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Introduce computation of the chromatic dispersion

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Change-Id: I3ee039154568d4255444fa8db5e89945851010f4
This commit is contained in:
Alessio Ferrari
2020-05-21 11:00:17 +02:00
committed by Jan Kundrát
parent b74d0a4919
commit 94949d955b
5 changed files with 76 additions and 16 deletions
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36
gnpy/core/elements.py
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@@ -22,7 +22,7 @@ instance as a result.
from numpy import abs, arange, array, divide, errstate, ones
from numpy import interp, mean, pi, polyfit, polyval, sum
from scipy.constants import h
from scipy.constants import h, c
from collections import namedtuple
from gnpy.core.utils import lin2db, db2lin, arrange_frequencies, snr_sum
@@ -82,6 +82,12 @@ class Transceiver(_Node):
self.snr = None
self.passive = False
self.baud_rate = None
self.chromatic_dispersion = None
def _calc_cd(self, spectral_info):
""" Updates the Transceiver property with the CD of the received channels. CD in ps/nm.
"""
self.chromatic_dispersion = [carrier.chromatic_dispersion * 1e3 for carrier in spectral_info.carriers]
def _calc_snr(self, spectral_info):
with errstate(divide='ignore'):
@@ -141,7 +147,8 @@ class Transceiver(_Node):
f'osnr_ase_01nm={self.osnr_ase_01nm!r}, '
f'osnr_ase={self.osnr_ase!r}, '
f'osnr_nli={self.osnr_nli!r}, '
f'snr={self.snr!r})')
f'snr={self.snr!r}, '
f'chromatic_dispersion={self.chromatic_dispersion!r})')
def __str__(self):
if self.snr is None or self.osnr_ase is None:
@@ -151,16 +158,19 @@ class Transceiver(_Node):
osnr_ase = round(mean(self.osnr_ase), 2)
osnr_ase_01nm = round(mean(self.osnr_ase_01nm), 2)
snr_01nm = round(mean(self.snr_01nm), 2)
cd = mean(self.chromatic_dispersion)
return '\n'.join([f'{type(self).__name__} {self.uid}',
f' OSNR ASE (0.1nm, dB): {osnr_ase_01nm:.2f}',
f' OSNR ASE (signal bw, dB): {osnr_ase:.2f}',
f' SNR total (signal bw, dB): {snr:.2f}',
f' SNR total (0.1nm, dB): {snr_01nm:.2f}'])
f' SNR total (0.1nm, dB): {snr_01nm:.2f}',
f' CD (ps/nm): {cd:.2f}'])
def __call__(self, spectral_info):
self._calc_snr(spectral_info)
self._calc_cd(spectral_info)
return spectral_info
@@ -377,6 +387,20 @@ class Fiber(_Node):
"""
return self.alpha(f_ref * ones(1))[0]
def chromatic_dispersion(self, freq=193.5e12):
""" Returns accumulated chromatic dispersion (CD).
:param freq: the frequency at which the chromatic dispersion is computed
:return: chromatic dispersion: the accumulated dispersion [s/m]
"""
beta2 = self.params.beta2
beta3 = self.params.beta3
ref_f = self.params.ref_frequency
length = self.params.length
beta = beta2 + 2 * pi * beta3 * (freq - ref_f)
dispersion = -beta * 2 * pi * ref_f**2 / c
return dispersion * length
def _gn_analytic(self, carrier, *carriers):
"""Computes the nonlinear interference power on a single carrier.
The method uses eq. 120 from `arXiv:1209.0394 <https://arxiv.org/abs/1209.0394>`__.
@@ -423,7 +447,8 @@ class Fiber(_Node):
pwr = pwr._replace(signal=pwr.signal / self.params.lin_attenuation / attenuation,
nli=(pwr.nli + carrier_nli) / self.params.lin_attenuation / attenuation,
ase=pwr.ase / self.params.lin_attenuation / attenuation)
yield carrier._replace(power=pwr)
chromatic_dispersion = carrier.chromatic_dispersion + self.chromatic_dispersion(carrier.frequency)
yield carrier._replace(power=pwr, chromatic_dispersion=chromatic_dispersion)
def update_pref(self, pref):
self.pch_out_db = round(pref.p_spani - self.loss, 2)
@@ -461,6 +486,9 @@ class RamanFiber(Fiber):
def propagate(self, *carriers):
for propagated_carrier in propagate_raman_fiber(self, *carriers):
chromatic_dispersion = propagated_carrier.chromatic_dispersion + \
self.chromatic_dispersion(propagated_carrier.frequency)
propagated_carrier = propagated_carrier._replace(chromatic_dispersion=chromatic_dispersion)
yield propagated_carrier

17
gnpy/core/info.py
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@@ -17,8 +17,16 @@ class Power(namedtuple('Power', 'signal nli ase')):
"""carriers power in W"""
class Channel(namedtuple('Channel', 'channel_number frequency baud_rate roll_off power')):
pass
class Channel(namedtuple('Channel', 'channel_number frequency baud_rate roll_off power chromatic_dispersion')):
""" Class containing the parameters of a WDM signal.
:param channel_number: channel number in the WDM grid
:param frequency: central frequency of the signal (Hz)
:param baud_rate: the symbol rate of the signal (Baud)
:param roll_off: the roll off of the signal. It is a pure number between 0 and 1
:param power (gnpy.core.info.Power): power of signal, ASE noise and NLI (W)
:param chromatic_dispersion: chromatic dispersion (s/m)
"""
class Pref(namedtuple('Pref', 'p_span0, p_spani, neq_ch ')):
@@ -42,6 +50,7 @@ def create_input_spectral_information(f_min, f_max, roll_off, baud_rate, power,
pref=Pref(pref, pref, lin2db(nb_channel)),
carriers=[
Channel(f, (f_min + spacing * f),
baud_rate, roll_off, Power(power, 0, 0)) for f in range(1, nb_channel + 1)
])
baud_rate, roll_off, Power(power, 0, 0), 0) for f in range(1, nb_channel + 1)
]
)
return si

