U.S. patent application number 11/651945 was filed with the patent office on 2008-01-03 for method and system for maximizing data throughput rate in a power line communications system by modifying payload symbol length.
This patent application is currently assigned to ARKADOS, Inc.. Invention is credited to Brion Ebert, David Lawrence, Oleg Logvinov, Dirk Walvis.
Application Number | 20080002655 11/651945 |
Document ID | / |
Family ID | 31888353 |
Filed Date | 2008-01-03 |
United States Patent
Application |
20080002655 |
Kind Code |
A1 |
Logvinov; Oleg ; et
al. |
January 3, 2008 |
Method and system for maximizing data throughput rate in a power
line communications system by modifying payload symbol length
Abstract
Data throughput rate in a power line communications ("PLC")
system is controlled by generating PLC carrier signals in
accordance with a PLC signal frame structure containing payload
symbols where the payload symbol length is selected based on at
least one of a PLC system channel quality and node configuration
data. The selected payload symbol length determines the processing
operations that a source PLC transceiver performs for generating
PLC signals or that a destination PLC transceiver performs for
extracting information content from received PLC signals. The
payload symbol lengths can be selected to maximize the data
throughput rate while maintaining compatibility with prior art PLC
system protocols and standards that require a PLC signal frame
structure and its payload portion to have fixed, predetermined
lengths.
Inventors: |
Logvinov; Oleg; (East
Brunswick, NJ) ; Walvis; Dirk; (Santa Cruz, CA)
; Ebert; Brion; (Easton, PA) ; Lawrence;
David; (Newton, NJ) |
Correspondence
Address: |
MINTZ LEVIN COHN FERRIS GLOVSKY & POPEO
666 THIRD AVENUE
NEW YORK
NY
10017
US
|
Assignee: |
ARKADOS, Inc.
Piscataway
NJ
|
Family ID: |
31888353 |
Appl. No.: |
11/651945 |
Filed: |
January 10, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10643316 |
Aug 19, 2003 |
7193506 |
|
|
11651945 |
Jan 10, 2007 |
|
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60404360 |
Aug 19, 2002 |
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Current U.S.
Class: |
370/340 |
Current CPC
Class: |
H04B 3/542 20130101;
H04B 2203/5416 20130101; H04L 1/0017 20130101; H04L 27/2608
20130101; H04B 3/54 20130101; H04L 1/0007 20130101; H04B 2203/5408
20130101 |
Class at
Publication: |
370/340 |
International
Class: |
H04Q 7/28 20060101
H04Q007/28 |
Claims
1. A method for transferring data on power line communications
("PLC") signals over a PLC system, wherein the PLC system operates
in accordance with a PLC signal frame structure including a payload
portion and wherein the payload portion has a predetermined, fixed
length and includes at least one payload symbol, the method
comprising: obtaining channel quality data for a PLC system signal
path extending between a source PLC transceiver and a destination
PLC transceiver; computing, based on at least one of the channel
quality data and node configuration data, a payload symbol length;
generating a payload portion including at least one payload symbol
of the computed length, wherein the length or sum of the lengths of
the at least one payload symbol contained in the generated payload
portion equals the predetermined length of the payload portion; and
modifying processing operations at the source PLC transceiver for
generating PLC carriers in accordance with the PLC signal frame
structure including the at least one payload symbol having the
computed payload length.
2. The method of claim 1 further comprising: modifying processing
operations at the destination PLC transceiver for extracting data
from the PLC signal frame structure based on the computed length
payload symbol.
3. The method of claim 1, wherein the source PLC transceiver
operates in a default mode for generating PLC carriers based on a
PLC signal frame structure including payload symbols having a first
length, wherein the computed payload symbol length exceeds the
first length, thereby increasing PLC data throughput rate and
efficiency of utilization of the PLC system as a channel for
transferring communications data.
4. The method of claim 1, wherein the destination PLC transceiver
operates in a default mode for extracting information content from
a received PLC signal generated based on a PLC frame structure
including payload symbols having a first length, wherein the
computed payload symbol length exceeds the first length.
5. The method of claim 1 further comprising: transmitting from the
PLC source transceiver, over the PLC system and for receipt at the
destination PLC transceiver, PLC carriers generated in accordance
with the frame structure; determining at the destination PLC
transceiver, from the PLC carriers transmitted from the source PLC
transceiver, whether the payload symbols used to generate the
received PLC carriers have a length other than a default mode
payload symbol length; and at the destination PLC transceiver,
extracting information content data from the received PLC carriers
based on the payload length determination.
6. The method of claim 3 further comprising: generating a
predetermined number of distinct PLC carriers based on the computed
payload symbol length, wherein the predetermined number of PLC
carriers exceeds an available number of distinct PLC carriers
generated during operation of the source PLC transceiver in the
default mode.
7. The method of claim 6, wherein the predetermined number of
distinct PLC carriers have a narrower bandwidth than the bandwidth
of the PLC carriers generated during operation of the source PLC
transceiver in the default mode.
