TCM decoder and decoding method thereof

Details TCM decoder and decoding method thereof TCM decoder and decoding method thereof

1998-12-30

2001-07-03

Britton, Howard (Department: 2713)

Pulse or digital communications

Bandwidth reduction or expansion

Television or motion video signal

C348S607000, C375S265000, C375S341000

Reexamination Certificate

active

06256352

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a trellis-coded modulation (TCM) decoder and a decoding method thereof, and more particularly, to a TCM decoder for a digital television receiver and a decoding method thereof.
2. Description of the Related Art
A grand alliance (GA)-HDTV which has been developed in the United States in accordance with the study of a large-scale screen and high resolution television, has adopted a vestigial side band (VSB) modulation of a digital transmission method, which is called a GA-VSB system.
One of characteristics of the GA-VSB system selected as the standard for American terrestrial HDTV broadcasting is to employ trellis-coded modulation (TCM) for increasing noise immunity. The TCM which concurrently applies a function of error correction to a conventional modulation technique, can increase transmission efficiency without increase in the bandwidth.
The structure of a TCM coder of the GA-VSB system is shown in FIG.
1
A. In the TCM coder, one bit I
2
of 2-bit input I
1
I
2
is input to a convolution coder
106
, which has a 2-bit output O
2
O
3
, and the other bit I
1
of 2-bit input I
1
I
2
is input to a precoder
100
, corresponding to an NTSC rejection filter used for a receiver of the GA-VSB system, which generates a 1-bit output O
1
.
If 3-bits O
1
O
2
O
3
are input to a mapper
114
, one symbol M
OUT
is output. M
OUT
has one of 8 levels corresponding to the respective 3-bit sequence O
1
O
2
O
3
as shown in the table of FIG.
1
B. Here, delays
104
,
108
and
112
indicated by the designation “D”, delay input data by a 12-symbol interval and have the same effect as that obtained by parallel-processing 12 coders having a unit delay, which is called 12-symbol interleaving. The 12-symbol interleaving can reduce a burst type noise, and the number of states of the TCM decoder increases when an NTSC rejection filter is used for a receiver, which is one of characteristics of the GA-VSB system.
The Trellis diagram of
FIG. 2
shows the state of the TCM coder shown in FIG.
1
A. The number of memories, which corresponds to delays, of a convolution coder
106
of
FIG. 1A
, is two, so that the total state number is four, and the convolution-uncoded bit is one, so that the number of parallel paths indicating the number of transition types is two. For example, in order to transit to the next state 00 when the previous state is 10, input data I
1
I
2
of the coder are 01 and 11, and two types of parallel paths are obtained.
The function of the TCM coder of the GA-VSB system of
FIG. 1A
is disclosed in Grand Alliance HDTV System Specification, submitted to the ACATS Technical Subgroup, February 1994, but the structure of the TCM decoder has not been disclosed.
SUMMARY OF THE INVENTION
It is an objective of the present invention to provide a TCM decoder realized by simple hardware for a GA-VSB system.
It is another objective of the present invention to provide a TCM decoder capable of decoding in a 12-symbol unit corresponding to 12-symbol interleaving and of decoding corresponding both when the NTSC rejection filter for the GA-VSB system is used and when it is not used.
It is still another objective of the present invention to provide a TCM decoding method for a GA-VSB system.
Accordingly, to achieve the first and second objectives, a TCM decoder according to the present invention includes: a branch metric generator calculating a Euclidian distance between a received input data and a reference signal, corresponding to the case of 8-state passing through the comb filter and the case of 4-state without passing through the comb filter, and generating a branch metric value of a path having the smallest value from parallel-transited paths, according to each state and a parallel-transition path select signal wherein said each state is based on a trellis state diagram having transition so that the structure for the 4-state and the 8-state is shared; an addition-comparison selector adding a branch metric value with respect to the parallel-transited path obtained by the branch metric generator to a previous accumulated path metric value, and comparing the added results according to each state to generate the smallest path metric value and a corresponding path select signal; and a trace-back memory tracing-back the trellis using the path select signal and the path metric values of each state, corresponding to both the 4-state and the 8-state, to thereby decode an original signal, in units of a predetermined number of symbols corresponding to interleaving in units of the predetermined number of symbols.
To achieve the third objective, a TCM decoding method decoding signals to 4-state or 8-state in accordance with whether to use a comb filter for removing the effect of an NTSC signal includes the steps of: calculating a Euclidian distance between received input data corresponding to the case of 8-state passing through the comb filter and the case of 4-state without passing through the comb filter and a reference signal, and generating a branch metric value of a path having the smallest value from the parallel-transited paths according to each state and a parallel-transition path select signal, wherein said each state is based on a trellis state diagram having transition to share the 4-state and 8-state, adding a branch metric value with respect to a generated parallel-transited path to a previous accumulated path metric value, comparing the added result in accordance with each of the states to accordingly generate a path metric value of the smallest state value and a corresponding path select signal, and tracing-back the trellis using the path select signal and the path metric value of each state, corresponding to both the 4-state and the 8-state, to thereby decode an original signal in units of a predetermined number of symbols corresponding to interleaving in units of the predetermined number of symbols.


REFERENCES:
patent: 5583889 (1996-12-01), Citta et al.
patent: 5594496 (1997-01-01), Nielsen et al.
patent: 5636251 (1997-06-01), Citta et al.
patent: 5875001 (1999-02-01), Kwak

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