6
tests/invocation/transmission_main_example
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@@ -11,7 +11,8 @@ Transceiver Site_A
OSNR ASE (0.1nm, dB): inf
OSNR ASE (signal bw, dB): inf
SNR total (signal bw, dB): inf
SNR total (0.1nm, dB): inf
SNR total (0.1nm, dB): inf
CD (ps/nm): 0.00
Fiber Span1
type_variety: SSMF
length (km): 80.00
@@ -37,7 +38,8 @@ Transceiver Site_B
OSNR ASE (0.1nm, dB): 32.03
OSNR ASE (signal bw, dB): 27.95
SNR total (signal bw, dB): 26.27
SNR total (0.1nm, dB): 30.35
SNR total (0.1nm, dB): 30.35
CD (ps/nm): 1336.00
Transmission result for input power = 0.00 dBm:
Final SNR total (0.1 nm): 30.35 dB

6
tests/invocation/transmission_main_example__raman
View File

@@ -11,7 +11,8 @@ Transceiver Site_A
OSNR ASE (0.1nm, dB): inf
OSNR ASE (signal bw, dB): inf
SNR total (signal bw, dB): inf
SNR total (0.1nm, dB): inf
SNR total (0.1nm, dB): inf
CD (ps/nm): 0.00
RamanFiber Span1
type_variety: SSMF
length (km): 80.00
@@ -37,7 +38,8 @@ Transceiver Site_B
OSNR ASE (0.1nm, dB): 32.65
OSNR ASE (signal bw, dB): 28.57
SNR total (signal bw, dB): 26.48
SNR total (0.1nm, dB): 30.56
SNR total (0.1nm, dB): 30.56
CD (ps/nm): 1336.00
Transmission result for input power = 0.00 dBm:
Final SNR total (0.1 nm): 30.56 dB

27
tests/test_propagation.py
View File

@@ -11,7 +11,7 @@ from gnpy.core.network import build_network
from gnpy.tools.json_io import load_network, load_equipment
from pathlib import Path
from networkx import dijkstra_path
from numpy import mean
from numpy import mean, ones
#network_file_name = 'tests/test_network.json'
network_file_name = Path(__file__).parent.parent / 'tests/LinkforTest.json'
@@ -61,7 +61,8 @@ def propagation(input_power, con_in, con_out, dest):
print(f'pw: {input_power} conn in: {con_in} con out: {con_out}',
f'OSNR@0.1nm: {round(mean(sink.osnr_ase_01nm),2)}',
f'SNR@bandwitdth: {round(mean(sink.snr),2)}')
return sink, nf
return sink, nf, path
test = {'a': (-1, 1, 0), 'b': (-1, 1, 1), 'c': (0, 1, 0), 'd': (1, 1, 1)}
@@ -74,13 +75,13 @@ def test_snr(osnr_test, dest):
pw = test[osnr_test][0]
conn_in = test[osnr_test][1]
conn_out = test[osnr_test][2]
sink, nf = propagation(pw, conn_in, conn_out, dest)
sink, nf, _ = propagation(pw, conn_in, conn_out, dest)
osnr = round(mean(sink.osnr_ase), 3)
nli = 1.0 / db2lin(round(mean(sink.snr), 3)) - 1.0 / db2lin(osnr)
pw = expected[osnr_test][0]
conn_in = expected[osnr_test][1]
conn_out = expected[osnr_test][2]
sink, exp_nf = propagation(pw, conn_in, conn_out, dest)
sink, exp_nf, _ = propagation(pw, conn_in, conn_out, dest)
expected_osnr = round(mean(sink.osnr_ase), 3)
expected_nli = 1.0 / db2lin(round(mean(sink.snr), 3)) - 1.0 / db2lin(expected_osnr)
# compare OSNR taking into account nf change of amps
@@ -89,6 +90,24 @@ def test_snr(osnr_test, dest):
assert osnr_diff < 0.01 and nli_diff < 0.01
@pytest.mark.parametrize("dest", ['trx B', 'trx F'])
@pytest.mark.parametrize("cd_test", ['a', 'b', 'c', 'd'])
def test_chromatic_dispersion(cd_test, dest):
pw = test[cd_test][0]
conn_in = test[cd_test][1]
conn_out = test[cd_test][2]
sink, _, path = propagation(pw, conn_in, conn_out, dest)
chromatic_dispersion = sink.chromatic_dispersion
num_ch = len(chromatic_dispersion)
expected_cd = 0
for el in path:
expected_cd += el.params.dispersion * el.params.length if isinstance(el, Fiber) else 0
expected_cd = expected_cd * ones(num_ch) * 1e3
assert chromatic_dispersion == pytest.approx(expected_cd)
if __name__ == '__main__':
from logging import getLogger, basicConfig, INFO
logger = getLogger(__name__)