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Re: [8023-10GEPON] Raman cross-talk calculations

Gentlemen,
 
I've been lurking on the list for quite a while, but first post.  Needed to make a couple of comments concerning this thread.
 
First, nearly every customer and potential customer to whom we talk is asking for an analog broadcast overlay.  About half the homes cable TV serves, and well over half the TVs (since there are multiple TVs per home) are receiving analog TV-only services at this point.  Of course the number is decreasing, but it is hard to predict when you will be able to have a digital-only broadcast service due to the cost of set tops on every TV.  So we find almost everyone asking for analog broadcast, regard,less of whether their premium service will be digital broadcast or IPTV.  This can be a competitive weapon against satellite: you don't need a set top on TVs where you don't want premium channels.
 
Secondly, I wanted to comment on the CNR number of 43 dB being mentioned.  This number originated in an agreement between US cities and their regulatory associations, and the NCTA, ca. 1990.  It was later picked up in the FCC cable TV rules as a minimum performance standard, and has promulgated since then.  It is NOT considered good engineering practice.  Good engineering practice in the cable TV industry is considered to be 48 dB, and some systems use 49 dB.  This does not mean that every system meets these numbers - some just meet the 43 dB number.  But all systems built or rebuilt in the last 15 years or so have been designed to at least 48 dB CNR.  And I can tell you from working with them, that they test to, and meet, that number.  If someone were to build an FTTH system meeting less, and he had competition from a decent quality cable system, he would look noticeably worse, and when the cable system discovered the deficiency, they would use it as a competitive weapon against the FTTH operator.
 
For reference, on a large picture 48 dB CNR will yield snow that is visible to an experienced engineer, and will be visible to a casual viewer once it is pointed out.  It would not be considered objectionable.  43 dB snow will be noticeable to the casual viewer, and will be considered somewhat objectionable by some viewers.
 
jim
 

Jim Farmer
Chief Technical Officer,
Wave7 Optics, Inc.
1075 Windward Ridge Parkway
Alpharetta, GA 30005 USA
678-339-1045
678-640-0860 (cell)
jim.farmer@w7optics.com
www.wave7optics.com

 

From: ±èºÀ±Ô [mailto:bongkim@etri.re.kr]
Sent: Friday, September 07, 2007 6:44 AM
To: STDS-802-3-10GEPON@LISTSERV.IEEE.ORG
Subject: Re: [8023-10GEPON] Raman cross-talk calculations

Dear all,
 
I have also calculated the allowed maximum launch power of the digital wave as a function of the wavelength.
The used parameters are almost same as the parameters used in the Mao's calculation. (presented in Sanfransisco meeting, June 2007)
The attached file is the results.
 
Analog signal needs more than 43 dB, 33 dB, 27 dB CNR for AM-VSC analog,  256 QAM, 64 QAM signal format, respectively. [Ref: ANSI/SCTE 40 2004]
 
For the 43 dB CNR, the maximum launch power was about 10 dBm and 11 dBm at 1530 nm and 1570 nm, respectively. The results are slightly higher than Effenberger's.( Here, I didn't consider an 1G signal.)
 
On the other hand, the results were quite different from Mao's results. (presented in June this year)
The simulation condition of Mao was 51 dB crostalk. 
However, because the CNR depend on the SRS crosstalk in the SRS dominant region,
the required CROSSTALK is almost same as the required CNR.
So, I have calculated the lanched power for the acquire 43 dB crosstalk induced by SRS.
 
Sincerely yours,
Bong Kyu Kim

Bong Kyu Kim, Ph.D.
Senior Research Staff
Optical Access Tech. Team
BcN Research Lab.
Electronics and Telecommunications Research Institute
Tel: +82-42-860-1344, Fax: +82-42-860-5213

-----¿øº» ¸Þ½ÃÁö-----
From: "Frank Effenberger" <feffenberger@HUAWEI.COM>
From Date: 2007-09-07 ¿ÀÈÄ 1:54:04
To: "STDS-802-3-10GEPON@LISTSERV.IEEE.ORG" <STDS-802-3-10GEPON@LISTSERV.IEEE.ORG>
Cc:
Subject: [8023-10GEPON] Raman cross-talk calculations

 

Dear all,

 

I note that there was a contribution regarding Raman interactions.  I have concerns that the calculations used there do not reflect the actual operational cases and trade-offs of fiber distance loss and Raman interaction strength, the significant effect of intra-office losses, the use of low-channel pre-emphasis, and so on.  

 

The bottom line is that these calculations have many parameters, and drawing any conclusions from un-audited calculations is dangerous.  

 

To help our progress, I have attached my calculation model for Raman cross talk with a video channel and 2 digital waves.  (This is a slight update of the file I used to prepare my January 07 presentation on this same topic.)  

 

There are two independent sheets.  The first computes the delivered CNR.  My calculations show that a 1G launch power of 2 dBm and a 10G launch power of 8 dBm seems to deliver more than 46 dBm (which is the current performance spec of important operators).  One must remember that typical in-office losses are 2 dB, so the maximum launch powers of the respective systems would be +4 and +10 dBm at the OLT face-plate.  That is a significant 3dB more than a number suggested recently. 

 

I invite others to work with the model, and provide their own comments. 

 

As a parting comment, I note that analog overlay use is rapidly declining.  I know of only one large application of such systems, and that user is now phasing out the support of analog.  So, the entire point may become moot. 

 

Sincerely,

Dr. Frank J. Effenberger      Ý×?к äïÝÒÚÏÌ«

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