Bandwidth loss in OFDM with USPR2 N210

Hi, guys,

I’m trying to use /ofdm/benchmark_tx.py and /ofdm/benchmark_rx.py in two
machines to implement ofdm transmission. But I found there are too heavy
packet loss or high BER with lot of ‘0’ print out at the receiver. So I
check the signal quality by using the received runing uhd_fft.py to
observe
the bandwidth. I set 500kbps at the sender with fft-size 512
occupied-tones
200, but I just get a 200k bandwidth at receiver. Then changing the
fft-size to 1024 occupied-tones 500, I get a 248k. I wonder if there is
anyone who can help me with this.

With the overrun ‘0’ problem, I try to modify the limit.conf but no
significant changes. When I modified the file, I was not sure which
group I
should set. Because this is a computer belong to our university, the
domain
shows @faculty and @student, I just set the group to student. Does
anyone
know is this correct?

I will appreciate any help with you guys.

Thanks,
Song

Hi,

If I understood it correctly, you set the sample rate to 500 kSsamples/s
with which you can transmit
a maximum of 500 kHz wide signal. In your OFDM transmission, the FFT
size is
512 and you
use only 200 subcarriers. Hence you are using 200/512 of the total
bandwidth
(i.e. 500 kHz)
the signal bandwidth now should be
(200/512)*500 kHz = 195.3125 kHz.
Only changing the sample rate or fraction of occupied carriers can
increase
the signal bandwidth.

The packet loss could be because of synchronization problem. you might
check
if all peaks are detected.

Lixing Song wrote:

200, but I just get a 200k bandwidth at receiver. Then changing the


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