U.S. patent application number 13/656694 was filed with the patent office on 2013-04-25 for sub-band power scaling reporting and sub-band transmit power estimation.
This patent application is currently assigned to TEXAS INSTRUMENTS INCORPORATED. The applicant listed for this patent is TEXAS INSTRUMENTS INCORPORATED. Invention is credited to Anand Dabak, Il Han Kim, Tarkesh Pande, Ramanuja Venantham, Kumaran Vijayasankar.
Application Number | 20130101055 13/656694 |
Document ID | / |
Family ID | 48135981 |
Filed Date | 2013-04-25 |
United States Patent
Application |
20130101055 |
Kind Code |
A1 |
Pande; Tarkesh ; et
al. |
April 25, 2013 |
Sub-Band Power Scaling Reporting and Sub-Band Transmit Power
Estimation
Abstract
Systems and methods for routing protocols for power line
communications (PLC) are described. In some embodiments, a method
performed by a PLC device, such as a PLC meter, may include
selecting one or more transmit sub-bands on which to transmit
frames, where the transmit sub-bands comprise groups of six carrier
frequencies. The PLC device then generates a frame comprising a
tone map that indicates which transmit sub-bands are used to carry
data for the frame. The tone map using two bits per transmit
sub-band to indicate a status of each transmit sub-band. The PLC
device then transmits the frame on the selected transmit sub-bands
using OFDM. A resolution bit and a mode bit may be used to provide
additional information about the transmit sub-bands, such as an
amount of power adjustment that has been applied to carrier
frequencies and whether dummy bits are transmitted on unused
carrier frequencies.
Inventors: |
Pande; Tarkesh; (Dallas,
TX) ; Dabak; Anand; (Plano, TX) ;
Vijayasankar; Kumaran; (Dallas, TX) ; Venantham;
Ramanuja; (Allen, TX) ; Kim; Il Han;
(Richardson, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TEXAS INSTRUMENTS INCORPORATED; |
Dallas |
TX |
US |
|
|
Assignee: |
TEXAS INSTRUMENTS
INCORPORATED
Dallas
TX
|
Family ID: |
48135981 |
Appl. No.: |
13/656694 |
Filed: |
October 20, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61550145 |
Oct 21, 2011 |
|
|
|
61562032 |
Nov 21, 2011 |
|
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|
61581334 |
Dec 29, 2011 |
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Current U.S.
Class: |
375/257 |
Current CPC
Class: |
H04L 27/2602 20130101;
H04L 5/0094 20130101; H04L 27/18 20130101; H04B 3/54 20130101; H04L
27/32 20130101; H04B 2203/5416 20130101; H04L 27/04 20130101 |
Class at
Publication: |
375/257 |
International
Class: |
H04B 3/54 20060101
H04B003/54 |
Claims
1. A method comprising: performing, by a power line communication
(PLC) device adapted to transmit frames to other devices using
Orthogonal Frequency-Division Multiplexing (OFDM) on multiple
carrier frequencies, selecting one or more transmit sub-bands on
which to transmit the frames, the transmit sub-bands comprising
groups of the carrier frequencies; generating a frame comprising a
tone map that indicates which transmit sub-bands are used to carry
data for the frame, the tone map using two bits per transmit
sub-band to indicate a status of each transmit sub-band; and
transmitting the frame on the selected transmit sub-bands using
OFDM.
2. The method of claim 1, wherein the transmit sub-bands comprise
groups of six carrier frequencies, the method further comprising:
providing a resolution bit and a mode bit, the resolution bit
indicating an amount of power adjustment that has been applied to
carrier frequencies in the transmit sub-bands, and the mode bit
indicating whether dummy bits are transmitted on carrier
frequencies in the transmit sub-bands that do not carry data.
3. The method of claim 2, wherein a number of carrier frequencies
is seventy-two, a number of transmit sub-bands is twelve, and the
tone map comprises twenty-four bits.
4. The method of claim 1, further comprising: setting the two bits
per transmit sub-band to indicate that a transmit sub-band has been
used to carry data and that the power in the transmit sub-band has
been adjusted.
5. The method of claim 4, further comprising: generating the frame
to further comprise a resolution bit, the resolution bit indicating
an amount of power adjustment that has been applied to carrier
frequencies in the transmit sub-bands that have been adjusted.
6. The method of claim 1, further comprising: setting the two bits
per transmit sub-band to indicate that a transmit sub-band has been
used to carry data and that the power in the transmit sub-band has
not been adjusted.
7. The method of claim 1, further comprising: setting the two bits
per transmit sub-band to indicate that a transmit sub-band has not
been used to carry data.
8. The method of claim 7, further comprising: generating the frame
to further comprise a mode bit, the mode bit indicating whether
dummy bits are transmitted on carrier frequencies in the transmit
sub-bands that do not carry data.
9. The method of claim 1, wherein the transmit sub-bands comprise
groups of six carrier frequencies, the method further comprising:
setting the two bits per transmit sub-band to indicate either that
a transmit sub-band has been used to carry data and that the power
in the transmit sub-band has been adjusted, or that a transmit
sub-band has not been used to carry data; and generating the frame
to further comprise a resolution bit and a mode bit, the resolution
bit indicating an amount of power adjustment that has been applied
to carrier frequencies in the transmit sub-bands that have been
adjusted, the mode bit indicating whether dummy bits are
transmitted on carrier frequencies in the transmit sub-bands that
do not carry data.
10. The method of claim 9, wherein the two bits per transmit
sub-band, the resolution bit, and the mode bit are grouped within a
frame control header segment of the frame.
11. The method of claim 1, further comprising: receiving a tone
response map from another device, the tone response map comprising
status recommendations for receive sub-bands, wherein two
consecutive receive sub-bands correspond to one transmit sub-band;
and configuring a frame transmission on the transmit sub-bands
based upon the status recommendations in the tone map.
12. The method of claim 11, wherein if a status recommendation for
either receive sub-band indicates that the receive sub-band should
not be used, then configuring the frame transmission to not use a
corresponding transmit sub-band.
13. The method of claim 11, wherein if a status recommendation for
either receive sub-band indicates that a power level for
transmissions in the receive sub-band should be boosted, then
configuring the frame transmission to boost a power level in a
corresponding transmit sub-band.
14. The method of claim 11, wherein if a status recommendation for
a first receive sub-band indicates that a power level for
transmissions in the first receive sub-band should be decreased and
a status recommendation for a second receive sub-band indicates
that a power level for transmissions in the second receive sub-band
should be maintained, then configuring the frame transmission to
maintain a power level in a corresponding transmit sub-band.
15. The method of claim 1, wherein a frame control header table
comprising a tone map that uses two bits per transmit sub-band to
indicate a status of each transmit sub-band is used only when
coherent modulation is used for transmitting the frame, and
otherwise using a frame control header table comprising a tone map
that uses one bit per transmit sub-band.
16. The method of claim 1, wherein a frame control header table
comprising a tone map that uses two bits per transmit sub-band to
indicate a status of each transmit sub-band is used only when
coherent 16 QAM modulation is used for transmitting the frame, and
otherwise using a frame control header table comprising a tone map
that uses one bit per transmit sub-band.
17. A method comprising: performing, by a power line communication
(PLC) device adapted to transmit frames to other devices using
Orthogonal Frequency-Division Multiplexing (OFDM) on multiple
carrier frequencies, generating a frame comprising a preamble, a
first synchronization symbol, a second synchronization symbol, and
a data payload; and scaling a power level for one or more of the
preamble, the first synchronization symbol, and the second
synchronization symbol using a power adjustment applied to the data
payload; and transmitting the frame using OFDM.
