Re: finally, the right SNR table

[BRIAN_LEMOFF@HP-PaloAlto-om16.om.hp.com]

     Jaime,
     
     You give the impression below that 8b/10b + 4-WDM will not support 
     installed fiber!  In fact, at 3.125 Gbaud, one can support ~300 meters of 
     standard 62.5 micron fiber.  Of course, at 1.25-Gigasymbols/s, a much 
     longer distance can be supported. 
     
     -Brian Lemoff
      HP Lsbs

______________________________ Reply Separator _________________________________
Subject: finally, the right SNR table
Author:  Non-HP-kardontchik.jaime (kardontchik.jaime@ulinear.com) at 
HP-PaloAlto,mimegw2
Date:    6/10/99 5:54 PM



Hello 10G'ers,

And finally, the really correct complete SNR table that
should replace the one I presented in Idaho:

    The Complete SNR Table
    Architecture vs Optical SNR

1) 1000BASE-X                                    - 1 dB
2) 8b/10b + 4-WDM                             - 5 dB
3) 10G-BASE-T- EVEN coding        - 5.5 dB
4) 10G-BASE-T- Trellis coding        - 4 dB

The main differences between the two 10 Gbps
solutions appear to be:

a) speed of the electronics and active optics
(1.25 GHz vs 3.125 GHz) (technology, cost)

b) optical fiber (installed fiber  vs higher bandwidth
fiber to allow a reasonable timing budget margin for
the 0.32 nsec bit period solution). Waveshaping is
still an additional option in 10G-BASE-T to reduce
dispersion in the optical fiber and increase the link
length.


The full explanation for the last change (line # 2 in
the Table) follows below. I sent it for double-checking
to the same HP researcher and it looks correct to
him too:

" ... it occurred to me that I might be penalyzing twice
the 8b/10b + 4-WDM approach.

In my presentation, I wrote that this approach incurres
in a signal penalty due to the smaller bit period of 0.32
nsec (compared to the 1000BASE-X reference of 0.8 nsec).
This signal penalty (or difference in bit energies) is 4 dB.

    10 * log (1 * 0.32) = - 5 dB

(compared to the 1000BASE-X reference of
10 * log(1 * 0.8) = - 1 dB).

Then, when I calculted the thermal noise of the
8b/10b + 4-WDM approach I said that we get here
another 4 dB penalty in noise because the bandwidth
is 3.125 GHz, instead of 1.25 GHz:

        10 *log(3.125/1.25) = 4 dB

Therefore, I concluded, the total penalty of 8b/10b + 4-WDM
is 8 dB compared to the reference 1000BASE-X.


Shouldn't I have calculated the  optical SNR of
8b/10b + 4-WDM compared to the 1000BASE-X as
follows ? :

    Signal Power = the same as in 1000BASE-X = - 1 dB

(the power levels of 1000BASE-X and 8b/10b+4-WDM
are the same, only the bit energies are different).

    Noise Power = (4kT/R) * B = (4kT/R) * 3.125 =

             = Noise power of 1000BASE-X  +  10*log(3.125/1.25)

            = Noise power of 1000BASE-X    +  4 dB

Hence, the optical SNR penalty  of 8b/10b + 4-WDM compared
with the reference of 1000BASE-X should be only 4 dB.

Therefore, in the optical SNR table, at the end of the presentation,
the first two entries should be:

1) 1000BASE-X                - 1 dB
2) 8b/10b + 4-WDM        - 5 dB

(and not -1 dB and - 9 dB, respectively, as I wrote)"

Jaime

Jaime E. Kardontchik
Micro Linear
San Jose, CA 95131
email: kardontchik.jaime@ulinear.com