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

[Martin Braun]

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).

M


> 
> 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 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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