subset
of the first subgroup and being defined by a second set of bits
common to the second subgroup, and retransmitting the
signal..Iaddend.
.Iadd.66. The method of claim 65, wherein the signal includes a
selection indicator that identifies a class of one or more of a
plurality of RFID devices from which a response is being
requested..Iaddend.
.Iadd.67. The method of claim 65, wherein the algorithm further
includes transmitting a command to silence the target device after
the determining of the random number generated by the target
device..Iaddend.
.Iadd.68. The method of claim 65, wherein the algorithm further
includes transmitting a number of time slots from which at least a
first RFID device is to randomly select a time slot in which to
communicate a random value generated by the first RFID
device..Iaddend.
.Iadd.69. The method of claim 65, wherein the algorithm further
comprises transmitting a number of time slots, and receiving a
random value from a first RFID device in a time slot randomly
determined by the first RFID device from among the number of time
slots..Iaddend.
.Iadd.70. The method of claim 65, wherein the second set of bits
includes the first set of bits and the algorithm further comprises
transmitting the second set of bits if the collision is detected in
the receiving of the response from the target device..Iaddend.
.Iadd.71. The method of claim 70, wherein the algorithm
accommodates the second set of bits being two or more bits longer
than the first set of bits..Iaddend.
.Iadd.72. A method, comprising: receiving a first signal from an
interrogator in accordance with an algorithm to identify a radio
frequency identification (RFID) device in a field of the
interrogator, the first signal comprising a first set of bits and
requesting a response from one or more RFID devices in the field
selected in accordance with at least the first set of bits;
responsive to receiving the first signal, determining if the first
set of bits is equal to a first portion of a random number
generated by the RFID device, and, if so, modulating an RF field,
provided by the interrogator, to communicate a reply to the
interrogator in accordance with the algorithm; and receiving, in
accordance with the algorithm, a retransmission of the first signal
from the interrogator in response to the interrogator receiving the
reply without detecting a collision..Iaddend.
.Iadd.73. The method of claim 72, further comprising communicating
with the interrogator in one of a first communication mode and a
second communication mode determined by the interrogator, wherein
in accordance with the first communication mode the RFID device
modulates an RF field generated by the RFID device and in
accordance with the second communication mode the RFID device
modulates an RF field generated by the interrogator..Iaddend.
.Iadd.74. The method of claim 73, further comprising communicating
with the interrogator at one of a plurality of bit rates determined
by the interrogator..Iaddend.
.Iadd.75. The method of claim 72, further comprising receiving a
wake up command from the interrogator and, in response,
transitioning from a sleep state..Iaddend.
.Iadd.76. The method of claim 75, further comprising receiving a
sleep command from the interrogator..Iaddend.
.Iadd.77. The method of claim 76, wherein the sleep command is
received in response to the interrogator receiving the reply
without detecting a collision, in accordance with the algorithm,
before the receiving of the retransmission of the first
signal..Iaddend.
.Iadd.78. The method of claim 72, wherein the reply comprises a
random value generated by the RFID device..Iaddend.
.Iadd.79. The method of claim 78, wherein the random number
comprises the random value..Iaddend.
.Iadd.80. The method of claim 79, wherein the random value is the
random number..Iaddend.
.Iadd.81. The method of claim 72, further comprising receiving, in
accordance with the algorithm, a second signal from the
interrogator in response to the interrogator detecting a collision
in the reply, the second signal comprising a second set of bits and
requesting a response from one or more RFID devices in the field
selected in accordance with at least the second set of bits; and
responsive to receiving the second signal, determining if the
second set of bits is equal to a second portion of the random
number generated by the RFID device, and, if so, modulating the RF
field to communicate a second reply to the interrogator in
accordance with the algorithm, wherein the second signal comprises
the first signal, the second set of bits comprises the first set of
bits plus at least two additional bits, and the second portion of
the random number comprises the first portion of the random
number..Iaddend.
.Iadd.82. The method of claim 81, wherein the second reply
comprises at least a portion of the random number..Iaddend.
.Iadd.83. The method of claim 82, further comprising communicating
a random value to the interrogator during a time slot randomly
selected from a number of time slots..Iaddend.
.Iadd.84. The method of claim 72, further comprising communicating
a random value to the interrogator during a time slot randomly
selected from a number of time slots..Iaddend.
.Iadd.85. A system, comprising: a radio frequency identification
(RFID) device comprising a receiver to receive a first command
including a portion of an identification number, a random number
generator to generate a random number to identify the device, and a
transmitter to communicate a reply to the first command if the
portion of the identification number is equal to a first portion of
the random number; and an interrogator configured to implement an
algorithm to identify one or more RFID devices in a field of the
interrogator, the algorithm comprising transmitting a first signal
with a first set of bits to request a response from a selected one
or more devices, receiving a first response thereto from the
selected one or more devices, detecting if a collision occurred in
the first response, and retransmitting the first signal with at
least the first set of bits to request a second response from at
least one of the selected one or more devices in response to
detecting no collision in the first response..Iaddend.
.Iadd.86. The system of claim 85, further comprising memory storing
a unique identification code to be transmitted by the
system..Iaddend.
.Iadd.87. The system of claim 85, wherein the transmitter is
configured to communicate by modulating an RF field provided by a
remote device..Iaddend.
.Iadd.88. The system of claim 87, wherein the algorithm further
comprises transmitting an indication of the number of bits of the
first set of bits..Iaddend.
.Iadd.89. The system of claim 85, wherein retransmitting the first
signal with at least the first set of bits comprises retransmitting
the first signal with no more than the first set of
bits..Iaddend.
.Iadd.90. The system of claim 85, wherein the system is configured
to communicate at one of a plurality of bit rates determined by a
remote device..Iaddend.
