U.S. patent application number 11/354251 was filed with the patent office on 2006-10-05 for modular wireless fixed network for wide-area metering data collection and meter module apparatus.
This patent application is currently assigned to M & FC Holding, LLC. Invention is credited to Carmel Heth, Shimon Zigdon.
Application Number | 20060220903 11/354251 |
Document ID | / |
Family ID | 25490678 |
Filed Date | 2006-10-05 |
United States Patent
Application |
20060220903 |
Kind Code |
A1 |
Zigdon; Shimon ; et
al. |
October 5, 2006 |
Modular wireless fixed network for wide-area metering data
collection and meter module apparatus
Abstract
A scalable and modular fixed-base wireless network system for
wide-area metering data collection, composed of at least one of
each of the following components: meter modules, which monitor,
store, encode and periodically transmit metering data via radio
signals (air messages). The network may contain both one-way
(transmit only) and two-way (transmit and receive) meter modules;
Receiver Base Stations, which receive, decode, store and forward
metering data to a central database and metering data gateway,
referred to here as the Data Operation Center (DOC). Base Stations
do not perform any meter data processing, but simply transfer
decoded air messages to the DOC; and a Data Operations Center,
which communicates with all of the network's Base Stations and
receives decoded air messages from the Base Stations. The DOC
processes, validates and stores metering data in a meter database
that it maintains for the entire meter population operating in the
network. The DOC has the capability to export or forward metering
data to other systems via standard data protocols, which may be
scaled up in its air message handling capacity and in its
application features, by integrating it with a wireless
data-forwarding (downlink) channel, such as a paging network, which
is required in order to provide service to two-way meter modules
that may be operating in the network. This channel enables the
sending of time synchronization and other commands to two-way meter
modules, thus providing the operator with considerable flexibility
in their choice of network capacity, features and system cost.
Inventors: |
Zigdon; Shimon; (Netanya,
IL) ; Heth; Carmel; (Bar-Heffer, IL) |
Correspondence
Address: |
BACON & THOMAS, PLLC
625 SLATERS LANE
FOURTH FLOOR
ALEXANDRIA
VA
22314
US
|
Assignee: |
M & FC Holding, LLC
|
Family ID: |
25490678 |
Appl. No.: |
11/354251 |
Filed: |
February 15, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09950623 |
Sep 13, 2001 |
7009530 |
|
|
11354251 |
Feb 15, 2006 |
|
|
|
Current U.S.
Class: |
340/870.02 ;
375/E1.002 |
Current CPC
Class: |
H04B 1/707 20130101;
H04M 15/68 20130101; Y02B 90/20 20130101; H04B 1/662 20130101; H04Q
2209/60 20130101; H04M 2215/0196 20130101; H04M 2215/32 20130101;
H04Q 2209/10 20130101; H04Q 9/00 20130101; H04Q 2209/40 20130101;
G01D 4/002 20130101; Y04S 20/30 20130101 |
Class at
Publication: |
340/870.02 |
International
Class: |
G08C 15/06 20060101
G08C015/06; G08B 23/00 20060101 G08B023/00 |
Claims
1. A scalable and modular fixed-base wireless network system for
wide-area metering data collection, composed of at least one of
each of the components a,b,c described below, which may be scaled
up in its air message handling capacity and in its application
features, by integrating it with a wireless data-forwarding
(downlink) channel (component d below), thus providing the operator
with considerable flexibility in their choice of network capacity,
features and system cost. The network components referred to above
are: a. Meter modules, which monitor, store, encode and
periodically transmit metering data via radio signals (air
messages). The network may contain both one-way (transmit only) and
two-way (transmit and receive) meter modules. b. Receiver Base
Stations, which receive, decode, store and forward metering data to
a central database and metering data gateway, referred to here as
the Data Operations Center (DOC). Base Stations do not perform any
meter data processing, but simply transfer decoded air messages to
the DOC. c. A Data Operations Center, which communicates with all
of the network's Base Stations and receives decoded air messages
from the Base Stations. The DOC processes, validates and stores
metering data in a meter database that it maintains for the entire
meter population operating in the network. The DOC has the
capability to export or forward metering data to other systems via
standard data protocols. d. An optional wireless downlink channel,
such as a paging network, which is required in order to provide
service to two-way meter modules that may be operating in the
network. This channel enables the sending of time synchronization
and other commands to two-way meter modules.
2. The network system of claim 1, which also enables optimal
adjustment of network control parameters, namely the quantity of
Base Stations, the number of reception frequency channels and meter
module message bit rate, according to the application requirements,
namely message delivery probability, metering data latency and
meter module battery life.
3. The network system of claim 2, which further includes Network
Transceiver/Repeater (NTR) devices, designed to enhance network
coverage in areas of poor or no initial coverage. The NTR devices
repeat messages only from designated meter modules, identified
either by module identification number or by an appropriate flag in
the meter module air message.
4. The network system of claim 2, which also includes a logarithmic
table encoding method for compressing interval consumption data air
messages, thus reducing the number of bits required in the message
per each consumption interval.
5. The logarithmic table encoding compression method of claim 4, in
which the DOC maintains a large list (bank) of consumption
encoding/decoding tables, adapted to various consumption patterns.
The DOC further maintains a registry specifying which set of
encoding/decoding tables is assigned to each meter module, these
sets of tables potentially different from one meter module to
another.
6. The network system of claim 2, which also includes an
interleaving encoding method for interval consumption data air
messages, thus increasing the data's redundancy level and/or
providing data for smaller consumption intervals. Each interval
consumption data message's time base is shifted, compared to the
previous message, in a cyclic manner, so that interval consumption
data may be reconstructed even if some of the messages are not
received.
7. A low-cost high-output-power meter module, which may operate on
the network system of claim 2, that includes a sensing means, data
storage and processing means, a direct sequence spread spectrum
transmitter and an antenna, all within the same physical
enclosure.
8. The meter module of claim 7, in which the module enclosure may
be assembled inside the enclosure of an electric meter.
9. The meter module of claim 7, in which the module enclosure may
be assembled between a gas meter and a gas meter index.
10. The meter module of claim 7, in which the output power of the
radio signal is between 0.5 and 1 Watt.
11. The meter module of claim 7, which is equipped with a power
supply, in which a capacitive element and a limited current source
are combined, in order to allow high output power during a short
transmission burst, which may also be initiated to immediately
notify of power outage; the capacitive element and the limited
current source also imposing a physical limitation on the charge
time and thus the transmission duty cycle, that way reducing
interference that may be caused by a malfunctioning meter module,
to an acceptable level that does not affect network
functionality.
12. The meter module of claim 7, which also maintains low power
consumption of its meter interface circuitry and low overall power
consumption, by using two sensors to detect rotation, of which at
one time only one (or none) may be at a closed switch status. By
disabling a sensor circuit immediately once it is detected at a
closed switch state, while simultaneously enabling the other sensor
circuit, near zero current is drawn by the circuit.