18. A method comprising: performing, by a power line communication
(PLC) device adapted to transmit frames to other devices using
Orthogonal Frequency-Division Multiplexing (OFDM) on multiple
carrier frequencies, receiving a frame comprising a preamble, a
first synchronization symbol, a second synchronization symbol, and
a data payload, wherein a power level for one or more of the
preamble, the first synchronization symbol, and the second
synchronization symbol has been scaled a using a power adjustment;
and estimating a power level adjustment by comparing power levels
in one or more of the preamble, the first synchronization symbol,
and the second synchronization symbol.
19. The method of claim 18, wherein the power levels of the first
synchronization symbol and the second synchronization symbol have
been scaled, the method further comprising: estimating the power
level adjustment by comparing power levels in the preamble to power
levels in the first synchronization symbol and the second
synchronization symbol.
20. The method of claim 18, wherein the power level of the first
synchronization symbol or the second synchronization symbol have
been scaled, the method further comprising: estimating the power
level adjustment by comparing power levels in the first
synchronization symbol to power levels in the second
synchronization symbol.
21. The method of claim 18, wherein the power level of the preamble
has been scaled but not the power levels of the first
synchronization symbol and the second synchronization symbol, the
method further comprising: estimating the power level adjustment by
comparing power levels in the preamble to power levels in the first
synchronization symbol and the second synchronization symbol.
22. A power line communication (PLC) device, comprising: a
processor; and a memory coupled to the processor, the memory
configured to store program instructions executable by the
processor to cause the PLC device to: select one or more transmit
sub-bands on which to transmit the frames, the transmit sub-bands
comprising groups of the carrier frequencies; generate a frame
comprising a tone map that indicates which transmit sub-bands are
used to carry data for the frame, the tone map using two bits per
transmit sub-band to indicate a status of each transmit sub-band,
the transmit sub-bands comprising groups of six carrier
frequencies, the frame further comprising a resolution bit and a
mode bit, the resolution bit indicating an amount of power
adjustment that has been applied to carrier frequencies in the
transmit sub-bands, and the mode bit indicating whether dummy bits
are transmitted on carrier frequencies in the transmit sub-bands
that do not carry data; and transmit the frame on the selected
transmit sub-bands using OFDM.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application claims the benefit of the filing date of
U.S. Provisional Patent Application No. 61/550,145, which is titled
"TXCOEF and TM Fields for Low Frequency Narrow Band Power Line
Communications for Smart Grid Applications" and was filed on Oct.
21, 2011; U.S. Provisional Patent Application No. 61/562,032, which
is titled "Sub-Band Transmit Power Estimation Using Preamble" and
was filed on Nov. 21, 2011; and U.S. Provisional Patent Application
No. 61/581,334, which is titled "TXCOEF and TM Fields for Low
Frequency Narrow Band Power Line Communications for Smart Grid
Applications" and was filed on Dec. 29, 2011, the disclosures of
which are hereby incorporated by reference herein in their
entirety.
BACKGROUND
[0002] Power line communications (PLC) include systems for
communicating data over the same medium that is also used to
transmit electric power to residences, buildings, and other
premises, such as wires, power lines, or other conductors. In its
simplest terms, PLC modulates communication signals over existing
power lines. This enables devices to be networked without
introducing any new wires or cables. This capability is extremely
attractive across a diverse range of applications that can leverage
greater intelligence and efficiency through networking. PLC
applications include utility meters, home area networks, lighting,
and solar.
[0003] Using PLC to communicate with utility meters enables
applications such as Automated Meter Reading (AMR) and Automated
Meter Infrastructure (AMI) communications without the need to
install additional wires. Consumers may also use PLC to connect
home electric meters to an energy monitoring device or in-home
display monitor their energy consumption and to leverage lower-cost
electric pricing based on time-of-day demand.
[0004] As the home area network expands to include controlling home
appliances for more efficient consumption of energy, OEMs may use
PLC to link these devices and the home network. PLC may also
support home and industrial automation by integrating intelligence
into a wide variety of lighting products to enable functionality
such as remote control of lighting, automated activation and
deactivation of lights, monitoring of usage to accurately calculate
energy costs, and connectivity to the grid.
[0005] PLC may also serve as an important enabling technology for
the mass deployment of solar equipment by providing a communication
channel to solar inverters for monitoring and managing power across
the grid by utility companies. While radio frequency (RF)
communications have made some progress in solar installations, PLC
offers an ideal means for connecting equipment with high
reliability and at a low cost on DC or AC lines.
[0006] PLC is a generic term for any technology that uses power
lines as a communications channel. Various PLC standardization
efforts are currently in work around the world. The different
standards focus on different performance factors and issues
relating to particular applications and operating environments. Two
of the most well-known PLC standards are G3 and PRIME. G3 has been
approved by the International Telecommunication Union (ITU). IEEE
is developing the IEEE P1901.2 standard that is based on G3. Each
PLC standard has its own unique characteristics.
[0007] The manner in which PLC systems are implemented depends upon
local regulations, characteristics of local power grids, etc. The
frequency band available for PLC users depends upon the location of
the system. In Europe, PLC bands are defined by the CENELEC
(European Committee for Electrotechnical Standardization). The
CENELEC-A band (3 kHz-95 kHz) is exclusively for energy providers.
The CENELEC-B, C, D bands are open for end user applications, which
may include PLC users. Typically, PLC systems operate between 35-90
kHz in the CENELEC A band using 36 tones spaced 1.5675 kHz apart.
In the United States, the FCC defines a single wide band from 10 to
535 kHz; however, PLC systems typically operate at 154-487.5 kHz
using seventy-two tones spaced at 4.6875 kHz apart. In other parts
of the world different frequency bands are used, such as the
Association of Radio Industries and Businesses (ARIB)-defined band
in Japan, which operates at 10-450 kHz, and the Electric Power
Research Institute (EPRI)-defined bands in China, which operates at
3-90 kHz.
SUMMARY
[0008] Systems and methods for implementing sub-band power control
and estimation in power line communications (PLC) are described. In
an illustrative embodiment, a method performed by a PLC device,
such as a PLC meter or data concentrator may include selecting one
or more transmit sub-bands on which to transmit frames. The
transmit sub-bands may comprise groups of six carrier frequencies,
for example. The PLC device generates a frame comprising a frame
control header (FCH) that indicates which transmit sub-bands are
used to carry data for the frame. The frame control header uses two
bits per transmit sub-band to indicate a status of each transmit
sub-band. The PLC device then transmits the frame on the selected
transmit sub-bands using Orthogonal Frequency-Division Multiplexing
(OFDM).
[0009] A resolution bit and a mode bit may be used to further
define the two-bits per sub-band. The resolution bit indicates an
amount of power adjustment that has been applied to carrier
frequencies in the transmit sub-bands. The mode bit indicates
whether dummy bits are transmitted on carrier frequencies in the
transmit sub-bands that do not carry data. In one embodiment using
a G3-FCC band, the number of carrier frequencies is seventy-two,
there are twelve transmit sub-bands, and the tone map comprises
twenty-four bits. The two bits per transmit sub-band, the
resolution bit, and the mode bit may be grouped within a frame
control header segment of the frame.
[0010] The PLC device may set the two bits per transmit sub-band to
indicate that a transmit sub-band has been used to carry data and
that the power in the transmit sub-band has been adjusted.
Alternatively, the two bits per transmit sub-band may indicate that
a transmit sub-band has been used to carry data and that the power
in the transmit sub-band has not been adjusted. In other
embodiments, the two bits per transmit sub-band indicate that a
transmit sub-band has not been used to carry data.
