U.S. patent application number 10/982955 was filed with the patent office on 2005-05-05 for method of and device for communication.
This patent application is currently assigned to Mitsubishi Denki Kabushiki Kaisha. Invention is credited to Matsumoto, Wataru, Miyata, Yoshikuni.
Application Number | 20050097427 10/982955 |
Document ID | / |
Family ID | 17984852 |
Filed Date | 2005-05-05 |
United States Patent
Application |
20050097427 |
Kind Code |
A1 |
Matsumoto, Wataru ; et
al. |
May 5, 2005 |
Method of and device for communication
Abstract
A communication device is provided with a turbo encoder (1)
which carries out a turbo encoding process on the lower two bits of
transmission data so as to output information bits of two bits and
redundant bits of two bits, a conversion (2) which carries out
calculations so as to uniform error-correction capabilities on
respective information bits by using the output, decoders (11 to
18) which carries out a soft-judgment on the lower two bits of the
received signal that are susceptible to degradation in the
characteristics so as to estimate the original transmission data,
and a second judging device (19) which carries out a hard-judgment
on the other bits in the received signal so as to estimate the
original transmission data.
Inventors: |
Matsumoto, Wataru; (Tokyo,
JP) ; Miyata, Yoshikuni; (Tokyo, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
Mitsubishi Denki Kabushiki
Kaisha
|
Family ID: |
17984852 |
Appl. No.: |
10/982955 |
Filed: |
November 8, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10982955 |
Nov 8, 2004 |
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09857461 |
Jun 5, 2001 |
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09857461 |
Jun 5, 2001 |
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PCT/JP00/07312 |
Oct 20, 2000 |
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Current U.S.
Class: |
714/755 |
Current CPC
Class: |
H03M 13/2966 20130101;
H03M 13/2957 20130101; H03M 13/27 20130101; H03M 13/258
20130101 |
Class at
Publication: |
714/755 |
International
Class: |
H03M 013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 29, 1999 |
JP |
11-308750 |
Claims
1. A communication device, which uses turbo codes as
error-correction codes, comprising: a turbo encoding unit which
carries out a turbo encoding process on lower bits of a
predetermined number in transmission data to output information
bits in accordance with the predetermined number and first and
second redundant bits that have been convolutionally encoded in
different sequences; a computing unit which carries out
calculations for uniforming error-correction capabilities on the
respective information bits by using the information bits of the
predetermined number and the redundant bits to output the results
of the calculations and the other bits in the transmission data as
the results of the encoding process; a first decoding unit which
extracts the information bits and the first redundant bits from the
lower bits of the predetermined number in the received signal, and
makes a soft-judgment based upon the results of the extraction and
a soft judgment output that is an output preceding by one given as
preliminary information (in some cases, not given); a second
decoding unit which extracts the information bits and the second
redundant bits, makes a soft-judgment based upon the results of the
extraction and the soft-judgment output from said first decoding
unit, and informs said first decoding unit of the results thereof
as the soft-judgment output preceding by one; a first judging unit
which executes the soft-judgment by said first decoding unit and
said second decoding unit a predetermined times repeatedly, and
then estimates the original information bit based upon the
soft-judgment output of said second decoding unit; and a second
judging unit which makes a hard-judgment on the other bits in the
received signal to estimate the original information bits.
2. The communication device according to claim 1, wherein said
turbo encoding unit includes a deinterleave processing unit for
carrying out a de-interleaving process on one group of the
redundant bits that have been encoded after the interleave process
to output the respective information bits and the redundant bits
with the times being coincident with each other.
3. The communication device according to claim 1, wherein Reed
Solomon codes and turbo codes are used combinedly, and on the
transmitting side, the turbo encoding is carried out after the Reed
Solomon encoding, while on the receiving side, the Reed Solomon
codes are decoded after decoding the turbo codes.
4. A communication device comprising an encoder that uses turbo
codes with the interleave process being incorporated into the
encoding process, and outputs results of the encoding process, said
encoder includes, a turbo encoding unit which receives transmission
data constituted by a plurality of bits, and carries out a turbo
encoding process on lower bits of a predetermined number in
transmission data to output information bits in accordance with the
predetermined number, first redundant bits that have been obtained
by convolutionally encoding the information bits and second
redundant bits that have been obtained by convolutionally encoding
the information bits after the interleave process; and a computing
unit which carries out calculations for uniforming error-correction
capabilities on the respective information bits by using the
information bits of the predetermined number and the redundant
bits, wherein the results of the calculations and the other bits in
the transmission data are outputted as the results of the encoding
process.
5. The communication device according to claim 4, wherein said
turbo encoding unit includes a deinterleave processing unit which
carries out a de-interleaving process on the second redundant bits,
wherein the respective information bits, the first redundant bits
and the second redundant bits that have been subjected to the
de-interleaving process are outputted with the times being
coincident with each other.
6. The communication device according to claim 4, wherein Reed
Solomon codes and turbo codes are used combinedly and the turbo
encoding is carried out after the Reed Solomon encoding.
7. A communication device comprising an encoder that uses turbo
codes with the interleave process being incorporated into the
encoding process, and outputs results of the encoding process, said
encoder includes a turbo encoding unit which receives transmission
data constituted by a plurality of bits, and carries out a turbo
encoding process on lower bits of a predetermined number in
transmission data to output information bits in accordance with the
predetermined number, first redundant bits that have been obtained
by convolutionally encoding the information bits and second
redundant bits that have been obtained by convolutionally encoding
the information bits after the interleave process, wherein, in
addition to the respective information bits and the first and
second redundant bits, the other bits in the transmission data are
outputted as the results of the encoding process.
8. The communication device according to claim 7, wherein Reed
Solomon codes and turbo codes are used combinedly and the turbo
encoding is carried out after the Reed Solomon encoding.
9. A communication device comprising a decoder that decodes a
received signal that has been turbo encoded by using a soft
judgment, said decoder including, a first decoding unit which
extracts information bits and first redundant bits that have been
convolutionally encoded from the lower bits of the predetermined
number in the received signal, and makes a soft-judgment based upon
the results of the extraction and a soft judgment output that is an
output preceding by one given as preliminary information (in some
cases, not given); a second decoding unit which extracts the
information bits in accordance with the number of outputs on the
encoder side and the second redundant bits that have been
convolutionally encoded in a method different from the first
redundant bits from the lower bits in the predetermined number in
the received signal, makes a soft-judgment based upon the results
of the extraction and the soft-judgment output from said first
decoding unit, and informs said first decoding unit of the results
thereof as the soft-judgment output preceding by one; a first
judging unit which executes the soft-judgment by said first
decoding unit and said second decoding unit a predetermined times
repeatedly, and then estimates the original information bit based
upon the soft-judgment output of said second decoding unit; and a
second judging unit which makes a hard-judgment on the other bits
in the received signal to estimate the original information
bits.
