Television – Synchronization
Reexamination Certificate
2001-01-12
2003-09-02
Hsia, Sherrie (Department: 2614)
Television
Synchronization
C348S521000, C348S524000
Reexamination Certificate
active
06614487
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital TV receiver which adopts a vestigial side band (VSB) mode, and more particularly to an apparatus and method for detecting a synchronizing signal in even case that channel change frequently occurs.
2. Description of the Related Art
A VSB transmission mode suggested by Grand Alliance (GA) has remarkable features, such as a pilot signal, a data segment synchronizing signal, and a field synchronizing signal, than other digital TV transmission modes. These signals can be used to improve carrier recovery characteristic and timing recovery characteristic. The recovery characteristics of the synchronizing signals greatly act on performance of the overall system of the VSB mode.
A transmission party such as a broadcasting station transmits a signal through a mapper that acts to convert the signal to a desired power level. As an example, in case of 8 VSB for ground broadcasting, an output level of the mapper is one of eight symbol values (amplitude level), −168, −120, −72, −24, 24, 72, 120, and 168. The mapper forcibly inserts a segment synchronizing signal of four symbols for each unit of 828 symbols by a protocol and forcibly inserts a field synchronizing signal into a 313rd data segment location.
At this time, the protocol of the segment synchronizing signal has a logic format of 1, 0, 0, and 1. The output level of the mapper is 120 when the synchronizing signal is 1 while the output level is −120 when the synchronizing signal is 0. That is, the segment synchronizing signal is repeated with two levels per data segment.
FIG. 1
shows a frame format of VSB data including the data and the synchronizing signal. Referring to
FIG. 1
, one frame includes two fields while one filed includes 313 data segments. One data segment includes 832 symbols. In this case, fourth symbols of a start point in one data segment correspond to a segment synchronizing portion, and the first data segment in one field corresponds to a field synchronizing portion.
FIG. 2
shows a configuration of the field synchronizing portion.
Referring to
FIG. 2
, a data segment synchronization of four symbols, a PN511 sequence which is a pseudo random sequence, three PN63 sequences, and VSB mode information of 24 symbols are provided, while other 014 symbols are reserved. In other words, the PN511 sequence includes 511 pseudo random symbols. The second PN63 sequence of the PN63 sequences has an inverted symbol configuration per field, wherein ‘1’ is inverted to ‘0’ while ‘0’ is inverted to ‘1’. Accordingly, one field may be divided into an even field and an odd field depending on polarity of the second PN63 sequence.
Therefore, in the digital TV receiver, the synchronizing signals inserted during transmission should be restored. If the synchronizing signals are detected in error, data recovery is not performed easily. This could lead to adverse effect to the overall system.
A scheme of the synchronizing signal recovery currently suggested in GA includes three portions, i.e., a segment synchronizing signal recovery portion, a field synchronizing signal recovery portion, and a synchronizing lock signal generating portion, so as to detect the segment synchronizing signals and the field synchronizing signals.
The detected synchronizing signals are used for equalization and forward error correction (FEC). The synchronization in the digital TV receiver means that the location of the segment synchronizing signals and the location of the field synchronizing signals are exactly detected in the received signals. The synchronization also includes a carrier recovery and timing recovery.
At this time, to detect the field synchronizing signals, the segment synchronizing signals should first be locked. As an example, recovery of the segment synchronizing signal is obtained by correlation of (1,0,0,1). A method for detecting the segment synchronizing signals is a pattern match method. In the pattern match method, binary data of transmitted data are compared with binary data set in advance in a receiving party (field synchronizing data equal to data inserted from the transmission party), and then a segment having the smallest difference is considered as a field synchronizing signal. In this case, the segment should be detected several times as a field synchronizing signal in the same location by a reliability counter, to be considered as a field synchronizing signal. The binary data of the transmitted data means 5~515(511 symbols) portions of all the segments(832 symbols). That is, in pattern matching, the PN511 sequence of the 832 symbols is only used considering required time in pattern matching and hardware without using all the data of the field synchronizing signal portion.
FIG. 3
a
is a block diagram of a field synchronizing signal detector. Referring to
FIG. 3
, an absolute value operation unit
102
obtains an absolute value of the binary data set by the receiving party in the same field synchronizing format as the data inserted from the transmission party, and outputs the absolute value to a subtractor
101
. The subtractor
101
obtains a difference value between the transmitted binary data and the output data of the absolute value operation unit
102
and outputs the resultant value to an absolute value operation unit
103
.
The absolute value operation unit
103
obtains an absolute value of the output of the subtractor
101
and outputs the absolute value to an integrated unit
104
.
The integrated unit
104
is reset by the segment synchronizing signal to accumulate the output of the absolute value operation unit
103
during
1
data segment period and output the accumulated value to a minimum error segment detector
105
. That is, the absolute value of the data(error) output from the subtractor
101
is integrated at a symbol interval for all periods of respective segments. The minimum error segment detector
105
detects the location of the segment having the minimum value among the outputs of the integrated unit
104
and outputs the detected value to a reliability counter
106
.
The reliability counter
106
identifies whether the location of the segment detected from the minimum error segment detector
105
is repeated per field. If so, the reliability counter
106
increases its value. If not so, the reliability counter
106
decreases its value. If the value of the reliability counter
106
exceeds a predetermined threshold value, the reliability counter
106
generates a field synchronizing detection signal.
FIG. 3
b
shows a difference between a field synchronizing period and a data period when the output signal of the absolute value operation unit
103
passes through the integrated unit
104
. The segment having the smallest error after one field (313 segments) is temporarily selected as a field synchronizing signal. If the temporarily selected segment reaches a given reliability value, the field synchronizing signal is finally obtained. It should be understood that the segment synchronizing signal should essentially be locked in a portion where the field synchronizing signal is detected, so that it is possible to detect which one among input segments has a field synchronizing signal. In this case, two counters are required. One counter is a 832-counter for symbol counting while other counter is a 313-counter for segment counting.
FIGS. 4
a
to
4
c
show data, a segment synchronizing signal, and a field synchronizing signal when the synchronizing signals are locked. In this structure, a ghost signal becomes greater than a main signal in a case that a main path is temporarily blocked by movement of human being when receiving a digital TV signal of a VSB format through an internal antenna. In this case, the main signal is converted to a ghost signal. That is, since the greatest gain signal among input signals acts as the main signal in view of the digital TV receiver, previous synchronization related information is converted. Accordingly, the location of the synchronizing signals should b
Gu Young Mo
Hong Sung Ryong
Birch & Stewart Kolasch & Birch, LLP
Hsia Sherrie
LG Electronics Inc.
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