Television – Plural transmitter system considerations
Reexamination Certificate
1997-03-24
2002-06-04
Flynn, Nathan (Department: 2711)
Television
Plural transmitter system considerations
C348S021000, C348S606000, C348S607000, C348S611000
Reexamination Certificate
active
06400393
ABSTRACT:
The present invention relates to digital television systems, such as the digital high-definition television (HDTV) system used for terrestrial broadcasting in the United States of America in accordance with the Advanced Television Sub-Committee (ATSC) standard, and more particularly, to digital television (DTV) signal receivers with filter circuitry for suppressing co-channel interference from analog television signals, such as those conforming to the National Television Systems Committee (NTSC) standard.
BACKGROUND OF THE INVENTION
Digital television (DTV) signal radio receivers convert digital television signals to baseband symbols and perform symbol decoding using data-slicing procedures. DTV signal radio receivers are found in complete digital television sets provided with viewing screens, and the inventor envisions that DTV signal radio receivers will be found in digital tape recorders. In digital tape recorders it is desirable to remove co-channel interfering analog TV signal before tape recording, so that the time-base stability in the co-channel interfering analog TV signal is good enough that comb filtering can be employed that involves differential delay of DTV signals that extends over several horizontal scan lines. Symbol decoding is done after The comb filtering to suppress co-channel interfering analog TV signal is followed by symbol decoding, so that the recoding effects of the comb filtering can be compensated for during the symbol decoding procedures. The decoded data can then be recoded in accordance with a symbol coding suitable to digital tape recording. The symbol coding can, for example, comprise interleaved non-return to-zero, invert-on-ONEs (I-NRZI) modulation.
A Digital Television Standard published Sep. 16, 1995 by the Advanced Television Subcommittee (ATSC) specifies vestigial sideband (VSB) signals for transmitting digital television (DTV) signals in 6-MHz-bandwidth television channels such as those currently used in over-the-air broadcasting of National Television Subcommittee (NTSC) analog television signals within the United States. The VSB DTV signal is designed so its spectrum is likely to interleave with the spectrum of a co-channel interfering NTSC analog TV signal. This is done by positioning the pilot carrier and the principal amplitude-modulation sideband frequencies of the DTV signal at odd multiples of one-quarter the horizontal scan line rate of the NTSC analog TV signal that fall between the even multiples of one-quarter the horizontal scan line rate of the NTSC analog TV signal, at which even multiples most of the energy of the luminance and chrominance components of a co-channel interfering NTSC analog TV signal will fall. The video carrier of an NTSC analog TV signal is offset 1.25 MHz from the lower limit frequency of the television channel. The carrier of the DTV signal is offset from such video carrier by 59.75 times the horizontal scan line rate of the NTSC analog TV signal, to place the carrier of the DTV signal about 309,877.6 kHz from the lower limit frequency of the television channel. Accordingly, the carrier of the DTV signal is about 2,690122.4 Hz from the middle frequency of the television channel.
The exact symbol rate in the Digital Television Standard is (684/286) times the 4.5 MHz sound carrier offset from video carrier in an NTSC analog TV signal: The number of data symbols per horizontal scan line period of an NTSC analog TV signal is 684, since 286 is the factor by which horizontal scan line rate in an NTSC analog TV signal is multiplied to obtain the 4.5 MHz sound carrier offset from video carrier in an NTSC analog TV signal. The symbol rate is 10.762238 megasymbols per second, which can be contained in a VSB signal extending 5.381119 MHz from DTV signal carrier. That is, the VSB signal can be limited to a band extending 5.690997 MHz from the lower limit frequency of the television channel.
The ATSC standard for digital HDTV signal terrestrial broadcasting in the United States of America is capable of transmitting either of two high-definition television (HDTV) formats with 16:9 aspect ratio. One HDTV display format uses 1920 samples per scan line and 1080 active horizontal scan lines per 30 Hz frame with 2:1 field interlace. The other HDTV display format uses 1280 luminance samples per scan line and 720 progressively scanned scan lines of television image per 60 Hz frame. The ATSC standard also accommodates the transmission of DTV display formats other than HDTV display formats, such as the parallel transmission of four television signals having normal definition in comparison to an NTSC analog television signal.
DTV transmitted by vestigial-sideband (VSB) amplitude modulation (AM) during terrestrial broadcasting in the United States of America comprises a succession of consecutive-in-time data fields each containing 313 consecutive-in-time data segments. The data fields may be considered to be consecutively numbered modulo-2, with each odd-numbered data field and the succeeding even-numbered data field forming a data frame. The frame rate is 20.66 frames per second. Each data segment is of 77.3 microseconds duration. So, with the symbol rate being 10.76 MHz there are 832 symbols per data segment. Each segment of data begins with a line synchronization code group of four symbols having successive values of +S, −S, −S and +S. The value +S is one level below the maximum positive data excursion, and the value −S is one level above the maximum negative data excursion. The initial line of each data field includes a field synchronization code group that codes a training signal for channel-equalization and multipath suppression procedures. The training signal is a 511-sample pseudo-noise sequence (or “PN-sequence”) followed by three 63-sample PN sequences. The middle ones of the 63-sample PN sequences in the field synchronization codes are transmitted in accordance with a first logic convention in the first line of each odd-numbered data field and in accordance with a second logic convention in the first line of each even-numbered data field, the first and second logic conventions being one's complementary respective to each other.
The data within data lines are trellis coded using twelve interleaved trellis codes, each a ⅔ rate trellis code with one uncoded bit. Prior to being trellis coded, the data are subjected to Reed-Solomon forward error-correction coding, which provides for correction of burst errors arising from noise sources such as a nearby unshielded automobile ignition system. The trellis coding coding results are transmitted as 8-level (3 bits/symbol) one-dimensional-constellation symbol coding for over-the-air transmission, which transmissions are made without symbol preceding separate from the trellis coding procedure. The trellis coding coding results are transmitted as 16-level (4 bits/symbol) one-dimensional-constellation symbol coding for cablecast, which transmissions are made without preceding. The VSB signals have their natural carrier wave, which would vary in amplitude depending on the percentage of modulation, suppressed.
The natural carrier wave is replaced by a pilot carrier wave of fixed amplitude, which amplitude corresponds to a prescribed percentage of modulation. This pilot carrier wave of fixed amplitude is generated by introducing a direct component shift into the modulating voltage applied to the balanced modulator generating the amplitude-modulation sidebands that are supplied to the filter supplying the VSB signal as its response. If the eight levels of 4-bit symbol coding have normalized values of −7, −5, −3, −1, +1, +3, +5 and +7 in the carrier modulating signal, the pilot carrier has a normalized vale of 1.25. The normalized value of +S is +5, and the normalized value of −S is −5.
The current ATSC DTV standard presumes that the suppression of co-channel interfering analog TV signal will be carried out by the DTV signal receiver in the trellis decoding process, after th
Bushnell , Esq. Robert E.
Flynn Nathan
Sam-Sung Electronics Co., Ltd.
Srivastava Vivek
LandOfFree
DTV receiver with filter in I-F circuitry to suppress FM... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with DTV receiver with filter in I-F circuitry to suppress FM..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and DTV receiver with filter in I-F circuitry to suppress FM... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2906892