U.S. patent application number 10/024977 was filed with the patent office on 2003-01-02 for wide area communications network for remote data generating stations.
This patent application is currently assigned to Itron, Inc.. Invention is credited to Holowick, Erwin, Jacob, Nathan R., Johnson, Dennis F., Murphy, Michael F., Schellenberg, James J., Stasenski, Michael S., Wiebe, Michael.
Application Number | 20030001754 10/024977 |
Document ID | / |
Family ID | 27383115 |
Filed Date | 2003-01-02 |
United States Patent
Application |
20030001754 |
Kind Code |
A1 |
Johnson, Dennis F. ; et
al. |
January 2, 2003 |
Wide area communications network for remote data generating
stations
Abstract
A wide area communications network communicating data from a
plurality of network service modules through a plurality of remote
cell nodes and intermediate data terminals to a central data
terminal. The wide area communicates network collects network
generated by a plurality of physical devices such as gas, water or
electricity meters, located within a geographical area. The wide
area communications network is a layered network have a
hierarchical communications topology. The central data terminal
controls network operation. Intelligence exists at all layers of
the network, thereby easing the workload of the central data
terminal. The intelligence attributed to each module is a function
of the application of that module.
Inventors: |
Johnson, Dennis F.;
(Winnipeg, CA) ; Wiebe, Michael; (Winnipeg,
CA) ; Holowick, Erwin; (Winnipeg, CA) ; Jacob,
Nathan R.; (Winnipeg, CA) ; Murphy, Michael F.;
(Winnipeg, CA) ; Schellenberg, James J.;
(Winnipeg, CA) ; Stasenski, Michael S.; (Winnipeg,
CA) |
Correspondence
Address: |
Brad Pedersen
Patterson, Thuente, Skaar & Christensen, P.A.
4800 IDS Center
80 South 8th Street
Minneapolis
MN
55402-2100
US
|
Assignee: |
Itron, Inc.
|
Family ID: |
27383115 |
Appl. No.: |
10/024977 |
Filed: |
December 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10024977 |
Dec 19, 2001 |
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09960800 |
Sep 21, 2001 |
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09960800 |
Sep 21, 2001 |
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09687785 |
Oct 13, 2000 |
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6373399 |
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09687785 |
Oct 13, 2000 |
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09296359 |
Apr 22, 1999 |
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6172616 |
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09296359 |
Apr 22, 1999 |
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08454678 |
May 31, 1995 |
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5963146 |
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08454678 |
May 31, 1995 |
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08271545 |
Jul 7, 1994 |
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5553094 |
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08271545 |
Jul 7, 1994 |
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08124495 |
Sep 22, 1993 |
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08124495 |
Sep 22, 1993 |
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07732183 |
Jul 19, 1991 |
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07732183 |
Jul 19, 1991 |
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07480573 |
Feb 15, 1990 |
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5056107 |
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Current U.S.
Class: |
340/870.02 |
Current CPC
Class: |
Y04S 40/00 20130101;
H02J 13/00028 20200101; G08C 15/00 20130101; H02J 13/00017
20200101; H04L 12/2854 20130101; Y04S 20/20 20130101; H04L 43/0829
20130101; H04Q 9/14 20130101; H04W 84/04 20130101; H04W 74/08
20130101; G08C 15/06 20130101; Y02B 90/20 20130101; H02J 13/0086
20130101; H04W 74/0833 20130101; G01D 4/008 20130101; Y02B 70/30
20130101; H02J 13/00034 20200101; H04L 43/0817 20130101; H04W 74/06
20130101; H04W 8/26 20130101; Y04S 20/30 20130101; H04L 43/022
20130101; H04W 24/10 20130101; G01D 4/004 20130101 |
Class at
Publication: |
340/870.02 |
International
Class: |
G08C 015/06; G08B
023/00 |
Claims
What is claimed:
20. A data collection system comprising: a) a plurality of
telemetry devices, each including i) a sensor configured to
generate a series of successive measurements by measuring a
parameter at a series of measurement times, ii) a memory configured
to store a plurality of measurements from said series of successive
measurements, and iii) a transmitter configured to transmit
measurements stored in memory to a collection device at a series of
transmission times, each of said transmitted measurements being
transmitted at a plurality of different transmission times; and b)
a collection device having i) a receiver configured to receive
transmissions from said telemetry devices, ii) a processor
configured to extract said series of successive measurements from a
series of received transmissions and further configured to generate
a metered function of said parameter by analyzing said series of
successive measurements, and iii) a transmitter configured to
transmit said metered function to a monitoring station.
21. The data collection system of claim 20 wherein the transmitter
of each telemetry device is configured to generate wireless
transmissions.
22. The data collection system of claim 20 wherein the sensor of
each telemetry device includes: a counter for storing a value,
means for incrementing said counter upon receipt of a trigger
signal, and means for storing said value from said counter in said
first memory and resetting said counter at said measurement
times.
23. The data collection system of claim 20 wherein each of said
telemetry devices discards the oldest measurement stored in memory
and stores in memory a new measurement from said sensor.
24. The data collection system of claim 20 wherein each of said
telemetry devices further includes a timer having a predetermined
time interval, wherein the expiration of said predetermined time
interval causes said sensor to generate a measurement.
25. The data collection system of claim 20 wherein said collection
device further includes a memory configured to store a data object
representing a given telemetry device from which the collection
device receives transmissions.
26. The data collection system of claim 25 wherein the memory of
each telemetry device is configured to store a number, the given
telemetry device increments said number each time a measurement is
generated, said stored number is transmitted by the transmitter of
the given telemetry device in a current transmission, the data
object representing the given telemetry device includes a number
transmitted in a previous transmission received from the given
telemetry device; and the processor of the collection device is
configured to compare the number transmitted in the current
transmission to the number transmitted in the previous
transmission.
27. The data collection system of claim 25 wherein each of said
telemetry devices includes means for detecting a power failure, the
memory of each telemetry device is configured to store power
failure information indicating whether each stored measurement was
generated following a power failure, said power failure information
is transmitted by the transmitter of the given telemetry device at
said transmission times, and the data object representing the given
telemetry device includes said transmitted power failure
information received by the collection device from the given
telemetry device.
28. The data collection system of claim 25 wherein said metered
function is a load profile, and the data object includes the
duration of a load profile period.
29. The data collection system of claim 25 wherein said metered
function is a demand profile, and the data object includes a
duration of a demand profile period.
30. The data collection system of claim 20 wherein said parameter
is selected from the group consisting of electrical power, fluid
flow, voltage, current, temperature, pressure, and humidity.
31. The data collection system of claim 30 wherein said parameter
is electrical power.
32. The data collection system of claim 30 wherein said parameter
is fluid flow.
33. The data collection system of claim 30 wherein said fluid is
natural gas.
34. The data collection system of claim 30 wherein said fluid is
water.
35. A method of collecting data comprising the steps of: a)
generating a series of successive measurements by measuring a
parameter with a telemetry device at a series of measurement times;
b) storing a plurality of said measurements in said telemetry
device; c) transmitting said stored measurements to a collection
device at a series of transmission times; d) extracting said series
of successive measurements from a series of said transmissions with
said collection device; e) generating a metered function of said
parameter with said collection device by analyzing said series of
successive measurements; and f) transmitting said metered function
to a monitoring station.
36. The method of claim 35 further comprising the steps of: storing
an old number in said collection device, generating a new number in
said telemetry device each time a measurement is generated,
transmitting said new number with stored measurements, and
comparing said old number to said new number at said collection
device to determine which measurements are new measurements which
were not previously received by said collection device and whether
there are missing measurements.
37. The method of claim 35 wherein said transmissions are wireless
transmissions.
38. The method of claim 36 further comprising the step of storing
said old number in said telemetry device, and wherein the step of
generating said new number includes incrementing said old
number.
39. The method of claim 38 further comprising the step of
determining the measurement times for new measurements received by
said collection device.
40. The method of claim 39 further comprising the steps of: storing
information in said telemetry device indicating whether a power
failure occurred between successive measurements, transmitting said
information to said collection device, and using said information
to determine whether there are new measurements for which the
measurement time cannot be determined.
41. The method of claim 40 further comprising the step of
performing a recovery operation for missing measurements or new
measurements for which the measurement time cannot be
determined.
42. The method of claim 35 further comprising the step of waiting
an alignment time following a measurement to transmit said stored
measurements.
43. The method of claim 42 wherein said alignment time is selected
randomly.
44. The method of claim 42 wherein said transmission occurs
following an integer number of measurements.
45. The method of claim 35 wherein said parameter is selected from
the group consisting of electrical power, fluid flow, voltage,
current, temperature, pressure, and humidity.
46. The method of claim 45 wherein said parameter is electrical
power.
47. The method of claim 45 wherein said parameter is fluid
flow.
48. The method of claim 45 wherein said fluid is natural gas.
49. The method of claim 45 wherein said fluid is water.
50. A network for collecting data generated by a plurality of
sensors, comprising: a) a plurality of data generating devices,
each including i) a sensor configured to generate measurements by
measuring a parameter, ii) a memory configured to store said
measurements, and iii) a transmitter configured to transmit at a
plurality of transmission times measurements stored in memory to an
intermediate device; and b) a plurality of intermediate devices,
there being fewer intermediate devices than data generating
devices, each of said intermediate devices including i) a receiver
configured to receive transmissions from a subset of said plurality
of data generating devices, ii) a processor configured to extract
said measurements from said transmissions and further configured to
generate a metered function of said parameter by analyzing said
measurements, and iii) a transmitter to transmit said metered
function; and c) a central station configured to receive said
transmitted metered functions from said plurality of intermediate
devices.
