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

From: Martin Braun
Subject: Re: [Discuss-gnuradio] OFDM Transmitter and Receiver - poor synchronization with USRP1
Date: Fri, 22 May 2015 11:20:24 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0

On 22.05.2015 10:54, Michal Vaclík wrote:
> Yes, I am using default flowgraphs (examples) just adding Multiply Const
> block to avoid clipping due to high PAPR and obviously UHD blocks. Using
> FFT of 64 and default carrier configuration, sync does get better if I
> stretch this to wider bandwidths by setting higher sample rates at USRP.

Hey Michal,

I meant using the same signal bandwidth at higher sampling rates (i.e.
bigger FFTs, same number of occupied bins).


> 2015-05-21 18:13 GMT+02:00 Martin Braun <address@hidden
> <mailto:address@hidden>>:
>     On 20.05.2015 20:19, Michal Vaclík wrote:
>     > 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.
>     Hm, not that I recall... but good for you :)
>     I forget, were you using the example codes with default settings? If so,
>     does doubling the sampling rate *without* changing the total bandwidth
>     (i.e. doubling the FFT size) help with sync at lower bandwidths?
>     M
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