# Re g : spectrum sensing code

Hi Community,

Question - 1

I was working with the UHD version of spectrum sensing code.

I have USRP2 with me. I learnt that USRP2 can achieve 50MHz of RF
bandwidth
with 8 bit samples and 25MHz of RF bandwidth with 16 bit samples.

I wanted to know how does this information translates while passing
min_freq
ans max_freq parameters to the spectrum sensing code. Does it mean
(max_freq

• min_freq) = 25MHz.

Please correct me if I am wrong :teeth:

Question - 2

Why the minimum center frequency is set as follows :

self.min_center_freq = self.min_freq + self.freq_step/2

Why it simply doesn’t take the minimum frequency as we provided. Setting
the
max_center_freq I understood somehow.

Question - 3

In non UHD version of spectrum sensing code the adc_rate was fixed fro
USRP-1 i.e. 64M and that was used to calculate usrp_rate while in UHD
version of the same code usrp_rate is calculated by the sampling rate we
give.

I was wondering how does the code manages to work with devices of
different
sampling rates i.e. USRP-1 with 64M USRP2 with 100M

Context : I am trying to scan WLAN channels 1, 6, 11 continuously. So I
have
to keep working with a total bandwidth of 76 MHz

## Sumit Kr. Research Assistant Communication Research center IIIT Hyderabad India

View this message in context:
http://old.nabble.com/Reg-%3A-spectrum-sensing-code-tp34330101p34330101.html
Sent from the GnuRadio mailing list archive at Nabble.com.

Please correct me if I am wrong :teeth:

As far as I understand spectrum sensing code is used for wideband
spectrum analysis, that is
to scan across wide RF bands which USRP is not able to analyze at a
time. So obviously
max_freq - min_freq > 25 MHz .

e.g Conider you have to analyze the spectrum from 400 MHz to 500 MHz.
You can keep
min_freq = 400 MHz and max_freq = 500MHz. If you have configured USRP
sample rate
to get 25 MHz bandwidth, ideally one round of scan will be complete by 4
tuning steps.
(practically 6 steps as the code is using 25% overlap to reduce
non-linearity in DDC response).

Firas posted a detailed explanation of the code in the mailing list long
back. You can find it
here Some usrp_spectrum_sense.py code Explanation - GNU Radio - Ruby-Forum.

Question - 2

Why the minimum center frequency is set as follows :

self.min_center_freq = self.min_freq + self.freq_step/2

Why it simply doesn’t take the minimum frequency as we provided. Setting the
max_center_freq I understood somehow.

e.g. Scan range 10MHz to 40 MHz
USRP1 B/W = 8MHz
First tuning step is with centre freq 14Mhz (10+8/2 ideally) which will
cover the bandwidth from 10 to 18 Mhz

Question - 3

In non UHD version of spectrum sensing code the adc_rate was fixed fro
USRP-1 i.e. 64M and that was used to calculate usrp_rate while in UHD
version of the same code usrp_rate is calculated by the sampling rate we
give.

I was wondering how does the code manages to work with devices of different
sampling rates i.e. USRP-1 with 64M USRP2 with 100M

sampling rate ----> Bandwidth ----> feq_step

Context : I am trying to scan WLAN channels 1, 6, 11 continuously. So I have
to keep working with a total bandwidth of 76 MHz

Check the tuning delay of the device you are using and make sure that
you are not losing any data during the sweeping process.I may be wrong
somewhere. Please go through Firas’s explanation which will make things
clear.

regards
Sreeraj Rajendran

Hi Sreeraj,

sreeraj r wrote:

Question - 1

I was working with the UHD version of spectrum sensing code.

I have USRP2 with me. I learnt that USRP2 can achieve 50MHz of RF
bandwidth
with 8 bit samples and 25MHz of RF bandwidth with 16 bit samples.

I wanted to know how does this information translates while passing
min_freq
ans max_freq parameters to the spectrum sensing code. Does it mean
(max_freq
e.g Conider you have to analyze the spectrum from 400 MHz to 500 MHz. You
here Some usrp_spectrum_sense.py code Explanation - GNU Radio - Ruby-Forum.
so shall I pass sampling rate = 2bandwidth i.e. for this case 225Mhz =
50MSPS (Pl correct if I am wrong)
Question - 2

Why the minimum center frequency is set as follows :

self.min_center_freq = self.min_freq + self.freq_step/2

Why it simply doesn’t take the minimum frequency as we provided. Setting
the

In non UHD version of spectrum sensing code the adc_rate was fixed fro
USRP-1 i.e. 64M and that was used to calculate usrp_rate while in UHD
version of the same code usrp_rate is calculated by the sampling rate we
give.

I was wondering how does the code manages to work with devices of
different
sampling rates i.e. USRP-1 with 64M USRP2 with 100M

sampling rate ----> Bandwidth ----> feq_step

Context : I am trying to scan WLAN channels 1, 6, 11 continuously. So I
have
regards
Sreeraj Rajendran