Encoding device

Details Encoding device Encoding device

2001-08-17

2003-05-06

Moise, Emmanuel L. (Department: 2133)

Error detection/correction and fault detection/recovery

Pulse or data error handling

Digital data error correction

C714S788000, C714S790000, C375S295000, C375S340000

Reexamination Certificate

active

06560748

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an error-correcting code, and more specifically to a communications system using an error-correcting code, and an encoding device and a decoding device used in the communications system.
2. Description of the Related Art
In a new generation communications system for realizing multimedia communications, high-speed and high-quality data transmission is required. Especially, in a mobile communications system frequently incurring transmission errors, research and development are actively performed to reduce the errors.
An error-correcting code is well-known as an aspect of the technology of transmitting data with high quality. The error-correcting code refers to the technology of, for example, detecting or correcting an error generated in a transmission path.
FIG. 1
shows an example of the configuration of an existing encoding device using an error-correcting code. An encoding device
10
includes a plurality of encoding units (an encoding unit
11
a
and an encoding unit
11
b
in
FIG. 1
) arranged in parallel to each other. Here, a code obtained from a plurality of encoding units arranged in parallel to each other is referred to as “parallel concatenation codes” or “turbo codes”. The parallel concatenation code has attracted much attention as the technology for realizing a high-speed and high-quality communications system.
The encoding device
10
outputs an encoded data sequence obtained by adding parity bits to source data when the source data is input. That is, the encoding device
10
generates a data sequence x and a parity data sequence y to correct the data sequence x for input source data u, and then multiplexes and outputs them. An output sequence z is the encoded data of the source data u. The encoding device has the configuration of performing an encoding operation in N bit units, and the source data u is a data sequence of N bits.
The input source data u is provided for a multiplexing unit
14
as the data sequence x to be transmitted. At the same time, the source data u is provided for the encoding unit
11
a
, and also provided for the encoding unit
11
b
through an interleaver
12
. The interleaver
12
temporarily stores the input source data u of N bits, and then reads and outputs the stored source data u in an order different from the input order. That is, the interleaver
12
rearranges the order of the data elements forming the source data u. Thus, the source data u is randomized. The output of the interleaver
12
is provided as a data sequence v for the encoding unit
11
b
. As a result, the encoding units
11
a
and
11
b
receives different data sequence from each other.
The encoding unit
11
a
generates a parity data sequence y
1
for the received source data u, and the encoding unit
11
b
generates a parity data sequence y
2
for the received data sequence v. Each of the encoding units
11
a
and
11
b
performs a convolutional encoding process.
A puncturing unit
13
selects the output of the encoding units
11
a
and
11
b
based on a predetermined selection pattern (puncturing pattern). The puncturing unit
13
normally selects 1 bit each from the output of the encoding units
11
a
and
11
b
alternately. In this case, the parity data sequence y output from the puncturing unit
13
includes the first bit of the sequence y
1
, the second bit of the sequence y
2
, the third bit of the sequence y
1
, the fourth bit of the sequence y
2
, and so forth. The encoding device
10
can also use a desired selection pattern depending on a requested encoding rate.
The multiplexing unit
14
multiplexes the data sequence x and the parity data sequence y for correction of the data sequence x, and outputs the result as the data sequence z.
The encoding device shown in
FIG. 1
is disclosed in detail by the U.S. Pat. No. 5,446,747.
FIG. 2
shows the characteristic of a code. “BER” refers to a bit error rate. “Eb/No” refers to the energy per bit for specific noise.
The characteristic of a code is normally evaluated by the “energy per bit required to obtain a specific bit error rate”. For example, an excellent code requires less energy per bit to obtain a specified bit error rate. In other word, an excellent code provides a lower bit error rate when a signal is transmitted with specified energy per bit.
A line
1
shows a result of the simulation of the characteristic when the encoding device shown in
FIG. 1
is used. The characteristic is much more excellent than that obtained when the conventional code other than the parallel concatenation code is used.
However, it is known that an error floor phenomenon occurs when a parallel concatenation code is used. The error floor phenomenon means a phenomenon that the tilt of the bit error rate to an “Eb/No” becomes smaller when the “Eb/No” increases. That is, the bit error rate basically lowers when the “Eb/No” increases, but the bit error rate hardly changes when the error floor phenomenon occurs although the “Eb/No” increases. For example, in the example shown in
FIG. 2
, it is desired that the line
1
indicates the characteristic as shown by broken lines. However, the error floor phenomenon practically occurs, and the characteristic shown in the solid line is obtained.
It is estimated that the error floor phenomenon occurs due to the shortest distance.
As a technology for suppressing the error floor phenomenon, a method of increasing the number of encoding units provided in parallel into three or more as shown in
FIG. 3
is known. This technology is often referred to as a “multi-dimensional turbo codes”.
In
FIG. 2
, a line
2
shows a result of the simulation of the characteristic when the multi-dimensional turbo code is used. Using the multi-dimensional turbo code, no error floor phenomenon occurs at least in the simulation. Therefore, a smaller “Eb/No” is required to obtain high transmission quality. In the example shown in
FIG. 2
, when a multi-dimensional turbo code is used, the energy required to obtain high transmission quality of the bit error rate of 10
−5
or lower is less than the energy required when the encoding device shown in
FIG. 1
is used.
However, when a multi-dimensional turbo code is used, the bit error rate sharply deteriorates when the “Eb/No” decreases. In the example shown in
FIG. 2
, when the “Eb/No” is equal to “1” or smaller, the characteristic obtained when the multi-dimensional turbo code is used is inferior to the characteristic obtained when the encoding device shown in
FIG. 1
is used.
In addition, when the multi-dimensional turbo code is used, the configuration of a decoding device becomes complicated. That is, the decoding device basically requires decoding units which are to be equal in number to the encoding units provided for the encoding device. Therefore, when the number of the encoding units provided in parallel increases, the number of the decoding units provided for the decoding device increases correspondingly. Therefore, the multi-dimensional turbo code prevents the realization of a smaller and cost-saving decoding device.
Thus, in the conventional technology, a encoding-decoding system cannot successfully improve the transmission characteristic with a smaller and cost-saving decoding device realized.
The present invention aims at providing an encoding-decoding system capable of obtaining an excellent transmission characteristic without a complicated configuration of a decoding device.
SUMMARY OF THE INVENTION
The encoding device according to the present invention includes a first encoding unit, a plurality of randomizing units, a second encoding unit, and an output unit. The first encoding unit encodes source data or a data sequence obtained by randomizing the source data. The plurality of randomizing units generate data sequence different from each other by randomizing the source data. The second encoding unit encodes the output from the plurality of the randomizing units. The output unit outputs the source data, and the parity data obtained based on the output from the

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