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Re: [Discuss-gnuradio] constellation object

From: Ben Reynwar
Subject: Re: [Discuss-gnuradio] constellation object
Date: Fri, 21 Jan 2011 08:01:14 -0700

On Fri, Jan 21, 2011 at 1:31 AM, Martin Braun <address@hidden> wrote:
> 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.

OK.  I think I need to do some reading on channel coding before I can really get
what's going on here.  Thanks for your help.


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