Re: PAM-5, what are your BERs ?
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.
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
> 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
> 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 E. Kardontchik
> Micro Linear
> San Jose, CA 95131
> email: firstname.lastname@example.org
Richard Taborek Sr. Phone: 408-845-6102
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