U.S. patent application number 11/534060 was filed with the patent office on 2007-04-05 for monitoring and adjustment of reader in an electronic toll collection system.
Invention is credited to Thua Van Ho, Daniel Terrier, Roger Tong.
Application Number | 20070075839 11/534060 |
Document ID | / |
Family ID | 37890058 |
Filed Date | 2007-04-05 |
United States Patent
Application |
20070075839 |
Kind Code |
A1 |
Ho; Thua Van ; et
al. |
April 5, 2007 |
MONITORING AND ADJUSTMENT OF READER IN AN ELECTRONIC TOLL
COLLECTION SYSTEM
Abstract
An electronic toll collection system that includes a reader with
internal monitoring circuitry. The reader includes a controller and
transceiver, which is connected to an antenna, wherein the
transceiver sends outgoing RF signals to the antenna and receives
incoming RF signals from the antenna. The reader includes
transceiver monitor circuitry for monitoring the characteristics of
the RF signals to assess transceiver performance. The transceiver
monitor circuitry provides a result signal to the controller. The
controller may adjust the operation of the transceiver through
adjustments to an adjustable element based upon the measurement
signals. The controller may also send measurement information to a
remote computer and receive instructions from the remote computer,
thereby enabling remote monitoring and adjustment of the electronic
toll collection system.
Inventors: |
Ho; Thua Van; (Mississauga,
ON) ; Terrier; Daniel; (Toronto, ON) ; Tong;
Roger; (Oakville, ON) |
Correspondence
Address: |
HANLEY, FLIGHT & ZIMMERMAN, LLC
150 S. WACKER DRIVE
SUITE 2100
CHICAGO
IL
60606
US
|
Family ID: |
37890058 |
Appl. No.: |
11/534060 |
Filed: |
September 21, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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60718742 |
Sep 21, 2005 |
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|
60718743 |
Sep 21, 2005 |
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60718744 |
Sep 21, 2005 |
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Current U.S.
Class: |
340/10.2 ;
235/384; 340/10.3; 340/928 |
Current CPC
Class: |
G07B 15/06 20130101;
G07B 15/063 20130101 |
Class at
Publication: |
340/010.2 ;
340/928; 235/384; 340/010.3 |
International
Class: |
H04Q 5/22 20060101
H04Q005/22 |
Claims
1. A electronic toll collection system for conducting toll
transactions with vehicle-mounted transponders travelling in a
roadway, the electronic toll collection system comprising: at least
one antenna having a coverage area for exchanging RF communications
with a transponder in the roadway; and a reader connected to said
at least one antenna, said reader including a transceiver having an
RF port for exciting the at least one antenna with an RF output
signal and for receiving RF input signals induced in the at least
one antenna by the transponder, the transceiver including an
adjustable element having a setting responsive to an adjustment
signal, a controller for controlling said transceiver and for
outputting said adjustment signal, and a transceiver monitor
circuit connected to the RF port for measuring characteristics of
the RF output signal and the RF input signal, said transceiver
monitor circuit providing a result signal to said controller, and
wherein said controller is configured to generate said adjustment
signal based upon said result signal.
2. The system claimed in claim 1, wherein said adjustable element
comprises a programmable attenuator.
3. The system claimed in claim 1, wherein said transceiver includes
an RF output stage for generating said RF output signal, said RF
output stage including said adjustable element, and wherein said
setting of said adjustable element determines a power level of said
RF output signal.
4. The system claimed in claim 1, wherein said transceiver includes
an RF input stage for receiving and detecting said RF input signal,
said RF input stage including said adjustable element, and wherein
said setting of said adjustable element determines a sensitivity of
said RF input stage in detecting said RF input signal.
5. The system claimed in claim 1, wherein said transceiver monitor
circuit comprises a low loss directional coupler and processing
circuitry, and wherein said processing circuitry includes a
down-converter, a peak detector, and a comparator for determining
whether the RF output signal has a power level above a minimum
threshold level, and wherein the result signal indicates whether
the RF output signal power level exceeds the minimum threshold
level.
6. The system claimed in claim 5, wherein the controller is
configured to calculate an adjustment for the adjustable element
based upon the result signal and to generate said adjustment signal
to implement said adjustment.
7. The system claimed in claim 1, wherein said transceiver monitor
circuit comprises a low loss directional coupler and processing
circuitry, and wherein said processing circuitry includes a
down-converter, a peak detector, and a comparator for determining
whether the RF input signal has a power level above a minimum
threshold level, and wherein the result signal indicates whether
the RF output signal power level exceeds the minimum threshold
level.
