Adaptive Nonlinear Compensation In Direct Detect Optical Transmission
An apparatus includes an optical receiver that includes a processor. The receiver is configured to direct a digital-electrical representation of a received symbol value of a pulse-amplitude modulated signal to a frequency-domain processing path of the processor and to a time-domain processing path of the processor. The processor is configured to compute, in the frequency-domain processing path, a first product of the received symbol value and a first coefficient, and to compute a second product of the received symbol value and a second coefficient. The processor is further configured to compute, in the time-domain processing path, an estimated error metric based on the first and second products, and to determine an updated first coefficient and an updated second coefficient based on said error metric. The processor is further configured to equalize a subsequent received symbol using the updated coefficients.
1 . A method, comprising:
directing to a frequency-domain processing path of a processor, and to a time-domain processing path of the processor, a digital-electrical representation of a received symbol sequence comprising sequential values of a pulse-amplitude modulated (PAM) signal;
in said frequency-domain processing path, computing a first product of a received symbol value and a first coefficient, and computing a second product of a squared value of said received symbol value and a second coefficient; and
in said time-domain processing path, estimating an error metric based on said first and second products, and determining an updated first coefficient and an updated second coefficient based on said error metric.
2 . The method of claim 1 , wherein said updated first coefficient and said updated second coefficient are determined based on said error metric and a time-delayed representation of said received symbol value.
3 . The method of claim 1 , wherein said error metric is determined as a squared difference between a decided value of said received symbol value and a sum of said first and second products.
4 . The method of claim 1 , further comprising performing a frequency-domain computation to determine said squared value.
5 . The method of claim 1 , wherein said pulse-amplitude modulated signal is a single-sideband (SSB) PAM4 signal.
6 . The method of claim 1 , wherein said digital-electrical representation includes two samples of each received symbol value.
7 . A non-transitory processor-readable medium having embodied therein executable program code that when executed by a processor causes the processor perform the method of claim 1 .
8 . A method of manufacturing an optical receiver, comprising:
configuring an optical receiver to direct a digital-electrical representation of a received optical symbol value of a pulse-amplitude modulated signal to a frequency-domain processing path of a receiver processor and to a time-domain processing path of said receiver processor;
configuring said receiver processor to compute, in said frequency-domain processing path, a first product of a first coefficient and said received symbol value, and to compute a second product of a second coefficient and a squared value of said received symbol value; and
configuring said processor to compute, in said time-domain processing path, an estimated error metric based on said first and second products, and to determine an updated first coefficient and an updated second coefficient based on said error metric.
9 . The method of claim 8 , wherein said updated first coefficient and said updated second coefficient are determined based on said error metric and a time-delayed representation of said received symbol value.
10 . The method of claim 8 , wherein said error metric is determined as a squared difference between a decided value of said received symbol value and a sum of said first and second products.
11 . The method of claim 8 , wherein said error metric is computed based on a first sample of said received symbol value, and a second sample of said received symbol value is equalized using said corrected first coefficient and said corrected second coefficient.
12 . The method of claim 8 , wherein said first and second products are computed in the frequency-domain processing path, and further comprising determining in said time domain processing path said corrected first coefficient and said corrected second coefficient based on a time-delayed representation of said squared value.
13 . The method of claim 8 , wherein said digital-electrical representation includes two samples of each received symbol value.
14 . An apparatus, comprising:
an optical receiver configured to direct a digital-electrical representation of a received optical symbol value of a pulse-amplitude modulated signal to a frequency-domain processing path of a processor and to a time-domain processing path of said processor,
the processor configured to:
compute, in said frequency-domain processing path, a first product of said received symbol value and a first coefficient, and to compute a second product of said received symbol value and a second coefficient;
compute, in said time-domain processing path, an estimated error metric based on said first and second products, and to determine an updated first coefficient and an updated second coefficient based on said error metric; and
equalize a subsequent received signal using the updated coefficients.
15 . The apparatus of claim 14 , wherein the updated first coefficient and the updated second coefficient are determined based on said error metric and a time-delayed representation of said received symbol value.
16 . The apparatus of claim 14 , wherein said error metric is determined as a squared difference between a decided value of said received symbol value and a sum of said first and second products.
17 . The apparatus of claim 14 , wherein said error metric is computed based on a first sample of said received symbol value, and a second sample of said received symbol value is equalized using the updated first coefficient and the updated second coefficient.
18 . The apparatus of claim 14 , wherein said the updated first coefficient and the updated second coefficient are determined in said time domain processing path based on a time-delayed representation of said squared value.
19 . The apparatus of claim 14 , wherein said pulse-amplitude modulated signal is a single-sideband (SSB) PAM4 signal.
20 . The apparatus of claim 14 , wherein said digital-electrical representation includes two samples of each received symbol value.