Re: [Discuss-gnuradio] OFDM Transmitter and Receiver - poor synchronization with USRP1

[Michal Vaclík]

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.

2015-05-21 18:13 GMT+02:00 Martin Braun <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 3.7.6.1 to 3.7.7.1 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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