Hi all, I am new to demodulation and FEC. How can I get each bit's soft-probability from the constellation? For example, the modulation method is 16QAM, How can I get P(bit1=0),P(bit2=0),P(bit3=0),P(bit4=0) from a symbol? Is it belong to the subject of detection and need viterbi algorithm? Or can you recommend some key words of this subject? Best regards, Davy
Constellation symbol to bit's soft-probability?
Started by ●January 19, 2006
Reply by ●January 20, 20062006-01-20
"Davy" <zhushenli@gmail.com> wrote in message news:1137726871.700967.266740@o13g2000cwo.googlegroups.com...> Hi all, > > I am new to demodulation and FEC. > > How can I get each bit's soft-probability from the constellation? > For example, the modulation method is 16QAM, How can I get > P(bit1=0),P(bit2=0),P(bit3=0),P(bit4=0) from a symbol? > > Is it belong to the subject of detection and need viterbi algorithm? > > Or can you recommend some key words of this subject? >"bayes theorem"+"soft input" should work. You could also look at page 72 to 74 of this for a very direct method; http://4more.av.it.pt/docs/D4.4.pdf Best of luck - Mike
Reply by ●January 20, 20062006-01-20
Davy wrote:> Hi all, > > I am new to demodulation and FEC. > > How can I get each bit's soft-probability from the constellation? > For example, the modulation method is 16QAM, How can I get > P(bit1=0),P(bit2=0),P(bit3=0),P(bit4=0) from a symbol? > > Is it belong to the subject of detection and need viterbi algorithm? > > Or can you recommend some key words of this subject? > > Best regards, > Davy >Viterbi decoding comes after soft decision making; the only real connection is that Viterbi decoding is enhanced by soft decisions. Mike's response is the correct one: you use Baysian estimation to figure out what the probability that a certain bit was transmitted. You need to know the probability density function of your noise and have a pretty good grasp of the signal characteristics for it to work right. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Reply by ●January 25, 20062006-01-25
In sci.electronics.design Mike Yarwood <mpyarwood@btopenworld.com> wrote:> > "Davy" <zhushenli@gmail.com> wrote in message > news:1137726871.700967.266740@o13g2000cwo.googlegroups.com... >> Hi all, >> >> I am new to demodulation and FEC. >> >> How can I get each bit's soft-probability from the constellation? >> For example, the modulation method is 16QAM, How can I get >> P(bit1=0),P(bit2=0),P(bit3=0),P(bit4=0) from a symbol?<snip> "bayes theorem"+"soft input" should work.> > You could also look at page 72 to 74 of this for a very direct method; > http://4more.av.it.pt/docs/D4.4.pdfIf you get any signal, is there a nice way of back propagating to get optimum probabilities?
Reply by ●January 26, 20062006-01-26
I don't completely comprehend what you mean by back propogation. But yes, it is possible to get optimum probabilities for bits mapped to a constellation symbol. You would find results on that if you search for Bit Interleaved Coded Modulation, or BICM in short.
Reply by ●January 27, 20062006-01-27
In sci.electronics.design PraZ <prasanna.sethuraman@patni.com> wrote:> I don't completely comprehend what you mean by back propogation. But > yes, it is possible to get optimum probabilities for bits mapped to a > constellation symbol. You would find results on that if you search for > Bit Interleaved Coded Modulation, or BICM in short.If you get a decoded signal of any form coming through the viterbi decoder, a nice way of propagating back the actual symbol properties into the decisions.