.Iadd.91. The system of claim 90, wherein the system is configured
to operate in a first communication mode during a first period of
time and in a second communication mode during a second period of
time, wherein in accordance with the first communication mode the
system is configured to modulate an RF field generated by the
remote device and in accordance with the second communication mode
the system is configured to generate and modulate an RF
field..Iaddend.
.Iadd.92. The system of claim 85, wherein the RFID device is
configured to receive a signal to silence the RFID
device..Iaddend.
.Iadd.93. The system of claim 92, wherein the RFID device is
configured to receive a wake up command and, in response, to
transition from a sleep state..Iaddend.
.Iadd.94. The system of claim 85, wherein the algorithm further
comprises transmitting a signal to silence at least one of the one
or more RFID devices in response to the detecting no collision and
before the retransmitting of the first signal..Iaddend.
.Iadd.95. The system of claim 85, wherein the replay comprises at
least a second portion of the random number that is not part of the
first portion of the random number..Iaddend.
.Iadd.96. The system of claim 95, wherein the interrogator is
further configured to use the first response to determine a random
value generated by the selected one or more devices in accordance
with the algorithm..Iaddend.
.Iadd.97. The system of claim 85, wherein the algorithm further
comprises transmitting a second signal from the interrogator in
response to detecting a collision in the first response, the second
signal comprising a second set of bits and requesting a response
from at least one of the one or more RFID devices in the field
selected in accordance with at least the second set of bits,
wherein the second set of bits includes the first set of bits plus
at least one additional bit..Iaddend.
.Iadd.98. The system of claim 97, wherein the interrogator is
configured to generate, as part of the algorithm, the second set of
bits including the first set of bits plus at least two additional
bits..Iaddend.
.Iadd.99. The system of claim 85, wherein the RFID device is
configured to communicate a random value during a first time slot
randomly selected from a first number of time slots..Iaddend.
.Iadd.100. The system of claim 99, wherein the transmitter is
configured to communicate by modulating an RF field provided by a
remote device..Iaddend.
.Iadd.101. The system of claim 100, wherein the random value
identifies the device to the remote device..Iaddend.
.Iadd.102. The system of claim 101, wherein the RFID device is
further configured to communicate the random value to the remote
device during a second time slot randomly selected from a second
number of time slots, wherein the first number of time slots is
different from the second number of time slots and is indicated by
the remote device..Iaddend.
.Iadd.103. The system of claim 102, wherein the algorithm further
comprises transmitting a second signal from the interrogator in
response to detecting a collision in the first response, the second
signal comprising a second set of bits and requesting a response
from at least one of the one or more RFID devices in the field
selected in accordance with at least the second set of bits,
wherein, in accordance with the algorithm, the second set of bits
include at least two bits in addition to the first set of
bits..Iaddend.
.Iadd.104. An apparatus for wirelessly reading radio frequency
identification (RFID) devices, comprising: a transmitter to
transmit a command along with a first portion of a set of random
numbers to request a response from at least one RFID device that
has generated a random number in the set; an antenna to provide an
RF field to be modulated by the device; a receiver to receive the
response; and processing circuitry to perform collision detection,
to determine the random number using the response, and to cause the
transmitter to retransmit the command along with at least the first
portion of the set of random numbers responsive to detecting no
collision in the response..Iaddend.
.Iadd.105. The apparatus of claim 104, wherein the transmitter is
configured to transmit the command along with an indication of the
number of bits on the first portion..Iaddend.
.Iadd.106. The apparatus of claim 105, wherein the transmitter is
configured to communicate with the RFID device at one of a
plurality of bit rates determined by the apparatus..Iaddend.
.Iadd.107. The apparatus of claim 104, wherein the processing
circuitry is configured to cause the transmitter to retransmit the
command along with no more than the first portion of the set of
random numbers responsive to the detecting..Iaddend.
.Iadd.108. The apparatus of claim 104, wherein the processing
circuitry is configured to cause the transmitter to transmit a
signal addressed to the RFID device responsive to receiving the
response without collision..Iaddend.
.Iadd.109. The apparatus of claim 108, wherein the signal is
configured to silence the RFID device..Iaddend.
.Iadd.110. The apparatus of claim 109, wherein the processing
circuitry is configured to cause the transmitter to transmit the
signal to silence the RFID device before causing the transmitter to
retransmit the command..Iaddend.
.Iadd.111. The apparatus of claim 104, wherein the transmitter is
configured to transmit a wake up command to transition the RFID
device from a sleep state..Iaddend.
.Iadd.112. The apparatus of claim 104, wherein the response
comprises at least a second portion of the random number that is
not part of the first portion..Iaddend.
.Iadd.113. The apparatus of claim 112, wherein the processing
circuitry is configured to determine a unique identification code
stored in the RFID device in addition to the random
number..Iaddend.
.Iadd.114. The apparatus of claim 104, wherein the processing
circuitry is configured to specify a second portion of the set of
random numbers in response to detecting a collision in the
response, the second portion being a subset of the first
portion..Iaddend.
.Iadd.115. The apparatus of claim 114, wherein the processing
circuitry is further configured to enable the second portion to be
less than half of the first portion..Iaddend.
.Iadd.116. The apparatus of claim 115, wherein the receiver is to
receive a reply from one or more RFID devices in one of a number of
time slots indicated by the apparatus to the one or more RFID
devices..Iaddend.
.Iadd.117. The apparatus of claim 116, wherein the reply comprises
a random value generated by the one or more RFID
devices..Iaddend.
.Iadd.118. The apparatus of claim 104, wherein the processing
circuitry if further configured to cause the transmitter to
transmit a signal to indicate a number of time slots in which one
or more RFID devices responds to the apparatus with a
reply..Iaddend.
.Iadd.119. The apparatus of claim 118, wherein the reply comprises
a random value generated by the one or more RFID
devices..Iaddend.
.Iadd.120. The apparatus of claim 119, wherein the one or more RFID
devices comprises the RFID device and the random value is equal to
the random number..Iaddend.
