U.S. patent application number 09/314430 was filed with the patent office on 2002-07-04 for random interval inventory system.
Invention is credited to GORHAM, KENNETH D., GUTHRIE, WARREN E..
Application Number | 20020087436 09/314430 |
Document ID | / |
Family ID | 24680111 |
Filed Date | 2002-07-04 |
United States Patent
Application |
20020087436 |
Kind Code |
A1 |
GUTHRIE, WARREN E. ; et
al. |
July 4, 2002 |
RANDOM INTERVAL INVENTORY SYSTEM
Abstract
A method for accounting for individual ones of a plurality of
items based upon random times that occur as a function of a first
specified time interval, and a random interval inventory system
that operates in accordance with the method. The method includes a
first step of transmitting information signals based upon random
times from individual ones of a plurality of tags (5a1-5xx) to at
least one of at least one master transceiver and at least one
transceiver (4a-4n). The individual tags (5a1-5xx) are affixed to
respective individual ones of a plurality of items. The information
signals transmitted from each tag (5a1-5xx) correspond at least to
the respective item to which the tag (5a1-5xx) is affixed. The
random times occur as a function of a first specified time
interval. For a case wherein the information signals are
transmitted to the at least one remote transceiver, each at least
one remote transceiver (4a-4n) receives information signals from at
least one of the tags (4a-4n), and in response to receiving each
information signal, relays the signal to the master transceiver
(3). In response to the master transceiver (3) receiving an
information signal, a next step includes supplying the signal to an
associated confirmation device (2). Within the confirmation device
(2), in response to receiving an information signal from the master
transceiver (3), a next step includes confirming that the item
corresponding to the information signal is accounted for.
Inventors: |
GUTHRIE, WARREN E.;
(GLENELLYN, IL) ; GORHAM, KENNETH D.; (PALATINE,
IL) |
Correspondence
Address: |
TERRY J. ANDERSON, ESQ.
NORTHROP GRUMMAN CORPORATION
ONE NORTHROP AVENUE
M/S 30/110/31
HAWTHORNE
CA
90250-3277
US
|
Family ID: |
24680111 |
Appl. No.: |
09/314430 |
Filed: |
May 18, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09314430 |
May 18, 1999 |
|
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|
08667896 |
Jun 20, 1996 |
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Current U.S.
Class: |
705/28 |
Current CPC
Class: |
H04Q 9/00 20130101; G01D
4/004 20130101; G06K 19/0716 20130101; Y02B 90/20 20130101; G08C
17/02 20130101; G06K 7/10356 20130101; Y04S 20/30 20130101; G06K
17/0022 20130101; G06Q 10/087 20130101; G06K 7/10059 20130101; G06K
7/0008 20130101 |
Class at
Publication: |
705/28 |
International
Class: |
G06F 017/60 |
Claims
What is claimed is:
1. A method for accounting for individual ones of a plurality of
items, comprising the steps of: transmitting information signals at
random times from individual ones of a plurality of tags to at
least one master transceiver, the individual ones of the plurality
of tags being affixed to respective individual ones of a plurality
of items, the information signals transmitted from the individual
tags corresponding at least to the respective items to which the
tags are affixed; in response to the at least one master
transceiver receiving an information signal, supplying the
information signal to an associated confirmation device; and within
the confirmation device, in response to receiving an information
signal from the master transceiver, confirming that the item
corresponding to the information signal is accounted for.
2. A method as set forth in claim 1, wherein the random times occur
as a function of a first specified time interval.
3. A method as set forth in claim 2, wherein the random times also
occur as a function of a rate at which specified events are
detected by at least one sensor.
4. A method as set forth in claim 1, wherein the step of
transmitting is performed to transmit the information signals from
individual ones of a plurality of tags to at least one of the at
least one master transceiver and at least one remote
transceiver.
5. A method as set forth in claim 4, wherein for a case in which
the information signals are transmitted to the at least one remote
transceiver, the remote transceiver receives information signals
from at least one of the plurality of tags and, in response to
receiving each of the information signals, relays the signal to the
master transceiver.
6. A method as set forth in claim 4, wherein the remote transceiver
receives information signals from the at least one of the plurality
of tags depending upon, at least in part, a position of the remote
transceiver relative to that of the at least one of the plurality
of tags.
7. A method as set forth in claim 4, wherein whether the individual
ones of the plurality of tags transmit information signals to the
master transceiver or to the remote transceiver depends upon, at
least in part, positions of the individual ones of the plurality of
tags relative to positions of the master transceiver and the remote
transceiver.
8. A method as set forth in claim 1, wherein individual ones of the
random times occur randomly during respective individual ones of
sequentially occurring time intervals.
9. A method as set forth in claim 1, further comprising the step
of: detecting an occurrence of a specified event affecting any of
the plurality of items, wherein in response thereto, the tag
affixed to an affected one of the plurality of items transmits
information signals based upon random times occurring as a function
of a second specified time interval.
10. A method as set forth in claim 9, wherein at least a first one
and a second one of the information signals are transmitted such
that they are temporally separated as a function of the second
specified time interval, thereby indicating the detection of the
specified event occurring to the affected item; and wherein the
step of confirming further comprises the step of: determining that
the first one and the second one of the information signals have
been received and are temporally separated as a function of the
second specified time interval, and recognizing thereafter the
detection of the specified event occurring to the affected
item.
11. A method as set forth in claim 10, wherein the specified event
is at least one of movement and a predetermined temperature.
12. A method as set forth in claim 10, wherein individual ones of
the random times occur randomly during respective individual ones
of sequentially occurring time intervals.
13. A method as set forth in claim 4, further comprising the step
of: within at least one of the master transceiver, the at least one
remote transceiver, and the confirmation device, in response to
receiving an information signal originally transmitted from an
individual one of the tags, measuring a signal strength of the
received information signal to obtain a measured signal strength of
the received information signal; and based upon a difference
between the measured signal strength of the received information
signal and a reference signal strength, determining at least one of
a displacement and a location of an item to which the tag is
affixed.
14. A method as set forth in claim 1, wherein the step of
transmitting is performed using a Direct Sequence Spread Spectrum
(DSSS) technique.
15. A method as set forth in claim 5, wherein the step of
transmitting is performed using a Direct Sequence Spread Spectrum
(DSSS) technique.
16. A method as set forth in claim 1, wherein each individual one
of the plurality of tags transmits information signals
independently from other ones of the plurality of tags, thereby
limiting a probability that the master transceiver will receive
more than one information signal simultaneously.
17. A method as set forth in claim 1, wherein a probability that an
individual one of the plurality of tags will transmit an
information signal during a period of time when none of the other
ones of the plurality of tags are transmitting information signals
is represented by Ptx, where: 5 Ptx = [ 1 - ton toff = ton ] n ;and
where: ton represents a duration of an information signal
transmission; toff represents an average time interval between
chronological information signal transmissions of interest; and n
represents the number of the other ones of the plurality of
tags.
18. A method as set forth in claim 1, where a probability that an
individual one of the plurality of tags will transmit an
information signal during a period of time that none of the other
ones of the plurality of tags are transmitting information signals
is represented by Pm, where: 6 Pm = 1 - [ 1 - [ 1 - ton toff + ton
] n ] m and where: m represents a number of transmissions attempted
during the time period; ton represents a duration of an information
signal transmission; toff represents an average time interval
between chronological information signal transmissions of interest;
and n represents the number of the other ones of the plurality of
tags.
19. A method as set forth in claim 1, wherein in response to a user
operating a user-interface associated with one of the tags to
indicate a personal distress alarm (PDA), the tag transmits
information signals based upon random times occurring as a function
of a second specified time interval, thereby indicating the
personal distress alarm.