10. The communication device according to claim 9, wherein, when
Reed Solomon codes and turbo codes are used combinedly on the
transmitting side, the Reed Solomon codes are decoded after
decoding the turbo codes.
11. A communication method, which uses turbo codes as
error-correction codes, the method comprising: a turbo encoding
step of carrying out a turbo encoding process on lower bits of a
predetermined number in transmission data to output information
bits in accordance with the predetermined number and first and
second redundant bits that have been convolutionally encoded in
different sequences; a computing step of carrying out calculations
for uniforming error-correction capabilities on the respective
information bits by using the information bits of the predetermined
number and the redundant bits to output the results of the
calculations and the other bits in the transmission data as the
results of the-encoding process; a first decoding step of
extracting the information bits and the first redundant bits from
the lower bits of the predetermined number in the received signal
so as to make a soft-judgment based upon the results of the
extraction and a soft judgment output that is an output preceding
by one given as preliminary information (in some cases, not given);
a second decoding step of extracting the information bits and the
second redundant bits so as to make a soft-judgment based upon the
results of the extraction and the soft-judgment output from the
first decoding step, thereby making the results thereof as the
soft-judgment output preceding by one; a first judging step of
executing the soft-judgment by the first decoding step and the
second decoding step a predetermined times repeatedly, and then
estimating the original information bit based upon the
soft-judgment output of the second decoding step; and a second
judging step of making a hard-judgment on the other bits in the
received signal to estimate the original information bits.
12. The communication method according to claim 11, wherein the
turbo encoding step includes a deinterleave processing step of
carrying out a de-interleaving process on one group of the
redundant bits that have been encoded after the interleave process,
wherein the respective information bits and the redundant bits are
outputted with the times being coincident with each other.
13. The communication method according to claim 11, wherein Reed
Solomon codes and turbo codes are used combinedly, and on the
transmitting side, the turbo encoding is carried out after the Reed
Solomon encoding, while on the receiving side, the Reed Solomon
codes are decoded after decoding the turbo codes.
Description
TECHNICAL FIELD
[0001] The present invention in general relates a method of and
device for communication that use a multi-carrier modem system.
More particularly, this invention relates to a communication device
which realizes data communication through the existing
communication lines by using a method such as the DMT (Discrete
Multi-Tone) modem system and the OFDM (Orthogonal Frequency
Division Multiplex) modem system and a communication method capable
of realizing such a communication device. However, the present
invention is not intended to be limited to the communication device
for carrying out data communication through the DMT modem system,
and is applicable to any communication device for carrying out
cable communication and radio communication through normal
communication lines by using the multi-carrier modem system and a
single carrier modem system.
BACKGROUND ART
[0002] The conventional communication methods will be explained
below. For example, in the wide band CDMA (W-CDMA: Code Division
Multiple Access) using the SS (Spread Spectrum) system, turbo codes
have been proposed as error-correction codes that greatly exceed
convolutional codes in their performances. In the turbo code, a
list formed by interleaving an information list is encoded in
parallel with a known coding list, and the turbo code is one of the
error-correction codes that have attracted the greatest public
attention at present, and is said to provide characteristics close
to Shannon limit. In the above-mentioned W-CDMA, since the
performances of the error-correction code give great effects on the
transmission characteristics in the voice transmission and data
transmission, the application of the turbo code makes it possible
to greatly improve the transmission characteristics.
[0003] Operation of transmitting and receiving systems of the
conventional communication device using the turbo code will be
explained in detail below. FIG. 8 is a drawing that shows the
construction of a turbo encoder used in the transmitting system. In
FIG. 8(a), reference numeral 101 denotes a first recursive system
convolutional encoder that subjects an information list to a
convolutional encoding process to output redundant bits. Reference
numeral 102 denote an interleaver, and reference numeral 103 denote
a second recursive system convolutional encoder that subjects the
information list that has been switched by the interleaver 102 to a
convolutional encoding process to output redundant bits. FIG. 8(b)
is a drawing that shows the inner structures of the first recursive
system convolutional encoder 101 and the second recursive system
convolutional encoder 103, and the two recursive system
convolutional encoders are encoders that only output redundant bits
respectively. Moreover, the interleaver 102, which is used in the
turbo encoder, randomly switches information bit lists.
[0004] The turbo encoder, which is arranged as described above,
simultaneously outputs an information bit list: x.sub.1, a
redundant bit list: x.sub.2 obtained by encoding the information
bit list through the operation of the first recursive system
convolutional encoder 101, and a redundant bit list: x.sub.3
obtained by encoding the information bit list that has been
interleaved through the operation of the second recursive system
convolutional encoder 103.
[0005] FIG. 9 is a drawing that shows the construction of the turbo
decoder that is used in the receiving system. Reference numeral 111
denotes a first decoder that calculates a logarithm likelihood
ratio from a receiving signal: y.sub.1 and a receiving signal:
y.sub.2. Reference numerals 112 and 116 denote adders, and
reference numeral 113 and 114 denote interleavers. Reference
numeral 115 denotes a second decoder that calculates a logarithm
likelihood ratio from a receiving signal: y.sub.1 and a receiving
signal: y.sub.3. Reference numeral 117 denotes a deinterleaver, and
reference numeral 118 denotes a judging device for judging the
output of the second decoder 115 to output an estimated value of
the original information bit list. The receiving signals: y.sub.1,
y.sub.2, y.sub.3 are signals that are formed by allowing the
information bit list: x.sub.1 and the redundant bit lists: x.sub.2,
x.sub.3 to include influences from noise and phasing in the
transmission path.
