| Author |
Message |
lanbaba
Guest
|
 Posted:
Tue Dec 06, 2005 9:15 am Post subject:
BER after Viterbi or RS decoding |
|
|
Hi all,
Does any one know a way to measure the BER after Viterbi or RS decoding a
the Rx side if the uncoded data at the Tx side is unknown? |
|
| Back to top |
|
 |
Nic
Guest
|
| Posted:
Tue Dec 06, 2005 4:33 pm Post subject:
Re: BER after Viterbi or RS decoding |
|
|
Hi,
I have once read a paper on how to estimate the BER without reference:
http://www.ebu.ch/en/technical/trev/trev_274-schramm.pdf
This is probably not exactly what you are looking for, as it estimates
the BER before viterbi decoding, but you might be able to work out a
solution from there.
Best wishes
Nic |
|
| Back to top |
|
|
Nic
Guest
|
| Posted:
Tue Dec 06, 2005 5:15 pm Post subject:
Re: BER after Viterbi or RS decoding |
|
|
Hi Lanbaba,
I think, this is exactly what the author in this paper also does, he
just calls it Pseudo-channel BER (pcBER), so not much new info for you,
I am sorry :(.
Anyhow, much luck with your search..
Best wishes
Nic |
|
| Back to top |
|
|
Vladimir Vassilevsky
Guest
|
| Posted:
Tue Dec 06, 2005 5:15 pm Post subject:
Re: BER after Viterbi or RS decoding |
|
|
lanbaba wrote:
| Quote: | Does any one know a way to measure the BER after Viterbi or RS decoding at
the Rx side if the uncoded data at the Tx side is unknown?
|
You can get a BER estimate based on the average cost of the survived
path for Viterbi. For the syndrome decoding of RS, the average number of
corrected errors per block gives you the BER estimate.
Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com |
|
| Back to top |
|
|
lanbaba
Guest
|
| Posted:
Tue Dec 06, 2005 5:16 pm Post subject:
Re: BER after Viterbi or RS decoding |
|
|
Hi Nic,
thank you for the reference. To estimate the BER before Viterbi I jus
re-encode the Viterbi output and compare the encoded bits with the Viterb
input. Sometimes this estimate is called Viterbi error flag rate (VEFR).
Cheers, Lanbaba |
|
| Back to top |
|
|
Guest
|
| Posted:
Thu Dec 08, 2005 4:25 pm Post subject:
Re: BER after Viterbi or RS decoding |
|
|
| Quote: | You can get a BER estimate based on the average cost of the survived
path for Viterbi.
|
That's a cool idea! So I guess you calibrate the system by injecting
known noise and measuring the path metric and the BER using a known
training sequence. Then the path metric in the case of unkown transmit
data will correspond to a particular BER (on average) using a lookup
table. How does this work with metric normalisation? |
|
| Back to top |
|
|
john
Guest
|
| Posted:
Thu Dec 08, 2005 5:16 pm Post subject:
Re: BER after Viterbi or RS decoding |
|
|
porterboy76@yahoo.com wrote:
| Quote: | You can get a BER estimate based on the average cost of the survived
path for Viterbi.
That's a cool idea! So I guess you calibrate the system by injecting
known noise and measuring the path metric and the BER using a known
training sequence. Then the path metric in the case of unkown transmit
data will correspond to a particular BER (on average) using a lookup
table. How does this work with metric normalisation?
|
One idea is to compare the survivor path to the average of the other
paths. In pure noise, no particular path will dominate so the survivor
path will on average have the same cost as the others. As the signal
rises out of the noise, a lowest cost path should emerge and its cost
compared to the others should give an indication of the BER. Another
idea is to compare the best and worst paths. I don't know how this is
best done in practice but the information should be there to get a BER
estimate.
John |
|
| Back to top |
|
|
Vladimir Vassilevsky
Guest
|
| Posted:
Thu Dec 08, 2005 5:16 pm Post subject:
Re: BER after Viterbi or RS decoding |
|
|
john wrote:
| Quote: | You can get a BER estimate based on the average cost of the survived
path for Viterbi.