13. The meter module of claim 7, which also includes an outage
recovery system, consisting of the following measures: Immediate
notification of outage (`last gasp`) Immediate notification of
power restoration Storage of interval consumption data prior to an
outage event, enabling a transmission of the last saved data
shortly after power restoration
14. A low cost Binary Phase Shift Keying (BPSK) RF signal
modulator, implemented on a four-layer PCB, providing high
performance at a very low cost compared to microwave monolithic
integrated circuit (MMIC) BPSK modulators.
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to wireless
messaging systems and methods. In particular, the present invention
relates to wireless messaging systems and methods for automated
meter reading (AMR) and metering data collection.
BACKGROUND
[0002] Automated Meter Reading (AMR) started out as a more
efficient and accurate method for utility metering data collection,
compared to manual meter reading of electric, gas and water meters.
Several important advantages of AMR over manual meter reading
helped develop it into a specialized branch of the data
communications and telemetry industry. Worth noting among these
advantages are the reliability, accuracy and regular availability
of metering data, collected from hard-to-reach meter locations as
well as from standard meter locations; higher customer security (no
need to enter homes) and satisfaction (accurate bills); and reduced
cost of customer service call center and service house calls for
settling billing disputes.
[0003] Various technologies are implemented in AMR. All
implementations perform the tasks of interfacing the meter in order
to sense consumption, communicating consumption data to a central
site and storing consumption data in a computer system at the
central site. Wireless technologies have become the most common in
AMR system implementation due to the ease of the installation
process and, in many cases, the low initial and operating costs of
the system.
[0004] Among wireless implementations of AMR, a categorization has
been established between mobile data collection systems and
fixed-base data collection systems, or networks. Fixed network
systems have some important distinctive advantages, brought about
by the frequent (typically at least daily) consumption data
collection, in comparison with mobile systems, which merely provide
a more reliable method of collecting monthly meter reads for
billing purposes. Worth noting among these advantages are:
flexibility of billing date; marketing tools such as time-of-use
(TOU) rates, demand analysis and load profiling, which enable
clearer market segmentation and more accurate forecasts for utility
resource generation, and also serve the goal of energy conservation
and efficient consumption; and maintenance tools such as immediate
notification of utility resource leakage or of account delinquency.
These advantages have triggered increased interest and commercial
activity regarding fixed network data collection systems for
utilities, particularly utilities in regions undergoing
deregulation of utility services.
[0005] Several methods and systems for implementing fixed-base data
collection from a plurality of remote devices, such as utility
meters, to a central location, have been developed and introduced
in the past years. A categorization has evolved as the AMR industry
developed, generally differentiating between one-way and two-way
wireless data networks. Some systems, such as those described in
U.S. Pat. No. 5,438,329 to Gastouniotis et al., U.S. Pat. No.
5,883,886 to Eaton et al. and U.S. Pat. No. 6,246,677 to Nap et
al., require that each meter module on the network be a two-way
module, i.e. contain a receiver circuit in the meter module.
Although two-way communication features such as on-demand meter
reading and other remote commands for meter configuration and
control are generally desirable, they may not be required for the
entire meter population of a utility. Since the inclusion of a
receiver in the meter module contributes significant cost to the
module, it would be most desirable to allow a utility service
company the flexibility to deploy an AMR network, which may contain
and support both one-way and two-way meter modules.
[0006] U.S. Pat. No. 5,963,146 and No. 6,172,616 to Johnson et al.,
assigned to Itron, Inc. of Spokane, Wash. (referred to henceforth
as the Itron network) and U.S. Pat. No. 6,163,276 to Irving et al.
and No. 6,195,018 to Ragle et al. (referred to henceforth as the
CellNet network) describe data collection networks that may also
operate as one-way (collection only) data networks. These networks
support the large volume of data, expected by advanced metering
applications, by deploying intermediate data collection nodes
(Remote Cell Nodes, or RCN's, in Itron's network and Microcell
Controllers in CellNet's network), each of which creates a small
data collection cell with a short-range RF link and a typical
service population of several hundreds of meters. In these
networks, the data collection nodes receive messages from meter
modules, perform metering data analysis and extract, or generate,
specific meter function values to be transmitted to the next level
in the network hierarchy. The wide-area network connecting the
intermediate level and the higher level is typically a wireless
network operating on an additional, licensed, RF channel, in order
to avoid interference. This configuration, which distributes the
`network intelligence` among many data collection nodes, serves the
purpose of reducing the data flow into the central database when a
large amount of meters is analyzed for load profile or interval
consumption data. It also serves the purpose of reducing
air-message traffic between the intermediate node and the
higher-level concentrator node, referred to as IDT (Intermediate
Data Terminal) in the Itron network and Cellmaster in the CellNet
network.
[0007] However, the configuration of the Itron and CellNet networks
becomes inefficient in the common case where only a part, or none,
of the meter population requires advanced metering services like
TOU rates, while basic daily metering service is required for the
whole meter population. This inefficiency is imposed by the
short-range radio link between the meters and the data collection
nodes, which significantly limits the number of meters a node can
serve, regardless of how many meters require or do not require to
be read frequently for interval consumption data. That way, an
expensive infrastructure of up to thousands of data collection
nodes may be deployed, which may often consist of plenty of unused
excess capacity. A more efficient network would therefore be
desirable, in order to reduce basic equipment cost, as well as
installation and ongoing maintenance costs.
[0008] In addition, because of the large number of data collection
nodes, the most cost-efficient means for the WAN layer in these
multi-tier networks would be a wireless WAN. However, to avoid
interference from meter modules, as well as over-complication of
the data protocols, a licensed frequency channel is typically used
for the WAN, adding to the overall cost of services to the network
operator. A network composed of only one wireless data collection
layer would therefore be desirable, particularly if operating in
the unlicensed Industrial, Scientific and Medical (ISM) band.
[0009] Yet another disadvantage of networks with distributed
intelligence among the data collection nodes is the limited storage
and processing power of the data collection nodes. A system that
could efficiently transfer all the raw data from the meter modules
to the network's central database would therefore be desirable,
since it would allow for more backup and archiving options and also
for more complex function calculations on the raw meter data.
[0010] The Itron patents also quote a previously developed system
by Data Beam. This data collection network included few reception
sites, each one capable of handling up to tens of thousands of
meters. In order to allow for long communication range, the meter
module antenna was installed in a separate (higher and/or out of
building) location from the meter module, creating significant
additional cost to the meter module installation, thus
significantly reducing the commercial feasibility for practical
deployment of the network. In addition, the meter module's power
consumption requirements required a mains power source or expensive
batteries, further reducing the network's commercial
feasibility.