20. A method as set forth in claim 1, further comprising the steps
of: at individual ones of the plurality of tags, in response to
transmitting a first one of the information signals, switching to a
receive mode of operation for a predetermined time interval; and in
response to an expiration of the predetermined time interval,
switching to a transmit mode of operation by which a second one of
the information signals is transmitted.
21. A method as set forth in claim 20, wherein in response to the
at least one master transceiver receiving a first information
signal from any one of the plurality of tags, the master
transceiver performs the steps of: determining a frequency of the
received first information signal to obtain a measured first
information signal frequency; and transmitting a response signal to
the tag from which the first information signal was received such
that the tag receives the response signal during the predetermined
time interval, wherein the response signal is transmitted on a
frequency that is offset from the measured first information signal
frequency by a predetermined amount.
22. A method as set forth in claim 21, wherein in response to
receiving the response signal, the tag error checks the response
signal, whereafter the tag transmits a signal to the master
transceiver indicating whether or not an error has been detected in
the response signal.
23. A method for inventorying a plurality of items, individual ones
of the plurality of items having respective individual ones of a
plurality of tags affixed thereto, the individual tags transmitting
information signals at random times to at least one remote
transceiver, the information signals transmitted from the
individual tags corresponding to the respective ones of the
plurality of items to which the tags are affixed, comprising the
steps of: at the at least one remote transceiver, setting a timer
to run in response to receiving a first information signal received
from an individual one of the tags; storing information which
indicates an alarm status and which identifies the item
corresponding to the first received information signal in response
to one of: (1) the timer reaching a first predetermined time value
before a second information signal is received and (2) the timer
not reaching a second predetermined time value before the second
information signal is received; and communicating the stored
information to a master transceiver in response to the remote
transceiver receiving an interrogation command from the master
receiver.
24. A method for inventorying a plurality of items, individual ones
of the plurality of items having respective individual ones of a
plurality of tags associated therewith, the individual tags
transmitting information signals at random times in a predefined
manner to at least one remote transceiver, the information signals
transmitted from the individual tags corresponding to respective
ones of the plurality of items with which the tags are associated,
comprising the steps of: monitoring for at least one change in
status effecting individual ones of the tags indicated by the at
least one remote transceiver receiving information signals
transmitted from the individual tags in a manner other than the
predefined manner; and notifying a master transceiver of the at
least one change in status effecting the individual tags in
response to the remote transceiver receiving an interrogation
command from the master transceiver.
25. A random interval inventory system, for accounting for
individual ones of a plurality of items, comprising: at least one
master transceiver having an output, said master transceiver for
receiving information signals and for providing said information
signals to said output; a security station, having an input coupled
to said master transceiver output, said security station for
confirming that an item corresponding to an information signal
received at said input is accounted for; and a plurality of
transmit-only tags, individual ones of said plurality of
transmit-only tags being affixed to respective individual ones of a
plurality of items, said individual ones of said plurality of
transmit-only tags for transmitting information signals, based upon
first random times to said at least one master transceiver, said
information signals transmitted from said individual ones of said
plurality of transmit-only tags correspond at least to said
respective individual ones of said plurality of items to which said
transmit-only tags are affixed.
26. A random interval inventory system as set forth in claim 25,
wherein said random times occur as a function of a first specified
time interval.
27. A random interval inventory system as set forth in claim 26,
further comprising at least one sensing means, wherein said random
times also occur as a function of a rate at which specified events
are detected by said at least one sensor.
28. A random interval inventory system as set forth in claim 25,
further comprising: at least one remote transceiving means, wherein
said individual ones of said plurality of transmit-only tags
transmit said information signals to at least one of said at least
one transceiver and said at least one remote transceiving
means.
29. A random interval inventory system as set forth in claim 28,
wherein for a case in which said information signals are
transmitted to said remote transceiving means, said remote
transceiving means receives said information signals from at least
one of said plurality of transmit-only tags, and in response
thereto, relays said received information signals to said master
transceiver.
30. A random interval inventory system as set forth in claim 28,
wherein said at least one of said master transceiver and said at
least one remote transceiver comprise at least one of a Direct
Sequence Spread Spectrum (DSSS) transmitter and at a DSSS
receiver.
31. A random interval inventory system as set forth in claim 25,
wherein individual ones of said plurality of transmit-only tags
comprise at least one DSSS transmitter.
32. A random interval inventory system as set forth in claim 25,
wherein each of said plurality of transmit-only tags further
comprises: at least one sensing means, said sensing means for
detecting an occurrence of a specified event affecting said one of
said plurality of items to which said transmit-only tags is
affixed, and for outputting a detection signal in response thereto;
and transmitting means responsive to an output of said sensing
means for transmitting information signals at a greater temporal
rate, thereby indicating the detection of the occurrence of the
specified event; and wherein said security station is also for
determining that information signals applied to said security
station input were originally transmitted at said second random
times, and for confirming thereafter the occurrence of the
specified event affecting said one of said plurality of items.
33. A random interval inventory system as set forth in claim 29,
further comprising at least one power line, wherein said remote
transceiving means relays said received information signals to said
master transceiver via said at least one power line.
34. A random interval inventory system as set forth in claim 25,
further comprising: user-interface means coupled to at least one of
said plurality of transmit-only tags, said user-interface means
being operable for indicating a personal distress alarm (PDA),
wherein in response to a user operating said user-interface means,
said at least one transmit-only tag transmits information signals
at random times occurring as a function of a second specified time
interval, thereby indicating a PDA.
35. A transmit-only tag, said transmit-only tag being associated
with an object of interest, said transmit-only tag for transmitting
information signals to a receiving station at random times that
occur as a function of at least one of a first average time
interval and a second average time interval.
36. A transmit-only tag as set forth in claim 35, wherein said
transmit-only tags transmit, in response to an occurrence of a
specified event, said information signals to said receiving station
at said random times that occur as a function of said second
average time interval.
37. A receive/transmit (RX/TX) tag, comprising: a controller; a
receiver portion; and a transmitter portion, wherein said
controller controls said transmitter portion to transmit signals at
random times occurring as a function of a specified time interval,
said controller turns off said transmitter portion after a first
one of said signals is transmitted, said controller thereafter
turns on said receiver portion for a predetermined time period, and
thereafter turns on said transmitter portion again for transmitting
a second one of said signals.
38. A random interval inventory system, comprising: a
receive/transmit (RX/TX) tag comprising means for transmitting
signals at random times occurring as a function of a specified time
interval, said RX/TX tag further comprising a receiver and a
controller, said controller turns off said means for transmitting
signals after a first one of said signals is transmitted, said
controller thereafter turns on said receiver for a predetermined
time period, and thereafter turns on said means for transmitting
signals for transmitting a second one of said signals; and at least
one transceiver, said at least one transceiver for receiving said
first one of said signals from said RX/TX tag, and for
transmitting, in response thereto, a response signal to said RX/TX
tag such that the response signal is received by said RX/TX tag
within the predetermined time period.
39. A Random interval inventory system as set forth in claim 38,
wherein said at least one transceiver comprises an On-Off Key (OOK)
transmitter, and wherein said receiver of said RX/TX tag is an OOK
receiver.
40. A Random interval inventory system as set forth in claim 38,
wherein said at least one transceiver comprises: means for
measuring a frequency of said first one of said signals from said
RX/TX tag to obtain a measured frequency, wherein said response
signal is transmitted on a frequency that is offset from the
measured frequency by a predetermined amount sufficient to optimize
the performance of the RX/TX tag.
