U.S. patent number RE43,918 [Application Number 11/864,718] was granted by the patent office on 2013-01-08 for method and apparatus for rfid communication.
This patent grant is currently assigned to Round Rock Research, LLC. Invention is credited to Rickie C. Lake, Steven F. Schicht, John R. Tuttle, Mark E. Tuttle.
United States Patent |
RE43,918 |
Tuttle , et al. |
January 8, 2013 |
Method and apparatus for RFID communication
Abstract
.[.A plurality of battery-operated transceivers encapsulated by
lamination to form a sheet of independent transceivers is tested in
a two piece fixture that forms an enclosure surrounding each
in-sheet transceiver. Each enclosure has an antenna for
transmitting a command signal to the transceiver at a known power
level and for receiving a reply message from the transceiver
containing a power level measurement made by the transceiver. Test
methods using the fixture of the present invention are also
described..]. .Iadd.An RFID tag and interrogator may each include a
transmitter and a receiver. The tag and interrogator may
communicate with each other at different frequency bands and may
communicate in accordance with a wireless communication
protocol..Iaddend.
Inventors: |
Tuttle; Mark E. (Boise, ID),
Lake; Rickie C. (Meridian, ID), Schicht; Steven F.
(Austin, TX), Tuttle; John R. (Longmont, CO) |
Assignee: |
Round Rock Research, LLC (Mt.
Kisco, NY)
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Family
ID: |
26975426 |
Appl.
No.: |
11/864,718 |
Filed: |
September 28, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10997556 |
Nov 24, 2004 |
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08306906 |
Sep 15, 1994 |
5983363 |
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07979607 |
Nov 20, 1992 |
6058497 |
|
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Reissue of: |
09437718 |
Nov 9, 1999 |
6487681 |
Nov 26, 2002 |
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Current U.S.
Class: |
714/25; 324/613;
324/605 |
Current CPC
Class: |
G01R
31/303 (20130101); G01R 31/3025 (20130101); G01R
31/01 (20130101); G06K 19/0701 (20130101); G06K
7/0095 (20130101); G01R 31/2822 (20130101) |
Current International
Class: |
G06F
11/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
USPTO Transaction History of related U.S. Appl. No. 07/979,607,
filed Nov. 20, 1992, entitled "Testing And Burn-In Of IC Chips
Using Radio Frequency Transmission," now U.S. Patent No. 6,058,497.
cited by other .
USPTO Transaction History of related U.S. Appl. No. 08/306,906,
filed Sep. 15, 1994, entitled "In-Sheet Transceiver Testing," now
U.S. Patent No. 5,983,363. cited by other .
USPTO Transaction History of related U.S. Appl. No. 09/193,002,
filed Nov. 16, 1998, entitled "Testing And Burn-In Of IC Chips
Using Radio Frequency Transmission," now U.S. Patent No. 6,161,205.
cited by other .
USPTO Transaction History of related U.S. Appl. No. 09/437,718,
filed Nov. 9, 1999, entitled "In-Sheet Teanseciever Testing," now
U.S. Patent No. 6,487,681. cited by other .
USPTO Transaction History of related U.S. Appl. No. 09/675,452,
filed Sep. 28, 2000, entitled "Testing and Burn-In of IC Chips
Using Radio Frequency Transmission," now U.S. Patent No. 6,357,025.
cited by other .
USPTO Transaction History of related U.S. Appl. No. 10/997,556,
filed Nov. 24, 2004, entitled "Method and Apparatus for RFID Label
Handling." cited by other .
USPTO Transaction History of related U.S. Appl. No. 11/864,708,
filed Sep. 28, 2007, entitled "Method and Apparatus for RFID
Communication." cited by other .
USPTO Transaction History of related U.S. Appl. No. 11/864,710,
filed Sep. 28, 2007, entitled "Method and Apparatus for RFID
Communication." cited by other .
USPTO Transaction History of related U.S. Appl. No. 11/864,715,
filed Sep. 28, 2007, entitled "Method and Apparatus for RFID
Communication." cited by other .
USPTO Transaction History of related U.S. Appl. No. 11/864,723,
filed Sep. 28, 2007, entitled "Method and Apparatus for RFID
Communication." cited by other.
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Primary Examiner: Chu; Gabriel
Attorney, Agent or Firm: Lerner, David, Littenberg, Krumholz
& Mentlik, LLP
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. 6,487,681. The reissue applications are
the initial reissue application Ser. No. 10/997,556 filed Nov. 24,
2004, a continuation reissue application Ser. No. 11/864,708 filed
Sep. 28, 2007, a continuation reissue application Ser. No.
11/864,710 filed Sep. 28, 2007, a continuation reissue application
Ser. No. 11/864,715 filed Sep. 28, 2007, another continuation
reissue application Ser. No. 11/864,723 filed Sep. 28, 2007 and the
present continuation reissue application..Iaddend.
CROSS REFERENCE TO RELATED APPLICATIONS
This application .Iadd.is .Iaddend.a .Iadd.continuation of a
reissue application Ser. No. 10/997,556, filed Nov. 24, 2004, which
is a reissue application of U.S. patent application Ser. No.
09/437,718, now U.S. Pat. No. 6,487,681, which is a
.Iaddend.continuation of application Ser. No. 08/306,906 filed Sep.
15, 1994, now U.S. Pat. No. 5,983,363, which is a continuation in
part of and claims priority from U.S. patent application Ser. No.
07/979,607 filed Nov. 20, 1992, now U.S. Pat. No. 6,058,497.Iadd.,
and the teachings of all of which are incorporated by reference
herein.Iaddend..
Claims
What is claimed is:
.[.1. A method of testing the RF communication operation of an RF
transponder, comprising the steps of: providing a sheet
characterized by first and second opposite faces and a thickness;
mounting on the sheet an RF transponder that includes a transponder
RF antenna; positioning a first RF shield so as to abut the first
face of the sheet; positioning a second RF shield so as to abut the
second face of the sheet, the second RF shield being in the shape
of a cup having a mouth abutting said second face, wherein the
first and second RF shields are positioned so that the first and
second RF shields together form a closed cavity which completely
surrounds and encloses the transponder RF antenna except where the
thickness of the sheet separates the first RF shield from the mouth
of the second RF shield, wherein said thickness is sufficiently
small so that the first and second RF shields prevent any RF
signals within the cavity from radiating outside the cavity;
positioning a test fixture RF antenna within the cavity;
transmitting an RF signal from the test fixture antenna; detecting
a response by the transponder to the RF signal; and subsequently
removing the transponder from proximity to the first and second
shields and the test fixture RF antenna, so that no shielding
obstructs the transponder RF antenna from sending and receiving RF
radiation at any angle..].
.[.2. A method according to claim 1, wherein the cavity encloses
the entire RF transponder..].
.[.3. A method according to claim 1, wherein the sheet has no
shielding mounted thereon that obstructs RF radiation from the
transponder RF antenna..].
.[.4. A method according to claim 1, wherein: the first RF shield
is in the shape of a cup having a mouth abutting the first face;
and the step of positioning the second RF shield further comprises
aligning the mouth of the second shield with the mouth of the first
shield..].
.[.5. A method according to claim 1, wherein the step of
positioning the test fixture RF antenna within the cavity
comprises: mounting the test fixture RF antenna to a surface of one
of the two RF shields; connecting an RF transmission line to the
test fixture RF antenna; and passing the transmission line through
an opening in said one RF shield to extend outside the
cavity..].
.[.6. A method according to claim 1, further comprising the step
of: fabricating the sheet to include electrically conductive
material adjacent the mouth of the second RF shield so as to
improve RF shielding of the cavity..].
.[.7. A method according to claim 1, wherein the RF signal is
transmitted at a predetermined wavelength, and wherein the RF
shields are dimensioned to improve the gain of the cavity at that
wavelength..].
.[.8. A method according to claim 1, wherein the RF signal is
transmitted at a predetermined wavelength, and wherein the RF
shields are dimensioned so that the cavity resonates at that
wavelength..].
.[.9. A method of testing the RF communication operation of a
plurality of RF transponders, comprising the steps of: providing a
sheet characterized by first and second opposite faces and a
thickness; mounting on the sheet a plurality of RF transponders,
wherein each transponder includes a transponder RF antenna;
positioning a first test fixture section having a first RF shield
so that the first RF shield abuts the first face of the sheet;
positioning a second test fixture section so as to abut the second
face of the sheet, wherein: the second test fixture section
includes a plurality of RF shields, each RF shield in the second
test fixture section is in the shape of a cup having a mouth
abutting said second face of the sheet, the first and second test
fixture sections so that each RF shield in the second test fixture
section encircles a corresponding one of the transponder RF
antennas so as to form, in combination with the first RF shield, a
closed cavity that completely surrounds and encloses said
corresponding transponder RF antenna except where the thickness of
the sheet separates the first RF shield from the mouth of said RF
shield in the second test fixture section, and said thickness is
sufficiently small so that the first and second RF shields prevent
any RF signals within the cavity from radiating outside the cavity;
positioning within each cavity a corresponding test fixture RF
antenna; transmitting an RF signal from each test fixture antenna;
detecting a response by each transponder to the RF signal
transmitted by its corresponding test fixture antenna; and
subsequently removing each transponder from proximity to the first
and second test fixture sections and the test fixture RF antennas,
so that no shielding obstructs each transponder RF antenna from
sending and receiving RF radiation at any angle..].
.[.10. A method according to claim 9, wherein the each cavity
encloses the entire corresponding RF transponder..].
.[.11. A method according to claim 9, wherein: the first RF shield
is in the shape of a plurality of cups so that each cup has a mouth
abutting the first face of the sheet; and the step of positioning
the second RF shield further comprises aligning each mouth of the
second shield with a corresponding mouth of the first
shield..].
.[.12. A test fixture for testing the RF communication operation of
an RF transponder which is mounted on a sheet which extends beyond
the perimeter of the transponder, the RF transponder having an
antenna for receiving RF signals, comprising: first and second RF
shields, the second RF shield being in the shape of a cup having a
mouth; an alignment mechanism for positioning the first and second
RF shields to abut opposite sides of the sheet so that the mouth
encircles the transponder antenna and so that the combination of
the first and second RF shields forms a closed cavity completely
surrounding and enclosing the transponder antenna except where the
sheet separates the two RF shields, wherein the distance by which
the sheet separates the two RF shields is small enough to prevent
any RF signals within the cavity from radiating outside the cavity;
and a test fixture RF antenna mounted within the cavity..].
.[.13. A test fixture according to claim 12, further comprising: a
test fixture RF transmitter having an output connected to the test
fixture RF antenna so that the RF antenna radiates RF signals to
the transponder RF antenna; and a test fixture RF receiver having
an input connected to the test fixture RF antenna so that the RF
receiver receives any responses transmitted by the RF transponder
in response to said RF signals..].
.[.14. A test fixture according to claim 12, wherein the cavity
encloses the entire transponder..].
.[.15. A test fixture according to claim 12, wherein: the first RF
shield is in the shape of a cup having a mouth abutting the first
face; and the alignment mechanism aligns the mouth of the second
shield with the mouth of the first shield..].
.[.16. A method according to claim 12, further comprising: an RF
transmission line connected to the test fixture RF antenna; wherein
the transmission line extends through an opening in one of the RF
shields so as to extend outside the cavity..].
.[.17. A test fixture according to claim 12, further comprising a
test fixture RF transmitter for providing to the transponder
antenna RF test signals having a predetermined wavelength, wherein
the first and second RF shields are dimensioned to improve the gain
of the cavity at that wavelength..].