51. A method of collecting data comprising the steps of: a)
generating measurements by measuring a parameter with a sensor; b)
storing a plurality of said measurements in a memory; c)
transmitting said stored measurements to an intermediate device; d)
extracting said measurements from said transmissions with said
intermediate device; e) generating a metered function of said
parameter with said intermediate device by analyzing said
measurements; and f) transmitting said metered function to a
central station.
52. A data collection system, comprising: a plurality of sensors
each of which has a meter configured to sample a parameter value at
discrete measurement times and a transmitter configured to transmit
data measured by the meter; and a collector having a receiver
configured to receive data transmitted by the plurality of sensors,
a processor configured to generate a summary profile of data
received by the receiver from the plurality of sensors, and a
transmitter configured to transmit the summary profile to a
monitoring station, wherein each sensor periodically transmits a
plurality of data measurements during a current data collection
period and, with each transmission, each sensor transmits redundant
data measurements corresponding to a prior transmission, and the
collector is configured to reduce the occurrence of usage profile
errors based upon the redundant data measurements contained in a
received transmission.
Description
RELATED PATENTS
[0001] This application is a continuation of U.S. application Ser.
No. 09/960,800, filed Sep. 21, 2001, entitled WIDE AREA
COMMUNICATIONS NETWORK FOR REMOTE DATA GENERATING STATIONS, which
is a continuation of Ser. No. 09/687,785, filed Oct. 13, 2000,
entitled WIDE AREA COMMUNICATION NETWORK FOR REMOTE DATA GENERATING
STATIONS, which is a continuation of U.S. application Ser. No.
09/296,359, filed Apr. 22, 1999, entitled WIDE AREA COMMUNICATIONS
NETWORK FOR REMOTE DATA GENERATING STATION, now issued as U.S. Pat.
No. 6,172,616, which is a continuation of U.S. application Ser. No.
08/454,678, filed May 31, 1995, entitled WIDE AREA COMMUNICATIONS
NETWORK FOR REMOTE DATA GENERATING STATIONS, now issued as U.S.
Pat. No. 5,963,146, which is a continuation of U.S. application
Ser. No. 08/271,545, filed Jul. 7, 1994, entitled, RADIO
COMMUNICATION NETWORK FOR REMOTE DATA GENERATING STATIONS, now
issued as U.S. Pat. No. 5,553,094, which is a file wrapper
continuation application of U.S. application Ser. No. 08/124,495,
filed Sep. 22, 1993 entitled RADIO COMMUNICATION NETWORK FOR REMOTE
DATA GENERATING STATIONS, which is a file wrapper continuation
application of U.S. application Ser. No. 07/732,183, filed Jul. 19,
1991, entitled RADIO COMMUNICATION NETWORK FOR REMOTE DATA
GENERATING STATIONS, which is a continuation-in-part of U.S.
application Ser. No. 07/480,573, filed Feb. 15, 1990, now issued as
U.S. Pat. No. 5,056,107, which issued on Oct. 8, 1991, entitled
RADIO COMMUNICATION NETWORK FOR REMOTE DATA GENERATING STATIONS.
The benefit of the earlier filing dates of the parent patent
applications is claimed pursuant to 35 U.S.C. .sctn. 120.
BACKGROUND OF THE INVENTION
[0002] This invention relates to a communications network for
collecting data from remote data generating stations, and more
particularly a radio based system for sending data from a plurality
of network service modules, with each network service module
attached to a meter, and communicating through remote cell nodes
and through intermediate data terminals, to a central data
terminal.
DESCRIPTION OF THE RELEVANT ART
[0003] Many attempts have been made in recent years to develop an
automatic meter reading system for utility meters such as used for
electricity, gas and water, which avoids meter reading personnel
inspecting and physically noting the meter readings. There are, of
course, many reasons for attempting to develop a system of this
type.
[0004] Most of the prior art systems have achieved little success.
The system, which has achieved some success or is most widely used
has an automatic meter reading unit mounted on an existing meter at
the usage site and includes a relatively small transmitter and
receiver unit of very short range. The unit is polled on a regular
basis by a traveling reading unit, which is carried around the
various locations on a suitable vehicle. The traveling reading unit
polls each automatic meter reading unit in turn to obtain stored
data. This approach is of limited value in that it requires
transporting the equipment around the various locations and, hence,
only very infrequent, for example monthly, readings can be made.
The approach avoids a meter reader person actually entering the
premises to physically inspect the meter which is of itself of some
value but only limited value.
[0005] Alternative proposals in which reading from a central
location is carried out have been made but have achieved little
success. One proposal involves an arrangement in which
communication is carried out using the power transmission line of
the electric utility. Communication is, therefore, carried out
along the line and polls each remote reading unit in return. This
device has encountered significant technical difficulties.
[0006] Another alternative attempted to use the pre-existing
telephone lines for communication. The telephone line proposal has
a significant disadvantage since it must involve a number of other
parties, in particular the telephone company, for implementing the
system. The utility companies are reluctant to use a system which
cannot be entirely controlled and managed by them.
[0007] A yet further system using radio communication has been
developed by Data Beam, which was a subsidiary of Connecticut
Natural Gas. This arrangement was developed approximately in 1986
and has subsequently received little attention and it is believed
that no installations are presently operative. The system includes
a meter reading device mounted on the meter with a transmitting
antenna which is separate from the meter reading device. The
transmitting antenna is located on the building or other part of
the installation site which enables to the antenna to transmit over
a relatively large distance. The system uses a number of receiving
units with each arranged to receive data from a large number of
transmitters, in the range of 10,000 to 30,000. The transmitters,
in order to achieve maximum range, are positioned to some extent
directionally or at least on a suitable position of the building to
transmit to the intended receiving station. This arrangement leads
to using a minimum number of receiving stations for optimum cost
efficiency.
[0008] The separate transmitter antenna, however, generated
significant installation problems due to wiring the antenna through
the building to the transmitter and receiver. The anticipated high
level of power used for transmitting involved very expensive
battery systems or very expensive wiring. The proposal to reduce
the excessive cost was to share the transmission unit with several
utilities serving the building so that the cost of the transmitter
could be spread, for example, between three utilities supplied to
the building. Such installation requires separate utility companies
to cooperate in the installation. While this might be highly
desirable, such cooperation is difficult to achieve on a practical
basis.
[0009] In order to avoid timing problems, the meter reading units
were arranged to communicate on a random time basis. However, the
very large number, up to 30,000, of meter reading units reporting
to a single receiving station, leads to a very high number of
possible collisions between the randomly transmitted signals. The
system, therefore, as proposed, with daily or more often reporting
signals could lose as many as 20% to 50% of the signals transmitted
due to collisions or interference which leads to a very low
efficiency data communication. The use of transmitters at the meter
reading units which are of maximum power requires a larger
interference protection radius between systems using the same
allocated frequency.
[0010] An alternative radio transmission network is known as ALOHA.
ALOHA has a number of broadcasting stations communicating with a
single receiving station, with the broadcasting stations
transmitting at random intervals. In the ALOHA system, collisions
occur so that messages are lost. The solution to this problem is to
monitor the retransmission of the information from the receiving
station so that each broadcasting station is aware when its
transmission has been lost. Each broadcasting station is then
programmed to retransmit the lost information after a predetermined
generally pseudorandom period of time. The ALOHA system requires
retransmission of the information from the receiving station to
take place substantially immediately and requires each broadcasting
station to also have a receiving capability.
[0011] Cellular telephone networks are implemented on a wide scale.
Cellular systems, however, use and allocate different frequencies
to different remote stations. While this is acceptable in a high
margin use for voice communications, the costs and complications
cannot be accepted in the relatively lower margin use for remote
station monitoring. The technology of cellular telephones leads to
the perception in the art that devices of this type must use
different frequency networks.
[0012] While theoretically automatic meter reading is highly
desirable, it is, of course, highly price sensitive and hence it is
most important for any system to be adopted for the price per unit
of particularly the large number of meter reading units to be kept
to a minimum. The high cost of high power transmission devices,
receiving devices, and battery systems generally leads to a per
unit cost which is unacceptably high.
OBJECTS OF THE INVENTION
[0013] A general object of the invention is a communications
network for communicating data from a plurality of network service
modules to a central data terminal.
[0014] Another object of the invention is a communications network
which is suitable for an automatic meter reading system.
[0015] A further object of the invention is a communications
network for collecting data from remote data generating stations
that is simple and economic to install and maintain.
[0016] A still further object of the invention is a communications
network for collecting data from network service modules that is
spectrum efficient, and has inherent communication redundancy to
enhance reliability and reduce operating costs.
[0017] An additional object of the invention is an open
architecture communication network which accommodates new
technology, and allows the network operator to serve an arbitrarily
large contiguous or non-contiguous geographic area.
SUMMARY OF THE INVENTION
[0018] According to the present invention, as embodied and broadly
described herein, a wide area communications network is provided
for sending data from a plurality of network service modules to a
central data terminal. The wide area communications network
collects NSM data generated by a plurality of physical devices
located within a geographical area. The physical devices may be,
for example, a utility meter as used for electricity, gas or water.