[0011] None of the above-mentioned systems of the prior art offers
a sufficient level of flexibility, enabling the network operator to
deploy a reliable, low cost, fixed data collection network, while
adjusting its initial and ongoing costs to a wide range of
application requirements, from basic daily meter reads to full
two-way capabilities. Inefficiencies exist in each two-way network,
in which the two-way capability is imposed on the entire meter
population, and also in each one-way network, in which small cell
configuration requires a large, unnecessary investment in
infrastructure.
[0012] It is therefore desirable to introduce a simple to deploy,
but highly scalable, modular and reliable data collection system,
which would offer a wide range of service options, from basic
metering to advanced applications based on interval consumption
data, to full two-way applications, while keeping the system's
deployment and ongoing costs proportional to the service options
and capacity requirements selected for various segments of the
meter population.
SUMMARY OF THE INVENTION
[0013] According to a particular embodiment of the present
invention, a one-way direct sequence spread spectrum (DSSS)
communications network is used as the data collection channel
(uplink) of an automatic meter reading (AMR) application and a
paging network, or other suitable downlink network, is used as an
optional forward (downlink) channel in a cost-effective manner. The
network is designed to provide a cost-effective wide-area data
collection solution, i.e. capable of supporting as many meters on
as large a geographical area as required by the associated metering
application.
[0014] The communications network includes one-way meter modules
(transmitters) communicatively coupled to electric, gas and water
utility meters, as well as two-way meter modules (transceivers)
coupled to such utility meters. The meter modules monitor, store,
encode and periodically transmit metering data via radio signals
(air messages), in an appropriate RF channel, typically within the
902-928 MHz Industrial, Scientific and Medical (ISM) band,
allocated by the Federal Communications Commission (FCC) for
unlicensed operation. Metering data messages are collected by a
network of receiver Base Stations. The reception range of each Base
Station is typically over 5 miles in urban areas, allowing sparse
infrastructure deployment for a wide variety of metering data
collection applications. The network also includes a Data
Operations Center (DOC) that communicates with all the Base
Stations, monitors their operation and collects metering data
messages from them. The DOC may also be communicatively coupled to
a paging network, or other wireless network, for sending downlink
commands to the two-way meter modules.
[0015] This invention also features a low-cost, energy efficient
meter module, which provides significant benefits to the system,
primarily contributing to the long range of the wireless link, by
implementing a direct sequence spread spectrum (DSSS) signal of
high output power and high interference rejection, while consuming
very low average power, thus enabling long life (many years)
battery operation. The meter module's PCB antenna is an integral
part of the module. The meter module is simple to install, and is
typically installed inside electric meters, integrated (between
meter and index) in gas meters, or as an external unit adjacent to
water meters. The meter module also supports the unique
configuration of the described system and limits the usage of
air-time by introducing data compression mechanisms into the
wireless link.
[0016] Main advantages of the invention include:
[0017] Long wireless communication link, which provides wide-area
coverage with a small number of sites (typically tens of thousands
of meters in a five-mile radius per Base Station), thereby
simplifying network deployment, reducing infrastructure initial and
ongoing costs, and reducing the number of potential failure points
in the network, thus increasing reliability;
[0018] As a data collection network, the system may operate
utilizing a single RF channel, such as a spread spectrum channel
within the 902-928 MHz band.
[0019] Modularity of network architecture, enabling flexibility in
network planning, in order to optimize cost and capacity in various
regions covered by the network. A part of the network's modularity
is that a forward channel, such as a paging network, can be
integrated with the data collection channel, providing a convenient
transition to supplying data services to both one-way and two-way
meter modules.
[0020] Scalability mechanisms, enabling gradual and cost-efficient
increase of infrastructure deployment in order to meet a wide range
of application and capacity requirements, including requirement
relating to interval consumption data applications;
[0021] Routing of all raw metering data to the DOC central
database, where it can be easily processed, archived and
accessed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The invention is herein described, by way of example only,
with reference to the accompanying drawings, wherein:
[0023] FIG. 1 is a block diagram illustrating required and optional
components of the data collection network system, according to an
embodiment of the present invention.
[0024] FIG. 2 is a block diagram illustrating a practical
configuration of a two-way meter module.
[0025] FIG. 3 is a block diagram of a transmitter meter module.
[0026] FIG. 4 is a functional block diagram of the BPSK modulator
described in FIG. 3.
[0027] FIG. 5 is a block diagram and illustration of the BPSK
modulator of FIG. 4.
[0028] FIG. 6 is a top and bottom drawing of the BPSK modulator of
FIG. 4.
[0029] FIG. 7 is a description of the interleaving encoding, which
is used by the meter module in order to generate interval
consumption data air messages.
[0030] FIG. 8 is a description of the `zero current` rotation
sensor interface logic.
[0031] FIG. 9 is a graphic illustration of interval consumption
data required to be transmitter in an air message.
[0032] FIG. 10 shows examples of logarithmic consumption data
encoding tables.
[0033] FIG. 11 demonstrates the evaluation process by which the
meter module determines which consumption data-encoding table to
select.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0034] General
[0035] This invention features a scalable and modular wireless
fixed-base data collection network system, comprising at least one
wireless meter module, one receiver site (Base Station) and one
central site (Data Operations Center) into which all metering data
is collected.
[0036] According to a particular embodiment of the present
invention, a one-way direct sequence spread spectrum (DSSS)
communications network is used as the data collection channel
(uplink) of an automatic meter reading (AMR) application and a
paging network, or other suitable downlink network, is used as an
optional forward (downlink) channel in a cost-effective manner. The
network is designed to provide a cost-effective wide-area data
collection solution, i.e. capable of supporting as many meters on
as large a geographical area as required by the associated metering
application.
[0037] The communications network includes one-way meter modules
(transmitters) communicatively coupled to electric, gas and water
utility meters, as well as two-way meter modules (transceivers)
coupled to such utility meters. The meter modules monitor, store,
encode and periodically transmit metering data via radio signals
(air messages), in an appropriate RF channel, typically within the
902-928 MHz Industrial, Scientific and Medical (ISM) band,
allocated by the Federal Communications Commission (FCC) for
unlicensed operation. Metering data messages are collected by a
network of receiver Base Stations. The reception range of each Base
Station is typically over 5 miles in urban areas, allowing sparse
infrastructure deployment for a wide variety of metering data
collection applications. The network also includes a Data
Operations Center (DOC) that communicates with all the Base
Stations, monitors their operation and collects metering data
messages from them. The DOC may also be communicatively coupled to
a paging network, or other wireless network, for sending downlink
commands to the two-way meter modules.
