Pulse or digital communications – Transmitters
Reexamination Certificate
1999-11-01
2003-06-17
Vo, Don N. (Department: 2631)
Pulse or digital communications
Transmitters
C375S262000, C375S265000, C375S316000, C714S794000, C714S795000
Reexamination Certificate
active
06580762
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a digital communication system, and in particular to a rate matching method for producing an output string of m symbols from an input string of n (n−m) symbols
2. Description of the Related Art
In the field of digital communication systems, there have been proposed several rate matching methods for obtaining output sequence of m symbols from input sequence of n symbols. In the case of n>m, the first (n−m) symbols of the input symbol string are deleted to produce the output string of the remaining m symbols. In the case of n<m, after repeating a top input symbol (m−n+1) times, m symbols following the top input symbol are output to produce the output string of m symbol.
In the case of the symbol sequence encoded with a convolution code, it is known that the original information can be reproduced correctly, even if the symbol sequence has been partly deleted, by inserting dummy symbols into the imperfect symbol sequence at the positions corresponding to the deleted symbols when decoded. Such error-correction decoding is allowed by the coding gain achieved by a convolution code.
In general, many decoding systems are susceptible to an error burst, and when a number of symbols have been consecutively deleted as mentioned above, they cannot fully exhibit the error correction capability.
On the other hand, in the case where the same symbol is consecutively repeated, the energy of the repeated symbol becomes large in equivalent by using the energy of the repeated symbol effectively. This may allow error rate to be effectively reduced around the repeated symbol. In the case of the convolution code, however, the reduction in error rate for symbols more than the constraint length away from that symbol cannot be expected at all.
To solve these problems to some extent, there has been proposed a rate matching method conforming to IMT-2000 scheme, which is now under standardization by ARIB (Association of Radio Industries and Businesses). The details of this method are described in “Volume 3, Specification of Air-Interface for the 3G Mobile System Version 0.5”. Hereafter, this specification will be described briefly.
Assuming that an input symbol sequence is denoted by S
0
the number of input symbols thereof by n, and the number of output, symbol of an output symbol sequence by m, a symbol-deletion rate matching method (n>m) is performed according to the following algorithm:
(a) j=0, x=n, and y=n−m;
(b) go to step (c) when y is equal to greater than 1, and exit otherwise with the current symbol sequence S being an output sequence;
(c) set z to a minimum integer which is not smaller than x/y;
(d) set k to a maximum integer which is not greater than x/z;
(e) delete a symbol every z symbols from the symbol sequence S
j
and the resultant symbol sequence is denoted by S
j,1
;
(f) x=x−k, y=y−k, and j=j+1; and
(g) go back to step (b).
A symbol-repetition rate matching method (n<m) is performed according to tho following algorithm:
(A) j=0;
(B) go to step (C) when 2n is smaller than m, and go to step (F) otherwise;
(C) repeat all symbols of S
j
one time and the resultant is denoted by S
j+1
;
(D) n=2n, and j=j+1,
(E) go back to step (B);
(F) x=n, and y=m−n;
(G) go to step (H) when y exceeds 1, and go to step (M) otherwise;
(H) set z to a minimum integer which is not smaller than x/y;
(I) set k to a maximum integer which Is not greater than x/z;
(J) repeat S
j
every z symbols unless it has been already repeated, and the resultant symbol sequence is denoted by S
j+1
;
(K) x=x−k, y=y−k, and j=j+1;
(L) go back to step (J); and
(M) when y=1, repeat only the first symbol of S
j
and the resultant symbol sequence is denoted by S
j+1
before exit, and when y in not equal to 1, exit with the current symbol sequence S being an output sequence.
FIG. 15
shows concrete operations of a conventional symbol-deletion rate matching method conforming to the IMT-2000 scheme. Here, it is assumed that the number of input symbols is 128 (n−128) and the number of output symbols is 100 (m−100).
As shown in
FIG. 15A
, symbol sequence S
0
of n=128 is inputted. According to the symbol-deletion rate matching algorithm, the steps (a)-(e) provide x=128, y=28, z=5, and k=25, resulting in a symbol sequence S
1
as shown in FIG.
15
B.
This symbol sequence S
1
is obtained by deleting S
0
every five symbols.
When the steps (a)-(e) are performed for a second time, x =x−k=103, y=y−k=3, z=35, and k=2 are obtained. Therefore the symbol sequence S
1
is deleted every 35 symbols, resulting in a symbol sequence S
2
as shown in FIG.
15
C.
When the steps (a)-(e) are performed for a third time, X=101, y=1, z=101, and k=1 are obtained. Therefore, the symbol sequence S
2
is deleted every 101 symbols that is only the last symbol is deleted, resulting in the final symbol sequence S
3
as shown in FIG.
15
D. Therefore, in this example the input symbol sequence of
128
symbols is converted into the output symbol sequence of 100 symbols by three-time symbol deletion operation.
It will be understood from the example shown in
FIGS. 15A-15D
that each deleting operation (steps (a)-(e)) provides the maximum interval between deleted symbols, resulting in optimum deletion processing, but the optimum deletion processing is not always performed between deleting operations because the relation between the current and the previous deleting operations is not sufficiently taken into account.
More specifically, since the interval between deleted symbols have been maximized in the previous deleting operation, the current deleting operation can provide a symbol-deletion interval equal to or smaller than that of the previous deleting operation (in most cases, a half or less the symbol-deletion interval achieved by the previous deleting operation).
As shown in
FIG. 15B
, the 45th symbol of the symbol sequence S
1
is deleted. Subsequently, the 43rd symbol is deleted as shown in FIG.
15
C. Similarly, the 85th and 87th symbols are deleted. In this case, the distance between deleted symbols is only two symbols.
As described above, according to the conventional algorithm, symbol deletion may be performed at a plurality of consecutive positions depending on the relation between the numbers of input and output symbols. There is a high possibility that the symbol sequence deleted like this causes problems when demodulated and decoded.
Similarly, in the case of symbol-repetition rate matching, the positions of repeated symbols may be distributed unevenly, producing a symbol region susceptible to error and a symbol region resistant to error.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a rate matching method that can achieve more reliable data communication.
According to the present invention, a rate matching method produces m output symbols from n (n≠m) input symbols by a selected one of symbol deletion and symbol repetition depending on a comparison result of n and m, where n and m are an integer greater than 0. The method comprises the step of maximizing a smallest interval between symbols subjected to the selected one of the symbol deletion and the symbol repetition and the step of maximizing a sum total of intervals of symbols subjected to the selected one of the symbol deletion and the symbol repetition.
An interval of symbols subjected to the selected one of the symbol deletion and the symbol repetition may be one of k and k−1, where k is an integer greater than 0.
According to the present invention, a rate matching method for inputting a first symbol string S(k) of n symbols and outputting a second symbol string d(j) of m (n≠m) symbols in a digital communication system, where n and m are
Dickstein Shapiro Morin & Oshinsky LLP.
NEC Corporation
Vo Don N.
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