.Iadd.121. The apparatus of claim 104, wherein the random number
identifies the device to the apparatus..Iaddend.
.Iadd.122. A radio frequency identification (RFID) reader,
comprising: a transmitter to transmit at least a first portion of
an identifier along with an indication of a first number of bits in
the first portion, and to request a first response from an RFID
device that has generated a first portion of a random number equal
to the first portion of the identifier; a receiver to receive the
first response from the device; and a processing circuit coupled to
the transmitter and receiver to implement an algorithm to detect at
least one from among potentially multiple RFID devices, wherein in
accordance with the algorithm the processing circuit is to perform
collision detection on the first response and, in response to
detecting no collision, to retransmit, via the transmitter, the at
least first portion of the identifier and to request a second
response thereto..Iaddend.
.Iadd.123. The reader of claim 122, wherein the processing circuit
is configured to determine the random number using the first
response..Iaddend.
.Iadd.124. The reader of claim 123, wherein the transmitter is
configured to provide an RF field to be modulated by the RFID
device to communicate the first response..Iaddend.
.Iadd.125. The reader of claim 122, wherein in accordance with the
algorithm the processing circuit is to retransmit no more than the
first portion of the identifier..Iaddend.
.Iadd.126. The reader of claim 122, wherein the transmitter is
configured to communicate at a first bit rate during a first period
of time, and at a second bit rate during a second period of
time..Iaddend.
.Iadd.127. The reader of claim 122, wherein the reader is
configured to operate in a first communication mode during a first
period of time and in a second communication mode during a second
period of time, wherein in accordance with the first communication
mode the receiver is configured to receive a remotely generated and
remotely modulated RF field and in accordance with the second
communication mode the receiver is configured to receive an RF
field locally generated by the transmitter and remotely
modulated..Iaddend.
.Iadd.128. The reader of claim 122, wherein the transmitter is
configured to transmit a signal to silence the RFID device and to
transmit a wake up command to transition the RFID device from a
sleep state..Iaddend.
.Iadd.129. The reader of claim 122, wherein in accordance with the
algorithm the processing circuit is to transmit, via the
transmitter, a signal to silence the RFID device in response to the
detecting no collision and before retransmitting the first
portion..Iaddend.
.Iadd.130. The reader of claim 122, wherein in accordance with the
algorithm the processing circuit is to transmit a second portion of
the identifier along with an indication of a second number of bits
in the second portion in response to detecting a collision on the
first response, wherein the second portion includes the first
portion..Iaddend.
.Iadd.131. The reader of claim 130, wherein in accordance with the
algorithm the second number of bits is greater than the first
number of bits by at least two bits..Iaddend.
.Iadd.132. The reader of claim 131, wherein the receiver is to
receive the first response comprising at least a second portion of
the random number that is not part of the first portion of the
random number..Iaddend.
.Iadd.133. The reader of claim 122, wherein the transmitter is
configured to transmit an indication of a first number of time
slots from which one or more RFID devices are to randomly select a
first time slot in which to communicate a random value identifier
to the reader..Iaddend.
.Iadd.134. The reader of claim 133, wherein the transmitter is
further configured to transmit an indication of a second number of
time slots, different from the first number of time slots,
responsive to collision detection by the processing
circuit..Iaddend.
.Iadd.135. The reader of claim 134, wherein the processing circuit
is to transmit a second portion of the identifier along with an
indication of a second number of bits in the second portion in
response to detecting a collision on the first response, wherein
the second portion includes the first portion and the processing
circuit supports the second number of bits being greater than the
first number of bits by at least two bits..Iaddend.
.Iadd.136. A system, comprising: an RFID target device to receive a
portion of an identifier, to compare the portion of the identifier
to a portion of a random value generated by the target device, and
to communicate a reply value if the portion of the identifier is
equal to the portion of the random value; and an RFID initiating
device to initiate communication with one or more RFID target
devices, the initiating device to transmit a first request
including a first command and first information, to receive a first
response to the first request from each of one or more RFID target
devices that has generated a respective random number that is
included in a first subgroup of one or more of a group of possible
random numbers indicated by the first information, to perform
collision detection on the first response, and to transmit a second
request including a retransmission of at least the first command
and the first information responsive to detecting no
collision..Iaddend.
.Iadd.137. The system of claim 136, wherein the target and
initiating devices are to implement a time slot method in
accordance with a protocol with which the target and initiating
devices are compliant..Iaddend.
.Iadd.138. The system of claim 137, wherein the target device is to
modulate an RF field provided by a remote device to communicate the
reply..Iaddend.
.Iadd.139. The system of claim 138, wherein the system is to
operate in a selectable one of a first communication mode and a
second communication mode in accordance with the protocol, wherein
in accordance with the first communication mode the target device
is to communicate by modulating a remotely generated RF field and
in accordance with the second communication mode the target device
is to generate an RF field..Iaddend.
.Iadd.140. The system of claim 139, wherein the target and
initiating devices are to communicate at a selectable one of a
plurality of bit rates in accordance with the
protocol..Iaddend.
.Iadd.141. The system of claim 140, wherein the target device is to
transition from a sleep state upon receiving a wake up
command..Iaddend.
.Iadd.142. The system of claim 136, further comprising memory
storing a unique identification code, separate from the random
value and random number, to be transmitted by the
system..Iaddend.
.Iadd.143. The system of claim 136, wherein the target device is to
modulate an RF field provided by a remote device to communicate the
reply..Iaddend.
.Iadd.144. The system of claim 136, wherein the initiating device
is to transmit a signal to silence the one or more target
devices..Iaddend.
.Iadd.145. The system of claim 144, wherein the initiating device
is to transmit the signal in response to the detecting no collision
before transmitting the second request..Iaddend.
.Iadd.146. The system of claim 136, wherein the random value
comprises the reply value..Iaddend.