[0038] Since transceiver power consumption is greater than
transmitter power consumption, it is generally preferable to use
transmitters where the power source is limited. Gas and water meter
modules generally have a limited power source, typically from a
battery, so the meter modules attached to such meters are generally
transmitters rather than transceivers. Electric meters can
typically take their power from the electric grid, so their power
is not limited, and hence transceivers are suitable for electric
meters. However, because the cost of the transceiver meter module
is greater than the cost of the transmitter meter module, electric
meters may use a transmitter to save on the end unit cost. Thus,
typically gas and water meters use transmitters only, while
electric meters use transmitters or transceivers according to the
application requirements. Transceivers are used to create a two-way
system, which has the advantage of greater capacity than a one-way
system, and which can provide additional services (such as remote
connect or disconnect, over-the-air programming or reprogramming of
meter module parameters, and others) that cannot be provided by a
one-way system.
[0039] Basic Network Architecture and Configuration
[0040] A high-level block diagram of a metering data collection
network system is depicted in FIG. 1. The system comprises both
one-way (transmitter) meter modules 04 and two-way (transceiver)
meter modules 06 coupled to meters. All meter modules are able to
transmit encoded DSSS radio signals representing metering data
stored in the meter modules, such as current meter reading, tamper
status, meter identification data and interval consumption data. A
variety of utility meter module types (electric, gas, water) and
models may operate in one metering data collection network,
utilizing the same infrastructure. Each receiver Base Station 02 is
able to receive and decode DSSS encoded signals (air messages)
generated by the meter modules. The bandwidth of the DSSS signal is
approximately 2 MHz. Base Stations 02 can be optimized to receive
signals in any radio frequency range between 800 MHz and 1 GHz,
including the 902-928 MHz Industrial, Scientific, and Medical (ISM)
band allocated by the FCC for unlicensed use. In a preferred
embodiment, the data collection network operates in the ISM band
under the rules for unlicensed operation (Part 15 of the FCC
Rules), and requires no licensing for any portion of its wireless
uplink channel.
[0041] According to the preferred embodiment, one or more Base
Stations 02 would be deployed to cover a geographic area. The
number of Base Stations 02 needed depends on the size and type of
terrain within the geographic coverage area, as well as upon
application requirements. A Base Station is typically installed at
a high location (communication tower or roof top) and consists of
the following components: at least one receiving antenna, RF cables
and connectors, a DSSS receiver and a communication interface, such
as a PPP router or CDPD modem. A Base Station may also contain a
backup power source for continued operation during a specified
period of outage. Base Stations 02 receive metering data air
messages from meter modules 04 and 06 on the uplink channel. The
Base Stations decode the radio signals and relay the decoded
metering data air messages to the DOC 01. The DOC 01 is coupled to
the Base Stations 02 via standard communication channels, typically
by using an IP network (such as frame relay or Internet). Other
communication means between the DOC and the Base Stations may be a
wireless cellular network, CDPD, PSTN and satellite data network.
The DOC 01 consists of a database of all the meter modules in the
network and an Internet server for accessing the database. This
embodiment also enables the DOC to provide alerts and event
notification services via email, fax, pager devices and voice
message generators. The DOC may be programmed to forward data
directly to a user or to export files to a buffer directory by
using standard data protocols.
[0042] According to the preferred embodiment, the DOC performs
metering data validation, processing and storage, while the Base
Stations' role is to decode air messages and forward raw metering
data to the DOC for central processing. This structure eliminates
the requirement to monitor and control metering data processing
tasks carried out in multiple locations. All metering data is
stored in a central location, enabling fast data access response
times and equipped with suitable backup storage means. Thus two
objectives are served: low initial and maintenance cost of Base
Station hardware and software; and convenient, permanent access to
all metering data collected by the network via one central data
repository.
[0043] The DOC may be constructed, according to the application
requirements to operate in a High Availability (HA) configuration,
that is two computer platforms having the capability to transfer
all processing and communication tasks and parameters
instantaneously from one to the other in the event of a failure of
one of the platforms. In addition, the DOC may be configured,
according to the application requirements, to communicate with a
computer platform at a remote mirror site and periodically transfer
the required data in order to maintain Disaster Recovery (DR)
capability at the remote mirror site.
[0044] Network Architecture Modularity
[0045] The network's basic architecture includes transmitter meter
modules, Base Stations and a DOC. However, the network is modular
and may include message-repeating devices and, as stated, two-way
meter modules and a downlink (forward) RF channel to communicate
between the DOC and the two-way meter modules. In addition, as will
be further described, the network includes a variety of scalability
mechanisms enabling cost-effective service in varying levels of
network air-message traffic and various metering data
applications.
[0046] Network Transceiver/Repeater (NTR)
[0047] According to a particular embodiment, in some cases, a
cost-efficient means for expanding network coverage is adding
Network Transceiver/Repeater devices (NTR) in order to provide
coverage for meter modules experiencing poor or no Base Station
coverage. This means provides more flexibility to the network
operator by creating another option for providing coverage to a
limited geographic area. NTR cost of deployment and maintenance is
significantly lower than that of a Base Station. Therefore, besides
being a cost effective solution to poor coverage, it also may cost
justify the enhancement of a network's coverage to areas of low
population density, thus extending the reach of its automated
metering data collection system. The deployment of NTR devices does
not require the network operator to perform any changes in any of
the other elements of the network infrastructure.
[0048] In the design of a network, there will be an analysis of
expected radio traffic. Many areas will have sufficiently high
radio traffic to cost-justify full Base Station coverage. However,
there will be certain areas, or "holes", in which radio traffic
will be very sparse, and cannot cost-justify Base Station coverage.
NTRs may provide sufficient coverage at much lower cost. For
example, a small number of meters in a deep valley may not be
covered by the nearest Base Station, but do not economically
justify the deployment of a Base Station. The NTR is smaller in
size compared to a Base Station and may be mounted on a pole top,
since it only needs to provide limited coverage. Therefore, its
ongoing site lease cost is also significantly lower than that which
an additional Base Station would create. The use of a NTR is thus a
low-cost means of covering holes in the coverage of the Base
Station network, or of extending the network's coverage to areas of
low air-message traffic.
[0049] Network Transceiver/Repeater devices (NTR), shown as 03 in
FIG. 1, receive metering data messages from meter models 04 and 06,
decode and retransmit messages of specific meter modules. NTR
devices 03 are used in specific terrains, which endure poor radio
coverage, or in other events of lack of coverage or of coverage
degradation in a certain area. The NTR is a low cost data
collection node, with lower RF sensitivity and smaller coverage
(hundreds of meters) compared to a Base Station. Like the Base
Station, the NTR does not perform any metering data analysis. It
only retransmits the raw data air messages that it receives and
that are identified as received from appropriate meter modules
listed in the NTR's memory.
