Reply by JAlbertoDJ May 8, 20062006-05-08
Thank you for answer.

I am thinking one thing. For example, in the Viterbi Algorith, if i need
to know confidence for two bits into a supposed block of 4 bits i can add
correlations of all symbols that have that bits in that positions.

For example, What would be the confidence for "10" into the block of 4
bits: "XX10 XXXX XXXX......"?

Confidence("10")= Correlation(0010)+Correlation(0110)+
                 +Correlation(1010)+Correlation(1110)+ 
 
That 4 symbols have in common that third bit is "1" and Fouth bit is "0"

For each two bits that i compare in Viterbi, I add Correlation of 4
frecuencies. One of that correlations will be very high (correlation with
recieved symbol), the other 3 correlations will be very low (correlation
with Noise).

I am not sure if this is the correct form for apply Viterbi to my 16FSK.


About burst noise, i will do interleaving with the bits. Also, i will
apply Spread Spectrum. In fact, a symbol will be compound of 4 frecuencies
scattered. But that is other questions.

About Reed-Solomon Codes, i know they are a good option for burst noise.
In fact, my aplication is for ionosphere communications, where burst noise
is very common. But in a first moment i want do it with convolucional code
(1/2, k=7), and see how works.

In a second moment, i would like do something like codes for CD-ROMS. I
think that it use Reed-Solomon into a Convolucional Code or so. I am not
sure.

I wait for your cooments

Reply by john May 8, 20062006-05-08
You can assign the symbol confidence to all four bits.

John

JAlbertoDJ wrote:
> Hi, > > I need to build a Viterbi for 16FSK. 1/2 with K=7. > > In the case of BFSK, Soft Decision is not a problem for me, I compare the > correlation for a symbol '0' and for a symbol '1' and i know the > confidence for '0' o for '1'. > > In the case of 16FSK, i am lost, because a symbol has 4 bits that belong > to a same frecuency. > > For example: "0000" belong to a tone of 1000 Hz > For example: "0001" belong to a tone of 1015 Hz > For example: "0010" belong to a tone of 1030 Hz > Etc....... > > Thats four bits arrived joined in the same symbol. > > How i do for programming the soft decision in this case? > > Help, please
Reply by May 8, 20062006-05-08
Hi,

Why don't you use Reed-Solomon codes in your application?  The problem
with Convolutional codes and the Viterbi decoder is that these codes do
not like burst errors, which is what will typically happen when a
symbol is incorrectly demodulated by the MFSK decoder.  There are a few
papers where MFSK and Reed-Solomon codes are used, and the
soft-decision values are used to declare erasures.  There is even a
Viterbi measure defined to determine whether an erasure should be
declared.  Two papers that I can think of is one by Matache
(www.ee.ucla.edu/~matache/MA4_3.pdf), and the other by Stark
(www.eecs.umich.edu/~stark/2002B.pdf).

Anonymous wrote:
> You can calculate some uncertainty bits for the symbol and then assign the > same uncertainty bits to all four data bits for decoding. I guess it depends > on how your symbols are numbered. For example, if they are numbered from 0 > to 15 in proportion to frequency and you detect that a 0000 was sent you can > probably assign the 2 MSBs a zero uncertainty since it would take a very > large frequency error for them to be wrong. Similiary, if they were grey > coded then maybe you would assign the bits that don't change with the > neighbors a zero uncertainty. As for the certainity for the symbol decision > maybe you can calculate a ratio of the energy in the selected symbol versus > the energy in all the other tones. > > > "JAlbertoDJ" <nietorosdj@yahoo.es> wrote in message > news:adSdnWcChYgyvsLZnZ2dnUVZ_tSdnZ2d@giganews.com... > > Hi, > > > > I need to build a Viterbi for 16FSK. 1/2 with K=7. > > > > In the case of BFSK, Soft Decision is not a problem for me, I compare the > > correlation for a symbol '0' and for a symbol '1' and i know the > > confidence for '0' o for '1'. > > > > In the case of 16FSK, i am lost, because a symbol has 4 bits that belong > > to a same frecuency. > > > > For example: "0000" belong to a tone of 1000 Hz > > For example: "0001" belong to a tone of 1015 Hz > > For example: "0010" belong to a tone of 1030 Hz > > Etc....... > > > > Thats four bits arrived joined in the same symbol. > > > > How i do for programming the soft decision in this case? > > > > Help, please > > > > > > > >
Reply by Anonymous May 8, 20062006-05-08
You can calculate some uncertainty bits for the symbol and then assign the
same uncertainty bits to all four data bits for decoding. I guess it depends
on how your symbols are numbered. For example, if they are numbered from 0
to 15 in proportion to frequency and you detect that a 0000 was sent you can
probably assign the 2 MSBs a zero uncertainty since it would take a very
large frequency error for them to be wrong. Similiary, if they were grey
coded then maybe you would assign the bits that don't change with the
neighbors a zero uncertainty. As for the certainity for the symbol decision
maybe you can calculate a ratio of the energy in the selected symbol versus
the energy in all the other tones.


"JAlbertoDJ" <nietorosdj@yahoo.es> wrote in message
news:adSdnWcChYgyvsLZnZ2dnUVZ_tSdnZ2d@giganews.com...
> Hi, > > I need to build a Viterbi for 16FSK. 1/2 with K=7. > > In the case of BFSK, Soft Decision is not a problem for me, I compare the > correlation for a symbol '0' and for a symbol '1' and i know the > confidence for '0' o for '1'. > > In the case of 16FSK, i am lost, because a symbol has 4 bits that belong > to a same frecuency. > > For example: "0000" belong to a tone of 1000 Hz > For example: "0001" belong to a tone of 1015 Hz > For example: "0010" belong to a tone of 1030 Hz > Etc....... > > Thats four bits arrived joined in the same symbol. > > How i do for programming the soft decision in this case? > > Help, please > > > >
Reply by JAlbertoDJ May 8, 20062006-05-08
Hi,

I need to build a Viterbi for 16FSK. 1/2 with K=7. 

In the case of BFSK, Soft Decision is not a problem for me, I compare the
correlation for a symbol '0' and for a symbol '1' and i know the
confidence for '0' o for '1'.

In the case of 16FSK, i am lost, because a symbol has 4 bits that belong
to a same frecuency. 

For example: "0000" belong to a tone of 1000 Hz 
For example: "0001" belong to a tone of 1015 Hz 
For example: "0010" belong to a tone of 1030 Hz 
         Etc.......

Thats four bits arrived joined in the same symbol.

How i do for programming the soft decision in this case?

Help, please