Joint carrier phase estimation and forward error correction
View Patent ↗Methods and systems for processing an optical signal in a communication system are disclosed. The disclosed methods yield benefits for estimation and tracking of carrier phase of received signals at a digital coherent receiver without the use of differential coding. Specifically, phase ambiguity is removed by calculating the slope of the CPE at a location where the CPE begins to lose track of the received carrier phase signal. As such, a CPE offset adjustment may be applied in accordance with the calculated slope to reduce the number of ones and zeros corrected by a FEC decoder. Thus, the FEC aided CPE scheme may be a feed forward scheme that requires no training.
1. A receiver utilized in an optical communication system comprising:
a decision circuit for receiving an input signal and providing an output signal representing logic ones and zeros in response to a comparison of said input signal with a Carrier Phase Estimation (CPE) of said input signal;
a forward error correction (FEC) decoder configured to decode said output signal and to provide feedback representative of the number of errors corrected by said FEC decoder and indicating a polarity of said input signal; and
a CPE offset adjuster configured to adjust said CPE in response to said feedback to reduce a number of said ones and zeros corrected by said FEC decoder.
2. The apparatus according to claim 1 , wherein said CPE offset adjuster is configured to adjust said CPE by an offset in a direction determined by the polarity of said input signal.
3. The apparatus according to claim 1 , wherein said CPE offset adjuster is configured to adjust said CPE by an offset in a direction determined by a slope of the CPE at a location where the CPE offset begins.
4. The apparatus according to claim 1 , wherein said input signal is a modulated signal using a quadrature phase shift keying (QPSK) format.
5. The apparatus according to claim 1 , wherein said CPE offset adjuster is configured to add said number errors corrected by said FEC decoder over one or more sampling periods to determine a total number of said errors corrected by said FEC decoder over said one or more sampling periods, and wherein said CPE offset adjuster is configured to adjust said CPE when said total number of said errors exceeds a predetermined error threshold.
6. The apparatus according to claim 1 , wherein said CPE offset adjuster is configured to add said number errors corrected by said FEC decoder over one or more frame alignment words to determine a total number of said errors corrected by said FEC decoder over said one or more frame alignment words, and wherein said CPE offset adjuster is configured to adjust said CPE when said total number of said errors exceeds a predetermined error threshold.
7. An optical communication system comprising:
an optical signal transmitter comprising an encoder for encoding a binary data stream and a modulator for modulating said encoded binary data stream to produce an encoded optical signal; and
an optical signal receiver for receiving said encoded optical signal, said optical signal receiver comprising:
a demodulator for demodulating said encoded optical signal to provide an input signal;
a decision circuit for receiving said input signal and providing an output signal representing logic ones and zeros in response to comparison of said input signal with a Carrier Phase Estimation (CPE) of said input signal;
a Forward Error Correction (FEC) decoder configured to decode said output signal and to provide feedback representative of a number of errors corrected by said FEC decoder and indicating a polarity of said input signal; and
a CPE offset adjuster configured to adjust said CPE in response to said feedback to reduce the number of said ones and zeros corrected by said FEC decoder.
8. The system according to claim 7 , wherein said CPE offset adjuster is configured to adjust said CPE by an offset in a direction determined by the polarity of said input signal.
9. The system according to claim 7 , wherein said CPE offset adjuster is configured to adjust said CPE by an offset in a direction determined by a slope of the CPE at a location where the CPE offset begins.
10. The system according to claim 7 , wherein said input signal is a modulated signal using a Quadrature Phase Shift Keying (QPSK) format.
11. The system according to claim 7 , wherein said CPE offset adjuster is configured to add said number errors corrected by said FEC decoder over one or more sampling periods to determine a total number of said errors corrected by said FEC decoder over said one or more sampling periods, and wherein said CPE offset adjuster is configured to adjust said CPE when said total number of said errors exceeds a predetermined error threshold.
12. The system according to claim 7 , wherein said CPE offset adjuster is configured to add said number errors corrected by said FEC decoder over one or more frame alignment words to determine a total number of said errors corrected by said FEC decoder over said one or more frame alignment words, and wherein said CPE offset adjuster is configured to adjust said CPE when said total number of said errors exceeds a predetermined error threshold.
13. A method for processing a received optical communication signal, comprising:
receiving an input signal and providing an output signal representing logic ones and zeros in response to comparing said input signal with a Carrier Phase Estimation (CPE) of said input signal;
decoding said output signal and providing a feedback representative of a number of errors corrected by a Forward error Correction (FEC) decoder and indicating a polarity of said input signal; and
adjusting said CPE in response to said feedback to reduce the number of said ones and zeros corrected by said FEC decoder.
14. The method of claim 13 further comprising, adjusting said CPE by an offset in a direction determined by the polarity of said input signal.
15. The method of claim 13 further comprising, adjusting said CPE by an offset in a direction determined by a slope of the CPE at a location where the CPE offset begins.
16. The method of claim 13 further comprising, modulating the input signal using a QPSK format.
17. The method of claim 13 wherein providing a feedback representative of a number of errors corrected by a FEC decoder, further comprising adding said number errors corrected by said FEC decoder over one or more sampling periods to determine a total number of said errors corrected by said FEC decoder over said one or more sampling periods, and wherein said CPE offset adjuster is configured to adjust said CPE when said total number of said errors exceeds a predetermined error threshold.
18. The method of claim 13 wherein providing a feedback representative of a number of errors corrected by a FEC decoder, further comprising adding said number errors corrected by said FEC decoder over one or more frame alignment words to determine a total number of said errors corrected by said FEC decoder over said one or more frame alignment words, and wherein said CPE offset adjuster is configured to adjust said CPE when said total number of said errors exceeds a predetermined error threshold.