[0006] In the turbo decoder that is arranged as described above,
first, the first decoder 111 calculates the logarithm likelihood
ratio: L (U.sub.k) (where k refers to the time) from a received
signal: y.sub.1k and a received signal: y.sub.2k. In this case, the
logarithm likelihood ratio: L(U.sub.k) is represented by the
following equation: 1 L ( u k ) = y 1 k + La ( u k ) + Le ( u k ) =
Ln Pr ( x 1 k ' = 1 | { Y } ) Pr ( x 1 k ' = 0 | { Y } ) ( 1 )
[0007] Here, Le (U.sub.k) represents external information, La
(U.sub.k) represents preliminary information that is external
information preceding by one, P.sub.r (x.sub.1k'=1.vertline.{Y})
represents the probability of an estimated information bit upon
receipt of the entire list {Y} of the received signals: x.sub.1k}'
being 1 and, Pr (x.sub.1k'=0.vertline.{Y}) represents the
probability of an estimated information bit upon receipt of the
entire list {Y} of the received signals: x.sub.1k' being 0. In
other words, equation (1) finds the probability of the estimated
information bit: x.sub.1k' becoming 1 with respect to the
probability of the estimated information bit: x.sub.1k' being
0.
[0008] Next, the adder 112 calculates external information to be
given to the second decoder 115 from a logarithm likelihood ratio
that is the result of the above-mentioned calculation. Based upon
the above-mentioned equation (1), the external information: Le
(U.sub.k) is represented by the following equation:
Le(U.sub.k)=L(U.sub.k)-y.sub.1k-La(U.sub.k) (2)
[0009] Since no preliminary information has been given at the time
of the first decoding process, La(U.sub.k)=0.
[0010] In the interleavers 113 and 114, in order to make the
received signal: y.sub.1k and the external information: Le
(U.sub.k) coincident with the time of the received signal: y.sub.3,
the signals are re-arranged. Then, in the same manner as the first
encoder 111, based upon the received signal: y.sub.1 and the
received signal: y.sub.3 as well as the external information:
Le(U.sub.k) preliminarily calculated, the second decoder 115
calculates a logarithm likelihood ratio: L(U.sub.k). Thereafter, in
the same manner as the adder 112, the adder 116 calculates the
external information Le(U.sub.k) by using equation (2). At this
time, the external information, rearranged by the interleave 117,
is fed back to the first decoder 111 as the preliminary
information: La(U.sub.k).
[0011] Finally, in the turbo decoder, the above-mentioned processes
are repeatedly executed predetermined times so that it is possible
to calculate a logarithm likelihood ratio with higher precision,
and the judgment device 118 makes a judgment based upon this
logarithm likelihood ratio, thereby estimating the bit list of the
original information. More specifically, for example, the logarithm
likelihood ratio shows that "L(U.sub.k)>0", the estimated
information bit: x.sub.1k' is judged as 1, while it shows that
"L(U.sub.k).ltoreq.0", the estimated information bit: x.sub.1k' is
judged as 0.
[0012] In this manner, in the conventional communication method, by
using the turbo code as the error-correction code, even when the
signal point-to-point distance becomes closer as the modulation
system is multi-valued, it becomes possible to greatly improve the
transmitting characteristics in the voice transmission and data
transmission, and consequently to obtain characteristics superior
to the known convolutional codes.
[0013] However, in the above-mentioned conventional communication
method, in order to carry out an error correction with high
precision, the turbo encoding process is carried out on all the
information lists on the transmitting side, and on the receiving
side, all the encoded signals are decoded, and a soft-judgment is
then executed thereon. More specifically, for example, in the case
of 16 QAM, a judgment is made with respect to all the 4-bit data
(0000 to 1111: 4-bit constellation), and in the case of 256 QAM, a
judgment is made with respect to all the 8-bit data. Therefore,
conventionally, the application of the conventional communication
method that carries out judgments on all the data as described
above causes a problem of an increase in the amount of calculations
in the encoder and decoder in response to the multi-valued
levels.
[0014] Therefore, the object of the present invention is to provide
a communication device and a communication method for such a
device, which is applicable to any communication system using the
multi-carrier modem system and the single-carrier modem system, and
makes it possible to achieve a reduction in the amount of
calculations and to provide a good transmitting characteristics in
the same manner as the conventional device, even when there is an
increase in the constellation due to multi-valued levels.
DISCLOSURE OF THE INVENTION
[0015] The communication device according to one aspect of this
invention, which uses turbo codes as error-correction codes, is
provided with a turbo encoding unit (corresponding to a turbo
encoder 1 in an embodiment which will be described later) which
carries out a turbo encoding process on lower bits of a
predetermined number in transmission data to output information
bits in accordance with the predetermined number and first and
second redundant bits that have been convolutionally encoded in
different sequences; a computing unit (corresponding to a
conversion 2) which carries out calculations for uniforming
error-correction capabilities on the respective information bits by
using the information bits of the predetermined number and the
redundant bits to output the results of the calculations and the
other bits in the transmission data as the results of the encoding
process; a first decoding unit (corresponding to a first decoder 11
and an adder 12) which extracts the information bits and the first
redundant bits from the lower bits of the predetermined number in
the received signal, and makes a soft-judgment based upon the
results of the extraction and a soft judgment output that is an
output preceding by one given as preliminary information (in some
cases, not given); a second decoding unit (corresponding to a
second decoder 15, an interleavers 13 and 14, an adder 16 and a
deinterleaver 17) which extracts the information bits and the
second redundant bits, makes a soft-judgment based upon the results
of the extraction and the soft-judgment output from the first
decoding unit, and informs the first decoding unit of the results
thereof as the soft-judgment output preceding by one; a first
judging unit (corresponding to a first judging device 18) which
executes the soft-judgment by the first decoding unit and the
second decoding unit a predetermined times repeatedly, and then
estimates the original information bit based upon the soft-judgment
output of the second decoding unit; and a second judging unit
(corresponding to a second judging device 19) which makes a
hard-judgment on the other bits in the received signal to estimate
the original information bits.
[0016] Furthermore, the turbo encoding unit is provided with a
deinterleave processing unit (corresponding to a deinterleaver 25)
for carrying out a de-interleaving process on one group of the
redundant bits that have been encoded after the interleave process
to output the respective information bits and the redundant bits
with the times being coincident with each other.
[0017] Furthermore, Reed Solomon codes and turbo codes are used
combinedly, and on the transmitting side, the turbo encoding is
carried out after the Reed Solomon encoding, while on the receiving
side, the Reed Solomon codes are decoded after decoding the turbo
codes.
