Frequency offset estimator

Abstract

A complex symbol sequence ( 13 ), which is a product of an orthogonally detected complex demodulated symbol sequence ( 1 ) and a conjugate complex number of a known symbol sequence ( 2 ), is applied to phase rotating units ( 4 a, 4 b, 4 c) which change the phase of the complex symbol sequence ( 13 ) based on frequency offsets (fa, fb, fc). N-symbol adders ( 5 a, 5 b, 5 c) each add N symbol values supplied from the phase rotating units ( 4 a, 4 b, 4 c), while M-power adders ( 6 a, 6 b, 6 c) each calculate the power of a value supplied from the N-symbol adders ( 5 a, 5 b, 5 c), and add the power M times. A frequency offset control unit ( 7 ) controls frequency offsets applied to the phase rotating units ( 4 a, 4 b, 4 c) based on three power sums supplied from the M-power adders ( 6 a, 6 b, 6 c), and delivers a power offset estimate ( 8 ).

1 . A frequency offset estimator comprising: 
 symbol information removing means for receiving an orthogonally detected complex demodulated symbol sequence, and removing a symbol information component;    a plurality of power sum calculating means each for calculating a power sum for said complex demodulated symbol sequence based on an applied frequency offset after the symbol information component has been removed; and    frequency offset control means for controlling a frequency offset applied to said each power sum calculating means based on power sums calculated by said plurality of power sum calculating means, estimating a frequency offset included in said complex demodulated symbol sequence, and delivering the estimated frequency offset,    wherein said each power sum calculating means include: 
 phase rotating means for changing the phase of the complex demodulated symbol sequence based on the frequency offset applied thereto after the symbol information component has been removed,  
 N-symbol adding means for adding one or more complex symbols delivered from said phase rotating means, and  
 M-power adding means for calculating the power of the complex symbol sum calculated by said N-symbol adding mean while adding the power of one or more symbols.  
   
     
     
         2 . A frequency offset estimator comprising: 
 a plurality of symbol information removing means each for receiving one of a plurality of orthogonally detected complex demodulated symbol sequences, and removing a symbol information component included in said complex modulated symbol sequence;    maximal-ratio combining means for combining said plurality of complex demodulated symbol sequences, from which the symbol information components are removed, at a maximal ratio to generate a single complex symbol sequence;    a plurality of power sum calculating means for calculating a power sum for said complex symbol sequence after the maximal-ratio combination based on applied frequency offsets; and    frequency offset control means for controlling a frequency offset applied to said each power sum calculating means based on power sums calculated by said plurality of power sum calculating means, estimating a frequency offset included in said complex demodulated symbol sequence, and delivering the estimated frequency offset,    wherein said each power sum calculating mean include: 
 phase rotating means for changing the phase of said complex symbol sequence after the maximal-ratio combination based on the applied frequency offset,  
 N-symbol adding means for adding one or more complex symbols delivered by said phase rotating means, and  
 M-power adding means for calculating the power of a complex symbol sum calculated by said N-symbol adding means, and adding the power of one or more symbols.  
   
     
     
         3 . A frequency offset estimator comprising: 
 a plurality of frequency offset estimating units each including: 
 symbol information removing means for receiving an orthogonally detected complex demodulated symbol sequence, and removing a symbol information component,  
 a plurality of power sum calculating means each for calculating a power sum for said complex demodulated symbol sequence based on an applied frequency offset after the symbol information component has been removed, and  
 frequency offset control means for controlling a frequency offset applied to said each power sum calculating means based on power sums calculated by said plurality of power sum calculating means, estimating a frequency offset included in said complex demodulated symbol sequence, and delivering the estimated frequency offset,  
 wherein each of said plurality of power sum calculating means include: 
 phase rotating means for changing the phase of the complex demodulated symbol sequence based on the frequency offset applied thereto after the symbol information component has been removed,  
 N-symbol adding means for adding one or more complex symbols delivered from said phase rotating means, and  
 M-power adding means for calculating the power of the complex symbol sum calculated by said N-symbol adding means, and adding the power of said one or more a symbols; and  
 
   a maximal-ratio combiner for combining frequency offset estimates provided by said plurality of frequency offset estimating units at a maximal ratio to generate a single frequency offset estimate.    
     
     
         4 . A frequency offset estimating method comprising: 
 a) receiving an orthogonally detected complex demodulated symbol sequence, and removing a symbol information component;    b) calculating a power sum for said complex demodulated symbol sequence based on an applied frequency offset after the symbol information component has been removed; and    c) controlling a frequency offset applied to said step b) based on power sums calculated at said step b), estimating a frequency offset included in said complex demodulated symbol sequence, and delivering the estimated frequency offset.    wherein said step b) further includes 
 a phase rotating step for changing the phase of the complex demodulated symbol sequence based on the frequency offset applied thereto after the symbol information component has been removed,  
 an N-symbol adding step for adding one or more complex symbols delivered from said phase rotating step, and  
 an M-power adding step for calculating the power of the complex symbol sum calculated at said N-symbol adding step while adding the power of one or more symbols.  
   
     
     
         5 . A frequency offset estimating method comprising: 
 a) receiving one of a plurality of orthogonally detected complex demodulated symbol sequences, and removing a symbol information component included in said complex modulated symbol sequence;    b) combining said plurality of complex demodulated symbol sequences, from which the symbol information components are removed, at a maximal ratio to generate a single complex symbol sequence;    c) calculating a power sum for said complex symbol sequence after the maximal-ratio combination based on applied frequency offsets; and    d) controlling a frequency offset applied to said step b) based on power sums calculated at said step b), estimating a frequency offset included in said complex demodulated symbol sequence, and delivering the estimated frequency offset,    wherein said step c) further includes: 
 a phase rotating step for changing the phase of said complex symbol sequence after the maximal-ratio combination based on the applied frequency offset,  
 an N-symbol adding step for adding one or more complex symbols delivered at said phase rotating step, and  
 an M-power adding step for calculating the power of a complex symbol sum calculated at said N-symbol adding step, and adding the power of said one or more symbols.