8. The system claimed in claim 7, wherein the controller is
configured to determine whether the transceiver detects the RF
input signal and, if not, to calculate an adjustment for the
adjustable element based upon the result signal and to generate
said adjustment signal to implement said adjustment.
9. The system claimed in claim 1, wherein said transceiver monitor
circuit and said controller are configured to determine the VSWR of
the RF output signal and to compare the VSWR to a threshold
level.
10. The system claimed in claim 1, wherein said controller is
configured to generate and output a report in response to said
result signal.
11. The system claimed in claim 1, wherein said controller includes
a communications subsystem and a data output port, and wherein said
communication subsystem is configured to output data regarding said
measured characteristics of the RF output signal and the RF input
signal.
12. The system claimed in claim 11, wherein the communications
subsystem is configured to generate a mark-up language document
containing said measured characteristics, and to transmit said
mark-up language document to a remote client device in response to
an authenticated request from the remote client device.
13. A method of monitoring operation of an electronic toll
collection system for conducting toll transactions with
vehicle-mounted transponders travelling in a roadway, the system
including at least one antenna having a coverage area for
exchanging RF communications with a transponder in the roadway and
a reader connected to the at least one antenna, wherein the reader
includes a transceiver having an RF port for exciting the at least
one antenna with an RF output signal and for receiving RF input
signals induced in the at least one antenna by the transponder, the
transceiver including an adjustable element having a setting
responsive to an adjustment signal, and a controller for
controlling said transceiver and for outputting said adjustment
signal, the method comprising steps of: measuring characteristics
of the RF output signal and the RF input signal; calculating an
adjustment based upon the measured characteristics; and generating
said adjustment signal to implement said calculated adjustment.
14. The method claimed in claim 14, wherein said adjustable element
comprises a programmable attenuator.
15. The method claimed in claim 14, wherein said transceiver
includes an RF output stage for generating said RF output signal,
said RF output stage including said adjustable element, and wherein
said setting of said adjustable element determines a power level of
said RF output signal.
16. The method claimed in claim 14, wherein said transceiver
includes an RF input stage for receiving and detecting said RF
input signal, said RF input stage including said adjustable
element, and wherein said setting of said adjustable element
determines a sensitivity of said RF input stage in detecting said
RF input signal.
17. The method claimed in claim 14, wherein said step of measuring
includes determining whether the RF output signal has a power level
above a minimum threshold level.
18. The method claimed in claim 17, wherein said step of
calculating includes determining whether said adjustment may be
implemented through the adjustable element.
19. The method claimed in claim 14, wherein said step of measuring
includes determining whether the RF input signal has a power level
above a minimum threshold level and, if so, determining whether the
transceiver detects the RF input signal.
20. The method claimed in claim 14, wherein said step of measuring
includes measuring the power of the RF output signal and measuring
the reflected power and calculating the VSWR of the RF output
signal.
21. The method claimed in claim 14, further including generating
and outputting a report regarding said measured
characteristics.
22. The method claimed in claim 21, wherein said report includes a
mark-up language document containing said measured characteristics,
and wherein said step of outputting includes transmitting said
report to a remote client device in response to an authenticated
request from the remote client device.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to U.S. provisional
patent application Ser. No. 60/718,742, U.S. provisional patent
application Ser. No. 60/718,743, and U.S. provisional patent
application Ser. No. 60/718,744, all filed Sep. 21, 2005.
FIELD OF THE INVENTION
[0002] The present invention relates to electronic toll collection
systems and, in particular, an electronic toll collection system
with monitoring and adjustment of a reader.
BACKGROUND OF THE INVENTION
[0003] Electronic toll collection systems conduct toll transactions
electronically using RF communications between a vehicle-mounted
transponder (a "tag") and a stationary toil plaza transceiver (a
"reader"). An example of an electronic toll collection system is
described in U.S. Pat. No. 6,661,352 issued Dec. 9, 2003 to Tiernay
et al., and owned in common with the present application. The
contents of U.S. Pat. No. 6,661,352 are hereby incorporated by
reference.
[0004] In a typical electronic toll collection (ETC) system, a set
of antennas are disposed to cover the roadway with overlapping
coverage zones. Each antenna broadcasts a wakeup or trigger RF
signal within its coverage zone. A tag on a vehicle passing through
the coverage area or zone detects the wakeup or trigger signal and
responds with its own RF signal. The tag responds by sending a
response signal containing information stored in memory in the
transponder, such as the transponder ID number. The response signal
is received by the antenna.