[0011] The PLC device may receive a tone response map from another
device. The tone map response (TMR) may include status
recommendations for receive sub-bands. Each transmit sub-band may
correspond to two consecutive receive sub-bands. For example,
receive sub-bands specified in a tone response message may include
three carrier frequencies, but sub-bands in the transmit sub-band
may include six carrier frequencies. The frame transmission on the
transmit sub-bands may be configured based upon the status
recommendations in the tone map.
[0012] If a status recommendation in a tone map response for either
receive sub-band indicates that the receive sub-band should not be
used, then the frame transmission is configured to not use the
corresponding transmit sub-band. If a status recommendation for
either receive sub-band indicates that a power level for
transmissions in the receive sub-band should be boosted, then the
frame transmission is configured to boost a power level in a
corresponding transmit sub-band. If a status recommendation for a
first receive sub-band indicates that a power level for
transmissions in the first receive sub-band should be decreased and
a status recommendation for a second receive sub-band indicates
that a power level for transmissions in the second receive sub-band
should be maintained, then the frame transmission is configured to
maintain a power level in a corresponding transmit sub-band.
[0013] In one embodiment, a frame control header table comprising a
tone map that uses two bits per transmit sub-band to indicate a
status of each transmit sub-band is used only when coherent
modulation is used for transmitting the frame. Otherwise, the PLC
device uses a frame control header table comprising a tone map that
uses one bit per transmit sub-band.
[0014] In other embodiments, a frame control header table
comprising a tone map that uses two bits per transmit sub-band to
indicate a status of each transmit sub-band is used only when
coherent 16 QAM modulation is used for transmitting the frame.
Otherwise, the PLC device uses a frame control header table
comprising a tone map that uses one bit per transmit sub-band.
[0015] A power line communication (PLC) device that is adapted to
transmit frames to other devices using OFDM on multiple carrier
frequencies may generate a frame comprising a preamble, a first
synchronization symbol, a second synchronization symbol, and a data
payload. The PLC device may scale a power level for one or more of
the preamble, the first synchronization symbol, and the second
synchronization symbol using a power adjustment applied to the data
payload. The PLC device then transmits the frame using OFDM.
[0016] A receiving PLC device may receive the frame comprising a
preamble, a first synchronization symbol, a second synchronization
symbol, and a data payload The power level for one or more of the
preamble, the first synchronization symbol, and the second
synchronization symbol may have been scaled a using a power
adjustment. The receiving PLC device may estimate a power level
adjustment by comparing power levels in one or more of the
preamble, the first synchronization symbol, and the second
synchronization symbol.
[0017] If the power levels of the first synchronization symbol and
the second synchronization symbol have been scaled, then the power
level adjustment is estimated by comparing power levels in the
preamble to power levels in the first synchronization symbol and
the second synchronization symbol.
[0018] If the power level of the first synchronization symbol or
the second synchronization symbol have been scaled, then the power
level adjustment is estimated by comparing power levels in the
first synchronization symbol to power levels in the second
synchronization symbol.
[0019] If the power level of the preamble has been scaled but not
the power levels of the first synchronization symbol and the second
synchronization symbol, then the power level adjustment is
estimated by comparing power levels in the preamble to power levels
in the first synchronization symbol and the second synchronization
symbol.
[0020] In some embodiments, one or more of the methods described
herein may be performed by one or more PLC devices (e.g., a PLC
meter, PLC data concentrator, etc.). In other embodiments, a
tangible electronic storage medium may have program instructions
stored thereon that, upon execution by a processor within one or
more PLC devices, cause the one or more PLC devices to perform one
or more operations disclosed herein. Examples of such a processor
include, but are not limited to, a digital signal processor (DSP),
an application specific integrated circuit (ASIC), a system-on-chip
(SoC) circuit, a field-programmable gate array (FPGA), a
microprocessor, or a microcontroller. In yet other embodiments, a
PLC device may include at least one processor and a memory coupled
to the at least one processor, the memory configured to store
program instructions executable by the at least one processor to
cause the PLC device to perform one or more operations disclosed
herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Having thus described the invention(s) in general terms,
reference will now be made to the accompanying drawings,
wherein:
[0022] FIG. 1 is a diagram of a PLC system according to some
embodiments.
[0023] FIG. 2 is a block diagram of a PLC device or modem according
to some embodiments.
[0024] FIG. 3 is a block diagram of a PLC gateway according to some
embodiments.
[0025] FIG. 4 is a block diagram of a PLC data concentrator
according to some embodiments.
[0026] FIG. 5 illustrates a transmit-receive pair according to one
embodiment.
[0027] FIG. 6 illustrates seventy-two individual tones that are
present in a G3-FCC band.
[0028] FIG. 7 illustrates the results of a simulation that compared
the performance of dummy bit transmission versus nulling for both
thirty-six-tone and eighteen-tone cases for a fixed time domain
transmit power level.
[0029] FIG. 8 is a pictorial representation of transmissions using
dummy bits and null bits.
[0030] FIG. 9 illustrates a frame transmitted between nodes
according to one embodiment.
[0031] FIG. 10 illustrates the grouping of six tones in the G3-FCC
band into FCH table sub-bands 1002.
[0032] FIG. 11 illustrates how the same tones are treated
differently in the TMR table and the FCH table.
[0033] FIG. 12 illustrates the relative transmit power levels in
different sub-bands for an OFD signal at the transmitter side.
[0034] FIG. 13 illustrates a frame structure in which two syncP
symbols are placed after FCH and before the data payload signal at
the transmitter side.
[0035] FIG. 14 illustrates a -syncP symbol that has been scaled by
the transmit node, where a syncP symbol is not scaled.
[0036] FIG. 15 illustrates a -syncP symbol that is not scaled,
where a syncP symbol is scaled by the transmit node.
[0037] FIG. 16 illustrates scaling of both -syncP and syncP
symbols.
[0038] FIG. 17 illustrates not scaling the syncP symbols, but
instead scaling a preamble.
[0039] FIG. 18 is a block diagram of an integrated circuit
according to some embodiments.
DETAILED DESCRIPTION
[0040] The invention(s) now will be described more fully
hereinafter with reference to the accompanying drawings. The
invention(s) may, however, be embodied in many different forms and
should not be construed as limited to the embodiments set forth
herein. Rather, these embodiments are provided so that this
disclosure will be thorough and complete, and will fully convey the
scope of the invention(s) to a person of ordinary skill in the art.
A person of ordinary skill in the art may be able to use the
various embodiments of the invention(s).
[0041] FIG. 1 illustrates a power line communication (PLC) system
according to some embodiments. Medium voltage (MV) power lines 103
from substation 101 typically carry voltage in the tens of
kilovolts range. Transformer 104 steps the MV power down to low
voltage (LV) power on LV lines 105, carrying voltage in the range
of 100-240 VAC. Transformer 104 is typically designed to operate at
very low frequencies in the range of 50-60 Hz. Transformer 104 does
not typically allow high frequencies, such as signals greater than
100 KHz, to pass between LV lines 105 and MV lines 103. LV lines
105 feed power to customers via meters 106a-n, which are typically
mounted on the outside of residences 102a-n. Although referred to
as "residences," premises 102a-n may include any type of building,
facility, electric vehicle charging station, or other location
where electric power is received and/or consumed. A breaker panel,
such as panel 107, provides an interface between meter 106n and
electrical wires 108 within residence 102n. Electrical wires 108
deliver power to outlets 110, switches 111 and other electric
devices within residence 102n.
