Turbo decoder

Details Turbo decoder Turbo decoder

2000-05-18

2003-02-25

Ton, David (Department: 2133)

Error detection/correction and fault detection/recovery

Pulse or data error handling

Digital data error correction

C714S786000

Reexamination Certificate

active

06526539

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a turbo decoder for decoding a sequence that has been generated according to a turbo-coding scheme.
2. Description of the Related Art
A transmission system using a turbo-decoding scheme can provide, for a desired transmission rate (SN ratio), an SN ratio (transmission rate) that is very close to the maximum SN ratio (transmission rate; generally called the Shannon limit) that is given by Shannon's channel coding theorem, because decoding that conforms to an error correcting coding scheme that was used in the transmitting end is repeatedly performed in the receiving end.
Therefore, the turbo coder and the turbo decoder are promising as devices that can be applied to not only deep space communication but also mobile communication, broadcast, and reproduction systems of magnetic recording media, and applications in these fields are now being studied, developed, and put into practical use enthusiastically.
FIG. 9
is a block diagram showing the configuration of a first example transmission system using a turbo-decoding scheme.
As shown in
FIG. 9
, a transmitting end
90
and a receiving end
91
are connected to each other via a transmission path
92
.
In the transmitting end
90
, transmission information U is supplied to a turbo coder
93
and the outputs of the turbo coder
93
are connected to one ends of the transmission path
92
.
In the turbo coder
93
, the transmission information U is supplied to the inputs of an elementary encoder
94
-
1
and an interleaver (&pgr;)
95
and the output of the interleaver
95
is connected to the input of an elementary encoder
94
-
2
. A transmission sequence consisting of the following items is obtained at the output of the turbo coder
93
:
Code words (non-coded words) Xa that have been generated without coding processing applied to the transmission information U.
Code words Xb that have been generated with prescribed error correcting coding processing applied to the transmission information U in the elementary encoder
94
-
1
.
Code words Xc that have been generated with prescribed error correcting coding processing applied to the transmission information U in the elementary encoder
94
-
2
.
In the receiving end
91
, a received sequence consisting of words ya, yb, and yc that have been transmitted over the transmission path
92
, correspond to the respective code words Xa, Xb, and Xc, and are obtained as results of soft decision is supplied to corresponding inputs of a receive buffer
96
.
In general, the received sequence is deteriorated in SN ratio because of a fluctuation of the transmission characteristics of the transmission path
92
and noise that has been superimposed in the transmission path
92
.
Among the outputs of the receive buffer
96
, the output corresponding to the words ya is connected to the first input of an elementary decoder
97
-
1
and the input of an interleaver (&pgr;)
98
-
1
. The output of the interleaver
98
-
1
is connected to the first input of an elementary decoder
97
-
2
. Among the outputs of the receive buffer
96
, the outputs corresponding to the words yb and yc are connected to the second inputs of the respective elementary decoders
97
-
1
and
97
-
2
. The output of the elementary decoder
97
-
1
is connected to the third input of the elementary decoder
97
-
2
via an interleaver
98
-
2
. One output of the elementary decoder
97
-
2
is connected to the third input of the elementary decoder
97
-
1
via a de-interleaver (&pgr;−1)
99
-
1
, and the other output of the elementary decoder
97
-
2
is connected to the input of a de-interleaver (&pgr;−1)
99
-
2
. A decoding result is obtained at the output of the de-interleaver
99
-
2
.
For the sake of simplicity, it is assumed that the coding that is performed by each of the elementary coders
94
-
1
and
94
-
2
is convolutional coding using a common constraint length and rate of coding.
In the above-configured receiving end
91
, a received sequence that has been transmitted over the transmission path
92
is separated into words ya, yb, and yc on a prescribed code block basis and stored in storage areas of the receive buffer
96
corresponding to the respective kinds of words ya, yb, and yc.
The elementary decoders
97
-
1
and
97
-
2
, the interleavers
98
-
1
and
98
-
2
, and the de-interleavers
99
-
1
and
99
-
2
are initialized prior to a start of decoding processing to be performed on those code blocks.
After completion of the initialization, the elementary decoder
97
-
1
outputs a likelihood L
1
by performing decoding processing that conforms to the coding processing that was performed by the elementary coder
94
-
1
in the transmitting end
90
on a likelihood that is supplied from the elementary decoder
97
-
2
via the de-interleaver
99
-
1
and words ya and yb that are supplied from the receive buffer
96
on a bit-by-bit basis.
The interleavers
98
-
1
and
98
-
2
perform the same interleave processing as performed by the interleaver
95
in the transmitting end
90
on the word ya that is supplied parallel from the receive buffer
96
and the likelihood L
1
, respectively.
The elementary decoder
97
-
2
outputs a likelihood L
2
and a demodulation result (for simplicity, it is assumed here that the demodulation result is obtained as a result of hard decision) by performing decoding processing that conforms to the coding processing that was performed by the elementary coder
94
-
2
in the transmitting end
90
on results of the above interleave processing and a word yc that is supplied from the receive buffer
96
on a bit-by-bit. basis.
The de-interleaver
99
-
2
outputs a most probable decoding result for the transmission information U by de-interleaving the demodulation result in the same manner as the de-interleaver
99
-
1
does.
In the receiving end
91
, the elementary decoders
97
-
1
and
97
-
2
, the interleavers
98
-
1
and
98
-
2
, and the de-interleavers
99
-
1
and
99
-
2
cooperate to repeatedly perform, together with the receive buffer
96
, the above processing on a bit-by-bit basis a prescribed number of times.
Since at the output of the de-interleaver
99
-
2
the above-mentioned likelihood is increased gradually during the course of the decoding that is repeated in the above-described manner, transmission information could be obtained that has been restored with higher precision than in a transmission system using a concatenated code.
FIG. 10
is a block diagram showing the configuration of a second transmission system using a turbo-decoding scheme.
The components in
FIG. 10
having the same function and configuration as the corresponding components in
FIG. 9
are given the same reference symbols as the latter and will not be described below.
The transmission system of
FIG. 10
is different in configuration from that of
FIG. 9
in a receiving end
91
A that replaces the receiving end
91
.
In the receiving end
91
A, as indicated by two-dot-chain-line frames in
FIGS. 9 and 10
, decoding processing corresponding to the coding processing performed by the elementary coder
94
-
1
in the transmitting end
90
and decoding processing corresponding to the coding processing performed under cooperation between the interleaver
95
and the elementary coder
94
-
2
are performed in order that is reverse to the order in the receiving end
91
shown in FIG.
9
.
Therefore, a most probable decoding result for transmission information U is obtained at the output of the elementary decoder
97
-
1
without intervention of the de-interleaver
99
-
2
.
FIG. 11
is a block diagram showing the configuration of a third transmission system using a turbo-decoding scheme.
The components in
FIG. 11
having the same function and configuration as the corresponding components in
FIG. 9
are given the same reference symbols as the latter and will not be described below.
The transmission system of
FIG. 11
is different in configuration from that of
FIG. 9
in a receiving end
91
B that replaces t

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