The wide area communications network comprises a plurality of
network service modules, a plurality of remote cell nodes, a
plurality of intermediate data terminals, and a central data
terminal. Each network service module is coupled to a respective
physical device.
[0019] The network service module (NSM) includes NSM-receiver
means, NSM-transmitter means, and NSM-processor means, NSM-memory
means and an antenna. The NSM-receiver means, which is optional,
receives a command signal at a first carrier frequency or a second
carrier frequency. In a preferred mode of operation, the
NSM-receiver means receives the command signal on the first carrier
frequency for spectrum efficiency. The wide area communications
network can operate using only a single carrier frequency, i.e.,
the first carrier frequency. The command signal allows the
oscillator of the NSM-transmitting means to lock onto the frequency
of the remote cell node, correcting for drift. Signaling data also
may be sent from the remote cell node to the network service module
using the command signal.
[0020] The NSM-processor means arranges data from the physical
device into packets of data, transfers the data to the NSM-memory
means, and uses the received command signal for adjusting the first
carrier frequency of the NSM transmitter. The NSM data may include
meter readings, time of use and other information or status from a
plurality of sensors. The NSM-processor means, for all network
service modules throughout a geographical area, can be programmed
to read all the corresponding utility meters or other devices being
serviced by the network service modules. The NSM-processor means
also can be programmed to read peak consumption at predetermined
intervals, such as every 15 minutes, throughout a time period, such
as a day. The NSM-memory means stores NSM data from the physical
device. The NSM-processor means can be programmed to track and
store maximum and minimum sensor readings or levels throughout the
time period, such as a day.
[0021] The NSM-transmitter means transmits at the first carrier
frequency the respective NSM data from the physical device as an
NSM-packet signal. The NSM-packet signal is transmitted at a time
which is randomly or pseudorandomly selected within a predetermined
time period, i.e., using a one-way-random-access protocol, by the
NSM-processor means. The NSM-transmitter includes a synthesizer or
equivalent circuitry for controlling its transmitter carrier
frequency. The NSM-transmitter means is connected to the antenna
for transmitting multi-directionally the NSM-packet signals.
[0022] A plurality of remote cell nodes are located within the
geographical area and are spaced approximately uniformly, such that
each network service module is within a range of several remote
cell nodes, and so that each remote cell node can receive
NSM-packet signals from a plurality of network service modules. The
remote cell nodes preferably are spaced such that each of the
network service modules can be received by at least two remote cell
nodes. Each remote cell node (RCN) includes RCN-transmitter means,
RCN-receiver means, RCN-memory means, RCN-processor means, and an
antenna. The RCN-transmitter means transmits at the first carrier
frequency or the second carrier frequency, the command signal with
signaling data. Transmitting a command signal from the
RCN-transmitter means is optional, and is used only if the
NSM-receiver means is used at the network service module as
previously discussed.
[0023] The RCN-receiver means receives at the first carrier
frequency a multiplicity of NSM-packet signals transmitted from a
multiplicity of network service modules. Each of the NSM-packet
signals typically are received at different points in time, since
they were transmitted at a time which was randomly or
pseudorandomly selected within the predetermined time period. The
multiplicity of network service modules typically is a subset of
the plurality of network service modules. The RCN-receiver means
also receives polling signals from the intermediate data terminal,
and listens or eavesdrops on neighboring remote cell nodes when
they are polled by the intermediate data terminal.
[0024] The RCN-memory means stores the received multiplicity of
NSM-packet signals. The RCN-processor means collates the NSM-packet
signals received from the network service modules, identifies
duplicates of NSM-packet signals, and deletes the duplicate
NSM-packet signals. When a polling signal is sent from an
intermediate data terminal (IDT), the RCN-transmitter means
transmits at the first carrier frequency the stored multiplicity of
NSM-packet signals as an RCN-packet signal.
[0025] When a first remote cell node is polled with a first polling
signal by the intermediate data terminal, neighboring remote cell
nodes receive the RCN-packet signal transmitted by the first remote
cell node. Upon receiving an acknowledgment signal from the
intermediate data terminal, at the neighboring remote cell nodes,
the respective RCN-processor means deletes from the respective
RCN-memory means messages, i.e., NSM-packet signals, received from
the network service modules that have the same message
identification number as messages transmitted in the RCN-packet
signal from the first remote cell node to the intermediate data
terminal.
[0026] The plurality of intermediate data terminals are located
within the geographic area and are spaced to form a grid overlaying
the geographic area. Each intermediate data terminal includes
IDT-transmitter means, IDT-memory means, IDT-processor means and
IDT-receiver means. The IDT-transmitter means includes a
synthesizer or equivalent circuitry for controlling the carrier
frequency, and allowing the IDT-transmitter means to change carrier
frequency. The IDT-transmitter means transmits preferably at the
first carrier frequency, or the second carrier frequency, the first
polling signal using a first polling-access protocol to the
plurality of remote cell nodes. When the first polling signal is
received by a remote cell node, that remote cell node responds by
sending the RCN-packet signal to the intermediate data terminal
which sent the polling signal. If the intermediate data terminal
successfully receives the RCN-packet-signal, then the
IDT-transmitter means sends an acknowledgment signal to the remote
cell node.
[0027] The IDT-receiver means receives the RCN-packet signal
transmitted at the first carrier frequency from the remote cell
node which was polled. Thus, after polling a plurality of remote
cell nodes, the IDT-receiver means has received a plurality of
RCN-packet signals.
[0028] The IDT-memory means stores the received RCN-packet signals.
The IDT-processor means collates the NSM-packet signals embedded in
the RCN-packet signals received from the plurality of remote cell
nodes, identifies duplicates of NSM-packet signals and deletes the
duplicate NSM-packet signals, i.e., messages from network service
modules that have the same message identification number. In
response to a second polling signal from a central data terminal,
the IDT-transmitter means transmits a plurality of RCN-packet
signals as an IDT-packet signal to the central data terminal.
[0029] The central data terminal (CDT) includes CDT-transmitter
means, CDT-receiver means, CDT-processor means and CDT-memory
means. The CDT-transmitter means transmits sequentially the second
polling signal using a second polling access protocol to each of
the intermediate data terminals. The CDT-receiver means receives a
plurality of IDT-packet signals. The central data terminal,
intermediate data terminals and the remote cell nodes may be
coupled through radio channels, telephone channels, fiber optic
channels, cable channels, or other communications medium. The
CDT-processor means decodes the plurality of IDT-packet signals as
a plurality of NSM data. The CDT-processor means also identifies
duplicates of NSM data and deletes the duplicate NSM data. The
CDT-memory means stores the NSM data in a data base.
[0030] Additional objects and advantages of the invention will be
set forth in part in the description which follows, and in part
will be obvious from the description, or may be learned by practice
of the invention. The objects and advantages of the invention also
may be realized and attained by means of the instrumentalities and
combinations particularly pointed out in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate preferred
embodiments of the invention, and together with the description
serve to explain the principles of the invention.
[0032] FIG. 1 illustrates the hierarchial communications network
topology;
[0033] FIG. 2 is a network service module block diagram;
[0034] FIG. 3 is a representative NSM-data packet;
[0035] FIG. 4 is a listing of representative applications supported
by the communications network;
[0036] FIG. 5 is a schematic diagram of a network service
module;
[0037] FIG. 6 shows a front elevation view of an electricity
utility meter with a detection unit;
[0038] FIG. 7 shows a bottom plan view of the electricity utility
meter;
[0039] FIG. 8 is an illustration of a typical printout of
information obtained by the network service module of FIG. 1;
[0040] FIG. 9 is a remote cell node block diagram;
[0041] FIG. 10 is an intermediate data terminal block diagram;
[0042] FIG. 11 is a central data terminal block diagram;
[0043] FIG. 12 shows the configuration of the communications
network for serving widely separated geographic areas; and
[0044] FIG. 13 illustrates a typical communications network with
gradual growth in the number of areas served.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0045] Reference will now be made in detail to the present
preferred embodiments of the invention, examples of which are
illustrated in the accompanying drawings, wherein like reference
numerals indicate like elements throughout the several views.
[0046] A wide area communications network communicates data from a
plurality of network service modules to a central data terminal.
The wide area communications network collects NSM data generated by
a plurality of physical devices located within a geographical area.
The wide area communications network, as illustratively shown in
FIG. 1, is a layered network having a hierarchial communications
topology comprising a plurality of network service modules 110, a
plurality of remote cell nodes 112, a plurality of intermediate
data terminals 114, and a central data terminal 120. The physical
devices may be, for example, a utility meter as used for
electricity, gas or water.
[0047] The central data terminal controls network operation.
Intelligence exists at all layers of the network, thereby easing
the workload of the central data terminal. The intelligence
attributed to each module is a function of the application of that
module.
Network Service Module
[0048] Information is acquired at the lowest level of the wide area
communications network of FIG. 1, and the network service module
110 performs the data acquisition functions. Network service
modules 110 include meter service modules for electricity, gas and
water, a service disconnect module, a load management module, an
alarm monitoring module, or any other module that can be used with
the wide area communications network.