.[.18. A test fixture according to claim 12, further comprising a
test fixture RF transmitter for providing to the transponder
antenna RF test signals having a predetermined wavelength, wherein
the first and second RF shields are dimensioned so that the cavity
resonates at that wavelength..].
.[.19. A test fixture for testing the RF communication operation of
a plurality of RF transponders mounted on a sheet, each RF
transponder having an RF antenna, comprising: a first test fixture
section including a first RF shield; a second test fixture section
including a plurality of RF shields each of which is in the shape
of a cup having a mouth; an alignment mechanism for positioning the
first and second test fixture sections to abut opposite sides of
the sheet so that each RF shield in the second test fixture section
encircles a corresponding one of the transponder antennas so as to
form, in combination with the first RF shield, a closed cavity that
completely surrounds and encloses said corresponding transponder RF
antenna except where the sheet separates the first RF shield from
the mouth of said RF shield in the second test fixture section,
wherein the distance by which the sheet separates the first RF
shield from each RF shield of the second test fixture section is
small enough to prevent any RF signals within each cavity from
radiating outside that cavity; and a test fixture RF antenna
mounted within each cavity..].
.[.20. A test fixture according to claim 19, wherein: the first RF
shield is in the shape of a plurality of cups so that each cup has
a mouth abutting the sheet; and the alignment mechanism aligns each
mouth of the second shield with a corresponding mouth of the first
shield..].
.Iadd.21. A system for performing radio frequency communications,
the system comprising: one or more first antennas; an interrogator
communicatively coupled to the one or more antennas to transmit a
first command; and a radio frequency identification (RFID) tag
comprising: one or more second antennas, at least one of the one or
more second antennas being a dipole antenna; a battery; a random
number generator to generate one or more random numbers; and
processing circuitry electrically coupled to the one or more
antennas, the battery, and the random number generator, the
processing circuitry configured to operate in a first state and a
second state that uses more battery power than the first state, and
a second state that uses more battery power than the first state,
the processing circuitry further configured to transition from the
first state to the second state upon receipt of the first command
and to communicate a message to the interrogator at a time based at
least in part on a first random number generated by the random
number generator..Iaddend.
.Iadd.22. The system of claim 21, wherein the message comprises at
least one random number generated by the RFID tag..Iaddend.
.Iadd.23. The system of claim 22, wherein the interrogator is
further configured to transmit at least an additional command
including the at least one random number to identify the RFID
tag..Iaddend.
.Iadd.24. The system of claim 21, wherein the interrogator is
further configured to transmit at least a second command that
includes a selection indicator, and the processing circuitry is
further configured to communicate the message if the selection
indicator corresponds to one or more bits stored on the RFID
tag..Iaddend.
Description
FIELD OF THE INVENTION
This invention relates to transponder testing and to test systems,
fixtures, and methods for testing transponders.
BACKGROUND OF THE INVENTION
As an introduction to the problems solved by the present invention,
consider the conventional transponder used for radio frequency
identification (RFID). Such a transponder includes a radio
transceiver with a built-in antenna for receiving command message
signals and for transmitting reply message signals. Inexpensive
transponders find application in systems for tracking material,
personnel, and animals, inventory management, baggage handling, and
the mail to name a few major areas.
A transponder necessarily includes a transceiver. Such transponders
may include an integrated circuit transceiver, a battery, and a
printed circuit antenna hermetically encapsulated in a laminated
package about 1 inch square and approximately as thick as a mailing
label or tag. In such a laminated package, manufacturing acceptance
tests on each unit become difficult and costly.
Conventional transponders are inexpensively manufactured in sheets
having for example 250 integrated circuit transceivers spaced apart
in a row and column array between polymer films. Prior to use, the
transponders are separated from each other by shearing the sheet
between adjacent rows and columns. Conventional testing methods and
apparatus cannot be used until the transponders are separated from
each other.
Conventional manufacturing acceptance tests for transponders are
based in part on antenna performance tests that simulate the
application in which the transponder will be used. These so called
"far-field" tests require a large anechoic chamber and individual
testing of a single transponder at a time. Such far-field testing
adds significantly to the per unit cost of inexpensive
transponders.
Without inexpensive transponder testing for manufacturing
acceptance tests, incomplete testing may perpetrate unreliable
tracking, inventory, and handling systems, increase the cost of
maintaining such systems, and discourage further development and
popular acceptance of transponder technology.
In view of the problems described above and related problems that
consequently become apparent to those skilled in the applicable
arts, the need remains in transponder testing for more accurate and
less costly test systems, fixtures, and test methods.
SUMMARY OF THE INVENTION
Accordingly, a test system in one embodiment of the present
invention includes a fixture, an interrogator, and a switch
cooperating for testing a sheet containing a plurality of
transceivers, each transceiver within a contour on the sheet. The
fixture, in one embodiment, admits a sheet of transceivers and
surrounds each transceiver at its contour so that each transceiver
is respectively enclosed within an enclosure. Within each enclosure
is an antenna for so called "near-field" communication. The
interrogator determines a command signal and evaluates reply
signals from each transceiver. The switch is coupled in series
between each antenna and the interrogator for selecting an antenna
for transmitting the command signal and for receiving the reply
signal.
According to a first aspect of such an embodiment, the fixture
isolates transceivers from each other so that multiple transceivers
are tested simultaneously. By isolating each transceiver,
interference from adjacent transceivers is minimized, transponder
identity and location are not confused, and test transmissions are
prevented from affecting external equipment including other test
stations.
According to another aspect, testing is facilitated by isolating
each transceiver at its contour.
According to another aspect, multiple transceivers are moved as a
sheet and tested without further handling so that rapid testing is
feasible and delays for physical alignment of the transceivers
within the fixture is minimized.
According to another aspect, near-field testing is used to
eliminate the need for large chambers.
According to another aspect of such a test system, the transfer
function of the antenna and detector portion of a transceiver
receiver is tested.
The present invention is practiced according to a method in one
embodiment which includes the steps of providing an enclosure that
admits a sheet of transceivers, each transceiver formed within a
respective region of the sheet, closing the enclosure to form an RF
seal about each respective region, and operating each transceiver
for receiving and transmitting signals.
According to a first aspect of such a method, independent testing
of individual transceivers is accomplished for in-sheet
transceivers and multiple transceivers are tested
simultaneously.
According to another aspect, far-field tests are used to confirm
the test signal used in manufacturing tests.
A method, in an alternate embodiment, for testing battery-operated
transceivers includes the step of transmitting a wake up signal to
a transceiver. According to a first aspect of such a method, only
transceivers under test are made operational so that battery power
is conserved in other transceivers.
These and other embodiments, aspects, advantages, and features of
the present invention will be set forth in part in the description
which follows, and in part will become apparent to those skilled in
the art by reference to the following description of the invention
and referenced drawings or by practice of the invention. The
aspects, advantages, and features of the invention are realized and
attained by means of the instrumentalities, procedures, and
combinations particularly pointed out in the appended claims.
.Iadd.An RFID tag and interrogator may each include a transmitter
and a receiver. The tag and interrogator may communicate with each
other at different frequency bands and may communicate in
accordance with a wireless communication protocol..Iaddend.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a test system of the present
invention.
FIG. 2 is a functional block diagram of the test system of FIG.
1.
FIG. 3 is a functional block diagram of a transponder of the
present invention to be tested in the test system of FIG. 1.
FIG. 4 is a cross sectional view of fixture 15.
A person having ordinary skill in the art will recognize where
portions of a diagram have been expanded to improve the clarity of
the presentation.
In each functional block diagram, a broad arrow symbolically
represents a group of signals that together signify a binary code.
For example, a group of bus lines is represented by a broad arrow
because a binary value conveyed by the bus is signified by the
signals on the several bus lines taken together at an instant in
time. A group of signals having no binary coded relationship is
shown as a single line with an arrow. A single line between
functional blocks represents one or more signals.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a plan view of a test system of the present invention.
Test system 10 provides manufacturing acceptance tests for an
in-sheet transponder 12 provided on continuous roll 20 of laminated
films. Transponders under test are located in fixture 15. Tested
transponders are received on roll 22. Fixture 15 is connected by
cable 18 to subsystem 24 so that signals generated by
instrumentation in subsystem 24 are coupled to fixture 15 and so
that signals received in fixture 15 are coupled to instruments in
subsystem 24 for analysis. Subsystem 24 includes interrogator 25
and computer 86, cooperating for signal generation and analysis.
Fixture 15 is characterized, according to a method of the present
invention, using a correlation to far-field testing.
Characterization of a system, fixture, or circuit conventionally
includes making measurements of characteristic features of its
structure and operation.
Transponders to be tested in an alternate embodiment are provided
to fixture 15 in separated sheets, each sheet having an array of
rows and columns of transponders. For example in one embodiment,
about 250 transponders are manufactured in a sheet measuring about
18 inches by about 24 inches.
Test system 10 also includes materials handling equipment, not
shown, for supplying sheets or rolls of transponders for testing,
for aligning transponders within fixture 15, and for receiving
tested transponders for further manufacturing steps. In one
embodiment, individual tested transponders are separated
(singulated) from the sheet in which testing occurred and are
provided on an adhesive backing for distribution as tape-and-reel
components or ready-to-use articles such as baggage tags, inventory
labels, or badges, to name a few feasible applications.
Roll 20 includes a plurality of identical transponders, such as
transponder 12. Transponder 12 is a radio frequency identification
(RFID) device of the type described in U.S. patent application Ser.
No. 07/990,918 by Snodgrass et al. filed Dec. 15, 1992,
incorporated herein by reference. In one embodiment, transponder 12
is about 1 inch square, includes a lithium battery, an integrated
circuit transceiver, and an antenna packaged using thin film and
lamination techniques.
FIG. 2 is a functional block diagram of a test system of the
present invention. Test system 10 includes six major functional
elements: operator console 26, test system computer 86,
interrogator 25, radio frequency (RF) switch 92, fixture 15, and
material handling apparatus 90.
In operation, test system computer 86 directs material handling
apparatus 90 to align a sheet of transponders (not shown) within
fixture 15. Alignment assures that each transponder is isolated
from other transponders in a manner to be discussed with reference
to FIG. 4. In one embodiment, alignment includes automatic
recognition by video camera of guide marks on the sheet and control
of stepper motors according to software performed by computer 86 or
in an alternate embodiment by a computer in material handling
apparatus 90. One of ordinary skill will recognize that alignment
includes the location of the fixture relative to the sheet so that
the fixture, the sheet, or both can be repositioned to accomplish
proper alignment.
When a sheet of transponders is aligned, computer 86 directs RF
switch 92 for independently testing individual transponders. In a
first embodiment, one transponder is tested at a time. In an
alternate embodiment, multiple interrogators are coordinated to
test multiple transponders simultaneously. Independent transponder
operation during simultaneous testing of multiple transponders is
accomplished in part by isolation provided by fixture 15.
During tests of each transponder, computer 86 directs interrogator
25, particularly interrogator central processing unit (CPU) 84, to
generate and transmit via transmitter 82 command messages through
switches 91 and 92, and to receive and interpret reply messages
generated by that transponder that are conveyed through RF switch
92 and switch 91 to receiver 83. Interrogator 25 is of the type
described in U.S. patent application Ser. No. 07/990,918 by
Snodgrass et al. filed Dec. 15, 1992, incorporated herein by
reference. Switch 91 and switch 92 are coax switches, common in the
RF testing art. In alternate embodiments, switch 91 is eliminated
and command and reply messages are separated by communication
techniques known in the art, for example separation by time
division or use of different frequency bands or different
modulation techniques.