8. The method of claim 6, wherein the predetermined number of
distinct frequency PLC carriers are distributed across a PLC
frequency spectrum broader than a PLC frequency spectrum required
by the default mode.
9. The method of claim 3 further comprising: increasing a sampling
rate of a clock included in the source PLC transceiver to a rate
exceeding a sampling rate associated with the default mode.
10. The method of claim 8, wherein the predetermined number of
distinct PLC carriers has a narrower bandwidth than the bandwidth
of the PLC carriers generated during operation of the source PLC
transceiver in the default mode.
11. The method of claim 9, wherein the predetermined number of
distinct PLC carriers has a narrower bandwidth than the bandwidth
of the PLC carriers generated during operation of the source PLC
transceiver in the default mode.
12. The method of claim 1, wherein the source PLC transceiver
operates in a default mode for generating PLC carriers based on a
PLC signal frame structure including payload symbols having a first
length, wherein the computed payload symbol length is less than the
first length.
13. The method of claim 1, wherein the PLC system includes power
and communications data distribution components operating in
accordance with at least one operating mode.
14. The method of claim 1, wherein the at least one operating mode
includes PLC system operation in accordance with processing
capabilities at a range of processing speeds.
15. The method of claim 1, wherein the PLC carriers have
frequencies within a PLC frequency spectrum extending between about
2 MHz and about 30 MHz.
16. A power line communications ("PLC") transceiver for
transferring, over a PLC system, PLC signals generated in
accordance with a PLC signal frame structure including a payload
portion, wherein the payload portion has a predetermined, fixed
length and includes at least one payload symbol, the PLC
transceiver comprising: a channel estimator for obtaining channel
quality data for a PLC system signal path extending to a
destination PLC transceiver; a symbol length controller coupled to
the channel estimator and for computing, based on at least one of
the channel quality data and node configuration data stored in the
symbol length controller, a payload symbol length, wherein the
computed payload symbol length is used for generating a payload
portion including at least one payload symbol of the computed
length, wherein the length or sum of the lengths of the at least
one payload symbol contained in the generated payload portion
equals the predetermined length of the payload portion; and a PLC
carrier generator coupled to the symbol length controller for
generating PLC carriers containing information content, wherein the
symbol length controller supplies the PLC signal generator with
control signals for modifying processing operations in accordance
with a PLC signal frame including the at least one payload symbol
having the computed symbol length.
17. The PLC transceiver of claim 16, wherein the PLC carrier
generator normally operates in a default mode, wherein in the
default mode a payload symbol has a predetermined length.
18. The PLC transceiver of claim 17, wherein the computed payload
symbol length exceeds or is less than the predetermined payload
symbol length for the default mode.
19. The PLC transceiver of claim 16, wherein the PLC carrier
generator further comprises a reprogrammable forward error
correction ("FEC") encoder and a reprogrammable FEC decoder capable
of being programmed to perform PLC processing on data blocks
containing information content data in accordance with a selected
payload symbol length, wherein the data blocks are selected from at
least one of a predetermined number of sizes.
20. The PLC transceiver of claim 16, wherein the PLC carrier
generator further comprises a reprogrammable interleaver module and
a reprogrammable deinterleaver module which are coupled
respectively to the FEC encoder and FED decoder, wherein each of
the interleaver and deinterleaver modules is capable of being
programmed to perform PLC signal processing on data blocks
containing information content data in accordance with a selected
payload symbol length.
21. The PLC transceiver of claim 16 further comprising: a computer
processing unit ("CPU") coupled to the symbol length controller and
the PLC carrier generator, wherein the CPU controls Phy layer
software operations and performs channel quality assessment
operations.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/404,360 filed Aug. 19, 2002, which is
incorporated by reference herein.
FIELD OF THE INVENTION
[0002] This invention relates to the field of communications over
conventional electric power conveying media, and more particularly,
to improving data throughput rate in a power line communications
("PLC") system by modifying the length of payload symbols included
in a PLC signal frame structure in view of PLC system channel
quality information.
BACKGROUND OF THE INVENTION
[0003] In a PLC system, information is conveyed over conventional
power line media on PLC data carrier signals. The PLC system
includes PLC transceivers that operate in accordance with
predetermined PLC protocols and standards. The protocols and
standards are formulated in view of the processing capabilities of
the PLC transceiver equipment and the expected PLC signal
transmission characteristics of the PLC system. The protocols and
standards, for example, define the spectrum of frequencies used for
PLC signal transmissions and how information content and associated
control data are carried on PLC signals. The arrangement of
information content and overhead data within a PLC signal is
typically referred to as a frame structure. The frame structure
establishes the sequence that PLC signals containing overhead and
information content data are generated for transmission over the
PLC system.