.Iadd.147. The system of claim 146, wherein the random number
comprises the first response..Iaddend.
.Iadd.148. The system of claim 136, wherein the target device is to
implement a slotted aloha algorithm in which the target device is
to communicate an identifier, randomly generated by the target
device, in a randomly selected time slot of a number of time slots
indicated to the target device..Iaddend.
.Iadd.149. The system of claim 148, further comprising memory
storing a unique identification code, separate from the random
value, to be transmitted by the target device..Iaddend.
.Iadd.150. The system of claim 149, wherein the target device is to
modulate a remotely generated RF field to communicate the
reply..Iaddend.
.Iadd.151. The system of claim 136, wherein the initiating device
is to transmit a third request, including a retransmission of at
least the first command and the first information responsive to
detecting a collision in the first response, wherein the third
request indicates a second subgroup that is a subset of the first
subgroup..Iaddend.
.Iadd.152. The system of claim 151, wherein the second subgroup is
less than half of the first subgroup in accordance with a protocol
with which the target and initiating devices are
compliant..Iaddend.
.Iadd.153. The system of claim 152, wherein the target device is to
implement a slotted aloha algorithm in which the target device is
to communicate an identifier, randomly generated by the target
device, in a randomly selected time slot of a number of time
slots..Iaddend.
.Iadd.154. The system of claim 153, wherein the initiating device
is to transmit a signal to indicate a number of time slots in which
the initiating device is to receive a response..Iaddend.
.Iadd.155. The system of claim 136, wherein the one or more target
devices comprises the target device..Iaddend.
.Iadd.156. The system of claim 136, wherein the first request
includes a mask to identify a common portion of random numbers
included in the first subgroup..Iaddend.
.Iadd.157. A radio frequency identification (RFID) device,
comprising: a random number generator to generate a first random
number identifier; a receiver coupled to an antenna to receive a
transmission of a first set of bits from a reader in accordance
with an algorithm to enable the reader to determine the first
identifier; processing circuitry to compare the first set of bits
to a first portion of the first identifier; and a modulating
circuit to modulate an RF field produced by the reader to
communicate a second set of bits to the reader if the first set of
bits is equal to the first portion of the first identifier, wherein
the first identifier comprises the second set of bits, and wherein
in accordance with the algorithm the receiver is to further receive
a retransmission of at least the first set of bits from the reader
if the reader receives the second set of bits without
collision..Iaddend.
.Iadd.158. The device of claim 157, wherein the second set of bits
comprises the first set of bits..Iaddend.
.Iadd.159. The device of claim 157, wherein the random number
generator is to generate a second random number identifier and a
random value, wherein the random value is to be used to select a
slot in which to communicate the second identifier in accordance
with a time slot method..Iaddend.
.Iadd.160. The device of claim 157, wherein the modulating circuit
is to operate in an alternate communication mode in which the
modulating circuit is to modulate an RF field produced by the
device itself..Iaddend.
.Iadd.161. The device of claim 157, wherein the modulating circuit
is to communicate at one of a plurality of selectable bit
rates..Iaddend.
.Iadd.162. The device of claim 161, wherein the receiver is receive
a wake up command from the reader to transition the device from a
sleep state..Iaddend.
.Iadd.163. The device of claim 157, wherein the processing
circuitry is to implement a slotted aloha algorithm..Iaddend.
.Iadd.164. The device of claim 163, further comprising memory
storing a unique identification code, separate from the first
identifier, to be wirelessly communicated..Iaddend.
.Iadd.165. The device of claim 157, further comprising memory
storing a unique identification code, separate from the first
identifier, to be wirelessly communicated to a reader..Iaddend.
.Iadd.166. The device of claim 157, wherein in accordance with the
algorithm the receiver is to receive a signal from the reader
addressed to the device responsive to the reader receiving the
second set of bits without collision..Iaddend.
.Iadd.167. The device of claim 166, wherein the signal is to
silence the device..Iaddend.
.Iadd.168. The device of claim 167, wherein in accordance with the
algorithm the signal is to be received by the receiver before the
retransmission of the at least first set of bits..Iaddend.
.Iadd.169. The device of claim 157, wherein the receiver is to
receive a retransmission of the first set of bits along with
additional bits from the reader for comparison to at least a second
portion of the first identifier in accordance with the algorithm if
the reader detects a collision upon receiving the second set of
bits, wherein in accordance with the algorithm, the additional bits
are at least two bits..Iaddend.
.Iadd.170. The device of claim 169, wherein the modulating circuit
is to communicate a second random number identifier in a randomly
selected time slot of a number of time slots..Iaddend.
.Iadd.171. The device of claim 157, wherein the receiver is to
receive an indication of a first number of time slots from which
the device is to randomly select a first time slot in which to
communicate a second random number identifier and to receive an
indication of a second number of time slots, different from the
first number of time slots..Iaddend.
Description
TECHNICAL FIELD
This invention relates to communications protocols and to digital
data communications. Still more particularly, the invention relates
to data communications protocols in mediums such as radio
communication or the like. The invention also relates to radio
frequency identification devices for inventory control, object
monitoring, determining the existence, location or movement of
objects, or for remote automated payment.
BACKGROUND OF THE INVENTION
Communications protocols are used in various applications. For
example, communications protocols can be used in electronic
identification 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 flow of objects. Additionally, there is a continuing goal to
interrogate the location of objects in an inexpensive and
streamlined manner. One way of tracking objects is with an
electronic identification system.
One presently available electronic identification system utilizes a
magnetic coupling system. In some cases, an identification device
may be provided with a unique identification code in order to
distinguish between a number of different devices. Typically, the
devices are entirely passive (have no power supply), which results
in a small and portable package. However, such identification
systems are only capable of operation over a relatively short
range, limited by the size of a magnetic field used to supply power
to the devices and to communication with the devices.