[0005] The antennas operate under the control of a reader that
typically uses time multiplexing to scan the roadway for
transponders using each antenna in turn. When an antenna receives a
response signal, the response signal is input to the reader, which
may then conduct an electronic toll transaction, such as by
debiting a user account associated with the transponder ID number.
The reader may then cause the antenna to broadcast a programming RF
signal to the tag. The programming signal provides the tag with
updated information for storage in its memory. It may, for example,
provide the tag with a new account balance.
[0006] In one electronic toll collection system, the reader may
include one or more RF transceivers and a controller. The
controller controls operation of the RF transceiver(s) and conducts
the toll transactions. The controller may cause a multiplexer to
selectively connect the RF transceiver to each of the antennas,
thereby implementing time multiplexed scanning. In some cases one
or more of the transceivers may fail or may experience degradation
in signal power. The possible reasons for this are numerous, but
the effect is that the radiated power from one or more of the
antennas is reduced, which can result in missed transactions. In
some cases, the receiver portion of the transceiver degrades or
fails. In yet other cases, the transmission line between the
transceiver and the antenna degrades or is damaged. In yet other
cases, the antenna degrades or is damaged. These situations can
give rise to a mismatch in impedance, increased path resistance,
and/or worse signal-to-noise performance.
[0007] The result of these problems may be a loss in output power
and/or in received power. These conditions can be difficult to
detect and may persist for long periods of time without being
noticed or repaired.
[0008] It would be advantageous to have an improved electronic toll
collection system.
SUMMARY OF THE INVENTION
[0009] The present invention provides an electronic toll collection
system that including internal monitoring circuitry. A reader
includes a controller and transceiver, which is connected to an
antenna, wherein the transceiver sends outgoing RF signals to the
antenna and receives incoming RF signals from the antenna. The
reader includes transceiver monitor circuitry for monitoring the
characteristics of the RF signals to assess transceiver
performance. The transceiver monitor circuitry provides a
measurement signal to the controller. The controller may adjust the
operation of the transceiver through adjustments to a digital
attenuator based upon the measurement signals. The controller may
also send measurement information to a remote computer and receive
instructions from the remote computer, thereby enabling remote
monitoring and adjustment of the electronic toll collection
system.
[0010] In one aspect, the present application provides an
electronic toll collection system for conducting toll transactions
with vehicle-mounted transponders travelling in a roadway. The
electronic toll collection system includes at least one antenna
having a coverage area for exchanging RF communications with a
transponder in the roadway, and a reader connected to the at least
one antenna. The reader includes a transceiver having an RF port
for exciting the at least one antenna with an RF output signal and
for receiving RF input signals induced in the at least one antenna
by the transponder, and the transceiver includes an adjustable
element having a setting responsive to an adjustment signal. The
reader also includes a controller for controlling the transceiver
and for outputting the adjustment signal, and a transceiver monitor
circuit connected to the RF port for measuring characteristics of
the RF output signal and the RF input signal, the transceiver
monitor circuit providing a result signal to the controller. The
controller is configured to generate the adjustment signal based
upon the result signal.
[0011] In another aspect, the present application provides a method
of monitoring operation of an electronic toll collection system for
conducting toll transactions with vehicle-mounted transponders
travelling in a roadway. The ETC system includes at least one
antenna having a coverage area for exchanging RF communications
with a transponder in the roadway and a reader connected to the at
least one antenna. The reader includes a transceiver having an RF
port for exciting the at least one antenna with an RF output signal
and for receiving RF input signals induced in the at least one
antenna by the transponder, and the transceiver includes an
adjustable element having a setting responsive to an adjustment
signal. The reader also includes a controller for controlling the
transceiver and for outputting the adjustment signal. The method
includes steps of measuring characteristics of the RF output signal
and the RF input signal, calculating an adjustment based upon the
measured characteristics, and generating the adjustment signal to
implement the calculated adjustment.
[0012] Other aspects and features of the present invention will be
apparent to those of ordinary skill in the art from a review of the
following detailed description when considered in conjunction with
the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Reference will now be made, by way of example, to the
accompanying drawings which show an embodiment of the present
invention, and in which:
[0014] FIG. 1 shows a block diagram of an embodiment of an
electronic toll collection (ETC) system.
[0015] FIG. 2 shows another block diagram of the ETC system shown
in FIG. 1.