That's a cool idea! So I guess you calibrate the system by injecting
known noise and measuring the path metric and the BER using a known
training sequence.
|
That is brute force approach however yes you can do it this way.
| Quote: |
One idea is to compare the survivor path to the average of the other
paths. In pure noise, no particular path will dominate so the survivor
path will on average have the same cost as the others. As the signal
rises out of the noise, a lowest cost path should emerge and its cost
compared to the others should give an indication of the BER. Another
idea is to compare the best and worst paths.
|
You can do it this way also. However you should compare the best path
and the next to the best path.
| Quote: | I don't know how this is
best done in practice but the information should be there to get a BER
estimate.
|
The cost of the best path is already directly proportional to BER. We
are takling about small BERs here.
Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com |
|
| Back to top |
|
|
Eric Jacobsen
Guest
|
| Posted:
Fri Dec 09, 2005 12:21 am Post subject:
Re: BER after Viterbi or RS decoding |
|
|
On Tue, 06 Dec 2005 02:35:54 -0600, "lanbaba" <lanbaba@gmx.ch> wrote:
| Quote: | Hi all,
Does any one know a way to measure the BER after Viterbi or RS decoding at
the Rx side if the uncoded data at the Tx side is unknown?
|
As mentioned already, re-encode and compare (with the uncorrected
stream) provides a good estimate of the Viterbi decoder's input error
rate. It's then a pretty simple mapping from input error rate to
output BER. Many (if not most) systems that report their BER on
payload data do it this way.
Eric Jacobsen
Minister of Algorithms, Intel Corp.
My opinions may not be Intel's opinions.
http://www.ericjacobsen.org |
|
| Back to top |
|
|
Vladimir Vassilevsky
Guest
|
| Posted:
Fri Dec 09, 2005 1:16 am Post subject:
Re: BER after Viterbi or RS decoding |
|
|
Eric Jacobsen wrote:
| Quote: | Does any one know a way to measure the BER after Viterbi or RS decoding at
the Rx side if the uncoded data at the Tx side is unknown?
As mentioned already, re-encode and compare (with the uncorrected
stream) provides a good estimate of the Viterbi decoder's input error
rate.
|
What if the input stream is in the soft decisions?
| Quote: | It's then a pretty simple mapping from input error rate to
output BER.
|
The cost of the best path is the distance between the input stream and
the data decoded. There is no need to re-encode the data since the
information is available already.
Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com |
|
| Back to top |
|
|
Eric Jacobsen
Guest
|
| Posted:
Fri Dec 09, 2005 1:16 am Post subject:
Re: BER after Viterbi or RS decoding |
|
|
On Thu, 08 Dec 2005 20:04:20 GMT, Vladimir Vassilevsky
<antispam_bogus@hotmail.com> wrote:
| Quote: | Eric Jacobsen wrote:
Does any one know a way to measure the BER after Viterbi or RS decoding at
the Rx side if the uncoded data at the Tx side is unknown?
As mentioned already, re-encode and compare (with the uncorrected
stream) provides a good estimate of the Viterbi decoder's input error
rate.
What if the input stream is in the soft decisions?
|
It usually is, but just taking the sign bit gives an easy comparison
for the re-encoder. It's not a problem at all. All you want is the
input BER, and the soft information isn't needed (or desired) for
that.
| Quote: | It's then a pretty simple mapping from input error rate to
output BER.
The cost of the best path is the distance between the input stream and
the data decoded. There is no need to re-encode the data since the
information is available already.
|
That sounds like a nice alternative, but re-encode and compare is
quite simple to implement and is a well-known and often used
technique. The re-encoder for a convolution code is, as I'm sure you
know, quite simple. The results that you can get with the re-encode
and compare technique are pretty accurate, usually well within
practical user requirements.
For people who implement their own Viterbi decoder I'm sure the
technique you mention has merit. Often, though, the decoder is
purchased either as a discrete part or an IP block, and access to the
internal metrics may be difficult or not possible.
Eric Jacobsen
Minister of Algorithms, Intel Corp.
My opinions may not be Intel's opinions.
http://www.ericjacobsen.org |
|
| Back to top |
|
|
|
|
|
|
FAQ
Memberlist
Register
Profile
Log in to check your private messages
Log in