Another wireless electronic identification system utilizes a large,
board level, active transponder device affixed to an object to be
monitored which receives a signal from an interrogator. The device
receives the signal, then generates and transmits a responsive
signal. The interrogation signal and the responsive signal are
typically radio-frequency (RF) signals produced by an RF
transmitter circuit. Because active devices have their own power
sources, and do not need to be in close proximity to an
interrogator or reader to receive power via magnetic coupling.
Therefore, active transponder devices tend to be more suitable for
applications requiring tracking of a tagged device that may not be
in close proximity to an interrogator. For example, active
transponder devices tend to be more suitable for inventory control
or tracking.
Electronic identification systems can also be used for remote
payment. For example, when a radio frequency identification device
passes an interrogator at a toll booth, the toll booth can
determine the identity of the radio frequency identification
device, and thus of the owner of the device, and debit an account
held by the owner for payment of toll or can receive a credit card
number against which the toll can be charged. Similarly, remote
payment is possible for a variety of other goods or services.
A communication system typically includes two transponders: a
commander station or interrogator, and a responder station or
transponder device which replies to the interrogator.
If the interrogator has prior knowledge of the identification
number of a device which the interrogator is looking for, it can
specify that a response is requested only from the device with that
identification number. Sometimes, such information is not
available. For example, there are occasions where the interrogator
is attempting to determine which of multiple devices are within
communication range.
When the interrogator sends a message to a transponder device
requesting a reply, there is a possibility that multiple
transponder devices will attempt to respond simultaneously, causing
a collision, and thus causing an erroneous message to be received
by the interrogator. For example, if the interrogator sends out a
command requesting that all devices within a communications range
identify themselves, and gets a large number of simultaneous
replies, the interrogator may not be able to interpret any of these
replies. Thus, arbitration schemes are employed to permit
communications free of collisions.
In one arbitration scheme or system, described in commonly assigned
U.S. Pat. Nos. 5,627,544; 5,583,850; 5,500,650; and 5,365,551, all
to Snodgrass et al. and all incorporated herein by reference, the
interrogator sends a command causing each device of a potentially
large number of responding devices to select a random number from a
known range and use it as that device's arbitration number. By
transmitting requests for identification to various subsets of the
full range of arbitration numbers, and checking for an error-free
response, the interrogator determines the arbitration number of
every responder station capable of communicating at the same time.
Therefore, the interrogator is able to conduct subsequent
uninterrupted communication with devices, one at a time, by
addressing only one device.
Another arbitration scheme is referred to as the Aloha or slotted
Aloha scheme. This scheme is discussed in various references
relating to communications, such as Digital Communications:
Fundamentals and Application, Bernard Sklar, published January 1988
by Prentice Hall. In this type 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 field
(i.e. in communications range, capable of responding) then there
must be many available slots or many collisions will occur. Having
many available slots slows down replies. If the magnitude of the
number of devices in a field is unknown, then many slots are
needed. This results in the system slowing down significantly
because the reply time equals the number of slots multiplied by the
time period required for one reply.
An electronic identification system which can be used as a radio
frequency identification device, arbitration schemes, and various
applications for such devices are described in detail in commonly
assigned U.S. .[.patent application Ser. No. 08/705,043, filed Aug.
29, 1996, and.]. .Iadd.Pat. No. 6,130,602, which is
.Iaddend.incorporated herein by reference.
SUMMARY OF THE INVENTION
The invention provides a wireless identification device configured
to provide a signal to identify the device in response to an
interrogation signal.
.Iadd.In one aspect, a method includes: transmitting by an
interrogator a first signal including a first set of bits, the
interrogator to identify a first subgroup of a group of possible
random numbers; communicating by each of one or more RFID devices a
first response if the one or more RFID devices has generated a
random number that is included in the first subgroup; receiving by
the interrogator one or more received responses from respective
ones of the one or more RFID devices; and responsive to receiving
one of the one or more received responses without a collision,
retransmitting by the interrogator at least the first
signal..Iaddend.
One aspect of the invention provides a method of establishing
wireless communications between an interrogator and individual ones
of multiple wireless identification devices. The method comprises
utilizing a tree search method to attempt to identify individual
ones of the multiple wireless identification devices so as to be
able to perform communications, without collision, between the
interrogator and individual ones of the multiple wireless
identification devices. A search tree is defined for the tree
search method. The tree has multiple nodes respectively
representing sub-groups of the multiple wireless identification
devices. The interrogator transmits a command at a node, requesting
that devices within the subgroup represented by the node respond.
The interrogator determines if a collision occurs in response to
the command and, if not, repeats the command at the same node.
Another aspect of the invention provides a communications system
comprising an interrogator, and a plurality of wireless
identification devices configured to communicate with the
interrogator in a wireless fashion. The interrogator is configured
to employ tree searching to attempt to identify individual ones of
the multiple wireless identification devices, so as to be able to
perform communications without collision, between the interrogator
and individual ones of the multiple wireless identification
devices. The interrogator is configured to follow a search tree,
the tree having multiple nodes respectively representing subgroups
of the multiple wireless identification devices. The interrogator
is configured to transmit a command at a node, requesting that
devices within the subgroup represented by the node respond. The
interrogator is further configured to determine if a collision
occurs in response to the command and, if not, to repeat the
command at the same node.
One aspect of the invention provides a radio frequency
identification device comprising an integrated circuit including a
receiver, a transmitter, and a microprocessor. In one embodiment,
the integrated circuit is a monolithic single die single metal
layer integrated circuit including the receiver, the transmitter,
and the microprocessor. The device of this embodiment includes an
active transponder, instead of a transponder which relies on
magnetic coupling for power and therefore has a much greater
range.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention are described below with
reference to the following accompanying drawings.
FIG. 1 is a high level circuit schematic showing an interrogator
and a radio frequency identification device embodying the
invention.
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 for
establishing communication with a radio frequency identification
device in a field of a plurality of such devices.
