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Soft Decision Viterbi Decoding?

Started by ssohaib December 19, 2007
On Dec 23, 11:35 am, "ssohaib" <ssoh...@gmail.com> wrote:
> Good to see your reply. Could you plz eleborate how can i quntize the I and > Q seperatly. Lets spoose after noise we have some thing like > 0.807-0.984j. How can i qunatize 0.807 and -0.984j in to 8 levels? > > Waiting.
I think you mentioned Matlab, in which case the function 'vitdec' is what you will probably use. There are examples of how to use it on www.mathworks.com, just type 'vitdec' into the search box. You have specifiy the soft I and Q values as K bit integers from 0 to (2^K)-1. Let's say K is 3. Then you must map the floating point I and Q samples to integers in [0,7]. If you expect a range of floating point values from -sqrt(2) to +sqrt(2), with nominal values -sqrt(2)/2 and +sqrt(2)/ 2, then the soft decisions would be: Isd = 4+floor(4*I/sqrt(2)) Qsd = 4+floor(4*Q/sqrt(2)) Happy Holidays, John
Hi,
Thanks for your kind reply. Could you please explain me if I quantize real
and imaginary part of my received coded QPSK separately how can I use these
3 bits from real and 3 bits from imaginary part in Viterbi soft decoding? 

P.S. I have looked on internet for it but couldn&rsquo;t get any answer, so if
you know any website kindly forward its address. Also I would be grateful
if you send me any solved example of Viterbi decoding of QPSK coded
signal. 

Bye

On Dec 24, 8:32 am, "ssohaib" <ssoh...@gmail.com> wrote:
> Hi, > Thanks for your kind reply. Could you please explain me if I quantize real > and imaginary part of my received coded QPSK separately how can I use these > 3 bits from real and 3 bits from imaginary part in Viterbi soft decoding? > > P.S. I have looked on internet for it but couldn't get any answer, so if > you know any website kindly forward its address. Also I would be grateful > if you send me any solved example of Viterbi decoding of QPSK coded > signal. > > Bye
Just feed them into the decoder: Isd Qsd Isd Qsd ... etc John
Hi,
I would be grateful if you please explain me how do u get these following
expressions:

Isd = 4+floor(4*I/sqrt(2))
Qsd = 4+floor(4*Q/sqrt(2))

Thanks.
On Dec 25, 8:26 pm, "ssohaib" <ssoh...@gmail.com> wrote:
> Hi, > I would be grateful if you please explain me how do u get these following > expressions: > > Isd = 4+floor(4*I/sqrt(2)) > Qsd = 4+floor(4*Q/sqrt(2)) > > Thanks.
I don't care to spoon feed this to you any more. I suggest you hire a tutor. John