[0050] The NTR 03 decodes the received air messages and then
encodes and retransmits them only if the message has been received
from a particular set of meter modules. Repeated messages may then
be received by a Base Station 02. Each NTR 03 retains a list of
some meter modules 04, 06 that reside in that area, and relays only
messages received from those meter modules. In another embodiment,
the NTR 03 checks for a NTR flag bit in the air message that
indicates whether or not to relay the message. A combination of
these two embodiments is applicable as well. These selective
measures enable network coverage enhancement without creating an
unnecessary load of air message traffic. The NTR's selectivity
allows planning for specific meter modules to have their air
messages repeated. Also, each meter module can be programmed to use
its NTR flag in order to have only some of its air messages
repeated, this way optimizing the increase in air message
traffic.
[0051] Two-Way Network
[0052] A two-way meter module is capable of transmitting metering
data air messages on demand (upon receiving an appropriate wireless
command) and may also be conveniently programmed to transmit at
specific times by maintaining a real-time clock synchronized by the
wireless downlink channel. Two-way meter modules also receive,
decode and execute other commands such as: programming meter
parameters, displaying messages or alerts on the meter's display,
disconnecting and reconnecting power to the utility meter's load.
FIG. 2 depicts a block diagram of a particular embodiment of a
two-way meter module, in which the elements added to a one-way
meter module (transmitter described herein), in order to produce a
two-way meter module, include a paging receiver and decoder. The
basic transmitter apparatus is described further in detail
separately below.
[0053] The DOC may be coupled to a wireless downlink channel, such
as a paging network, cellular network, etc., 05 through a
communication link, such as a leased line, frame relay link etc.,
and by using suitable standard data protocols. The metering data
collection system operates as a one-way data collection system if
not coupled to a downlink channel. The basic one-way network may be
scaled up to several higher levels of capacity and application
features, as described herein, the highest level being reached by
integrating a downlink channel in the system.
[0054] Network Performance Scalability
[0055] One of the key features of the system claimed herein is the
ability to ramp up the system's air message capacity. This feature
is called "Network Performance Scalability". In a metering data
collection application, various levels of message delivery
probability or message redundancy may be required, as well as
various data latency requirements, thus affecting the amount of
messages transmitted per time period, i.e. air message capacity
requirement. In addition, a trade-off exists between the amount of
data required by the application and the maximum amount of air
messages transmissions allowed, in order to maintain air message
traffic or meter module battery life at acceptable levels. In the
preferred embodiment, the network is designed so that the network
operator or deployment planner has the flexibility to optimize
space diversity, frequency diversity and air message duration
according to the application requirements of delivered metering
data, meter module battery life, metering data latency and air
message delivery probability.
[0056] Following is a description of the levels of capacity that
may be provided, depending upon customer demand. Note that levels 2
to 4 described herein may be implemented in any order.
[0057] Level 1: A sparse Base Station network is deployed,
combined, if necessary, with NTR devices covering areas with very
limited radio traffic. This level provides adequate geographic
coverage, and the minimum level of system capacity. This level is
roughly defined as the capacity required in order to provide daily
reads to an urban meter population. A typical urban deployment for
this level would include Base Stations spaced 5 miles apart, each
covering up to several tens of thousands of meters, with few to no
deployments of NTR devices.
[0058] Basic Network Control Parameters
[0059] Level 2: Space diversity is implemented to adjust network
capacity, by controlling the amount of Base Stations used in order
to provide coverage to specified meter population and metering data
application in a specified geographical area. The initial phase of
planning network coverage includes optimal selection of the number
and locations of Base Stations to be deployed in the specified
area. When a Base Station covers a large area and the meter module
density or air message frequency requirements continuously
increase, at some stage the farthest meter modules would endure
interference from the closer meter modules, and message reception
probability from the farthest meter modules will decrease. Base
Stations may be added at appropriate locations in the same
geographic area, in order to increase network capacity and message
reception rate. Adding Base Stations reduces the effective range
between each meter module to be deployed and the Base Station
closest to it, so that more meter modules or potential meter module
locations are within a range of high air-message reception
probability. Thus, the placement of additional Base Stations in the
same geographic area, without any other change in the network or
the meter modules, will in itself increase overall network
capacity.
[0060] Level 3: Frequency diversity is implemented by utilizing
more than one uplink frequency channel within a coverage area.
Meter modules may be programmed to alter their transmission
frequency channel each air message transmission. In addition, a
Base Station may consist of several receivers in multiple frequency
channels, thus significantly increasing the Base Station's air
message reception capacity. Frequency diversity may thus eliminate
or postpone coverage problems, which would otherwise require adding
Base Station sites. In addition, frequency diversity may be
combined with space diversity by feeding receivers operating in
different uplink frequency channels at the same Base Stations with
signals from separate antennas. In the 902-928 MHz unlicensed ISM
band, a particular embodiment of the network may operate in up to
57 channels, spaced 400 kHz apart, but a more practical limit for
reliable operation would be about 10 channels. Each new frequency
channel receiver added, increases the Base Station's capacity. When
performed on a regional Base Station network, adding channels
significantly increases the entire network's capacity.
[0061] Level 4: Another network control parameter included in the
preferred embodiment consists of the direct sequence code length,
which forms a trade-off with the air message's raw data bit rate
parameter. In a particular embodiment, the direct sequence chip
rate is 1 Mchips/sec and the maximum code length is 255 chips,
yielding a data rate of about 4 kbps. The network operator/planner
may select shorter codes, namely 63, 31 or 15 chips long, thus
increasing the raw data bit rate. Reducing code length reduces the
signal spreading and decreases coverage range per Base Station, but
on the other hand increases each Base Station's air message
capacity because of the shortened air messages.
[0062] Network Up-Scaling by Adding a Downlink Channel
[0063] Level 5 (highest level of air-message capacity): In a
one-way data collection network, an additional, higher level of
capacity may be reached by adding a downlink channel and deploying
transceivers rather than transmitter meter modules. A two-way
system has the inherent potential to be more efficient with radio
airtime resource, since field units may be synchronized to a
central clock, allowing transmission according to allocated time
slots. The higher the rate of two-way meter modules in the metered
population, the higher the capacity increase provided by adding the
downlink channel. The wireless data collection network described
above may be scaled up from one-way (data collection only) to
two-way by connecting the DOC to a wireless downlink channel in a
modular way as described above. In addition, the measures described
in levels 2 to 4 above may be implemented in a two-way network as
well in order to further increase network capacity.
[0064] Integrating a downlink channel consists a cost-efficient
scaling-up procedure, which provides significant enhancement of
both network air message capacity and metering data application
functionality. This enhancement does not require the network
operator to perform any changes in any of the already existing
elements of the network infrastructure.