41. A random interval inventory system, for accounting for
individual ones of a plurality of items, comprising: a plurality of
tags, individual ones of said plurality of tags for transmitting
information signals in a predefined manner based upon random times,
said information signals transmitted from said individual ones of
said plurality of tags corresponding to respective ones of said
plurality of items; at least one remote transceiver, said at least
one remote transceiver for monitoring at least one change in status
effecting individual ones of the items indicated by the at least
one transceiver receiving information signals transmitted from
individual ones of the tags in a manner other than the predefined
manner; at least one master transceiver for providing an
interrogation command to said at least one remote transceiver,
wherein said at least one remote transceiver responds to an
interrogation command received from said master receiver by
notifying said master transceiver of a monitored at least one
change in status effecting individual ones of the items.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to inventory systems and to
telemetering. In particular, this invention relates to a system
that accounts for items based upon signals transmitted at random
time intervals.
BACKGROUND OF THE INVENTION
[0002] It is known in the art to provide an identification system
using transponders communicating with an identification receiver.
For example, U.S. Pat. No. 5,491,468, issued to Everett et al.,
discloses a portable tag which receives energy from a reading
device via magnetic coupling for charging a storage capacitor. A
discharge of the capacitor powers a coded information transmission
circuit during a small percentage of the duty cycle. Transmissions
are made from the portable tag to the reading device.
[0003] It is also known in the art to provide an identification
system using transponders communicating with an identification
receiver to reduce the probability that more than one transponder
simultaneously transmits to the receiver at a same frequency. U.S.
Pat. No. 5,302,954, issued to Brooks et al., and U.S. Pat. No.
5,153,583, issued to Murdoch, disclose a base station for applying
a magnetic field to a plurality of transponders. Each of the
transponders extracts energy from the magnetic field. The energy
extracted by individual ones of the transponders enables the
individual transponders to transmit identification codes and/or
specially stored or other information to be identified by a base
station receiver.
[0004] The transponders can generate one or more carrier
frequencies from an available set of carrier frequencies. As such,
many transponders simultaneously transmitting to the base station
may be identified under conditions where co-interference would
normally preclude correct identification. An idle state, during
which individual ones of the transponders do not transmit signals,
is employed to reduce the probability that more than one
transponder will transmit signals at the same frequency, thereby
ensuring that correct identification of a transmitting transponder
is made. Signals which may have been corrupted or co-interfered
with can be ignored by the receiver. Each transponder can
sequentially transmit an identifying code on a randomly selected
frequency that is selected from an available set of carrier
frequencies.
[0005] The use of an idle state and randomly selected frequencies
may reduce the probability that more than one transponder will
transmit signals of a same frequency at a same time. However, the
degree of reduction attainable by these techniques is still limited
because, for example, there are typically a restricted number of
frequency bands available owing to finite receiver and/or
transmitter bandwidths.
OBJECTS OF THE INVENTION
[0006] It is a first object of this invention to provide a method
and apparatus for increasing a probability that individual ones of
a plurality of transponders will successfully transmit signals to a
receiver.
[0007] It is a second object of this invention to provide a method
and apparatus for accounting for individual ones of a plurality of
items based upon random times that occur as a function of a
specified time interval.
[0008] It is a third object of this invention to provide a method
and apparatus for sensing an occurrence of a specified event
occurring to any one of a plurality of items, and in response
thereto, reporting the detection of the occurrence of the specified
event to a user.
[0009] It is a fourth object of this invention to provide at least
one transmitter tag that initiates communication with at least one
of a master transceiver and a transceiver in order to provide an
inventorying of at least one item.
[0010] Further objects and advantages of this invention will become
apparent from a consideration of the drawings and ensuing
description.
SUMMARY OF THE INVENTION
[0011] The foregoing and other problems are overcome and the
objects of the invention are realized by a method for accounting
for individual ones of a plurality of items based upon random
times, and by a random interval inventory transceiver system that
operates in accordance with the method. The method includes a first
step of transmitting information signals at random times from a
plurality of individual transmitters (hereinafter also referred to
as "tags") to at least one transceiver. The random times occur as a
function of a specified first time interval. The first time
interval may be programmed by, for example, a user operating a user
interface to enter information into a controller of one of the
transmitters for specifying an average time interval (i.e., the
first time interval). As such, the programmed transmitter transmits
information signals at the random times, chronologically occurring
ones of which are temporally spaced by intervals having varying
durations that are a function of the first specified time interval.
In this manner, a general average frequency (e.g., every 5 minutes)
with which a routine inventorying of an item is performed can be
specified.
[0012] Individual ones of the transmitters are affixed to
respective individual ones of a plurality of items to be
inventoried. The information signals transmitted from the
individual ones of the plurality of transmitters correspond to the
respective individual ones of the plurality of items to which the
transmitters are affixed. By example, an information signal
corresponding to one of the items represents information
identifying the item.
[0013] Each at least one transceiver receives information signals
from at least one of the plurality of transmitters. In accordance
with one embodiment of the invention, in response to receiving an
information signal at each at least one transceiver, a next step
includes relaying the signal from the transceiver to at least one
master transceiver. The master transceiver thereafter provides the
signal to an associated security station. The security station has
information stored within corresponding to each of the information
signals transmitted by the plurality of transmitters, and hence
corresponding to each of the plurality of items. A next step
includes, within the security station, determining that the
information signal received from the master transceiver corresponds
to at least a portion of the information stored within the security
station. Upon such a determination, a next step includes confirming
that the item corresponding to the received information signal is
accounted for. In this manner a routine inventorying is performed
of each item based upon random times that are a function of the
first specified time interval. While performing the inventory, the
system is deemed to be operating in a confidence mode.
[0014] In accordance with the method of this invention, individual
ones of the random times occur randomly during respective
individual ones of sequentially occurring predetermined time
intervals.
[0015] Further in accordance with the method of this invention, the
at least one transceiver receives information signals from at least
one of the plurality of transmitters depending upon, at least in
part, a position of the transceiver relative to that of the at
least one of the plurality of transmitters. By example, one
transceiver may be located within a same room as a number of the
transmitters in order to relay, and thus facilitate, the
communication of information signals from the transmitters to a
master transceiver. For a case in which at least one of the
transmitters is positioned such that it can effectively communicate
information signals directly to the master transceiver without a
need for relaying the signals to a transceiver, no relaying
transceiver is employed. In such a case, the information signals
are communicated directly to the master transceiver, which
thereafter provides the signals to the associated security station
wherein the step of confirming is performed in the manner as
described above.
[0016] The invention can also operate in a so called "panic"
operating mode, wherein an occurrence of a specified condition
(e.g., movement or a temperature condition) affecting any of the
plurality of items is detected and ultimately reported to the
security station and to a user for verification of the detection.
In accordance with this mode of the invention, a sensor coupled to
a tag that is affixed to an affected one of the items detects an
occurrence of the specified event. In response to the detection of
the occurrence of the specified event, the tag transmits
information signals ("distress alarm signals") to one of the
transceivers at random times occurring as a function of a second
specified time interval. The second time interval can be specified
in a manner that is similar to that described above for the
specification of the first time interval. Chronological
transmissions of the information signals based upon the second
specified time interval are temporally separated as a function of
the second time interval, thereby indicating the detection of the
specified event occurring to the affected item. Such transmissions
during the panic mode occur, by example, at a rate (e.g., every 10
seconds) that is greater than that of transmissions made by the tag
during the confidence (routine inventory) mode. Such an increase in
the rate of transmission of information signals is ultimately
recognized by the security station. As such, the station, and
ultimately a user, are notified of the occurrence of the specified
condition affecting the item. In one embodiment of the invention,
the panic mode may also be implemented by a user operating a "panic
alarm" button associated with one of the tags.
[0017] In accordance with a preferred embodiment of the invention,
in addition to the random transmissions, each tag also transmits
signals using a direct sequence spread spectrum technique.