FIG. 5 is a diagram illustrating a modified tree splitting sort
method for establishing communication with a radio frequency
identification device in a field of a plurality of such
devices.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
This disclosure of the invention is submitted in furtherance of the
constitutional purposes of the U.S. Patent Laws "to promote the
progress of science and useful arts" (Article 1, Section 8).
FIG. 1 illustrates a wireless identification device 12 in
accordance with one embodiment of the invention. In the illustrated
embodiment, the wireless identification 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 wireless or radio frequency transmission and
reception by the circuitry 16. In the illustrated embodiment, the
RFID circuitry is defined by an integrated circuit as described in
the above-incorporated .[.patent application Ser. No. 08/705,043,
filed Aug. 29, 1996.]. .Iadd.U.S. Pat. No. 6,130,602.Iaddend..
Other 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 18
comprises a battery.
The device 12 transmits and receives radio frequency communications
to and from an interrogator 26. An exemplary interrogator is
described in commonly assigned U.S. .[.patent application Ser. No.
08/907,689, filed Aug. 8, 1997.]. .Iadd.Pat. No. 6,289,209
.Iaddend.and incorporated herein by reference. Preferably, the
interrogator 26 includes an antenna 28, as well as dedicated
transmitting and receiving circuitry, similar to that implemented
on the integrated circuit 16.
Generally, the interrogator 26 transmits an interrogation signal or
command 27 via the antenna 28. The device 12 receives the incoming
interrogation signal via its antenna 14. Upon receiving the signal
27, the device 12 responds by generating and transmitting a
responsive signal or reply 29. The responsive signal 29 typically
includes information that uniquely identifies, or labels the
particular device 12 that is transmitting, so as to identify any
object or person with which the device 12 is associated. Although
only one device 12 is shown in FIG. 1, typically there will be
multiple devices 12 that correspond with the interrogator 16, and
the particular devices 12 that are in communication with the
interrogator 26 will typically change 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
field of an interrogator 26 (i.e., within communications range of
an interrogator 26).
The radio frequency data communication device 12 can be included in
any appropriate housing or packaging. Various methods of
manufacturing housings are described in commonly assigned U.S.
.[.patent application Ser. No. 08/800,037, filed Feb. 13, 1997,
and.]. .Iadd.Pat. No. 5,988,510 which is .Iaddend.incorporated
herein by reference.
FIG. 2 shows but one embodiment in the form of a card or 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 identification
features such as interrogators, text, information found on
identification or credit cards, etc.
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 define a tag which
can be supported by an object (e.g., hung from an object, affixed
to an object, etc.). Although two particular types of housings have
been disclosed, other forms of housings are employed in alternative
embodiments.
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 particular
application. In one embodiment, the battery 18 is a thin profile
button-type cell forming a small, thin energy cell more commonly
utilized in watches and small electronic devices requiring a thin
profile. 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 connected pair of button type cells. In other alternative
embodiments, other types of suitable power source are employed.
The circuitry 16 further includes a backscatter transmitter and is
configured to provide a responsive signal to the interrogator 26 by
radio frequency. More particularly, the circuitry 16 includes a
transmitter, a receiver, and memory such as is described in U.S.
.[.patent application Ser. No. 08/705,043.]. .Iadd.Pat. No.
6,130,602.Iaddend..
Radio frequency identification has emerged as a viable and
affordable alternative to tagging or labeling small to 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 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 may not be able
to interpret any of these replies. Therefore, arbitration schemes
are provided.
If the interrogator 26 has prior knowledge of the identification
number of a device 12 which the interrogator 26 is looking for, it
can specify that a response is requested only from the device 12
with that identification number. To target a command at a specific
device 12, (i.e., to initiate point-on-point communication), the
interrogator 26 must send a number identifying a specific device 12
along with the command. At start-up, or in a new or changing
environment, these identification numbers are not known by the
interrogator 26. Therefore, the interrogator 26 must identify all
devices 12 in the field (within communication range) such as by
determining the identification numbers of the devices 12 in the
field. 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-access
communication system. The distance between the interrogator 26 and
devices 12 within the field 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 potential for a large
number of transmitting devices 12 and there is a need for the
interrogator 26 to work in a changing environment, where different
devices 12 are swapped in and 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 resolution (i.e., for dealing with collisions between
devices 12 attempting to respond to the interrogator 26 at the same
time).
RFID systems have some characteristics that are different from
other communications systems. For example, one characteristic of
the illustrated RFID systems is that the devices 12 never
communicate without being prompted by the interrogator 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 identified, 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 restrictions on size, power, and cost. The
lifetime of a device 12 can often be measured in terms of number of
transmission 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 consumed by the devices 12 during the process.
This is in contrast to the measures of throughput and packet delay
in other types of multiaccess systems.
FIG. 4 illustrates one arbitration scheme that can be employed for
communication between the interrogator and 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. By transmitting requests for identification to
various subsets of the full range of arbitration numbers, and
checking for an error-free response, the interrogator 26 determines
the arbitration number of every responder station capable of
communicating at the same time. Therefore, the interrogator 26 is
able to conduct subsequent unterrupted communication with devices
12, one at a time, by addressing only one device 12.
Three variables are used: an arbitration value (AVALUE), an
arbitration mask (AMASK), and a random value ID (RV). The
interrogator sends an Identify command (IdentifyCmnd) causing each
device of a potentially large number of responding devices to
select a random number from a known range and use it as that
device's arbitration number. The interrogator sends an arbitration
value (AVALUE) and an arbitration mask (AMASK) to a set of devices
12. The receiving devices 12 evaluate the following 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 evaluates 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 employed depending, for example, on the
number of devices 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
field, one with a random value RV) of 1100 (binary), and another
with a random value (RV) of 1010 (binary). The interrogator is
tying 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
respective devices 12 selected. If the equation evaluates to "1"
(TRUE), then the device 12 will reply. If the equation evaluates to
"0" (FALSE), then the device 12 will not reply. In the first level
of the illustrated tree, AMASK is 0000 and anything bitwise ANDed
with all zeros results in all zeros, so both the devices 12 in the
field respond, and there is a collision.
