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US 8,913,901 B2Granted
System and method for blind equalization and carrier phase recovery in a quadrature amplitude modulated system
AssigneeTyco Electronics Subsea Communications LLC
InventorsHongbin Zhang, Yu Sun, Alexei N. Pilipetskii
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Abstract
A system and method for blind equalization of a QAM signal. Equalization is achieved using an algorithm characterized by cost function that is a function the Euclidian distance, e.g. the minimum Euclidian distance, between points of the constellation associated with the QAM signal, i.e. the distance between symbols.
Claims17
An optical receiver system comprising:
- a digital signal processor (DSP) comprising an equalizer configured to equalize a signal representative of a quadrature amplitude modulated (QAM) optical signal transmitted over an optical transmission path,
- said equalizer being configured to equalize said signal by application of an equalization algorithm to said signal, said equalization algorithm being characterized by a cost function,
- said cost function being a function of a Euclidian distance between detected symbols of said QAM optical signal at an output of said equalizer, wherein said cost function is:
- J=E[(D2−|R2−|Re(u(n))|2|)2]+E[(D2−|R2|Im(u(n))|2|)2]
- where J represents the cost function value E[.] denotes expectation, D is said Euclidian distance and is a minimum Euclidian distance between said symbols, R2 is equal to ½ of the average symbol power at said output of said equalizer, Re(u(n)) is a real portion of said output of said equalizer for a current update cycle, and Im(u(n)) is an imaginary portion of said output of said equalizer for said current update cycle.
2 more elements
An optical receiver system comprising:
- a coherent receiver for receiving a polarization multiplexed quadrature amplitude modulated (QAM) optical signal and providing a first plurality of outputs in response to a first polarization of said optical signal and a second plurality of outputs in response to a second polarization of said optical signal;
- and
- a digital signal processor (DSP) comprising an equalizer configured apply an equalization algorithm to a first digital signal established in response to said first plurality of outputs and a second digital signal established in response to said second plurality of outputs to provide first and second digital outputs representative of a first polarization state of said QAM optical signal at which data is modulated and a second polarization state of said QAM optical signal at which data is modulated,
- said equalization algorithm being characterized by a cost function that is a function of a Euclidian distance between detected symbols of said QAM optical signal in said first digital output of said equalizer, wherein said at least one cost function is:
- J=E[(D2−|R2−|Re(u(n))|2|)2]+E[(D2−|R2|Im(u(n))|2|)2]
- where J represents the cost function value E[.] denotes expectation, D is said Euclidian distance and is a minimum Euclidian distance between said symbols, R2 is equal to ½ of the average symbol power in said first digital output of said equalizer, Re(u(n)) is a real portion of said first digital output of said equalizer for a current update cycle, and Im(u(n)) is an imaginary portion of said first digital output of said equalizer for said current update cycle.
3 more elements
A method of demodulating a quadrature amplitude modulated (QAM) optical signal using a digital signal processor (DSP) without a carrier phase estimation function for estimating a carrier phase of said QAM signal, said method comprising:
- equalizing a signal representative of said (QAM) optical signal transmitted over an optical transmission path using an equalizer configured to apply equalization algorithm to said signal, said equalization algorithm being characterized by a cost function that is a function of a Euclidian distance between detected symbols of said QAM optical signal at an output of said equalizer, wherein said cost function is:
- J=E[(D2−|R2−|Re(u(n))|2|)2]+E[(D2−|R2|Im(u(n))|2|)2]
- where J represents the cost function value E[.] denotes expectation, D is said Euclidian distance and is a minimum Euclidian distance between said symbols, R2 is equal to ½ of the average symbol power at said output of said equalizer, Re(u(n)) is a real portion of said output of said equalizer for a current update cycle, and Im(u(n)) is an imaginary portion of said output of said equalizer for said current update cycle.
Dependencies are inferred from the claim text.