[0018] In another embodiment of the invention, the remote
transceivers autonomously perform data reduction by identifying
what information needs to be communicated to the master transceiver
(e.g., what has changed in the inventory or alarm status). The
master transceiver transmits commands to the remote transceivers in
order to interrogate them for sending back inventory and alarm
status signals. In this manner, information provided from the
remote transceivers to the master transceiver relates to changes in
inventory or alarm status, as opposed to a complete inventory
status.
[0019] In accordance with the method of the invention, each
individual one of a plurality of tags transmits information signals
independently from other ones of the plurality of tags, thereby
limiting the probability that the at least one master transceiver
will receive more than one information signal simultaneously.
[0020] In a further embodiment of the invention, a receive/transmit
(RX/TX) tag is provided. The RX/TX tag comprises a transmitter
portion and a receiver portion. The RX/TX tag transmits signals at
random times occurring as a function of a specified time interval
in the same manner as described above. However, the transmitter
portion is turned off after a first one of the signals is
transmitted, and thereafter the receiver portion is turned on for a
predetermined time period. After the predetermined time period has
expired, the transmitter portion is turned on again for
transmitting a second one of the signals. For this embodiment of
the invention, a transceiver which receives the first one of the
signals transmitted from the RX/TX tag responds by measuring the
frequency of the received signal and by transmitting a response
signal to the RX/TX tag on a frequency that is offset by a fixed
amount from the measured frequency. The transceiver transmits the
response signal in a manner such that the response signal is
received by said RX/TX tag within the predetermined time
period.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The above set forth and other features of the invention are
made more apparent in the ensuing Detailed Description of the
Invention when read in conjunction with the attached Drawings,
wherein:
[0022] FIG. 1 is a diagram of a random interval inventory system
that is constructed in accordance with this invention.
[0023] FIG. 2 illustrates a block diagram of a transmit-only tag
that is constructed in accordance with one embodiment of the random
interval inventory system of FIG. 1.
[0024] FIG. 3 illustrates a receiver portion of a transceiver that
is constructed in accordance with a preferred embodiment of the
random interval inventory system of FIG. 1.
[0025] FIG. 4a is an illustration of sequentially occurring average
time intervals, during each of which occurs a random time slot at
which the tag of FIG. 2 transmits a signal.
[0026] FIG. 4b is an illustration of a dual receive band tag scheme
in accordance with the invention.
[0027] FIG. 4c is an illustration of a transmit/receive tag
constructed in accordance with a further embodiment of the random
interval inventory system of FIG. 1.
[0028] FIG. 5 illustrates a graph representing probabilities that
none of a plurality of the tags of FIG. 2 are transmitting distress
signals at any one time, for various numbers of tags randomly
transmitting information signals based upon second intervals.
[0029] FIG. 6 illustrates a graph representing probabilities that a
particular one of 500 of the tags of FIG. 2 will successfully
communicate distress signals with the master transceiver of FIG. 3
per each of a number of random transmissions occurring based upon
15 second intervals.
[0030] FIG. 7 illustrates a graph representing probabilities that
no activated ones of a plurality of the tags of FIG. 2 are
transmitting distress signals at any one time, for various numbers
of tags randomly transmitting information signals based upon 1
second intervals.
[0031] FIG. 8 illustrates a graph representing probabilities that a
particular one of 50 of the tags of FIG. 2 will successfully
communicate distress signals with the master transceiver of FIG. 3
per each of a number of transmissions, wherein each tag randomly
transmits information signals based upon 1 second intervals.
[0032] FIG. 9 illustrates a graph representing probabilities that
none of a plurality of the tags of FIG. 2 are transmitting
information signals at any one time during a confidence mode of
operation, for various numbers of tags that are randomly
transmitting information signals of 17 millisecond pulse duration,
based upon 5 minute intervals.
[0033] FIG. 10 illustrates a graph representing probabilities that
none of a plurality of the tags of FIG. 2 are transmitting
information signals at any one time, during a confidence mode of
operation, for various numbers of tags that are randomly
transmitting information signals of 141 millisecond pulse duration,
based upon 5 minute intervals.
[0034] FIG. 11 illustrates a graph representing probabilities that
a particular one of 1000 of the tags of FIG. 2 will successfully
communicate 17 millisecond pulse duration information signals with
the master transceiver of FIG. 3 per each of a number of random
transmissions occurring based upon 5 minute intervals.
[0035] FIG. 12 illustrates a graph representing probabilities that
a particular one of 1000 of the tags of FIG. 2 will successfully
communicate 141 millisecond pulse duration information signals with
the master transceiver of FIG. 3 per each of a number of random
transmissions occurring based upon 5 minute intervals.
DETAILED DESCRIPTION OF THE INVENTION
[0036] FIG. 1 illustrates one embodiment of a random interval
inventory system 1 (hereinafter also referred to as "RIIS") that is
constructed in accordance with this invention. The system 1
comprises at least one console (hereinafter also referred to as a
"master transceiver") 3 and a plurality of transmitters
(hereinafter also referred to as "tags", "transmit-only tags", or
"TXs") 5a1-5xx. In accordance with the embodiment of the invention
illustrated in FIG. 1, the RIIS 1 also comprises at least one
remote transceiver (hereinafter also referred to as a
"transceiver") 4a-4n, and at least one security station
(confirmation device), which is, by example, a security console 2.
In certain other embodiments of the invention, which will be
described below, the at least one remote transceiver 4a-4n is not
utilized, and the security console 2 is replaced with another
suitable device. These components may thus be considered as
optional.
[0037] For the purposes of clarity, the ensuing description is made
in a context wherein a plurality of transceivers, one security
console 2, and one master transceiver 3 are being employed, as is
illustrated in FIG. 1. The master transceiver 3 is associated with
the security console 2, and can be, by example, mounted thereon.
The security console 2 stores inventory information corresponding
to each of the plurality of tags 5a1-5xx, as will be described
below. The master transceiver 3 has an antenna 3a; each of the
remote transceivers 4a-4n has an antenna 4a1-4n1, respectively;
and, referring to FIG. 2, each tag 5a1-5xx has a respective antenna
22.
[0038] It should be noted that although the ensuing description
discusses the RIIS 1 in the context of an application for
inventorying paintings in an art gallery, it is not intended that
the invention be so limited. For instance, the invention may also
be employed in other inventory control maintenance applications
wherein it is necessary to inventory items such as, by example,
laboratory test equipment, or hazardous (e.g., radioactive,
poisonous, explosive) materials. Also, the RIIS 1 may be employed
to perform inventory and/or person location tracking in defined
areas such as, by example, hospitals, laboratory complexes, etc. In
addition, the RIIS 1 may be employed in security applications to
monitor, by example, infant security in hospitals, the
opening/closing of doors and windows, or to determine the
entrancing or exiting of a particular item from a home or
industrial building. Moreover, the RIIS 1 may be employed to
perform remote meter reading (gas, water, electric, etc.), access
control, in-building two-way paging, prisoner monitoring,
industrial and process control, and control of lighting, heating,
and other utilities in buildings.
[0039] As mentioned above, in an exemplary application the RIIS 1
may be employed in an art gallery to maintain routine inventory
control over paintings that are located within various rooms of an
art gallery. For this example, the invention is embodied as
follows. Each of the paintings (not illustrated) is associated with
a respective one of the tags 5a1-5xx (e.g., each painting has a
respective one of the tags 5a1-5xx mounted thereon). In a preferred
embodiment of the invention, each individual tag (e.g, tag 5a1) is
mounted on a portion of a respective one of the painting's frame in
a manner such that, depending upon the tag's effective transmission
range and relative location within the art gallery with respect to
the locations of the master transceiver 3 and the remote
transceivers 4a-4n, the tag 5a is able to communicate effectively
with at least one of the master transceiver 3 and one remote
transceiver (e.g., remote transceiver 4a), as will be described
below.
