I am trying to measure the RSSI on an usrpn200 which acts as a receiver.
have used the rx_ascii_dft.py and uhd_fft.py both and i have made a
measurements but the received power is not reliable for different
powers at different amplitude of 0.25,0.50 and 0.85 (which i took
randomly ) … the channel attenuation is not less for more transmit
Is there any other way to measure the RSSI values besides these two apps
uhd_fft.py and rx_ascii_dft.py ?i have run a set of measurements and the
resultant received powers are not reliable at all ,according to me . i
still an amateur regarding this .
how about running the rssi.v verilog file ? … will i be able to extract
rssi values directly from the fpga ?
Hi Marcus ,
Sorry i did not explain to you my set-up , i have two usrpn200’s with
RX2400 as the daughterboards . i have omnidirectional antennas . Its a
line of sight experiment . i used .benchmark_tx.py -f 2475M -m bpsk
–from-file=test.pdf -S 2 -s 50 --tx-amplitude=0.25 -v
and on the receiver side i ran ./uhd_fft.py and ./rx_ascii_art_dft.py .
the problem i get in uhd_fft.py is that , as i vary the transmit
powers from 0.25 to 0.85 , i am getting -20 dB constant peak at a
fixed distance . logically it should increase as you said but i am
getting constant received values .
My suspicion, having not looked at the code, is that the magnitude of
the signals arriving at the
“amp” block in that flow-graph are already sufficiently larger than
“1”, that you’re seeing clipping
somewhere in the chain.
You could read the RX-side aux_adc, but it would give you mis-leading
results, since the power-detector
is showing you the power across the entire post-mixer bandwidth. It
really, really is better to calculate
the RSSI from the incoming data, and since you’d have to modify your
application anyway to
read the aux_adc, you might as well add a couple of blocks to
calculate received power properly.
Also, not all cards have an RSSI detector available in hardware, so
assuming that they do is
non-portable to other types of cards.
and the resultant received powers are not reliable at all ,according
to me . i am still an amateur regarding this .
how about running the rssi.v verilog file ? … will i be able to
extract the rssi values directly from the fpga ?
Anticipating your feedback in earnest
Received power is proportional to the average of the square of the I and
Q voltages. If you
use a Complex-to-Mag**2 block, followed by a low-pass filter, you’ll
get an (uncalibrated!!)
An increase in voltage magnitude from 0.25 to 0.5 should create a
received power increase of
6dB, since doubling the voltage increases the power by a factor of 4
(6dB), assuming a reasonably
linear channel between TX and RX.
You haven’t said what your test setup is: antennae, daughtercards, etc.
What are you using to transmit? Is it another USRP device, or something