[0049] The network service modules 110 are linked to the wide area
communications network via high frequency radio channels, typically
in the 928 MHz-952 MHz band, as well as related frequencies in the
902 MHz-912 MHz, and 918 MHz -928 MHz bands. Radio channels in
these bands are the preferred communications medium because use of
radio communications eliminates the need for physical connections
to the service modules which drastically reduces installation costs
compared to other communication media such as telephone, cable
networks and power line carriers. Also, operation in the high
frequency bands permits the use of small antennas so that
retrofitting standard watt hour meters is simplified. Radio
communication channels in other bands may work equally as well,
however.
[0050] In the exemplary arrangement shown in FIG. 2, the network
service module (NSM) 110 includes NSM-receiver means,
NSM-transmitter means, NSM-processor means, NSM-memory means, and
an NSM antenna 322. The NSM-transmitter means and the NSM-receiver
means are coupled to the NSM antenna 322. The NSM-processor means
is coupled to the NSM-transmitter means, NSM-receiver means,
NSM-memory means, and the physical device. The physical device is
shown as basic 320 and other sensors 322, and application control
interface 324. The network service module also includes an AC power
supply 310 and a back-up battery power supply 312.
[0051] The NSM-receiver means is embodied as an NSM receiver 316,
and is optional. If an NSM receiver 316 is included with the
network service module, then the NSM receiver 316 can be used for
receiving a command signal, which includes signaling data. The
command signal can be transmitted at either a first carrier
frequency or a second carrier frequency. Normally, the first
carrier frequency is used by the NSM-transmitter means for
transmitting to a remote cell node. In a preferred embodiment, the
NSM receiver 316 receives the command signal on the first carrier
frequency for spectrum efficiency. Thus, the wide area
communications network can operate using only a single carrier
frequency, i.e., the first carrier frequency. The command signal
can provide a time reference for updating a local clock, and serve
as a frequency reference to the network service module. Signaling
data, such as manage service disconnect or control loads, also may
be sent from the remote cell node to the network service module
using the command signal. While the network service modules could
be polled by the command signal, in general, such polling is not
required and preferably not used with the present invention.
[0052] The NSM-processor means, which is embodied as an NSM
controller 314, arranges data from the physical device into packets
of data, and transfers the data to the NSM-memory means which is
embodied as an NSM memory 315. The NSM controller 314 may be a
microprocessor or equivalent circuit for performing the required
functions. The NSM controller 314 uses the received command signal
for adjusting and setting the first carrier frequency of the NSM
transmitter. The NSM data may include meter readings, time of use
and other information or status from a plurality of sensors. The
NSM controllers 314, for each network service module throughout a
geographical area, can be programmed to read all the corresponding
utility meters or other devices being serviced by the network
service module, respectively. The NSM controller 314 can be
programmed to read peak consumption at predetermined intervals,
such as every 15 minutes, throughout a time period, such as a day.
The NSM controller 314 also can be programmed to track and store
maximum and minimum sensor readings or levels throughout the time
period, such as a day.
[0053] The NSM memory 315 stores NSM data from the physical device.
NSM data may include meter reading data and time of use (TOU) and
other information or status from a plurality of sensors. The NSM
memory 315 may be random access memory (RAM) or any type of
magnetic media or other memory storage devices known in the art.
The NSM controller 314 uses the received command signal for
adjusting the first carrier frequency of the NSM transmitter
318.
[0054] The NSM-transmitter means is embodied as an NSM transmitter
318. The NSM transmitter 318 transmits at a first carrier frequency
the respective NSM data from the physical device in brief message
packets called an NSM-packet signal. The NSM-packet signal might
have a time duration of 100 milliseconds, although any time
duration can be used to meet particular system requirements. The
NSM-packet signal transmitted by the NSM transmitter 318 follows a
generic or fixed format, and a representative message packet is
illustrated in FIG. 3. Included in the message is: preamble;
opening frame; message type; message identification; service module
type; message number; service module address; data field; error
detection; and closing frame.
[0055] The NSM transmitter 318 is connected to an NSM antenna 322
for transmitting multi-directionally the NSM-packet signals. The
NSM transmitter 318 includes a synthesizer or equivalent circuitry
for controlling its transmitter carrier frequency and schedule.
[0056] The NSM-packet signal is transmitted at a time which is
randomly or pseudorandomly selected within a predetermined time
period, i.e., using a one-way-random-access protocol, by the
NSM-processor means. In order to simplify network operation and
reduce costs, the wide area communications network does not poll
individual network service modules. Rather, each network service
module reports autonomously at a rate appropriate for the
application being supported. Routine reports are therefore
transmitted randomly or pseudorandomly at fixed average intervals,
while alarm signals are transmitted immediately following detection
of alarm conditions. Alarm signals may be transmitted several times
with random delays. This avoids interference among alarm messages
if many alarms occur simultaneously, as in an area-wide power
outage.
[0057] As an alternative arrangement, the network service module
may be programmed to transmit three different types of messages at
different intervals. The first type of message can relate to the
accumulated usage information. The second type of message can
relate to an alarm condition which is basically transmitted
immediately. The alarm conditions that occur might relate to a
tamper action or to the absence of electrical voltage indicative of
a power failure. The third type of information which may be
transmitted less frequently can relate to the housekeeping
information.
[0058] After preparing the packet of data for transmission, the
controller 314 is arranged to hold the data packet for a random
period of time. This random period can be calculated using various
randomizing techniques including, for example, a psuedo-random
sequence followed, for example, by an actual random calculation
based upon the rotation of the metering disk at any particular
instant. In this way each of the network service modules is
arranged to transmit at a random time. The controller 314 is
arranged so that the transmission does not occur within a
particular predetermined quiet time so that none of the network
service modules is allowed to transmit during this quiet time. This
quiet time could be set as one hour in every eight hour period. In
this way after an eight hour period has elapsed, each of the
network service modules would transmit at a random time during the
subsequent seven hours followed by a quiet one hour.
[0059] Network capacity or throughput is limited by the probability
of message collisions at each remote cell node 112. Because all
network service modules 110 share a single carrier channel and
transmit at random times, it is possible for several network
service modules 110 within a range of a particular remote cell node
112 to transmit simultaneously and to collide at the remote cell
node. If the received signal levels are comparable, the overlapping
messages will mutually interfere, causing receive errors and both
messages will be lost. However, if one signal is substantially
stronger than the other, the stronger signal will be successfully
received. Moreover, since both signals are received by at least two
and preferably four of the remote cell nodes, the probability of
both messages being received is fairly high unless the network
service modules are in close spatial proximity. During an interval
T, each transmitter within a cell surrounding a single remote cell
node sends a single randomly timed message of duration M to several
potential receive stations.
[0060] N=no. of transmitters/cell
[0061] M=message duration (seconds)
[0062] T=message interval
[0063] P.sub.c=probability of collision
[0064] P.sub.s=probability of no collision
[0065] Once any Transmitter, T.sub.i, starts transmitting the
probability that another particular transmitter, T.sub.j, will
complete or start another transmission is 1 1 - 2 M T .
[0066] The probability that there will be no collision is 1- 2 P s
- ( 1 - 2 M ) N T
[0067] If there are N-1 other transmitters the probability of no
collision, P.sub.s, is given by 3 P s = ( 1 - ( 2 M ) ) N - 1 T
)
[0068] For large N 4 2 M T .
[0069] For a given Transmitter, T.sub.i, the probability of a
collision occurring during the interval T is 5 P c = 1 - P s = 1 -
( 1 - ( 2 M ) ) N T
[0070] The probability of collisions occurring on successive tries
is
P.sub.cn=(P.sub.c).sup.An
[0071] For M=0.3 Sec T=8 hrs.=28.8.times.10.sup.3 secs. 6 P s = ( 1
- ( 2 M ) ) N T 1 - 2.08 .times. 10 - 5 = ( .999979 ) N
1 N Ps Pc1 Pc2 Pc3 100 .9979 .0021 4 .times. 10.sup.-6 8 .times.
10.sup.-9 200 .9958 .0042 1.6 .times. 10.sup.-5 6.4 .times.
10.sup.-8 500 .9896 .0104 10.sup.-4 10.sup.-6 1,000 .9794 .0206 4
.times. 10.sup.-4 8 .times. 10.sup.-6 2,000 .9591 .041 1.6 .times.
10.sup.-3 6.8 .times. 10.sup.-5 5,000 .9010 .099 9.8 .times.
10.sup.-3 9.7 .times. 10.sup.-4 10,000 .811 .189 3.5 .times.
10.sup.-2 6.7 .times. 10.sup.-3
[0072] From the viewpoint of a remote cell node, the number of
transmitters, N.sub.T, whose signal level exceeds the receiver
noise level and can, therefore, be received reliably depends
on:
[0073] (a) the density of transmitters;
[0074] (b) transmit power level;
[0075] (c) propagation pathloss;
[0076] (d) background noise.
[0077] Propagation pathloss is highly variable due to attenuation,
reflection, refraction and scattering phenomena which are a
function of terrain, building structures, and antenna location.
Some of these parameters can even vary on a diurnal and seasonal
basis.
[0078] In estimating network performance however, the simple
message collision model is not completely accurate because:
[0079] 1. random noise bursts from various sources can obscure
messages which do not collide;
[0080] 2. some colliding message signals will be of sufficiently
different amplitude that the stronger signal will still be received
correctly.
[0081] A statistical model can be developed to provide data by
which determination can be made of the best location and number of
remote cell nodes for a particular geographical location. Thus, the
model can include data relating to house density the N- value
defmed above relating to the attenuation of the signal, the
location and presence of trees.
