Method and apparatus for performing joint timing recovery of multiple received signals

Abstract

Method and apparatus for performing joint timing recovery in a digital receiver using multiple input signals. The apparatus comprises a plurality of phase detectors, a summer, a level shifter, a loop filter and a numerically controlled oscillator NCO. The phase detectors produce a phase signal by comparing a timing signal produced by the NCO with the input signals. The phase signals are then summed and the level shifter adjusts the summed value to compensate for the number of signals used to form the sum, i.e., the summed value is adjusted to be within the input range of the NCO.

1. A method for performing timing recovery comprising:
 producing a phase signal  plurality of phase signals by comparing a signal received at each of a plurality of inputs to a timing signal produced by a numerically controlled oscillator (NCO);  
 summing said plurality of phase signals to produce a sum;  
 adjusting said sum into an input range for the numerically controlled oscillator (NCO), wherein said adjusting comprises: 
 determining whether the signal received at each input can be accurately received, wherein said determining comprises ignoring a received signal having a low amplitude or signal level; and  
 dividing the sum by a number of potentially receivable inputs  the received signals that were determined to be accurately received to produce an adjusted sum, wherein the number of the received signals that were determined to be accurately received is less than a number of the inputs that received a signal; and  
 
 producing a  the timing signal within the NCO in response to the adjusted sum.  
 
     
     
       2. The method of  claim 1  wherein said determining comprises:
 determining whether an amplitude of the signal received at each input is greater than a threshold value.  
 
     
     
       3. A method for performing timing recovery comprising:
 a plurality of phase detectors producing a plurality of phase signals, wherein each of the phase detectors comprises a respective first input that receives a respective signal, wherein each of the phase detectors comprises a respective second input that receives a timing signal produced by a numerically controlled oscillator ( NCO ) , and wherein each of the phase detectors produces a respective phase signal of the plurality of phase signals  by comparing a phase of the respective signal received at each of a plurality of inputsthe first input of the phase detector to a phase of the timing signal produced by a numerically controlled oscillator (NCO)received at the second input of the phase detector;  
 summing said plurality of phase signals to produce a sum;  
 adjusting said sum into an input range for the numerically controlled oscillator (NCO), wherein said adjusting comprises: 
 determining whether each  a number of the first inputs that have a receivable signal, is receivable,  wherein said determining comprises: 
 determining whether an amplitude of each signal at the first inputs is above a threshold value;  
 
 determining an offset using a number of receivable inputs; and  
 adjusting the sum using the offset; and  
 dividing said sum by the number of the first inputs that have a receivable signal to produce an adjusted sum, wherein the number of the first inputs that have a receivable signal is less than a number of the first inputs that receive a respective signal; and  
 
 producing a  the timing signal within the NCO in response to the adjusted sum.  
 
     
     
       4. A method for performing timing recovery comprising:
 producing a phase signal  plurality of phase signals by comparing a signal received at each of a plurality of inputs to a timing signal produced by a numerically controlled oscillator (NCO);  
 summing said plurality of phase signals to produce a sum;  
 adjusting said sum into an input range for the numerically controlled oscillator (NCO), wherein said adjusting comprises: 
 determining whether each input is receivable  has a receivable signal;  
 determining an offset using a number of the inputs determined to have a receivable inputs  signal; and  
 adjusting the sum using the offset to produce an adjusted sum, wherein said adjusting by said offset comprises: 
 adding the sum by  to the offset if the sum is below the input range; and  
 
 
 producing a  the timing signal within the NCO in response to the adjusted sum.  
 
     
     
       5. A method for performing timing recovery comprising:
 producing a phase signal  plurality of phase signals by comparing a signal received at each of a plurality of inputs to a timing signal produced by a numerically controlled oscillator (NCO);  
 summing said plurality of phase signals to produce a sum;  
 adjusting said sum into an input range for the numerically controlled oscillator (NCO), wherein said adjusting comprises: 
 determining whether each input is receivable  has a receivable signal;  
 determining an offset using a number of the inputs determined to have a receivable inputs  signal; and  
 adjusting the sum using the offset to produce an adjusted sum, wherein said adjusting by said offset comprises: 
 subtracting the offset from the sum by the offset  if the sum is above the input range; and  
 
 
 producing a  the timing signal within the NCO in response to the adjusted sum.  
 
