Complexity reduced feed forward carrier recovery methods for m-qam modulation formats

Abstract

The present disclosure provides a method of carrier phase error removal associated with an optical communication signal. The method includes estimating and removing a first phase angle associated with an information signal using coarse phase recovery, the information symbol being associated with a digital signal, the digital signal representing the optical communication signal; estimating a carrier frequency offset between a receiver light source and a transmitter light source by using the estimated first phase angle, the carrier frequency offset being associated with the information signal; removing carrier phase error associated with the carrier frequency offset; and estimating and removing a second phase angle associated with the information signal, the estimated second phase angle being based on the estimated first phase angle and the estimated carrier frequency offset.

1 . A method of carrier phase error removal, the method comprising:
 removing, using a coarse phase recovery device, a first phase angle associated with an information symbol to provide a coarse phase recovered signal, the information symbol being associated with a digital signal, the digital signal being an optical high-order communication signal;   removing a carrier frequency offset by using the first phase angle to provide a carrier frequency offset removed signal, the carrier frequency offset being associated with a current information symbol;   removing carrier phase error associated with the carrier frequency offset; and   removing, using the coarse phase recovered signal and the carrier frequency offset removed signal, a second phase angle associated with the optical high-order communication signal modulated with the current information symbol to provide a refined phase recovered signal, the second phase angle being removed by performing a maximum likelihood carrier phase estimation.   
     
     
         2 . The method of  claim 1 , wherein removing the first phase angle comprises estimating the first phase angle using a decision-directed phase-locked loop. 
     
     
         3 . The method of  claim 1 , wherein removing the first phase angle comprises estimating the first phase angle using a coarse blind phase search. 
     
     
         4 . The method of  claim 1 , wherein removing the second phase angle comprises performing a maximum likelihood estimate based on the first phase angle and the carrier frequency offset. 
     
     
         5 . The method of  claim 1 , wherein removing the second phase angle comprises performing a phase-constrained blind phase search. 
     
     
         6 . The method of  claim 1 , further comprising removing a third phase angle associated with the information symbol, the third phase angle being based on the second phase angle and the carrier frequency offset. 
     
     
         7 . The method of  claim 6 , wherein removing the third phase angle comprises performing a maximum likelihood estimate to generate a maximum likelihood estimator, the maximum likelihood estimator being used to adjust the carrier frequency offset based on the second phase angle. 
     
     
         8 . An apparatus to perform carrier phase error removal, the apparatus comprising:
 a processing device; and   a receiver, the receiver receiving an information symbol, the information symbol being associated with a digital signal, the digital signal being an optical high-order communication signal, the receiver transmitting the information symbol to the processing device,   the processing device removing a first phase angle associated with the information symbol using coarse phase recovery to provide a coarse phase recovered signal, the processing device removing a carrier frequency offset using the first phase angle to provide a carrier frequency offset removed signal, the carrier frequency offset removed signal being associated with the optical high-order communication signal modulated with a current information symbol, the processing device removing carrier phase error associated with the carrier frequency offset, the processing device removing a second phase angle associated with the optical high-order communication signal modulated with the current information symbol to provide a refined phase recovered signal, the second phase angle being removed using the coarse phase recovered signal and the carrier frequency offset removed signal by performing a maximum likelihood carrier phase estimation.   
     
     
         9 . The apparatus of  claim 8 , wherein removing the first phase angle by the processing device comprises estimating the first phase angle using a decision-directed phase-locked loop. 
     
     
         10 . The apparatus of  claim 8 , wherein removing the first phase angle by the processing device comprises estimating the first phase angle using a coarse blind phase search. 
     
     
         11 . The apparatus of  claim 8 , wherein removing the second phase angle by the processing device comprises performing the maximum likelihood carrier phase estimation based on the first phase angle and the carrier frequency offset. 
     
     
         12 . The apparatus of  claim 8 , wherein removing the second phase angle by the processing device comprises performing a phase-constrained blind-phase search. 
     
     
         13 . The apparatus of  claim 12 , further comprising removing a third phase angle associated with the information symbol by the processing device, the third phase angle being based on the second phase angle and the carrier frequency offset. 
     
     
         14 . The apparatus of  claim 13 , wherein removing the third phase angle by the processing device comprises performing a maximum likelihood estimate to generate a maximum likelihood estimator used to adjust the carrier frequency offset based on the second phase angle. 
     
     
         15 . A computer-readable storage medium storing instructions that, when executed by a processing device, cause the processing device to perform operations comprising:
 removing a first phase angle associated with an information symbol using coarse phase recovery to provide a coarse phase recovered signal, the information signal being associated with a digital signal, the digital signal being an optical high-order communication signal;   removing a carrier frequency offset by using the first phase angle to provide a carrier frequency offset removed signal, the carrier frequency offset being associated with the optical high-order communication signal modulated with a current information symbol;   removing carrier phase error associated with the carrier frequency offset; and   removing, using the coarse phase recovered signal and the carrier frequency offset removed signal, a second phase angle associated with the optical high-order communication signal modulated with the current information symbol to provide a refined phase angle recovered signal, the second phase angle being removed by performing a maximum likelihood carrier phase estimation.   
     
     
         16 . The computer-readable storage medium of  claim 15 , wherein removing the first phase angle comprises estimating the first phase angle using a decision-directed phase-locked loop. 
     
     
         17 . The computer-readable storage medium of  claim 15 , wherein removing the first phase angle comprises estimating the first phase angle using a coarse blind phase search. 
     
     
         18 . The computer-readable storage medium of  claim 15 , wherein removing the second phase angle comprises performing a phase-constrained blind phase search. 
     
     
         19 . The computer-readable storage medium of  claim 15 , wherein the operations further comprise removing a third phase angle associated with the information symbol, the third phase angle being based on the estimated second phase angle and the carrier frequency offset. 
     
     
         20 . The computer-readable storage medium of  claim 19 , wherein removing the third phase angle comprises performing a maximum likelihood estimate to generate a maximum likelihood estimator used to adjust the carrier frequency offset based on the second phase angle.