[0018] The communication device according to another aspect of this
invention has an encoder that uses turbo codes with the interleave
process being incorporated into the encoding process. This encoder
is provided with a turbo encoding unit (corresponding to a turbo
encoder 1 in an embodiment which will be described later) which
receives transmission data constituted by a plurality of bits, and
carries out a turbo encoding process on lower bits of a
predetermined number in transmission data to output information
bits in accordance with the predetermined number, first redundant
bits that have been obtained by convolutionally encoding the
information bits and second redundant bits that have been obtained
by convolutionally encoding the information bits after the
interleave process; and a computing unit (corresponding to a
conversion 2) which carries out calculations for uniforming
error-correction capabilities on the respective information bits by
using the information bits of the predetermined number and the
redundant bits, in such a manner that the results of the
calculations and the other bits in the transmission data are
outputted as the results of the encoding process.
[0019] Furthermore, the turbo encoding unit is provided with a
deinterleave processing unit (corresponding to a deinterleaver 25)
for carrying out a de-interleaving process on the second redundant
bits so that the respective information bits, the first redundant
bits and the second redundant bits that have been subjected to the
de-interleaving process are outputted with the times being
coincident with each other.
[0020] The communication device according to still another aspect
of this invention has an encoder that uses turbo codes with the
interleave process being incorporated into the encoding process.
This encoder is provided with a turbo encoding unit which receives
transmission data constituted by a plurality of bits, and carries
out a turbo encoding process on lower bits of a predetermined
number in transmission data to output information bits in
accordance with the predetermined number, first redundant bits that
have been obtained by convolutionally encoding the information bits
and second redundant bits that have been obtained by
convolutionally encoding the information bits after the interleave
process, in such a manner that in addition to the respective
information bits and the first and second redundant bits, the other
bits in the transmission data are outputted as the results of the
encoding process.
[0021] Furthermore, Reed Solomon codes and turbo codes are used
combinedly, and the turbo encoding is carried out after the Reed
Solomon encoding.
[0022] The communication device according to still another aspect
of this invention has a decoder that decodes a received signal that
has been turbo encoded by using a soft judgment. This decoder is
provided with a first decoding unit (corresponding to a first
decoder 11 and an adder 12) which extracts information bits and
first redundant bits that have been convolutionally encoded from
the lower bits of the predetermined number in the received signal,
and makes a soft-judgment based upon the results of the extraction
and a soft judgment output that is an output preceding by one given
as preliminary information (in some cases, not given); a second
decoding unit (corresponding to a second decoder 15, an
interleavers 13 and 14, an adder 16 and a deinterleaver 17) which
extracts the information bits in accordance with the number of
outputs on the encoder side and the second redundant bits that have
been convolutionally encoded in a method different from the first
redundant bits from the lower bits in the predetermined number in
the received signal, makes a soft-judgment based upon the results
of the extraction and the soft-judgment output from the first
decoding unit, and informs the first decoding unit of the results
thereof as the soft-judgment output preceding by one; a first
judging unit (corresponding to a first judging device 18) which
executes the soft-judgment by the first decoding unit and the
second decoding unit a predetermined times repeatedly, and then
estimates the original information bit based upon the soft-judgment
output of the second decoding unit; and a second judging unit
(corresponding to a second judging device 19) which makes a
hard-judgment on the other bits in the received signal to estimate
the original information bits.
[0023] Furthermore, when Reed Solomon codes and turbo codes are
used combinedly on the transmitting side, the Reed Solomon codes
are decoded after decoding the turbo codes.
[0024] The communication method according to still another aspect
of this invention, which uses turbo codes as error-correction
codes, is provided with a turbo encoding step of carrying out a
turbo encoding process on lower bits of a predetermined number in
transmission data to output information bits in accordance with the
predetermined number and first and second redundant bits that have
been convolutionally encoded in different sequences; a computing
step of carrying out calculations for uniforming error-correction
capabilities on the respective information bits by using the
information bits of the predetermined number and the redundant bits
to output the results of the calculations and the other bits in the
transmission data as the results of the encoding process; a first
decoding step of extracting the information bits and the first
redundant bits from the lower bits of the predetermined number in
the received signal so as to make a soft-judgment based upon the
results of the extraction and a soft judgment output that is an
output preceding by one given as preliminary information (in some
cases, not given); a second decoding step of extracting the
information bits and the second redundant bits so as to make a
soft-judgment based upon the results of the extraction and the
soft-judgment output from the first decoding step, thereby
informing the first decoding unit of the results thereof as the
soft-judgment output preceding by one; a first judging step of
executing the soft-judgment by the first decoding step and the
second decoding step a predetermined times repeatedly, and then
estimating the original information bit based upon the
soft-judgment output of the second decoding step; and a second
judging step of making a hard-judgment on the other bits in the
received signal to estimate the original information bits.
[0025] Furthermore, the turbo encoding step is provided with a
deinterleave processing step of carrying out a de-interleaving
process on one group of the redundant bits that have been encoded
after the interleave process to output the respective information
bits and the redundant bits with the times being coincident with
each other.
[0026] Furthermore, Reed Solomon codes and turbo codes are used
combinedly, and on the transmitting side, the turbo encoding is
carried out after the Reed Solomon encoding, while on the receiving
side, the Reed Solomon codes are decoded after decoding the turbo
codes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a drawing that shows constructions of an encoder
and a decoder that are used in a communication device in accordance
with the present invention;
[0028] FIG. 2 is a drawing that shows a construction of a
transmitting system of a transmitter in accordance with the present
invention;
[0029] FIG. 3 is a drawing that shows a construction of a receiving
system in accordance with the present invention;
[0030] FIG. 4 is a drawing that shows a tone construction in a
multi-carrier modem system and a construction of an encoder that is
applicable to a 4-bit constellation;
[0031] FIG. 5 is a drawing that shows a layout of signal points in
various digital modulations;
[0032] FIG. 6 is a drawing that shows a circuit construction of a
turbo encoder 1;
[0033] FIG. 7 is a drawing that shows a difference in bit error
rates;
[0034] FIG. 8 is a drawing that shows a construction of a
conventional turbo encoder; and
[0035] FIG. 9 is a drawing that shows a construction of a
conventional turbo encoder.
