Frequency modulation method and modem unit employing such method

Abstract

A frequency modulation method and modem unit for a frequency modulation using a common filter which uses a large number of carrier frequencies include a frequency-shifting unit for subjecting an input data to a frequency shift corresponding to a binary data value, a filter for limiting an output obtained by the frequency-shifting unit to a common band, and a modulation unit for frequency-modulating an output obtained by the filter, by a carrier frequency having an intermediate value of the frequencies respectively corresponding to the binary data values.

What is claimed is:  
     
         1 . A frequency modulation method comprising: 
 a frequency-shifting step for subjecting an input data to a frequency shift corresponding to a binary data value;    a filtering step for limiting an output obtained by said frequency-shifting step to a common band; and    a modulation step for frequency-modulating an output obtained by said filtering step by a carrier frequency having an intermediate value of the frequencies respectively corresponding to the binary data values.    
     
     
         2 . The frequency modulation method as claimed in    claim 1   , wherein said frequency-shifting step subjects the input data to the frequency shift with a frequency shift quantity corresponding to a frequency difference of corresponding binary data values.  
     
     
         3 . The frequency modulation method as claimed in    claim 1   , wherein said filtering step limits an unwanted band corresponding to a data transmission rate.  
     
     
         4 . The frequency modulation method as claimed in    claim 2   , wherein said filtering step limits an unwanted band corresponding to a data transmission rate.  
     
     
         5 . The frequency modulation method as claimed in    claim 1   , and further comprising: 
 a step for limiting the input data within a frequency band of a transmission medium through which frequency modulated data obtained by said modulation step is transmitted, before said frequency-shifting step.    
     
     
         6 . The frequency modulation method as claimed in    claim 1   , and further comprising: 
 a step for automatically setting parameters used in at least said frequency-shifting step and said filtering step depending on a data transmission rate.    
     
     
         7 . A modem unit comprising: 
 frequency-shifting means for subjecting an input data to a frequency shift corresponding to a binary data value;    filtering means for limiting an output obtained by said frequency-shifting means to a common band; and    modulation means for frequency-modulating an output obtained by said filtering means by a carrier frequency having an intermediate value of the frequencies respectively corresponding to the binary data values.    
     
     
         8 . The modem unit as claimed in    claim 7   , wherein said frequency-shifting means subjects the input data to the frequency shift with a frequency shift quantity corresponding to a frequency difference of corresponding binary data values.  
     
     
         9 . The modem unit as claimed in    claim 7   , wherein said filtering means limits an unwanted band corresponding to a data transmission rate.  
     
     
         10 . The modem unit as claimed in    claim 8   , wherein said filtering means limits an unwanted band corresponding to a data transmission rate.  
     
     
         11 . The modem unit as claimed in    claim 7   , and further comprising: 
 means for limiting the input data within a frequency band of a transmission medium through which frequency modulated data obtained by said modulation means is transmitted, at a stage before said frequency-shifting means.    
     
     
         12 . The modem unit as claimed in    claim 7   , and further comprising: 
 means for automatically setting parameters used in at least said frequency-shifting means and said filtering means depending on a data transmission rate.    
     
     
         13 . A modem unit comprising: 
 demodulation means for demodulating a frequency modulated data which is obtained by frequency-modulating an input data, by a carrier frequency having an intermediate value of the frequencies respectively corresponding to the binary data values;    means for obtaining a phase shift quantity from a phase difference of vector signals of a baseband obtained from said demodulation means; and    judging means for judging a binary data value from the input data based on the phase shift quantity obtained by said means for obtaining a phase shift quantity.    
     
     
         14 . The modem unit as claimed in    claim 13   , wherein said means for obtaining a phase shift quantity includes means for normalizing the vector signals of the baseband obtained from said demodulation means.  
     
     
         15 . The modem unit as claimed in    claim 13   , wherein said judging means includes first means for judging the binary data value of said input data based on a polarity of the phase shift quantity.  
     
     
         16 . The modem unit as claimed in    claim 14   , wherein said judging means includes first means for judging the binary data value of said input data based on a polarity of the phase shift quantity.  
     
     
         17 . The modem unit as claimed in    claim 15   , wherein said judging means further includes second means for holding a judgement result of the binary data value corresponding to the polarity for a predetermined holding time after said first means judges the polarity of the phase shift quantity.  
     
     
         18 . The modem unit as claimed in    claim 16   , wherein said judging means further includes second means for holding a judgment result of the binary data value corresponding to the polarity for a predetermined holding time after said first means judges the polarity of the phase shift quantity.  
     
     
         19 . The modem unit as claimed in    claim 13   , and further comprising: 
 means for holding the binary data value when a carrier is off.