[0065] In a preferred embodiment of a two-way metering data
network, both one-way (transmitter) and two-way (transceiver) meter
modules operate on the same network. Transceivers can be
interrogated for data at the time that the data is required, thus
eliminating the need for repeated transmissions, which are required
in a one-way network in order to maintain a certain level of data
latency. In addition, by synchronizing all transceiver modules to
one central real-time clock, a time slot for transmission may be
allocated and specified for each transceiver in a coverage area,
thereby increasing the efficiency of network airtime usage.
[0066] Although several advanced metering applications, such as
demand and TOU metering, are available from a one-way metering data
collection network, two-way meter modules operating in the
described two-way metering data network are capable of providing
additional features, including: accurate interval consumption data
measurement enabled by a regularly synchronized real-time clock,
on-demand meter reading, remote disconnect and reconnect, remote
programming of meter parameters and remote notification of rate
changes or other messages.
[0067] The particular embodiment of the described two-way data
network enables the operator to mix on the same network, in a cost
efficient manner, low cost transmitters, which provide a wide range
of metering data collection features, and higher cost transceivers,
which further enhance metering data application features, while
maintaining the core advantages of sparse infrastructure and the
low cost associated with unlicensed operation of the metering data
collection branch of the network.
[0068] Network Application Scalability
[0069] In addition to the scalability and flexibility provided by
the levels of network architecture described previously, there is
another key feature of the system claimed herein, referred to as
"Application Scalability", which includes a cost-efficient method
of enhancing the metering applications supported on the network
from basic (typically daily) meter reading services to
interval-consumption related applications, such as demand analysis,
load profiling and TOU rates, and further to two-way data features.
As described, some application features, including on-demand meter
reading, remote disconnect and reconnect, remote programming of
meter parameters and remote notification of rate changes or other
messages, require that the network architecture be scaled up to a
two-way network by adding a downlink channel. However, applications
based on interval consumption data can operate successfully on a
one-way network and, by using the method described herein, a
relatively minor increment in air message traffic is incurred.
[0070] In prior art, extensive infrastructure is deployed in order
to collect interval consumption data frequently (e.g. every 15
minutes). However, in many cases, particularly in residential
metering applications, consumption data may be required in high
resolution, but some latency is permitted in data availability. For
example, fifteen-minute demand analysis could be required, but may
be performed each morning on data collected the previous night,
allowing several hours in order to collect the required interval
consumption data. It would therefore be beneficial for the network
service provider to have the flexibility to deploy infrastructure
appropriate to the application and invest in additional
infrastructure for high-end applications, such as on-demand reads,
only in proportion to the meter population for which it is
required.
[0071] In a particular embodiment, an interval consumption data
message includes an array of interval consumption values, each one
representing the consumption increment of one interval. In order to
reduce the total length of air messages, or the total number of
fixed-length interval data air messages, a method referred to as
"logarithmic table encoding" of consumption values is used, which
encodes interval consumption data in the air message. It is a
method to map the range of consumption values into a more limited
number of values, for the purpose of reducing the number of bits of
information transmitted over the air. This mapping is executed by a
series of tables, which have been predefined by the customer,
according to the expected dynamic range of the interval
consumption.
[0072] FIG. 9 shows an example of interval consumption data that
may be required by a demand analysis application. In this example,
it is assumed that an accuracy of 0.1 kWh is sufficient. Also by
way of example, a 12 hour total time period is measured for 15
minute consumption data. In order to optimize the consumption
profile reconstructed, the total time period may be divided to
several sub-periods, in this example 3 periods of 4 hours. The
flexibility of assigning different encoding tables to different
sub-periods reduces the statistical error of the decoded
consumption profile compared to the actual one.
[0073] The numeric consumption values given in FIG. 9 would
traditionally require an encoding table with values ranging from
zero to 1800 Wh, in 100 Wh increments, i.e. 19 values, requiring 5
bits per each consumption interval to encode. In order to reduce
the overall air message traffic associated with interval
consumption data applications, only 2 bits are used in this example
for interval consumption encoding. This approximation inevitably
creates an error in the reconstruction of a consumption profile
compared to the actual consumption, but with appropriate definition
of a set of encoding tables for the meter module to use, an
acceptable error level may be reached.
[0074] The set of tables assigned to a meter module may differ from
one meter module to another according to the expected consumption
patterns. The DOC maintains a bank of available tables from which a
set of tables is defined for each meter module during installation.
An example of such a set of encoding tables is shown in FIG.
10.
[0075] An interval consumption air message in the provided example
would therefore contain 2 bit interval data for 48 intervals of 15
minutes, i.e. 96 bits, plus two bits identifying the table chosen
per each period, to a total of 102 bits, compared to 19
bits.times.48 intervals, or 912 bits, in a traditional system with
no logarithmic encoding.
[0076] The meter module selects an encoding table by building a
consumption profile with each of the tables stored in its memory,
and comparing it to the actual profile, stored in its memory as a
series of actual reading values. Then the meter module applies a
criterion by which to select the best table, e.g. the table that
yields the lowest maximum error during the metered period, or the
lowest variance between the encoded and actual profile.
[0077] The encoded consumption profile is built in the following
process: if during an interval, actual (aggregated) consumption
reached a value X, the interval consumption value, which would
bring the encoded consumption profile to the closest value less or
equal X, and which is also represented by a two-bit code in the
encoding table, is used in order to build the encoded consumption
profile. An example illustration of the profiles constructed vs the
actual consumption is shown in FIG. 11. In the example, if a
minimum error criterion is applied for the 6-10 four-hour period
shown, then Table 3 would be chosen, as it yields a maximum error
of 200 Wh (0.2 kWh) during the period. A table is selected for the
other two periods in the example (10-14, 14-18) in an identical
process. A reverse process is applied at the DOC in order to
extract the interval consumption data, in which the table set used
by the meter module is retrieved and then the consumption profile
is reconstructed for each sub-period.
[0078] In order to provide a high level of redundancy of interval
consumption data, another data encoding method is provided,
referred to as interval consumption data "interleaving air message
encoding", which splits interval consumption values between
separate messages. In a particular embodiment, depicted graphically
in FIG. 7, three separate interval consumption data air messages
are transmitted that relate to the same consumption period b-a. The
first air message includes samples taken at times a, a+x, a+2x, . .
. b. The second air message includes samples taken at times a+x/3,
a+4x/3, a+7x/3, . . . b+x/3. The third air message includes samples
taken at times a+2x/3, a+5x/3, a+8x/3, . . . b+2x/3. Two bits
identifying the reference time are appended to the interval
consumption data air message described above (to a total of 104),
enabling the DOC to correctly correlate different interval
consumption air messages received from the same meter module.
[0079] Interval consumption data is defined to have a resolution
value corresponding to the size of the time interval between
consecutive consumption values sampled. If a message is lost,
interval consumption data is still available at the DOC with a
resolution of x or better. If no messages are lost, interval data
is provided at the DOC with a resolution of x/3. This way, the
meter module maintains the potential to provide high resolution
interval consumption data, but also provides lower resolution
interval consumption data with a higher redundancy level than that
available when data is not split as described above.