BEST MODE FOR CARRYING OUT THE INVENTION
[0036] Preferred embodiments of the method of and device for
communication in accordance with the present invention will be
explained below with reference to the accompanying drawings.
However, the present invention is not intended to be limited by
these embodiments.
[0037] FIG. 1 is a drawing that shows constructions of an encoder
(a combination of a turbo encoder and a conversion) and a decoder
(a combination of a turbo decoder and a hard judging device) used
in a communication device in accordance with the present invention
in which. More specifically, FIG. 1(a) shows the construction of
the encoder, and FIG. 1(b) shows the construction of the decoder
according to this embodiment. In the communication device in
accordance with the present embodiment, both of the constructions
of the encoder and decoder are installed so that it is possible to
provide a data error-correction capability with high precision, and
consequently to obtain a superior transmitting characteristics in
data communication and voice communication. Here, in the present
embodiment, for convenience of explanation, both of the
constructions are provided; however, for example, of the two
devices, only the encoder may be installed in a transmitter, or
only the decoder may be installed in a receiver.
[0038] Moreover, in the encoder in FIG. 1(a), reference numeral 1
denote a turbo encoder that uses turbo codes as error-correction
codes so as to provide a performance close to the Shannon limit and
2 is a conversion for converting data received from the turbo
encoder 1. In the turbo encoder 2, for example, with respect to an
input of two-bit information bits, two-bit information bits and
two-bit redundant bits are outputted, and in the conversion 2, with
respect to the received 4-bit data, calculations are carried out so
as to uniform the correction capabilities with respect to the
information bits on the receiving side.
[0039] In the decoder shown in FIG. 1(a), reference numeral 11
denotes a first decoder for calculating the logarithm likeliness
ratio from a receiving signal: Lcy (corresponding to receiving
signals: v.sub.0, v.sub.1, w.sub.0 and w.sub.1, as will be
described later), 12 and 16 are adders. Reference numerals 13 and
14 denote interleavers. Reference numeral 15 denotes a second
decoder for calculating the logarithm likeliness ratio from the
receiving signal: Lcy (corresponding to receiving signals: v.sub.0,
v.sub.1, w.sub.0 and w.sub.1, as will be described later).
Reference numeral 17 denotes a deinterleaver. Reference numeral 18
denotes a first judging device for judging the output of the second
decoder 15 to output an estimated value of the original information
bit list, and reference numeral 19 denotes a second judging device
for hard-judging the Lcy (corresponding to receiving signals:
v.sub.2 . . . , w.sub.2 . . . , as will be described later) to
output an estimated value of the original information bit list.
[0040] Prior to explaining the operations of the encoder and
decoder, an explanation will be briefly given of the basic
operation of the communication device in the present invention by
reference to Figures. For example, with respect to the cable-type
digital communication system for carrying out data communication by
using the DMT (Discrete Multi Tone) modem system, there are xDSL
communication systems including an ADSL (Asymmetric Digital
Subscriber Line) communication system that executes a high-speed
digital communication with several megabits/second by using the
existing telephone lines and an HDSL (high-bit-rate Digital
Subscriber Line) communication system. Here, these systems are
standardized in T1.413 of the ANSI, etc. In the explanation of the
present embodiment, for example, a communication device that is
applicable to the ADSL is used.
[0041] FIG. 2 is a drawing that shows the construction of a
transmitting system of a communication device in accordance with
the present invention. In this transmitting system, the
transmission data is multiplexed by a multiplex/synch control
(corresponding to a MUS/SYNC CONTROL in the Figure) 41, and
error-correction codes are added to the transmission data that has
been multiplexed in cyclic redundancy checks (corresponding to CRC:
Cyclic Redundancy Checks) 42, 43, and FEC-use codes are added
thereto and a scrambling process is also applied thereto in forward
error corrections (corresponding to SCRAM & FEC) 44, 45.
[0042] There are two paths from the multiplex/synch control 41 to a
tone ordering 49, and one is an interleaved data buffer path
containing the interleave 46, and the other is a fast data buffer
path that does not contain the interleave 46; thus, for example,
the interleaved data buffer path for executing an interleaving
process has a greater delay.
[0043] Thereafter, the transmission data is subjected to a rate
converting process in rate converters (corresponding to
RATE-CONVERTORS) 47, 48, and then subjected to a tone ordering
process in the tone ordering (corresponding to TONE ORDERRING) 49.
Based upon the transmission data after the tone ordering process,
constellation data is formed in a constellation encoder/gain
scaling (corresponding to CONSTELLATION AND GAIN SCALING) 50, and
this is subjected to an inverse Fast Fourier transform in an
inverse Fast Fourier transform section (corresponding to IFFT:
Inverse Fast Fourier transform) 51.
[0044] Finally, after the Fourier transform, the parallel data is
converted to serial data in an input parallel/serial buffer
(corresponding to INPUT PARALLEL/SERIAL BUFFER) 52, and the digital
waveform is converted to an analog waveform in analog
processing/digital-analog converter (corresponding to ANALOG
PROCESSING AND DAC) 53; then, after having been subjected to a
filtering process, the resulting transmission data is transmitted
to a telephone line.
[0045] FIG. 3 is a drawing that shows a construction of a receiving
system of the communication device in accordance with the present
invention. In this receiving system, the received data
(corresponding to the above-mentioned transmission data) is
subjected to a filtering process in an analog
processing/analog-digital converter (corresponding to ANALOG
PROCESSING AND ADC in the Figure) 141, and the analog waveform is
converted to a digital waveform; thereafter, this is subjected to
an adaptive equalization process with respect to the time domain in
a time domain equalizer (corresponding to TEQ) 142.
[0046] With respect to the data having been subjected to the
adaptive equalization process, this is converted from serial data
to parallel data in an input serial/parallel buffer (corresponding
to INPUT SERIAL/PARALLEL BUFFER) 143, and this parallel data is
subjected to a fast Fourier transform in a fast Fourier transform
section (corresponding to FFT: Fast Fourier transform) 144;
thereafter, this is subjected to an adaptive equalization process
with respect to the frequency domain in a frequency domain
equalizer (corresponding to FEQ) 145.