[0016] FIGS. 3 and 4 show, in flowchart form, a method for
monitoring and adjusting transceivers in the ETC system.
[0017] FIG. 5 diagrammatically shows an example embodiment of a
portion of the transceiver monitor circuitry within the reader of
the ETC system.
[0018] FIG. 6 diagrammatically shows another example embodiment of
a portion of the transceiver monitor circuitry within the
reader.
[0019] Similar reference numerals are used in different figures to
denote similar components.
DESCRIPTION OF SPECIFIC EMBODIMENTS
[0020] Reference is first made to FIG. 1, which shows a block
diagram of an embodiment of an electronic toll collection system
10. The system 10 operates to send and receive RF communications
with vehicle-borne transponders 12. In one embodiment, the system
10 is associated with a gated toll plaza. In another embodiment,
the system 10 is associated with an open-road toll processing zone.
Other applications for the system 10 will be appreciated by those
skilled in the art.
[0021] In the embodiment shown in FIG. 1, the system 10 is
associated with a multi-lane roadway 14. Individual lanes are shown
as lanes 14a, 14b, 14c, and 14d.
[0022] The system 10 includes a set of antennas 16 (shown
individually as 16a, 16b, 16c, and 16d). FIG. 1 shows that each
antenna 16 is associated with a laneway. In particular, each
antenna 16 is a directional antenna having a beam path that defines
an antenna-specific capture zone 18 within the roadway 14. The
antennas 16 may, in some embodiments, be mounted to an overhead
gantry or other structure. In many embodiments, the antennas 16 may
be positioned such that their respective capture zones 18 span the
width of the roadway 14 to ensure total coverage of all lanes of
traffic.
[0023] It will be appreciated that there may be more antennas 16 or
fewer antennas 16 than lanes in the roadway 14. In one embodiment,
midpoint or mid-lane antennas are also deployed defining a capture
zone roughly centered at the midpoint between lanes. The mid-lane
antennas provide overlapping coverage with the center-lane antennas
16 and may be useful in determining lane position of a transponder
12 within the roadway 14. Other configurations of the antennas 16
will be appreciated by those skilled in the art.
[0024] The antennas 16 are connected to a roadside reader 20. The
roadside reader 20 excites each antenna 16 so as to induce
propagation of an RF signal in the associated capture zone 18. The
antenna 16 receives incoming RF signals, which are input to the
reader 30. The incoming RF signals include transmissions from any
active transponders within the capture zone 18. It will be
appreciated that the electronic toll collection system 10 may be
based upon one or more pre-defined communications protocols and may
involve the use of active or backscatter transponders.
[0025] The pre-defined communications protocols used in the system
10 include propagation of a trigger signal or wake-up signal by the
antennas 16 in their respective capture zones 18. Any transponder
12 within a particular capture zone 18 may respond by transmitting
a response signal, which is received by the antenna 16 and input to
the reader 20.
[0026] In many embodiments, the reader 20 employs a time
multiplexed scan, whereby each antenna 16 is assigned a time slot
within which the antenna 16 broadcasts its trigger signal and
awaits a response, if any. In the embodiment depicted in FIG. 1,
the protocol may provide for four time slots during which each
antenna is sequentially used to poll for transponders 12 in its
respective capture zone 18.
[0027] The roadside reader 20 includes a transceiver bank 22 and a
controller 26. The transceiver bank 22 contains transceivers 24.
The transceivers 24 are configured to modulate signals from the
controller 26 for transmission as RF signals over the antennas 16,
and to de-modulate RF signals received by the antennas 16 into a
form suitable for use by the controller 26. In this regard, the
reader 20 employs hardware and signal processing techniques that
will be well understood by those skilled in the art. The controller
26 may include a programmable processing unit, volatile and
non-volatile memory storing instructions and data necessary for the
operation of the controller 26, and communications interfaces to
permit the controller 26 to communicate with the transceivers
24.
[0028] In some embodiments, the transceiver bank 22 may include a
dedicated transceiver 24 for each antenna 16. In some embodiments,
the transceiver bank 22 may include a single transceiver 24 that is
used for each antenna 16. In other embodiments, the transceiver
bank 22 may include some operative transceivers and some redundant
transceivers as described in U.S. provisional patent application
Ser. No. 60/718,742 filed Sep. 21, 2005 and owned in common
herewith, the contents of which are hereby incorporated by
reference.