[0042] The power line topology illustrated in FIG. 1 may be used to
deliver high-speed communications to residences 102a-n. In some
implementations, power line communications modems or gateways
112a-n may be coupled to LV power lines 105 at meter 106a-n. PLC
modems/gateways 112a-n may be used to transmit and receive data
signals over MV/LV lines 103/105. Such data signals may be used to
support metering and power delivery applications (e.g., smart grid
applications), communication systems, high speed Internet,
telephony, video conferencing, and video delivery, to name a few.
By transporting telecommunications and/or data signals over a power
transmission network, there is no need to install new cabling to
each subscriber 102a-n. Thus, by using existing electricity
distribution systems to carry data signals, significant cost
savings are possible.
[0043] An illustrative method for transmitting data over power
lines may use a carrier signal having a frequency different from
that of the power signal. The carrier signal may be modulated by
the data, for example, using an OFDM technology or the like
described, for example, by the PRIME, G3 or IEEE 1901
standards.
[0044] PLC modems or gateways 112a-n at residences 102a-n use the
MV/LV power grid to carry data signals to and from PLC data
concentrator or router 114 without requiring additional wiring.
Concentrator 114 may be coupled to either MV line 103 or LV line
105. Modems or gateways 112a-n may support applications such as
high-speed broadband Internet links, narrowband control
applications, low bandwidth data collection applications, or the
like. In a home environment, for example, modems or gateways 112a-n
may further enable home and building automation in heat and air
conditioning, lighting, and security. Also, PLC modems or gateways
112a-n may enable AC or DC charging of electric vehicles and other
appliances. An example of an AC or DC charger is illustrated as PLC
device 113. Outside the premises, power line communication networks
may provide street lighting control and remote power meter data
collection.
[0045] One or more PLC data concentrators or routers 114 may be
coupled to control center 130 (e.g., a utility company) via network
120. Network 120 may include, for example, an IP-based network, the
Internet, a cellular network, a WiFi network, a WiMax network, or
the like. As such, control center 130 may be configured to collect
power consumption and other types of relevant information from
gateway(s) 112 and/or device(s) 113 through concentrator(s) 114.
Additionally or alternatively, control center 130 may be configured
to implement smart grid policies and other regulatory or commercial
rules by communicating such rules to each gateway(s) 112 and/or
device(s) 113 through concentrator(s) 114.
[0046] FIG. 2 is a block diagram of PLC device 113 according to
some embodiments. As illustrated, AC interface 201 may be coupled
to electrical wires 108a and 108b inside of premises 112n in a
manner that allows PLC device 113 to switch the connection between
wires 108a and 108b off using a switching circuit or the like. In
other embodiments, however, AC interface 201 may be connected to a
single wire 108 (i.e., without breaking wire 108 into wires 108a
and 108b) and without providing such switching capabilities. In
operation, AC interface 201 may allow PLC engine 202 to receive and
transmit PLC signals over wires 108a-b. In some cases, PLC device
113 may be a PLC modem. Additionally or alternatively, PLC device
113 may be a part of a smart grid device (e.g., an AC or DC
charger, a meter, etc.), an appliance, or a control module for
other electrical elements located inside or outside of premises
112n (e.g., street lighting, etc.).
[0047] PLC engine 202 may be configured to transmit and/or receive
PLC signals over wires 108a and/or 108b via AC interface 201 using
a particular frequency band. In some embodiments, PLC engine 202
may be configured to transmit OFDM signals, although other types of
modulation schemes may be used. As such, PLC engine 202 may include
or otherwise be configured to communicate with metrology or
monitoring circuits (not shown) that are in turn configured to
measure power consumption characteristics of certain devices or
appliances via wires 108, 108a, and/or 108b. PLC engine 202 may
receive such power consumption information, encode it as one or
more PLC signals, and transmit it over wires 108, 108a, and/or 108b
to higher-level PLC devices (e.g., PLC gateways 112n, data
aggregators 114, etc.) for further processing. Conversely, PLC
engine 202 may receive instructions and/or other information from
such higher-level PLC devices encoded in PLC signals, for example,
to allow PLC engine 202 to select a particular frequency band in
which to operate.
[0048] FIG. 3 is a block diagram of PLC gateway 112 according to
some embodiments. As illustrated in this example, gateway engine
301 is coupled to meter interface 302, local communication
interface 304, and frequency band usage database 304. Meter
interface 302 is coupled to meter 106, and local communication
interface 304 is coupled to one or more of a variety of PLC devices
such as, for example, PLC device 113. Local communication interface
304 may provide a variety of communication protocols such as, for
example, ZIGBEE, BLUETOOTH, WI-FI, WI-MAX, ETHERNET, etc., which
may enable gateway 112 to communicate with a wide variety of
different devices and appliances. In operation, gateway engine 301
may be configured to collect communications from PLC device 113
and/or other devices, as well as meter 106, and serve as an
interface between these various devices and PLC data concentrator
114. Gateway engine 301 may also be configured to allocate
frequency bands to specific devices and/or to provide information
to such devices that enable them to self-assign their own operating
frequencies.
[0049] In some embodiments, PLC gateway 112 may be disposed within
or near premises 102n and serve as a gateway to all PLC
communications to and/or from premises 102n. In other embodiments,
however, PLC gateway 112 may be absent and PLC devices 113 (as well
as meter 106n and/or other appliances) may communicate directly
with PLC data concentrator 114. When PLC gateway 112 is present, it
may include database 304 with records of frequency bands currently
used, for example, by various PLC devices 113 within premises 102n.
An example of such a record may include, for instance, device
identification information (e.g., serial number, device ID, etc.),
application profile, device class, and/or currently allocated
frequency band. As such, gateway engine 301 may use database 304 in
assigning, allocating, or otherwise managing frequency bands
assigned to its various PLC devices.
[0050] FIG. 4 is a block diagram of PLC data concentrator or router
114 according to some embodiments. Gateway interface 401 is coupled
to data concentrator engine 402 and may be configured to
communicate with one or more PLC gateways 112a-n. Network interface
403 is also coupled to data concentrator engine 402 and may be
configured to communicate with network 120. In operation, data
concentrator engine 402 may be used to collect information and data
from multiple gateways 112a-n before forwarding the data to control
center 130. In cases where PLC gateways 112a-n are absent, gateway
interface 401 may be replaced with a meter and/or device interface
(now shown) configured to communicate directly with meters 116a-n,
PLC devices 113, and/or other appliances. Further, if PLC gateways
112a-n are absent, frequency usage database 404 may be configured
to store records similar to those described above with respect to
database 304.
[0051] FIG. 5 illustrates a transmit-receive pair comprising Node
501 and Node 502. Nodes 501 and 502 may be PLC nodes, for example,
that communicate using a G3-FCC band on a power line network 503.
For purposes of simplifying the following description, node 501 is
referred to the transmit node and node 502 is referred to a receive
node; however, it will be understood that both nodes 501 and 502
are transceivers that are capable of both transmit and receive
operations. Upon an initial connection between nodes 501 and 502,
transmit node 501 transmits data on all seventy-two tones within
the assigned band (e.g., the G3-FCC band). Receive node 502
receives the data and evaluates or estimates the channel
characteristics for each one on the communication medium. Receive
node 502 then sends channel information to transmit node 501 in the
form of Tone Map Response (TMR) table that indicates which
sub-bands are good or bad. Transmit node 501 may then use the data
in the TMR table to select which sub-bands to use for future
transmissions to receive node 502. The use of the TMR table data is
an optional recommendation for transmit node 501. So the transmit
node 501 may or may not use the sub-band and channel information
provided by the receive node 502 in the TMR table.
