qpsk viterbi decoding

Started by khurram712 March 22, 2007
hello everybody

what the customer have specified us for making viterbi decoding 


includes some units that i want to know about

"SOFT SLICER"

what it is doing is converting 10 bits I and Q inputs to

two 3-bits output pair....any idea what it is....

and can someone provide some insight on "Node Synchronizer" used for
viterbi decoder...please provide some web links(one that dont ask for
money.. ;) ) if possible...
On Mar 22, 12:42 am, "khurram712" <khurram...@hotmail.com> wrote:
> hello everybody > > what the customer have specified us for making viterbi decoding > > includes some units that i want to know about > > "SOFT SLICER" > > what it is doing is converting 10 bits I and Q inputs to > > two 3-bits output pair....any idea what it is.... > > and can someone provide some insight on "Node Synchronizer" used for > viterbi decoder...please provide some web links(one that dont ask for > money.. ;) ) if possible...
No idea what a "node synchronizer" is, but the "soft slicer" is one that gives the probabilities for one symbol (say -1) versus another (say +1). Let's simplify by assuming BPSK (sending -1 or +1). You see a noisy version y[n] = x[n] + z[n], x[n] is the transmitted symbols, z[n] is white Gaussian noise. If you know the mean/variance of z[n], then from the observed y[n] you can compute (with some abuse of notation): p(y[n] | x[n]=1) and p(y[n] | x[n]=-1). Using Bayesian rule etc you can find p( x[n]=1 | y[n]=Y), p( x[n]=-1 | y[n]=Y). In many cases you only care about the ratio of the log of the two quantities above. Look up "log likelihood ratio". This is probably what a "soft slicer" is. The customer needs to tell you what format exactly he/she wants. Julius