[0029] The reader 20 further includes a switching network 28 for
selectively connecting one of the transceivers 24a, 24b, and 24n,
with one of the antennas 16. In some embodiments, the switching
network 28 may only connect one transceiver 24 to one antenna 16 at
any given time; however, in other embodiments, the switching
network 28 may allow for connections between more than one antenna
16 and respective transceivers 16. For example, the switching
network 28 may contemporaneously connect the first antenna 16a to
the first transceiver 24a and the fourth antenna 16d to the second
transceiver 24b. In this latter circumstance, the antennas 16 that
are contemporaneously connected to a respective one of the
transceivers 24 may be spatially displaced to ensure no overlap. In
other words, the switching network 28 may not simultaneously
connect transceivers 24 to two antennas 16 located in adjacent
lanes of the roadway 14, since RF interference may result.
[0030] The switching network 28 operates under the control of the
controller 26, which causes the switching network 28 to connect and
disconnect specified antennas 16 to selected transceivers 24 so as
to implement a scanning pattern. The scanning pattern may include a
fixed pattern of equal length timeslots. In some embodiments, the
scanning pattern may include an adaptive pattern that adjusts to
traffic volume differences between the laneways, as described in
U.S. provisional Ser. No. 60/718,743, filed Sep. 21, 2005 and owned
in common herewith, the contents of which are hereby
incorporated.
[0031] The reader 30 may further include transceiver monitor
circuitry 30 for providing the controller 26 with information
regarding the transceiver(s) 24 and/or antennae 16. In one
embodiment, through the transceiver monitor circuitry 30 the
controller 26 may receive a portion or sample of the RF signal
output by each of the transceivers 24. In another embodiment, the
transceiver monitor circuitry 30 also or alternatively provides a
portion or sample of the incoming RF signal input to the
transceiver 24.
[0032] Based upon the transceiver monitor circuitry 30, the
controller 26 may determine the power level of the output RF signal
for the transceiver 24 and/or the power level of the input RF
signal to the transceiver 24. The controller 26 may also determine
the voltage standing wave ratio (VSWR) of the RF output signal for
the transceiver 24. These signal characteristics may be used by the
controller 26 to assess the transceiver 24 state and operating
condition. For example, if the power level of the RF output signal
drops below a threshold level, it may be indicative of a problem in
the transceiver 24. As another example, if the RF input signal has
a strength that should be detectable by the transceiver 24 and the
transceiver 24 does not detect the RF input signal, then it may
indicate a problem with the sensitivity setting of the transceiver
24. As yet another example, if the voltage standing wave ratio
(VSWR) exceeds a threshold level, it may indicate a problem with
the transceiver 24, the transmission line to the antenna 16, and/or
the antenna 16 itself.
[0033] In one embodiment, the transceiver monitor circuitry 30 may
include a directional coupler 31a, 31b, 31c for obtaining a portion
of each transceiver output. The directional couplers 31 may include
a low loss tap for obtaining a small portion of the RF signal
without significantly reducing the dBmV of the through signal. The
transceiver monitor circuitry may further include directional
couplers 33a, 33b, 33c for obtaining a portion of the return signal
to the transceivers 24. The directional couplers 33a, 33b, 33c may
similarly include a low loss tap for obtaining a small portion of
the RF signal without significantly reducing the dBmV of the
through signal.
[0034] In one embodiment, the system 10 operates within the 915 MHz
frequency band. In other embodiments, the system 10 may use other
frequency bands, such as, for example, 5.9 GHz. By way of example
only, to minimize impact on the power transmitted to or from the
antenna 16, the directional couplers 31, 33 may be 20 dB taps in
which 99% of the power of the input signal passes through the
directional couplers 31, 33 and 1% of the power is split off for
use in monitoring, as is described below. Selection of appropriate
directional couplers 31, 33 for a specific application will be
within the knowledge of a person ordinarily skilled in the art.
[0035] The transceiver monitor circuitry 30 may further include
processing circuitry 32, 34 (shown individually as 32a, 32b, 32c,
34a, 34b, 34c). The tapped signals from the directional couplers
31, 33, may be filtered and/or digitized and/or otherwise processed
in the processing circuitry 32a, 32b, 32c, 34a, 34b, 34c,
respectively, before being provided to the controller 26. The
appropriate filtering, digitization, and other processing for the
tapped signals in order to obtain information regarding the signal
characteristics will be appreciated by those skilled in the art.
The processing circuitry 32a, 32b, 32c, 34a, 34b, 34c may output
measurement signals to the controller 26.
