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 code 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 receiving 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-correction 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 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.    
     
     
       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 turner;    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 turner 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 transmission and receiving system comprising a transmission apparatus and a receiving apparatus,
 said transmission apparatus comprising: 
 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 VSB modulated signal and an  8 -level VSB modulated signal, respectively; and  
 a transmitter operable to transmit the  2 -level VSB modulated signal and the  8 -level VSB modulated signal;  
   said receiving apparatus comprising: 
 a demodulator operable to demodulate the  2 -level VSB modulated signal and the  8 -level VSB modulated signal to the first data stream and the second data stream, respectively. 
   
     
     
       14. A signal transmission apparatus comprising:
 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 VSB modulated signal and an  8 -level VSB modulated signal, respectively; and    a transmitter operable to transmit the  2 -level VSB modulated signal and the  8 -level VSB modulated signal.   
     
     
       15. A signal receiving apparatus comprising:
 a receiver operable to receive a  2 -level VSB modulated signal, having information of a first data stream, and an  8 -level VSB modulated signal, having information of a second data stream, wherein the  2 -level VSB modulated signal has two levels separated by a first amount and includes a carrier produced by a DC offset, the  8 -level VSB modulated signal has eight levels, each adjacent two levels of which are separated by a second amount that is less than the first amount, and includes the carrier produced by the DC offset; and    a demodulator operable to demodulate the  2 -level VSB modulated signal to the first data stream and the  8 -level VSB modulated signal to the second data stream.   
     
     
       16. A signal receiving apparatus according to  claim 15 , wherein said demodulator is operable to demodulate the  2 -level VSB modulated signal and the  8 -level VSB modulated signal by using the carrier. 
     
     
       17. A signal receiving apparatus according to  claim 16 , wherein said demodulator includes a carrier reproducer operable to reproduce the carrier according to a portion of the carrier passed through the DC offset. 
     
     
       18. A signal transmission and receiving method comprising a transmission method and a receiving method,
 said transmission method comprising: 
 mapping a first data stream to a  2 -level mapped signal having two levels separated by a first amount, and mapping 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 VSB modulated signal and an  8 -level VSB modulated signal, respectively; and  
 transmitting the  2 -level VSB modulated signal and the  8 -level VSB modulated signal;  
   said receiving method comprising: 
 demodulating the  2 -level VSB modulated signal and the  8 -level VSB modulated signal to the first data stream and the second data stream, respectively. 
   
     
     
       19. A signal transmission method comprising:
 mapping a first data stream to a  2 -level mapped signal having two levels separated by a first amount, and mapping 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 VSB modulated signal and an  8 -level VSB modulated signal, respectively; and    transmitting the  2 -level VSB modulated signal and the  8 -level VSB modulated signals.   
     
     
       20. A signal receiving method comprising:
 receiving a  2 -level VSB modulated signal, having information of a first data stream, and an  8 -level VSB modulated signal, having information of a second data stream, wherein the  2 -level VSB modulated signal has two levels separated by a first amount and includes a carrier produced by a DC offset, the  8 -level VSB modulated signal has eight levels, each adjacent two levels of which are separated by a second amount that is less than the first amount, and includes the carrier produced by the DC offset; and    demodulating the  2 -level VSB modulated signal to the first data stream and the  8 -level VSB modulated signal to the second data stream.   
     
     
       21. A signal receiving method according to  claim 20 , wherein said demodulating comprises demodulating the  2 -level VSB modulated signal and the  8 -level VSB modulated signal by using the carrier.