     
     
       6. An apparatus for performing timing recovery of a signal received at a plurality of inputs, said apparatus comprising:
 a plurality of phase detectors each detecting a phase of said signal at a different input by comparing the input signal to a timing signal from a numerically controlled oscillator (NCO);  
 a summer for adding said detected phases to form a sum;  
 a level shifter for adjusting the sum to produce an adjusted sum that is within an input range of said NCO;  
 a loop filter for filtering the adjusted sum;  
 the NCO for generating a  the timing signal in response to the filtered sum;  
 a plurality of signal detectors each for determining whether an input signal is receivable; and  
 a decision circuit using a total of receivable input signals to determine an adjustment to the sum by said level shifter,  
   wherein said decision circuit determines an offset that is added to or subtracted from the sum by said level shifter.    
 
     
     
       7. The apparatus of  claim 6  wherein said decision circuit divides the sum by the total of receivable input signals. 
     
     
       8. The apparatus of  claim 6  wherein said decision circuit determines an offset that is added to or subtracted from the sum by said level shifter. 
     
     
       9. An apparatus for performing timing recovery of a signal received at a plurality of inputs, said apparatus comprising:
   a plurality of phase detectors each detecting a phase of said signal at a different input by comparing the input signal to a timing signal from a numerically controlled oscillator  ( NCO );      a summer for adding said detected phases to form a sum;        a level shifter for adjusting the sum to produce an adjusted sum that is within an input range of said NCO;        a loop filter for filtering the adjusted sum to produce a filtered sum;        the NCO for generating the timing signal in response to the filtered sum;        a plurality of signal detectors each for determining whether an input signal is receivable; and        a decision circuit using a total number of inputs determined to have a receivable input signal so as to determine an offset that is added to or subtracted from the sum by said level shifter.      
     
     
       10. An apparatus for performing timing recovery of a signal received at a plurality of inputs, the apparatus comprising:
   means for producing a plurality of phase signals by comparing a signal received at each of a plurality of inputs to a timing signal produced by a numerically controlled oscillator  ( NCO );      means for summing the plurality of phase signals to produce a sum;        means for adjusting the sum into an input range for the numerically controlled oscillator  ( NCO ) , wherein the means for adjusting includes means to determine an offset using a number of receivable inputs and to adjust the sum so as to produce an adjusted sum by adding the offset to the sum or subtracting the offset from the sum; and        means for producing the timing signal within the NCO in response to the adjusted sum.      
     
     
       11. The apparatus of  claim 10 ,
   wherein the means for adjusting the sum into an input for the NCO comprises means for determining whether each input has a receivable signal, and        wherein determining whether each input has a receivable signal includes determining whether an amplitude of each input is greater than a threshold value.      
     
     
       12. An apparatus for performing timing recovery of a signal received at a plurality of inputs, the apparatus comprising:
   means for producing a plurality of phase signals by comparing a signal received at each of a plurality of inputs to a timing signal produced by a numerically controlled oscillator  ( NCO );      means for summing the plurality of phase signals to produce a sum;        means for adjusting the sum to produce an adjusted sum that is within an input range for the numerically controlled oscillator  ( NCO ) , wherein the means for adjusting the sum comprises means for using a total number of inputs determined to have a receivable input signal so as to determine an offset for adjusting the sum; and        means for producing the timing signal within the NCO in response to the adjusted sum,        wherein if the sum is greater than the input range for the NCO, then adjusting the sum includes subtracting the offset from the sum, and        wherein if the sum is less than the input range for the NCO, then adjusting the sum includes adding the offset to the sum.      
     
     
       13. A method for performing timing recovery comprising:
   producing a plurality of phase signals by comparing a signal received at each of a plurality of inputs to a timing signal produced by a numerically controlled oscillator  ( NCO );      summing the plurality of phase signals to produce a sum;        adjusting the sum into an input range for the numerically controlled oscillator  ( NCO ) , wherein the adjusting comprises  ( i )  determining an offset using a number of inputs determined to have a receivable signal, and  ( ii )  adjusting the sum using the offset to produce an adjusted sum, wherein adjusting the sum comprises adding the offset to the sum if the sum is less than the input range; and        producing the timing signal within the NCO in response to the adjusted sum.      
     
     
       14. A method for performing timing recovery comprising:
   producing a plurality of phase signals by comparing a signal received at each of a plurality of inputs to a timing signal produced by a numerically controlled oscillator  ( NCO );      summing the plurality of phase signals to produce a sum;        adjusting the sum into an input range for the numerically controlled oscillator  ( NCO ) , wherein the adjusting comprises  ( i )  determining an offset using a number of inputs determined to have a receivable signal, and  ( ii )  adjusting the sum using the offset to produce an adjusted sum, wherein adjusting the sum comprises subtracting the offset from the sum if the sum is greater than the input range; and        producing the timing signal within the NCO in response to the adjusted sum.