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[Discuss-gnuradio] Question about the bandwidth of OFDM
From: |
Yan Wang |
Subject: |
[Discuss-gnuradio] Question about the bandwidth of OFDM |
Date: |
Tue, 7 Jul 2009 16:18:13 +0000 (UTC) |
User-agent: |
Loom/3.14 (http://gmane.org/) |
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
- [Discuss-gnuradio] Question about the bandwidth of OFDM,
Yan Wang <=