[0040] Each of the tags 5a1-5xx operates in a first operating mode
and a second operating mode. The first operating mode, which, for
the purposes of this description is also deemed to be a confidence
mode, is the operating mode during which regular inventorying is
performed of the items (e.g., paintings) to which the tags 5a1-5xx
are mounted. While operating in the confidence mode, each
individual tag 5a1-5xx independently communicates RF energy (e.g.,
confidence signals) over its antenna 22 to one of the remote
transceivers (e.g., transceiver 4a) at random time intervals (to be
described below). In a preferred embodiment of the invention for
the transmit-only tags, the tags 5a1-5xx employ Direct Sequence
Spread Spectrum (DSSS), for transmitting signals. The second
operating mode is discussed below.
[0041] Each of the confidence signals transmitted by an individual
tag (e.g., tag 5a1) represents bits of information corresponding to
the tag 5a1, and hence to the particular painting to which the tag
5a1 is mounted. The information may represent, by example,
information (e.g., a serial number) identifying the particular
painting. This information corresponds to information stored within
the security console 2, and may be programmed into the controller
10 of a tag via an external user interface 13 (see FIG. 2).
[0042] FIG. 2 illustrates a block diagram of a transmit-only tag
(e.g., tag 5a1) constructed in accordance with a first and a second
embodiment of this invention. A microprocessor controller 10 having
a clock 10a emits control signals at random times that are
determined by the clock 10a in a manner that will be described
below. Each control signal emitted by the controller 10 is provided
to a modulator 15, wherein the signal is mixed with a carrier
signal generated by a local oscillator 18. Thereafter, the signal
is amplified to an appropriate amplitude by an amplifier 16. The
amplifier 17 shown in FIG. 2 is employed in the second (Personal
Distress Alarm) embodiment of the invention, which will be
discussed further below. Amplifier 17 does not necessarily need to
be employed in the transmit-only tags of the first embodiment.
[0043] Thereafter, the signal is filtered by filter 19, and
transmitted as a confidence signal over the antenna 22 to the
master transceiver 3 or one of the remote transceivers 4a-4n. Each
tag 5a1-5xx has an effective transmission range of, by example, at
least 200 meters, and has a relatively low effective radiated power
(ERP). Also, in a preferred embodiment of the invention, each tag
5a1-5xx transmits signals on a fixed frequency of, by example,
2.414GHz.
[0044] In accordance with a preferred embodiment of the invention,
antenna 22 for the individual tags 5a1-5xx is small in size and has
an ability to radiate energy efficiently in a ground plane and/or
in free space. By example, for an operating frequency of 2.414 GHz,
the size of the antenna 22 is approximately 1 inch.times.1 inch,
with a thickness of 0.050 inches.
[0045] In a preferred embodiment of this invention, the confidence
signal is a relatively short duration (e.g., 10 to 100 ms) pulse
signal. The generation of such short pulse signals allows each tag
5a1-5xx to use relatively small amounts of energy over time, and
therefore preserves the energy of a power supply, such as a battery
(not illustrated).
[0046] In a preferred embodiment of the invention, the transmission
times are produced truly randomly by employing "external" signals
to "seed" a pseudo-random number generator (located within the
controller 10) such as, by example, a binary shift register
sequence generator, or another means known in the art for producing
a pseudo-random sequence. First, in accordance with one of the
techniques for generating a pseudo-random sequence, a period (e.g.,
5 minutes, or 60 minutes) is specified by, for example, a user
entering appropriate initialization data (e.g., a seed) into the
controller 10 via the external user interface 13. This period is
deemed to be, for the purposes of this description, a first average
time interval. Second, "external" signals are supplied to the
controller 10 in response to, by example, detections of events
(e.g., "bumps", the reaching of a specified temperature, or the
reaching of specified local battery voltage) made by at least one
sensor (see below for a discussion of sensors 12 and 14). The
controller 10 then determines a temporal separation between, for
example, two of the "external" signals supplied from the sensor,
and uses this determined temporal spacing to "seed" the
pseudo-random sequence generator. Based upon the first average time
interval and the "seeding" of the pseudo-random number generator
via the "external" signals, the controller 10 then emits control
signals at random times, individual ones of which occur randomly
during respective individual ones of sequentially occurring time
intervals having durations equal to the first average time
interval. In this manner, the applicable tag (e.g., tag 5a1)
transmits confidence signals at random times, thereby enabling
routine inventory checks (e.g., occurring approximately every 5
minutes, or every 60 minutes) of the painting to which the tag 5a1
is affixed to be performed. FIG. 4 illustrates an example of the
sequentially occurring time intervals, during each of which occurs
a random time slot designated as ton (time-on). For the purposes of
this description, the random times associated with the confidence
mode are designated as "first random times".
[0047] Each remote transceiver 4a-4n functions as a communication
relay to enable effective indirect communication between the master
transceiver 3 and at least one tag 5a1-5xx for cases in which, by
example, the master transceiver 3 is not located within the
effective transmission range of a tag (e.g., tag 5a1). For example,
for the case in which a tag 5a1 is mounted on a painting located
within a room of the art gallery such that the tag 5a1 cannot
otherwise effectively communicate directly with the master
transceiver 3, a remote transceiver (e.g., remote transceiver 4a)
is employed to facilitate such communication. For this example, the
remote transceiver 4a is positioned with respect to the tag 5a1 and
master transceiver 3 in a manner such that it can relay signals
from the tag 5a1 to the master transceiver 3. The remote
transceiver 4a may be mounted near the entrance of the room where
the tag 5a1 of interest is located, for example. This remote
transceiver 4a may also serve to relay communications from other
tags (e.g., tags 5a2-5ax) that are located within the same room, to
the master transceiver 3.
[0048] In some cases, a single remote transceiver 4a may not be
adequate to facilitate communications between the tag 5a1 and the
master transceiver 3. In such cases additional remote transceivers
4a-4n may be employed in order to relay the transmissions. It
should be noted that this description describes the invention
primarily in the context of an application wherein only a single
remote transceiver (e.g., remote transceiver 4a) is employed to
facilitate communication between at least one of the tags 5a1-5xx
and the master transceiver 3. It also should be noted that, for the
case in which a tag (e.g., tag 5a1) is able to communicate directly
with the master transceiver 3, no remote transceivers 4a-4n need be
employed in order to relay the communications.
[0049] In accordance with one alternate embodiment of this
invention, the remote transceivers 4a-4n inter-communicate with one
another and/or with the master transceiver 3 via AC power lines.
FIG. 3 illustrates a power line link 50 for a remote transceiver
4a-4n (or a master transceiver 4).
[0050] FIG. 3 illustrates a block diagram of a transceiver which
may function as a master transceiver 3 or one of the remote
transceivers 4a-4n, and which is constructed in accordance with
various embodiments of the invention. An antenna 48 (which forms
antenna 3a for a master transceiver or antennas 4a1-4nn for the
respective remote transceivers), is coupled to a Direct Sequence
Spread Spectrum receiver (DSSS RX) block 42, a DSSS transmitter
(DSSS TX) block 44, and an "ON-OFF" key transmitter (OOK TX) block
46. The DSSS RX block 42 is employed in all embodiments of the
invention for receiving signals from tags 5a1-5nn, other remote
transceivers 4a-4n, and the master transceiver 3. The DSSS RX block
42 employs a known type of Direct Sequence Spread Spectrum
technique for receiving signals. When a signal is received by the
transceiver via antenna 48, the signal is provided to the DSSS RX
block 42 wherein it is decoded and checked for errors. Signals that
are received with errors from tags 5a1-5xx are ignored. Signals
received by a remote transceiver 4a from the master transceiver 3
are error-checked. If the signal is received without error, the
remote transceiver 4a responds back to the master receiver 3 with a
verification signal. If there is no verification signal received by
the master transceiver 3, the master transceiver transmits again,
with a random delay determined by the processor 40 of the master
transceiver 3, which handles appropriate protocol functions. It
should be noted that a situation in which the master transceiver 3
transmits signals to remote transceivers 4a-4n is addressed below
with respect to an embodiment of the invention employing data
reduction.
