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Re: [10GBT] More on Fixed Point Decoder of the (1024, 833) Code



Dariush,

The a-priori probability of the received points is a 12D function in the
case of the PAM12T constellation. It is a 2D function in the case of the
donut constellation.

It may be that the BER loss due to the uniform a-priori probability
approximation is very small at higher BERs. However, if this additional BER
loss is caused by an induced error floor due to the approximation, then this
is a very serious issue.

Regards,
Sailesh.
srao@phyten.com

>From: Dariush Dabiri <DDabiri@TERANETICS.COM>
>Reply-To: Dariush Dabiri <DDabiri@TERANETICS.COM>
>To: STDS-802-3-10GBT@LISTSERV.IEEE.ORG
>Subject: Re: [10GBT] More on Fixed Point Decoder of the (1024, 833) Code
>Date: Wed, 6 Oct 2004 18:19:29 -0700
>
>Sailesh,
>
>I do not know what you mean by '1D LLR estimator'. If you mean the a
>posteriori LLR's of the coded bits coming from the channel, we just
>follow the basics:
>
>We assume that all points of the 12 PAM constellation are equi-probable
>and their probabilities are independent across dimensions. It follows
>immediately that the channel LLR's are separable across dimensions, i.e.
>for each bit, one only need to consider the received signal on the wire
>that carried the bit.
>(One may argue that this method is 'suboptimal', however it is
>well-known that the loss due to this approximation is very very small.)
>
>The derivation of bit LLR's from the received 1D symbols is also
>straightforward.
>One good example can be found in ungerboeck_2_0904.pdf.
>
>Regards,
>
>Dariush
>
>-----Original Message-----
>From: stds-802-3-10gbt@IEEE.ORG [mailto:stds-802-3-10gbt@IEEE.ORG] On
>Behalf Of sailesh rao
>Sent: Tuesday, October 05, 2004 5:36 AM
>To: STDS-802-3-10GBT@listserv.ieee.org
>Subject: Re: [10GBT] More on Fixed Point Decoder of the (1024, 833) Code
>
>Dariush,
>
>Please specify the 1D LLR estimator used in these simulations.
>
>Thanks,
>Sailesh.
>srao@phyten.com
>
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