Hi,

I am trying to use benchmark_ofdm_tx.py and benchmark_ofdm_rx.py to test

the

OFDM communication between two usrp nodes.

While the transmitter is sending data, I use a sprctrum analyzer to

observe

the spectrum, and find the signal bandwidth far beyond my calculation,

which

is 330kHz around with the --fft-length/–occupied-tones=512/256. With my

calculation, the sampling rate of DAC is 128Msamples/second, and each

sample

has 14bits, so the with the interpolation setting to default(256) the

bandwidth of signal should be 128M*14/256=7MHz. Is that correct? If not

could

anyone tell me how to calculate in a right way?

Another problem is when I change the occupied-tones to 64, the bandwidth

of

signal will drop to 180kHz. I think the bandwidth of signal should be

fixed to

some bandwidth if you don’t change the interpolation, and the

occupied-tones

should only affect the bandwidth of each sub-carrier. Is that a correct

understanding?

I also tried changing packet size, seemed it also affected the bandwidth

of

ofdm signal. I am really confused.

By the way, the bandwidth I mentioned above with out specified are all

null to

null bandwidth.

Thanks,

Best regards,

Yan