I tend to agree with Carlo. If we are not changing the receiver implementation (king_01a_0617_smf)
then why are we changing the unstressed receiver sensitivity specification ?
Ps. I think there is a typo on slide 7 in Jonathan’s presentation. I believe that the yellow arrow below should also include MPI penalty, i.e. it should be “connector
and channel insertion loss + MPI penalty” ?
Please note that, as Brian pointed out, Pete’s tables do show changed unstressed RX sensitivities.
If the power budget is not really changing, I would deem preferable to leave the unstressed RX sensitivity as it is (at the end of the day the SRS
of the RX is not changing either, since the RX is the same) with the note that, even if ideal, the reference TX has SECQ = 0.9dB (pending Jonathan confirmation, see below).
My reasoning is as follows: under the assumption that both RX and – of course - reference TX are not changing (what is changing is the methodology
for TDECQ and SECQ calculation: let me call the new one TDECQ’/SECQ’), to me it seems you cannot at the same time do the following:
1) apply
the usual link budget calculations:
(Launch power in OMAouter minus TDECQ) - Channel IL (- MPI) = unstressed
RX sensitivity
2) keep
the unstressed RX sensitivity unchanged
3) assume
SECQ’ of the reference TX (let me call it SECQ’ref_TX ) equal to 0dB
I see a couple of options. Let me rewrite the link budget calculation as follows:
(Launch power in OMAouter minus TDECQ) - Channel IL (- MPI) = unstressed RX sensitivity -
SECQref_TX
When the original definitions applies (where SECQref_TX= 0), you end up with the following numbers
-3.5dBm – 3dB (- 0.1dB) = -6.6dBm -0dB = -6.6dBm
With the new TDECQ’/SECQ’ methodology the max TDECQ’ is 0.9dB higher, so you may have:
a) SECQ’ref_TX = 0dB Þ (-3.5-0.9)
- 3 (- 0.1) = -7.5 - 0
b) SECQ’ref_TX = 0.9dB Þ (-3.5-0.9)
- 3 (- 0.1) = -6.6 - 0.9
Option a) requires an improved RX performance and is consistent with the fact that a zero stress TX has 0dB SECQ’. But I find this extra requirement
not justified, given the fact that the same considerations in Jonathan’s presentation regarding ‘SRS remaining unchanged’ should also apply here.
Option b) leaves the RX requirement unchanged but assumes that SECQ’ref_TX is actually 0.9dB,
something that I am leaving Jonathan to confirm/reject (is the 0.9dB increase constant with stress amount? If not it would be difficult to do the usual elementary math).
Of course we’ll face the drawback/paradox that a TX with ideal properties has a SECQ’ ≠ 0dB.
Please correct me if I am wrong…maybe I did not correctly catch what is being proposed.
“…non men che saver, dubbiar m'aggrata…” (Inferno - Canto XI)
CISCO | TMG Technical Leader|
The presentation that Pete referenced (prepared for next weeks Ad Hoc) is proposing to make the unstressed RX sensitivity more stringent by 0.9 dB,
and increasing the SECQ for the SRS value by 0.9 dB.
The definition for unstressed receiver sensitivity has always been with zero stress. Saying that SECQ = 0dB clarifies what is meant by zero stress.
It is harder for the Rx to achieve the BER with a SECQ of 0.9dB rather than SECQ of 0dB and we aren’t changing the Unstressed sensitivity so I don’t understand why you are saying this makes the Rx unstressed sensitivity test harder.
I have a question related to the added text in the notes on unstressed receiver sensitivity “…and is defined for a transmitter with SECQ of 0dB”.
Based on such value, the proposed change in TDECQ has an impact on the RX side, as it is captured by the corrections in unstressed
sensitivity values: the same RX which was OK with the reference TX when using the old TDECQ definition is now not working anymore with the new TDECQ definition and needs an improvement of 0.9dB in the unstressed sensitivity.
I am wondering – but honestly I am not sure if this is physically sound and consistent with the new proposed TDECQ methodology: shouldn’t the note
say instead “…and is defined for a transmitter with SECQ of 0.9dB” (admittedly
this looks pretty ugly…)?
“…non men che saver, dubbiar m'aggrata…” (Inferno - Canto XI)
CISCO | TMG Technical Leader|
I think that the file I have generated for next week’s SMF Ad Hoc should answer your question:
Pete Anslow | Senior
Standards Advisor
43-51 Worship Street | London,
EC2A 2DX, UK
Direct +44 2070 125535 |
I’m sorry to have missed the most recent ad hoc where you presented king_01a_0617_smf.
I find myself confused as to what you mean by: “a similar decrease in the OMAouterminus TDECQ spec”. Can you show an example with what would happen for the TX or RX table for any of the clause 122 PMD’s?
I think this all stems from a mixing of terms increase/decrease with negative numbers…
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As previously announced, there is an SMF Ad Hoc meeting starting at 8:00 am Pacific today, Tuesday 13 June.
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I currently have requests for 1 presentation so the draft agenda is:
- TDECQ changes and consequent spec limits Jonathan King, Finisar
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Pete Anslow | Senior
Standards Advisor
43-51 Worship Street | London,
EC2A 2DX, UK
Direct +44 2070 125535 |