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 a first and a 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 digital TV receiver comprising:
 a receiving section for receiving a PSK (Phase Shift Key) modulation signal comprising a plurality of signal points disposed on specific phases of a given constellation in a signal space diagram;   a demodulator for demodulating the received signal from said receiving section into a digital signal;   an error correcting section for error correcting a demodulation signal from said demodulator; and   an image expander for expanding an error-corrected signal from said error correcting section to a video signal, thereby outputting a video signal,   wherein said demodulator demodulates the received signal as first and second PSK signals, said first PSK signal representing a first data stream to be reproduced, said first PSK signal comprising n-value signal points, said second PSK signal representing both said first data stream and a second data stream to be reproduced, said second PSK signal comprising m-value signal points, where m is an integer larger than n,   wherein the m-value signal points of said second PSK signal are divisible into n groups of signal points which are distinguishable from one another in the signal space, and said demodulator distinguishes said n groups of signal points from one another as the n-value signal points of said first PSK signal by demodulating the received signal as said first PSK signal, and wherein   high priority information is demodulated at least in said first data stream.   
     
     
       2. The digital TV receiver in accordance with  claim 1 , wherein said demodulator demodulates information relating to a low-resolution component of the video signal from said first data stream and demodulates information relating to a high-resolution component of the video signal from said second data stream. 
     
     
       3. The digital TV receiver in accordance with  claim 1 , comprising means for stopping output of said second data stream when an error rate of the received signal is high. 
     
     
       4. The digital TV receiver in accordance with  claim 1 , wherein said demodulator comprises first means for demodulating the received signal as a QPSK signal to reproduce the first data stream and second means for demodulating the received signal as a 8PSK signal to reproduce both of the first data stream and the second data stream. 
     
     
       5. A digital TV receiver comprising:
 a receiving section for receiving a PSK (Phase Shift Key) modulation signal comprising m-value signal points disposed on specific phases of a given constellation in a signal space diagram and representing a first data stream and a second data stream to be reproduced;   a demodulator for demodulating said PSK modulation signal from said receiving section into a digital signal;   an error correcting section for error correcting a demodulation signal from said demodulator; and   an image expander for expanding an error-corrected signal from said error correcting section to a video signal,   wherein said demodulator includes means for demodulating said PSK signal comprising m-value signal points as another PSK signal,   said another PSK signal comprising n-value signal points and representing only said first data stream, where n is an integer smaller than m, and wherein   high priority information is demodulated at least in said first data stream.   
     
     
       6. A signal transmission and receiving apparatus for transmitting and receiving a VSB modulated signal including 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:
 an interleaver operable to interleave the second data stream to produce an interleaved data stream; 
 a trellis encoder operable to trellis encode the interleaved data stream to produce a trellis encoded interleaved data stream; 
 a modulator operable to modulate the first data stream, without being interleaved and without being trellis encoded, to produce a 2-level VSB modulated signal, and modulate the trellis encoded interleaved data stream to produce an 8-level VSB modulated signal, wherein the first data stream includes synchronization data; and 
 a transmitter operable to transmit the 2-level VSB modulated signal and the 8-level VSB modulated signal; and 
   said receiving apparatus comprising:
 a demodulator operable to demodulate the 2-level VSB modulated signal to produce the first data stream and demodulate the 8-level VSB modulated signal to produce a demodulated data stream; 
 a trellis decoder operable to trellis decode the demodulated data stream to produce a trellis decoded data stream; and 
 a de-interleaver operable to de-interleave the trellis decoded data stream to produce a second data stream; 
   wherein a code rate of the trellis encoder is 2/3 and a code rate of the trellis decoder is 2/3.   
     
     
       7. A signal transmission apparatus for transmitting a VSB modulated signal including information of a first data stream and a second data stream, the apparatus comprising:
 an interleaver operable to interleave the second data stream to produce an interleaved data stream;   a trellis encoder operable to trellis encode the interleaved data stream to produce a trellis encoded interleaved data stream, wherein a code rate of the trellis encoder is 2/3;   a modulator operable to modulate the first data stream, without being interleaved and without being trellis encoded, to produce a 2-level VSB modulated signal, and modulate the trellis encoded interleaved data stream to produce an 8-level VSB modulated signal, wherein the first data stream includes synchronization data; and   a transmitter operable to transmit the 2-level VSB modulated signal and the 8-level VSB modulated signal.   
     
     
       8. A signal receiving apparatus comprising:
 a receiver operable to receive a transmitted VSB modulated signal,   wherein said transmitted VSB modulated signal including a 2-level VSB modulated signal and an 8-level VSB modulated signal;   a demodulator operable to demodulate the 2-level VSB modulated signal to produce a first data stream including information of synchronization data and demodulate the 8-level VSB modulated signal to produce a demodulated data stream, the first data stream without being interleaved and without being trellis encoded;   a trellis decoder operable to trellis decode the demodulated data stream to produce a trellis decoded data stream;   a de-interleaver operable to de-interleave the trellis decoded data stream to produce a second data stream; and   wherein a code rate of the trellis decoder is 2/3.   
     
     
       9. A signal transmission and receiving method for transmitting and receiving a VSB modulated signal including 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:
 interleaving the second data stream to produce an interleaved data stream; 
 trellis encoding the interleaved data stream to produce a trellis encoded interleaved data stream; 
 modulating the first data stream, without being interleaved and without being trellis encoded, to produce a 2-level VSB modulated signal, and modulating the trellis encoded interleaved data stream to produce an 8-level VSB modulated signal, wherein the first data stream includes synchronization data; and 
 transmitting the 2-level VSB modulated signal and the 8-level VSB modulated signal; and 
   said receiving method comprising:
 demodulating the 2-level VSB modulated signal to produce the first data stream and demodulating the 8-level VSB modulated signal to produce a demodulated data stream; 
 trellis decoding the demodulated data stream to produce a trellis decoded data stream; and 
 de-interleaving the trellis decoded data stream to produce a second data stream; 
   wherein a code rate of the trellis encoding is 2/3 and a code rate of the trellis decoding is 2/3.   
     
     
       10. A signal transmission method for transmitting a VSB modulated signal including information of a first data stream and a second data stream, the method comprising:
 interleaving the second data stream to produce an interleaved data stream;   trellis encoding the interleaved data stream to produce a trellis encoded interleaved data stream, wherein a code rate of the trellis encoding is 2/3;   modulating the first data stream, without being interleaved and without being trellis encoded, to produce a 2-level VSB modulated signal, and modulating the trellis encoded interleaved data stream to produce an 8-level VSB modulated signal, wherein the first data stream includes synchronization data; and   transmitting the 2-level VSB modulated signal and the 8-level VSB modulated signal.   
     
     
       11. A signal receiving method comprising:
 receiving a transmitted VSB modulated signal,   wherein said transmitted VSB modulated signal including a 2-level VSB modulated signal and an 8-level VSB modulated signal;   demodulating the 2-level VSB modulated signal to produce a first data stream including information of synchronization data and demodulating the 8-level VSB modulated signal to produce a demodulated data stream, the first data stream without being interleaved and without being trellis encoded;   trellis decoding the demodulated data stream to produce a trellis decoded data stream; and   de-interleaving the trellis decoded data stream to produce a second data stream;   wherein a code rate of the trellis decoding is 2/3.