Pulse or digital communications – Transmitters
Reexamination Certificate
1999-12-30
2003-09-16
Chin, Stephen (Department: 2634)
Pulse or digital communications
Transmitters
C375S265000, C375S259000, C714S786000, C714S790000
Reexamination Certificate
active
06621873
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a puncturing device and method for a turbo encoder in a mobile communication system, and in particular, to a puncturing device and method for minimizing puncturing of tail symbols.
2. Description of the Related Art
In mobile communication systems such as satellite, ISDN (Integrated Services Digital Network), digital cellular, W-CDMA (Wideband Code Division Multiple Access) and IMT-2000 communication systems, a channel codec punctures encoded data in order to match symbol rates during transmission of data having different data rates. In particular, the IMT-2000 system can use either a convolutional encoder or a turbo encoder. However, in either case, the rates of the output symbols should be identical to one another because an interleaver typically follows the encoder and has the same memory capacity for storing the symbols.
Generally, the number of output nodes of the convolutional encoder is equal to a code rate. However, in the turbo specific encoder, the number of output nodes is not equal to the code rate and therefore puncturing should be performed to match the code rate. At this point, the tail symbols output from the turbo encoder are also punctured according to the same puncturing pattern as that used for the parity part of the code symbol.
In the convolutional encoder and the turbo encoder, the number of tail symbols required for termination varies depending on the code rate. For example, a constraint; length K=9 convolutional encoder requires (8×(1/code rate)) tail symbols, Column A of Table 1, and a K=4 turbo encoder requires 3×6=18 tail symbols regardless of the code rate (when using two component encoders and separate termination), Column B of Table 1. Therefore, turbo encoder has extra symbols (or reserved symbols, Column C of Table 1) except for the case of the code rate 1/2, as compared with the convolutional encoder. The extra symbols correspond to the difference between Columns A and B and are equal to 0 if negative. When using the turbo encoder, for symbol rate matching, invalid information.(‘0’ or ‘1’ which is known to the receiving side) is added to the reserved symbols to create a frame. Herein, the invalid information added for symbol rate matching will be referred to as invalid symbols. Column C of Table 1 below shows the invalid number of symbols.
TABLE 1
Tail Symbols for
Convolutional
Tail Symbols for
Reserved Symbol
Code Rate
Code (A)
Turbo Code (B)
Number (C)
R = 1/2
16(=8 × 2)
18(=3 × 6)
0 bit
R = 1/3
24(=8 × 3)
18(=3 × 6)
6 bits
R = 1/4
32(=8 × 4)
18(=3 × 6)
14 bits
FIG. 1
shows a conceptional block diagram of a common turbo encoder. A description will be made of an operation of puncturing a turbo code, with reference to FIG.
1
.
The turbo encoder comprises a first encoder
110
, an interleaver
130
and a second encoder
120
, and receives an L-bit information frame X. The first encoder
110
encodes the L-bit one information frame X, which is source data, into a first systematic symbol L, a first L-bit parity symbol Y
0
, a second L-bit parity symbol Y
1
, and m bit tail symbols for each of the parity signals Y
0
, Y
1
and m tail symbols for first systematic symbol X. The m tail symbols for first systematic symbol L are a tail bit itself, generated by first encoder terminating memory of the encoder. The m tail symbols are generated when the first encoder receives the last three bits of the tail bit, thereby to reset a shift register in the first encoder
110
. Further, the information frame X is output, as it is, without coding, and only the m tail symbols for the information frame X are created by the first encoder
110
. The interleaver
130
interleaves the input one frame data X and outputs interleaved source data X′. The second encoder
120
encodes the interleaved source data X′ into a third parity symbol Y′
0
, a fourth parity symbol Y′
1
, and m tail symbols for each of the parity symbol Y′
0
, Y′
1
and m tail symbols for second systematic symbol L′. The m tail symbols for second systematic symbol L′ are a tail bit itself, generated by second encoder terminating memory of the encoder. The second encoder can output second systematic symbol X′, but all of the second systematic symbol X′ is punctured at all of the code rate. Therefore, it is equal to do not output the second systematic symbol X′. In this specification, we describe the turbo encoder outputs several coded symbol frames X, Y
0
, Y
1
, Y′
0
and Y′
1
in response to an input frame, and excluding the interleaved information frame X′, and m tail symbols for each of the signals X, Y
0
, Y
1
, Y′
0
, Y′
1
and X′. Commonly, there are provided 3 tail symbols for each of the coded symbol frame. However, it is also possible to output the interleaved frame X′, as it is, and then delete it in the following stage by puncturing.