[0082] FIG. 4 is an illustrative listing of applications supported
by the network service module within the wide area communications
network. The following is a detailed discussion of the electricity
meter application.
Network Service Module with an Electricity Meter
[0083] A network service module 110 schematically is shown in FIG.
5 and is mounted in a suitable housing 211 illustrated in FIGS. 6
and 7 with the housing including suitable mounting arrangement for
attachment of the housing into the interior of a conventional
electricity meter 212. Each network service module is coupled to a
respective physical device. In FIG. 6, the physical device is an
electricity meter 212.
[0084] Referring to FIGS. 5, 6, and 7, the electricity meter 212
includes an outer casing 213 which is generally transparent. Within
the casing is provided the meter system which includes a disk 214
which rotates about a vertical axis and is driven at a rate
dependent upon the current drawn to the facility. The numbers of
turns of the disk 214 are counted by a counting system including
mechanical dials 215. The meter is of conventional construction and
various different designs are well known in the art.
[0085] An antenna 217 is mounted on a bracket 216 carried on the
housing inside the cover 213. The antenna 217, as shown, is
arc-shaped extending around the periphery of the front face. Other
antenna configurations are possible.
[0086] As illustrated in FIG. 6, the antenna 217 is mounted within
the cover 213 of the meter. Thus the NSM antenna 217 is mounted on
the support structure itself of the network service module 110.
This enables the network service module 110 to be manufactured
relatively cheaply as an integral device which can be installed
simply in one action. However, this provides an NSM antenna 217
which can transmit only relatively short distances. In addition,
the power level is maintained in relatively low value of the order
of 10-100 milliwatts, the energy for which can be provided by a
smaller battery system which is relatively inexpensive. An NSM
antenna 217 of this type transmitting at the above power level
would have a range of the order of one to two kilometers.
[0087] The network service module 110 is in a sealed housing which
prevents tampering with the sensors, microprocessor 220, and memory
221 located within the housing 211.
[0088] Turning now to FIG. 5, the network service module optionally
may include a detection device which uses the microprocessor 220
which has associated therewith a storage memory 221. An essential
sensor is for meter reading, for measuring the amount of
electricity, amount of water, or amount of gas consumed. Such a
sensor alleviates having a meter reader person by allowing the
system to automatically report the amount of usage of the physical
device.
[0089] Any number of sensors may be provided for detection of
tampering events with the network service module of the present
invention, and the sensors may be adapted for electricity, gas,
water, or other applications. For the most part, information
reported by the various sensors would be considered low data rate.
The wide area communications network supports distributed
automation functions including basic meter reading, time of use
meter reading, service connect, and disconnect operations, alarm
reporting, theft of service reporting, load research, residential
load control, commercial and industrial load curtailment, and
distributed supervisory control and data acquisition (SCADA).
Furthermore, the wide area communications network is readily
expandable to support new applications as they are developed.
[0090] While the emphasis, by way of example, is automatic meter
reading and on measuring time of use of an electricity meter, other
functions such as 15-minute peak consumption recording, line power
monitoring, i.e., outage and restoration, tamper sensing and
timekeeping are supported.
[0091] The following is a representative listing of possible
sensors that may be used with the network service module of the
present invention. Each sensor is optional, and to a person skilled
in the art, variants may be added to the network service module of
the present invention. For example, FIG. 6 illustratively shows a
temperature sensor 227 and a battery sensor 228; however, each
sensor 227, 228 may be substituted by or may be in addition to
other possible sensors from the following representative listing of
sensors.
[0092] (a) A tilt sensor 222 detects movement of the housing
through an angle greater than a predetermined angle so that once
the device is installed indication can be made if the device is
removed or if the meter is removed from its normal orientation.
[0093] (b) A field sensor 223 detects the presence of an electric
field. Unless there is power failure, the electric field sensor
should continue to detect the presence of an electric field unless
the meter is removed from the system.
[0094] (c) An acoustic sensor 224 detects sound. The sounds
detected are transmitted through a filter 225 which is arranged to
filter by analog or digital techniques the sound signal so as to
allow to pass through only those sounds which have been determined
by previous experimentation to relate to cutting or drilling action
particularly on the cover.
[0095] (d) A magnetic sensor 226 detects the presence of a magnetic
field. A magnetic field is generated by the coils driving the disk
214 so that magnetic fields should always be present unless the
meter has been by-passed or removed. As is well known, the rate of
rotation of the disk is dependent upon the magnetic field and,
therefore, this rate of rotation can be varied by changing the
magnetic field by applying a permanent or electromagnet in the area
of the meter to vary the magnetic field. The sensor 226 is,
therefore, responsive to variations in the magnetic field greater
than a predetermined amount so as to indicate that an attempt has
been made to vary the magnetic field adjacent the disk to slow down
the rotation of the disk.
[0096] (e) A heat sensor 227 detects temperature so that the
temperature associated with a particular time period can be
recorded. A battery level sensor is indicated at 228. The sensors
226, 227, and 228 communicate information through analog digital
converter 328 to the microprocessor 220. The information from
sensors 227 and 228 can be communicated to provide "housekeeping"
status of the operation of the unit. The temperature sensor 227 can
be omitted, if required, and this information replaced by
information gained from a public weather information source. In
some cases the meter is located inside the building and hence the
temperature will remain substantially constant whereas the outside
temperature is well known to vary consumption quite
dramatically.
[0097] (f) A consumption sensor comprises a direct consumption
monitor 229 which can be of a very simple construction since it is
not intended to act as an accurate measure of the consumption of
the electricity used. The direct consumption monitor 229 can,
therefore, simply be a device which detects the value of the
magnetic field generated on the assumption this is proportional to
the current drawn. The direct consumption value obtained can then
be competed with a measurement of the consumption as recorded by
the rotation of the disk 214. In the event that the direct
consumption monitor 229 provides a sum of the consumption over a
time period which is different from the consumption measured by
rotation of the disk 214 by an amount greater than a predetermined
proportion then the direct consumption monitor can be used to
provide a tamper signal. This would be indicative, for example, of
a mechanical tag applied to the disk to reduce recorded
consumption.
[0098] (g) A reverse sensor 230, discussed in more detail
hereinafter, detects reverse rotation of the disk 214 and provides
an input to the microprocessor on detection of such an event.
[0099] (h) A cover sensor 231 is used to detect the continual
presence of the cover 213. The cover sensor comprises a light
emitting diode (LED) 232 which generates a light beam which is then
reflected to a photo diode 233. The absence of the reflected beam
at the photo diode 233 is detected and transmitted as a tamper
signal to the microprocessor. The reflected beam is generated by a
reflective strip 234 applied on the inside surface of the cover
adjacent the diode 232 as shown in FIG. 6.
[0100] The above sensors thus act to detect various tampering
events so that the presence of such tampering events can be
recorded in the storage memory 221 under the control of the
microprocessor 220.
[0101] The microprocessor 220 also includes a clock signal
generator 335 so that the microprocessor 220 can create a plurality
of time periods arranged sequentially and each of a predetermined
length. In the example of the present invention shown, the time
periods are eight hours in length and the microprocessor 220 is
arranged to record in each eight hour period the presence of a
tamper event from one or more of the tamper signals.
[0102] As shown in FIG. 8 the series of the predetermined time
periods is recorded with the series allocated against specific
dates and each eight hour period within the day concerned having a
separate recording location within the storage memory 221. One such
series is shown in FIG. 8 where a number of tampering events 236
are indicated. The print-out thus indicates when any tampering
event 236 has occurred and in addition then identifies which type
of tampering event has taken place.
[0103] The rotation of the disk 214 also is detected to accurately
record the number of rotations of the disk both in a forward and in
a reverse direction. In FIG. 8, a table 237 shows in graphical form
the amount of rotation of a disk recorded in eight hour periods as
previously described. For one period of time the disk is shown to
rotate in a reverse direction 238. Whenever the disk rotates in a
reverse direction, the reverse rotation subtracts from the number
of turns counted on the conventional recording system 215 shown in
FIG. 6.
[0104] As shown in FIGS. 6 and 7, detection of the rotation of the
disk is carried out by the provision of a dark segment 239 formed
on the undersurface of the disk leaving the remainder of the disk
as a reflective or white material. The detection system thus
provides a pair of light emitting diodes 240, 241 which are
positioned on the housing so as to direct light onto the underside
of the disk. The light emitting diodes 240, 241 are angularly
spaced around the disk. The diodes are associated with the photo
diodes 242, 243 which receive light when the disk is positioned so
that the light from the associated light emitting diode 240, 241
falls upon the reflective part of the disk and that light is cut
off when the dark part of the disk 214 reaches the requisite
location. Basically, therefore, one of the pairs of light emitting
diodes 240, 241 and photo diodes 242, 243 is used to detect the
passage of the dark segment, that is of course, one rotation of the
disk. The direction of rotation is then detected by checking with
the other of the pairs as the dark segment reaches the first of the
pairs as to whether the second pair is also seeing the dark segment
or whether it is seeing the reflective part. Provided the sensors
are properly spaced in relation to the dimension of the segment,
therefore, this indicates the direction which the disk rotated to
reach the position which is detected by the first pair of
diodes.
[0105] In order to conserve energy, the sensors are primarily in a
sampling mode using an adaptive sensing rate algorithm. In one
example, the dark or non-reflective segment is 108.degree. of arc
and there is provided a 50.degree. displacement between the
sensors. In a practical example of a conventional meter, the
maximum rotation rate is of the order of 2 rps. A basic sample
interval can be selected at 125 m/sec, short enough to ensure at
least one dark sample is obtained from the dark segment. In
operation, only the first pair of sensors is sampled continuously.
