Hi Muneeba,

please stay on-list with your replies!

So,

On 12.05.2016 12:48, Raja
Muneeba wrote:

Thankyou for your answers. Im trying to solve this. I
am now using fft Sink at receiver to see the power(db)
vs frequency plot. I turn off the transmitter and see
the power at fft, and consider it noise. Then I turn on
the transmitter and get the value at fft. I conside that
signal strength+noise. So (signal
strength+noise)-noise=signal strength. And SNR could be
signal strength/noise. Am I going in the right
direction?

I think so! You should start to model your noise. Is your
noise model "white"? If it is, what does it say about the
power of noise contained in different, equally wide
bandwidths?

What is the power(db) on fft actually? Is it dbm?

No,

If its db, then in comparison to what?

Full scale! This is DSP, there's no physical units to the
numbers you handle. So, if you feed in a constant 1 into
your fft plot, you'll see a specific value.

One more basic thing as I am extremely new to signal
processing. What frequency of signal source ,sampling
rate and gain should I choose for transmitting over
centre frequency of 2.48GHZ.

That doesn't have to do anything with each other:

Sampling rate is just a number that the signal source uses
together with the signal frequency to calculate how many
*samples* long a full period will be – there's no "real
world" time in this kind of DSP, just samples. So a signal
source with f_sample=1 and f_signal = 0.2 will have exactly
the same output as a signal source with f_sample = 5e6 and
f_signal = 1e6.

Now, you don't sample at 2.48GHz directly – your USRP is an
upconverter that allows you to get complex baseband
equivalent to what happens in a real passband at RF
frequencies.

The idea of complex baseband is very important here – GNU
Radio has a suggested reading wiki page[1], but seeing that
you're probably a student at the Aalto university, I'd just
ask for the scriptum or recommended book of the basic
digital communications lecture[2] in electrical engineering,
and read up till you reach the baseband receiver. Such a
lecture was where I learned those principles!

So, now the sampling rate you chose for your USRP sink or
source does have a real-world effect: it actually sets the
rate at which samples are converted to/from analog values.
And hence, the sampling rate you use with the hardware
directly sets the Nyquist rate, and hence, your signals'
bandwidth.

What would be the reason for choosing that. Right now
I have 1M sampling rate and 1k frequency of signal
source. My USRP is N210 with SBX daughter board.

That are in any case values that the SBX and the N210
support.

Best regards,

Marcus

Can you suggest some documentation which can help me
deciding these factors?

[1]

http://gnuradio.org/redmine/projects/gnuradio/wiki/SuggestedReading
[2]

https://mycourses.aalto.fi/course/view.php?id=5109

SNR is signal strength/noise

Yeah, obviously, but what does that mean? how can
you *describe* signal strength with a mathematical
formula based on the digital samples you have in GNU
Radio?

The point is that you'll just need an estimator for
the signal energy, and an estimator for the noise
power.

There's a lot of estimators for both; for a single
tone, Welch's method might be pretty usable. Another
approach would be a narrow filter, and a
signal-to-magnitude-squared converter.

For noise power, you could just calculate the
overall receive signal power, and subtract the
signal power estimate.

Best regards,

Marcus

On 11.05.2016 11:56,
Raja Muneeba wrote:

SNR is signal strength/noise

Hi
Muneeba,

so the point is: What *is* SNR? Can you
define it mathematically?

Best regards,

Marcus

On 11.05.2016
11:47, Raja Muneeba wrote:

HI,

I am using usrp N210 with db SBX,
and I do not have any message wave
(or source file). I simply transmit
and receive a sin wave via USRPs
(find my graphs attached). I am not
doing any modulation/de modulations.

I need to know the SNR value at
the receiver end. I also want to
adjust the signal strength to change
SNR. SNR is signal strength/noise in
db. How can I do this?

I see solutions with modulation
schemes, but since I don’t use any
modulation, how can it be done
without that?

Regards,

Muneeba R.