[0036] In one embodiment the processing circuitry 32, 34 may
include threshold circuits for determining whether the RF power
level of the tapped signal drops below a threshold level. The
threshold level may be predetermined or may be controlled
dynamically by the controller 26. Output signals from the threshold
circuitry corresponding to each transceiver 24 may be input to the
controller 26. On this basis, the controller 26 may assess whether
the individual transceivers 24 are operating normally. The
threshold circuitry 32 may include various discrete components,
including filters, etc., for determining or detecting the power
level of an RF signal and comparing it against a threshold level,
as will be appreciated by those of ordinary skill in the art.
[0037] Reference is made to FIG. 5, which diagrammatically shows an
example embodiment of a portion of the transceiver monitor
circuitry 30. The circuitry 30 includes the directional coupler 31
for obtaining a portion of the output signal from the transceiver
24 (FIG. 1). The directional coupler 31 outputs the portion as a
tapped signal 38. The tapped signal 38 is input to the processing
circuitry 32. In this embodiment, the processing circuitry 32
includes a down-converter or mixer 40 and a peak detector 41. The
mixer 40 receives the tapped signal 38 and the carrier frequency,
which in some embodiments is in the 915 MHz band, and outputs a
baseband or IF signal. This signal is then input to the peak
detector 41, which outputs a DC signal 42 that has a voltage level
that may be used as a proxy for measuring the power output level of
the transceiver 24.
[0038] The processing circuitry 32 may also include a comparator
46. The comparator 46 receives, as inputs, the DC signal 42 and a
threshold signal 44. The threshold signal 44 has a pre-set DC level
that represents the minimum level that the DC signal 42 must
exhibit. If the DC signal 42 falls below the threshold signal 44
level, it is indicative that the output power of the transceiver 24
has fallen below the minimum level permitted. The threshold signal
44 may be predetermined through a voltage divider within the
processing circuitry 32. In another embodiment, the threshold
signal 44 is generated by a digital circuit pre-programmed to
output the threshold signal 44 and the predetermined level. In yet
another embodiment, the threshold signal 44 is output by a signal
generator circuit 52 operating under the control of the controller
26. In such an embodiment, the controller 26 may adjust the level
of the threshold signal 44 from time-to-time.
[0039] The comparator 46 outputs a result signal 50 based upon the
comparison between the DC signal 42 and the threshold signal 44.
For example, the comparator 46 may output a LOW signal if the DC
signal 42 remains above the threshold signal 44, and may output a
HIGH signal if the DC signal 42 falls below the threshold signal
44. In some embodiments, the comparator 46 may be implemented using
an op-amp or similar integrated circuit. The result signal 50 may
be buffered through a buffer circuit 48 before being input to a
failure detection input port 54 of the controller 26.
[0040] It will be appreciated that similar circuitry may be used in
conjunction with the directional coupler 33 to implement the
processing circuitry 34 for tapping and analyzing the RF input
signal. The down-converted and peak-detected RF input signal may be
compared with a minimum detectable threshold signal that is preset
to indicate the minimum RF level at which the transceiver 24
sensitivity ought to be set in order to detect a response signal
from a transponder. A concurrent failure by the transceiver 24 to
detect a response signal when the RF input signal has a power level
above the threshold indicates that the transceiver 24 input stage
sensitivity requires some adjustment or has failed altogether.
[0041] Reference is now made to FIG. 6, which shows another example
embodiment of a portion of the transceiver monitor circuitry 30. In
this embodiment, the transceiver monitor circuitry 30 includes the
mixer 40 and the peak detector 41 and includes an analog-to-digital
converter 60 for receiving the DC signal 42 and converting it to a
digital signal 62. The analog-to-digital converter 60 quantizes and
digitizes the DC signal 42, outputting the digital signal 62
containing data regarding the signal level of the DC signal 42. The
digital signal 62 may then be input to the controller 26, which
may, through operations implemented in software or firmware,
analyze the digital signal 62 to detect whether the output signal
level of the transceiver 24 falls below a predetermined
threshold.
[0042] Other methods and mechanisms for implementing the
transceiver monitor circuitry 30, and the processing circuitry 32,
34 in particular, will be understood by those of ordinary skill in
the art having regard to the present description.
[0043] Reference is again made to FIG. 1. The transceivers 24 may
each include one or more digital attenuators 36 (shown individually
as 36a, 36b, 36c) or other adjustable elements. The digital
attenuators 36 may be programmable adjustable impedances placed in
line with the RF input port or output port of the transceiver 24.