In one embodiment of the present invention, a test of the
sensitivity of the receiver portion of the transceiver portion of a
transponder under test includes transmitting from interrogator 25 a
test signal, for example, a command message at a test power level.
Transponders that fail to respond by transmitting a proper reply
message fail the test at a first point. In another embodiment, the
reply message includes a measurement of the signal strength seen by
the receiver portion of the transponder under test. Transponders
that report measurements of received signal strength that do not
exceed an expected signal strength fail the test at a second point.
By setting both test points as requirements, the population of
tested transponders is of higher quality because marginal units are
rejected. Therefore, the determination of the test power level and
the expected signal strength are important to production and
application economics.
Fixture 15 surrounds each transponder so that each transceiver's
antenna is within one enclosure. In one embodiment, the enclosure
surrounds an entire transponder and a small volume of ambient air
so that the enclosure forms a cavity. In an alternate embodiment,
only the transceiver's antenna is enclosed. In yet another
alternate embodiment, the small volume is filled with potting
material so that, for example, the cleanliness of the enclosure and
the position of the antenna within the enclosure are maintained. In
one embodiment, the potting material includes polyimide. In
alternate embodiments, conventional potting materials and
conventional materials used for films for encapsulating the
transponder are used. The power level to be used for each so
enclosure depends on the materials and dimensions of the enclosure
and the transponder.
To determine the test power level appropriate for one of several
enclosures formed by fixture 15, far-field test results are
correlated to conventional characterization tests of the
transponder, potting material (if any), and the enclosure. By
repeating characterization tests in each enclosure, a so called
cavity transfer function relating test power level to received
signal strength is determined for each enclosure of fixture 15.
FIG. 3 is a functional block diagram of a transponder of the
present invention to be tested in the test system of FIG. 1.
Transponder 12 includes battery 120, antenna 110, transceiver 115,
multiplexer 122, analog to digital (A/D) converter 124, and central
processing unit (CPU) 126. Transceiver 115 includes
transmit/receive switch 112, receiver 114, and transmitter 128.
Transponder 12 operates from battery power provided by battery 120.
All functional blocks are coupled to receive battery power signal
VB.
In operation, CPU 126 directs multiplexer 122 to select one of
several analog signals for conversion. For example, when a report
of battery voltage is desired, line 121 is selected and coupled to
A/D converter 124. In response to a signal on line 123, A/D
converter 124 provides a digital signal on line 125 to CPU 126. CPU
126 then forms a message signal on line 127 and directs
transmission by transmitter 128 through switch 112 and antenna
110.
Except for antenna 110 and battery 120, the circuitry of
transponder 12 is conventionally formed as an integrated circuit,
manufactured in large number on a wafer. In a preferred test method
of the present invention, some manufacturing acceptance tests are
conducted after fabrication of a wafer containing perhaps a
thousand independent integrated circuits. For example, the
conversion accuracy of A/D converter 124 varies from wafer to wafer
depending on variations in the fabrication process. Prior to
forming dice from the wafer, all or a representative sample of A/D
converters, are tested by introducing stimulus signals and
obtaining response signals via wafer probes, as is well known in
the art. Test results are generalized to determine an A/D transfer
function relating signals 123 and 125 for the A/D converters on a
particular wafer.
Operation of transponder 12 includes at least two modes of
operation. In a first mode, power is conserved by disabling most
transponder circuits. When a wake up signal is received by antenna
110, coupled to receiver 114 through switch 112, detected and
demodulated by receiver circuit 118, and interpreted by CPU 126 as
a proper wake up signal, transponder 12 enters a second mode of
operation. In the second mode, power is applied to substantially
all transponder circuitry for normal operation. In a preferred
embodiment, the test signal is both a wake up signal and a request
for a report of received signal strength.
Receiver 114 includes detector 116 for detecting received signal
strength. Antenna 110 is coupled through switch 112 to convey an RF
signal on line 130 to detector 116. Detector 116 provides on line
117 to multiplexer 122 signal RSS1 proportional to received signal
strength. When a report of received signal strength is desired,
line 117 is selected and signal RSS1 is coupled to A/D converter
124. In response to a signal on line 123, A/D converter 124
provides a digital signal on line 125 to CPU 126. CPU 126 then
forms a message signal on line 127 and directs transmission by
transmitter 128 through switch 112 and antenna 110.
FIG. 4 is a cross sectional view of fixture 15. Fixture 15 includes
first section 14, second section 16, and an antenna in each
enclosure (or cavity). For example, cavities 71, 72 and 74 are
shown with antenna 66 in cavity 72. First section 14 includes a
matrix of ridges, for example 52 and 56. Second section 16 includes
a matching matrix of ridges, for example 54 and 58. Each pair of
ridges for example 56 and 58 separates and defines adjacent
cavities, for example cavities 72 and 74.
The upper surface of ridges 54 and 58 in second section 16 define a
horizontal plane onto which a portion of roll 20 of laminated films
is positioned. When that portion includes in-sheet transponders,
material handling apparatus position the portion for in-sheet
transponder testing. First section 14 and second section 16 are
then pressed together against sheet 20 so that each transponder,
for example transponder 51, is isolated from each other transponder
in sheet 20. Ridges about each cavity form an RF seal.
The RF seal provides isolation. Isolation prevents RF energy
radiated from antenna 66 in cavity 72 from interfering with tests
conducted in adjacent cavity 74. The RF seal is not perfect and,
therefore, isolation is not perfect, due to leakage for example
between ridges 52 and 54 and between 56 and 58. Since leakage RF
energy must pass through films 44 and 46, conventional shielding in
the neighborhood of the contact between adjacent ridges is
effective to further reduce leakage and thereby improve isolation.
Such shielding includes placement of conductors and conductive
materials within, between, and on the surfaces of films 44 and
46.
Isolation is operative to decouple an antenna in one enclosure from
an antenna in an adjacent enclosure. From the point of view at
antenna 66, when a signal originating in cavity 72 is stronger than
a signal originating in cavity 74, for example, the signal sources
and their respective antennas are considered decoupled from each
other. Decoupling can also be accomplished by improving the gain of
cavity 72, for example, by making its dimensions compatible with a
wavelength of the signal originating in cavity 72.
In an alternate embodiment, first section 14 and second section 16
are fabricated as flat plates having no ridges 52, 54, 56, or 58.
The distance between these plates is smaller than one wavelength of
the signal originating in cavity 72 so that adjacent transponder
antennas are effectively decoupled for purposes including
manufacturing acceptance testing. In such an embodiment, first
section 14 and second section 16 sandwich the sheet
therebetween.
In a preferred embodiment, each transponder is formed within a
square contour and each cavity has a matching square cross section
so that transponders are isolated each one at its contour. In this
sense, a contour extends through both films 44 and 46 to
circumscribe one transponder. In a mathematical sense, a contour is
defined on a surface. Since top film 44 has an upper surface, a
first contour is defined on that top surface. Since bottom film 46
has a bottom surface, a second contour is defined on that bottom
surface. The square cavity formed by ridges 54 and 58 in the second
section is circumscribed by a third contour in the plane defined by
the tops of the ridges on which the sheet is positioned. Thus,
alignment includes positioning the sheet and the fixture so that
the third contour formed on ridges 54 and 58 touches the sheet at
the second contour on the bottom of film 46. When properly aligned,
the first section, having a similar fourth contour on ridges 52 and
56, touches the first contour on the top of film 44. In a preferred
embodiment, the first and second contours are directly opposed
through the sheet. In alternate embodiments, ridges 52 and 54 touch
film 44 along a sloped, concave, notched, or stepped surface for
greater isolation. In such embodiments, important contours are not
necessarily directly opposed.
Transponder 51 is identical to transponder 12 as previously
described. Transponder 51 is of the type described as an enclosed
transceiver in U.S. patent application Ser. No. 08/123,030, filed
Sep. 14, 1993, incorporated herein by reference. The
cross-sectional view of transponder 51 shows integrated circuit 48
and battery 50 between film 44 and film 46. Integrated circuit 48
includes the transceiver circuitry of transponder 51. Battery 50,
in one embodiment, includes a metal surface coupled to operate as
part of the antenna for the transceiver circuitry. Additional
conductive traces on film 44 and film 46 cooperate for coupling
battery power to integrated circuit 48 and for operation as part of
the antenna for the transceiver. Films 44 and 46 are sealed to each
other around a contour that encircles integrated circuit 48 and
battery 50. In one embodiment, the seal is made by embossing so
that the thickness of films 44 and 46 is reduced as shown at seal
42. After testing, transceiver 51 is separated from the sheet by
cutting through films 44 and 46 at a point outside seal 42 so that
transceiver 51 remains sealed after testing.
The central internal conductor of coax cable 70 is extended into
cavity 72 for operation as a near-field antenna. Feed through
fitting 68 holds coax cable 70 onto second section 16, shields the
central conductor, and provides continuity of impedance from cable
70 up to antenna 66.
The amount of radiation coupled between antenna 66 and transponder
51 depends in part on several variables including the dimensions of
cavity 72, the wavelengths of the radiated signals, potting or
other materials (if any) within the enclosure, and the distance
between antenna 66 and film 46. Although the location of
transponder 51 is controlled by maintaining tension on sheet 20 as
first section 14 is pressed against second section 16, these
variables are expected to vary to some extent from cavity to
cavity, from test to test, and over time with wear and handling of
fixture 15 and operation and wear in materials handling apparatus
used to position fixture 15, sheet 20, or both.
In a preferred embodiment, antenna 110 of transponder 12 is a
square loop antenna for communication at about 2.45 gigahertz. The
wavelength at that frequency is about 12.2 centimeters or about
4.82 inches. One of ordinary skill in the art will understand that
cavity dimensions discussed above must lie outside the loop
antenna. Conventional simulation may be used to arrive at
sufficient or optimal dimensions of the cavity and sufficient or
optimal dimensional characteristics of the antenna, including its
placement and type (dipole, loop, stub, Marconi, etc).
According to a method of the present invention, the magnitude of
signal 117 as shown in FIG. 3 is determined so that the effect of
variation in the variables discussed above is removed from
transponder test results and the pass rate for tested transponders
is improved. Such a method begins with a first step of
characterizing the encapsulated transponder with far-field tests.
Before transponder 51 is tested in fixture 15, the digitization
transfer function for analog to digital converter 124 shown in FIG.
3 is determined in a second step. As with the first step, in this
second step 1, a desired level of accuracy for manufacturing
acceptance tests is achieved using one of several approaches
including design simulation, theoretical analysis, tests of a
prototype, tests of representative samples, or tests of every
transponder. In a preferred embodiment, sufficient accuracy is
obtained for a manufacturing lot of transponders by conducting
wafer probe tests for the second step.
In a third step, the cavity is characterized by design simulation,
theoretical analysis, or conventional tests.
Fourth, a prototype or representative transponder 51 is placed in
the cavity shown in FIG. 4 that was characterized in the third
step. In a fifth step, a pass/fail test power level and the
expected reported signal strength are determined by analysis of the
results of tests made with the representative transponder, the
characterization data, and the results of simulation and other
techniques known in the art. Together the process of determining in
this fifth step is defined as correlating far-field measurements
with transceiver responses.
After test power level and response data are determined,
manufacturing acceptance testing can proceed by replacing the
representative transponder with an untested transponder 51. While
in the cavity and isolated from other transponders, several tests
are performed including a receiver sensitivity test.
A receiver sensitivity test of the present invention includes the
following steps: radiating a test signal from antenna 66;
converting analog signal RSS1 received by antenna 110 to a digital
result on line 125; transmitting, by means of transmitter 128 and
antenna 110, a message conveying the digital result; receiving the
message via antenna 66; and making a pass/fail determination based
on the response (if any) from the untested transponder. As one
result, defects in antenna 110, switch 112, and receiver circuit
118 are made apparent.