[0047] The data, which has been subjected to the adaptive
equalization process with respect to the frequency domain, is
subjected to a composite process (most likeliness composite method)
and a tone ordering process in a constellation decoder/gain scaling
(corresponding to CONSTELLATION DECODER AND GAIN SCALING) 146 and a
tone ordering (corresponding to TONE ORDERING) 147 so that this is
converted to serial data. Thereafter, this is subjected to
processes, such as a rate converting process by rate converters
(corresponding to RATE-CONVERTER) 148, 149, a de-interleaving
process in a deinterleave (corresponding to DEINTERLEAVE) 150, an
FEC process and a de-scrambling process in forward error
corrections (corresponding to DESCRAM & FEC) 151, 152, and a
cyclic redundancy check in cyclic redundancy checks (corresponding
to cyclic redundancy checks) 153, 154; thus, the received data is
finally reproduced from a multiplex/synch control (corresponding to
MUX/SYNC CONTROL) 155.
[0048] In the communication device as described above, the two
paths are provided respectively in the receiving system and
transmitting system, and by using these two paths properly or using
these two paths at the same time, it is possible to realize a
low-transmission delay and data communication with high rates.
[0049] In the communication device, the encoder shown in FIG. 1(a)
is positioned at the constellation encoder/gain scaling 50 in the
transmitting system, and the decoder shown in FIG. 1(b) is
positioned at the constellation decoder/gain scaling 146 in the
receiving system.
[0050] Operations of the encoder (transmitting system) and the
decoder (receiving system) will now be explained in details. First,
operations of the encoder which is shown in FIG. 1(a) will be
explained. FIG. 4 shows a tone structure (see (a)) in the
multi-carrier modem system and a construction (see (b)) of the
encoder that is applicable to the 4-bit constellation. Here, in the
present embodiment, as illustrated in FIG. 4(a), with respect to
the multi-value Quadrature Amplitude Modulation (QAM), for example,
a 16 QAM system is adopted, and with respect to two tones in the
multi-carrier, an encoding process is carried out. Moreover, in the
encoder of the present embodiment, different from the conventional
technique that executes a turbo encoding process on all the input
data, the turbo encoding process is executed on the input data of
the lower two bits as illustrated in FIG. 4(b), and with respect to
the other upper bits, the input data, as it is, is outputted.
[0051] Here, the following description will discuss why only the
lower two bits of the input data are subjected to the turbo
encoding process. FIG. 5 is a drawing that shows the layout of
signal points in various digital modulations; and more
specifically, FIG. 5(a) shows the layout of signal points in the
4-phase shift keying (PSK) system, FIG. 5(b) shows the layout of
signal points in the 16 QAM system, and FIG. 5(c) shows the layout
of signal points in the 64 QAM system.
[0052] For example, when, in the layout of signal points in all the
modulation systems, the received signal points are a or b
positions, on the receiving side, normally, the data having the
most likelihood is estimated as the information bit list
(transmission data) through a soft-judgment. In other words, the
signal point having the closest distance to the received signal
point is judged as the transmission data. However, at this time,
for example, when attention is given to the received signal points
a and b in FIG. 5, it is found that the four points, which are
closest to the received signal point, have lower two bits
represented by (0, 0) (0, 1) (1, 0) (1, 1), in any of the cases
(corresponding to FIGS. 5(a), (b) and (c)). Therefore, in the
present embodiment, with respect to the lower two bits of the four
signal points (the four points closest to received signal point)
that are more likely to have degradation in the characteristics,
the turbo encoding process having a superior error-correction
capability is applied thereto, and a soft-judgment is carried out
on the receiving side. In contrast, with respect to the other
higher bits that are less likely to have degradation in the
characteristics, these bits are outputted as they are, and a
hard-judgment is made on the receiving side. Here, with respect to
information bit lists u.sub.3, u.sub.4, u.sub.5 and u.sub.6,
v.sub.2, v.sub.3, w.sub.2 and w.sub.3 respectively correspond to
these.
[0053] Thus, in the present embodiment, the characteristics that
might have degradation due to multi-valued levels can be improved,
and since the turbo encoding process is carried out only on the
lower two bits of the received signal, it is possible to greatly
reduce the amount of calculations as compared with the conventional
technique that applies the turbo encoding process to all the
bits.
[0054] The following description will discuss the operation of the
turbo encoder 1 shown in FIG. 4(b) that carries out the turbo
encoding process on the inputted lower two bits of the received
data: u.sub.1 and u.sub.2. FIG. 6 is a drawing that shows the
circuit construction of the turbo encoder 1. Reference numeral 21
denotes a first recursive system convolutional encoder. Reference
numerals 22 and 23 denote interleavers. Reference numeral 24
denotes a second recursive system convolutional encoder, and
reference numeral 25 denotes a deinterleaver. In the turbo encoder
1, the transmission data: u.sub.1k and u.sub.2k (with k
representing the time) corresponding the information list,
redundant data: u.sub.ak obtained by encoding the transmission data
through the process of the first recursive system convolutional
encoder 21 and redundant data: u.sub.bk obtained by encoding the
transmission data that has been interleave-processed through the
second recursive system convolutional encoder 24, and then allowing
it to have the original time through the deinterleave process, are
simultaneously outputted.
[0055] In this manner, in the present embodiment, the arrangement
in which the di-interleaver 25 is added to the second recursive
convolutional encoder 24 as its following stage is used so that the
times of the transmission data and the redundant data are made
coincident with each other; thus, it is possible to efficiently
carry out the calculating processes in the succeeding conversion
2.
[0056] Next, the conversion 2, which has received the two-bit
transmission data: u.sub.1 and u.sub.2 and the two-bit redundant
data: u.sub.a and u.sub.b from the turbo encoder 1, carries out
calculating processes so as to provide uniform correction
capabilities with respect to the transmission data on the receiving
side.
[0057] For example, when the transmission data: u.sub.1 and u.sub.2
and the redundant data: u.sub.a and u.sub.b are transmitted without
the conversion 2, on the receiving side, the original transmission
data: u.sub.1 and u.sub.2 are estimated by using the received
signals: u.sub.a' and u.sub.b' (' represents the received signal
containing influences from noise and phasing in the transmission
path) However, in this case, the received data: u.sub.a'
corresponding to the output of the first recursive system
convolutional encoder 21 and the received data: u.sub.b' outputted
through each interleaver, the second recursive system convolutional
encoder 24 and each di-interleaver are different in their
error-correction capability; therefore, as illustrated in FIG. 7,
they come to have a difference in the probability in bit errors.
