Re: PAM-5, what are your BERs ?
Rich,
I re-read yesterday your presentations. I think that you
can not have both 8b/10b and FEC included in PAM-5
unless you go to a PAM-6 scheme or increase the baud
rate. In either case, I do not see the value of adding the
8b/10b coding in a PAM-5 transmission scheme.
For a complete explanation, please, see the email I
sent yesterday late at night, titled:
"PAM5 and 8B10B and FEC and SAME_BAUD"
March 2, 2000, 2:15 am EST
(under Kardont@xxxxxxx)
Jaime
Jaime E. Kardontchik
Micro Linear
San Jose, CA 95131
email: kardontchik.jaime@xxxxxxxxxxx
Rich Taborek wrote:
> Jaime,
>
> Please refer to the MAS 802 tutorial Bob Dahlgren and I presented at the July
> '99 Montreal meeting as well as the update to the same proposal presented in
> November '00 in Kauai. It is clear in both proposals that both the XGMII and
> Hari are used to feed 10 Gbps of data to the MAS PCS. Therefore, in terms of
> mapping, 36-bit XGMII data is mapped to Hari 8B/10B encoded data which is
> decoded prior to encoding by the PAM5 PCS.
>
> Please tell me if this response does not completely address your issue.
>
> Best Regards,
> Rich
>
> --
>
> Jaime Kardontchik wrote:
> >
> > Rich Taborek wrote:
> >
> > > Ed,
> > >
> > > Sean is simply stating that FEC can be used to provide a significant improvement
> > > in "effective" BER over "raw" BER.
> > >
> > > .....
> > >
> > > You point out that FEC requires a higher line rate, which mitigates the benefits
> > > of FEC. This is true for a traditional Binary signaled system.
> > >
> > > However, for a MultiLevel system such as PAM5, an additional level can easily
> > > accomodate the FEC overhead. Several HSSG PAM5 proposals as well as 1000BASE-T
> > > utilize FEC in this fashion. As an example, my 5 Gbaud PAM5 proposal used 4 of
> > > the levels to respresent 2 bits and the 5th level to represent FEC as well as
> > > special characters. In terms mapping, one 8B/10B code-group could be mapped to 4
> > > PAM5 symbols creating a PAM5x4 "code-group" symbol. Note that the PAM5x4 symbol
> > > period is 800 ps, and is used to convey 10 bits and .....
> > > .....
> > >
> > > It is possible to add FEC to MultiLevel signaling WITHOUT increasing the line
> > > rate.....
> > >
> > > Rich
> > >
> >
> > Rich,
> >
> > Somethink in the math does not add up: I think that
> > you cannot have it all: both PAM-5 and include 8b/10b
> > and include FEC and still transmit at the 1.25 Gbaud
> > using 800 psec symbols.
> >
> > The raw data consists of 8 bits at 1.25 Gbaud that come
> > from the MAC layer. These 8 bits represent 2^8 = 256
> > possible symbols. Using four PAM-5 transmitters at
> > 1.25 Gbaud the number of possible 4-dimensional symbols
> > is 5^4 = 625.
> >
> > Since we have 625 possible 4-dimensional symbols
> > in one baud period and we only need 256 symbols for
> > the raw data, we have more than twice the number of
> > points in the constellation than we really need for raw
> > data:
> >
> > 625 > 2 * 256 = 512
> >
> > It is this fact that enables to add trellis coding and
> > 6 dB coding gain using FEC.
> >
> > Now, it you also want to add the 8b/10b you would
> > now have 2^10 "raw" data = 1,024 points. You do not
> > have so many points in the 4-dimensional PAM-5
> > constellation (5^4 = 625). If you want to include
> > the 8b/10b coding you will have to increase the
> > symbols rate above 1.25 Gbaud.
> >
> > Jaime
> >
> > Jaime E. Kardontchik
> > Micro Linear
> > San Jose, CA 95131
> > email: kardontchik.jaime@xxxxxxxxxxx
>
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