Television – Image signal processing circuitry specific to television – Noise or undesired signal reduction
Reexamination Certificate
1999-12-30
2003-02-04
Miller, John (Department: 2614)
Television
Image signal processing circuitry specific to television
Noise or undesired signal reduction
C348S021000, C348S607000, C375S346000, C455S065000
Reexamination Certificate
active
06515713
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital TV system, and more particularly to a method and apparatus for compensating channel distortion in the digital TV system.
2. Discussion of Related Art
Generally, a digital TV system removes ghost signals generated in a channel using the equalizer. Specifically, in the digital TV system, the received signal includes a training sequence signal in a field synchronous section of each field to help a receiver perform equalization. The receiver compensates for distortion generated in the channel using the training sequence.
FIG. 1
shows the structure of one frame of a conventional digital TV signal and
FIG. 2
shows a structure of the field synchronizing signal of FIG.
1
.
Referring to
FIG. 1
, a frame includes two fields. Each field has 313 data segments where one including one field synchronous segment containing the training sequence signal and 312 general data segments. Also, each data segment consists of a 4 symbol data segment synchronizing signal and 828-symbol data.
FIG. 2
shows a field synchronizing signal of one data segment length including a data segment synchronizing pattern in the first four symbols, pseudo random sequences of PN
511
, PN
63
, PN
63
and PN
63
in the following symbols, and information related with the VSB mode is in the next symbols. The polarity of the second of the three PN
63
sections alternates. That is, the polarity changes from ‘1’ to ‘0’ and from ‘0’ to ‘1’. Accordingly, even and odd fields are determined according to the polarity of the second PN
63
.
FIG. 3
shows modelling of a conventional channel having no moving ghost. When there is no moving ghost in the channel, a high definition TV (HDTV) receiver receives an original signal and ghost signal, as shown in FIG.
3
. This ghost signal loaded in the channel is removed by the equalizer of the receiver using the training sequence signal in the field synchronizing signal. When a moving ghost signal does not exist in the channel, the level of the received signal as seen by the HDTV is almost always uniform. Thus, the HDTV receiver is able to remove the ghost using only the training sequence in each field synchronizing section.
However, when a moving ghost is loaded on the channel, the training sequence is not sufficient to remove a moving ghost because the state of the received signal would changes constantly. For example, a moving ghost generated due to an airplane, as shown in
FIG. 4
, varies in sequence of 1→2→3. Accordingly, the conventional method of removing the ghost existing in the channel using only the training sequence cannot effectively cope with the moving ghost in the channel, resulting in a deterioration in the performance of the system.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to solve at least the problems and disadvantages of the related art.
An object of the present invention is to provide a method and apparatus for compensating channel distortion by detecting and removing a moving ghost included in a received signal.
Another object of the present invention is to provide a method and apparatus for compensating channel distortion performing equalization using a data portion as well as a training sequence when a received signal has a moving ghost, to thereby effectively cope with a case where the ghost changes quickly in a channel.
A further object of the present invention is to provide a method and apparatus which compensates for channel distortion by detecting and removing a moving ghost that moves slowly.
A still further object of the present invention is to provide a method and apparatus which compensates for channel distortion by performing equalization in a blind mode when it is possible for an equalizer to diverge, to thereby carry out stable equalization.
A still further object of the present invention is to provide a method and apparatus which compensates for channel distortion by resetting a channel decoder including the equalizer to start from the beginning when the equalizer is already diverged, to thereby perform stable equalization.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purposes of the invention, as embodied and broadly described herein, a method for compensating channel distortion comprises calculating a DC value from input data, reading the DC value a predetermined number of times in a specific cycle, detecting maximum and minimum values from the read DC values, judging if there is a moving ghost in the channel from the difference between the maximum and minimum values, and judging if three is a possibility that the equalizer diverges from the MSE of a signal equalized by the equalizer; performing the equalization in the training sequence mode if it is judged that the moving ghost does not exist in the channel and if there is no possibility that the equalizer would diverge; carrying out the equalization in the blind mode if it is judged that the moving ghost does not exist in the channel but there is a possibility that the equalizer would diverge; executing the equalization in the data mode if it is judged that the moving ghost exists in the channel and there is no possibility that the equalizer would diverges; and performing the equalization in the data mode and blind mode when it is judged that the moving ghost exists in the channel and there is a possibility that the equalizer would diverges.
Particularly, the present invention includes judging that a moving ghost does not exist in the channel if the difference between the maximum and minimum values of the DC values, which are read a predetermined number of times in a specific cycle, is smaller than a predetermined first critical value; cancelling the data mode when it is judged that there is no moving ghost in the channel; and deciding that there is no possibility that the equalizer would diverge when it is judged that the MSE value of the signal equalized by the equalizer is smaller than a predetermined second critical value, to operate the equalizer in the training sequence mode.
The present invention also comprises deciding that there is no moving ghost in the channel when it is judged that the difference between the maximum and minimum values of the DC values, read a predetermined number of times in a specific cycle, is smaller than the predetermined first critical value; cancelling the data mode when it is judged that there is no moving ghost in the channel; and deciding that there is a possibility that the equalizer would diverge when it is judged that the MSE value of the signal equalizer by the equalizer is larger than the predetermined second critical second critical value, to operate the equalizer in the blind mode.
The present invention further comprises deciding that the moving ghost exists in the channel when it is judged that the difference between the maximum and minimum values of the DC values, read a predetermined number of times in a specific cycle, is larger than the predetermined first critical value; turning on the data mode when the moving ghost exists in the channel and the VSB mode of the input data corresponds to a mode for terrestrial broadcasting; and deciding that there is no possibility that the equalizer would diverge when it is judged that the MSE value of the signal equalized by the equalizer is smaller than the predetermined second critical value, to operate the equalizer in the data mode.
The present invention further comprises deciding that the moving ghost exists in the channel when it is judged that the difference between the maximum and minimum values of the DC values, read a predetermined number of times i
Birch & Stewart Kolasch & Birch, LLP
Desir Jean W.
LG Electronics Inc.
Miller John
LandOfFree
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