Method and apparatus of algorithm for coherent receivers with M-QAM modulation format
An improved Eighth-Order Statistics (EOS) blind phase recovery method is proposed for high-order coherent modulation formats. The method combining EOS blind phase estimate with maximum-likelihood (ML) carrier phase estimate uses multi-stage feed-forward carrier phase recovery algorithm. Experimental results show that the proposed new algorithm can reduce the required computational effort by more than a factor of 3 for 16-QAM system.
1. A method for carrier phase recovery of a carrier wave, the method comprising:
receiving a carrier wave that was modulated at a signaling rate with a plurality of digital signals;
generating a first estimate of the carrier wave's phase angle using eighth-order statistics (EOS) comprising
dividing the digital signal into M number of blocks, wherein M does not exceed 10,
performing signal decimation on each of the M number of blocks by lowering the symbol sequences by an integer factor N to form a new signal sequence in each of the M number of blocks,
performing EOS blind phase recovery estimation on each of the new signal sequences; and
generating a second estimate of the carrier wave's phase angle comprising performing a maximum likelihood estimate based at least in part on the first estimate.
2. The method of claim 1 , wherein the carrier wave is modulated with M-ary quadrature amplitude modulation.
3. The method of claim 1 , wherein the computational effort of estimating the carrier wave's phase using the eighth order statistics estimate based on the group of selected samples, followed by generating at least one additional estimate of the carrier wave's phase angle including performing a maximum likelihood estimate based at least in part on the preceding estimate, is reduced by more than a factor of 3 for a 16-QAM system as compared to the computational effort of estimating the carrier wave's phase using a single stage eighth -order statistics method based on all of the contiguous samples from which the group of selected samples was selected, while maintaining at least the same bit error rate (BER) performance.
4. The method of claim 1 , further comprising generating a third estimate of the carrier wave's phase angle based at least in part on the second estimate.
5. An article of manufacture including a non-transitory computer-readable medium having instructions stored thereon, the instructions comprising:
instructions for sampling a received carrier wave modulated at a signaling rate with a plurality of digital signals;
instructions for generating a first estimate of the carrier wave's phase angle comprising
dividing the digital signal into M number of blocks, wherein M does not exceed 10,
performing signal decimation on each of the M number of blocks by lowering the symbol sequences by an integer factor N to form a new signal sequence in each of the M number of blocks,
performing EOS blind phase recovery estimation on each of the new signal sequences; and
instructions for generating a second estimate of the carrier wave's phase angle based at least in part on the first estimate.
6. The article of manufacture of claim 5 , wherein the carrier wave is modulated with M-ary quadrature amplitude modulation.
7. The article of manufacture of claim 5 , wherein the generating a second phase angle estimate comprises performing a maximum likelihood estimate based at least in part on the first phase angle estimate.
8. The article of manufacture of claim 7 , wherein the instructions stored thereon further comprise generating a third phase angle estimate based at least in part on the second estimate.
9. An apparatus for carrier phase recovery of a carrier wave, the apparatus comprising:
a receiver for receiving a carrier wave modulated at a signaling rate with a plurality of digital signals;
a first phase angle estimator for generating a first estimate of the carrier wave's phase angle using eighth-order statistics comprising
dividing the digital signal into M number of blocks, wherein M does not exceed 10,
performing signal decimation on each of the M number of blocks by lowering the symbol sequences by an integer factor N to form a new signal sequence in each of the M number of blocks,
performing EOS blind phase recovery estimation on each of the new signal sequences; and
a second phase angle estimator for generating a second estimate of the carrier wave's phase angle based at least in part on the first estimate.
10. The apparatus of claim 9 , wherein the carrier wave is modulated with M-ary quadrature amplitude modulation.
11. The apparatus of claim 10 , wherein the second phase angle estimator generates a second phase angle estimate, including performing a maximum likelihood estimate based at least in part on the first phase angle estimate.
12. The apparatus of claim 11 , further comprising a third phase angle estimator for generating a third estimate of the carrier wave's phase angle based at least in part on the second phase angle estimate.