The foregoing description discusses preferred embodiments of the
present invention, which may be changed or modified without
departing from the scope of the present invention.
For example, the orientation and shape of fixture 15 as two plates
as shown in FIGS. 1 and 4 in alternate and equivalent embodiments
are modified for cooperation with material handling apparatus, not
shown. In one such modified orientation, the plane at which first
section 14 and second section 16 meet is vertical rather than
horizontal. In one such modified shape, the fixture has a spherical
shape (rather than generally hexahedral), each contour surrounding
a transponder is circular (rather than square), and each cavity is
spherical (rather than generally hexahedral). In other embodiments,
antenna 66 is located in various positions including, for example,
in an opposite section of a cavity, within a ridge, in an adjoining
cavity not completely isolated by ridges, or (for multiple antennas
per cavity) at several of these locations.
Still further, those skilled in the art will understand that first
section 14, second section 16, or both in alternate and equivalent
embodiments are formed along an axis of turning to permit advancing
a portion of sheet 20 as a portion of the fixture turns about its
axis. In one embodiment, such movement moves and aligns sheet
20.
In a preferred embodiment, a microwave frequency band is used for
transponder communication. The same band is used for transponder
testing. In alternate embodiments that a person skilled in the art
with knowledge of the teachings of the present invention would
recognize as equivalents, another one or more frequency bands are
utilized.
As still another example, the complexity of transponder 12 shown in
FIG. 3 in alternate embodiments is simplified. Without departing
from the scope of the present invention, for example, transmitter
128 is replaced with a transmitter responsive to an analog instead
of a digital input, receiver circuit 118 is replaced with a circuit
providing an analog rather than a digital output, analog to digital
converter 124 is eliminated and CPU 126 is replaced with an analog
rather than a digital circuit.
These and other changes and modifications known to those of
ordinary skill are intended to be included within the scope of the
present invention.
While for the sake of clarity and ease of description, several
specific embodiments of the invention have been described; the
scope of the invention is intended to be measured by the claims as
set forth below. The description is not intended to be exhaustive
or to limit the invention to the form disclosed. Other embodiments
of the invention will be apparent in light of the disclosure to one
of ordinary skill in the art to which the invention applies.
The words and phrases used in the claims are intended to be broadly
construed. A "system" refers generally to electrical apparatus and
includes but is not limited to rack and panel instrumentation, a
packaged integrated circuit, an unpackaged integrated circuit, a
combination of packaged or unpackaged integrated circuits or both,
a microprocessor, a microcontroller, a memory, a register, a
flip-flop, a charge-coupled device, combinations thereof, and
equivalents.
A "signal" refers to mechanical and/or electromagnetic energy
conveying information. When elements are coupled, a signal is
conveyed in any manner feasible with regard to the nature of the
coupling. For example, if several electrical conductors couple two
elements, then the relevant signal comprises the energy on one,
some, or all conductors at a given time or time period. When a
physical property of a signal has a quantitative measure and the
property is used by design to control or communicate information,
then the signal is said to be characterized by having a "magnitude"
or "value." The measure may be instantaneous or an average.
.Iadd.The following disclosure corresponds to the Detailed
Description Section and figures of U.S. Pat. No. 5,365,551 (the
'551 patent) incorporated by reference above. FIG. 1 of the '551
patent is a functional block diagram of communication system 30 of
the present invention as described in the '551 patent. In FIG. 1 of
the '551 patent, commander stations 10 and 34 and responder
stations 40 and 36 are coupled to common medium 32 by network
interfaces 26 and 60, respectively. In practice, a plurality of
commander and responder stations would be distributed
geographically. The type of medium selected for communication
depends on the communication system application; see below for
equivalent variations. The embodiment depicted in FIG. 1 of the
'551 patent illustrates the invention in an application such as
airport baggage handling. For this embodiment, the medium is free
space through which radio frequency communication are
transmissible..Iaddend.
.Iadd.Commander station 10 is designed to achieve a flexible system
architecture while incorporating many commercially available
components. Commander station 10 includes personal computer system
12 having data and control bus 14 shared by central processor 16,
memory 18, and peripheral controllers 20a and 20c. Monitor 22, disk
drive 24, and network interface 26 connect to individual peripheral
controllers 20a-20c via connecting signals 28a-28c, respectively.
Network interface 26 is coupled to common medium 32. Network
interface 26 could be implemented in a chassis separate from the
chassis of personal computer system 12 or equivalently could be
implemented in combination with the functions of the network
interface peripheral controller 20c for connection directly to data
and control bus 14..Iaddend.
.Iadd.The configuration of commander station 10 illustrates several
advantages. Communication system configuration and operation are
largely dictated by software loaded via disk drive 24, stored in
memory 18, and performed by central processor 16. Disk drive 24,
memory 18, central processor 16, as well as monitor 22 and
peripheral controllers 20a20c are all conventional, general
purpose, and readily available apparatus. Therefore, additional
functions and changes to communication system 30 can be made in
software with little or no mechanical changes to commander station
10. The operation of commander station software will be discussed
below..Iaddend.
.Iadd.Responder station 40 is designed for minimal circuitry to
achieve, among other things, small size and low power consumption.
Small size permits convenient use, for example, as a baggage tag.
Low power consumption permits further size reduction and reduces
manufacturing and operating costs. Small size and low manufacturing
costs combine to permit implementing responder station 40 as a
convenient, dispensable, throwaway item such as a baggage tag,
package label, or the like..Iaddend.
.Iadd.In essence, microsequencer 42 forms the core of responder
station 40. Microsequencer 42 is a read only memory that produces
data signal 48 in response to address signal 44. In operation, a
value is presented as address signal 44 once every period of clock
signal 46. Data signal 48 from microsequencer 42 is stored in state
register 50 once every period of clock signal 46. The output of
state register 50 is state signal 52, which forms control bus 54.
Control bus 54 causes register transfer operations to be described
below. A portion of state signal 52 defines a portion of address
signal 44. Thus, a sequence of state transitions occurs in
synchronism with clock signal 46 as defined by the internal
operation of microsequencer 42 and other signals together
comprising address signal 44, as will be described below. A state
transition diagram is also discussed below. In the typical
microsequencer, internal multiplexers reduce the range of read only
memory addresses that would otherwise be required. Microsequencer
42 is of a class of devices described by Charles Belove in
"Handbook of Modern Electronics and Electrical Engineering," pp
2135-2142, published by John Wiley & Sons, New York, N.Y.
(1986), incorporated herein by reference; and by Y. Chu in
"Computer Organization and Microprogramming," published by
Prentice-Hall, Englewood Cliffs, N.J. (1972) incorporated in full
herein by reference..Iaddend.
.Iadd.Network interface 60 of responder station 40 is coupled to
common medium 32 in a way similar to the coupling of network
interface 26 of commander station 10 to common medium 32. Network
interface 60 connects to state register 50 to supply clock signal
46. Network interface 60 connects to control bus 54 so that send
and receive operations are directed in part by state signal 52.
When microsequencer 42 is in an appropriate state, data received by
network interface 60 is transferred from network interface 60 to
command register 56 by data bus 62 in conjunction with load signal
58. Command register output 59 defines a portion of address signal
44. Network interface 60 also connects via data bus 62 to memory
64, register array 66, flag register 84, and random number
generator 90 for transfer of data between these function blocks,
for storage of received data, and for recall of data to be
sent..Iaddend.
.Iadd.In one embodiment, data bus 62 is byte-wide. Network
interface 60 converts received data from serial to byte-parallel
organization. The several devices that connect to data bus 62 make
a byte-parallel connection..Iaddend.
.Iadd.In another embodiment, data bus 62 is bit-serial. Control bus
54, in such an embodiment, includes serial clock signal (not
shown), Register transfer among network interface 60, register
array 66, memory 64, flag register 84, and random number generator
90 are accomplished in bit-serial fashion with appropriate
electrical interfaces known in the art..Iaddend.
.Iadd.In yet another embodiment, a combination of serial and
parallel data paths are implemented. The system designer's choices
of serial or parallel as well as the number of bits per register
transfer operation, depends on factors including system and device
timing limitations, noise immunity, power dissipation, device size,
topology, and layout constraints..Iaddend.
.Iadd.Memory 64 connects to read/write signal 68 and memory address
signal 70 which are part of control bus 54. Memory 64 is used to
store values for responder station identification and data related
to the communication system application. For example, when a
responder station is used as an airline baggage tag, postal mailing
label, or inventory control tag, memory 64 would store data
describing a destination for the item to which the tag is
attached..Iaddend.
.Iadd.Register array 66 performs functions similar to a multi-port
memory. Register array 66 connects to arithmetic-logic unit (ALU)
72 for the presentation of operand signals 74 and 76, and storage
of result signal 78. Operand and result signals are multi-bit
digital signals for arithmetic operations such as addition,
bit-wise parallel logical operations such as logical-AND, and
bit-wise serial operations such as shift-left. Register array 66
connects to control bus 54 so that registers to be coupled to
operand and result signals are selected and stored according to
state signal 52..Iaddend.
.Iadd.In addition to the connections already described, a portion
of control bus 54 connects to ALU 72 to supply opcode signal 80 to
ALU 72. Opcode signal 80 selects one of a plurality of possible
operations to be conducted by ALU 72. When an equality comparison
has been selected by opcode signal 80 and operand signals 74 and 76
are bitwise identical, A=B signal 82 is asserted by ALU 72. A=B
signal 82 defines a portion of address signal 44..Iaddend.
.Iadd.Control bus 54 connects to individual bits arranged in flag
register 84. Addressed-bit 86, part of flag register 84, is set
under control of state signal 52 to indicate whether responder
station 40 has been addressed in a received command message.
Locked-bit 88, also part of flag register 84, is set under control
of state signal 52 to indicate whether responder station 40 should
ignore messages from a commander station because responder station
40 has already announced its identification to a commander station.
The significance of addressed-bit 86 and locked-bit 88 will become
more readily apparent in the description below..Iaddend.
.Iadd.Random number generator 90 connects to control bus 54 and
data bus 62 for transferring a random number of a predetermined
precision to register array 66. When retained in register array 66,
the random number is called an ARBITRATION NUMBER whose function
will be discussed below. Circuit techniques for generating a random
number in digital format are well known and described, for example,
by H. F. Murray in "General Approach for Generating Natural Random
Variables", IEEE Transactions on Computers, Vol. C-19, No. 12, pp
1210-1213, December 1970, incorporated herein by reference. In one
embodiment, random number generator 90 is similar to an integrated
circuit implementation described by Alan Folmsbee, et. al., in
their article, "128K EPROM with Encrypted Read Access", published
in the Digest of Technical Papers IEEE International Solid-State
Circuits Conference pp 46-47 and 103, by Lewis Winner, Coral
Gables, Fla., 1985, incorporated herein by reference..Iaddend.
.Iadd.FIG. 2 of the '551 patent is a functional block diagram of
network interface 26 shown in FIG. 1 of the '551 patent. Within
network interface 26, connecting signal 28c couple to output buffer
110. Byte-parallel loading of output buffer 110 is accomplished by
network interface peripheral controller 20c shown in FIG. 1 of the
'551 patent. Bytes are removed from output buffer 110 by
transmitter logic 112 to accomplish several processing objectives.
