>On Wed, 16 Jul 2008 08:53:36 -0500, "cpshah99" ><cpshah99@rediffmail.com> wrote: > >>>On Jul 16, 2:10 am, "cpshah99" <cpsha...@rediffmail.com> wrote: >>>> >On Jul 15, 3:03 pm, "cpshah99" <cpsha...@rediffmail.com> wrote: >>>> >>>> >> What should I do to make it fair? or is this comparision valid at >>all? >>>> >>>> >Which is better for chiseling wood, a screwdriver >>>> >or a ball-peen hammer? Neither is very good for >>>> >the task, but you could do a little bit, maybe, with >>>> >the screwdriver and hardly anything with the >>>> >hammer. So, "clearly" the screwdriver is the >>>> >"better" tool. But, ah, when you have to drive >>>> >nails, the hammer is far far better than the >>>> >screwdriver (think of CDs and DVDs), isn't it? >>>> >And when you need to drive screws, the >>>> >screwdriver is the best tool, though you might >>>> >be able to do a little with a chisel if you have a >>>> >flat-head screw (forget Phillips heads!) and >>>> >nothing with the hammer. >>>> >>>> %%%%% >>>> >>>> Hi >>>> >>>> Thanks for this carpentry stuff which I already know!!!! >>>> >>>> chintan >>> >>>Good. Now tell your boss that the convolutional code >>>is going to be better in almost any application and the >>>Reed-Solomon code is useless (unless he has a CD or >>>DVD (or a concatenated coding scheme) in mind.) >>>Reed-Solomon codes are not very good as channel >>>codes, but they make great straw men to be knocked >>>down while touting the merits of a coding scheme that >>>you really ought to be using in the first place. >>> >>%%%% >> >>Hi >> >>Thanks again. I had expected convolutional code to do better and it is >>doing the same. >> >>But another advantage of RS code is that it corrects burst error, whichis>>problem in fading channel, and because of burst errors DFE (Decision >>Feedback Equaliser) will not work properly. But if you use RS, thisproblem>>is solved. >> >>Now to solve the same problem with convolution encoder, u will have touse>>'interleaver', otherwise forget that even BCJR will decode the burst >>errors. >> >>So my system with convolution encoder and interleaver outperforms RS >>system. >> >>Everything is same when I am comparing both the systems, channel,doppler,>>noise, adaptive algorithm for DFE. >> >>But I was wondering that if I can claim that given the channelperticular>>channel conditions, convolution code will outperform RS. >> >>BTW, nobody is boss. >> >>Chintan > >The bottom line is that care has to be taken to match codes to >channels. The assumptions about the error distributions in the >channel can make a big difference in how the code is applied or >architected into the system. > >While on the surface the fact that RS codes can correct "burst errors" >is true, the nature of the "burst error" can make a big difference. >Often the length of the error burst can overwhelm the correcting >capability of the RS code. The performance curve (in an error >probability vs SNR sense) of a system with an RS code is pretty steep. >What often happens is that the region from performing well to >performing poorly is small, and RS codes exhibit a sometimes >undesirable characteristic of aliasing codewords when in the "poor" >region. i.e., many of the codewords coming out of the decoder will be >marked as corrected, but they'll be incorrect. At least with a >convolution code and a Viterbi decoder you can tell when it's unlocked >and spewing garbage. > >So the nature of the error bursts matters, and the sensitivity of the >system to output errors matters. Interleavers are often used to >reduce the length of error bursts so that the channel code works >better. There are all kinds of considerations, and I think Dr. >Sarwate's initial response hints at the complexities of picking the >appropriate tool depending on the situation. > > >Eric Jacobsen >Minister of Algorithms >Abineau Communications >http://www.ericjacobsen.org > >Blog: http://www.dsprelated.com/blogs-1/hf/Eric_Jacobsen.php >%%%% Hi Eric Thanks for your reply. So it all depends on burst error patterns. And as Dr. Sarwate said, convolution will do better than RS and I can confirm (I am nobody to do this, but I am just saying) that from my results. Thanks a lot to everybody. Chintan
Fair comparision: Reed Solomon code and convolutional code
Started by ●July 15, 2008
Reply by ●July 16, 20082008-07-16
Reply by ●July 17, 20082008-07-17
Are these arguments true for soft-decision Reed-Solomon as well? Wouldn't soft-decision Reed-Solomon decoding outperform convolutional decoding, especially when the RS block lengths are longer , for instance(255,k) RS codes? Just wondering Jaco _______________ Jaco Versfeld http://dept.ee.wits.ac.za/~versfeld "It is not the best team that wins, but the team that gets along best that wins" John C. Maxwell
Reply by ●July 17, 20082008-07-17
jaco.versfeld@gmail.com wrote:> Are these arguments true for soft-decision Reed-Solomon as well? > Wouldn't soft-decision Reed-Solomon decoding outperform convolutional > decoding, especially when the RS block lengths are longer , for > instance(255,k) RS codes?The good comparison of the properties of cyclic codes and convolutional codes is in this book: Johannesson, Zigangirov. "Fundamentals of convolutional coding". According to the results, the moderately complex convolutional codes outperform the cyclic codes by their properties. The optimal decoding of cyclic codes is possible, however it is cumbersome and not very practical. The main advantage of RS is the efficient algebraic hard decision decoding. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by ●July 30, 20082008-07-30
On Jul 16, 8:33�am, "sarw...@YouEyeYouSee.edu" <dvsarw...@gmail.com> wrote:> Good. �Now tell your boss that the convolutional code > is going to be better in almost any application and the > Reed-Solomon code is useless (unless he has a CD or > DVD (or a concatenated coding scheme) in mind.) > Reed-Solomon codes are not very good as channel > codes, but they make great straw men to be knocked > down while touting the merits of a coding scheme that > you really ought to be using in the first place.I think that is a bit unfair especially when you have enough bandwidth to afford to use Reed-Solomon codes with orthogonal waveforms, such as FSK.
