[USRP-users] Question related to captured data validation

Marcus Müller marcus.mueller at ettus.com
Wed Oct 14 11:08:33 EDT 2015


Hi Alok,

a few general notes:
> For my initial studies I am using *benchmark_tx * programme for
> transmitting the signals and *benchmark_rx* for the reception purpose.
There's two of them, a narrowband one and an OFDM one. Which one are you
using?
> *In the next step, i am converting the complex data captured (using
> the uhd_rx_cfile) into .mat format with the help of "Octave".*
You don't have to do that. There's a matlab/octave script within GNU
Radio, called "gr-utils/octave/read_complex_binary.m" [1] that just
reads the samples from the file without any conversion!

> I would like to know that how to validate that the data i have
> captured using uhd_rx_cfile is valid and having the information of
> transmitted signals.
Well, the only 100% correct way to do that is to decode and validate the
data using benchmark_rx. It has a --from-file option, so you can read
samples stored in a file!
>  Also, is it a good practice to use the converted .mat data to extract
> the Average RSSI per samples using the convolution formula i.e.
>
> *Conv(abs(IQ data vector).^2, ones(1,N)/N,'valid').*
abs(IQ data vector).^2 is element-wise magnitude squared; I'm not quite
sure why you're convolving that with a 1-vector, but I assume you want
to apply a moving average on these digital power samples, which does
sound like a good idea to measure RX signal strength.
However, I'd argue that RSSI ("received signal strength indicator")
needs to figure out what in your RX signal is noise, and what's signal
power (otherwise, you could just put your receive antenna in a microwave
oven, and turn it on[2] to maximize RSSI). But: To my knowledge, there's
no "canonical" definition of RSSI (which makes it a "bad" measure, in my
humble opinion), so you can also say that RSSI is only the strength of
the overall received signal, in which case your approach is correct.

It might be worthwhile noting that for the simpler benchmark_{rx,tx},
namely the narrowband one, you can just apply the pulse shaping filter
to get a matched filter response. That will maximize SNR in the
post-filter signal, and the power of that hence can be a useful signal
quality indicator.

Best regards,
Marcus


[1]
https://github.com/gnuradio/gnuradio/blob/master/gr-utils/octave/read_complex_binary.m
[2] Please don't do that.


On 10/14/2015 06:16 AM, alok ranjan via USRP-users wrote:
> Hello All,
>
> I am using two USRP N210, one as a transmitter and another one as a
> receiver both are connected to the same host.
>
> However, both  USRPs are separated from each other (say 2, 4, 6, 8, 10
> meters). 
>
> For my initial studies I am using *benchmark_tx * programme for
> transmitting the signals and *benchmark_rx* for the reception purpose.
>
> Next, I am capturing the transmitted base band signals (Complex) using
> the *uhd_rx_cfile* with all the valid assignments to be passed. I am
> giving  all the valid configuration same as the configuration
> maintained while reception.
>
> *In the next step, i am converting the complex data captured (using
> the uhd_rx_cfile) into .mat format with the help of "Octave".*
>
>
> I would like to know that how to validate that the data i have
> captured using uhd_rx_cfile is valid and having the information of
> transmitted signals.
>
>  Also, is it a good practice to use the converted .mat data to extract
> the Average RSSI per samples using the convolution formula i.e.
>
> *Conv(abs(IQ data vector).^2, ones(1,N)/N,'valid').*
> *
> *
> *
> *
> Any help in this matter is appreciated. 
>
> Thank you, regards
>
> Alok Ranjan
>
>
> _______________________________________________
> USRP-users mailing list
> USRP-users at lists.ettus.com
> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com

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