When a dark response is observed, a second confirming sample is
obtained and the sample rate increased to 16 pps. As soon as a
light segment of the disk is sensed, the second sensor is sampled.
The second sensor still sees the dark segment then cw rotation is
confirmed while if a light segment is observed then ccw rotation is
indicated.
[0106] At slower speeds, the algorithm results in a sample rate of
8 pps for 70% of a rotation and 16 pps for 30% of a rotation for
the first pair of sensors plus two samples for direction sensing
for the second pair. For an annual average consumption of 12,000
kwh, the disk rotates approximately 1.6 million times.
[0107] In order to sense the presence of stray light which could
interfere with measurements, the photo diode output is sampled
immediately before and immediately after the LED is activated. If
light is sensed with the LED off, and stray light is indicated an
alarm may be initiated after confirming test. The latter may
include a test of other sensors such as the optical communication
port sensor discussed hereinafter.
[0108] As shown in FIG. 5, communication from the meter reading
unit is carried out by radio transmission from the microprocessor
220 through a modulation device 250 which connects to the antenna
322. The transmission of the signal is carried under control of the
microprocessor 220. Modulation carried out by the modulation device
250 can be of a suitable type including, for example, phase
modulation using phase shift keying (PSK) such as binary PSK
(BPSK), frequency modulation using frequency shift keying (FSK),
such as, for example, binary FSK, or spread spectrum modulation in
which the signals are modulated onto a number of separate
frequencies at timed intervals so that no single frequency channel
is used. This allows the system to be used without the allocation
of a dedicated frequency so that the signal appears merely as noise
to receivers which do not have access to the decoding algorithm by
which the signal can be recovered from the different frequencies on
which it is transmitted.
Remote Cell Node
[0109] A plurality of remote cell nodes 112 are located within the
geographical area and are spaced approximately uniformly and such
that each network service module 110 is within a range of several
remote cell nodes 112 to provide overlapping coverage. The remote
cell nodes 112 typically might be spaced at 0.5 mile intervals on
utility poles or light standards. Each remote cell node 112
provides coverage over a limited area much like the cell in a
cellular telephone network. Remote cell nodes 112 preferably are
spaced to provide overlapping coverage so that, on an average, each
NSM-packet signal transmitted by a network service module 110 is
received by three or four remote cell nodes 112, even in the
presence of temporary fading. As a consequence, erection of a tall
building near a network service module 110 has little or no effect
on message reception, nor does the failure of a remote cell node
112 result in loss of NSM-packet signals or NSM data.
[0110] As illustratively shown in FIG. 9, each remote cell node
(RCN) 112 of FIG. 1 includes RCN-transmitter means, RCN-receiver
means, RCN-memory means, RCN-processor means and an RCN antenna
422. The RCN-transmitter means, RCN-receiver means, RCN-memory
means and RCN-processor means may be embodied as an RCN transmitter
418, RCN receiver 416, RCN memory 415 and RCN processor 414,
respectively. The RCN transmitter 418 and the RCN receiver 416 are
coupled to the RCN antenna 422. The RCN processor 414 is coupled to
the RCN transmitter 418, RCN receiver 416, and RCN memory 415.
[0111] The RCN transmitter 418, under the control of the RCN
processor 414, transmits at the first carrier frequency or the
second carrier frequency a command signal. The choice of frequency
depends on which frequency is being used for the NSM receiver 316
at each of the plurality of network service modules 110.
Transmitting a command signal from the RCN transmitter is optional,
and is used if the NSM receiver 316 is used at the network service
module 110. The command signal can include signaling data being
sent to network service modules 110. The signaling data may require
the network service module 110 to transmit status or other data;
set reporting time period, e.g., from an eight hour period to a
four hour period; and any other command, control or "housekeeping"
jobs as required.
[0112] The RCN receiver 416 receives at the first carrier frequency
a multiplicity of NSM-packet signals transmitted from a
multiplicity of network service modules 110. Each of the
multiplicity of NSM-packet signals typically are received at
different points in time, since they are transmitted at a time
which is randomly or pseudorandomly selected within the
predetermined time period. The multiplicity of network service
modules 110 usually is a subset of the plurality of network service
modules 110. Received NSM-packet signals are time stamped by the
RCN processor 414 and temporarily stored in the RCN memory 415
before being transmitted to the next higher network level. The RCN
receiver 416 also receives polling signals from the intermediate
data terminal, and listens or eavesdrops on neighboring remote cell
nodes when they are polled by the intermediate data terminal.
[0113] The RCN processor 414 collates the NSM-packet signals
received from the network service modules, identifies duplicates of
NSM-packet signals and deletes the duplicate NSM-packet signals.
The RCN processor 414 controls the RCN transmitter 418 and RCN
receiver 416. The RCN memory 415 stores the received multiplicity
of NSM-packet signals. Thus each remote cell node 112 receives,
decodes and stores in RCN memory 415 each of these NSM-packet
signals as received from the network service modules 110.
[0114] The remote cell node comprises simply a suitable resistant
casing which can be mounted upon a building, lamp standard, or
utility pole at a suitable location in the district concerned. The
remote cell node can be battery powered with a simple
omni-directional antenna as an integral part of the housing or
supported thereon.
[0115] Information accumulated at remote cell nodes 112
periodically is forwarded via a polled radio communications link to
a higher level network node, as illustrated in FIG. 1, termed an
intermediate data terminal 114. The intermediate data terminals 114
are spaced typically at 4 mile intervals and can be conveniently
sited at substations, providing coverage for up to 100 cells.
Remote cell nodes also receive timing information and command
signals from intermediate data terminals.
[0116] When a polling signal is sent from an intermediate data
terminal 114, the RCN transmitter 418 transmits at the first
carrier frequency the stored multiplicity of NSM-packet signals as
an RCN-packet signal to the intermediate data terminal 114.
[0117] When a first remote cell node is polled with a first polling
signal by the intermediate data terminal, neighboring remote cell
nodes 112 receive the RCN-packet signal transmitted by the first
remote cell node. Upon receiving an acknowledgment signal from the
intermediate data terminal that polled the first remote cell node,
at the neighboring remote cell nodes 112, the respective RCN
processor deletes from the respective RCN memory messages from the
network service modules that have the same message identification
number as messages transmitted in the RCN-packet signal from the
first remote cell node to the intermediate data terminal. The
message identification number is illustrated in a typical NSM-data
packet in FIG. 3.
[0118] FIG. 1 illustrates a plurality of the network service
modules 110. The network service modules 110 are set out in a
pattern across the ground which is dependent upon the positions of
the utility usage which generally does not have any particular
pattern and the density will vary significantly for different
locations.
[0119] The remote cell nodes 112 are arranged in an array with the
spacing between the remote cell nodes 112 relative to the network
service modules 110 so that each remote cell node 112 can transmit
to at least two and preferably four of the remote cell nodes 112.
Thus, the remote cell TO nodes 112 are provided in significantly
larger numbers than is absolutely necessary for each network
service module 110 to be received by a respective one of the remote
cell nodes 112. The remote cell nodes 112 theoretically receive
high levels of duplicate information. In a normal residential
situation, the location of the remote cell nodes 112, so that each
network service module 110 can be received by four such remote cell
nodes 112, would lead to an array in which each remote cell node
112 would be responsive to approximately 1,000 of the network
service modules 110.
[0120] Each of the network service modules 110 is arranged to
calculate an accumulated value of utility usage for a set period of
time which in the example shown is eight hours. Subsequent to the
eight hour period, the NSM controller 314 prepares to transmit the
information in a packet of data as an NSM-packet signal. The packet
of data includes:
[0121] (a) The total of usage during the set period, i.e., eight
hours.
[0122] (b) The accumulated total usage stored in the NSM memory 315
to date. The transmission of this information ensures that even if
a message is lost so that the total for one of the time periods is
not communicated to the central data terminal, the central data
terminal 120 can recalculate the amount in the missing time periods
from the updated accumulated total.
[0123] (c) Some or all of the tamper signals defined above.
[0124] (d) The time of transmission.
[0125] (e) A message number so that the messages are numbered
sequentially. In this way, again the remote cell node 112 can
determine whether a message has been lost or whether the
information received is merely a duplicate message from a duplicate
one of the receiving stations.
[0126] (f) "Housekeeping information" concerning the status of the
network service module 110, for example, the temperature and the
battery level indicator sensor values.
[0127] When information is received at the remote cell node 112,
the RCN controller 414 acts to store the information received in
the RCN memory 415 and then to analyze the information. The first
step in the analysis is to extract from the received messages the
identification code relating to the respective network service
module 110. The information relating to that network service module
110 is introduced into a RCN memory register relating to that
network service module 110 to update the information already
stored.
[0128] One technique for avoiding transmission of duplicate
information from the remote cell nodes 112 to the intermediate data
terminal 114 can be used in which each remote cell node 112
monitors the transmissions of the other remote cell nodes 112. When
the signals are monitored, the information transmitted is compared
with information stored in any other remote cell node 112 doing the
monitoring, and if any information is found in the memory of the
remote cell node 112 which is redundant, that information is then
canceled. In this way when very high levels of redundancy are used,
the time for transmission from the remote cell node 112 to the
intermediate data terminal is not significantly increased.