[0004] When many of the prior art PLC systems, such as orthogonal
frequency division multiplexing ("OFDM") PLC systems, were
designed, the lack or limited availability of high speed processing
technology dictated the characteristics of the PLC signal frame
structure. The current and widely used PLC signal frame structure,
which is substantially the same as the frame structure adopted in
early prior art PLC systems, includes a payload portion interposed
between start and end delimiters. See Gardner, S. et al., "HomePlug
Standard Bring Networking to the Home",
http://www.commsdesign.com/main/2001/12/0012feat5.htm, Dec. 12,
2000, incorporated by reference herein. The start and end
delimiters include communications overhead data, such as a
preamble, destination address, source address, network protocol
type and frame check (error correction), which a destination PLC
transceiver requires for extracting information content and other
control data from the PLC signals transmitted by a source PLC
transceiver. The payload portion contains a plurality of payload
symbols. Each of the payload symbols represents one or more
information content data modulated PLC carriers which are to be
generated at and transmitted from the PLC transceiver.
[0005] Based on the prior art PLC system design, each of the
payload symbols has a fixed, predetermined length determined by the
fixed, predetermined length of the payload portion and a portion of
the fixed length of each of the payload symbols is allocated to a
cyclic prefix. See Gardner. The cyclic prefix is essentially a
replication of the last few microseconds of the payload symbol. As
well known in the art, the cyclic prefix length is included in the
payload symbol to avoid the adverse effects of intersymbol
interference, which may occur because network segments in the PLC
system can cause different PLC carriers to experience different
respective transmission delays. If the cyclic prefix is not
included in a payload symbol, some of the data samples obtained
when converting the received time domain PLC carrier waveforms
generated for a subject payload symbol to frequency domain data
could represent energy associated with PLC carriers generated for a
payload symbol that precedes or follows the subject payload symbol
in a frame structure. Thus, in PLC system design, the length of the
cyclic prefix in a payload symbol usually is set equal to the
expected worst case delay variation across the PLC frequency
spectrum for the PLC system. This cyclic prefix length ensures that
conversion of the PLC carrier waveform into frequency domain data
begins at the portion of the PLC carrier waveform following the end
of the cyclic prefix, thereby providing that the frequency domain
data obtained based on the received PLC carrier waveforms generated
for the subject payload symbol is not degraded by any of the PLC
carriers generated for the payload symbols preceding or following
the subject payload symbol.
[0006] It is further noted that the prior art fixed length payload
symbol requirement provides that, for each payload symbol, time
domain PLC signals having only predetermined carrier frequencies
can be generated. The predetermined carrier frequencies for the PLC
signals are within a predetermined PLC frequency spectrum and, in
addition, only selected modulation methods can be applied for
modulating data onto the PLC carrier signals. See, for example,
U.S. Pat. No. 6,523,256, incorporated by reference, for a
description of modulation methods that can be used in connection
with PLC carriers generated for payload symbols. Also according to
the prior art PLC system design, a single modulation method must be
used in connection with each of the PLC carriers generated for a
payload symbol. As is well known in the art, the modulation method,
which establishes predetermined orders of modulation that can be
used to modulate PLC carriers, determines the amount of data that a
PLC carrier can carry.
[0007] Although the prior art PLC signal frame structure design
limits the maximum available data throughput rate in a PLC system,
this result was tolerated or required in view of the limitations of
the data and signal processing technologies available in the prior
art and to ensure reliable and accurate transfer of information
content using PLC signals.
[0008] Since the development of the prior art PLC frame structure
design, which continues to be used in a vast majority of current
PLC systems, advanced, higher speed signal and data processing
technologies have become available and cost effective for use in
PLC transceiver equipment. PLC systems and PLC equipment, however,
continue to utilize the prior art PLC signal frame structure
design, which in many circumstances unnecessarily limits the
maximum available data throughput rate for the PLC system.
[0009] Therefore, a need exists for a system and method for
maximizing data throughput rate in a PLC system in view of
available higher speed data processing technologies and while also
permitting that existing PLC transceiver equipment can continue to
be used without difficult or costly modifications.
SUMMARY OF THE INVENTION
[0010] In accordance with the present invention, the data
throughput rate associated with PLC signal transmission in a PLC
system is maximized by selectively controlling the length of
payload symbols included in a PLC signal frame structure from which
PLC data signal carriers are generated. The selected payload symbol
length is computed based on PLC system signal transmission
performance channel quality data obtained in real time, based on
non-real time processing configuration data ("node configuration
data") obtained from PLC signals transmitted over the PLC system
to, or pre-programmed at, PLC transceiver equipment or based on a
combination of the channel quality data and the node configuration
data.
