>
>lanbaba wrote:
>> > From fig.29 it is clear that the 7/8 code actually results in the
loss
>> >in BER at the channel BER = 7e-3, and this is what is anticipated.
>> >
>> >VLV
>> >
>>
>> Sorry, but why that? In Fig. 29 of the Xilinx data sheet, the coded BER
is
>> about 0.0008 with code rate 7/8 for uncoded BER = 0.007, 10 times
lower, or
>> do I see something fundamentally wrong?
>>
>> LBB
>
>Thats what I see also....
>
>I see approx 2dB gain?????
>
>please explain....
>
>Mark
>


I could not verify Xilinx data with Matlab's vitdec.m nor with own Viterbi
decoder. Would really want to know how to interpret that curves in Xilinx
data sheet. Hopefully they are not fakes.

LBB

lanbaba wrote:
> > From fig.29 it is clear that the 7/8 code actually results in the loss
> >in BER at the channel BER = 7e-3, and this is what is anticipated.
> >
> >VLV
> >
>
> Sorry, but why that? In Fig. 29 of the Xilinx data sheet, the coded BER is
> about 0.0008 with code rate 7/8 for uncoded BER = 0.007, 10 times lower, or
> do I see something fundamentally wrong?
>
> LBB

Thats what I see also....

I see approx 2dB gain?????

please explain....

Mark

On Tue, 10 Jan 2006 16:12:16 -0600, "lanbaba" <lanbaba@gmx.ch> wrote:

>
>>You might try some of the common FEC/ECC textbooks or Lindsay and
>>Simon.  Data sheets used to be a good source for this, and perhaps
>>somebody like AHA has it on their website.
>>
>
>Eric,
>
>Who/what is AHA?
>
>Lanbaba

www.aha.com

Eric Jacobsen
Minister of Algorithms, Intel Corp.
My opinions may not be Intel's opinions.
http://www.ericjacobsen.org

I wrote a small matlab program and get coded BER = 0.0110 for uncoded BER =
0.0078 for the aformentioned code with hard decision Viterbi. This verifies
Vladimir's statement. Still wondering about Xilinx's data sheet.

LBB

    

> From fig.29 it is clear that the 7/8 code actually results in the loss 
>in BER at the channel BER = 7e-3, and this is what is anticipated.
>
>VLV
>

Sorry, but why that? In Fig. 29 of the Xilinx data sheet, the coded BER is
about 0.0008 with code rate 7/8 for uncoded BER = 0.007, 10 times lower, or
do I see something fundamentally wrong?

LBB

lanbaba wrote:

>>Indeed the R = 5/6 K = 7 code looks inadequate for the input BER = 7e-3, 
>>and I doubt if there is going to be any BER improvement at all. I would 
>>use a code with R ~ 1/2...1/3 for this kind of BER, expecting the 
>>improvement about a factor of 10.
> 
> 
> Hi Vladimir,
> 
> actually I share your view. But when I saw a performance curve of the
> Xilinx Viterbi decoder I was a bit surprised. In Figure 29 of their data
> sheet in www.xilinx.com/bvdocs/ipcenter/data_sheet/viterbi.pdf a large
> gain is achieved for channel BER 7e-3 even with code rate 7/8! Any
> advice?

 From fig.29 it is clear that the 7/8 code actually results in the loss 
in BER at the channel BER = 7e-3, and this is what is anticipated.

VLV

>You might try some of the common FEC/ECC textbooks or Lindsay and
>Simon.  Data sheets used to be a good source for this, and perhaps
>somebody like AHA has it on their website.
>

Eric,

Who/what is AHA?

Lanbaba

>Indeed the R = 5/6 K = 7 code looks inadequate for the input BER = 7e-3, 
>and I doubt if there is going to be any BER improvement at all. I would 
>use a code with R ~ 1/2...1/3 for this kind of BER, expecting the 
>improvement about a factor of 10.

Hi Vladimir,

actually I share your view. But when I saw a performance curve of the
Xilinx Viterbi decoder I was a bit surprised. In Figure 29 of their data
sheet in www.xilinx.com/bvdocs/ipcenter/data_sheet/viterbi.pdf a large
gain is achieved for channel BER 7e-3 even with code rate 7/8! Any
advice?

Cheers, Zhenlan

On Tue, 10 Jan 2006 08:08:29 -0600, "lanbaba" <lanbaba@gmx.ch> wrote:

>Hi all,
>
>does anyone know what BER should I expect after the Viterbi decoding if
>the channel BER is 7.0e-3? Constraint length 7, Generator (177, 133),
>punturing to code rate 5/6. Thanks!
>
>Cheers, Lanbaba

There are a lot of curves available for the (177, 133) code, since it
is nearly universally used.  I'm assuming you mean for antipodal
(BPSK) signalling in AWGN, and that curve shouldn't be too difficult
to find.

You might try some of the common FEC/ECC textbooks or Lindsay and
Simon.  Data sheets used to be a good source for this, and perhaps
somebody like AHA has it on their website.

If I had one handy I'd make it available, but I don't.
Eric Jacobsen
Minister of Algorithms, Intel Corp.
My opinions may not be Intel's opinions.
http://www.ericjacobsen.org

lanbaba wrote:

> Hi all,
> 
> does anyone know what BER should I expect after the Viterbi decoding if
> the channel BER is 7.0e-3? Constraint length 7, Generator (177, 133),
> punturing to code rate 5/6. Thanks!
> 

Indeed the R = 5/6 K = 7 code looks inadequate for the input BER = 7e-3, 
and I doubt if there is going to be any BER improvement at all. I would 
use a code with R ~ 1/2...1/3 for this kind of BER, expecting the 
improvement about a factor of 10.

Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

http://www.abvolt.com