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 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 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 transmission and receiving apparatus for transmitting and receiving a PSK or QAM modulated signal having information of a first data stream and a second data stream, the apparatus comprising a transmission apparatus and a receiving apparatus,
   said transmission apparatus comprising:      a Reed - Solomon encoder operable to Reed - Solomon encode the second data stream to produce a Reed - Solomon encoded data stream;        a modulator operable to modulate the first data stream, without being Reed - Solomon encoded, to an m - level PSK or QAM modulated signal and modulate the Reed - Solomon encoded data stream to an n - level PSK or QAM modulated signal;        wherein the first data stream has data for demodulation including the number of signal points of the constellation of the second data stream; and        a transmitter operable to transmit the m - level PSK or QAM modulated signal and the n - level PSK or QAM modulated signal;          said receiving apparatus comprising:      a demodulator operable to demodulate the m - level PSK or QAM modulated signal to the first data stream and demodulate the n - level PSK or QAM modulated signal to a demodulated data stream,        wherein the demodulated data stream is reproduced according to the data for demodulation included in the first data stream; and        a Reed - Solomon decoder operable to Reed - Solomon decode the demodulated data stream to the second data stream.       
     
     
       14. A signal transmission apparatus for transmitting a PSK or QAM modulated signal having information of a first data stream and a second data stream, the apparatus comprising:
   a Reed - Solomon encoder operable to Reed - Solomon encode the second data stream to produce a Reed - Solomon encoded data stream;        a modulator operable to modulate the first data stream, without being Reed - Solomon encoded, to an m - level PSK or QAM modulated signal and modulate the Reed - Solomon encoded data stream to an n - level PSK or QAM modulated signal;        wherein the first data stream has data for demodulation including the number of signal points of the constellation of the second data stream; and        a transmitter operable to transmit the m - level PSK or QAM modulated signal and the n - level PSK or QAM modulated signal.     
     
     
       15. A signal receiving apparatus comprising:
   a receiver operable to receive a transmitted PSK or QAM modulated signal,        wherein said transmitted PSK or QAM modulated signal includes an m - level PSK or QAM modulated signal and an n - level PSK or QAM modulated signal;        a demodulator operable to demodulate the m - level PSK or QAM modulated signal to a first data stream having data for demodulation including the number of signal points of the constellation of a Reed - Solomon encoded data stream and demodulate the n - level PSK or QAM modulated signal to a demodulated data stream, wherein the first data stream is not Reed - Solomon encoded and the demodulated data stream is Reed - Solomon encoded,        wherein the demodulated data stream is reproduced according to the data for demodulation in the first data stream; and        a Reed - Solomon decoder operable to Reed - Solomon decode the demodulated data stream to a second data stream.     
     
     
       16. A signal transmission and receiving method for transmitting and receiving a PSK or QAM modulated signal having information of a first data stream and a second data stream, the method comprising a transmission method and a receiving method,
   said transmission method comprising:      Reed - Solomon encoding the second data stream to produce a Reed - Solomon encoded data stream;        modulating the first data stream, without being Reed - Solomon encoded, to an m - level PSK or QAM modulated signal and modulating the Reed - Solomon encoded data stream to an n - level PSK or QAM modulated signal;        wherein the first data stream has data for demodulation including the number of signal points of the constellation of the second data stream; and        transmitting the m - level PSK or QAM modulated signal and the n - level PSK or QAM modulated signal;          said receiving method comprising:      demodulating the m - level PSK or QAM modulated signal to the first data stream and demodulating the n - level PSK or QAM modulated signal to a demodulated data stream;        wherein the demodulated data stream is reproduced according to the data for demodulation included in the first data stream; and        Reed - Solomon decoding the demodulated data stream to the second data stream.       
     
     
       17. A signal transmission method for transmitting a PSK or QAM modulated signal having information of a first data stream and a second data stream, the method comprising:
   Reed - Solomon encoding the second data stream to produce a Reed - Solomon encoded data stream;        modulating the first data stream, without being Reed - Solomon encoded, to an m - level PSK or QAM modulated signal and modulating the Reed - Solomon encoded data stream to an n - level PSK or QAM modulated signal;        wherein the first data stream has data for demodulation including the number of signal points of the constellation of the second data stream; and        transmitting the m - level PSK or QAM modulated signal and the n - level PSK or QAM modulated signal.     
     
     
       18. A signal receiving method comprising:
   receiving a transmitted PSK or QAM modulated signal,        wherein said transmitted PSK or QAM modulated signal including an m - level PSK or QAM modulated signal and an n - level PSK or QAM modulated signal;        demodulating the m - level PSK or QAM modulated signal to a first data stream having data for demodulation including the number of signal points of the constellation of a Reed Solomon encoded data stream and demodulating the n - level PSK or QAM modulated signal to a demodulated data stream, wherein the first data stream is not Reed - Solomon encoded and the demodulated data stream is Reed - Solomon encoded,        wherein the demodulated data stream is reproduced according to the data for demodulation included in the first data stream; and        Reed - Solomon decoding the demodulated data stream to a second data stream.