Communication system
DCFirst Claim
1. A signal transmission and reception apparatus for transmitting and receiving an n-level VSB signal, the apparatus comprising a transmitter and a receiver;
- said transmitter comprising;
a compression means for compressing an input video signal to a digital video compression signal;
an error correction encoding means for adding an error correction code to the digital video compression signal to produce an error correction coded signal;
a modulation means for modulating the error correction coded signal to an n-level VSB modulation signal, said modulation means comprising a means for allocating code points along a uniaxial modulation coordinate system, and a filter means having a plurality of coefficients which are a series of impulse responses defined by plotting timebase responses to the VSB modulation signal along the in-phase axis and its orthogonal axis for filtering a series of said code points allocated along the uniaxial modulation coordinate system; and
a transmission means for transmitting the modulation signal, andsaid receiver comprising;
a means for receiving a transmitted n-level VSB modulation signal;
a demodulation means for demodulating the received n-level VSB modulation signal into a digital reception signal;
an error correction means for error correcting the digital reception signal to obtain an error-corrected digital signal; and
an expanding means for expanding the error-corrected digital signal to obtain a video output signal.
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Abstract
At the transmitter side, carrier waves are modulated according to an input signal for producing relevant signal points in a signal space diagram. The input signal is divided into, two, first and second, data streams. The signal points are divided into signal point groups to which data of the first data stream are assigned. Also, data of the second data stream are assigned to the signal points of each signal point group. A difference in the transmission error rate between first and second data streams is developed by shifting the signal points to other positions in the space diagram expressed at least in the polar coordinate system. At the receiver side, the first and/or second data streams can be reconstructed from a received signal. In TV broadcast service, a TV signal is divided by a transmitter into low and high frequency band components which are designated as first and second data streams respectively. Upon receiving the TV signal, a receiver can reproduce only the low frequency band component or both the low and high frequency band components, depending on its capability. Furthermore, a communication system based on an OFDM system is utilized for data transmission of a plurality of subchannels, wherein the subchannels are differentiated by changing the length of a guard time slot or a carrier wave interval of a symbol transmission time slot, or changing the transmission electric power of the carrier.
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Citations
16 Claims
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1. A signal transmission and reception apparatus for transmitting and receiving an n-level VSB signal, the apparatus comprising a transmitter and a receiver;
said transmitter comprising; a compression means for compressing an input video signal to a digital video compression signal; an error correction encoding means for adding an error correction code to the digital video compression signal to produce an error correction coded signal; a modulation means for modulating the error correction coded signal to an n-level VSB modulation signal, said modulation means comprising a means for allocating code points along a uniaxial modulation coordinate system, and a filter means having a plurality of coefficients which are a series of impulse responses defined by plotting timebase responses to the VSB modulation signal along the in-phase axis and its orthogonal axis for filtering a series of said code points allocated along the uniaxial modulation coordinate system; and a transmission means for transmitting the modulation signal, and said receiver comprising; a means for receiving a transmitted n-level VSB modulation signal; a demodulation means for demodulating the received n-level VSB modulation signal into a digital reception signal; an error correction means for error correcting the digital reception signal to obtain an error-corrected digital signal; and an expanding means for expanding the error-corrected digital signal to obtain a video output signal. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A signal transmission and reception apparatus for transmitting an n-level VSB signal, comprising:
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a compression means for compressing an input video signal into a digital video compression signal; an error correction encoding means for adding an error correction code to the digital video compression signal to produce an error correction coded signal; a modulation means for modulating the error correction coded signal to an n-level VSB modulation signal, said modulation means comprising a means for allocating code points along a uniaxial modulation coordinate system, and a filter means having a plurality of coefficients which are a series of impulse responses defined by plotting timebase responses to the VSB modulation signal along the in-phase axis and its orthogonal axis for filtering a series of said code points allocated along the uniaxial modulation coordinate system; and a transmission means for transmitting the modulation signal. - View Dependent Claims (9)
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10. A signal receiving apparatus comprising:
