Re: [Discuss-gnuradio] Question about OFDM Transmitter/Receiver

[Martin Braun]

If you change the FFT size, the allocated carriers do not change. Hence,
you'll be using a much smaller fraction of your bandwidth. This is by
design. As you point out, if you want to occupy more carriers, you have
to modify 'Occupied Carriers'.

Cheers,
M

On 11/30/2016 09:49 AM, address@hidden wrote:
> Hi list,
> 
> I’m messing around with the OFDM Transmitter/Receiver provided by
> GNURadio to test different configurations (basically I want to increase
> the throughput, buts thats not the topic of this mail).
> 
> So, I used the basic ofdm/ofdm_loopback.grc example. 
> 
> First, I run the example with a FFT size of 64 points (parameter fft_len
> in the .grc file). What I have notice is that with this configuration
> almost the entire bandwidth of the signal is used by the FFT carriers
> (see the file fft_64_spectrum.png for a screenshot)
> Afterwards, I changed the FFT size to 256. For my surprise, the
> bandwidth used by the FFT reduced significantly (see
> fft_256_spectrum.png for a screeshot)?
> 
> 
> Do anyone know how to solve this?  I think that there may have to
> perform some additional configuration in the “Occupied Carriers” of the
> OFDM Transmitter/Receiver block.
> 
> Best Regards
> 
> 
> 
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