In one embodiment, a 5-bit cyclic redundancy check (CRC) code is
joined to each 8-bit byte to form a 13-bit word. Redundancy,
provided by the 5-bit code, facilitates error detection and limited
error correction by responder station 40. Table 1 describes the
format of the 13-bit word and includes a description of the eRC
code used in one embodiment. Suitable CRC encoder and decoder
circuits used in transmitter logic 112 and receiver logic 178 are
described in detail in "Error Control Coding: Fundamentals and
Applications," by Shu Lin and Daniel J. Costello Jr., Prentice-Hall
Englewood Cliffs, N.J. 1983, pp 62-94. Transmitter logic 112 also
generates transmit serial bit stream 114 which includes a message
preamble bit stream, one or more successive 13 bit words from
output buffer 110, and a postamble bit stream. When permitted by
OK-to-transmit signal 116, transmit serial bit stream 114 is
presented to transmitter 118. Transmitter 118 in one embodiment
produces a radio frequency transmit signal 120 by modulation and
couples that signal to antenna 122. Appropriate modulation methods
depend on the communication medium..Iaddend.
TABLE-US-00001 .Iadd.TABLE 1 Bit Order of Transmission D7, D6 . . .
D0, P4, P3, . . . PO (PO transmitted first) CRC Generation
Equations P0 = 01 + 02 + 05 + 07 P1 = 01 + 03 + 04 + 06 P2 = 0 + D2
+ 03 + 06 + 07 P3 = 00 + 04 + 05 + 06 + 07 P4 = 00 + 01 + 02 + 03 +
04 + 05.Iaddend.
.Iadd.For a communication system for airport baggage handling,
modulation includes, for example, spread spectrum modulation having
pseudo noise characteristics. Other techniques for transmitter
design appropriate to radio transmission and other media will be
readily apparent to those skilled in the arts applicable to
communication on a particular medium. A power level of
approximately 1 watt is sufficient to excite responder station
network interface 60 at distances and noise levels typically
required for a communication system for airport baggage
handling..Iaddend.
.Iadd.Receiver 124 is coupled to antenna 122 for amplifying and
filtering radio frequency received signal 126. Receiver 124 derives
OK-to-transmit signal 116 from power level measurements on received
signal 126 and provides signal 116 to transmitter logic 112.
Although responder station network interface 60 need not generate a
transmitted signal using the same modulation technique employed in
transmitter logic 112 and transmitter 118, a common method is
preferred, for example, in order to minimize circuitry in responder
station network interface 60. Thus, receiver 124 removes the
carrier signal and other artifacts of modulation generated by
responder station network interface 60 in one embodiment by
synchronizing with the spread spectrum signal and removing pseudo
noise characteristics through known detection and filtering
methods. Resulting received serial bit stream 128 is coupled to
receiver logic 130, in one embodiment, for determining whether a
proper message has been received and for decomposing the message
into successive 8 bit bytes. The method and circuitry required to
determine whether a proper message has been received depend on the
redundancy that responder station network interface 60 incorporates
into received serial bit stream 128..Iaddend.
.Iadd.For a communication system for airport baggage handling,
responder station 40 may transmit at a power level of 1 milliwatt
or less. Multiple and more sophisticated error detection schemes
transmitted from responder station 40 will extend the limit of
physical separation between commander station 10 and responder
station 40. Error detection schemes are well known. Such schemes
may also permit reliable communication in environments having
substantial noise levels. On the other hand, limits to the
complexity and power consumption of responder station 40 may limit
the extent of encoding circuitry therein. Where responder station
network interface 60 facilitates one or more particular error
detection schemes, receiver logic 128 decomposes, decodes, detects,
and to a limited extent corrects errors in received serial bit
stream 128. In one embodiment, receiver logic 130 determines
proper-message-received signal 132 by decoding Viterbi encoding
using model Q1601 decoder available from Qualcomm, Inc., San Diego,
Calif. according to Qualcomm application notes and the parameters:
Rate R=1/2, Generating Functions GO=171(octal) and G1=133(octal),
and Constraint Length K=7. Receiver logic 130 also performs serial
to parallel conversion to produce successive 8-bit bytes which are
stored in input buffer 134..Iaddend.
.Iadd.Network interface peripheral controller 20c, responsive to
OK-to-transmit signal 116 and proper-message-received signal 132,
generates signals on data and control bus 14 from which central
processor 16 can determine whether a proper message has been
received as of a predetermined time after transmission and if not,
whether no message was received. Other control signals, known in
the art and not shown, are generated and sensed to orchestrate the
loading of output buffer 110 and the unloading of input buffer 134
under control of central processor 16..Iaddend.
.Iadd.FIG. 3 of the '551 patent is a functional block diagram of
responder station network interface 60 shown in FIG. 1 of the '551
patent. The configuration illustrated in FIG. 3 of the '551 patent
performs functions similar to those already described above for
commander station network interface 26. Differences between the two
serve primarily to limit the complexity of responder station
circuitry. Data bus 62 connects to transmitter logic 160. When
directed by microseguencer 42 via signals on control bus 54,
transmitter logic 160 generates a message preamble bit stream.
Then, for each bit of each word read from memory 64 or register
array 66, transmitter logic 160 develops a Viterbi code. Functional
descriptions suitable for designing circuits or computer programs
for generating Viterbi and similar convolutional codes are
explained in "Error Control Coding: Fundamentals and Applications,"
by Shu Lin and Daniel J. Costello Jr., PrenticeHall Englewood
Cliffs, N.J. 1983, pp 287-456; and "Error-Correction Coding for
Digital Communications", by George C. Clark, Jr. and J. Bibb Cain,
Plenum Press, New York, N.Y. 1981, pp 227-266. Message signal 162
presents the codes to transmitter 164. Following the last code,
transmitter logic 160 generates a message postamble bit stream.
Transmitter 164 modulates message signal 162 in a way compatible
with receiver 124 and receiver logic 130. The resulting transmit
radio frequency signal 166 is coupled to antenna 168. Redundancy,
provided by the Viterbi codes, facilitates error detection and
limited error correction when the message is received at commander
station 10..Iaddend.
.Iadd.Receiver 170 is coupled to antenna 168 for amplifying and
filtering radio frequency received signal 172. Receiver 170 derives
wake-up signal 174 from power-level measurements on received signal
172 and provides wake-up signal 174 to power control and restart
circuits not shown. In a communication system for airport baggage
handling, non-critical circuitry in responder station 60 is powered
by battery only after the preamble of a packet has been detected.
Receiver 170 also removes the carrier signal and other artifacts of
modulation generated by commander station network interface 26 in
one embodiment by synchronizing with the spread spectrum signal and
removing pseudo noise characteristics through detection,
demodulation, decoding, and filtering methods known in the radio
communication arts. Resulting received serial bit stream 176 is
coupled to receiver logic 178. In one embodiment, receiver logic
178 performs several functions: Determining whether a proper byte
has been received, consequently generating improper-byte-received
signal 180, and decomposing the packet into successive 8-bit bytes
forming received message signal 182. The method and circuitry
required to determine whether a proper byte has been received
depend on the redundancy that commander station network interface
26 incorporates into transmit serial bit stream 114. Receiver logic
178 detects the first byte of a command and in response generates
load signal 58. Clock signal 46 is also generated by receiver logic
178 to drive state register 50..Iaddend.
.Iadd.Microsequencer 42 and network interface 60 cooperate via
control bus 54 which includes improper-byte-received signal 180.
Other signals included in control bus 54, known in the art and not
shown, orchestrate transfer of bytes between memory 64, register
array 66, transmitter logic 160, and receiver logic 178. If an
improper byte is received, as indicated by improper-byte-received
signal 180, microsequencer 42 responds by reverting to an idle
state and ignoring incoming bytes until another command is
received..Iaddend.
.Iadd.For a detailed description of suitable circuits of the type
that can be used for transmitters 118 and 164 and receivers 124 and
170, implemented in spread spectrum technologies, see U.S. Pat. No.
5,121,407 by Partyka et al., incorporated herein by
reference..Iaddend.
.Iadd.FIG. 4 of the '551 patent is a diagram of the packet format
sent by commander station 10 to responder station 40. Each command
packet 140 includes, in order of transmission, a preamble followed
by a command followed by a postamble. The preamble and postamble
are designed for synchronizing a transmitter circuit and a receiver
circuit for a particular packet..Iaddend.
.Iadd.In one embodiment, the preamble bit stream comprises 768 `1`
bits followed by a 7-bit Barker code of `0001101`. In one
embodiment, the postamble comprises a 7-bit Barker code of `111001
0`..Iaddend.
.Iadd.In one embodiment, each bit of the command format is
modulated using a pseudo noise (PN) sequence for direct sequence
spread spectrum communication. The sequence is generated in part by
a linear feedback shift register (LFSR) of the form [5,2]. In this
form, the input to the first of five registers is the result of
combining the output of register 5 by exclusive-OR with the output
of register 2. The generator in this embodiment has 32 states so
that the 1 and 0 states occur with equal probability. Since the
LFSR generates only 31 states, an additional state is inserted by
support circuitry. For a detailed description of a suitable PN
modulator circuit of the type employed in transmitter 118 see
"Spread Spectrum Systems", by R. C. Dixon, published by John Wiley
and Sons, Inc. 1984 pp 1528 and 56-151 incorporated herein by
reference. Suitable demodulator techniques and circuits (of the
type used in receiver 170 to recover the response format) are also
described at pages 153-290 incorporated herein by
reference..Iaddend.
.Iadd.FIG. 5 of the '551 patent is a table that describes several
commands and refers to command formats described in FIG. 6 of the
'551 patent. As shown in FIG. 6 of the '551 patent, each command
begins with an opcode and has one of four formats varying in length
from 3 bytes to 258 bytes. Opcode values were selected to
facilitate accurate decoding and obtain high noise immunity. Each
byte is an 8-bit word as it would appear in output buffer 110 and
on received message signal 182. The opcode hexadecimal value is
stored on receipt in command register 56. Bytes following the
opcode have the following meanings. MASK and BRANCH as used in
format 142 are binary numbers chosen by a commander station to
specify a group of responder stations that should act on the
command and should reply. LOCAL ID in format 142 is a unique
identification number assigned, for example, by the communication
system installer to each commander station 10, 34 coupled to common
medium 32. Responder stations 36, 40 coupled to common medium 32
can then direct a response to one of several commander stations
10,34 by, for example, including a particular LOCAL ID in each
response. When one commander station chooses to specify only one
responder station that should act on a command and should reply,
that commander station includes in its command an ARBITRATION
NUMBER as in formats 144 and 146 identifying the responder station.
An ARBITRATION NUMBER is a short value, for example 1 byte, chosen
for self identification by a responder station. On the other hand,
A TAG, as in format 146, is a long value, for example 8 bytes,
assigned by a communication system designer at the time a responder
station is manufactured or commissioned. The ARBITRATION NUMBER
distinguishes responder stations when coupled simultaneously with
at least one commander station to a common medium. However, the
TAG, distinguishes responder stations throughout the life of the
communication system application. Finally, DATA in format 146
includes some or all of the contents for any or all devices
including memory 64, register array 66, flag register 84, and
random number generator 90..Iaddend.
.Iadd.FIG. 7 of the '551 patent is a diagram of the packet format
sent by responder station 60 to commander station 10. Each response
packet 190 includes, in order of transmission, a preamble followed
by a response followed by a postamble. The preamble and postamble
are designed for synchronizing a transmitter circuit and a receiver
circuit for a particular packet. In one embodiment, the preamble
bit stream comprises 768 `1` bits followed by a 7-bit Barker code
of `0001101`. In one embodiment, the postamble comprises a 7-bit
Barker code of `1110010`..Iaddend.
