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Re: [Discuss-gnuradio] The sinusiodal waveform is drifting from input to

From: Johnathan Corgan
Subject: Re: [Discuss-gnuradio] The sinusiodal waveform is drifting from input to output.
Date: Wed, 3 Mar 2010 10:06:07 -0800

On Wed, Mar 3, 2010 at 03:26, srinivas naga vutukuri
<address@hidden> wrote:

> I am transmitting the sinusoidal wave form (IQ samples), in the following
> methods, and found that when i stem plot in the MATLAB both the input wave
> form data on one USRP2 and the received data on another USRP2, initially the
> waveform is exactly fitting (i mean overlapping), and after certain samples,
> it starts ie., in the input wave form and the output data waveform drifting
> slightly and at the end samples both the waveforms overlaps perfectly. Why
> this slight drifting is happening when transmitting the I Q samples from one
> USRP2 to another USRP2.

This is almost certainly due to receiver frequency and timing drift
between transmitter and receiver USRPs.  It's a fact of life in
real-world radio systems, requiring significant design effort to
compensate for; you're seeing exactly what you should expect to see.

The digital demodulators in GNU Radio typically use DSP blocks like
Costas loops for frequency/phase synchronization and Mueller&Mueller
timing recovery blocks to track timing drift.


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