Re-send - I thought I
sent this to the reflector, but it seems not.
Haim,
The optical gain that
you get from FEC can be well estimated from looking at the BER vs optical
power curves and taking the difference between the power required for 1E-12
(i.e. the no FEC case) and the power required for ~ 1E-4 (the BER at the input
of RS (255, 239) FEC for 1E-12 at
the output.
While I agree the
optical improvement will be greater in the case of an APD (because the BER vs
power curve is not so steep) typically the slope of an APD curve is not half
that of a PIN and therefore the optical improvement will not be twice as
much.
I also take issue
with the value of 1.5 dB improvement for a PIN. The theoretical
improvement for RS (255, 239) FEC
(net coding gain) is 2.8 dB. Of course this assumes that the only
penalty for the 7% increase in bit rate is additional noise caused by a wider
electrical bandwidth. If the receiver used for the measurement has too
little bandwidth even for the lower rate, then you can see a large sensitivity
penalty for 7% increase in rate. Alternatively, if a large dispersion
penalty is included in the measurement setup you can see a big increase in
this for the increased rate.
If either of these
cases is not true, then the BER vs power curve for typical PIN based receivers
is, if anything, somewhat less steep than the theoretical curve leading to a
larger improvement for the with FEC case than theory would
suggest.
As a consequence of
all of this, I am surprised by the claim that RS (255, 239) FEC gives only
1.5 dB improvement for a PIN receiver if this is in the context of a
continuous downstream signal.
Burst mode in the
upstream has, however, been said to be potentially different because of some
OLT receivers showing very abrupt BER vs power
curves.
Pete
Anslow
Nortel Networks UK Limited, London Rd, Harlow,
Essex CM17 9NA, UK
External +44 1279 402540 ESN 742
2540
Fax +44 1279 402543
From: Haim Ben-Amram
[mailto:Haim_Ben-Amram@PMC-SIERRA.COM]
Sent: 08 February 2007 13:12
To:
STDS-802-3-10GEPON@listserv.ieee.org
Subject: Re: [8023-10GEPON]
[POWER_BUDGET] ad hoc group 2nd meeting
Pete,
Regarding your first
question.
RS FEC can provide
you 3-4dB optical gain, but depends on the receiver type.
In case of APD, which
is limited by Shot Noise the
coding gain is quite similar to the electrical SNR. While in PIN, which is
limited by the Thermal Noise the
coding gain is around half of the
electrical gain (APD gain).
Haim.
From: Pete
Anslow [mailto:pja@NORTEL.COM]
Sent: Thursday, February 08, 2007 1:08
PM
To:
STDS-802-3-10GEPON@listserv.ieee.org
Subject: Re: [8023-10GEPON]
[POWER_BUDGET] ad hoc group 2nd meeting
Robert,
Thanks for the notes
from the Ad-Hoc call.
I have comments
on three
sections:
“It was stated that
for a 7% overhead code, such as RS, a 1.5 dB coding gain would be appropriate
for PIN case, but a 3 dB gain for APD case. It was not known how to evaluate
the pre-amplified PIN case. This seems to be a major area requiring
clarification.“
Was this for
RS (255,
239) as defined in
G.709? Upstream or downstream? If it is for (255,
239)
downstream I find this
surprising are there
measurements to support this?
Secondly,
“Assuming
a value of 13 dBm for minimum Psat and subtracting 3 dB to avoid patterning
and 2 dB for min/max range would yield a minimum SOA output power of 8 dBm as
a working assumption. ”
I don’t think that
there is any need to subtract anything for the min/max range.
If +13 dBm is
the guaranteed
minimum Psat, then
subtracting 3 dB to avoid distortion would give +10 dBm
minimum. Surely a min/max
range of 2 dB
means that the spec
for output power would be +10 dBm min and +12 dBm max?
Thirdly,
“It was
not known how to evaluate the pre-amplified PIN case. This seems to be a major
area requiring clarification.”
There is some
information on the slope of the BER
vs power curve for pre-amplified receivers in Supplement 39 to the
G-Series Recommendations clause 9.5.2 which is relevant to the
FEC gain that might
be expected. This can be found at:
http://www.itu.int/rec/T-REC-G.Sup39/en
Regards,
Pete
Anslow
Nortel Networks UK Limited, London Rd, Harlow,
Essex CM17 9NA, UK
External +44 1279 402540 ESN 742
2540
Fax +44 1279 402543
_____________________________________________
From: Lingle,
Jr, Robert (Robert) [mailto:rlingle@OFSOPTICS.COM]
Sent: 07 February 2007 22:40
To:
STDS-802-3-10GEPON@LISTSERV.IEEE.ORG
Subject:
Re: [8023-10GEPON] [POWER_BUDGET]
ad hoc group 2nd meeting
Please find attached the notes
from today's call.
Please review it carefully and
discuss issues on the reflector. If you wish to volunteer to take action
items, please let me know. Otherwise I will raise issues on the reflector and
begin asking people to take action items
:-)
Robert
-----Original
Message-----
From: Lingle, Jr, Robert (Robert) [mailto:rlingle@OFSOPTICS.COM]
Sent: Tuesday, February 06, 2007
5:27 PM
To:
STDS-802-3-10GEPON@listserv.ieee.org
Subject: Re: [8023-10GEPON]
[POWER_BUDGET] ad hoc group 2nd meeting
Please find attached the file for
the call today 2/6 at 7PM EST and 2/7 at 9AM.
-----Original
Message-----
From: Lingle, Jr, Robert (Robert) [mailto:rlingle@OFSOPTICS.COM]
Sent: Friday, February 02, 2007
4:37 PM
To:
STDS-802-3-10GEPON@listserv.ieee.org
Subject: Re: [8023-10GEPON]
[POWER_BUDGET] ad hoc group 2nd meeting
Please find attached the notes for
the first Power Budget Ad Hoc meeting.
Please direct any corrections to
me.
Robert
-----Original
Message-----
From: Lingle, Jr, Robert (Robert) [mailto:rlingle@OFSOPTICS.COM]
Sent: Thursday, February 01, 2007
3:09 PM
To:
STDS-802-3-10GEPON@LISTSERV.IEEE.ORG
Subject: [8023-10GEPON]
[POWER_BUDGET] ad hoc group 2nd meeting
All,
I
will send the notes from this week's meeting tomorrow 2/2.
As discussed in the previous call,
the next call(s) will occur on Tuesday Feb 6 at 7PM EST and Wednesday Feb 7 at
9AM EST.
Notes from this week's call as
well as agenda for next week will be sent Friday.
Toll-free in US
866-263-8899
Outside US
816-249-6061
Conf.
Code 7707985015
Robert
Robert Lingle,
Jr.
Fiber Design and Transmission
Simulation OFS Corporate R&D, Atlanta
404-886-3581
(cell)
770-798-5015
(office)