[0011] In a preferred embodiment of the present invention, payload
symbol length is modified while providing that PLC signal
processing otherwise follows prior art PLC frame structure
("legacy") design requirements, i.e., each of the frame structure
and the payload portion of the frame structure has a fixed,
predetermined length that cannot be changed. When the PLC signal
transmission characteristics ("channel quality") for the PLC system
is at a sufficiently high level, a length is selected for a payload
symbol that exceeds the fixed payload symbol length of the legacy
design. By increasing the length of the payload symbols in the
payload portion, while maintaining the payload portion at the fixed
legacy length, the sum of the lengths of cyclic prefixes, which are
included within the respective payload symbols and occupy portions
of the symbol lengths, in the frame structure is reduced. Each of
the increased length payload symbols provides that a PLC
transceiver generates and transmits a greater number of PLC carrier
signals containing information content, during the time interval of
the frame structure corresponding to the increased length symbol,
than that which would be generated and transmitted based on a
legacy payload symbol having a shorter length. In other words, the
increased length payload symbols in the payload portion provide
that more data can be transmitted in a PLC signal transmission than
that transmitted for a legacy PLC signal transmission for the time
interval corresponding to the length of the PLC signal frame
structure, thereby increasing the data throughput rate for the PLC
system.
[0012] In a preferred embodiment of the present invention, a PLC
transceiver within a PLC system generates a PLC signal frame
structure including payload symbols each having a same selected
length, where the payload symbol length is selected for maximizing
the data throughput rate in the PLC system in view of PLC system
channel quality data and the node configuration data. The PLC
transceiver itself computes channel quality, or receives node
configuration data on PLC signals transmitted from another PLC
transceiver source. The PLC transceiver processes the channel
quality or the node configuration data, or both of the channel
quality and node configuration data, to determine the longest
possible payload symbol length likely to ensure accurate
reproduction of information content at a destination PLC
transceiver based on transmission of a PLC signal, which is
generated based on the selected payload symbol length, over the PLC
system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Other objects and advantages of the present invention will
be apparent from the following detailed description of the
presently preferred embodiments, which description should be
considered in conjunction with the accompanying drawings in
which:
[0014] FIG. 1 is an exemplary power line distribution system for
high speed data communications.
[0015] FIG. 2 is a block diagram of a preferred OFDM PLC
transceiver in accordance with the present invention.
[0016] FIG. 3 is an illustration of an exemplary prior art PLC
signal frame structure.
[0017] FIG. 4 is a high level flow diagram of a process for
maximizing data throughput rate by selecting a payload symbol
length in accordance with the present invention.
[0018] FIG. 5 is an illustration of an arrangement of payload
symbols in a payload portion of an exemplary prior art PLC signal
frame structure.
[0019] FIG. 6 is an illustration of an arrangement of payload
symbols in a payload portion of an exemplary prior art PLC signal
frame structure generated in accordance with the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The present invention of selectively controlling the length
of a payload symbol of a PLC signal frame structure is explained in
connection with operations performed at a PLC transceiver of an
OFDM PLC system which is designed for conveying PLC data signals
over conventional utility electrical power media. It is to be
understood, however, that the present invention can be applied to
OFDM based or other communication systems operating on other types
of wired or wireless media.
[0021] FIG. 1 illustrates an exemplary, prior art electric power
distribution and high speed data communications system 10, which
includes both utility electric power distribution and in premise
power distribution capabilities and over which PLC data signals
generated in accordance with the present invention can be conveyed.
Referring to FIG. 1, the system 10 includes a standard medium power
substation 12 coupling a high voltage power line 14 to a common
medium voltage power line and data distribution access network 16
via a switch cabinet 15. The network 16 is typically configured in
a loop, several miles in length, and positioned in proximity to low
voltage access points 20A-20H, which can be homes, businesses or
other entities. Step down transformers 18 couple the network 16 to
low voltage access lines 22, which are at 110-240 V AC and extend
to the respective low voltage access points 20. It is to be
understood that the network 16 can include power and communications
data distribution elements located above as well as below ground.
Thus, the network 16 forms a wide area data network ("WAN") for
data communications and supplies electricity to the low voltage
access points 20. Electric power meters 24 couple respective ends
of the low voltage lines 22 to conventional in-home or in-building
electricity distribution networks 26, which are contained within
the low voltage access points 20. As well known in the art,
electronic appliances 21 include PLC transceivers (not shown)
having PLC data signal processing capabilities and which can be
connected to one another to form a local access network ("LAN") for
data communications within a home, business or other environment,
are coupled to the network 26 within an access point 20. Also as
well known in the art, PLC data signals can be used to transmit
high speed data across all segments of the network 10.
[0022] In accordance with the present invention, a PLC transceiver
selectively controls the length of the payload symbols in a PLC
frame structure from which PLC signals are generated, based on the
results of an evaluation of PLC system channel quality data,
processing configuration data ("node configuration data") obtained
from PLC signals transmitted over the PLC system to, or
pre-programmed at, the PLC transceiver, or a combination of the
channel quality data and the node configuration data, to maximize
the data throughput rate and, therefore, increase the efficiency of
utilization of the PLC system as a channel for transferring
communications data. Referring to FIG. 1, the inventive PLC
transceiver can be installed in all segments of the PLC system 10
where a higher data throughput rate is desired. For example, each
of a first electronic appliance 21 coupled to the network 26 within
a first access point 20 and a second electronic appliance 21
coupled to the electric distribution network (not shown) within a
second access point 20 can contain the inventive PLC transceiver
for maximizing the data throughput rate for PLC signal transmission
between the first and second access points 20. Also for example, in
the PLC system 10, each of the electronic appliances 21A and
electronic appliance 21D is coupled at a different point to the
network 26 within the access point 20A and can contain the
inventive PLC transceiver for maximizing the data throughput rate
for PLC signal transmission between the two coupled points of the
network 26.