[0052] FIG. 6 illustrates seventy-two individual tones 601 that are
present in a G3-FCC band. These individual tones 601 may be grouped
together and combined into sub-bands. For example, if the
seventy-two individual tones 601 are taken in groups of three, then
the G3-FCC band may be divided into twenty-four sub-bands 602
(i.e., 72 tones/3=24 sub-bands). In the G3-FCC band, the
seventy-two tones that are used may actually correspond to tone
numbers 33-104 within the entire FCC band. In other frequency
bands, the sub-bands may comprise a different number of tones. For
example, for operations in a CENELEC band, the sub-bands may
comprise six tones each.
[0053] In the IEEE P1901.2 standard, a tone map response (TMR)
payload consisting of eighty bits enables a transmit-receive pair
(e.g., nodes 501/502) to exchange information that identifies which
tones 601 have good signal-to-noise ratio (SNR) and provides
preferred communication parameters for these tones.
[0054] Table 1 illustrates an example TMR payload. A brief
description of the fields is given as follows.
[0055] TXRES (1 bit) controls the gain resolution for one step. In
one embodiment, if the TXRES bit is set to 1, then the gain
resolution is 6 dB, and if the bit is set to 0, then the gain
resolution if 3 dB.
[0056] TXGAIN (4 bits) specifies the number gain steps that are
requested on all active sub-bands.
[0057] MOD (3 bits) specifies the modulation type. In one
embodiment, the three MOD bits are set to represent the following
modulation types: [0058] 000: ROBO [0059] 001: DBPSK/BPSK [0060]
010: DQPSK/QPSK [0061] 011: DBPSK/BPSK [0062] 100: 16 QAM [0063]
101 to 111: reserved
[0064] LQI (8 bits) is a Link Quality Indicator that characterizes
the quality of the channel estimates.
[0065] TMTXCOEFF (32 bits) specifies whether or not a sub-band
should be used for communication. Each sub-band (602) comprises
three tones (601). If a sub-band is not used, then the transmit
node 501 then may either transmit dummy bits in that sub-band
instead of data or it may not transmit anything at all. The
TMTXCOEFF field further specifies the transmit gain in a
sub-band.
TABLE-US-00001 TABLE 1 TONE MAP RESPONSE (TMR) PAYLOAD BIT FIELD
OCTET NUMBER BITS DEFINITION TXRES 0 7 1 Transmit gain resolution
corresponding to one gain step TXGAIN 6-3 4 Desired Transmitter
gain specifying how many gain steps are requested on all active
sub-bands MOD 2-0 3 Modulation type LQI 1 7-0 8 Link Quality
Indicator TMTXCOEF[1:0] 2 7-6 2 Specifies power control for
sub-band 1 TMTXCOEF[3:2] 5-4 2 Specifies power control for sub-band
2 TMTXCOEF[5:4] 3-2 2 Specifies power control for sub-band 3
TMTXCOEF[7:6] 3 1-0 2 Specifies power control for sub-band 4
TMTXCOEF[9:8] 7-6 2 Specifies power control for sub-band 5
TMTXCOEF[11:10] 5-4 2 Specifies power control for sub-band 6
TMTXCOEF[13:12] 3-2 2 Specifies power control for sub-band 7
TMTXCOEF[15:14] 1-0 2 Specifies power control for sub-band 8
TMTXCOEF[17:16] 4 7-6 2 Specifies power control for sub-band 9
TMTXCOEF[19:18] 5-4 2 Specifies power control for sub-band 10
TMTXCOEF[21:20] 3-2 2 Specifies power control for sub-band 11
TMTXCOEF[23:22] 1-0 2 Specifies power control for sub-band 12
TMTXCOEF[25:24] 5 7-6 2 Specifies power control for sub-band 13
TMTXCOEF[27:26] 5-4 2 Specifies power control for sub-band 14
TMTXCOEF[29:28] 3-2 2 Specifies power control for sub-band 15
TMTXCOEF[31:30] 1-0 2 Specifies power control for sub-band 16
TMTXCOEF[33:32] 6 7-6 2 Specifies power control for sub-band 17
TMTXCOEF[35:34] 5-4 2 Specifies power control for sub-band 18
TMTXCOEF[37:36] 3-2 2 Specifies power control for sub-band 19
TMTXCOEF[39:38] 1-0 2 Specifies power control for sub-band 20
TMTXCOEF[41:40] 7 7-6 2 Specifies power control for sub-band 21
TMTXCOEF[43:42] 5-4 2 Specifies power control for sub-band 22
TMTXCOEF[45:44] 3-2 2 Specifies power control for sub-band 23
TMTXCOEF[47:46] 1-0 2 Specifies power control for sub-band 24
ONOFFMODE 8 7 1 Specifies whether inactive sub-bands shall be
turned ON or OFF Coherent Mode 8 6 1 Coherent mode support
indication Capable (Reserved) 8 5-0 6 Reserved (Reserved) 9 8
Reserved
[0066] Sub-bands that are not used may either transmit dummy bits
or not transmit or may not transmit anything on them. This choice
is made using the ONOFFMODE bit where a 0 indicates no energy
transmitted and a 1 indicates dummy bits are transmitted.
Transmission of dummy bits in unused sub-bands is wasteful given a
fixed or target average output power (or rms voltage). It is better
to redistribute the power to the good sub-bands. This is analogous
to what is done in water-filling (an optimal power control
strategy) whereby more power is allocated to good sub-bands.
[0067] As mentioned above, not transmitting in a sub-band or
nulling an unused sub-band is better than wasting power by
transmitting dummy bits in that sub-band. FIG. 7 illustrates the
results of a simulation that compared the performance of dummy bit
transmission versus nulling for both thirty-six-tone and
eighteen-tone cases for a fixed time domain transmit power level.
Curve 701 represents the results for transmission on the full
seventy-two tone FCC sub-band (i.e., tones 33-104), and curves 702
and 703 represent the transmission of dummy bits on the center
thirty-six (i.e., tones 51-86) and center eighteen tones (i.e.,
tones 60-77), respectively, within the seventy-two-tone FCC band.
Curve 704 represents a transmission with nulling for the center
thirty-six tones within the seventy-two-tone FCC band. Curve 705
represents a transmission with nulling for the center eighteen
tones within the seventy-two-tone FCC band.
[0068] FIG. 8 is a pictorial representation of the transmissions
for curves 701 and 703. The seventy-two-tone FCC band represents
tones numbered 33-104 (801). Null tone method 802 transmits data in
the center eighteen tones 803 and nulls the remaining tones 804.
Dummy tone method 805 transmits data in the center eighteen tones
806 and dummy bits the remaining tones 807.
[0069] In FIG. 7, it can be seen that a 3-dB gain is observed when
going from seventy-two tones (701) to thirty-six tones (704) with
the nulling scheme as compared to the dummy bit transmission scheme
(702). An additional 3-dB is gained when going from thirty-six
tones (704) to eighteen tones (705). Note that even though this
example is for AWGN, it clearly illustrates that transmitting dummy
bits is less than optimal. For the case of frequency selective
channels, it has been shown that waterfilling or transmitting power
in good tones is the optimal capacity achieving energy
distribution. Waterfilling is also used in ADSL (another OFDM on
the line communication system).