Such a turbo encoder internally creates the five coded symbol frames and six sets of tail symbols using one input information frame. The five coded symbol frames and six sets of tail symbols should undergo the same puncturing pattern during creation of a transmission frame, for transmission at a previously defined code rate.
For code rate matching, the proposed IMT-2000 system performs select (inversely say puncturing) as shown in Table 2.
TABLE 2
R = 1/2
R = 1/3
R = 1/4
X(t) & X(t)
t = m + i
t = m + i
t = m + i
(Tail Bit)
Y0(t)
None
None
t = m + 2
Y1(t)
Alternate at t = m + 2
t = m + 2
Alternate at t = m + 3
X′(t) (Info
None
None
None
Frame)
X′(t) (Tail
t = m + 3
t = m + 4
t = m + 5
Bit)
(when tail bit X′(t)
selection)
Y′0(t)
None
None
t = m + 4
Y′1(t)
Alternate at t = m + 2
t = m + 3
Alternate at t = m + 3
In Table 2, ‘m’ denotes a given time point, and ‘i’ in m+i (i=1,2,3,4,5, . . . ) denotes the order of selection at the time m. For example, for a code rate R=1/2, at the time m, the systematic frame X is first selected, the encoded information frame Y
0
is punctured all, where “None” means not selected, and one of the encoded symbols Y
1
and Y′
1
is selected and the non selected one (Y
1
OR Y′
1
) is punctured. Further, after the tail symbols for the systematic frame X are selected, one of the tail symbols for the encoded parity symbol frames Y
1
and Y′
1
are selected and the non selected one (Y
1
OR Y′
1
) is punctured and thereafter, the tail symbols for the interleaved frame X′ are selected. After puncturing in this manner, multiplexing is performed to transmit the frame.
FIGS. 2A
to
2
C show puncturing methods according to Table 2, for R=1/2, 1/3 and 1/4, respectively. In the drawings, the hatched boxes denote the tail symbols; and the ‘X’-marked boxes denote the punctured bits. The boxes corresponding to X′(t) are surrounded by a dashed line as they are not output. This can be expressed with the factors output from the turbo encoder as follows, wherein the underlined factors denote the punctured factors (i.e. not selected).
1) For the case of R =1/2:
X(
0
),
Y
0
(
0
)
,Y
1
(
0
),
Y′
0
(
0
),Y′
1
(
0
)
, X(
1
),
Y
0
(
1
),Y
1
(
1
)Y′
0
(
1
)
,Y′
1
(
1
), . . . , X(L−1),
Y
0
(L−1),Y
1
(L−1)Y′
0
(L−1)
Y′
1
(L−1),
T
1
(
0
),TP
11
(
0
),TP
12
(
0
),T
2
(
0
),
TP
21
(
0
),TP
22
(
0
)
,
T
1
(
1
),TP
11
(
1
),TP
12
(
1
),T
2
(
1
),TP
21
(
1
),T
22
(
1
) . . .
T
1
(m−1),TP
11
(m−1),
TP
12
(m−1)
,T
2
(m−1),TP
21
(m−1),
T
22
(m−1)
where T
1
is tail symbol for systematic symbol, TP
11
is tail parity for parity Y
0
, TP
12
IS
Kim Beong-Jo
Kim Min-Goo
Lee Young-Hwan
Chin Stephen
Dilworth & Barrese LLP
Odom Curtis
Samsung Electronics Co,. Ltd.
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