Therefore, in the present embodiment, the bit error rates on the
receiving side are uniformed by executing the following computation
formulas:
v.sub.1=u.sub.2+u.sub.a (3)
v.sub.0=u.sub.2 (4)
w.sub.132 u.sub.2+u.sub.1+u.sub.a+u.sub.b (5)
w.sub.0=u.sub.2+u.sub.1 (6)
[0058] Here, the above-mentioned v and w correspond to the
respective tones shown in FIG. 4(a).
[0059] In this manner, in the present embodiment, the turbo encoder
1 and the conversion 2 are provided in the encoder so that the
device can be applied to the communication using the multi-carrier
modem system, and even when the constellation increases due to
multi-valued levels in the modulation system, it is possible to
reduce the amount of calculations, and also to achieve a good
transmitting characteristics in the same manner as the conventional
device. Here, in the present embodiment, the turbo encoder 1 and
the conversion 2 are installed in the encoder; however, the present
invention is not intended to be limited to this arrangement, and
for example, when a difference in the bit error rate is permitted,
the conversion 2 may be omitted, and it is still possible to reduce
the amount of calculations. Moreover, in the present embodiment,
the explanation has been given of the 16 QAM system as an example;
however, the present invention is not intended to be limited by
this, and even in the case of the application to the other
modulation systems (256 QAM system, etc.), the same effects can be
obtained.
[0060] Next, operations of the decoder which is shown in FIG. 1(b)
will be explained now. Here, in the present embodiment, for
example, the 16 QAM system is adopted as the multi-value quadrature
amplitude modulation (QAM), and the following description will
discuss a case in which two tones in the multi-carrier are
subjected to a decoding process. Moreover, in the encoder of the
present embodiment, the turbo encoding process is carried out on
the lower two bits of the received data, and the original
transmission data is estimated by a soft-judgment, and with respect
to the other upper bits, the original transmission data is
estimated by carrying out a hard-judgment on the received data in
the second judging device 19. Here, the received signals Lcy:
v.sub.0, v.sub.1, v.sub.2, v.sub.3, w.sub.0, w.sub.1, w.sub.2,
w.sub.3 are signals obtained by allowing the outputs on the
transmitting side: v.sub.0, v.sub.1, v.sub.2, v.sub.3, w.sub.0,
w.sub.1, w.sub.2, w.sub.3 to contain influences from noise and
phasing due to the transmission path.
[0061] First, in the turbo encoder, upon receipt of the signals
Lcy: v.sub.0, v.sub.1, w.sub.0, w.sub.1, the first decoder 11
calculates the logarithm likelihood ratio: L(u.sub.1k'),
L(u.sub.2k') (with k representing the time) of estimated bits:
u.sub.1k', u.sub.2k' estimated by these received signals. Here,
with respect to the decoder for calculating the logarithm
likelihood ratio, for example, the known maximum A-Posteriori (MAP
algorithm) is often used; however, for example, the known Vitabi
decoder may be used.
[0062] In this case, the logarithm likelihood ratio: L (u.sub.1k'),
L (u.sub.2k') are represented by the following equations: 2 L ( u 1
k ' ) = L cy + La ( u 1 k ) + Le ( u 1 k ) = Ln Pr ( u 1 k ' = 1 |
{ Lcy } ) Pr ( u 1 k ' = 0 | { Lcy } ) ( 7 ) L ( u 2 k ' ) = L cy +
La ( u 2 k ) + Le ( u 2 k ) = Ln Pr ( x 2 k ' = 1 | { Lcy } ) Pr (
x 2 k ' = 0 | { Lcy } ) ( 8 )
[0063] Here, in the present embodiment, Le (u.sub.1k), Le
(u.sub.2k) represent external information; La (u.sub.1k), La
(u.sub.2k) represent pre-information that is external information
preceding by one; P.sub.r (u.sub.1k'=1.vertline.{Lcy}) represents
the post-probability of the estimated information bit: u.sub.1k'
being 1 upon receipt of all the lists of the received signals:
{Lcy}; P.sub.r (u.sub.1k'=0.vertline.{Lcy}- ) represents the
post-probability of the estimated information bit: u.sub.1k' being
0; Pr (u.sub.2k'=1.vertline.{Lcy}) represents the post-probability
of the estimated information bit: u.sub.2k' being 1 upon receipt of
all the lists of the received signals: {Lcy}; and P.sub.r
(u.sub.2k'=0.vertline.{Lcy}) represents the post-probability of the
estimated information bit: u.sub.2k' being 0. In other words, in
equations (7) and (8), the probability of u.sub.2k' being 1 with
respect to the probability of u.sub.2k' being 0, and the
probability of u.sub.1k' being 1 with respect to the probability of
u.sub.1k' being 0 are found.
[0064] Next, in the adder 12, external information for the second
decoder 15 is calculated from the logarithm likelihood ratio that
is the above calculation result. The external information: Le
(u.sub.1k), Le (u.sub.2k) is represented as follows based upon the
above-mentioned equations (7) and (8):
Le(u.sub.1k)=L(u.sub.1k')-Lcy-La(u.sub.1k) (9)
Le(u.sub.2k)=L(u.sub.2k')-Lcy-La(u.sub.2k) (10)
[0065] Here, in the first decoding process, since no
pre-information is found, La (u.sub.1k)=0, and La (u.sub.2k)=0.
[0066] Next, in the interleavers 13 and 14, the signals are
re-arranged based upon the received signal Lcy and the external
information Le (u.sub.1k), Le (u.sub.2k). Then, in the second
decoder 15, in the same manner as the first decoder 11, based upon
the received signal Lcy and pre-information: La(u.sub.1k), La
(u.sub.2k) that has been preliminarily calculated, the logarithm
likelihood ratio: L(u.sub.1k'), L(u.sub.2k') is calculated.
Thereafter, in the adder 16, in the same manner as the adder 12,
external information: Le(u.sub.1k), Le(u.sub.2k) is calculated by
using equations (9) and (10). At this time, the external
information, re-arranged by the deinterleave 17, is fedback to the
first decoder 11 as the pre-information: La(u.sub.1k), La
(u.sub.2k).
