31 Dec
2011
31 Dec
'11
11:16 p.m.
Hi
I'm newbie in DSP and SDR, but I'm really interested in this matter and I want to
learn. I have bunch of questions which has short answers, if you can please answer them in
easy terms and words, so I can understand them well. I hope this thread will help a lot of
other newbies to understand DSP stuff better.
I have a Linux with every needed tools like osmocomm, gnuradio, openbts, kalibrate, uhd
drivers, ... and USRP N210 hardware ready. Everything works normal and well.
A) Sometimes when I scan a network bandwidth like GSM1800 using kalibrate, I see some
channels like 820, 538, etc. When I re-scan, I cannot find them. Does this mean that
kalibrate finds a channel when a mobile handset has a live conversation or sms send or
receive in progress? or what?
B) I want to wideband capture for example 125 ARFCN. It needs 25MHz bandwidth which USRP
N210 can handle and stream it easily. Even AFAIK I can double this number and capture 250
ARFCN using single N210 (50MHz, in USRPN210 data sheet it says it's capable of
streaming 50MHz wide signals).
How can I wideband capture 125 ARFCNs? I tried to do it using:
./uhd_rx_cfile.py -f `arfcncalc -a 512 -b 1800 -d` --samp-rate=25000000 -N 200000000 -g 70
b1.cfile
What I understood and decided to write such command above:
B-1) arfcncalc calculates frequency of first GSM1800 channel (512 ARFCN) which is start
point (in above command)
B-2) Sampling Rate is the bandwidth I want to capture, in our case it's 25MHz means
125 ARFCN which each ARFCN has 200kHz bandwidth
B-3) 200M samples will be received (-N parameter)
B-4) Gain value is 70, means it will boost antennas to maximum power to receive signals, I
think USRPN210 max. gain is 80
B-5) My decimation rate here using 25M sampling rate and USRP N210 which has 100MHz ADC,
will be 4. So if I decided to read cfile I have to use 4 as decimation rate.
Please explain and tell me if I'm correct or wrong about above statements.
Does this will work and I'll have a 125 ARFCN from 512 to 637 ARFCNs captures into
b1.cfile?
If so why in
http://gnuradio.org/doc/doxygen-3.4/classusrp__source__base.html#adf8529d74…
documentation, it says set_rx_freq should set center of frequency, so for example if you
want to capture from 512 to 637, you should set frequency to frequency of ARFCN 574?
C) How can I seperate and process 200khz by 200khz channels in wideband captured file?
Thank you so much for your time
Your help and answers will solve problem of a lot of newbies like me.
Best Wishes
3 Jan
3 Jan
2:03 p.m.
On Sat, Dec 31, 2011 at 02:16:14PM -0800, Avner Ezra wrote:
Hi
I'm newbie in DSP and SDR, but I'm really interested in this matter and I want to
learn. I have bunch of questions which has short answers, if you can please answer them in
easy terms and words, so I can understand them well. I hope this thread will help a lot of
other newbies to understand DSP stuff better.
I have a Linux with every needed tools like osmocomm, gnuradio, openbts, kalibrate, uhd
drivers, ... and USRP N210 hardware ready. Everything works normal and well.
Hi
Avner,
there are people on this list who are very skilled when it comes to DSP
stuff, although I think your questions are better suited for the
gnuradio ML.
8:11 p.m.
On Sat, Dec 31, 2011 at 5:16 PM, Avner Ezra <avner.ezra(a)yahoo.com> wrote:
A) Sometimes when I scan a network bandwidth like
GSM1800 using kalibrate, I
see some channels like 820, 538, etc. When I re-scan, I cannot find them.
Does this mean that kalibrate finds a channel when a mobile handset has a
live conversation or sms send or receive in progress? or what?
No, it most cases it means a weak signal. Kalibrate performs
per-channel energy detection prior to offset calculation against the
FCCH, which is always active. The variance is probably just noise.
B) I want to wideband capture for example 125 ARFCN.
It needs 25MHz
bandwidth which USRP N210 can handle and stream it easily. Even AFAIK I can
double this number and capture 250 ARFCN using single N210 (50MHz, in
USRPN210 data sheet it says it's capable of streaming 50MHz wide signals).
To capture 50MHz you need to 8-bit samples to avoid saturating the
Ethernet bus. So yes it's possible, though I'm not sure about the
current state of device or API support for the feature.
How can I wideband capture 125 ARFCNs? I tried to do
it using:
./uhd_rx_cfile.py -f `arfcncalc -a 512 -b 1800 -d` --samp-rate=25000000 -N
200000000 -g 70 b1.cfile
What I understood and decided to write such command above:
B-1) arfcncalc calculates frequency of first GSM1800 channel (512 ARFCN)
which is start point (in above command)
B-2) Sampling Rate is the bandwidth I want to capture, in our case it's
25MHz means 125 ARFCN which each ARFCN has 200kHz bandwidth
B-3) 200M samples will be received (-N parameter)
B-4) Gain value is 70, means it will boost antennas to maximum power to
receive signals, I think USRPN210 max. gain is 80
B-5) My decimation rate here using 25M sampling rate and USRP N210 which has
100MHz ADC, will be 4. So if I decided to read cfile I have to use 4 as
decimation rate.