[0129] In addition to the transmission periodically of the usage
data, each network service module 110 can be arranged to transmit
an alarm signal upon detection of the removal of the electric
voltage. The transmission of the alarm signal can be delayed by a
short random period of time so that if the loss of the voltage is
due to a power outage covering a number of locations all signals
are not received at the same time. The remote cell nodes 112 and
intermediate data terminals 114 also can be programmed to
retransmit such alarm signals immediately. In this way, the central
data terminal 120 has immediate information concerning any power
outages including the area concerned. This can, of course, enable
more rapid repair functions to be initiated.
[0130] Furthermore, the remote cell nodes 112 can be arranged to
transmit control signals for operating equipment within the
premises in which the network service module 110 is located. The
remote cell nodes 112 are necessarily arranged in a suitable array
to transmit such information so that it is received in each of the
premises concerned using again relatively low transmission power
and using the equipment provided for the meter reading system. This
transmission capability can be used to control, for example, radio
controlled switches within the premises of relatively high power
equipment for load shedding at peak periods. In similar
arrangements the network service module 110 may include a receiving
facility to enable detection of signals transmitted by the remote
cell nodes 112. In one example, these signals may relate to
synchronizing signals so that each of the network service modules
110 is exactly synchronized in time with the remote cell node 112
and/or intermediate data terminal 114 and central data terminal
120. This exact synchronization can be used for accurately
detecting usage during specific time periods so that the utility
may charge different rates for usage during different time periods
for the purpose of particularly encouraging use at non-peak times
again for load shedding purposes.
[0131] The attenuation of a radio signal is proportional to the
inverse of the distance from the source to the power N. In free
space, N is equal to 2. In more practical examples where buildings,
trees, and other geographical obstructions interfere with the
signal, N generally lies between 4.0 and 5.0. This effect,
therefore, significantly reduces the distance over which the signal
from the network service module can be monitored. Thus, the number
of network service modules is significantly reduced which can be
monitored by a single remote cell node.
[0132] Furthermore, the large N rapidly reduces the signal strength
after a predetermined distance so that while a network service
module can be effectively monitored at a certain distance, the
signal strength rapidly falls off beyond that distance. This
enables the cells defined by each remote cell node 112 to be
relatively specific in size and for the degree of overlap of the
cells to be controlled to practical levels without wide statistical
variations.
[0133] An advantage of the present system is that network service
modules 110, which are located at a position which is
geographically very disadvantageous for transmission to the closest
remote cell node 112, may be monitored by a different one of the
remote cell nodes 112. Thus, in conventional systems some of the
network service modules 110 may not be monitored at all in view of
some particular geographical problem. In the present invention,
this possibility is significantly reduced by the fact that the
network service module 110 concerned is likely to be in a position
to be monitored by a larger number of the remote cell nodes 112 so
that the geographical problem most probably will not apply to all
of the remote cell nodes.
[0134] The increased density of remote cell nodes 112 permits the
network service modules 110 to operate with an integral NSM antenna
322 which can be formed as part of the meter reading unit housed
within the conventional electric utility meter. In this way, the
network service module 110 can be totally self-contained within the
meter housing thus allowing installation within a very short period
of time, avoiding customer dissatisfaction caused by wiring
problems, and reducing the possibility of damage to a separately
mounted NSM antenna 322. In addition, this arrangement
significantly reduces the cost of the network service module 110 to
a level which is economically viable to allow installation of the
system.
[0135] The present invention can employ a system in which the
network service modules 110 are permitted to transmit only during a
predetermined time period so that an open time period is available
for communication on the same frequency between the intermediate
data terminal 114 and the remote cell node 112 without any
interference from the remote cell nodes 112. This level of
communication can be carried out using a polling system from the
intermediate data terminals 114 to each of the remote cell nodes
112, in turn, preferably including a directional transmission
system at the intermediate data terminal 114. This system allows
optimization of the remote cell node 112 density to meet
cost/performance criteria in different deployment scenarios.
[0136] The present invention, by recognizing the non-volatile
nature of the information source and the acceptability of missing
an occasional update through transmission errors or collisions
enables the implementation of data collection networks of greater
simplicity and at lower cost than is possible with established
communication network approaches involving two-way communication.
The present invention, therefore, provides a radio communication
network which can be employed to acquire data from a large number
of remote meter monitoring devices disposed over a wide area using
very low power transmitters in conjunction with an array of remote
cell nodes all operating on a single radio communication channel or
frequency.
Intermediate Data Terminal
[0137] The plurality of intermediate data terminals 114 are located
within the geographic area and are spaced to form a grid overlaying
the geographic area. The intermediate data terminals 114 typically
are spaced to cover large geographic areas. Intermediate data
terminals 114 preferably are spaced to provide overlapping
coverage, so that on an average, an RCN-packet signal transmitted
from a remote cell node 112 is received by two or more intermediate
data terminals.
[0138] As illustratively shown in FIG. 10, each intermediate data
terminal 114 includes first IDT-transmitter means, second
IDT-transmitter means, IDT-memory means, IDT-processor means, first
IDT-receiver means, second IDT-receiver means and an IDT antenna.
The first IDT-transmitter means, second IDT-transmitter means,
IDT-memory means, IDT-processor means, first IDT receiver means and
second IDT-receiver means may be embodied as a first IDT
transmitter 518, second IDT transmitter 519, IDT memory 515, EDT
processor 514, first IDT receiver 521 and second IDT receiver 522,
respectively. The first IDT transmitter 518 and the first IDT
receiver 521 are coupled to the IDT antenna 522. The IDT processor
514 is coupled to the first and second IDT transmitters 518, 519,
the first and second IDT receivers 521, 522, and IDT memory 515.
The second IDT transmitter 519 and second IDT receiver 522 may be
embodied as a device such as a modem 523.
[0139] The first IDT transmitter 518 under the control of the IDT
processor 514, includes a synthesizer or equivalent circuitry for
controlling the carrier frequency, and allowing the first IDT
transmitter 518 to change carrier frequency. The first IDT
transmitter 518 transmits preferably at the first carrier
frequency, or the second carrier frequency, the first polling
signal using a first polling-access protocol to the plurality of
remote cell nodes 112. When the first polling signal is received by
a remote cell node, that remote cell node responds by sending the
RCN-packet signal to the intermediate data terminal 114 which sent
the first polling signal. If the intermediate data terminal 114
successfully receives the RCN-packet-signal, then the first IDT
transmitter 518 sends an acknowledgment signal to the remote cell
node. Upon receiving the acknowledgment signal, the RCN processor
414 at that remote cell node deletes, from the RCN memory 415, the
data sent in the RCN-packet signal to the intermediate data
terminal.
[0140] Intermediate data terminals 114 also communicate timing
information and command signals to remote cell nodes 112. Remote
cell nodes 112 serving important SCADA functions can be polled more
frequently by an intermediate data terminal 114 to reduce network
response time.
[0141] The first IDT receiver 521 receives the RCN-packet signal
transmitted at the first carrier frequency from the remote cell
node which was polled. Thus, after sequentially polling a plurality
of remote cell nodes 112, the first IDT receiver 521 has received
sequentially in time a plurality of RCN-packet signals.
[0142] The IDT memory 515 stores the received RCN-packet signals.
The IDT processor 514 collates the NSM-packet signals embedded in
the RCN-packet signals received from the plurality of remote cell
notes, identifies duplicates of NSM-packet signals and deletes the
duplicate NSM-packet signals, i.e., messages from network service
modules that have the same message identification number.
[0143] In response to a second polling signal from a central data
terminal 120, the second IDT transmitter 519 transmits a plurality
of RCN-packet signals as an IDT-packet signal to the central data
terminal 120. The second IDT transmitter 519 and second IDT
receiver 522 may be embodied as a modem 523 or other device for
communicating information over a communications medium 525 linking
the intermediate data terminal with the central data terminal.
[0144] The intermediate data terminals 114 may include one or more
directional antennas 522. During the quiet time, the intermediate
data terminal 114 is arranged to direct the antenna 522 or antennas
to each of the remote cell nodes 112, in turn, and to transmit to
the respective remote cell node 112 the first polling signal
calling for the remote cell node 112 to transmit the stored
information from the RCN memory 415. Use of more than one antenna
can allow communication with more than one remote cell node 112 at
a time. The remote cell node 112 is required, therefore, merely to
transmit the information upon request in a collated package of the
information which is transmitted to the intermediate data terminal
114 and collected for analysis.
Central Data Terminal
[0145] At the upper level of the hierarchy is a central data
terminal 120 which acts as a network control center and data
consolidation point. The central data terminal 120 controls basic
network operation, allowing it to make global decisions regarding
network organization. The central data terminal's purpose is to
integrate information from a variety of network nodes into a
coherent form which may be forwarded to different utility operating
groups for specific applications. In addition to linking regional
data terminals, the central data terminal 120 is connected to
critical SCADA sites some of which may be co-located with
intermediate data terminals 114 at sub-stations. At this level,
there are relatively few communication links, so those required can
be selected to optimize cost, speed, and reliability. The
transmission between the central data terminal 120 and the
plurality of intermediate data terminals 114 is carried out using a
communications medium 525 such as telephone lines, Ti carriers,
fiber optic channels, coaxial cable channels, microwave channels,
or satellite links.