[0023] FIG. 2 is a preferred embodiment of an OFDM PLC transceiver
50 that establishes the physical connection and electronic signal
link between the power line network 26 in an access point 20 and a
data input/output ("I/O") device, such as a computer 51, as well
known in the art, and furthermore selectively controls the length
of payload symbols included in a PLC signal frame structure in
accordance with the present invention. The inventive PLC
transceiver 50 is described below as containing modules, which
perform PLC signal processing using techniques well known in the
prior art, and which are modified in accordance with the present
invention to perform PLC signal processing where a PLC signal frame
structure from which PLC signals are generated has a selected and
controllable payload symbol length. See, for example, U.S. patent
application Ser. No. 10/211,033, filed Aug. 2, 2002 and Ser. No.
10/309,567, filed Dec. 4, 2002, each of which is assigned to the
assignee of this application and incorporated by reference herein,
for a description of conventional PLC transceiver construction and
operation. It is to be understood that the modules of the PLC
transceiver 50 described below as performing data or signal
processing operations constitute a software module, a hardware
module or a combined hardware/software module. In addition, each of
the modules suitably contains a memory storage area, such as RAM,
for storage of data and instructions for performing processing
operations in accordance with the present invention. Alternatively,
instructions for performing processing operations can be stored in
hardware in one or more of the modules.
[0024] Referring to FIG. 2, the PLC transceiver 50 includes a
central processor unit ("CPU") 52 coupled to a data forward error
correction ("FEC") encoder 54 and a data FEC decoder 56. An OFDM
modulator 58 couples the encoder 54 to an analog front end ("AFE")
59, and an OFDM demodulator 60 couples the AFE 59 to the decoder
56. The encoder 54 includes a scrambler module 62, a Reed-Solomon
encoder module 64, a convolution encoder module 68 and a bit
interleaver module 70 connected to one another in the recited
sequence. The decoder 56 includes a de-interleaver module 72, a
de-puncture module 74, a viterbi decoder module 76, a Reed Solomon
decoder module 78 and a de-scrambler module 80 connected to one
another in the recited sequence. The modulator 58 includes a mapper
module 82, a reconfigurable inverse fast fourier ("IFFT") processor
module 84, a preamble module 86, a cyclic prefix module 88 and an
RC shaping module 90 connected to one another in the recited
sequence. The demodulator 60 includes a reconfigurable FFT
processor module 82, a polar converter module 84 and a demodulator
module 86 connected to one another in the recited sequence. In
addition, a channel estimator 88 is coupled to the outputs of the
polar converter module 84 and the FFT module 82, respectively, and
a synchronization detector 91. The detector 91 also is coupled to
the FFT module 82.
[0025] The modules 59, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82,
84, 86, 88, 90 and 91 are well known prior art PLC transceiver
components that can perform prior art PLC signal processing
operations which are also well known in the art. It is important to
note that, in the prior art, all of the modules in the encoder 54
and the modulator 58 cannot be reprogrammed to process PLC signals
based on different, selected payload symbol lengths. In other
words, the encoder 54 and modulator 58 only can perform PLC signal
processing operations in accordance with fixed payload symbol
length parameters, such that, for example, the mapper module 82 and
the IFFT module 84 cannot generate, for each payload symbol,
different numbers of distinct PLC carriers for carrying information
content. Similarly, all of the modules in the decoder 56 and the
modules 82, 84 and 86 in the demodulator 60 also cannot be
reprogrammed to process received PLC signals based on different,
selected payload symbol lengths.
[0026] In accordance with the present invention, the PLC
transceiver 50 further includes a symbol length controller ("SLC")
module 100 which is coupled to the CPU 52 and to each of modules
contained in the encoder 54, the decoder 56 and the modulator 58
and to the modules 82, 84 and 86 of the demodulator 60.
Furthermore, each of the modules in the encoder 54, the modulator
58 and the decoder 56, and the modules 82, 84 and 86 of the
demodulator 60 is reprogrammable and modifies its processing
operations based on control parameter signals, which are associated
with a payload symbol of a selected length and are supplied from
the SLC module 100 of the inventive PLC transceiver 50. As
discussed in further detail below, the SLC module 100 generates and
transmits to the modules in the encoder 54 and the modulator 58
control parameter signals, which are generated based on the payload
symbol length selected for generating PLC signals. The control
signals modify the processing operations that the modules perform
for generating PLC signals based on a PLC signal frame structure
having payload symbols whose length is selected in accordance with
the present invention. Further, the SLC module 100 generates and
transmits to the modules 82, 84 and 86 in the demodulator 60 and to
each of the modules in the decoder 56 control parameter signals,
which are generated based on the selected payload symbol length
associated with received PLC signals. The control signals modify
the processing operations performed for processing received PLC
signals, such that information content data bits are extracted from
the received PLC signals in accordance with the length selected for
the payload symbols of the PLC signal frame structure from which
the received PLC signals were generated.