[0070] Note that with TM and TXCOEFF combined, both G3-FCC and
FCC-low can be simultaneously supported in the TMR table. G3-FCC
has twenty-four sub-bands while FCC-low has seven sub-bands, where
each sub-band has three tones. Hence, if two bits are allocated per
sub-band, both G3-FCC and FCC-low can be easily represented in the
same TMR (i.e., (24 G3-FCC bands+7 FCC-low bands)'2 bits=62
bits).
[0071] FIG. 9 illustrates a frame 900 transmitted between nodes
according to one embodiment. Frame 900 comprises a preamble 901,
Frame Control Header (FCH) 902, and payload data 903. FCH 902 is
seventy-two bits long and contains information regarding the
current frame, such as the type of frame, the tone map index of the
frame, the length of the frame, etc. Although the tone map in FCH
902 tells the receiving node what sub-bands are being used, frame
900 does not tell the receiving node what the gain values, if any,
have been applied. The receiving node may not operate properly if
it does not know what boosting has been applied by the transmitting
node.
[0072] The receiver needs to know the gains applied on a sub-band
basis at the transmitter. This is especially important for 16 QAM
where the decision regions are dependent on the gain. In cases
where unitary constellations are used (e.g., BPSK, QPSK or 8PSK),
knowledge of sub-band gains can be used to get improved noise
variance estimates. Hence it is important for the FCH table to
contain sub-band gain information.
[0073] The FCH table has a total of seventy-two bits of which
thirty-two are allocated for tone map and sub-band power control.
Table 2 illustrates some of the possibilities for bit allocation in
order to choose the sub-bands and for power control.
TABLE-US-00002 TABLE 2 NUMBER OF TOTAL TONES PER NUMBER OF NUMBER
SUB-BAND BITS PER BITS OPTION (BANDWIDTH) SUB-BAND REQUIRED
COMMENTS 1 3-tones 1 24 .times. 1 = 24 Does not allow for (14 kHz)
sub-band power control. Only tells which sub-band is used 2 3-tones
2 24 .times. 2 = 48 Requires 16 extra bits (14 kHz) to be added to
FCH 3 6-tones 2 12 .times. 2 = 24 Fits into current FCH (28 kHz)
without addition of extra bits and provides power control 4 9-tones
4 8 .times. 4 = 32 Sub-band size is large (42 kHz) and the fine bit
resolution is excessive for power control.
[0074] As observed, Option 3 allows for the best trade-off between
(a) the number of power control levels, (b) sub-band size, and (c)
number of bits required in the FCH. A further advantage is that
eight extra bits are saved which allows them to be used for other
purposes. The two TMTXCOEF bits indicate one of two types of
information: [0075] a) either dummy data or no data is being
transmitted. (The ONOFFMODE bit described below may be used to
decide between the two options). [0076] b) when data is
transmitted, the bits indicate what gain has been used in that
sub-band.
[0077] In one embodiment, four possible options are enumerated by
two TMTXCOEF bits are used to specify the power control for each
sub-band.
[0078] In a first example configuration, the TMTXCOEF power control
bits may be set as follows: [0079] 00: either dummy data or no data
is transmitted on this subband, [0080] 01: data transmitted on this
sub-band is scaled by a value -X dB, [0081] 10: data transmitted on
this sub-band is scaled by a value X dB, [0082] 11: data
transmitted on this sub-band and is not scaled.
[0083] In a second example configuration, the TMTXCOEF power
control bits may be set as follows: [0084] 00: either dummy data or
no data is transmitted on this subband, [0085] 01: data transmitted
on this sub-band is scaled by a value X dB, [0086] 10: data
transmitted on this sub-band is scaled by a value 2X dB, [0087] 11:
data transmitted on this sub-band and is not scaled.
[0088] The TMTXCOEFF bits are used in connection with the TXRES
bit, which specifies a gain resolution (i.e., x=gain specified by
TXRES).
[0089] ONOFFMODE Bit
[0090] If the TMTXCOEF bits are set to 00 for a given sub-band,
this implies that either dummy data or no data is transmitted in
that sub-band (i.e., no data on that sub-band). The ONOFFMODE bit
can be used to indicate the state of the unused sub-band. [0091] 0:
indicates that all in-active sub-bands should be turned OFF (i.e.,
no energy is transmitted on them) [0092] 1: indicates that all
in-active sub-bands should be turned ON and have dummy bits
transmitted on them.
[0093] TXRES Bit
[0094] The TXRES bit specifies the power scaling factor (X) for
TMTXCOEF options 01 and 10. In one embodiment, if the TXRES bit is
set to 1, then the gain resolution is 6 dB, and if the bit is set
to 0, then the gain resolution if 3 dB.
[0095] In the first example configuration above, if TXRES is 0,
then X=3 dB, and [0096] for TMTXCOEF (01) the scaling is 3 dB,
[0097] for TMTXCOEF (10) the scaling is -3 dB; and
[0098] if TXRES is 1, then X=6 dB, and [0099] for TMTXCOEF (01) the
scaling is 6 dB, [0100] for TMTXCOEF (10) the scaling is -6 dB.
[0101] In the second example configuration above, if TXRES is 0,
then X=3 dB, and [0102] for TMTXCOEF (01) the scaling is 3 dB,
[0103] for TMTXCOEF (10) the scaling is 6 dB (i.e., 2X); and
[0104] if TXRES is 1, then X=6 dB, and [0105] for TMTXCOEF (01) the
scaling is 6 dB, [0106] for TMTXCOEF (10) the scaling is 12 dB.
[0107] Table 3 is a proposed FCH table.
TABLE-US-00003 TABLE 3 BIT FIELD OCTET NUMBER BITS DEFINITION PDC 0
7 to 0 8 Phase detection counter MOD 1 7 to 5 3 Modulation type
Coherent Mode 4 1 Differential/Coherent Mode DT 3 to 1 3 Delimiter
type: FL 0 9 PHY frame length in 2 7 to 0 PHY symbols TMTXCOEF[1:0]
3 7-6 2 Specifies power control for sub-band 1. TMTXCOEF[3:2] 3 5-4
2 Specifies power control for sub-band 2 TMTXCOEF[5:4] 3 3-2 2
Specifies power control for sub-band 3 TMTXCOEF[7:6] 3 1-0 2
Specifies power control for sub-band 4 TMTXCOEF[1:0] 4 7-6 2
Specifies power control for sub-band 5 TMTXCOEF[3:2] 4 5-4 2
Specifies power control for sub-band 6 TMTXCOEF[5:4] 4 3-2 2
Specifies power control for sub-band 7 TMTXCOEF[7:6] 4 1-0 2
Specifies power control for sub-band 8 TMTXCOEF[1:0] 5 7-6 2
Specifies power control for sub-band 9 TMTXCOEF[3:2] 5 5-4 2
Specifies power control for sub-band 10 TMTXCOEF[5:4] 5 3-2 2
Specifies power control for sub-band 11 TMTXCOEF[7:6] 5 1-0 2
Specifies power control for sub-band 12 DTM 6 7 1 Data Tone Mask CP
Mode 6 6 1 CP Mode TXRES 6 5 1 Gain value ONOFFMODE 6 4 1 Specifies
whether inactive sub-bands shall be turned ON or OFF. Reserved 6 3
to 0 7 reserved 7 7 to 6 ConvZeros 5 to 0 6 Zeros for convolutional
encoder FCCS 8 7 to 0 8 Frame control check sequence (CRC8 or
CRC5)
[0108] The MOD field identifies the type of modulation used. In one
embodiment, the three bits in the MOD field are configured as
follows to identify the modulation type. [0109] 000: ROBO [0110]
001: DBPSK/BPSK [0111] 010: DQPSK/QPSK [0112] 011: DBPSK/BPSK
[0113] 100: 16 QAM [0114] 101: Super ROBO [0115] 110-111:
Reserved
[0116] The Coherent Mode bit identifies whether the modulation is
coherent or differential using the following coding: [0117] 0:
Differential Mode [0118] 1: Coherent Mode
[0119] The bits in the Delimiter Type (DT) field are set as
follows: [0120] 000: Start of frame with no response expected
[0121] 001: Start of frame with response expected [0122] 010:
Positive acknowledgment (ACK) [0123] 011: Negative acknowledgment
(NACK) [0124] 100: Busy negative acknowledgment (BUSY_REJECT)
[0125] 101: Busy accept acknowledgement (BUSY_ACCEPT) [0126] 110:
NO_EARLIER_SEGMENTS [0127] 111: Reserved
[0128] The TMTXCOEF fields in FCH Table 3 correspond to six
contiguous tones, instead of representing three tones as used in
the TMR (Table 1). Given the seventy-two tones in the G3-FCC band,
the band can be divided into twelve sub-bands if each sub-band has
six tones (i.e., 72 tones/6 tones/sub-band=12 sub-bands). Two bits
can be used to represent each sub-band in this configuration and
still maintain a twenty-four bit space in the FCH table (12
sub-bands.times.2 bits/sub-band=24 bits).
