Dual stage carrier phase estimation in a coherent optical signal receiver
View Patent ↗A system and method implementing dual stage carrier phase estimation (CPE) in a coherent receiver for an optical fiber communication system. In the first stage, a feed-forward CPE is implemented to make an initial carrier phase estimation of a training sequence. The initial carrier phase estimation is coupled to the second stage which implements a decision-feedback CPE. After a training period, accurate bit decision for system traffic can be achieved using the decision-feedback CPE.
1. A system for estimating a phase of an optical signal having data modulated thereon according to a phase shift keying modulation format, the system comprising:
an optical signal receiver for receiving said optical signal and providing at least one electrical signal representative of said optical signal; and
a digital signal processor (DSP) configured to receive said electrical signal, to perform a feed forward carrier phase estimation function to provide an initial carrier phase estimation, and to perform a decision feedback carrier phase estimation function using said initial carrier phase estimation to provide an operational carrier phase estimation in response to feed back from a bit decision function, said bit decision function configured to determine data values from said electrical signal in response to said operational carrier phase estimation to provide an output representative of the data modulated on said optical signal.
2. A system according to claim 1 , wherein said feed forward carrier phase estimation function uses an Mth power scheme.
3. A system according to claim 1 , wherein said optical signal comprises a training sequence in a training mode of said system, and wherein said DSP is configured to perform a training sequence bit error rate test function, said training sequence bit error rate test function being configured to attempt synchronization of said training sequence using a carrier phase estimation provided by said feed forward carrier phase estimation function.
4. A system according to claim 3 , wherein said feed forward carrier phase estimation function is configured to provide said initial carrier phase estimation only after said training sequence is synchronized in said training sequence bit error rate test function.
5. A system according to claim 3 , wherein said training sequence comprises a pseudo random bit sequence.
6. A system according to claim 1 , wherein said system is configured to enter an operating mode after said initial carrier phase estimation is provided to said decision feedback carrier phase estimation function, wherein said optical signal comprises user data, and wherein said DSP is configured to provide said electrical signal to said decision feedback carrier phase estimation function during said operating mode by bypassing said feed forward carrier phase estimation function.
7. A optical communication system comprising:
a transmitting terminal for transmitting a plurality of optical signals, each at a different associated wavelength, on an optical information path, at least one of said optical signals being a phase shift keying (PSK) signal having data modulated thereon according to a phase shift keying modulation format;
a receiving terminal coupled to said optical information path for receiving at least one of said plurality of optical signals, said receiving terminal comprising:
an optical signal receiver for receiving said PSK signal and providing at least one electrical signal representative of said PSK signal; and
a digital signal processor (DSP) configured to receive said electrical signal, to perform a feed forward carrier phase estimation function configured to provide an initial carrier phase estimation, and to perform a decision feedback carrier phase estimation function using said initial carrier phase estimation to provide an operational carrier phase estimation in response to feed back from a bit decision function, said bit decision function configured to determine data values from said electrical signal in response to said operational carrier phase estimation to provide an output representative of the data modulated on said PSK signal.
8. A system according to claim 7 , wherein said feed forward carrier phase estimation function uses an Mth power scheme.
9. A system according to claim 7 , wherein said PSK signal comprises a training sequence in a training mode of said system, and wherein said DSP is configured to perform a training sequence bit error rate test function, said training sequence bit error rate test function being configured to attempt synchronization of said training sequence using a carrier phase estimation provided by said feed forward carrier phase estimation function.
10. A system according to claim 9 , wherein said feed forward carrier phase estimation function is configured to provide said initial carrier phase estimation only after said training sequence is synchronized in said training sequence bit error rate test function.
11. A system according to claim 9 , wherein said training sequence comprises a pseudo random bit sequence.
12. A system according to claim 9 , wherein said system is configured to enter an operating mode after said initial carrier phase estimation function is provided to said decision feedback carrier phase estimation function, wherein said PSK signal comprises user data and said DSP is configured to provide said electrical signal to said decision feedback carrier phase estimation function during said operating mode by bypassing said feed forward carrier phase estimation function.
13. A detection method for demodulating an optical signal having data modulated thereon according to a phase shift keying modulation format, the method comprising
converting said optical signal into at least one electrical signal representative of said optical signal;
performing a feed forward carrier phase estimation function to provide an initial carrier phase estimation associated with said optical signal;
performing a decision feedback carrier phase estimation function using said initial carrier phase estimation to provide an operational carrier phase estimation associated with said optical signal in response to feedback from a bit decision function; and
performing the bit decision function to determine data values from said electrical signal in response to said operational carrier phase estimation to provide an output representative of the data modulated on said optical signal.
14. A method according to claim 13 , wherein said feed forward carrier phase estimation function uses an Mth power scheme.
15. A method according to claim 13 , wherein said optical signal comprises a training sequence in a training mode of said system, and wherein said method further comprises performing a training sequence bit error rate test function to attempt synchronization of said training sequence using a carrier phase estimation provided by said feed forward carrier phase estimation function.
16. A method according to claim 15 , wherein said performing said feed forward carrier phase estimation function comprises providing said initial carrier phase estimation only after said training sequence is synchronized using said training sequence bit error rate test function.
17. A method according to claim 15 , wherein said training sequence comprises a pseudo random bit sequence.
18. A method according to claim 15 , said method comprising entering a operating mode after said initial carrier phase estimation function is provided to said decision feedback carrier phase estimation function, wherein said optical signal comprises user data, and wherein said method comprises providing said electrical signal to said decision feedback carrier phase estimation function during said operating mode by bypassing said feed forward carrier phase estimation function.
19. A method of training a decision feedback carrier phase estimation function in a digital signal processing (DSP) based optical signal receiver, said method comprising:
transmitting an optical signal to said receiver, said optical signal having a training sequence modulated thereon according to a phase shift keying modulation format;
converting said optical signal into at least one electrical signal representative of said optical signal;
performing a feed forward carrier phase estimation function to provide an initial carrier phase estimation associated with said optical signal;
performing a training sequence bit error rate test function to attempt to synchronize said training sequence using said initial carrier phase estimation;
providing said initial carrier phase estimation to said decision feedback carrier phase estimation function if said training sequence bit error rate test function synchronizes said training sequence; and
performing said decision feedback carrier phase estimation function using said initial carrier phase estimation to provide an operational carrier phase estimation associated with said optical signal in response to feedback from a bit decision function.
20. A method according to claim 19 , wherein said feed forward carrier phase estimation function uses an Mth power scheme to provide the initial carrier phase estimation.
21. A method according to claim 19 , wherein performing said training sequence bit error rate test function includes rotating test sequence signal samples through a plurality of possible phase rotation values until synchronization is achieved.
22. A method according to claim 19 , wherein said feed forward carrier phase estimation function uses an Mth power scheme to provide an Mth power carrier phase estimation, wherein performing said training sequence bit error rate test function includes rotating test sequence signal samples through a plurality of possible phase rotation values until synchronization is achieved, and wherein said initial carrier phase estimation includes the Mth power carrier phase plus a phase rotation value that resulted in synchronization.