[0027] For purpose of highlighting the inventive features, it is
assumed that each of the modules in the encoder 54, the modulator
58, the decoder 56 and of the demodulator 60 normally operates in a
default legacy PLC mode. In the legacy mode, PLC signal processing
operations are performed in accordance with a legacy PLC signal
frame structure design, which requires a fixed, predetermined
length frame structure, a fixed, predetermined length payload
portion and that the payload symbols contained in the payload
portion have a same fixed, predetermined length. The control
signals supplied by the SLC module 100 modify the processing
operations performed at (i) the encoder 54 and modulator 58 to
provide that a PLC signal frame structure having the payload symbol
length identified in the control signal is generated, and (ii) the
demodulator 60 and decoder 56 to provide that a received PLC signal
is processed in accordance with a PLC signal frame structure having
the payload symbol length identified in the control signals. For
ease of reference, the present invention is described in connection
with an exemplary prior art PLC signal frame structure 120 shown in
FIG. 3. Referring to FIG. 3, the frame structure 120 includes a
payload portion 122, which primarily contains information content,
interposed between a start delimiter 124 and an end delimiter 126,
both of which contain overhead data.
[0028] In a preferred embodiment, the SLC module 100 selects a
payload symbol length and generates and transmits to the encoder 54
and the modulator 58 control signals which provide that the overall
length of the payload portion of a PLC signal frame structure
generated based on the selected payload symbol length is the same
as the length of the legacy PLC payload portion.
[0029] The operation of the PLC transceiver 50 is illustrated below
with reference to the transmission of PLC signals from a source PLC
transceiver 50A (not shown), which is contained in the electronic
appliance 21A that is coupled to the network 26 in the access point
20A, to a destination PLC transceiver 50D, which is contained in
the electronic appliance 21D that is coupled to a different point
of the network 26 in the access point 20A than the transceiver 50A,
in the PLC system 10 as shown in FIG. 1. For ease of reference, the
modules within the respective transceivers 50A and 50D are referred
to below using corresponding alphabetical suffixes, e.g., the
transceiver 50A includes the SLC module 100A.
[0030] FIG. 4 shows an exemplary preferred process 200 that the
source and destination PLC transceivers 50A, 50D perform for
generating PLC signals based on a PLC frame structure having a
payload symbol length selected based on channel quality data and
node configuration data. Based on the channel quality data and the
node configuration data, the SLC module 100A preferably selects a
length for the payload symbols that maximizes the data throughput
rate and also conforms to legacy requirements concerning the
maximum length of the payload portion of the PLC frame
structure.
[0031] Referring to FIG. 4, in step 202, the source PLC transceiver
50A, which desires to transmit information content to the
destination PLC transceiver 50D, initially generates PLC
maintenance data signals in the ROBO mode and transmits the
maintenance PLC data signals onto the network 26 for receipt by the
destination PLC transceiver 50D. The estimator module 88D, using
well known prior art techniques, analyzes the PLC signals
transmitted by the transceiver 50A to determine channel quality in
the segment of the network 26 of the PLC system 10 extending
between the transceivers 50A and 50D, and then routes the channel
quality data to the CPU 52D. The CPU 52D, in turn, suitably
provides that the PLC transceiver 50D transmits the channel quality
data on maintenance PLC signals, over the network 26, for receipt
at the transceiver 50A. The transceiver 50A, using techniques well
known in the art, extracts the channel quality data from the
received PLC signal and routes the channel quality data, via the
CPU 52A, to the SLC module 100A. In a preferred embodiment, the SLC
module 100A further includes node configuration data that was
supplied on PLC signals or preprogrammed into the module 100A using
suitable, well known techniques in the art. At this point, the SLC
module 100A has obtained, using well known prior art techniques,
the channel quality and the node configuration data from which to
select a length for data payload symbols in a PLC signal frame
structure for maximizing data throughput rate between the
transceivers 50A and 50D.
[0032] In step 204, the SLC module 100A continuously processes the
channel quality and the node configuration data to determine a
configuration for the payload symbol length that is more efficient,
in terms of data throughput rate, than the default legacy payload
symbol length for the PLC transceivers 50A and 50D, which has
limited throughput rate capability.
