Synchronization determining circuit, demodulator and communication system

A demodulator for demodulating a multiplexed data stream derived by multiplexing a plurality of data streams having the same contents with a time lag provided therebetween, the demodulator comprising:

• a synchronization determining circuit for determining a synchronization state of said multiplexed data stream;
• first separating means for separating said multiplexed data stream to output a plurality of data streams based on a determination result outputted from said synchronization determining circuit;
• first delaying means for delaying at least one of said plurality of data streams outputted from said first separating means by a time corresponding to said time lag;
• combining means for combining said data stream outputted from said first delaying means and at least one other of said plurality of data streams outputted from said first separating means which is not delayed by said first delaying means so as to output a combined signal;
• and
• demodulating means for demodulating said combined signal.

A demodulator for demodulating a multiplexed data stream derived by multiplexing a plurality of data streams having the same contents with a time lag provided therebetween, the demodulator comprising:

• a synchronization determining circuit for determining a synchronization state of said multiplexed data stream;
• first separating means for separating said multiplexed data stream to output a plurality of data streams based on a determination result outputted from said synchronization determining circuit;
• first delaying means for delaying at least one of said plurality of data streams outputted from said first separating means by a time corresponding to said time lag;
• selecting means for detecting a receiving level and selecting, based on detected receiving level, either one of the data stream outputted from said first delaying means and one other data stream of said plurality of data streams outputted from said first separating means without being delayed by said first delaying means;
• and
• demodulating means for demodulating said selected signal.

A communication system comprising:

• a modulating section for modulating an inputted signal to output a modulated signal, said modulating section includes
• convolutional encoding means for convolutionally encoding said inputted signal and outputting at least a first data stream and a second data stream,
• multiplexing means for multiplexing data strings having the same contents in said first data stream and said second data stream with a time lag provided therebetween and outputting a multiplexed data stream, and
• modulating means for modulating said multiplexed data stream and outputting a modulated signal;
• and
• a demodulating section for demodulating said modulated signal to output demodulated data, said demodulating section includes
• a synchronization determining circuit for determining synchronization of said multiplexed data stream of said modulated signal and outputting a determination result,
• separating means for separating said multiplexed data stream based on the determination result outputted from said synchronization determining circuit and outputting a plurality of data streams,
• delaying means for delaying at least one of said plurality of data streams outputted from said separating means by a time corresponding to said time lag,
• combining means for combining the data stream outputted from said delaying means and another of said plurality of data streams outputted from said separating means which is not delayed by said delaying means and outputting a combined signal, and
• demodulating means for Viterbi-decoding said combined signal.

A communication system comprising:

• a modulating section for modulating an inputted signal to output a modulated signal, said modulating section includes
• encoding means for encoding the inputted signal and outputting at least a first data stream and a second data stream,
• multiplexing means having first branching means for branching said first data stream so as to generate a third data stream and a fourth data stream each having the same contents as said first data stream and second branching means for branching said second data stream so as to generate a fifth data stream and a sixth data stream each having the same contents as said second data stream, said multiplexing means delaying the fourth data stream, the fifth data stream and the sixth data stream relative to said third data stream by fixed times 2T, T and 3T, respectively, and thereafter multiplexing them to output a multiplexed data stream, and
• modulating means for modulating said multiplexed data stream and outputting a modulated signal;
• and
• a demodulating section for demodulating said modulated signal to output demodulated data, said demodulating section includes
• a synchronization determining circuit for determining synchronization of said multiplexed data stream of said modulated signal and outputting a determination result,
• separating means for separating said multiplexed data stream based on the determination result outputted from said synchronization determining circuit and outputting a plurality of data streams,
• delaying means for delaying said plurality of data streams outputted from said second separating means by fixed times 2T, T and 3T, respectively, relative to at least one reference data stream,
• combining means for combining said reference data stream and the data stream delayed by the fixed time 2T at said delaying means so as to output as a first combined signal and for combining the data stream delayed by the fixed time T at said third delaying means and the data stream delayed by the fixed time 3T at said third delaying means so as to output as a second combined signal, and
• demodulating means for decoding said first combined signal and said second combined signal.

A synchronization determining method for determining a synchronization state of a multiplexed data stream derived by multiplexing a plurality of data streams having the same contents with a time lag provided therebetween, the synchronization determining method comprising the steps of:

• separating said inputted multiplexed data stream into a plurality of data streams;
• delaying at least one of said plurality of data streams by a time corresponding to said time lag;
• comparing said delayed data stream and another one of said plurality of data streams which is not delayed so as to generate comparison data;
• and
• determining the synchronization state of said multiplexed data stream based on said comparison data.