[0146] As illustratively shown in FIG. 11, the central data
terminal (CDT) 120 includes CDT-transmitter means, CDT-receiver
means, CDT-processor means and CDT-memory means. The
CDT-transmitter means, CDT-receiver means, CDT-processor means and
CDT-memory means may be embodied as a CDT transmitter 618, CDT
receiver 616, CDT processor 614 and CDT memory 615, respectively.
The CDT transmitter 618 and CDT receiver 616 are coupled to the
communications medium 525. The CDT processor 614 is coupled to the
CDT transmitter 618, CDT receiver 616 and CDT memory 615. The CDT
transmitter 618 and CDT receiver 616 may be a modem 625 or other
device suitable for communicating information over the
communications medium 525 between the central data terminal 120 and
each intermediate data terminal 114.
[0147] The CDT transmitter 618 transmits sequentially in time the
second polling signal using a second polling access protocol to the
plurality of intermediate data terminals 114. The CDT receiver 616
receives a plurality of IDT-packet signals. The CDT processor 614
decodes the plurality of IDT-packet signals as a plurality of NSM
data. The CDT processor 614 also identifies duplicates of NSM data
and deletes the duplicate NSM data. The CDT memory 615 stores the
NSM data in a data base. The NSM data is outputted, analyzed, or
processed as desired.
Utility Overview
[0148] The performance of the network is in large part determined
by the network service module 110 to remote cell node 112 link
performance, which is defined by the network service module message
loss rate. The network architecture is designed to minimize the
network service module message loss rate, which is defined as the
fraction of transmitted network service module messages which are
not received by the remote cell nodes. The two issues that affect
the message loss rate are:
[0149] 1. relatively large and varying pathloss which is caused by
the nature of the urban propagation environment; and
[0150] 2. simultaneous message transmissions, or collisions, which
are a problem for any multiple-access system.
[0151] The issue of large and varying pathloss is resolved through
the use of:
[0152] 1. transmit power adjustment;
[0153] 2. path redundancy, controlled by the remote cell node grid
spacing; and
[0154] 3. multiple transmissions per day.
[0155] The collision issue is resolved using:
[0156] 1. path redundancy, controlled by the remote cell node grid
spacing;
[0157] 2. multiple transmission per day;
[0158] 3. partitioning of traffic according to priority; and
[0159] 4. capture effect.
[0160] Remote cell node spacing can be selected to control the path
redundancy, thus leading to an adjustable level of performance.
Notice that path redundancy and multiple transmission per day are
used to resolve both issues, and thus are principle features of the
wide area communications network. The effect of collisions is
minimal, so the probability of receiving a packet any time during
the day is maintained at exceptionally high levels.
[0161] The link budget contains all of the gains and losses between
the network service module power amplifier and the remote cell node
receiver, and is used to calculate the maximum pathloss which can
be allowed on any link. The minimum receivable signal at the remote
cell node is estimated as -115 dBm, which is equal to the sum of
the noise floor and the carrier to noise level which is required in
order to receive the message (10 dB).
[0162] Every network service module has many remote cell nodes
within receiving range, which increases the reliability of packet
reception. When a network service module transmits it has the
potential to be received by many remote cell nodules. Some of the
remote cell nodules are in shadow fading zones and do not receive
the signal whereas others have an increased signal due to
shadowing.
[0163] Even though some of the remote cell nodes 112 are quite far
from the network service module 110, and thus the average pathloss
is below the maximum allowed limit, it is still possible to receive
the network service module if the signal level fluctuations,
shadowing, multipathing, etc., contribute enough to the signal
level. Similarly, some remote cell nodes which are close to the
network service module do not hear the network service module
because the signal variations decrease the signal network level by
a significant amount.
[0164] During the life of the system, the urban landscape changes
due to building construction and demolition and foliage growth.
These changes in landscape affect the network service module-remote
cell node links, causing some remote cell nodes to no longer
receive the network service module while new remote cell nodes do
receive the network service module. For each link that is no longer
available it is expected that a new link becomes operational.
[0165] The wide area communications network can readily and cost
effectively expand to support new hardware and application software
growth scenarios. The wide area communications network can be
implemented in those regions of the user's service territory and
for those services which are most needed on an implementation plan
which is not affected by geographic distribution. FIG. 12
illustrates the configuration of the wide area communications
network for serving widely separated geographic areas. This
includes the provision of wide area communications network services
to isolated smaller communities via satellite, fiber optic,
microwave, or other back bone network. Due to the unique nature of
wide area communications network's single channel, micro cellular
scattering propagation concept, it is immune to traditional radio
problems such as fading, nulls, multi-path, lack of line of sight
typical of mountainous, hilly, valley, or high density urban
setting.
[0166] The wide area communications network supports a broad range
of monitoring, verifiable control and fast response transaction
applications. A number of these application needs are and continue
to be identified by utilities. Due to the standardized network
interface protocol and message packet configuration, the wide area
communications network is able to readily augment its service
offerings in either new hardware or software. The wide area
communications network offers not only specialized network service
modules for electric, gas, and water meters but also provides a
series of generic modules with industry standard in/output
interfaces for contact closure, voltage or current sensing. This
allows a variety of vendors to incorporate a wide area
communications network communication interface into their own
products be they fuses, alarms, temperature sensors, etc.
[0167] The wide area communications network can provide a single
integrated data channel for other utility operational applications.
Some of these applications are hardware oriented but many are
application software oriented. They involve the generation of new
value-added information reports or services. Although some are
primarily for use by the utility, many of them could be offered for
sale to the customer thus resulting in a new revenue stream for the
utility.
[0168] The wide area communications network can support the
expansion of SCADA due to its highly reliable wireless
communication capabilities. Many utilities would like to add
instrumental monitoring points to their SCADA, however, the wiring
costs or difficulties often associated with these prohibits SCADA
growth at a sub-station or other site. Generic network service
modules could be used to solve these problems.
[0169] The hierarchical design of wide area communications network
allows the customer to service an arbitrarily large contiguous or
non-contiguous geographic area, as shown in FIG. 12, containing
many applications and a large number of end points.
[0170] The key issues related to expansion are:
[0171] 1. The size and arrangement of the geographic area;
[0172] 2. The number of end points which can be serviced; and
[0173] 3. The ease with which the number of applications can be
increased.
[0174] The hierarchical design of the network allows non-contiguous
areas to be serviced over a wide geographic area. Separate areas
have their own intermediate data terminal communicating with the
central data terminal. Data from non-contiguous areas would be
transferred at the central data terminal level.
[0175] As the number of end points increases, either due to an
increase in the number of applications in a geographic area or due
to an increase in the size of the geographic area being serviced,
the network traffic increases. The amount of additional traffic
created depends on the type of application being added. Traffic
increases in the wide area communications network are dealt with by
hardware expansion at the central data terminal and by installation
of additional intermediate data terminals in the new area. FIG. 13
illustrates a typical communications network with gradual growth in
the number of areas served.
[0176] As the number of end points increases, another issue of
concern is the identification of the message source. Wide area
communications network provides over one trillion serial numbers
for each type of service module, which allows unique module
identification over the life of the system.
[0177] As the number of applications increases, the amount of
traffic from a given square mile is assumed to also increase.
Simulations to the present time have indicated that more than
20,000 end points can be serviced per square mile, with this
maximum number depending on the details of remote cell node
deployment, house density and message reporting frequency. A dense
urban area with 35 ft. by 100 ft. lots contains approximately 5,000
homes per square mile.
[0178] Centralized control of wide area communications network is
achieved by allowing the central data terminal to have access to
network status data, which it uses to make decisions regarding
network optimization. These decisions are downloaded to the
intermediate data terminals and remote cell nodes as required.
[0179] Centralized traffic control is achieved at the remote cell
node and intermediate data terminal levels by using priority
tables, message storage instructions and alarm storage
instructions. The structure of the priority tables is described as
follows.
[0180] In each message that is transferred through the system,
there is a set of identification tags stating the message type and
the source. The priority tables in the remote cell nodes 112 and
intermediate data terminals 114 contain a listing of all
identification tags in the system and the priority tables are first
installed at the time of deployment, but can be updated from the
central data terminal 120 as required. During the network
operational period there may be a need to change message
priorities, which can then be performed with minimal impact on the
network traffic.
[0181] Control of the alarm traffic within the network requires
another table because alarm reporting generates higher traffic
levels for a short period of time. This bursty traffic generation
can lead to congestion problems, and so an alarm instruction table
allows the central data terminal to clear alarm messages out of
remote cell node and intermediate data terminal buffers at the end
of the alarm. This priority table also allows the utility to tailor
the alarm traffic delay to suit its particular needs.
[0182] Both the priority tables and the alarm instructions are used
by the message storage instruction module to properly manage
traffic on the network. The message storage instructions maintain
the message queue, ensure that response times are within
specification, and transmit performance data to the central data
terminal to be used for network control.
[0183] The network service modules transmit messages to the remote
cell nodes, which then use the tables discussed above to organize
the message queue. All messages reach the application switch with
the specified delay. The central data terminal downloads data to
the three control modules and tables as required.
[0184] It will be apparent to those skilled in the art that various
modifications can be made to the communications network for
collecting data from remote data generating stations of the instant
invention without departing from the scope or spirit of the
invention, and it is intended that the present invention cover
modifications and variations of the communications network provided
they come within the scope of the appended claims and their
equivalents.
* * * * *