Communication system

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.

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.  
 
   
     
     
       2. A transmission and reception apparatus according to  claim 1 , wherein the error correction means comprises a trellis decoder. 
     
     
       3. A transmission and reception apparatus according to  claim 2 , wherein the trellis decoder is associated with a plurality of memories which each holds a number of selectable correct codes. 
     
     
       4. A transmission and reception apparatus according to  claim 1 , wherein the digital reception signal is divided into a high priority signal and a low priority signal, and wherein said error correction means comprises a high code gain first error correction means and a low code gain second error correction means, said first error correction means correcting the high priority signal. 
     
     
       5. A transmission and reception apparatus according to  claim 4 , wherein the high priority signal carries the address data for all data. 
     
     
       6. A transmission and reception apparatus according to  claim 4 , wherein the first error correction means comprises a trellis decoder. 
     
     
       7. A signal transmission and reception apparatus according to  claim 1 , further comprising a band path filtering means for filtering the n-level VSB modulation signal before being transmitted. 
     
     
       8. A signal transmission and reception apparatus for transmitting an n-level VSB signal, 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.    
     
     
       9. A signal transmission apparatus according to  claim 8 , further comprising a band path filtering means for filtering the n-level VSB modulation signal before being transmitted. 
     
     
       10. A signal receiving apparatus comprising:
 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.    
     
     
       11. A signal receiving apparatus according to  claim 10 , wherein the digital modulation signal is an n-level VSB modulation signal. 
     
     
       12. A signal receiving apparatus comprising:
 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.    
     
     
       13. A signal receiving apparatus comprising:
   a receiver operable to receive a digital modulated signal;        a demodulator operable to demodulate the digital modulated signal to a data stream;        a decoder operable to decode the data stream to an HDTV signal;        a controller operable to examine the quality of the data stream; and        an output unit operable to output the HDTV signal and to stop outputting the HDTV signal after the quality of the data stream continues being lower than a predetermined acceptable quality for a predetermined period of time.     
     
     
       14. A signal receiving apparatus according to  claim 13 , further comprising a display operable to display the HDTV signal. 
     
     
       15. A signal receiving apparatus comprising:
   a receiver operable to receive a digital modulated signal;        a demodulator operable to demodulate the digital modulated signal to a data stream;        a decoder operable to decode the data stream to an HDTV signal;        a controller operable to detect an error rate of the data stream; and        an output unit operable to output the HDTV signal and to stop outputting the HDTV signal after the error rate of the data stream continues being higher than a predetermined error rate for a predetermined period of time.     
     
     
       16. A signal receiving apparatus according to  claim 15 , further comprising a display operable to display the HDTV signal. 
     
     
       17. A signal receiving method comprising:
   receiving a digital modulated signal;        demodulating the digital modulated signal to a data stream;        decoding the data stream to an HDTV signal;        examining the quality of the data stream; and        outputting the HDTV signal and stopping outputting the HDTV signal after the quality of the data stream continues being lower than a predetermined acceptable quality for a predetermined period of time.     
     
     
       18. A signal receiving method according to  claim 17 , further comprising displaying the HDTV signal. 
     
     
       19. A signal receiving method comprising:
   receiving a digital modulated signal;        demodulating the digital modulated signal to a data stream;        decoding the data stream to an HDTV signal;        detecting an error rate of the data stream; and        outputting the HDTV signal and stopping outputting the HDTV signal after the error rate of the data stream continues being higher than a predetermined error rate for a predetermined period of time.     
     
     
       20. A signal receiving method according to  claim 19 , further comprising a display operable to display the HDTV signal. 
     
     
       21. A signal receiving apparatus comprising:
   a receiver operable to receive a digital modulated signal;        a demodulator operable to demodulate the digital modulated signal to a data stream;        a decoder operable to decode the data stream to a TV signal;        a controller operable to examine the quality of the data stream; and        an output unit operable to output the TV signal and to stop outputting the TV signal after the quality of the data stream continues being lower than a predetermined acceptable quality for a predetermined period of time.     
     
     
       22. A signal receiving apparatus according to  claim 21 , further comprising a display operable to display the TV signal. 
     
     
       23. A signal receiving apparatus comprising:
   a receiver operable to receive a digital modulated signal;        a demodulator operable to demodulate the digital modulated signal to a data stream;        a decoder operable to decode the data stream to a TV signal;        a controller operable to detect an error rate of the data stream; and        an output unit operable to output the TV signal and to stop outputting the TV signal after the error rate of the data stream continues being higher than a predetermined error rate for a predetermined period of time.     
     
     
       24. A signal receiving apparatus according to  claim 23 , further comprising a display operable to display the TV signal. 
     
     
       25. A signal receiving method comprising:
   receiving a digital modulated signal;        demodulating the digital modulated signal to a data stream;        decoding the data stream to a TV signal;        examining the quality of the data stream; and        outputting the TV signal and stopping outputting the TV signal after the quality of the data stream continues being lower than a predetermined acceptable quality for a predetermined period of time.     
     
     
       26. A signal receiving method according to  claim 25 , further comprising displaying the TV signal. 
     
     
       27. A signal receiving method comprising:
   receiving a digital modulated signal;        demodulating the digital modulated signal to a data stream;        decoding the data stream to a TV signal;        detecting an error rate of the data stream; and        outputting the TV signal and stopping outputting the TV signal after the error rate of the data stream continues being higher than a predetermined error rate for a predetermined period of time.     
     
     
       28. A signal receiving method according to  claim 27 , further comprising a display operable to display the TV signal.