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*To*: STDS-802-3-10GBT@listserv.ieee.org*Subject*: [10GBT] Information bits, coded bits and framing complexity*From*: sailesh rao <sailesh_rao@HOTMAIL.COM>*Date*: Fri, 30 Jul 2004 18:12:43 -0400*Reply-To*: "IEEE P802.3an" <STDS-802-3-10GBT@listserv.ieee.org>*Sender*: stds-802-3-10gbt@IEEE.ORG

Hi All, In coded modulation communication systems, such as the PAM8 and PAM12 proposals on the table, it is customary to speak of information bits and coded bits. Information bits represent the actual data being transmitted and the coded bits are the remainder in the modulation scheme. For the cabling media under consideration, it is natural to consider a 4D symbol as the unit entity since there are 4 wire pairs in the media. For a 10GBASE-T system that employs k coded bits over an M-level 4D-PAM system, the transmitted symbol rate can be calculated using the formula: Symbol Rate (Ms/s) = 10000/(4*log2(M) – k) The PAM8 proposal uses k=2, M=8. Using a simple integer for k allows this PAM8 system to also use simple data frames that span exactly 1 LDPC code block each. For k=2, M=8, the symbol rate is 10000/(4*log2(8)-2) = 1000Ms/s With a little expenditure of clock generation complexity, we can also achieve rational values for k. Naturally, the smaller the k, the more efficient the coded modulation scheme. Therefore, for instance, if k=1.5, M=8, the symbol rate becomes 10000/(4*log2(8)-1.5) = 952.381 Ms/s and the resulting PAM8 system can also be made to use data frames that span exactly 1 LDPC block each. It provides an additional 1dB of SNR margin, adding another 1dB to the Total EMI Penalty of PAM12. For PAM12, using k=2 results in a symbol rate of 10000/(4*log2(12)-2) = 810.3826 Ms/s If a more efficient coding scheme that achieves k=1.5 is employed, the symbol rate becomes 10000/(4*log2(12)-1.5) = 778.8253 Ms/s However, the symbol rate proposed in powell_1_0704.pdf for the PAM12 system is 825Ms/s, which corresponds to k=2.2186bits. The number of information bits in each 4D PAM12 symbol is 10000/825 = 12.1212bits. Therefore, not only is the PAM12 proposal using a sub-optimal modulation rate (mainly due to the bit-to-symbol mapping losses described earlier), but it is also using a complex data framing scheme spanning 33 LDPC blocks each in order to achieve this sub-optimality. Regards, Sailesh Rao. srao@phyten.com _________________________________________________________________ Don’t just search. Find. Check out the new MSN Search! http://search.msn.click-url.com/go/onm00200636ave/direct/01/

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