Next, the interrogator sets AMASK to 0001 and AVALUE to 0000 and
transmits an Identify command. Both devices 12 in the field have a
zero for their least significant bit, and (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
equation is true for both devices 12 in the field, both devices 12
in the field respond, and there is another collision.
Recursively, the interrogator next sets AMASK to 0011 with AVALUE
still at 0000 and transmits an Identify command. (AMASK &
AVALUE)==(AMASK & RV) is evaluated 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 (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
evaluated as (0011 & 0000)=0000. The right side is evaluated as
(0011 & 1010)=0010. The left side does not equal the right
side, so the equation is false for the device 12 with the random
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 identification number) for the device 12 that
does respond.
De-recursion takes place, and the devices 12 to the right for the
same AMASK level are accessed when AVALUE is set at 0010, and AMASK
is set to 0011.
The device 12 with the random value of 1010 receives a 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 with the random value of 1010. Because there
are no other devices 12 in the subtree, a good reply is returned by
the device 12 with the random value of 1010. There is no collision,
and the interrogator 26 can determine the identity (e.g., an
identification 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 statement after the
function call.
For instance, consider a function that has four statements
(numbered 1,2,3,4) in it, and the second statement is a recursive
call. Assume that the fourth statement is a return statement. The
first time through the loop (iteration 1) the function executes the
statement 2 and (because it is a recursive call) calls itself
causing iteration 2 to occur. When iteration 2 gets to statement 2,
it calls itself making iteration 3. During execution in iteration 3
of statement 1, assume that the function does a return. The
information that was saved on the stack from iteration 2 is loaded
and the function resumes execution at statement 3 (in iteration 2),
followed by the execution of statement 4 which is also a return
statement. Since there are no more statements in the function, the
function de-recurses to iteration 1. Iteration 1, had 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 implement
operation of the method shown in FIG. 4 and described above.
TABLE-US-00001 Arbitrate(AMASK, AVALUE) {
collision=IdentifyCmnd(AMASK, AVALUE) if (collision) then { /*
recursive call for left side */ Arbitrate ((AMASK<<1)+1,
AVALUE) /* recursive call for right side */ Arbitrate
((AMASK<<1)+1, AVALUE+(AMASK+1)) } /* endif */ }/* return
*/
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 first
recursive call, AMASK=(AMASK<<1)+1. So for the first
recursive call, the value of AMASK is 0000+0001=0001. For the
second call, AMASK=(0001<<)+1=0010+1=0011. For the third
recursive call, AMASK=(0011<<1)+1=0110+1=0111.
The routine generates values for AMASK and AVALUE to be used by the
interrogator in an Identify command "IdentifyCmnd." 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 following assuming collisions take place all the way down to
the bottom of the tree.
TABLE-US-00002 AVALUE AMASK 0000 0000 0000 0001 0000 0011 0000 0111
0000 1111* 1000 1111* 0100 0111 0100 1111* 1100 1111*
This sequence of AMASK, AVALUE binary numbers assumes that there
are collisions all the way down to the bottom of the tree, at which
point the Identify command sent by the interrogator is finally
successful so that no collision occurs. Rows in the table for which
the interrogator is successful in receiving a reply without
collision are marked with the symbol "*". Note that if the Identify
command was successful at, for example, the third line in the table
then the interrogator would stop going down that branch of the tree
and start down another, so the sequence would be as shown in the
following table.
TABLE-US-00003 AVALUE AMASK 0000 0000 0000 0001 0000 0011* 0010
0011 . . . . . .
This method is referred to as a splitting method. It works by
splitting groups of colliding devices 12 into subsets that are
resolved in turn. The splitting method can also be viewed as a type
of tree search. Each split moves the method one level deeper in the
tree. Either depth-first or breadth-first traversals of the tree
can be employed. Depth first traversals are performed by using
recursion, as is employed in the code listed above. Breadth-first
traversals are accomplished by using a queue instead of
recursion.
Either depth-first or breadth-first traversals of the tree can be
employed. Depth first traversals are performed by using recursion,
as is employed in the code listed above. Breadth-first traversals
are accomplished by using a queue instead of recursion. The
following is an example of code for performing a breadth-first
traversal.
TABLE-US-00004 Arbitrate(AMASK, AVALUE) { (AMASK,AVALTE)=dequeue( )
collision=IdentifyCmnd(AMASK, AVALUE) if (collision) then { TEMP =
AMASK+1 NEW_AMASK = (AMASK<<1)+1 enqueue(NEW_AMASK, AVALUE)
enqueue(NEW_AMASK, AVALUE+TEMP) } /* endif */ endwhile }/* return
*/
The symbol "!=" means not equal to. AVALUE and AMASK would have
values such as those indicated in the following table for such
code.
TABLE-US-00005 AVALUE AMASK 0000 0000 0000 0001 0001 0001 0000 0011
0010 0011 0001 0011 0011 0011 0000 0111 0100 0111 . . . . . .
Rows in the table for which the interrogator is successful in
receiving a reply without collision are marked with the symbol
"*".
FIG. 5 illustrates an embodiment wherein the interrogator 26
retries on the same node that yielded a good reply. The search tree
has a plurality of nodes 51, 52, 53, 54 etc. at respective levels
32, 34, 36, 38, or 40. The size of subgroups of random values
decrease in size by half with each node descended.
The interrogator performs a tree search, either depth-first or
breadth-first in a manner such as that described in connection with
FIG. 4, except that if the interrogator determines that no
collision occurred in response to an Identify command, the
interrogator repeats the command at the same node. This takes
advantage of an inherent capability of the devices, particularly if
the devices use backscatter communication, called self-arbitration.