.Iadd.In one embodiment, each bit of the response format is
modulated using a pseudo noise (PN) sequence for direct sequence
spread spectrum communications. The sequence is generated in part
by a linear feedback shift register (LFSR) of the form [6,1] or
[8,4,3,2] for either a 64 chip sequence or a 256 chip sequence
respectively. In the form [6,1], the input to the first of six
registers is the result of combining the output of register 6 by
exclusive-OR with the output of register 1. Similarly, for the
[8,4,3,2] form, the input to the first of eight registers is the
result of the exclusive-OR of the outputs of registers 8, 4, 3, and
2. The 64 chip sequence requires less time for signal
synchronization than the 256 chip sequence; however, the latter
provides better performance in systems having poor signal to noise
ratio. The generator in this embodiment has an even binary multiple
of states, so that the 1 and 0 states occur with equal probability.
Since the LFSR generates one less state, an additional state is
inserted by support circuitry. For a detailed description of a
suitable PN modulator circuit of the type employed in transmitter
164, see "Spread Spectrum Systems", by R. C. Dixon, published by
John Wiley and Sons. Inc. 1984 pp 1528 and 56-151 incorporated
herein by reference. Suitable demodulator techniques and circuits
of the type used in receiver 124 to recover the response format are
also described at pages 153-290 incorporated herein by
reference..Iaddend.
.Iadd.FIG. 8 of the '551 patent is a table that describes several
responses and refers to response formats described in FIG. 9 of the
'551 patent. As shown in FIG. 9 of the '551 patent, response
formats 192-196 include LOCAL ID, ARBITRATION NUMBER, and TAG,
which have the meanings already described above. By including LOCAL
ID and ARBITRATION NUMBER in each response, in cooperation with
locked bit 88 one responder station can respond unambiguously to
one commander station in the presence of a plurality of commander
and responder stations. The INVERTED ARBITRATION NUMBER in format
192 is the binary ones-complement of the ARBITRATION NUMBER and is
included for increased accuracy of communication. REVISION in
format 192 is a one-byte value set by a communication system
developer at the time of manufacture or commissioning of a
responder station. REVISION represents the responder station
configuration and connotes its capability. STATUS in format 196 is
a one-byte code chosen by responder station 40 to convey current
conditions of important system events such as low battery,
uncorrectable data received, write protection. And similar
information which may indicate to commander station 10 that
communication should be repeated or abandoned. DATA in response
format 194 includes some or all of the contents of any or all
devices including memory 64, register array 66, flag register 84,
or random number generator 90..Iaddend.
.Iadd.A communication system, according to the present invention as
described in the '551 patent, includes commander and responder
stations that adhere to a method of communicating called a
protocol. In general, the protocol of the present invention as
described in the '551 patent places different requirements on a
commander station than on a responder station. Thus, there is a
commander station method (FIG. 10 of the '551 patent) and a
responder station method (FIG. 11 of the '551 patent). These
methods together implement the communication system
protocol..Iaddend.
.Iadd.Operation according to the present invention as described in
the '551 patent produces the following characteristic effects at
the system level. First, a commander station will not begin
transmitting during the transmission by another commander station
or by a responder station. Operation, according to the present
invention as described in the '551 patent, does not prevent more
than one commander station from beginning transmission
simultaneously; however, it is feasible to couple commander
stations to a second medium or to constrain commander stations to a
second or expanded protocol on common medium 32. For example,
commander stations 10 and 34 include personal computer system 12,
which can be augmented with a peripheral controller for operation
over ethernet. Communication over the second medium can be used to
prevent simultaneous broadcast over common medium 32. For example,
a second protocol on common medium 32 may include operator action
to assign time slots, back off delays, or similar means for media
access whether central or distributed. Several embodiments for
these means for media access have been described by Stallings in
his work already incorporated by reference above..Iaddend.
.Iadd.Second, a responder station will not transmit unless it has
first received a command to which it determines it must respond.
The response is made within a predetermined time immediately
following receipt of the command..Iaddend.
.Iadd.Third, a commander station can form a command in a manner
calling for all, more than one, or one responder station to
respond. An important object of the communication system protocol
in a communication system of the present invention as described in
the '551 patent, i.e. uninterrupted communication, is achieved
after a commander station determines how to cause only one
responder station to respond. The program flow diagram of FIG. 10
of the '551 patent and the state diagram of FIG. 11 of the '551
patent describe how uninterrupted communication between one
commander station and each responder station is achieved when a
plurality of commander stations and a plurality of responder
stations are simultaneously coupled to a common
medium..Iaddend.
.Iadd.FIG. 10 of the '551 patent is a program flow diagram of the
protocol followed by a commander station of the present invention
as described in the '551 patent. A practical example of a
communication system will be used to describe the flow
diagram..Iaddend.
.Iadd.In a communication system for airport baggage handling the
quantity and identity of responder stations within the radio
communication range of a commander station varies over time. A
commander station may be at a fixed operator station within radio
range of a moving belt conveying baggage toward a V-junction of
conveyors. When baggage tags are constructed as responder stations
and when each tag has destination information stored in memory 64,
the commander station, through communication with each baggage tag,
can control the routing of each bag through the junction onto one
of two conveyors. Assume that each responder station also has
information in memory 64 describing its sequential position on the
conveyor. Such a sequence number could be a date and time of day
when the bag passed through a chute upstream of the commander
station..Iaddend.
.Iadd.As a group of bags approaches the commander station, the
commander station has a fixed amount of time to determine the
identity of each responder station, in order to establish
uninterrupted communication. For proper baggage handling, the
commander station must routinely and repeatedly identify all bags
on the conveyor. To do so, at FIG. 10 of the '551 patent block 210,
commander station 10 specifies a group of responder station
addresses by choosing values for BRANCH and MASK. BRANCH and MASK
values are determined in a manner to be explained by reference to
FIG. 12 of the '551 patent below. In one embodiment, the initial
group specification, i.e. BRANCH and MASK values, would specify all
possible responder stations. Commander station 10 at block 212
generates an "identify, clear, and generate" (IDCG) command having
a format according to FIGS. 4,5, and 6 of the '551 patent. When the
media is clear to broadcast, block 214, as indicated by
OK-to-transmit signal 116, the IDCG message is broadcast, block
216. An IDCG message causes each responder station that is a member
of the group to clear locked-bit 88, generate a random number and
retain it as its ARBITRATION NUMBER, and broadcast a response. The
responder station's reactions to 10, lOG, IDC, and IDCG commands
are explained further in reference to FIG. 11 of the '551 patent
below..Iaddend.
.Iadd.Commander station 10 now loops through blocks 220 and 218 for
a response to be received as indicated by OK-to-transmit signal 116
or a time out elapsed condition. If a response was received, as
indicated by a false state of OK-to-transmit signal 116, commander
station 10 at block 222 determines whether a collision occurred, as
indicated by a false state of proper-message-received signal 132.
If commander station 10 determines that a collision occurred, it
will determine at block 224 whether all possible members of the
initial group of responder station addresses specified at block 210
have been addressed in an 1D, lDG, IDC, or IDCG command. How this
determination is made will be further explained with reference to
FIG. 12 of the '551 patent below. If all subgroups have not been
tried, the commander station again specifies a group of responder
station addresses, for example, a subgroup or disjoint group of a
prior group. At block 228 commander station 10 generates an 10
command according to FIGS. 4, 5, and 6 of the '551 patent and
continues the method from block 214..Iaddend.
.Iadd.If, at block 218, a predetermined time elapsed without a
false condition appearing on OK-to-transmit signal 116, commander
station concludes that no response was transmitted and continues
the method at block 224..Iaddend.
.Iadd.If, at block 222, the proper-message-received signal is true,
then commander station 10 concludes that only one responder station
responded. At block 230, commander station 10 determines and
validates the responding responder station's ARBITRATION NUMBER
according to response format 192 using ARBITRATION NUMBER and
INVERTED ARBITRATION NUMBER. According to a particular system
communication objective, commander station 10 now selects a command
from FIG. 5 of the '551 patent which will cause the responder
station to set its locked-bit 88. For determining baggage
destination and positional sequence on the conveyor, commander
station 10 could select RD. Using the appropriate command format
shown in FIG. 6 of the '551 patent, commander station 10 generates
a message at block 232, loops until the OK-to-transmit signal
indicates that the medium is clear to broadcast at block 234, then
broadcasts the command at block 236. Commander station 10 again
awaits a proper response message by looping at block 238 through
block 240. If a predetermined time elapses at block 240, commander
station 10 continues the method at block 234. If a response is
received without error at block 244, as indicated by
proper-message-received signal 132, then two party uninterrupted
communication between commander station 10 and one responder
station 60 has been established. Further communication may be
required, as indicated by the STATUS code in the received response
format 192 or to accomplish other system communication
objectives..Iaddend.
.Iadd.It is possible at block 224 for the commander station to
determine that no further subgroup, super group, or disjoint group
remains to be commanded using the 10 command. Suppose, for example,
that all practical values of BRANCH and MASK have been used. If the
immediately preceding broadcast at block 216 elicited no response
at block 218, then commander station 10 can conclude that all
responder stations have been identified. Otherwise, at block 248,
commander station 10 generates an identify and generate command
(lOG) according to the format in FIGS. 4, 5, and 6 of the '551
patent using the same group that was specified in block 210.
Commander station 10 continues the method at block
214..Iaddend.
.Iadd.Although the same group is specified, a responder station
that has been identified at block 244 will not respond, since its
locked-bit 88 has been set. Collisions are less likely to occur
with each pass through the loop from block 214 to block 248 because
a smaller number of responder stations can respond. Hence, the
method of FIG. 10 of the '551 patent converges toward identifying
all responder stations. The communication system designer must
select the precision of BRANCH and MASK values to assure conversion
within system time allowances, for example, 8-bit BRANCH and MASK
values are compatible with conveyor speeds and radio ranges needed
for airport baggage handling..Iaddend.
.Iadd.FIG. 11 of the '551 patent is a state diagram of the protocol
followed by a responder station of the present invention as
described in the '551 patent. Responder station 40, begins in idle
state 310 when power is applied or restored according to wake-up
signal 174. In part, the idle state is indicated by contents of
command register 56 not corresponding to a valid command. The idle
state is re-entered to interrupt command processing when
improper-byte-received signal 180 is raised by receiver logic 178.
A valid command loaded into command register 56 causes state
transition to address check state 312..Iaddend.
.Iadd.In address check state 312, microsequencer 42 determines
whether responder station 40 has been addressed by one of two
methods. First if the command conforms to format 142, the responder
station is addressed when the result of ARBITRATION NUMBER
logically ANDed with MASK is bitwise identical to BRANCH.
ARBITRATION NUMBER is the current contents of a particular register
in register array 66. MASK and BRANCH are values received in the
command and stored in register array 66. Logical operations and
comparisons are performed by ALU 72 which produces A=B signal 82.
If A=B signal 82 is not asserted, state 314 is entered. Responder
station 40 may remain in state 314 until a predetermined time
elapses. Responder station 10 re-enters idle state 310, after the
predetermined time elapses..Iaddend.
.Iadd.To illustrate the importance of such a delay, suppose that
commander and responder stations employed radio transceivers for
network interfaces 60 and 26. Then, suppose responder station 40 is
within range of two commander stations 10 and 34, but commander
stations 10 and 34 are out of range of each other. When commander
stations 10 and 34 validly produce back to back commands, the delay
interposed by state 314 prevents responder station 40 (not
addressed by commander station 10 in the first occurring command)
from responding to commander station 34 in the second occurring
command. Without the delay, a collision could occur that may
confuse commander station 10..Iaddend.
.Iadd.A second way to determine whether responder station 40 has
been addressed applies for commands having formats 194 and 196.