[0080] By combining the two encoding methods described, a highly
reliable and efficient interval consumption data collection system
is provided. In the example of FIG. 9, 8 daily messages (typical
length about 100 bits) are required to deliver interval data, with
a redundancy level of 3, whereas without using the provided
methods, at least 14 daily messages would be required to achieve
the same redundancy level. The encoding methods provided therefore
maintain high channel reliability while increasing network
capacity, by 75% in this example.
[0081] The system supports interval consumption data applications
even when a power outage occurs. This is performed by appropriate
utilization of the meter module non-volatile memory, and without
requiring any backup battery. Following is described a method,
combined with the methods described above for data encoding, for
retrieving interval consumption data in a one-way data collection
network, after an outage event has occurred.
[0082] The meter module periodically and frequently executes a
procedure, which updates and stores an interval consumption data
message. The purpose of this process is to prevent from losing
interval consumption data upon an outage event.
[0083] A general distinction exists in the system between a regular
metering data air message, referred to as "full data message", and
an interval consumption data air message, which includes only a
series of consumption data values, as sampled by the meter module.
Upon power restoration after outage, the meter module transmits a
full data message, also including a flag signifying that power has
just been restored. In parallel, a new interval consumption data
cycle (period) begins as the module's microcontroller wakes up.
Shortly thereafter, the last saved interval consumption data air
message is transmitted. The meter module maintains an internal flag
called `first interval consumption message transmitted`. Only once
this flag is set, can the procedure that updates and stores an
interval consumption data message operate. The flag is reset upon
power restoration, and set once the last saved interval consumption
message is transmitted. The DOC identifies the power restoration
message and thus identifies the interval consumption message that
follows it as the last saved interval consumption message to
follow, enabling the DOC to reconstruct interval consumption data
prior to the outage event. In addition, the next scheduled full
data message, following the power restoration message, is also
flagged by the meter module as the `second full data message since
power restored`. This acts as a redundant measure to identify the
last saved interval consumption message before the outage
event.
[0084] Meter Module
[0085] Following is a description of the meter module apparatus
used in the network system. The meter module described has unique
features of low overall power consumption, high output power and
low cost overall design, enabling long battery life and long
communication range in a commercially feasible fixed wireless
network for a variety of metering applications.
[0086] Each meter module in the network continuously monitors the
resource consumption according to an input sensor that is coupled
to the utility meter. In a particular embodiment, the meter module
may be integrated inside, or as a part of, the meter enclosure. The
meter module stores and transmits a wide array of data fields
related to the meter, including consumption data, meter
identification and calculation factor data, and various status
alerts. Meter reading is stored as an aggregated value and not as
an increment value, thus maintaining the reading value's integrity
if an air message is not received at the DOC. A one-way meter
module transmits a metering data air message once every
preprogrammed time interval. A block diagram of the transmitter is
depicted in FIG. 3 according to a particular embodiment of the
present invention. In this particular implementation, the
transmitter includes a meter interface logic module 50 that
collects consumption, tamper status and other data from an
associated utility meter 51. It should be noted that, although FIG.
3 depicts a single meter interface module for purposes of
simplification, multiple meter interface logic modules may be used
in a single transmitter to interface with more than one utility
meter. The meter interface logic module 51 operates continuously
and draws only a small amount of current. It includes several
standard sensors, such as magnetic reed switches or optical sensors
in order to track consumption, tilt sensors for tamper detection
and voltage sensors to determine outage or power restoration
events.
[0087] The transmitter includes a serial data communication
interface 20, which is used for testing and initialization at the
shop or in the field by using a short-range wireless magnetic loop
interface or a PC with a serial data port. The wake-up circuit 40
is designed in order to save power, particularly in battery
operated transmitters, by keeping the controller 60, RF module 70,
DSSS encoder 80 and LPF 85 in a turned off (no power) state, which
is interrupted only if an event was triggered by the meter via the
meter interface logic 50, by an external device via the serial data
interface 20, or by the timer completing its timing cycle and
triggering a wake-up signal. In another embodiment, particularly
with an unlimited power source as may be the case with electric
meters, the controller operates continuously and also maintains a
timer, and a wake-up circuit is not used.
[0088] If an event occurred which is determined by the controller
60 to trigger air message transmission, the controller module 60
prepares a data packet, which is converted to a direct sequence (PN
code generation and signal spreading) by the DSSS encoder 80. The
spread signal is filtered by a low pass filter (LPF) 85 and is the
used as the modulating signal for the BPSK modulator. The RF module
70 includes a synthesizer controlled local oscillator (LO) 71, a
Binary-Phase-Shift-Keying (BPSK) modulator 73 and a power amplifier
(PA) 75. The power amplifier 75 produces up to 1 W of power for
output to an on-board printed antenna 76. Once the controller has
handled the event that woke it up from its power-down mode, whether
an air message transmission or other task was performed, it returns
to its power-down (idle) mode.
[0089] Restrained Power Supply
[0090] In a particular embodiment of the meter module, a restrained
power supply 10 is implemented in the meter module, which is
essential in order to maintain an acceptable level of radio
interference in the event of uncontrolled transmission by a
malfunctioning meter module. One source of danger in the system is
the possibility that a transmitter will malfunction and begin
transmitting continuously. The result may be that the entire
frequency channel would be blocked in that coverage area during the
time of transmission, until the transmitter's power source dies
(and this would continue indefinitely if the power source is
unlimited, such as an electric grid). Although this event is highly
unlikely, measures have been designed into the system to prevent it
from happening. In the meter module described herein, a cost
effective mechanism has been introduced to prevent an uncontrolled
transmission from blocking network air message traffic. This
mechanism provides two additional benefits to the system: high
output power with a limited power source and an immediate outage
notification feature, also known as a `last gasp` transmission.
[0091] The meter module's power supply hardware is designed to
prevent the described phenomenon of continuous uncontrolled
transmission. Two specific physical limits have been designed into
the meter module to meet this purpose. A capacitive element and a
limited current source are combined in the meter module's power
supply. The capacitive element is used as a buffer stage between
the energy source and the load. The capacitive element stores
sufficient energy, as required for a high-power air message
transmission. Due to its inherent physical limitations, the
capacitive element can deliver sufficient power for transmission
but only for a limited period of time. Since the duration of
transmission is relative to the element's physical capacitance, and
physical capacitance is related to the size of the element, the
size of the capacitive element is selected to be big enough to
deliver enough energy for a complete transmission session, but not
more than that. This way, the maximum potential blockage duration
due to unwanted transmission is restricted to one transmission
session. In addition, the limited current source imposes a physical
limitation on the recharge time required for the capacitive element
to reach the required energy level for another air message
transmission, thus limiting the on-off transmission duty cycle to a
level that is harmless in terms of network capacity. In a
particular embodiment, the transmitted power is one watt, for a
duration of 150 msec and with a recharge time of 90 seconds. This
translates to a maximum of 960 messages per day, which is about 1%
of an estimated channel capacity of 86,400 messages per day. Since
network coverage is designed with a much higher safety margin than
1%, a malfunctioning transmitter would not be destructive to the
network operation, allowing sufficient time for software means to
detect and identify the source of the problem.
