Eric Jacobsen wrote:> On Fri, 21 Apr 2006 16:28:51 GMT, Oli Filth <catch@olifilth.co.uk> > wrote: > > >>john said the following on 21/04/2006 16:59: >> >>>Oli Filth wrote: >>> >>>Thank you for the helpful replies. Intuitively, I think that the hard >>>decision coding gain should be the same whether FSK or BPSK is used, as >>>long as the uncoded BER entering the Viterbi decoder is the same in >>>each case. But I was wondering if the specifics of the noise >>>distribution influence the coding gain. >> >>As long as the errors are independent, I would imagine the distribution >>is irrelevant. By definition, in hard-decision decoding, the error >>magnitudes (statistically given by noise distribution) are not used. >>Therefore, the only thing directly affected by noise is pre-decoder bit >>errors. > > > The distribution does matter for a lot of coding systems including > convolutional coding. If the errors are clumped and about as long as > the contraint length or longer, the decoder will have a much harder > time maintaining the proper path through the trellis than if the > errors are randomly distributed. > > This is often why convolutional codes are the inner codes for > concatenated coding systems in gaussian channels...they work well on > randomlly distributed errors. If the errors are clumped then block > codes (like RS) are often a better choice. >I think you're confusing the noise's probability distribution with the time-domain characteristics of the noise. Noise can be bursty or not, independently of whether it is Gaussian, uniformly distributed, a Cauer density, bivalued or anything else. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/
Coding Gain
Started by ●April 21, 2006
Reply by ●April 21, 20062006-04-21
Reply by ●April 25, 20062006-04-25
On Fri, 21 Apr 2006 16:01:49 -0700, Tim Wescott <tim@seemywebsite.com> wrote:>Eric Jacobsen wrote: > >> On Fri, 21 Apr 2006 16:28:51 GMT, Oli Filth <catch@olifilth.co.uk> >> >>>john said the following on 21/04/2006 16:59: >>> >>>>Oli Filth wrote: >>>> >>>>Thank you for the helpful replies. Intuitively, I think that the hard >>>>decision coding gain should be the same whether FSK or BPSK is used, as >>>>long as the uncoded BER entering the Viterbi decoder is the same in >>>>each case. But I was wondering if the specifics of the noise >>>>distribution influence the coding gain. >>> >>>As long as the errors are independent, I would imagine the distribution >>>is irrelevant. By definition, in hard-decision decoding, the error >>>magnitudes (statistically given by noise distribution) are not used. >>>Therefore, the only thing directly affected by noise is pre-decoder bit >>>errors. >> >> The distribution does matter for a lot of coding systems including >> convolutional coding. If the errors are clumped and about as long as >> the contraint length or longer, the decoder will have a much harder >> time maintaining the proper path through the trellis than if the >> errors are randomly distributed. >> >> This is often why convolutional codes are the inner codes for >> concatenated coding systems in gaussian channels...they work well on >> randomlly distributed errors. If the errors are clumped then block >> codes (like RS) are often a better choice. >> >I think you're confusing the noise's probability distribution with the >time-domain characteristics of the noise. Noise can be bursty or not, >independently of whether it is Gaussian, uniformly distributed, a Cauer >density, bivalued or anything else.I thought it was pretty clear that this part of the discussion was talking about bit error distribution. Clearly that's related to the channel characteristics (often something other than the noise), but it was on point to the OPs concerns. Eric Jacobsen Minister of Algorithms, Intel Corp. My opinions may not be Intel's opinions. http://www.ericjacobsen.org