[0051] The DSSS TX block 44 is employed to transmit, in response to
a signal received from the processor 40, signals using a DSSS
technique. Signals provided from the DSSS TX block 44 are
transmitted via the antenna 48 to other ones of the remote
transceivers 4a-4n, or to the master transceiver 3, as is required
by the application of interest. The DSSS TX block 44 is primarily
employed in the first embodiment of the invention, and in the
second embodiment of the invention which will be described
below.
[0052] The OOK TX block 46 is employed (in lieu of the DSSS TX
block 44) in an embodiment of the invention employing
receive/transmit (RX/TX) tags, which also will be described below.
In the RX/TX embodiment, the OOK TX block 46 is used for
transmitting signals to the RX/TX tags.
[0053] Depending upon the range being transmitted over, the antenna
48 can be, for example, an omni-directional antenna with low gain,
or a high gain, directional antenna (which will increase
transmission range approximately 2-3 times) where appropriate.
Also, similar to the tags 5a1-5XX, each transceiver has a
user-interface 54 for programming information into the
transceiver.
[0054] In accordance with the embodiment of the invention wherein
AC power lines are used to facilitate communications between, by
example, remote transceivers 4a-4n and/or between a remote
transceiver 4a and the master transceiver 3, power line link block
50 is employed instead of the DSSS TX block 44.
[0055] Also illustrated in FIG. 3 is an interface link 52 which is
used in a master transceiver 3 to interface with the security
console 2, or to a pager system.
[0056] Having described in detail the operations and construction
of the transceiver illustrated in FIG. 3, the operation of the RIIS
1 will now be further discussed. After a signal is received by the
master receiver 3, it is forwarded to the security console 2
wherein the signal is recognized as corresponding to a portion of
the information stored within the security console 2. More
particularly, information stored within the security console 2
corresponds to the bits of information transmitted by each tag
5a1-5xx. As such, when the security console 2 receives a confidence
signal from one of the tags (e.g., tag 5a1) that is mounted on a
particular painting, and thereafter recognizes the received
information as corresponding to information stored within the
security console 2, it is confirmed that the particular painting is
present in the art gallery. In this manner, the painting is
inventoried.
[0057] The second mode in which the tags 5a1-5xx operate is deemed,
for the purposes of this description, to be a "panic mode". This
operating mode is useful for tracking the movement of items, and
for identifying an occurrence of a specified event, such as, for
example, the removal of a painting from its assigned location
within the art gallery, or the reaching of a specified temperature
within the art gallery environment. The panic mode is implemented
in a manner that is made apparent by the following example.
Referring to FIG. 2, "bump monitor" sensor 12 associated with a tag
(e.g., tag 5a1) senses the movement of a painting (which may
indicate, for example, the removal of the painting from its
assigned location within the art gallery). The sensor 12, which may
be, by example, an accelerometer, a motion-sensitive switch, a
temperature sensor, etc., supplies information representing the
occurrence of the specified event to the controller 10 which, in
response, emits control signals at second random time intervals.
The second random time intervals are based upon a second average
time interval. The second average time interval is predetermined
by, for example, a user entering information into the controller 10
via the user interface 13 for specifying an approximate average
frequency (e.g., every 1 second, or every 15 seconds) at which it
is desired to be notified of distress signals once the specified
event has been detected. Each control signal is mixed at modulator
15 with a carrier signal generated by local oscillator 18 and
amplified by amplifier 16 in the same manner as described above for
the confidence mode. Then, the signal is transmitted as a
"distress" signal over antenna 22 to one of the remote transceivers
(e.g., remote transceiver 4a). Thereafter the distress signal is
relayed to the master transceiver 3, in the same manner as
described above for the confidence mode. The master transceiver 3
then supplies the distress signal to the security console wherein
it is determined that, based upon the frequency of reception of the
distress signals with respect to that of the confidence signals,
the specified event (e.g., movement of the painting) has occurred.
It should be noted that the second operating mode may also be
invoked by the "over-temperature" monitoring sensor 14 associated
with tag 5a1 sensing that a surrounding temperature has reached a
predetermined "over-threshold" level, or by any other type of
sensor interfaced with the tag 5a1 sensing an occurrence of a
specified event. For the purposes of this invention, tags 5a1-5xx
which are operating in the panic mode are deemed to be "active
tags".
[0058] In accordance with the second embodiment of the invention,
the second operating mode may also be invoked by a user operating,
by example, the user interface 13 or a "panic" button (which may be
coupled to, by example, user-the interface 13) to indicate a
personal distress alarm (PDA). For this embodiment, each tag
5a1-5xx is similar to the tags of the previously-discussed
embodiment, with the addition of a power amplifier 17 interposed
between the amplifier 16 and filter 19, as is illustrated in FIG.
2. Amplifier 17 is, by example, a 25 dBm amplifier. Additionally,
the tags of this embodiment accommodate a larger battery and have
higher transmit power/ERP which permits the probability of linking
to the master receiver 3 to be increased. Moreover, the tags of
this embodiment may be programmed to have different first and
second average time intervals, a different "over-temperature"
threshold, and different transmission responses to, by example,
movement and/or temperature, than tags of the first embodiment. By
example, a tag may be programmed to transmit a distress signal if
sensor 12 detects no movement during a time when the painting
associated with the tag is known to be experiencing movement, thus
indicating, for example, that the tag has been removed from the
painting. Furthermore in this embodiment, the master receiver 3
interfaces with a pager system (not illustrated) in lieu of, or in
addition to the security console 2, such that when a PDA signal is
received from a tag (e.g., tag 5a1), the master receiver 3 sends
signals specifying, by example, a name or a message, to the pager
system.
[0059] In another embodiment of the invention, the RIIS 1 performs
tracking of the objects (e.g., paintings). The technique by which
the RIIS 1 performs tracking of objects may be any technique known
in the art for determining relative locations of objects based upon
power measurements of signals received from transmitters located on
or near the respective objects. The technique can be performed at,
for example, the individual remote transceivers 4a-4n, the master
transceiver 3, and/or the security console 2. By example, for a
case in which the technique is performed at the security console 2,
a first signal received by the security console 2 is measured to
determine the received signal's strength. The determined signal
strength is stored within the security console 2. Upon a receipt of
a following second signal transmitted by the same tag, the security
console 2 measures the signal strength of this second signal. Based
upon the relative signal strengths of the first and second signals,
a displacement of the tag and its associated painting occurring
between the time when the first signal was transmitted and the time
when the second signal was transmitted can be determined. A
calculation can then be made to determine the location of the
painting. The same process occurs for subsequently received
signals. The process can also be carried out by comparing measured
signal strengths of signals received from a tag with a reference
signal strength transmitted by the tag when at its assigned
location.
[0060] In another embodiment of the invention, the remote
transceivers 4a-4n autonomously perform data reduction by
identifying what information needs to be communicated to the master
transceiver 3 (e.g., what has changed in the inventory or alarm
status). This information is provided to the master transceiver 3
in response to a command received from the master transceiver 3
interrogating the remote transceivers 4a-4n to transmit inventory
and alarm status signals. In this manner, as opposed to providing a
complete list of all current inventory, the remote transceivers
4a-4n simply provide information indicating, by example, changes in
alarm or inventory status. This protocol is applicable in
applications using the transmit-only tags and the remote
interrogators 4a-4n for facilitating communications (e.g., limited
data loading) with the master transceiver 3.
