Fair comparision: Reed Solomon code and convolutional code

Started by July 15, 2008
```Hello People

I want to compare Reed Solomon code [255,239] and rate 1/2 convolution
code with constraint length 5, i.e. generator polynomials are [23 35]_8;

Now, my channel is frequency selective, doppler effect and noise.

Also the way I am scaling the noise is

sigma=sqrt(0.5*Eb/(Rc*snr_lin))

where for RS, the Rc=239/255 and for convolution encoder Rc=1/2;

Is this fair comparision?

What should I expect in terms of performance? Which one will perform
better?

Your help will be greatly appreciated.

Chintan
```
```>Hello People
>
>I want to compare Reed Solomon code [255,239] and rate 1/2 convolution
>code with constraint length 5, i.e. generator polynomials are [23 35]_8;
>
>Now, my channel is frequency selective, doppler effect and noise.
>
>Also the way I am scaling the noise is
>
>sigma=sqrt(0.5*Eb/(Rc*snr_lin))
>
>where for RS, the Rc=239/255 and for convolution encoder Rc=1/2;
>
>
>Is this fair comparision?
>
>What should I expect in terms of performance? Which one will perform
>better?
>
>Your help will be greatly appreciated.
>
>Chintan
>

This doesn't look like a fair comparison as their coding rate difference
is too significant.

Also, if you add random noise, convolution code is sure to win.

Michael
```
```>>Hello People
>>
>>I want to compare Reed Solomon code [255,239] and rate 1/2 convolution
>>code with constraint length 5, i.e. generator polynomials are [23
35]_8;
>>
>>Now, my channel is frequency selective, doppler effect and noise.
>>
>>Also the way I am scaling the noise is
>>
>>sigma=sqrt(0.5*Eb/(Rc*snr_lin))
>>
>>where for RS, the Rc=239/255 and for convolution encoder Rc=1/2;
>>
>>
>>Is this fair comparision?
>>
>>What should I expect in terms of performance? Which one will perform
>>better?
>>
>>Your help will be greatly appreciated.
>>
>>Chintan
>>
>
>This doesn't look like a fair comparison as their coding rate difference
>is too significant.
>
>Also, if you add random noise, convolution code is sure to win.
>
>Michael
>

%%%%

Hi

I have not much experience of RS codes, I am jsut doing it because it is
the requirement.

Anyways, if you forget doppler for now, just frequency selective channel
and noise (random but scaled properly), convolution code performs better
than RS (same set up).

What should I do to make it fair? or is this comparision valid at all?

Thanks

chintan
```
```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
nothing with the hammer.
```
```>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
>nothing with the hammer.
>

%%%%%

Hi

Thanks for this carpentry stuff which I already know!!!!

chintan
```
```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
> >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.
```
```>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
>> >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, which is
problem in fading channel, and because of burst errors DFE (Decision
Feedback Equaliser) will not work properly. But if you use RS, this problem
is solved.

Now to solve the same problem with convolution encoder, u will have to use
'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,

But I was wondering that if I can claim that given the channel perticular
channel conditions, convolution code will outperform RS.

BTW, nobody is boss.

Chintan
```
```cpshah99 wrote:

...

> Thanks for this carpentry stuff which I already know!!!!

Some of us think that knowledge from one field can carry over to a
related one, and go so far as believing that analogy can have a useful
place in explanation. Others feel that the only way to deal with a
subject is in its own terms, with no reference to parallel disciplines.
You apparently belong to the second group. I'll try to keep that in mind

Jerry
--
Engineering is the art of making what you want from things you can get.
&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
```
```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
>>> >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, which is
>problem in fading channel, and because of burst errors DFE (Decision
>Feedback Equaliser) will not work properly. But if you use RS, this problem
>is solved.
>
>Now to solve the same problem with convolution encoder, u will have to use
>'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,
>
>But I was wondering that if I can claim that given the channel perticular
>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
```
```>cpshah99 wrote:
>
>   ...
>
>> Thanks for this carpentry stuff which I already know!!!!
>
>Some of us think that knowledge from one field can carry over to a
>related one, and go so far as believing that analogy can have a useful
>place in explanation. Others feel that the only way to deal with a
>subject is in its own terms, with no reference to parallel disciplines.
>You apparently belong to the second group. I'll try to keep that in mind

>
>Jerry
>--
>Engineering is the art of making what you want from things you can get.
>&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;
>

%%%%

Hi Jerry

I am really sorry but you misunderstood me. But I am also from first
group, because when I explain something to some stranger or to my friends
what I am doing (who are not from EE filed) I use real life examples,
because this is what makes it simple isn't it?

But sometimes you are in such a state that you dont know what to do. So I
just replied like that.

I am asking abt this comparision because I dont want to cliam something
which is not true on paper.

And please use these sort of examples when u answer my posts next time.

Sorry for any misunderstanding. :-)

chintan
```