[0067] Thereafter, in the above-mentioned turbo decoder, the
above-mentioned processes are repeated predetermined times so that
the logarithm likelihood ratio with higher precision is calculated;
and lastly, the first judging device 18 judges the signals based
upon the logarithm likelihood ratio so as to estimate the original
transmission data. More specifically, for example, if the logarithm
likelihood ratio shows "L(u.sub.1k')>0"; then, u.sub.1k' is
judged as 1, and if it shows "L(u.sub.1k').ltoreq.0"; then,
u.sub.1k' is judged as 0; in the same manner, if the logarithm
likelihood ratio shows "L(u.sub.2k') >0"; then, u.sub.2k' is
judged as 1, and if it shows "L(u.sub.2k') .ltoreq.0"; then,
u.sub.2k' is judged as 0. Here, with respect to the received
signals Lcy: v.sub.2, v.sub.3, w.sub.2, w.sub.3 that are
simultaneously received, they are hard-judged by using the second
judging device 19.
[0068] In this manner, in the present embodiment, even when the
constellation increases as the modulation system is multi-valued,
the turbo decoder for carrying out a soft-judgment on the lower two
bits of the received signal that are more susceptible to
degradation in the characteristics and the judging device for
carrying out a hard-judgment on the other bits of the received
signal are provided; thus, it is possible to reduce the
soft-judgment portions having a great amount of calculations, and
also to achieve a good transmitting characteristic in the same
manner as the conventional device. Additionally, in the
transmission path having random errors and burst errors in a mixed
manner as described in the present embodiment, by adopting the R-S
codes (Reed Solomon) for carrying out error corrections on a symbol
basis and other known error-correction codes in a combined manner,
it is possible to obtain a further superior transmission
characteristic.
[0069] As described above, in accordance with the present
invention, the communication device is made applicable to
communication using the multi-carrier modem system, and is provided
with a turbo encoding unit and a computing unit. Therefore, even
when the constellation increases as the modulation system is
multi-valued, it is possible to reduce the amount of calculations,
and also to achieve a good transmitting characteristic in the same
manner as the conventional device. Moreover, a soft-judgment is
carried out on the lower two bits of the received signal that are
more susceptible to degradation in the characteristics, and a
hard-judgment is carried out on the other bits of the received
signal. Therefore, even when the constellation increases as the
modulation system is multi-valued, it is possible to provide a
communication device which can reduce the soft-judgment portions
having a great amount of calculations, and also achieve a good
transmitting characteristic in the same manner as the conventional
device.
[0070] In accordance with the next invention, the communication
device has an arrangement in which a deinterleave processing unit
is added to the turbo encoding unit so that the times of the
transmission data and redundant data are made coincident with each
other. Therefore, it is possible to provide a communication device
which can effectively carry out calculation processes in the
succeeding computing unit.
[0071] In accordance with the next invention, even in a
transmission path having random errors and burst errors in a mixed
manner, since the R-S codes for carrying out error corrections on a
symbol basis are combinedly used, it becomes possible to provide a
communication device which can provide a further superior
transmission characteristic.
[0072] In accordance with the next invention, the communication
device is made applicable to communication using the multi-carrier
modem system, and is provided with a turbo encoding unit and a
computing unit. Therefore, even when the constellation increases as
the modulation system is multi-valued, it is possible to reduce the
amount of calculations, and also to achieve a good transmitting
characteristic in the same manner as the conventional device.
[0073] In accordance with the next invention, the communication
device has an arrangement in which a deinterleave processing unit
is added to the turbo encoding unit so that the times of the
transmission data and redundant data are made coincident with each
other. Therefore, it is possible to provide a communication device
which can effectively carry out calculation processes in the
succeeding computing unit.
[0074] In accordance with the next invention, when a difference in
the bit error rate with respect to respective information bits is
permitted, the computing unit may be omitted, and it is possible to
further reduce the amount of calculations.
[0075] In accordance with the next invention, even in a
transmission path having random errors and burst errors in a mixed
manner, since the R-S codes for carrying out error corrections on a
symbol basis are combinedly used, it becomes possible to provide a
further superior transmission characteristic.
[0076] In accordance with the next invention, a soft-judgment is
carried out on the lower two bits of the received signal that are
more susceptible to degradation in the characteristics, and a
hard-judgment is carried out on the other bits of the received
signal; thus, even when the constellation increases as the
modulation system is multi-valued, it is possible to provide a
communication device which can reduce the soft-judgment portions
having a great amount of calculations, and also achieve a good
transmitting characteristic in the same manner as the conventional
device.
[0077] In accordance with the next invention, even in a
transmission path having random errors and burst errors in a mixed
manner, since the R-S codes for carrying out error corrections on a
symbol basis are combinedly used, it becomes possible to provide a
further superior transmission characteristic.
[0078] In accordance with the next invention, the communication
made is made applicable to communication using the multi-carrier
modem system, and is provided with a turbo encoding unit and a
computing unit. Therefore, even when the constellation increases as
the modulation system is multi-valued, it is possible to reduce the
amount of calculations, and also to achieve a good transmitting
characteristic in the same manner as the conventional method.
Moreover, a soft-judgment is carried out on the lower two bits of
the received signal that are more susceptible to degradation in the
characteristics, and a hard-judgment is carried out on the other
bits of the received signal. Therefore, even when the constellation
increases as the modulation system is multi-valued, it is possible
to provide a communication method which can reduce the
soft-judgment portions having a great amount of calculations, and
also achieve a good transmitting characteristic in the same manner
as the conventional method.
[0079] In accordance with the next invention, a deinterleave
processing step is added to the turbo encoding step so that the
times of the transmission data and redundant data are made
coincident with each other; therefore, it is possible to provide a
communication method which can effectively carry out calculation
processes in the succeeding computing step.
[0080] In accordance with the next invention, even in a
transmission path having random errors and burst errors in a mixed
manner, since the R-S codes for carrying out error corrections on a
symbol basis are combinedly used, it becomes possible to provide a
communication method which achieve a further superior transmission
characteristic.
[0081] Industrial Applicability
[0082] As described above, the communication device in accordance
with the present invention is effectively applied to data
communications using the DMT (Discrete Multi Tone) modem system and
the OFDM (Orthogonal Frequency Division Multiplex) modem system,
and in particular, to xDSL communication systems such as the xDSL
communication systems including an ADSL (Asymmetric Digital
Subscriber Line) communication system and an HDSL (high-bit-rate
Digital Subscriber Line) communication system that execute a
high-speed digital communication with several mega bits/second by
using the existing telephone lines.
* * * * *