[0061] In an exemplary situation, a change in status may be
identified by the remote transceiver recognizing that a signal has
not been received from a particular tag within a first
predetermined time period. By example, after a signal is received
by remote transceiver 4a from tag 5a1, an internal clock (not
illustrated) within the remote transceiver 4a begins to run. If the
time kept by the clock then exceeds the first predetermined time
period stored within the remote transceiver 4a, a change in status
is recognized by the remote transceiver 4a. The change in status
may indicate, for example, that a painting to which tag 5a1 is
affixed has been moved out of range of the remote transceiver 4a.
The remote transceiver 4a stores information which indicates this
change in status and which identifies the particular tag (and/or
the painting to which it is affixed) from which the signal was
originally transmitted.
[0062] It should be noted that these examples are intended to be
exemplary in nature and not limiting in scope, and that other
changes in status may be identified by a remote transceiver. For
example, a remote transceiver can recognize that two signals
received from a particular one of the tags have been received by
the remote transceiver within a second predetermined time period
(i.e., indicating the panic mode). Also, as described above, the
remote transceiver may measure signal strengths of received signals
in order to determine whether a painting has been displaced from an
assigned or reference location.
[0063] As indicated above, the master transceiver 3 transmits
commands to the remote transceivers 4a-4n in order to interrogate
them for sending back status signals. This may occur at, for
example, predetermined time intervals. Once a command signal
transmitted by the master transceiver 3 is received by a remote
transceiver (e.g., remote transceiver 4a), the remote transceiver
4a responds by transmitting stored information which indicates any
changes in status and which identifies particular tags and/or
paintings associated with those changes in status identified by the
remote transceiver 4a since, by example, a last command was
received by the master transceiver 3. Thereafter, the information
is received by the master transceiver 3 and is then supplied to the
security console 2 for notifying, by example, a user of the changes
in status effecting the particular tag and/or painting identified
by the information. In another embodiment, the remote interrogator
4a responds to commands received from the master transceiver 3 by
providing the information indicating changes in status that have
been identified and stored by the remote interrogator 4a over a
predetermined time period.
[0064] Having described several embodiments of the invention,
another aspect of the invention will now be discussed which applies
to all of the embodiments of the invention, including those
discussed below. For this aspect of the invention the manner in
which signals are transmitted from each tag 5a1-5xx can be set to
minimize the possibility that signals transmitted by more than one
tag 5a1-5xx will be received simultaneously by the master
transceiver 3. For example, this may be accomplished by operating
the user interface or by using detections made by a sensor (e.g.,
sensor 12 and/or 14) of each tag 5a1-5xx to vary a seed value in
order to specify a unique first and second average time interval
for each tag 5a1-5xx. Also by example, this may be accomplished by
varying the random timing variations (frequencies) of the clock 10a
associated with each tag 5a1-5xx such that they differ from those
of the other tags 5a1-5xx. As such, the probability that more than
one tag 5a1-5xx will transmit simultaneously, and that the master
transceiver 3 will simultaneously receive signals from more than
one tag 5a1-5xx, is minimized. This can be further understood in
consideration of the following probability equations.
[0065] The probability P.sub.tx that a particular one of the tags
(e.g., tag 5a1) is transmitting at a particular time is represented
by the equation: 1 P tx = [ ton ton + toff ]
[0066] where: P.sub.tx represents the probability that a particular
tag (e.g., tag 5a1) is transmitting a signal; ton represents the
duration of the transmission of a randomly occurring signal; and
toff represents an average time interval between random
transmissions.
[0067] The probability P.sub.ntx that a particular tag will not
transmit a confidence signal at a particular time is represented by
the equation: 2 P ntx = 1 - ton ton + toff
[0068] Where: ton and toff represent the same information as
defined above.
[0069] Based upon the foregoing equations, the probability P.sub.tx
that one tag (e.g., tag 5a1) transmits a first confidence signal
during a time at which no other tags (e.g., tags 5a2-5xx) are
transmitting confidence signals, and hence the probability that the
master transceiver 3a correctly receives the first confidence
signal, is represented by the equation: 3 Ptx = [ 1 - ton toff +
ton ] n ,
[0070] where: Ptx represents the probability that an individual
transmitting tag (e.g., tag 5a1) is the only one of the tags
5a1-5xx that is transmitting a signal at a particular time; ton and
toff have the same meanings as described above; and n represents
the total number of tags (e.g., tags 5a2-5ax), not including a
transmitting tag of interest (e.g., tag 5a1), that may be
transmitting a signal at the same time as the transmitting tag
5a1.
[0071] Similarly, the probability Pm that a tag (e.g., tag 5a1)
transmits at least one of m confidence signals during a time at
which no other tags (e.g., tags 5a2-5xx) are transmitting
confidence signals, and hence the probability that the master
transceiver 3a correctly receives at least one confidence signal
out of m transmitted confidence signals, is represented by the
equation: 4 Pm = 1 - [ 1 - [ 1 - ton toff + ton ] n ] m
[0072] Where: n, ton, and toff have the same meanings as described
above, and m represents the number of confidence signal
transmissions made by a transmitting tag of interest (e.g., tag
5a1).
[0073] It should be noted that in accordance with these equations,
during a PDA the values of ton, toff and n are relatively smaller
during the confidence mode. In light of the above probability
analysis, it has been determined that where a substantial number
(i.e., more than one thousand) of tags 5a1-5xx are employed in the
RIIS 1, the probability that each tag 5a1-5xx will successfully
link with the master transceiver 3 at any one time is substantial.
FIGS. 5 to 12 illustrate probability graphs for various numbers of
tags 5a1-5xx, data bit packets, and data bit rates. FIG. 5
illustrates a graph representing probabilities that no tags 5a1-5xx
are transmitting distress signals at any one time, for a case
wherein there are various numbers (0 to 1000) of tags 5a1-5xx
randomly transmitting 12 bit packet, 1 kbps information signals
based upon a second average time interval of 15 second
duration.
[0074] FIG. 6 illustrates a graph representing probabilities that a
particular one tag (e.g., tag 5a1) of 500 tags 5a1-5xx will
successfully communicate 12 bit packet, 1 kbps distress signals
with the master transceiver 3 per each of 10 successive random
transmissions occurring based upon a second average time interval
of 15 second duration.
[0075] FIG. 7 illustrates a graph representing probabilities that
no activated ones of various numbers (0 to 1000) of tags 5a1-5xx
are transmitting distress signals at any one time, for a case
wherein the tags 5a1-5xx are randomly transmitting 12 bit packet, 1
kbps information signals based upon a second average time interval
of 1 second duration.
[0076] FIG. 8 illustrates a graph representing probabilities that a
particular one tag (e.g., tag 5a1) of 50 transmitting tags 5a1-5xx
will successfully communicate 12 bit packet, 1 kbps distress
signals with the master transceiver 3 per each of 10 successive
transmissions, wherein each tag 5a1-5xx randomly transmits distress
signals based upon a second average time interval of 1 second
duration.
[0077] FIG. 9 illustrates a graph representing probabilities that
no tags 5a1-5xx are transmitting information signals at any one
time while the tags 5a1-5xx are operating in the confidence mode,
wherein there are various numbers (0 to 10000) of tags 5a1-5xx
randomly transmitting 17 bit packet, 1 kbps information signals of
17 millisecond pulse duration, based upon a first average time
interval of 5 minute duration.
[0078] FIG. 10 illustrates a graph representing probabilities that
no tags 5a1-5xx are transmitting information signals at any one
time, during the confidence mode of operation, for various numbers
(0 to 10000) of tags 5a1-5xx that are randomly transmitting 17 bit
packet, 120 bps information signals of 141 millisecond pulse
duration, based upon a first average time interval of 5
minutes.