[0129] The bit in the Data Tone Mask (DTM) field is set as follows:
[0130] 0: This is the default value for the non multi-tone mask
mode. For multi-tone mask mode, this value indicates that the data
tone mask is same as preamble/header [0131] 1: Data Tone Mask for
either the FCC above CENELEC or FCC above CENELEC plus the CENELEC
band.
[0132] As indicated above, the bit in the TXRES field is set as
follows: [0133] 0: +/-6 dB gain for TMTXCOEF values 01/10, [0134]
1: +/-3 dB gain for TMTXCOEF values 01/10.
[0135] The ONOFFMODE field specifies whether inactive sub-bands
shall be turned ON or OFF. When a receiving node communicates in
the TMR table that a transmit node should not use certain
sub-bands, the transmit node may insert dummy bits on the tones for
the unused sub-bands. However, the transmission of such dummy bits
wastes energy that is better used for tones carrying actual data
bits. The ONOFFMODE field allows the transmit node to notify the
receiving node if dummy bits have been used or if nothing was
transmitted in unused sub-bands.
[0136] The ONOFFMODE bit is set as follows: [0137] 0: indicates
that all inactive sub-bands shall be turned OFF (no energy is
transmitted on them) [0138] 1: indicates that all inactive
sub-bands shall be turned ON and have dummy bits transmitted on
them.
[0139] Note that an inactive sub-band is a sub-band where no
payload data is transmitted (i.e., its TMTXCOEF value=00).
[0140] The FCH table format proposed in Table 3 allows the
transmitting node to provide transmit power information per
sub-band to the receiving node, where each sub-band in the FCH
table represents six tones. However, the TMR table that is sent by
the receiving node users sub-bands having three tones. As a result,
two TMR sub-bands correspond to one FCH table sub-bands.
[0141] FIG. 10 illustrates how groups of six tones 1001 in the
G3-FCC band, for example, are combined into FCH table sub-bands
1002.
[0142] FIG. 11 illustrates how the same six tones are treated
differently in the TMR table and the FCH table. On the receive node
side, tones 1-3 correspond to TMR sub-band 1, and tones 4-6
correspond to TMR sub-band 2. Two sets of TMR TMTXCOEF bits
(b.sub.1b.sub.2) 1102, 1103 are used to specify the power control
for each of these TMR sub-bands. On the transmit node side, tones
1-6 correspond to a single FCH sub-band 1. Once set of FCH TMTXCOEF
bits (b.sub.1b.sub.2) 1104 is used to specify the power control for
all six tones in this FCH sub-band.
[0143] It is apparent from FIG. 11 that a conflict may result if,
for example, the receiving node sends a TMR table that specifies
boosting TMR sub-band 1 in bits 1102 and specifies decreasing TMR
sub-band 2 in bits 1103. The FCH table used by the transmit node is
unable to indicate such a split within the six-tone FCH sub-band.
Accordingly, FCH bits 1104 must specify the power control for all
six tones in the FCH sub-band.
TABLE-US-00004 TABLE 4 TMR TABLE FCH TABLE TMTXCOEF VALUES TMTXCOEF
VALUE if either TMR sub-band is specified as do not use any of
tones in the do not use corresponding FCH sub-band if either or
both TMR sub-bands increase the power on all tones in the specify
increasing power corresponding FCH sub-band if one TMR sub-band
specifies all of the tones in the corresponding decreasing power,
and the other TMR FCH sub-band are kept the same (i.e., sub-band
specifies keeping the power no power scaling) the same (i.e., no
power scaling) if both TMR sub-bands specify decrease the power on
the decreasing power corresponding FCH sub-band
[0144] As shown in Table 4, the emphasis is toward increasing power
where indicated in the TMR table from the receiving node.
[0145] It is important for the transmitting node to notify the
receiving node when it is boosting power on a sub-band. Knowing
when power scaling occurs on a sub-band is relevant to decoding of
non-unitary modulation, such as 16 QAM. However, boosting is not as
critical for differential or unitary modulation. Knowledge of
sub-band transmit power scaling is helpful to improve noise
variance estimation.
[0146] Table 5 is an FCH table that may be used with differential
modulation. The bit definitions correspond to the similarly named
fields described above.
TABLE-US-00005 TABLE 5 BIT FIELD OCTET NUMBER BITS DEFINITION PDC 0
7 to 0 8 Phase detection counter MOD 1 7 to 5 3 Modulation type:
Coherent Mode 4 1 Differential/Coherent Mode DT 3 to 1 3 Delimiter
type FL 0 9 PHY frame length in PHY 2 7 to 0 symbols TM[7:0] 3 7 to
0 8 TM[7:0]: Tone Map TM[15:8] 4 7 to 0 8 TM[15:8]: Tone Map
TM[23:16] 5 7 to 0 8 TM[23:16]: Tone Map DTM 6 7 1 Data Tone Mask
CP Mode 6 6 1 CP Mode Reserved 6 5 to 0 8 reserved 7 7 to 6
ConvZeros 5 to 0 6 Zeros for convolutional encoder FCCS 8 7 to 0 8
Frame control check sequence (CRC8 or CRC5)
[0147] In some embodiments, a pair of transmit-receive nodes may
select which FCH table to use based upon the type of modulation
used. One type of FCH table is a default table that uses one bit to
represent a three-tone sub-band, such as Table 5. The other type of
FCH table uses two bits to represent a six-tone sub-band, such as
Table 3.
[0148] In a first option, the nodes will use a default FCH table
(Table 5) when differential modulation is being used. However, when
coherent modulation is being used, then the nodes will use the
modified FCH table (Table 3 or a similar table) that uses two bits
to represent a six-tone sub-band.
[0149] In a second option, the nodes will use a default FCH table
(Table 5) when differential modulation or unitary coherent
modulation is being used. However, when coherent 16 QAM modulation
is used, then the nodes will use the modified FCH table (Table 3 or
a similar table) that uses two bits to represent a six-tone
sub-band.
[0150] In a third option, the nodes will use the modified FCH table
(Table 3 or a similar table) for all modulation types. In this
option, the nodes always use two bits to represent a six-tone
sub-band in the FCH table.
[0151] In a fourth option, the nodes will always use the default
FCH table (Table 5) and scaling will be performed when 16 QAM
modulation is used.