[0092] The described power supply therefore also enables the
transmitter to generate high-power air message transmissions, even
with a power source that supports a very low current drain. It also
enables an enhancement of electric metering applications by
enabling a `last gasp` metering data air message transmission when
an outage event is detected by an electric meter module.
[0093] Low Power Rotation Sensor Circuit
[0094] In a particular embodiment of the meter module, appropriate
circuitry and controller logic enable near zero power consumption
of the rotation sensing mechanism, which is a part of the meter
interface logic 50. This may be a decisive factor in the expected
operating life of a meter module powered by a limited power source
such as a battery.
[0095] A typical prior art sensor configuration appears in FIG. 8A.
The switch has two operation states, open and closed. When the
switch is open the current circuit is broken and the voltage
measured at the V-sense node equals the supply voltage Vcc. When
the switch is closed the voltage measured at V-sense node is the
circuit's ground level reference voltage i.e. zero voltage.
Distinguishing between the two electrical states at the V-sense
node allows distinguishing between the two switch states open and
closed.
[0096] Although most switches have finite conductivity, typical
power consumption in the open state is acceptable for long
operating life. However, during the closed state, power is consumed
at a level that may be significant when the energy source is
limited as in battery-powered devices, and when that limited source
must operate for lengthy periods of time, such as is the case with
meter modules. In addition, the amount of energy wasted typically
cannot be predicted, and may vary widely with utility customer
consumption patterns.
[0097] An alternative to the standard sensor configuration may be
referred to as "Zero Current Sensors Configuration". The
implementation is based upon a component selection and geometrical
arrangement of two sensors, such that at any possible position of
the sensed rotating element, such as a magnet or a light reflector,
only one of the two sensors may be triggering a closed switch
state.
[0098] FIG. 8B illustrates the solution. The two switch circuits
are activated or deactivated by control commands of the controller
60. Loading high state voltage into a register causes the
activation of the associated switch. Loading low state voltage into
a register causes deactivation of a switch. When a switch is
deactivated, no current can flow via the switch, even when the
switch state is close and of course, no current flows when the
switch is open. The result is that no current flows, and hence no
energy is wasted, when the switch is open, or if the switch is
de-activated without regard to the state of the switch.
[0099] The controller module 60 is programmed to deactivate a
sensor circuit immediately once that sensor has been detected in a
closed switch state. In addition, the controller module activates
the other sensor circuit. For example, if the initial state was
that Switch 1 is activated and Switch 1 is projected by the
projection element (magnet/reflector), it changes its state from
open to close, the voltage at V-sense 1 is changed from high state
voltage to zero. The voltage drop wakes up the controller module
60, which then deactivates Switch 1 and activates Switch 2. Since
Switch 2 is located in different projection zone than Switch 1,
Switch 2's state when activated is open so no current flows via
Switch 2. Since Switch 1 is now de-activated, no current flows via
Switch 1 either. When the rotation of disk or wheel continues and
the projection element reaches the projection zone of Switch 2,
Switch 2 changes its state from open to close, the V-sense 2 is
changed from high state voltage to zero, the controller unit 60 is
woken up, and the controller unit 60 then immediately deactivates
Switch 2 and activates Switch 1. One rotation of the disk or wheel
is defined as state change of Switch 1 from open to close followed
by state change of Switch 2 from open to close, after which the
controller increments the meter revolution count. However, neither
switch is ever active and closed. Therefore the continuous current
drain of the sensor circuitry only includes that of the open
switch, which is near zero.
[0100] Low Cost RF Modulator
[0101] FIG. 4 is a block diagram depicting an example arrangement
for implementing the BPSK modulator 73 of FIG. 3. Unlike
conventional microwave monolithic integrated circuit (MMIC) BPSK
modulators, which are large and expensive, the arrangement
illustrated in FIG. 4 is compact and can be implemented at a low
cost. The BPSK modulator of the present invention includes a diode
bridge 1202 that can be switched to provide either an in-phase
output signal (upper configuration of FIG. 4) or an inverted-phase
output signal (lower configuration of FIG. 4). Balun
(balance/unbalance) circuits 1201, implemented as 180.degree. power
dividers, are used at the inputs and outputs of the diode bridge
1202. The balun circuit 1201 at the input of the diode bridge 1202
feeds the cross switch implemented by the diode bridge 1202, and
the balun circuit 1201 at the output of the diode bridge 1202 sums
the energy either in phase or in inverted phase. The balun circuits
1201 are implemented using an FR4-type printed circuit board (PCB),
avoiding the need for tuning during production. The PCB has four
layers, the inner two of which are used to implement the balun
circuits 1201. Each balun circuit 1201 includes three broadside
coupled transmission line pairs.
[0102] FIG. 5 is a schematic diagram illustrating the arrangement
of FIG. 4 in greater detail. Diodes 5A, 5B, 6A and 6B form the
diode bridge 1202. An input balun 1201 is formed by three pairs of
coupled transmission lines, namely, transmission lines 1A and 1B,
transmission lines 2A and 2B, and transmission lines 3A and 3B.
Similarly, an output balun 1201 is also formed by three pairs of
coupled transmission lines: transmission lines 10A and 10B,
transmission lines 11A and 11B, and transmission lines 12A and 12B.
The input balun 1201 feeds the diode pair formed by diodes 5A and
5B and the diode pair formed by diodes 6A and 6B with antipodal
signals that are approximately 180.degree. apart in phase. The
modulation provided through the baseband signal bi-phase modulates
each branch. The output balun 1201 sums the two branches. Small
transmission lines 4 and 9 provide small corrections to ensure that
the two branches are 180.degree. apart in phase.
[0103] FIG. 6 is a cross-sectional diagram depicting an example
physical implementation of the arrangement of FIG. 5. The modulator
is implemented using a PCB made of FR4-type material. The PCB has
four layers and is surrounded by a shield. For 1 MHz modulation,
the modulator measures 15 mm by 23 mm and has a bandwidth of
750-1500 MHz. Half octave phase accuracy is within 1.degree., and
full octave phase accuracy is within 2.5.degree.. Amplitude
imbalance is preferably less than 0.2 dB, and signal loss is
preferably less than 6 dB. Carrier suppression is preferably at
least 17 dB.
* * * * *