[0079] FIG. 11 illustrates a graph representing probabilities that
a particular one tag (e.g., tag 5a1) of 1000 tags 5a1-5xx will
successfully communicate 17 bit packet, 1 kbps, and 17 millisecond
pulse duration information signals with the master transceiver 3
per each of 10 successive random transmissions occurring based upon
a first average time interval of 5 minutes.
[0080] FIG. 12 illustrates a graph representing probabilities that
a particular one tag (e.g., tag 5a1) of 1000 tags 5a1-5xx will
successfully communicate 141 millisecond pulse duration information
signals with the master transceiver 3 per each of 10 successive
random transmissions occurring based upon a first average time
interval of 5 minutes.
[0081] Having described embodiments of the invention for
transmit-only tags, a further embodiment of the invention will now
be described which employs receive/transmit (RX/TX) tags. For the
purposes of this description, this further embodiment is referred
to as a "Transmit-Then-Receive" (TTR) protocol embodiment wherein
individual tags 5a1-5xx transmit signals at intervals to the master
transceiver 3 or a remote interrogator (e.g., remote interrogator
4a) in order to perform an inventorying of items (e.g., a
paintings) associated with the tags, in the same manner as was
described above. However, for the TTR protocol embodiment each
transmission is followed by a predetermined waiting period, during
which the tag operates in a receive mode, instead of a transmit
mode, for a predetermined time interval. Also, as described above,
each of the master transceiver 3 and the remote transceivers 4a-4n
comprises (in lieu of the DSSS TX block 44) the OOK TX block 46
which functions as described below. The OOK TX block 46 is a less
complex system than the DSSS TX block 44.
[0082] FIG. 4c illustrates an RX/TX tag constructed in accordance
with a preferred embodiment of this invention. The RX/TX tag is
similar to the transmit-only tag of the first embodiment of the
invention in that it comprises a local oscillator 18, a modulator
15, an amplifier 16, a filter 19, a microprocessor controller 10,
an "over-temperature" monitor sensor 14, a "bump" monitor sensor
12, an antenna 22, and an external user-interface 13. These
elements function in a similar manner to the same elements of the
transmit-only tag, although the controller 10 performs additional
functions over that for the transmit-only tags. In addition to
these elements, the RX/TX tag also comprises a larger memory (e.g.,
1 to 100 kilobyte) 60 than the transmit-only tag (whose memory is
not illustrated in FIG. 2) and circuitry, namely an OOK receiver
circuit, enabling it to receive signals. By example, after a signal
is transmitted from the RX/TX tag, the controller 10 controls the
RX/TX tag to change its operating mode from the transmit mode to
the receive mode for a time interval that is predetermined by, for
example, information entered previously into controller 10 via the
user-interface 13. The time interval is preferably a short time
interval. First, an amplifier 64 has an input that is coupled to
antenna 22 such that when the RX/TX tag is in a receive mode and a
signal is received by the antenna 22, the signal is amplified to an
appropriate level by amplifier 64. The amplifier 64 is tunable by
an off-chip tuning block 66. A mixer 62 thereafter mixes the
amplified signal with an output of local oscillator 18, whereafter
the signal is amplified by amplifier 68 and thence filtered by a
bandpass filter 70 (e.g., a 4.5MHz IF bandpass filter). A detector
circuit 72 detects an output of the filter 70 and thereafter
provides a signal to a logic block 74 which is, by example, a
comparator. The comparator 74 determines whether a signal received
from the detector 72 is of a sufficient magnitude (e.g., above a
noise level). If so, the comparator 74 provides a signal to the
controller 10, which thereafter changes the operating mode to the
transmit mode (i.e., the controller 10 "turns off" or "cycles-off"
the receiver circuitry and "turns on" or "cycles-on" the receiver
circuitry). Having a receive capability, the RX/TX tag can have its
parameters (e.g., an ID number, a bill of lading, and first and/or
second average time intervals) programmed from a remote location,
as will be described below.
[0083] In an exemplary application, after an individual one of the
RX/TX tags (e.g., RX/TX tag 5a1) transmits a signal identifying the
tag 5a1 at a first random time to, by example, one of the remote
transceivers (e.g., remote transceiver 4a), the controller 10
controls the RX/TX tag to change its operating mode from the
transmit mode to the receive mode as described above. Thereafter,
the remote transceiver 4a receives the signal over antenna 48,
which then provides the received signal to DSSS RX block 42,
wherein appropriate receiving functions are performed to the signal
(FIG. 3). After the signal passes through the DSSS RX block 42, the
signal is provided to the processor 40. The processor 40 measures
the frequency of the signal, which frequency was set originally at
the transmitting RX/TX tag 5a1. This frequency measurement process
occurs as a first step in the spread spectrum signal receive
operation, and as such does not increase the complexity of the
system. Following the frequency determination, the processor 40
controls the OOK TX block 46 to "cycle-on" so as to transmit a
return data signal to the RX/TX tag 5a1 at a frequency that is
offset from the measured frequency by a predetermined amount
sufficient to optimize the performance of the RX/TX tag 5a1. The
return data signal may carry information specifying, by example, a
new first and/or second average time interval for the RX/TX tag
5a1, an identification number, or that the controller 10 of the
RX/TX tag 5a1 shall cease the RX/TX tag 5a1 from making further
transmissions. After the signal transmission by the remote
transceiver 4a, the processor 40 controls the OOK TX block 46 to
turn off. This frequency adjustment scheme allows for improved
system characteristics such as, by example, a relatively simple,
inexpensive tag Local Oscillator (LO), the minimization of tag IF
bandwidth requirements (thereby maximizing sensitivity and
operational range), and an inexpensive OOK style receiver.
[0084] Following a reception by the RX/TX tag 5a1 of the return
signal transmitted from the remote transceiver 4a, the signal
traverses the receiving circuitry in the manner described above,
ultimately being provided to controller 10. Thereafter, the
controller 10 changes the operating mode from the receive mode to
the transmit mode, and performs an error check to determine whether
the received signal carries error-free data. If it is determined
that the return signal does carry error-free data, the tag may
indicate same by transmitting an acknowledgement signal back to the
remote interrogator 4a. If the controller 10 determines that
erroneous data is received, the RX/TX tag 5a1 may transmit a signal
to the remote transceiver 4a requesting a re-transmission,
whereafter the remote transceiver 4a re-transmits the signal until
the TX/RX tag 5a1 controller 10 determines that the signal has been
received without error. If the RX/TX controller 10 continually
finds an error in the signals received from remote interrogator 4a,
and the RX/TX tag 5a1 transmits a re-transmission request signal to
the remote transceiver 4a a predetermined number of times, the
remote transceiver 4a transmits a signal back to the master
transceiver 3 indicating failure.
[0085] It should be noted that this application is intended to be
exemplary and not limiting in scope to the invention. For instance,
the master transceiver 3 can function in the same manner as
described above for the remote interrogator 4a. Moreover, although
the application is described in the context in which the remote
interrogator 4a sends a response signal to the RX/TX tag 5a1, in
some applications it may not be necessary to send a response
signal. By example, data that is received without error need not be
acknowledged back to the remote transceiver 4a.
[0086] It is desirable to have the RX/TX tags 5a1-5xx operate at a
fixed frequency. For example, FIG. 4b illustrates a preferable
approximate frequency (i.e., 2.414 GHz) of an RX tag local
oscillator. FIG. 4b also shows possible receive band schemes for
the RX/TX tag embodiment of the invention, including an ISM band
for low power receive applications, and a higher-frequency licensed
band for higher power applications.
[0087] In accordance with an aspect of this invention, because the
tags transmit for short intervals, pause, and then change to a
receive mode for a short interval, the tags operate in an
energy-efficient manner.
[0088] While the invention has been particularly shown and
described with respect to preferred embodiments thereof, it will be
understood by those skilled in the art that changes in form and
details may be made therein without departing from the scope and
spirit of the invention.
* * * * *