Accordingly, responder station 40 is addressed when ARBITRATION
NUMBER, retained in register array 66, is bit-wise identical to
ARBITRATION NUMBER as received in the command. Comparison is
performed by ALU 72 which produces A=B signal 82. If A=B signal 82
is not asserted, state 314 is entered as already described.
Otherwise, transition is made to decode state 316..Iaddend.
.Iadd.Decode state 316 follows address check state 312 in response
to A=B signal 82. If the command opcode is not recognized then no
response state 314 is entered. For some commands, a further
condition such as the state of locked-bit 88, if not met will cause
the command to be treated as not recognized. Each recognized
command opcode causes microcode execution to begin at a section of
microcode for the purpose of directing microsequencer operations to
process the particular received command. Four commands are
illustrated as separate states 318 through 324 and other commands
are illustrated in summary by pseudo state 326..Iaddend.
.Iadd.When the opcode for command IDCG has been received, state 318
is entered for identify, clear, and generate operations. An lOR
response (according to FIGS. 8 and 9 of the '551 patent) is
selected, locked-bit 88 is cleared, the content of random number
generate 90 is stored in register array 66 as ARBITRATION NUMBER,
and transition is made to state 328..Iaddend.
.Iadd.When the opcode for command lDG has been received and
locked-bit 88 is not set, state 320 is entered for identify, and
generate operations. An lOR response is selected and a new
ARBITRATION NUMBER is generated as already described for state 318.
Transition is then made to state 328..Iaddend.
.Iadd.When the opcode for command IDC has been received, state 322
is entered for identify and clear operations. An lOR response is
selected and locked-bit 88 is cleared. Transition is then made to
state 328..Iaddend.
.Iadd.When the opcode for command 10 is received and locked-bit 88
is not set, state 324 is entered for an identify operation. An lOR
response is selected. Transition is then made to state
328..Iaddend.
.Iadd.When the opcode for other commands (including RD and WD) is
received, locked-bit 88 may be set and other functions may be
performed. Other functions may include writing data to memory 64,
writing data to register array 66, altering the state of registers
including flag register 84, and other operations controlling
responder station configuration and operation. Transition is then
made to state 328..Iaddend.
.Iadd.Upon transition to state 328, the response selected by a
prior state is generated according to FIGS. 7, 8, and 9 of the '551
patent and broadcast. In one embodiment, the response is broadcast
as it is being generated. Transition to idle state 310 is made,
after broadcasting the response. Note that responder station 40
does not wait for clear medium prior to broadcasting the response.
According to the present invention as described in the '551 patent,
collision detection by responder stations is not necessary to
accomplish uninterrupted communication..Iaddend.
.Iadd.The ARBITRATION NUMBER generated by responder station 40 and
the BRANCH and MASK numbers chosen by commander station 10 operate
to establish uninterrupted communication. We now turn to a further
explanation of the method used by commander station 10 to choose
BRANCH and MASK values..Iaddend.
.Iadd.FIG. 12 of the '551 patent is a binary tree diagram of BRANCH
values and MASK values chosen by a commander station. A tree is a
type of graphic representation. There are several types of trees
known in mathematics and computer science. The tree depicted is a
binary tree where a node can have two branches, shown descending
left and right from a node. Each node corresponds to a unique
combination of values for BRANCH and MASK, which are nbit binary
numbers having the same precision. As illustrated, BRANCH and MASK
are n-bit binary numbers. In a communication system for airport
baggage handling, a-bit numbers would be used. The precision
employed for BRANCH and MASK must be identical to the precision
selected for ARBITRATION NUMBER generated by responder station
40..Iaddend.
.Iadd.Recall that responder station 40 uses the expression
ARBITRATION NUMBER AND MASK=BRANCH to determine if it is addressed,
where ARBITRATION NUMBER is the value retained in register array 66
from random number generator 90. When MASK is 0 and BRANCH is 0 all
values of ARBITRATION NUMBER satisfy the expression, i.e. all
responder stations coupled to common medium 32 conclude they are
addressed. On the other hand, if MASK has a `1` bit in every
position, then the expression is satisfied for only one value of
ARBITRATION NUMBER..Iaddend.
.Iadd.When MASK is arranged with `0` and `1` bits, the expression
is satisfied by a group of values for ARBITRATION NUMBER, and
potentially a group of responder stations could conclude they are
addressed. Note for a responder station to be addressed, BRANCH at
bit position `q` must be `0` when MASK at bit position `q` is `0`,
for all values of `q`. When MASK at bit position `q` is `1`, BRANCH
can take two values for that bit position which correspond to the
left and right branches of a binary tree..Iaddend.
.Iadd.At the first level of the tree, nodes 702 and 703, MASK is
`1` in bit position `r`. The corresponding bit position of BRANCH
is `0` at node 702 and `1` at node 703. At the second level of the
tree, nodes 704 through 707, MASK is `1` at bit positions `r` and
`s`. For example, the value for BRANCH at node 707 is the parent
node BRANCH value (001 at node 703) modified by forcing a `1` (for
the right-hand branch) at bit position `s`, hence 011. In like
manner, the BRANCH and MASK values for any node in the tree can be
determined. In FIG. 12 of the '551 patent MASK bit positions have
been given in an order right to left. Any other order of bit
positions would be equivalent. Methods for choosing first and
subsequent values for BRANCH and MASK can now be explained in terms
of traversing from node to node on a binary tree..Iaddend.
.Iadd.When commander station 10 broadcasts a request for
identification (an ID, IDC, lDG, or IDCG command) one of three
events can occur. BRANCH and MASK values given at a particular node
that represents a first group of responder stations. First,
commander station 10 could receive no response from which it could
conclude that no responder station in the first group is currently
coupled to the common medium 32. Second, a proper response could be
received. From that event, commander station 10 could conclude that
only one responder station in the first group is currently coupled
to common medium 32. Third, from an improper response received,
commander station 10 could conclude that a collision of more than
one response occurred. An improper response could be caused by, for
example, weak coupling, high noise levels, or weak received
signals. However, these causes can be treated in the same way as a
collision to simplify the commander station protocol without
substantially degrading system performance for applications
including airport baggage handling. Therefore, an improper response
simply merits further search..Iaddend.
.Iadd.An efficient search for the identity of each of several
responding responder stations is equivalent to an efficient search
for the leaves of a binary tree. A leaf is a node having no further
branches. When use of the values for BRANCH and MASK at a node
produces no collision, the node is a leaf. Tree search methods are
easily implemented using known computer programming
methods..Iaddend.
.Iadd.Tree search methods are essentially of two types, breadth
first and depth first. A particular communication system
application may use one method or the other to optimize commander
station computing time and memory space objectives. An explanation
of these methods using the programming language PASCAL is given by
E. Horowitz and S. Sahni in "Fundamentals of Data Structures in
PASCAL" pp 203-265 and 326-332 published by Computer Science Press
Inc., Rockville, Md. (1984), incorporated herein by
reference..Iaddend.
.Iadd.Suppose that two responder stations 40 and 36 and one
commander station 10 are coupled to common medium 32. The binary
tree in FIG. 12 of the '551 patent illustrates a sequence of BRANCH
and MASK values used by commander station 10 to identify responder
stations. Timing diagrams in FIGS. 13 and 14 of the '551 patent
illustrate the same sequence showing decisions at commander station
10 decision blocks (according to the commander station method of
FIG. 10 of the '551 patent) and responder station control signals
(according to the responder station method of FIG. 11 of the '551
patent) as commander station 10 establishes uninterrupted
communication with each responder station..Iaddend.
.Iadd.Beginning at FIG. 10 of the '551 patent block 210, FIG. 12 of
the '551 patent node lOt and FIG. 13 of the '551 patent time 810,
commander station 10 chooses BRANCH=OOO and MASK=OOO, calling for
all responder stations to respond. At time 815, responder station
40 has determined that it is addressed, has cleared its locked-bit
88, has generated ARBITRATION NUMBER 101, and has begun
transmitting response lDR. Simultaneously, responder station 36 has
determined that it has been addressed, has generated ARBITRATION
NUMBER 111, and has begun transmitting response lDR. Also, at time
815, simultaneous transmissions collide on common medium
32..Iaddend.
.Iadd.At time 820, commander station 10 at block 226 chooses node
702 having BRANCH=OOO and MASK=001. Responder station 40 is not
addressed because ARBITRATION NUMBER (101) ANDed with MASK (001)
yields 001 which is not equal to BRANCH (000). Similarly, responder
station 36 is not addressed. Neither station responds. At time 826,
time out at block 218 occurs..Iaddend.
.Iadd.At time 830 and block 226, a third group of responder station
addresses is chosen. From FIG. 12 of the '551 patent the
appropriate group is specified by traversing the tree according to
a search method. If a breadth first search were used, all nodes at
the same level would be visited before testing at a deeper level.
Hence, node 703 would be next. If a depth first search were used,
search would proceed upward from node 702 (because it is a leaf)
and then downward from the first node having an untested branch.
Hence, up to node 701 and down to node 703. As a refinement to
either method, node 703 can be skipped because a collision at node
701 and no response at node 702 implies a collision at node 703
without testing. A depth first search would now traverse from node
703 directly to node 706. A breadth first search would first
consider nodes 704 and 705 and conclude not to visit them because
each is a descendent from a leaf node..Iaddend.
.Iadd.Having selected node 706 at time 830, commander station 10
broadcasts an 10 command with BRANCH=001 and MASK=011 at block 216.
At time 835 responder, station 40 has determined that it is
addressed and has begun transmitting response IDR. Simultaneously,
responder station 36 determines it is not addressed and remains in
state 314. At time 840, shown on FIGS. 13 and 14 of the '551
patent, commander station 10 has received the response from
responder station 40 as a proper message, concluded that only one
responder station responded, derived received ARBITRATION NUMBER
(101), set BRANCH to received ARBITRATION NUMBER, set MASK to all
1's so that a responder station must match ARBITRATION NUMBER (101)
in all bit positions to respond, and begins to perform blocks 232
through 244 in FIG. 10 of the '551 patent. At time 845, responder
station 40 has determined that it is addressed, has decoded a read
command, has set its locked-bit 88 in state 326, and has begun
generating the read response in state 328. At time 850, commander
station 10 has received the response as a proper message. Thus,
commander station 10 has conducted a first two-party uninterrupted
command-response scenario from time 840 to time 850 with one
responder station..Iaddend.
.Iadd.The search by commander station 10 for another responder
station proceeds from block 244 to block 224 in FIG. 10 of the '551
patent. At block 226, another node from FIG. 12 of the '551 patent
is selected. Having elicited a proper response at node 706, the
depth first search proceeds up to the first node having an untested
branch, here node 703. Then, down the untested branch to node 707.
Having selected node 707 at time 850, commander station 10
broadcasts an 10 command with BRANCH=011 and MASK=011 at block 216.
At time 855, responder station 36 has determined that it has been
addressed and has begun generating an lOR response. At time 860,
the response is received by commander station 10 as a proper
message. After time 860, events proceed in a manner similar to
events from time 840 to time 850, as commander station 10 conducts
a second two-party uninterrupted command-response scenario with a
second responder station..Iaddend.
.Iadd.At block 224, following the uninterrupted scenario, commander
station 10 can conclude that all groups have been tested. On a
depth first search, a proper response or no response at a node
having BRANCH=MASK indicates all groups have been tested. On a
breadth first search, all groups have been tested when an
investigation of all levels up to the level having all MASK bits
set to `1` yields no node that is not descendent from a leaf
node..Iaddend.
.Iadd.In a branch/mask embodiment of the type described above, a
responder station concludes that it has been addressed when
ARBITRATION NUMBER logically ANDed with MASK is equal to BRANCH.