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a tuner for receiving a transmission signal containing a digital modulation signal and an analog modulation signal and for selecting the digital modulation signal using a local oscillation signal; an interference detecting means for detecting interference caused by the analog modulation signal from the digital modulation signal selected by the tuner; a notch filter means responsive to the interference detected by the interference detecting means for removing a carrier of the analog modulation signal in a same frequency band as a frequency band of the digital modulation signal; an error ratio calculating means for calculating a bit error ratio of an output of the notch filter means; and an automatic frequency correcting means for changing a frequency of the local oscillation signal of the tuner according to a level of the interference detected by the interference detecting means and the bit error ratio calculated by the error ratio calculating means to compensate for a frequency offset of the carrier of the analog modulated signal. - View Dependent Claims (11)
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12. A signal receiving apparatus comprising:
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a tuner for receiving a transmission signal containing at least one of a VSB modulated signal and a QAM modulated signal and for selecting one of the VSB modulated signal and the QAM modulated signal to obtain a selected signal; an analog-to-digital converter for converting the selected signal into a series of digital codes; a transversal filter provided on an orthogonal axis for suppressing a transmission distortion of the series of digital codes with respect to both orthogonal axes to obtain a series of filtered digital codes allocated on the orthogonal axes; a carrier recovery means for phase-compensating a carrier of the filtered digital codes allocated on the orthogonal axis outputted from the transversal filter; and a control means for producing a control signal to extract detected codes at equal time intervals from the VSB modulated signal; a clock reproducing means for phase synchronizing entire codes of the QAM modulated signal when the selected signal is the QAM modulated signal and for phase synchronizing codes of the VSB modulated signal intermittently at predetermined intervals when the selected signal is the VSB modulated signal; and a decoding means for decoding an output of the carrier recovery means.
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13. A signal transmission apparatus comprising:
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a mapper operable to map a first data stream to a 2-level mapped signal having two levels separated by a first amount, and to map a second data stream to an 8-level mapped signal having eight levels, each adjacent two levels of which are separated by a second amount that is less than the first amount; a DC offset generator operable to add a DC offset to both the 2-level mapped signal and the 8-level mapped signal to produce a 2-level digital signal and an 8-level digital signal, respectively; a digital filter having an amplitude versus frequency characteristic which comprises (i) a VSB characteristic covering a frequency band including a carrier frequency, and (ii) a roll-off characteristic, said digital filter being operable to filter the 2-level digital signal and the 8-level digital signal to produce a VSB modulated signal; and a transmitter operable to transmit the VSB modulated signal.
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14. A signal receiving apparatus comprising:
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a tuner operable to receive a VSB modulated signal resulting from; (a) a mapper mapping a first data stream to a 2-level mapped signal having two levels separated by a first amount, and a second data stream to an 8-level mapped signal having eight levels, each adjacent two levels of which are separated by the second amount that is less than the first amount; (b) a DC offset generator adding a DC offset to both the 2-level mapped signal and the 8-level mapped signal to produce a 2-level digital signal and an 8-level digital signal, respectively; and (c) a digital filter filtering the 2-level digital signal and the 8-level digital signal, wherein the digital filter has an amplitude versus frequency characteristic which comprises (i) a VSB characteristic covering a frequency band including a carrier frequency, and (ii) a roll-off characteristic; and a demodulator operable to demodulate the received signal to reproduce the first data stream and the second data stream.
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15. A signal transmission method comprising:
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mapping a first data stream to a 2-level mapped signal having two levels separated by a first amount, and to map a second data stream to an 8-level mapped signal having eight levels, each adjacent two levels of which are separated by a second amount that is less than the first amount; adding a DC offset to both the 2-level mapped signal and the 8-level mapped signal to produce a 2-level digital signal and an 8-level digital signal, respectively; filtering the 2-level digital signal and the 8-level digital signal to produce a VSB modulated signal with a digital filter having (i) a VSB characteristic on frequency characteristic covering a frequency band including a carrier frequency, and (ii) a roll-off characteristic; and transmitting the VSB modulated signal.
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16. A signal receiving method comprising:
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receiving a VSB modulated signal resulting from; (a) a mapper mapping a first data stream to an 2-level mapped signal having two levels separated by a first amount, and a second data stream to an 8-level mapped signal having eight levels, each adjacent two levels of which are separated by the second amount that is less than the first amount; (b) a DC offset generator adding a DC offset to both the 2-level mapped signal and the 8-level mapped signal to produce a 2-level digital signal and an 8-level digital signal, respectively; and (c) a digital filter filtering the 2-level digital signal and the 8-level digital signal, wherein the digital filter has an amplitude versus frequency characteristic which comprises (i) a VSB characteristic covering a frequency band including a carrier frequency, and (ii) a roll-off characteristic; and demodulating the received signal to reproduce the first data stream and the second data stream.
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Specification