[0033] FIG. 5 illustrates the features of the payload portion 122
of the legacy frame structure 120 shown in FIG. 3. As well known in
the art, the length of a payload symbol Ts in a PLC system frame
structure is determined as follows: Ts=(NFFT+N.sub.--CP)/Clock rate
(1) where NFFT is the number of IFFT samples generated by the IFFT
module 84A and corresponds to the number of distinct PLC carriers
that can be generated for transmission during the payload portion
of the PLC signal frame structure, N_CP is the number of data
samples corresponding to the length of the cyclic prefix in a
payload symbol and Clock rate is the sampling rate of the system
clock operating at a PLC transceiver. Referring to FIG. 5, the
legacy payload portion 122 includes 160 payload symbols 123 and
each payload symbol has the same length. For purposes of
illustration, the legacy PLC system design of FIG. 5 requires that
the IFFT module 84A is pre-programmed to generate only 256 samples,
the length of the cyclic prefix within each payload symbol is 184
samples and the system clock is at 50 MHz, such that Ts is 8.4
.mu.sec.
[0034] If the channel quality data is high, the SLC module 100A
computes a length for the payload symbols that is greater than the
length of the legacy payload symbol. The increased length of a
payload symbol within the fixed length payload portion of the
legacy frame structure translates into a predetermined number of
available PLC carriers that can be modulated with information
content data and generated for transmission, where the
predetermined number is greater that the number of PLC carriers
that can be generated based on the legacy PLC symbol length. In
preferred embodiments, the SLC module 100A provides that more than
the legacy number of PLC carriers are generated for a payload
symbol as follows.
[0035] (1) The SLC module 100 decreases the bandwidth of each of
the distinct available PLC carriers, such that a larger number of
narrower bandwidth distinct PLC carriers, evenly spaced across the
legacy PLC spectrum, can be generated. For example, in the legacy
PLC system, 256 distinct PLC carriers are evenly spaced across the
legacy PLC spectrum, which for example is between about 2 MHz and
about 20 MHz. By narrowing the bandwidth of each of the 256
distinct PLC carriers by, for example, one-half, 512 distinct PLC
carriers evenly spaced across the same 18 MHz legacy spectrum can
be generated for carrying the increased information content data
associated with an increased length payload symbol.
[0036] (2) The SLC module 100A provides that distinct PLC carriers
are distributed across a PLC frequency spectrum which is a wider
than the legacy PLC frequency spectrum. For example, the SLC module
100 increases the available PLC frequency spectrum from between
about 2 MHz to about 19 MHz (as in a legacy PLC system) to between
about 2 MHz and about 25 MHz. In this expanded PLC frequency
spectrum, the SLC module 100A provides that distinct PLC carriers
are evenly distributed across the expanded PLC frequency spectrum,
where the bandwidth of each of the distinct PLC carriers is (a) the
same as in the legacy PLC system or (b) narrower than in the legacy
PLC system as described above in (1).
[0037] (3) The SLC module 100A resets the system clock to a higher
frequency, such as 60 MHz, than the legacy PLC system clock
frequency. The increase in the system clock frequency increases the
sampling rate, which permits the range of the available PLC
frequency spectrum to be increased relative to the legacy PLC
system frequency spectrum. Thus, the SLC module 100A provides that
more distinct PLC carriers can be generated, similarly as described
in (2)(a) or (2)(b), for the longer payload symbol lengths.
[0038] Further in step 204, based on the selected increased symbol
length, the SLC module 100A accordingly determines a corresponding
NFFT, which exceeds the NFFT for the PLC legacy system.
[0039] By increasing the payload symbol length while maintaining
the legacy payload portion length unchanged, the payload portion
includes fewer symbols than in the PLC legacy system. The increased
length of a payload symbol, however, does not result in a
proportional increase in the length of the cyclic prefix for a
payload symbol. The cyclic prefix length for the increased length
payload symbol is maintained substantially the same as in the
legacy system, because the characteristics of the PLC system are
the same and because the high channel quality permits a relatively
short cyclic prefix length between consecutive PLC signal
transmissions corresponding to consecutive payload symbols. Thus,
the cyclic prefix in the increased length payload symbol occupies a
smaller fraction of the length of the payload symbol than the
length that a cyclic prefix in the shorter, legacy length payload
symbol occupies. Consequently, the information content portion of
the increased length payload symbols occupies a portion of the PLC
frame structure that is greater than the portion of the legacy PLC
frame structure occupied by information content contained in the
shorter, legacy PLC length payload symbols, thereby increasing the
data throughput rate.
[0040] Referring to FIG. 6, which shows a payload portion of a
fixed legacy PLC system length including increased length payload
symbols, the SLC module 100A in a preferred embodiment selects an
increased payload symbol length corresponding to a NFFT of 2048
samples. Further, the SLC module 100A, by evaluating the channel
quality data and also based on the node configuration data,
determines that N_CP needs to be 368 samples to provide a
sufficiently long cyclic prefix to avoid degradation based on
intersymbol interference. Therefore, referring to Equation (1), for
a 50 MHz system clock, the length Ts_new of the new increased
length payload symbol is 48 .mu.sec and the payload portion
includes 28 symbols. The selected length provides that the total
payload portion length (28 symbols)(48 .mu.sec/symbol) is the same
as the legacy PLC system payload portion length (160 symbols)(8.4
.mu.sec/symbol). It is be understood that the SLC module 100A can
suitably select the symbol length to have values corresponding to
NFFT equal to 512, 1024, etc. samples.
