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Re: [Discuss-gnuradio] Fwd: Cyclic Time drift while sending I&Q samples

From: Johnathan Corgan
Subject: Re: [Discuss-gnuradio] Fwd: Cyclic Time drift while sending I&Q samples through USRP2
Date: Sun, 7 Mar 2010 22:21:38 -0800

On Sun, Mar 7, 2010 at 21:17, Madan <address@hidden> wrote:

> 1) Is this synchronization error between TWO RF's.


> 2)Do i have to synchronize the two USRP2's with a master clock using GPS
> receiver ?

If you wish to transmit and receive using two USRP2s, without making
the effort to engineer carrier and timing recovery, then yes, they
will both need to be driven from the same external reference.

>  (because in the benchmark_tx.py and benchmark_rx.py ....certain
> algorithms are being used for CLOCK Recovery ( Muller & Muller), and i am
> not in favour of using these programs being a overhead to my programs which
> are processing OFDM I&Q samples.

The recovery techniques used in the digital examples are appropriate
to the type of modulation they are using.  For OFDM, there are other
techniques, such as sending pilot tones and training symbols.

> 3) Can you please suggest me are there any better ways to for me SEND and
> RECIEVE  I&Q samples properly.?

It sounds like you do not have a clear concept of your communications
requirements.  Only by analyzing what you need to accomplish and the
channel over which you are transmitting can you engineer the correct


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