Re: [Discuss-gnuradio] OFDM Example, 'Noisy' final symbol

[Martin Braun]

On 30.04.2014 11:51, David Halls wrote:
> Hi Martin, All,
>
> Has anyone noticed that the final symbol of any burst (no matter how
> many packets in a transmission) appears slightly 'noisy' in the OFDM
> example code? Is it something to do with my set-up?
>
> I attach a picture of the eq'd FD constellation when I send two packet:
> a) the first packet, b) the second packet (excluding the final (16th)
> symbol), and c) second packet (with all symbols)
>
> Is it to do with sample alignment/timing error? I have tried sliding the
> samples passed to the FFT at the receiver, moving the window backwards
> and forwards and can't get a better result...

This was my first thought when I read the subject line... where are you 
getting symbols? Before the equalizer? And is this OTA, or simulated?

Really, all OFDM symbols should be equally noisy. A timing offset will 
normally only make the acquisition start somewhere between start and end 
of the cyclic prefix. So, I'm unsure what this is without any further 
analysis.

Martin