Through control signals from the controller 26, the setting of the
digital attenuators 36 may be adjusted. Accordingly, the controller
26 may boost RF output signal power by adjusting the setting of the
digital attenuator 36 within the transceiver 24, or may change the
transceiver 24 sensitivity for detecting RF input signals. In this
regard, the controller 24 may adapt or control the RF output and/or
input of the transceiver 24 in response to the measurement signals
received from the transceiver monitor circuitry 30. The digital
attenuators 36 allow the controller 26 to retune the transceiver 24
to compensate for component drift within the transceiver 24 or
degradation in the transmission line or antenna 16.
[0044] Reference is now also made to FIG. 2, which shows another
block diagram of the ETC system shown in FIG. 1. The controller 26
may include a data port for exchanging data with a communication
subsystem 40 (FIG. 1). The communication subsystem 40 facilitates
communication with a remote system through a network (indicated
generally using reference number 50). In some embodiments, the
communication subsystem 40 may include a serial data port, a
wireless communications port, a modem, or other system for sending
and receiving data communications with a remote computer and/or
system. The communication subsystem 40 is operable to output a
communication signal to a remote destination and to receive a
communication signal from the remote destination.
[0045] In one embodiment the communication subsystem 40 is
configured to send and receive data with a remote computer or
client device 80 over the network 50. The remote client device 80
monitors the state and operation of the reader 20 and other readers
in an overall electronic toll transaction system. The remote client
device 80 may further provide instructions to individual readers by
way of a data communication signal sent to the communications
subsystem 40. In this regard, the remote client device 80 may
monitor the reader 20 performance, including the performance of the
individual transceiver(s) 24, and may make adjustments by way of
the digital attenuators 36 within the respective transceivers
24.
[0046] In one embodiment, the communication subsystem 40 operates
as a server in relation to the client device 80. For example, the
subsystem 40 may implement an http server for receiving and
responding to information requests from the remote client device 80
over the network 50. The communications subsystem 40 may include
one or more mark-up language documents configured to contain data
regarding the transceivers 24, their state, operating parameters,
and other data. The documents may be created using HTML, XML, or
any other suitable mark-up language.
[0047] The subsystem 40, together with the controller 26, may be
configured to receive authenticated instructions to vary one or
more parameters, such as the setting of one of the digital
attenuators 36, from the remote client device 80 over the network
50. Various security mechanisms and protocols may be implemented by
the subsystem 40 to ensure that the reader 20 and parameters within
the transceivers 24 are altered only by authorized persons.
[0048] The network 50 may be private, public, or a combination of
both. The network 50 may be wired or wireless or a combination
thereof. In one embodiment, the network 50 includes the
Internet.
[0049] Reference is now made to FIGS. 3 and 4, which show, in
flowchart form, a method 100 for monitoring and adjusting
transceivers in an electronic toll collection system.
[0050] The method 100 begins in step 102 with the transmission of
the RF trigger signal by one of the transceivers. The transceiver
generates an RF output signal conforming to the predefined
communications protocol. By way of example, the RF trigger signal
may be a burst of RF energy at about 915 MHz for a predefined pulse
duration, such as about 20 Ps.
[0051] The transceiver monitor circuitry taps the outgoing RF
trigger signal to obtain a tapped signal. The power level of the
tapped signal is compared to a threshold level to determine whether
the outgoing RF trigger signal meets the minimum power level
requirement. In step 104, it is determined whether the transceiver
generated an RF trigger signal having sufficient power. If so, then
the method 100 continues at step 106. Otherwise, the method 100
proceeds to step 108.
[0052] In step 108, it is determined whether the problem is
correctable through adjustment. For example, if the RF output power
is slightly low and if the transceiver includes a mechanism, such
as a programmable attenuator, in its output path that may be
adjusted to provide a power boost, then the problem may be
correctable. If the mechanism has reached a limit point, then the
problem may not be correctable. For example, this may occur if the
programmable attenuator has reached a boundary maximum beyond which
it cannot be further adjusted. Step 108 may include testing various
conditions, such as whether the RF output power is sufficiently
close to zero to indicate total failure in the transceiver, or
whether the adjustment mechanism has scope for further adjustment.
If the problem appears correctable, then the method 100 continues
to step 110.
[0053] In step 110, the adjustment required to compensate for the
low power output from the transceiver. It will be appreciated that
various algorithms may be used to determine an appropriate
adjustment to bring the output power level up to an acceptable
level.
