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Re: [Discuss-gnuradio] OFDM Transmitter and Receiver - poor synchronizat

From: Michal Vaclík
Subject: Re: [Discuss-gnuradio] OFDM Transmitter and Receiver - poor synchronization with USRP1
Date: Thu, 21 May 2015 05:19:33 +0200

Hi, I am sorry for the delayed response.

I checked the centering of the OFDM signal and it looks pretty good. Even looking at the signal's spectrum using SDR# on other computer was very nice - book-grade example of nicely shaped OFDM spectrum. Today I upgraded from GNU Radio v to and reception (syncrhonization and detection) has improved dramatically. Even at relatively low sample rate (1M, anything lower simply doesn't synchronizie). Unfortunately the received packets still weren't enough for any kind of real world transmission. 

Was OFDM improved in some kind of way in v3.7.7.1 (I don't see anything related to OFDM in changelog)? I simply launched the same flowgraph on newer version and it works much better.

2015-05-11 21:02 GMT+02:00 Martin Braun <address@hidden>:
On 09.05.2015 15:47, Michal Vaclík wrote:
> Doesn't seem so - by connecting scope to DETECT port on S&C block I can
> see only randomly timed peeks as opposed to running with channel model
> where the peeks happen at fixed time periods.
> Detection seems to get better with higher sample rates.

This might be an issue of high relative frequency offsets (which get
less severe for higher sub-carrier bandwidths). You could check how well
your OFDM signal is centered.


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