[0041] Referring again to FIG. 4, in step 206 the SLC module 100A
transmits control parameter signals associated with the selected
symbol length to the modules within the encoder 54A to provide that
the encoder 54A groups the raw data into data blocks in accordance
with the selected symbol length. In addition, the interleaver
module 70A based on the control signals, assigns a greater number
of data bits for mapping into a payload symbol, because an
increased number of distinct PLC carriers can be generated for the
increased length payload symbol.
[0042] In step 208, the SLC module 100A transmits control signals,
which are generated based on the channel quality data, the node
configuration data and known prior art tone maps and masks, to the
mapper module 82A and the IFFT module 84A to provide that
processing operations are performed in accordance with the selected
symbol length. For example, the control signals reprogram the IFFT
module 84A to operate in a 2048 sample mode.
[0043] In step 210, the SLC module 100A transmits control signals
to the preamble module 86A which indicate the length of a cyclic
prefix to be inserted in each payload symbol. Further in step 210,
the SLC module 100A transmits control signals to the RC shaper 90A
to adjust filtering operations, as suitable, based on either (i)
the expanded PLC frequency spectrum or (ii) the narrowing of the
bandwidth of individual PLC carriers within the PLC frequency
spectrum, where the PLC frequency spectrum is legacy sized or
expanded.
[0044] In step 212, the PLC transceiver 50A transmits, over the
network 26 for receipt at the transceiver 50D, the PLC signals
generated based on the selected payload symbol length within the
legacy for the frame structure. It is further noted that the frame
structure further includes frame control configuration data in the
start delimiter. The configuration data, which includes channel
quality data and selected payload symbol length data, is
transmitted on PLC signals to the PLC transceiver 50D before the
PLC signals containing information content, and corresponding to
the payload symbols, are transmitted.
[0045] In step 214, the PLC transceiver 50D receives the PLC
signals transmitted from the PLC transceiver 50A. The demodulator
and decoder modules 60D and 56D, using well known techniques in the
art, demodulate and decode the overhead data transmitted in
connection with the start and stop delimiter portions of the frame
structure to extract the selected symbol length, and the associated
frame control, channel quality and node configuration data included
therein. The decoder module 56D then routes the payload symbol
length and the other associated control data to the CPU 52D, which
in turn routes the symbol length and the associated control data to
the SLC module 100D. Based on the symbol length and the associated
control data, the SLC module 100D generates and transmits to the
modules 82, 84 and 86 of the demodulator 60 and to each of the
modules of the decoder 56 suitable control parameter signals to
provide that demodulation and decoding of the received PLC signals
is performed based on the selected payload symbol length. For
example, the FFT module 82 is reconfigured to perform a FFT
processing at 2048 samples, rather than at the default PLC legacy
mode of 256 samples. Processing modifications analogous to those
implemented at the mapper and the encoder module in the transceiver
50A are performed at the demodulator module 86D and the modules of
the decoder module 56D to provide for proper demodulation and
decoding based on the longer length payload symbols.
[0046] It is known that some legacy PLC frame structures have a
design that precludes the introduction of data indicating a
particular symbol length based upon which PLC signal processing
should be performed at a destination PLC transceiver. In these
circumstances, the source PLC transceiver 50 includes symbol length
information in a higher protocol layer, such as the IP layer,
associated with a PLC signal transmission. Alternatively, the
source PLC transceiver includes symbol length information in a PLC
maintenance signal transmission routinely transmitted to the
destination PLC transceiver, as well known in the art. The PLC
destination transceiver suitably extracts the symbol length
information from the maintenance PLC signal.
[0047] In a further preferred embodiment, the CPU 52 in the PLC
transceiver 50 controls exchanges of maintenance signals with other
PLC transceivers in the PLC system and, based on the exchanges,
determines whether the other PLC transceivers have the processing
capability to select payload symbol length. The CPU 52 generates a
table representative of the PLC signal transmission capabilities of
the respective PLC transceivers and causes the information
contained in the table to be transmitted on maintenance PLC signals
over the PLC system for receipt by other PLC transceivers having
the capability to process PLC signals based on a select payload
symbol length.
[0048] In a preferred embodiment, the CPU 52 in a source PLC
transceiver transmits to a destination PLC transceiver maintenance
PLC signals identifying the length of payload symbols to be
included in subsequent PLC signal transmissions from the source PLC
transceiver. In a further preferred embodiment, a destination PLC
transceiver transmits maintenance signals to the source PLC
transceiver acknowledging receipt of the symbol length information
provided by the source PLC transceiver and accordingly processes
PLC signals received from the source PLC transceiver at the
selected payload symbol length.
[0049] Although preferred embodiments of the present invention have
been described and illustrated, it will be apparent to those
skilled in the art that various modifications may be made without
departing from the principles of the invention.
* * * * *
References