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Re: [Discuss-gnuradio] Recovering x(t) from IQ samples

From: Jens Elsner
Subject: Re: [Discuss-gnuradio] Recovering x(t) from IQ samples
Date: Sat, 18 Aug 2007 15:00:39 +0200
User-agent: Mutt/1.5.9i

> So the problem remains: Given only the i(t) and q(t) samples, which is all 
> the USRP gives back, how do I reconstruct x(t)?

Two options: 

1) you need some kind of phase reference (coherent
demodulation), insert pilot symbols into x(t)

2) use AM modulation over one carrier only; this requires x(t) to have a
known maximum amplitude:

Let's assume x(t) in [-1, 1] and zero mean.

The carrier c(t) = c_0 cos(wt+phi) is used to modulate x(t):

s(t) = ( c_0 + x(t) ) cos(wt+phi) .

This requires c_0 to be greater than 1, otherwise the sign
ambiguity you've been talking about occurs. 

Please correct me if I'm mistaken. All in all it would be best to know
what this BBC application is supposed to do.


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