Non-linear propagation impairment equalization

Patent metadata

Field	Value
Publication number	US-9941963-B2
Application number	US-201415309113-A
Country	US
Kind code	B2
Filing date	May 12, 2014
Priority date	May 12, 2014
Publication date	Apr 10, 2018
Grant date	Apr 10, 2018

Abstract

A method ( 10 ) of non-linear propagation impairment equalization, the method comprising the steps of: a. receiving ( 12 ) communications traffic carried by an optical communications signal transmitted over an optical communications link; b. generating ( 14 ) a time dependent filter representation of a nonlinear time-variant impulse response of the inverse of the optical communications link; and c. applying ( 16 ) the time dependent filter representation to the received communications traffic to form non-linear propagation impairment equalized communications traffic. An optical communications link nonlinear propagation impairment equalizer and optical communications signal receiver apparatus are also provided.

First claim

The invention claimed is:

1. A method of non-linear propagation impairment equalization, the method comprising the steps of:
a. receiving communications traffic carried by an optical communications signal transmitted over an optical communications link;
b. generating a time dependent filter representation of a nonlinear time-variant impulse response of the inverse of the optical communications link by generating a discrete-time representation of the nonlinear time-variant impulse response of the inverse of the optical communications link using a frequency resolved log perturbation analytical approximation of the nonlinear Schrödinger equation; and
c. applying the time dependent filter representation to the received communications traffic to form non-linear propagation impairment equalized communications traffic.

2. A method as claimed in claim 1 , wherein:
step a. additionally comprises sampling the optical communications signal at a sampling rate, 1/T, to obtain a sequence of input samples, {x k }, of the communications traffic;
step b. comprises, at a sampling time, kT, generating a plurality of coefficients, h k,i , of the discrete-time representation of the nonlinear time-variant impulse response of the inverse of the optical communications link;
the optical communications signal has a signal bandwidth and the optical communications link has a nonlinear transfer function, and the nonlinear time-variant impulse response is a Fourier transform of said nonlinear transfer function; and
step c. comprises obtaining a first frequencies parameter, N f , being a number of frequencies selected to represent the nonlinear transfer function of the optical communications link over the signal bandwidth, and step c. comprises generating a sequence of equalized samples, {y k }, from the sequence of input samples, each equalized sample, y k , being generated as

y
k

=

∑

i
=

-

N
2

N
2

⁢

⁢

h

k
,
i

⁢

x

k
-
i

,

where N 2 =(N f −1)/2.

3. A method as claimed in claim 2 , wherein the coefficients, h k,i are generated by:
obtaining a second frequencies parameter, M, being a number of frequencies selected to represent a time- and frequency-dependent nonlinear distortion term of the nonlinear transfer function of the optical communications link over the signal bandwidth;
selecting one of the input samples, x k , and then selecting a plurality, M, of the input samples centered around the selected one of the input samples;
calculating a discrete Fourier transform, X k,m , of the selected plurality of input samples as

X

k
,
m

=

∑

ℓ
=

-

M
2

M
2

⁢

⁢

x

k
+
ℓ

⁢

e

-
j

⁢

⁢
2
⁢

π
⁢
ℓ

/
M

,

m
=

-

M
2

,

…
⁢

⁢

M
2

,

where M 2 =(M−1)/2; calculating a discrete Fourier transform Ø k, h , of said nonlinear distortion term as

ϕ

k
,
h

=

∑

m
=

-

M
2

M
2

⁢

∑

n
=

M
2

M
2

⁢

⁢

K
⁡

(

h

N
f

Assignees

• Ericsson Telefon Ab L M

Inventors

• Magri Roberto
• Forestieri Enrico
• Secondini Marco
• Marsella Domenico

Classifications

• H04B10/2531

  using spectral inversion · CPC title

• H04B10/25133 Primary

  including a lumped electrical or optical dispersion compensator (H04B10/2519, H04B10/2525 takes precedence) · CPC title

• H04L25/03191

  in which the receiver makes a selection between different metrics · CPC title

• H04B10/25073

  using spectral equalisation, e.g. spectral filtering · CPC title

• H04B10/07951

  Monitoring or measuring chromatic dispersion or PMD · CPC title