Television – Plural transmitter system considerations
Reexamination Certificate
1999-02-02
2003-12-23
Lee, Michael H. (Department: 2714)
Television
Plural transmitter system considerations
C348S725000, C348S726000, C348S608000, C375S346000
Reexamination Certificate
active
06667760
ABSTRACT:
BACKGROUND OF THE INVENTION
A Digital Television Standard published Sep. 16, 1995 by the Advanced Television Systems Committee (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 System Committee (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 Hz 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 symbols per horizontal scan line in an NTSC analog TV signal is 684, and 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*10
6
symbols 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.
VSB signals using 8-level symbol coding will be used in over-the-air broadcasting within the United States, and VSB signals using 16-level symbol coding can be used in over-the-air narrowcasting systems or in cable-casting systems. 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 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 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 formats other than HDTV 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) for terrestrial broadcasting in the United States of America comprises a succession of consecutive-in-time data field each containing 313 consecutive-in-time data segments. There are 832 symbols per data segment. So, with the symbol rate being 10.76 MHz, each data segment is of 77.3 microseconds duration. 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 posit ve 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 signa for channel-equalization and multipath suppression procedures. The training signal is a 511 sample pseudo-random noise sequence (or “PN-sequence”) followed by three 63-sample PN sequences. The middle one of these 63-sample PN sequences is 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 with respect to each other. The other two 63-sample PN sequences and the 511-sample PN sequence are transmitted in accordance with the same logic convention in all data fields.
The remaining lines of each data field contain data that have been Reed-Solomon forward error-correction coded after having been randomized and subjected to diagonal byte interleaving. In over-the-air broadcasting the error-correction coded data are then trellis coded using twelve interleaved trellis codes, each a ⅔ rate punctured trellis code with one uncoded bit. Trellis coding results are parsed into three-bit groups for over-the-air transmission in eight-level one-dimensional-constellation symbol coding, which transmission is made without symbol pre-coding separate from the trellis coding procedure. Trellis coding is not used in cablecasting proposed in the ATSC standard. The error-correction-coded (ECC) data are parsed into four-bit groups for transmission as sixteen-level one-dimensional-constellation symbol coding, 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 3-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 value of 1.25. The normalized value of+S is+5, and the normalized value of−S is−5.
The VSB modulation transmitted to DTV receivers in accordance with the September 1995 standard differs from that transmitted to NTSC receivers in that the low-end roll-off of the vestigial sideband ends in the portion of the frequency spectrum containing the lower frequencies of the more complete sideband, with the overall channel response being reduced 3 dB at frequencies close to the frequency of the suppressed carrier. Insofar as the high-end roll-off of the complete sideband is concerned the overall channel response of VSB modulation transmitted to DTV receivers is already reduced 3 dB at frequencies close to baud rate. DTV receiver designs proposed by the Grand Alliance further reduce the overall channel response at upper frequencies offset from carrier close to baud rate; this high-end roll-off introduces a Nyquist slope limitation on overall channel response, which is desired for minimizing intersymbol interference (ISI). The DTV receiver designs proposed by the Grand Alliance introduce further low-end roll-off beginning in the portion of the frequency spectrum containing the lower frequencies of the more complete sideband. This further low-end roll-off reduces the response at carrier frequency by another 3 dB at frequencies close to the frequency of the suppressed carrier, to match the Nyquist slope roll-off. When the DTV signals are demodulated, the amplitude response of the demodulation result is essentially flat at frequencies close to zero frequency, easing problems with equalizing at lower frequencies of baseband symbol response.
Beginning the low-end roll-off below carrier frequency introduces other problems, however. The resultant asymmetry of passband affe
Bushnell , Esq. Robert E.
Desir Jean W.
Lee Michael H.
Samsung Electronics Co,. Ltd.
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