You want the centre frequency of the spectrum you want to capture -
not the start point. Also, the maximum gain value will also vary
depending on the daughterboard. Otherwise, you are correct.
C) How can I seperate and process 200khz by 200khz
channels in wideband
captured file?
The brute force approach is to individually frequency translate each
channel down to baseband, low-pass filter, and perform sample rate
conversion. The more efficient method it to construct a multirate
channelizer. GNU Radio has blocks for either approach, though
construction may not be straightforward.
Thomas
4 Jan
4 Jan
9:34 p.m.
Hi
Thank you so much Thomas, I learned too much from you.
Is there a good sample for UHD USRPs like USRP N210 which can send and receive file in
other side?
I connected 2 USRPs to 2 laptops, sent a file using rx_send_from_file.py in ARFCN channel
no: 560 and in other side I listened for incoming signals on same frequency, same sampling
rate, same gain, etc. Two USRPs was about 10 meters far from each other. But I was not
able to see my file's context in rx_recv_cfile.py, it captures cfile from same ARFCN
channel using same frequency and sampling rate, but I was not able to see any related data
to my file being trasmitted, any reason you can see here?
I heard that USRPs need hardware modification to be able to capture GSM signals, is it
correct for N210?
Could you guide me a little on translating frequency to channels, low-pass filter and
performing sample rate conversation? When I receive file using rx_recv_cfile, it asks for
sampling rate parameter, it will not do all those steps? If not, please help me on this
part which is your previous email's last part, I need a little more detail here.
Thank you once again
________________________________
From: Thomas Tsou <ttsou(a)vt.edu>
To: Avner Ezra <avner.ezra(a)yahoo.com>
Cc: "baseband-devel(a)lists.osmocom.org" <baseband-devel(a)lists.osmocom.org>
Sent: Tuesday, January 3, 2012 10:41 PM
Subject: Re: Newbie DSP Questions
On Sat, Dec 31, 2011 at 5:16 PM, Avner Ezra <avner.ezra(a)yahoo.com> wrote:
A) Sometimes when I scan a network bandwidth like
GSM1800 using kalibrate, I
see some channels like 820, 538, etc. When I re-scan, I cannot find them.
Does this mean that kalibrate finds a channel when a mobile handset has a
live conversation or sms send or receive in progress? or what?
No, it most cases it means a weak signal. Kalibrate performs
per-channel energy detection prior to offset calculation against the
FCCH, which is always active. The variance is probably just noise.
B) I want to wideband capture for example 125 ARFCN.
It needs 25MHz
bandwidth which USRP N210 can handle and stream it easily. Even AFAIK I can
double this number and capture 250 ARFCN using single N210 (50MHz, in
USRPN210 data sheet it says it's capable of streaming 50MHz wide signals).
To capture 50MHz you need to 8-bit samples to avoid saturating the
Ethernet bus. So yes it's possible, though I'm not sure about the
current state of device or API support for the feature.
How can I wideband capture 125 ARFCNs? I tried to do
it using:
./uhd_rx_cfile.py -f `arfcncalc -a 512 -b 1800 -d` --samp-rate=25000000 -N
200000000 -g 70 b1.cfile
What I understood and decided to write such command above:
B-1) arfcncalc calculates frequency of first GSM1800 channel (512 ARFCN)
which is start point (in above command)
B-2) Sampling Rate is the bandwidth I want to capture, in our case it's
25MHz means 125 ARFCN which each ARFCN has 200kHz bandwidth
B-3) 200M samples will be received (-N parameter)
B-4) Gain value is 70, means it will boost antennas to maximum power to
receive signals, I think USRPN210 max. gain is 80
B-5) My decimation rate here using 25M sampling rate and USRP N210 which has
100MHz ADC, will be 4. So if I decided to read cfile I have to use 4 as
decimation rate.
You want the centre frequency of the spectrum you want to capture -
not the start point. Also, the maximum gain value will also vary
depending on the daughterboard. Otherwise, you are correct.
C) How can I seperate and process 200khz by 200khz
channels in wideband
captured file?
The brute force approach is to individually frequency translate each
channel down to baseband, low-pass filter, and perform sample rate
conversion. The more efficient method it to construct a multirate
channelizer. GNU Radio has blocks for either approach, though
construction may not be straightforward.
Thomas
5 Jan
5 Jan
10 a.m.
New subject: [OT] Re: Newbie DSP Questions
Avner,
as it has been suggested in this thread before, please follow-up-to a
mailinglist where this is on-topic.
neither Kalibrate nor the USRP are used in OsmocomBB, for which this
mailinglist was creted.
Thanks for your attention.
--
- Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/
============================================================================
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participants (4)
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Alexander Huemer -
Avner Ezra -
Harald Welte -
Thomas Tsou