[0152] In a fifth option, the nodes will always use the default FCH
table (Table 5) and no scaling will allowed for any modulation
types.
[0153] Sub-Band Transmit Power Estimation Using Preamble
[0154] FIG. 12 illustrates the relative transmit power levels in
different sub-bands 12-01 to 12-24 for an OFDM signal at the
transmitter side. This scaling may be performed in response to
channel information in a TMR table, for example; however, the
transmitting node does not have to follow the power specifications
in the TMR table.
[0155] The transmit power level in each sub-band needs to be
accounted for at the receiver. If the transmitting node does not
specify how it has scaled the sub-bands, then the receiver must
estimate the transmit power scaling factor in each sub-band--i.e.,
the receiver must estimate if the sub-band power has been scaled
and, if so, by how much.
[0156] Coherent modulation offers one way to obtain better
performance in a PLC network. FIG. 13 illustrates a frame structure
1300 in which two syncP symbols 1301, 1302 are placed after FCH
1303 and before the data payload 1304. The syncP symbols 1301, 1302
may be used to assist with channel estimation in coherent
modulation. It will be understood that the inverse syncP symbol
(-syncP) 1301 may also be referred to as a syncM symbol. In other
contexts, -syncP (syncM) may be identified as "s1", and syncP may
be identified as "s2".
[0157] The preamble 1305 typically comprises a series of syncP and
syncM symbols. In one embodiment, preamble 1305 comprises eight
syncP symbols followed by one and half syncM symbols. The preamble
1305 and FCH 1303 are not scaled by the transmit node. Only the
data bits 1304 are scaled in current embodiments. However, if the
-syncP and syncP symbols 1301, 1302 are also scaled, then the
sub-band transmit power levels can be estimated by comparing the
scaled -syncP and syncP symbols 1301, 1302 to each other or to the
-syncP and syncP symbols in the preamble 1305. FIGS. 14-17
illustrate different combinations of -syncP and syncP scaling that
can be used to estimate sub-band power levels.
[0158] In FIG. 14, the -syncP symbol 1301 has been scaled by the
transmit node, but the syncP symbol 1302 is not scaled. In FIG. 15,
the opposite scaling is used so that the -syncP 1301 is not scaled,
but the syncP symbol 1302 is scaled by the transmit node. In the
examples of FIGS. 14 and 15, the transmit power scaling factor in
each sub-band may be obtained at the receiver by comparing the
channel estimates in each sub-band from the two syncP symbols 1301,
1302 to each other.
[0159] In FIG. 16, both syncP symbols 1301, 1302 are scaled. For
example, both syncP symbols 1301, 1302 may have the same sub-band
transmit power scaling as the data 1304. The preamble 1305 is not
scaled, so the channel estimates from syncP symbols 1301, 1302 may
be combined and compared with channel estimates from the preamble
1305 to determine scaling in each sub-band.
[0160] In FIG. 17, neither syncP symbol 1301, 1302 is scaled;
however, the preamble 1305 is scaled. For example, preamble 1305
may have the same sub-band transmit power scaling as the data 1304.
Again, the channel estimates from syncP symbols 1301, 1302 may be
combined and compared with channel estimates from the scaled
preamble 1305 to determine scaling in each sub-band.
[0161] The sub-band power scaling estimates determined from the
formats illustrated in FIGS. 14-17 can be used to by the receiver
when demodulating the data 1304.
[0162] FIG. 18 is a block diagram of a circuit for implementing PLC
communications and channel estimation according to some
embodiments. In some cases, one or more of the devices and/or
apparatuses shown in FIGS. 1-4 may be implemented as shown in FIG.
18. In some embodiments, processor 1802 may be a digital signal
processor (DSP), an application specific integrated circuit (ASIC),
a system-on-chip (SoC) circuit, a field-programmable gate array
(FPGA), a microprocessor, a microcontroller, or the like. Processor
1802 is coupled to one or more peripherals 1804 and external memory
1803. In some cases, external memory 1803 may be used to store
and/or maintain databases 304 and/or 404 shown in FIGS. 3 and 4.
Further, processor 1802 may include a driver for communicating
signals to external memory 1803 and another driver for
communicating signals to peripherals 1804. Power supply 1801
provides supply voltages to processor 02 as well as one or more
supply voltages to memory 1803 and/or peripherals 1804. In some
embodiments, more than one instance of processor 1802 may be
included (and more than one external memory 1803 may be included as
well).
[0163] Peripherals 1804 may include any desired circuitry,
depending on the type of PLC system. For example, in an embodiment,
peripherals 1804 may implement local communication interface 303
and include devices for various types of wireless communication,
such as WI-FI, ZIGBEE, BLUETOOTH, cellular, global positioning
system, etc. Peripherals 1804 may also include additional storage,
including RAM storage, solid-state storage, or disk storage. In
some cases, peripherals 1804 may include user interface devices
such as a display screen, including touch display screens or
multi-touch display screens, keyboard or other input devices,
microphones, speakers, etc.
[0164] External memory 1803 may include any type of memory. For
example, external memory 1803 may include SRAM, nonvolatile RAM
(NVRAM, such as "flash" memory), and/or dynamic RAM (DRAM) such as
synchronous DRAM (SDRAM), double data rate (DDR, DDR2, DDR3, etc.)
SDRAM, DRAM, etc. External memory 1803 may include one or more
memory modules to which the memory devices are mounted, such as
single inline memory modules (SIMMs), dual inline memory modules
(DIMMs), etc.
[0165] It will be understood that in various embodiments, the
modules shown in FIGS. 2-4 may represent sets of software routines,
logic functions, and/or data structures that are configured to
perform specified operations. Although these modules are shown as
distinct logical blocks, in other embodiments at least some of the
operations performed by these modules may be combined in to fewer
blocks. Conversely, any given one of the modules shown in FIGS. 2-4
may be implemented such that its operations are divided among two
or more logical blocks. Moreover, although shown with a particular
configuration, in other embodiments these various modules may be
rearranged in other suitable ways.
[0166] Many of the operations described herein may be implemented
in hardware, software, and/or firmware, and/or any combination
thereof. When implemented in software, code segments perform the
necessary tasks or operations. The program or code segments may be
stored in a processor-readable, computer-readable, or
machine-readable medium. The processor-readable, computer-readable,
or machine-readable medium may include any device or medium that
can store or transfer information. Examples of such a
processor-readable medium include an electronic circuit, a
semiconductor memory device, a flash memory, a ROM, an erasable ROM
(EROM), a floppy diskette, a compact disk, an optical disk, a hard
disk, a fiber optic medium, etc.
[0167] Software code segments may be stored in any volatile or
non-volatile storage device, such as a hard drive, flash memory,
solid state memory, optical disk, CD, DVD, computer program
product, or other memory device, that provides tangible
computer-readable or machine-readable storage for a processor or a
middleware container service. In other embodiments, the memory may
be a virtualization of several physical storage devices, wherein
the physical storage devices are of the same or different kinds The
code segments may be downloaded or transferred from storage to a
processor or container via an internal bus, another computer
network, such as the Internet or an intranet, or via other wired or
wireless networks.
[0168] Many modifications and other embodiments of the invention(s)
will come to mind to one skilled in the art to which the
invention(s) pertain having the benefit of the teachings presented
in the foregoing descriptions, and the associated drawings.
Therefore, it is to be understood that the invention(s) are not to
be limited to the specific embodiments disclosed. Although specific
terms are employed herein, they are used in a generic and
descriptive sense only and not for purposes of limitation.
* * * * *