Two other types of embodiments will now be described that lie
within the scope and spirit of the present invention as described
in the '551 patent. First, in an example of a high/low embodiment,
BRANCH and MASK (as shown in format 142) are replaced with HIGH
LIMIT and LOW LIMIT. Each of these limit values has the same
precision as the MASK value. Using these limit values, responder
station 40 concludes that it is addressed when HIGH LIMIT is
greater than or equal to ARBITRATION NUMBER, and LOW LIMIT is less
than or equal to ARBITRATION NUMBER. Second, in an example of a
limit/bound embodiment, BRANCH and MASK (as shown in format 142)
are replaced with a single LIMIT value having the same precision as
MASK. Using a value called BOUND which by design choice may be 0 or
the maximum permitted by the precision of LIMIT, responder station
40 concludes that it is addressed when ARBITRATION NUMBER is
between BOUND and LIMIT, inclusive of both BOUND and LIMIT
values..Iaddend.
.Iadd.An example of a limit/bound embodiment is implemented with a
structure similar to that already described for the branch/mask
embodiment. Subtraction capability or equivalent must be added to
ALU 72. Operation of microsequencer 42 must be revised to perform
the arithmetic operations outlined above in state 312 shown on FIG.
11 of the '551 patent. The high/low embodiment is implemented with
the structure already described for the limit/bound
embodiment..Iaddend.
.Iadd.In FIG. 10 of the '551 patent (blocks 210 and 226) commander
station 10 specifies a group of responder station addresses. For a
branch/mask embodiment, a method using the binary tree of FIG. 12
of the '551 patent has already been discussed. For a high/low
embodiment, a similar binary tree (not shown) with HIGH and LOW
values at each node is used. At the root node, LOW is 0 and HIGH is
the maximum value permitted by the precision of the value HIGH. At
a node on the lower left from a parent node, the value of LOW is
the value of LOW at the parent node and the value of HIGH is a
value 1/2 the value of HIGH at the parent node discarding a
remainder, if any. At a node on the lower right from a parent node,
the value of HIGH is the value of HIGH at the parent node and the
value of LOW is 1/2 the value of HIGH at the parent node plus one.
Although a binary tree has been described, a tree having more than
two branches at each node can be employed to practice the present
invention as described in the '551 patent as is readily apparent to
those skilled in the art. Trees with varying number of branches at
each node can also be employed. Operation of the high/low
embodiment is otherwise identical to operation of the branch/mask
embodiment already discussed..Iaddend.
.Iadd.In a limit/bound embodiment, the method used to specify a
group of responder station addresses is similar to the method
described for a high/low embodiment with a minor variation in the
tree. When BOUND is zero, then the value for LOW is not used and
the value for HIGH is used as the LIMIT value at each node. When
BOUND is a maximum value, then the value for HIGH is not used and
the value of LIMIT at each node is the value of LOW. Operation of a
limit/bound embodiment is otherwise identical to operation of a
branch/mask embodiment already discussed. Note that the command at
block 232 on FIG. 10 of the '551 patent sets locked-bit 88 to
prevent unnecessary collisions when an 10 command using LIMIT is
broadcast subsequently at block 228..Iaddend.
.Iadd.FIG. 15 of the '551 patent is a fibonacci tree diagram for
use in an example of an embodiment of the type already described as
limit/bound. An advantage of using a fibonacci tree is that the
LIMIT value for a node descendent from a parent node can be derived
without a multiplication or division operation. In systems where it
is desirable to improve calculation speed or reduce the complexity
of circuitry and software at commander station 10, the fibonacci
tree is used. An implementation of a high/low embodiment using a
fibonacci tree similar to FIG. 15 of the '551 patent is within the
ordinary skill of the systems design and programming
arts..Iaddend.
.Iadd.As described in several embodiments above, a commander
station can quickly determine the identity of all responder
stations coupled to a common medium at a given time. After the
identity of a responder station has been determined, a commander
station can conduct uninterrupted communication at any subsequent
time using the responder station's ARBITRATION NUMBER. Since the
ARBITRATION NUMBER is not unique, there is some risk that at a
subsequent time, more than one responder station having a given
value for ARBITRATION NUMBER may become coupled to the common
medium. For increased accuracy, use of a unique responder station
identity, such as the TAG field in format 146 of FIG. 6 of the '551
patent, may be used for subsequent communication..Iaddend.
.Iadd.When more than one commander station is coupled to a common
medium, it is possible for one commander station to thwart the
objective of a second commander station. For example, when
commander station 10 is attempting to identify all responder
stations and commander station 34 issues an 10CG command, commander
station 10 may subsequently incorrectly conclude that all responder
stations have been identified. Several methods of preventing this
incorrect conclusion are available to those skilled in
communication and computer programming arts. Exemplary methods
include enabling a commander station to monitor commands issued by
another commander station to avoid inappropriate conclusions;
enabling a commander station 10 to record the TAG fields sent in
messages to another commander station and communicate directly with
each such responder station, perhaps prior to and so simplifying,
the task of identifying all responder stations; modifying the
communication protocol used among commander stations; and causing a
second commander station to delay its own attempt to identify all
responder stations until after a time sufficient for a first
commander station to identify all responder stations. The latter
suggestion is practical using the media access control scheme of
the present invention as described in the '551 patent. It is
practical because the time required to identify a worst-case
population of responder stations can be predetermined..Iaddend.
.Iadd.The present invention as described in the '551 patent can be
implemented in several alternate embodiments. As already discussed,
various alternatives are available for common medium 32 including
all media that support forms of electromagnetic energy, all sound,
vibration, and pressure wave conducting media, and all media
capable of transporting variation in chemical concentration, to
name a few. If a medium other than radio communication is selected
as an embodiment of the present invention as described in the '551
patent, variations in network interface 26 and 60 can be made by
those skilled in the arts that apply to the selected medium.
Appropriate signal sensors and generators are well known in
applications including measurement and control apparatus. Packet
synchronization techniques, packet formats, error detection
techniques, and error correction techniques may vary or be omitted
as a matter of design choice depending on the need for receiver
synchronization, the signal to noise properties of the selected
media, and the desired simplicity of network
interfaces..Iaddend.
.Iadd.Another group of alternative embodiments uses various means
to specify a set of responder station identities or designations.
The embodiments described above employ an ARBITRATION NUMBER
selected from a predetermined range of numbers and expressed as
part of a message. For example, alternate sets of designations
include a set of operating modes, a set of modulation techniques,
and a range of values used to shift in time all or a portion of a
command. Various alternatives are also available for specifying
(i.e. addressing) a subset of designations. The branch/mask,
high/low, and limit/bound subset addressing techniques can each be
applied to one or more parametric quantities related to the above
mentioned set designations. For example, if onemember of the set is
characterized by a bandwidth, a channel frequencies, a phase
variation, or a duration in time, then a range of each of these
parameters could be described by a branch/mask pair of
values..Iaddend.
.Iadd.Various alternatives for transmitting the command signal are
within the scope of the present invention as described in the '551
patent. In the embodiments described at length above, the BRANCH
and MASK values in the message format characterize the transmitted
command signal according to a subset of responder stations to which
the command is directed. In addition to the variations in
modulation already described, the transmitted signal can be
characterized by variation in the spread spectrum chip sequence or
initial code within a chip sequence when spread spectrum
transmission is employed..Iaddend.
.Iadd.Other characteristics of a command signal can be used to
limit or expand the subset of responder stations to which the
command is directed. For example, the operation of commands
including RO and WR to set locked-bit 88 and the operation of
commands including IDG and IDCG to conditionally clear locked-bit
88 show how the command opcode can be used to characterize a
command signal according to a selected subset or address range.
Alternatively, modulation variations, timing variations, or other
message content variations could also be used to set or clear an
equivalent of the locked-bit function..Iaddend.
.Iadd.Various means are suitable for use by a responder station to
determine whether it is addressed by, i.e. whether it is a member
of the subset indicated by, a command signal. Several arithmetic
comparison techniques based on message content have been described
above. Other means, based on whether the signal received by the
responder is received without error, are appropriate when
variations in modulation are used to address a subset of responder
stations. For example, received signal strength below a threshold
over one or more frequencies or at a particular time could cause
commands to be received or rejected. Similarly, operation of
functions similar to locked-bit 88 as already described and
variation in spread spectrum chip sequence could be used to cause
commands to be received or rejected..Iaddend.
.Iadd.Within the scope of the present invention as described in the
'551 patent, each responder station includes means for establishing
a self designation. In the embodiments discussed at length above,
the self designation is determined by a random number generator,
held in a register, and included in a response packet. Alternative
techniques include various means for sampling a random process to
acquire an analog parametric value and using either a digital or an
analog value to control the functions of network interface
60..Iaddend.
.Iadd.Network interface 60 can be constructed and operated in
several alternative embodiments to transmit a response packet in a
way characterized by the responder station self designation. All of
the following variations could be used in embodiments that fall
within the scope of the present invention as described in the '551
patent: variations in the modulation technique, including variation
within a range of values used to shift in time all or a portion of
a response; variation in the spread spectrum chip sequence or
initial code within a chip sequence when spread spectrum
transmission is employed; variation in message content including
preamble, postamble, response type indicator e.g. IDR, RDR, and
WDR, register contents, status and locked-bit information; and
variation based on signal rejection including variation in
bandwidth, channel frequencies, signal phase variations, signal
duration, or variation in the redundancies used to detect or
correct transmission error..Iaddend.
.Iadd.Another group of alternative embodiments uses alternative
means for selecting a subgroup in response to collision detection.
The tree search method that was described as part of the commander
station protocol can be implemented in various ways depending on
the selected representation of the tree in commander station memory
18. Binary trees have been described above. Other tree structures
including n-ary trees could be employed to perform the commander
station identification function in an equivalent manner. Depending
on the type of tree selected for representation, the use of
strings, arrays, stacks, pointers, linked lists, or derivative
memory organizations are feasible and equivalent. Finally, tree
search methods include depth first, breadth first, and combinations
of both depth and breadth searching..Iaddend.
.Iadd.Each computer used as part of commander station 10 and as
part of responder station 40 includes hardware and software
designed to conduct the protocol shown and described in S. 10 and
11 respectively of the '551 patent. Variations in the extent and
complexity of hardware and software are well known by designers of
ordinary skill in communication and computer arts. Equivalent
hardware can include the general purpose computer such as an IBM
PC; a calculator, such as an HP21C; the special purpose computer,
such as application specific automated controllers used in weighing
systems; the microprocessor based system, such as a circuit using
an Intel 8048; the microsequencer based system using programmable
devices and logic devices; and the integrated circuit or chip set,
such as developed from a cell library using semiconductor device
design techniques. Variations in the extent and complexity of
software compatible with one or more of the above mentioned
hardware variations are also well known by the programmer of
ordinary skill..Iaddend.
.Iadd.The systems designer of ordinary skill chooses to implement
each control function in either hardware or software or a
combination of both. A computer is said to conclude a certain
result when it has determined the state of a control function. When
a control function is implemented using a computer system,
variations in the form of the result of the control function are
well known. For example, a parameter that results from a first
control function and is relied upon by a second control function
can take the form of a signal when the second control function is
in part hardware or the form of a pointer, value, or symbol stored
in a register or memory when the second control function is in part
software..Iaddend.
.Iadd.The present invention as described in the '551 patent has
been described in the preferred embodiment. Several variations and
modifications have also been described and suggested. Other
embodiments, variations, and modifications known to those skilled
in the art may be implemented without departing from the scope and
spirit of the invention as recited in the claims
below..Iaddend.
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