[0054] If the problem cannot be corrected through an adjustment to
the transceiver, then the method 100 jumps to step 112, wherein the
transceiver is disabled. This may include excluding the transceiver
from use in the scanning pattern and replacing it with a redundant
transceiver, or shifting its load onto other transceivers in the
reader.
[0055] In any event, following step 112 or 110 in step 114 a report
or alert message may be generated and/or output from the reader to
indicate that a problem was detected with one of the transceivers.
The report or message may be logged to memory within the reader,
may be output through the communications subsystem, and/or may be
displayed or otherwise output locally. The message may indicate the
nature of the problem detected, including measurement data, and
which transceiver was determined to be deficient.
[0056] If, in step 104, no problem is detected with the RF output
power from the transceiver, then the method 100 proceeds to step
106, where the VSWR is assessed. The VSWR is the ratio of the
reflected signal power to the outgoing signal power. Ideally the
VSWR is zero, meaning that no energy is reflected back and it is
all propagated from the antenna as RF waves. However, various
discontinuities and mismatches in the transmission line, antenna,
and various couplings and connectors along the signal path may give
rise to reflected energy. The transceiver monitor circuitry taps
the input RF signal that arises during the transmission of the RF
trigger signal and based upon it, and the tapped RF output signal,
the VSWR is assessed. If the VSWR rises above a maximum limit, it
is indicative of degraded or damaged transmission facilities.
[0057] If a problem is detected in step 106, then the method 100
jumps to step 114. A problem with the VSWR is most likely an issue
in an antenna or transmission line, which likely cannot be
corrected or compensated for through adjusting the transceiver
output or sensitivity. Accordingly, detection of the VSWR leads to
generation of a report or message indicating the detected problem.
The report or message may include information regarding the
transceiver, antenna, and measured data to enable personnel to
identify and diagnose the potential problem.
[0058] After step 114, or after it is determined that no problems
exist in step 106, then the method 100 continues in step 116 in
which an RF input signal is received. In step 118, using the
transceiver monitor circuitry, the reader assesses whether the RF
input signal falls below the minimum level that should be
detectable by the transceiver in detecting a response signal from a
transponder. If the RF input signal is above the minimum level,
then in step 120 the reader assesses whether the transceiver
detects the RF input signal. If not, then it is indicative of a
problem with the sensitivity of the RF input stage of the
transceiver, and the method 100 proceeds to step 122.
[0059] In step 122, the controller assesses whether the problem
with transceiver sensitivity can be corrected through adjustment of
a programmable attenuator or other adjustable element within the RF
input stage of the transceiver. The adjustable element may not have
further scope for adjustment--i.e. it may have reached a maximum or
minimum setting. Alternatively, the magnitude of the problem, if
the measured RF input level is reasonable robust, may indicate a
total failure of the transceiver RF input stage rather than a drift
in the sensitivity setting. In either case, the problem may not be
correctable through adjustment. In these circumstances, the method
100 may proceeds to step 124 to disable the transceiver,
effectively by excluding it from use in the scanning functions of
the reader.
[0060] If the problem appears correctable, then in step 126 an
appropriate adjustment is calculated by the controller and the
controller sends a signal or command to the adjustable element,
such as a programmable attenuator, to change its setting.
[0061] After steps 124 or 126, a report or message is generated, as
was described above in connection with step 114. Then the method
100 may return to step 102.
[0062] It will be appreciated that during operation of any of the
foregoing methods, the various parameters and test results obtained
through the transceiver monitor circuitry and input to the
controller may be logged or saved to memory. For example, the
reader may include volatile or non-volatile memory, such as flash
memory, to which the transceiver data may be logged from
time-to-time. In some embodiments, the logged data may be accessed
by the remote client devices through the communications subsystem.
In another embodiment, the logged data is periodically "pushed" to
a remote location over the network as a reporting function of the
controller and communications subsystem.
[0063] The setting of the various threshold maximum and minimum
signal levels in particular applications will be within the
understanding of a person of ordinary skill in the art.
[0064] The present invention may be embodied in other specific
forms without departing from the spirit or essential
characteristics thereof. Certain adaptations and modifications of
the invention will be obvious to those skilled in the art.
Therefore, the above discussed embodiments are considered to be
illustrative and not restrictive, the scope of the invention being
indicated by the appended claims rather than the foregoing
description, and all changes which come within the meaning and
range of equivalency of the claims are therefore intended to be
embraced therein.
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