Pulse or digital communications – Systems using alternating or pulsating current – Plural channels for transmission of a single pulse train
Reexamination Certificate
2001-08-27
2003-01-14
Bocure, Tesfaldet (Department: 2631)
Pulse or digital communications
Systems using alternating or pulsating current
Plural channels for transmission of a single pulse train
C375S295000, C375S341000, C714S784000
Reexamination Certificate
active
06507621
ABSTRACT:
TECHNICAL FIELD
The present invention relates a method of and device for communications that use a multi-carrier modem system, and, more particularly, concerns a communication device which realizes data communication through the existing communication lines by using a system such as the DMT (Discrete Multi Tone) modem system and the OFDM (Orthogonal Frequency Division Multiplex) modem system and a communication method for 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
The conventional communication methods will be explained here. 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.
Operation of transmitting and receiving systems of a conventional communication device using the turbo code will be explained in detail.
FIG. 6
is a drawing that shows the construction of a turbo encoder used in the transmitting system. In FIG.
6
(
a
), reference number
101
is a first recursive system convolutional encoder that subjects an information list to a convolutional encoding process to output redundant bits,
102
is an interleaver, and
103
is 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.
6
(
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.
The turbo encoder, which is arranged as described above, simultaneously outputs an information bit list: x
1
, a redundant bit list: x
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
3
obtained by encoding the information bit list that has been interleaved through the operation of the second recursive system convolutional encoder
103
.
FIG. 7
is a drawing that shows the construction of the turbo decoder that is used in the receiving system. In
FIG. 7
, reference number
111
indicates a first decoder that calculates a logarithm likelihood ratio from the received signals y
1
and y
2
. Reference numbers
112
and
116
indicate adders,
113
and
114
indicate interleavers,
115
indicates a second decoder that calculates a logarithm likelihood ratio from the received signals y
1
and y
3
. Reference number
117
indicates a de-interleaver,
118
indicates a judging device which judges the output of the second decoder
115
to output an estimated value of the original information bit list. The received signals y
1
, y
2
, y
3
are signals that are formed by allowing the information bit list x
1
and the redundant bit lists x
2
, x
3
to include influences from noise and phasing in the transmission path.
In this turbo decoder, first, the first decoder
111
calculates the logarithm likelihood ratio: L (x
1k
′) (where k refers to the time) of estimated information bit: x
1k
′ from received signals: y
1k
and y
2k
. In this case, the logarithm likelihood ratio: L (x
1k
′) is represented by the following equation:
L
(
x
1
k
′
)
=
y
1
k
+
La
(
x
1
k
)
+
Le
(
x
1
k
)
=
Ln
Pr
(
x
1
k
=
1
&LeftBracketingBar;
{
Y
}
)
Pr
(
x
1
k
=
0
&LeftBracketingBar;
{
Y
}
)
(
1
)
In equation (1), Le (x
1k
) represents external information, La (x
1k
) represents preliminary information that is external information preceding by one, P
r
(x
1k
=1|{Y}) represents the probability of an actually transmitted information bit: x
1k
being 1 under the condition that the entire list {Y} of the received signals has been received, and P
r
(x
1k
=0{y}) represents the probability of an actually transmitted information bit: x
1k
being 0 under the condition that the entire list {Y} of the received signals has been received. In other words, equation (1) finds a ratio of the probability of the information bit: x
1k
becoming 1 to the probability of the information bit: x
1k
being 0.
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 equation (1), the external information: Le (x
1k
) is represented by the following equation:
Le
(
x
1k
)=
L
(
x
1k
)−
y
1k
−La
(
x
1k
) (2)
Since no preliminary information has been given at the time of the first decoding process, La (x
1k
)=0.
In the interleavers
113
and
114
, in order to make the received signal: y
1k
and the external information: Le (x
1k
) coincident with the time of the received signal: y
3
, the signals are re-arranged. Then, in the same manner as the first decoder
111
, based upon the received signal: y
1
and the received signal: y
3
as well as the external information: Le (x
1k
) preliminarily calculated, the second decoder
115
calculates a logarithm likelihood ratio: L (x
1k
′). Thereafter, in the same manner as the adder
112
, the adder
116
calculates the external information Le (x
1k
) 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 (x
1k
).
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 (x
1k
′)>0”, the estimated information bit: x
1k
′ is judged as 1, while it shows that “L (x
1k
′)≦0”, the estimated information bit: x
1k
′ is judged as 0.
In this manner, in the conventional communication method, by using the turbo code as the error-correction code, even in the case when the signal point-to-point distance becomes closer as the modulation system is multi-valued, it becomes possible to greatly improve the transmitting property in the voice transmission and data transmission, and consequently to obtain characteristics superior to the known convolutional codes.
However, in the 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
Matsumoto Wataru
Miyata Yoshikuni
Bocure Tesfaldet
Mitsubishi Denki & Kabushiki Kaisha
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