Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
2000-05-10
2004-06-29
Tu, Christine T. (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
Reexamination Certificate
active
06757865
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a turbo-code error correcting decoder, a turbo-code error correction decoding method, a turbo-code decoding apparatus, and a turbo-code decoding system for decoding a coded sequence which has been submitted to turbo-coding in a wireless communication device or other communication fields.
2. Description of the Related Art
Referring to
FIG. 26
, there is shown a block diagram of a constitution of a general turbo encoding apparatus.
In
FIG. 26
, reference numerals
301
,
302
,
303
,
304
,
305
,
306
, and
307
designate a first systematic convolutional encoder, a second systematic convolutional encoder, an interleaver, an input point, a first sequence output point, a second sequence output point, and a third sequence output point, respectively.
Referring to
FIG. 27
, there is shown a block diagram of a constitution of a conventional turbo-code decoding apparatus described in “Turbo Code for Deep-Space Communications” (P. 29 to P. 39, D. Divsalar and F. Pollara, Feb. 15 in 1995) in the TDA Progress Report.
In
FIG. 27
, reference numerals
401
,
402
,
403
,
404
,
405
,
406
,
407
,
408
,
409
,
410
, and
411
designate a first MAP decoder for an error correction decoding called an MAP decoding on a first sequence and a second sequence encoded by the first systematic convolutional encoder
301
in
FIG. 26
, a second MAP decoder for an error correction decoding called an MAP. decoding on a first sequence and a third sequence encoded by the second systematic convolutional encoder
302
, a first interleaver, a second interleaver, a first deinterleaver, a second deinterleaver, a hard decision circuit for generating hard decision information from soft decision information, a first sequence input point, a second sequence input point, a third sequence input point, and an output point.
Operations of the first interleaver
403
and the second interleaver
404
are the same as for those of the interleaver
303
of the turbo encoding apparatus in FIG.
26
. In addition, the first deinterleaver
405
and the second deinterleaver
406
change an order of data in a procedure reverse to that of the interleaver
303
.
Referring to
FIG. 28
, there is shown a flowchart of an operation for error correction decoding with the first MAP decoder. The second MAP decoder performs the same operation.
In
FIG. 28
, there are shown a step S
201
of setting an initial value, a step S
202
of calculating a state transition probability, a step S
203
of calculating a probability of a transition to each state at tracing a path in a forward direction, a step S
204
of calculating a probability of a transition to each state at tracing a path in a backward direction, and a step S
205
of calculating soft decision information after decoding on the basis of values calculated in Steps S
202
, S
203
, and S
204
, respectively.
Next, an operation of the turbo encoding apparatus is described below with reference to FIG.
26
.
In the turbo encoding apparatus, N bits of an information sequence is input from the input point
304
and output from the first output point
305
as the first sequence directly. In addition, N bits of the input information sequence is also entered into the first systematic convolutional encoder
301
in the same order and N bits of the sequence is output from the second output point
306
as the second sequence. Furthermore, N bits of the input information sequence is converted to one having a different order in the interleaver
303
and then entered into the second systematic convolutional encoder
302
to output N bits of the sequence as the third sequence from the third output point
307
.
The first, second, and third sequences each having N bits and generated in this manner are combined so as to be a coded sequence and then transmitted through a communication line or transmitted as a radiowave.
Next, an operation of a turbo-code decoding apparatus on a reception side is described below with reference to FIG.
27
.
The transmitted coded sequence is received with errors appended. The received sequence is separated to the first, the second, and the third sequences, which are input from the first input point
408
, the second input point
409
, and the third input point
410
to the turbo-code decoding apparatus, respectively.
The first MAP decoder
401
generates soft decision information L
1
after decoding from the first sequence, the second sequence, and value L
1
* generated on the basis of the soft decision information generated in the second MAP decoder
402
in the previous stage. At the first decoding, however, an L
1
* value entered in the first MAP decoder
401
is set to zero (0) as the lowest reliability for all the bits. Next, it generates L
1
−L
1
* and enters it to the first interleaver
403
and its order is changed so as to be L
2
*.
Next, the second MAP decoder
402
generates soft decision information L
2
after decoding from the first sequence interleaved by the second interleaver
404
, the third sequence, and L
2
* generated by the first interleaver
403
. L
2
−L
2
* is calculated for the generated L
2
and its order is changed so as to be L
1
* in the first deinterleaver
405
. L
1
* is used in the first MAP decoder
401
when L
1
* is repeatedly decoded.
This operation is repeated by the predetermined number of times. When the decoding operation is terminated, the second deinterleaver
406
changes an order of the soft decision information L
2
generated by the second MAP decoder
402
and the hard decision circuit
407
judges whether it is 0 or 1 and outputs the result from the output point
411
. Subsequently, an operation of the first MAP decoder
401
is described below with reference to a flowchart in FIG.
28
. The second MAP decoder
402
performs the same operation.
In Step S
201
, an initial value is set for a transition probability in the state in the forward direction and in the state in the backward direction. Next in Step S
202
, a channel state is measured based on the received soft decision information and a state transition probability is calculated in accordance with a state of the channel. Then, in Step S
203
calculation is made for a probability of a transition to each state when a path is traced in the forward direction from the state transition probability calculated in Step S
202
, and in Step S
204
calculation is made for a probability of a transition to each state when a path is traced in the backward direction from the state transition probability calculated in Step S
202
. Finally in Step S
205
, soft decision information after decoding is calculated on the basis of the values calculated in Steps S
202
, S
203
, and S
204
.
In a conventional turbo-code decoding apparatus, however, it is necessary to calculate a state transition probability in an execution of MAP decoding for convolutional codes composing turbo-codes in an error correcting decoder and the calculation of the probability requires a measurement of a state of a channel on the basis of soft decision information, by which an arithmetic operation amount is enormously increased disadvantageously.
Furthermore, in order to increase a precision of decoding, error correction decoding processing needs to be performed by a regular number of times with the first MAP decoder and the second MAP decoder until hard decision information is obtained. This number of times, however, is a fixed value and therefore processing is performed even if almost no error occurs, by which the processing is disadvantageously delayed by an intrinsically unnecessary time period.
In addition, only a single coded sequence can be input to a turbo-code decoder, and therefore the second MAP decoder is put in an idle state for a time period during which processing is performed by the first MAP decoder, thereby disadvantageously lowering a processing efficiency.
SUMMARY OF THE INVENTION
The present invention is provided to solve the above problems. It is a first object of the present invention to reduce a calculati
Fujita Hachiro
Nakamura Takahiko
Yoshida Hideo
Birch & Stewart Kolasch & Birch, LLP
Mitsubishi Denki & Kabushiki Kaisha
Tu Christine T.
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