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Re: [Discuss-gnuradio] OFDM results.

From: Jeff Brower
Subject: Re: [Discuss-gnuradio] OFDM results.
Date: Fri, 06 Jun 2008 08:39:20 -0500


> In your sixteen QAM and other figures I see two effects.
> Notice just the slightest hint that arcs through the top four
> constellation points in the 16 QAM is not straight.  This curvature is
> caused by nonlinearity.
> Your result almost surely can NOT be clock jitter.  If you had a lot of
> clock jitter,  the pictures would look much worse.  Notice the
> dispersion gets larger as your proceed away from the origin.  This is
> almost surely phase noise in some oscillator.

"Phase noise" of an oscillator to me means jitter.  Can you clarify?  Do you 
mean a
sinusoid oscillator that has some issue with shape; i.e. non-linearity?  Thanks.


> Per Zetterberg wrote:
> > Dear all,
> >
> > I am experimenting with OFDM between two USRPs. Unfortunately, I am not yet
> > able to master the gnuradio framework so I have made my own implementation.
> > The results are given in the link below.
> >
> > http://www.s3.kth.se/~perz/usrp/OFDM_results.pdf
> >
> >
> > How does this compare with the gnuradio OFDM implementation ?
> >
> > What is the cause of the problems. Clock jitter ?, non-linearities ?
> >
> >
> > BR/
> > Per Zetterberg

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