Re: [Discuss-gnuradio] constellation object

[Martin Braun]

On Thu, Jan 20, 2011 at 01:36:46PM -0700, Ben Reynwar wrote:
> > You've got that right: a soft decider doesn't really decide, but rather
> > gives a value how good the estimate is. Say you have a binary output,
> > 1 and -1. A soft decider can also give any value in between. If you get
> > a 0, then the soft decider really has no clue what was actually
> > transmitted and instead of guessing a binary value, it relays this
> > uncertainty.
> > One place this is really important is the channel decoding.
> >
> 
> That makes sense.  What kind of values would you output when you have more
> than 2 symbols?  Would you just give the distances to the closest n points?

Good question--but it also depends on where you need the soft values.
Say you have a 4-QAM and a binary channel code. Then you'd split every symbol
in two soft values, one for each bit. In this case, assuming phase was
corrected, the real and imaginary values.

Cheers,
MB

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