Arbitration times can be reduced, and battery life for the devices
can be increased.
When a single reply is read by the interrogator, for example, in
node 52, the method described in connection with FIG. 4 would
involve proceeding to node 53 and then sending another Identify
command. Because a device 12 in a field of devices 12 can override
weaker devices, this embodiment is modified such that the
interrogator retries on the same node 52 after silencing the device
12 that gave the good reply. This, after receiving a good reply
from node 52, the interrogator remains on node 52 and reissues the
Identify command after silencing the device that first responded on
node 52. Repeating the Identify command on the same node often
yields other good replies, thus taking advantage of the devices
natural ability to self-arbitrate.
AVALUE and AMASK would have values such as the following for a
depth-first traversal in a situation similar to the one described
above in connection with FIG. 4.
TABLE-US-00006 AVALUE AMASK 0000 0000 0000 0001 0000 0011 0000
1111* 0000 1111* 1000 1111* 1000 1111* 0100 0111 0100 1111* 0100
1111* 1100 1111* 1100 1111*
Rows in the table for which the interrogator is successful in
receiving a reply without collision are marked with the symbol
"*".
In operation, the interrogator transmits a command at a node,
requesting that devices within the subgroup represented by the node
respond. The interrogator determines if a collision occurs in
response to the command and, if not, repeats the command at the
same node.
In one alternative embodiment, the upper bound of the number of
devices in the field (the maximum possible number of devices that
could communicate 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. The level of the
search tree on which to start the tree search is selected based on
the determined maximum possible number of wireless identification
devices that could communicate with the interrogator. The tree
search is started at a level determined by taking the base two
logarithm of the determined maximum possible number. More
particularly, the tree search is started at a level determined by
taking the base two logarithm of the power of two nearest the
determined maximum possible number of devices 12. The level of the
tree containing all subgroups of random values is considered level
zero, and lower levels are numbered 1, 2, 3, 4, etc.
consecutively.
Methods involving determining the upper bound on a set of devices
and starting at a level in the tree depending on the determined
upper bound are described in a commonly assigned .[.patent
application (attorney docket MI40-118).]. .Iadd.U.S. Pat. No.
6,118,789, .Iaddend.naming Clifton W. Wood, Jr. as an inventor,
titled "Method of Addressing Messages and Communications System,"
.[.filed concurrently herewith, and.]. .Iadd.which is
.Iaddend.incorporated herein by reference.
In one alternative embodiment, a method involving starting at a
level in the tree depending on a determined upper bound (such as
the method described in the commonly assigned patent application
mentioned above) is combined with a method comprising re-trying on
the same node that gave a good reply, such as the method shown and
described in connection with FIG. 5.
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 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 field to
transmit their identification numbers in the next time slot. If the
response is garbled, the interrogator informs the devices 12 that a
collision has occurred, and the slotted Aloha scheme is put into
action. This means that each device 12 in the field 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 identification number with a certain
probability.
The Aloha method is based on a system operated by the 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 computers 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 different users will sometimes overlap in time (collide),
causing reception errors in the data in each of the contending
messages. The errors are detected by the receiver, and the receiver
sends a negative acknowledgment to the users. 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 receive either an
acknowledgment or a negative acknowledgment within a certain amount
of time, the user "times out" and retransmits the message.
There is a scheme known as slotted Aloha which improves the Aloha
scheme by requiring a small amount of coordination 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 are constant. Messages are required to
be sent in a slot time between synchronization pulses, and can be
started only at the beginning of a time slot. This reduces the rate
of collisions because only messages transmitted in the same slot
can interfere with one another. The retransmission mode of the pure
11 Aloha scheme is modified for slotted Aloha such that if 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 (attorney docket MI40-089).]. .Iadd.U.S. Pat. No.
6,275,476, .Iaddend.naming Clifton W. Wood, Jr. as an inventor,
titled "Method of Addressing Messages and Communications System,"
.[.filed concurrently herewith, and.]. .Iadd.which is
.Iaddend.incorporated herein by reference.
In one alternative embodiment, an Aloha method (such as the method
described in the commonly assigned patent application mentioned
above) is combined with a method involving re-trying on the same
node that gave a good reply, such as the method shown and described
in connection with FIG. 5.
In another embodiment, levels of the search tree are skipped.
Skipping levels in the tree, after a collision caused by multiple
devices 12 responding, reduces the number of subsequent collisions
without adding significantly to the number of no replies. In
real-time systems, it is desirable to have quick arbitration
sessions on a set of devices 12 whose unique identification 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, thus saving
battery power in the devices 12. Skipping deeper (skipping more
than one level) further reduces the number of collisions. The more
levels that are skipped, the greater the 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 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 significantly increasing the number of
queries.
Level skipping methods are described in a commonly assigned
.[.patent application (attorney docket MI40-117).]. .Iadd.U.S. Pat.
No. 6,072,801, .Iaddend.naming Clifton W. Wood, Jr. and Don Hush as
inventors, titled "Method of Addressing Messages, Method of
Establishing Wireless Communications, and Communications System,"
.[.filed concurrently herewith, and.]. .Iadd.which is
.Iaddend.incorporated herein by reference.
In one alternative embodiment, a level skipping method is combined
with a method involving re-trying on the same node that gave a good
reply, such as the method shown and described in connection with
FIG. 5.
In yet another alternative embodiment, any two or more of the
methods described in the commonly assigned, concurrently filed,
applications mentioned above are combined.
In compliance with the statute, the invention has been described in
language more or less specific as to structural and methodical
features. It is to be understood, however, that the invention is
not limited to the specific features shown and described, since the
means herein disclosed comprise preferred forms of putting the
invention into effect. The invention is, therefore, claimed in any
of its forms or modifications within the proper scope of the
appended claims appropriately interpreted in accordance with the
doctrine of equivalents.
* * * * *
References