<html><body><div style="color:#000; background-color:#fff; font-family:times new roman, new york, times, serif;font-size:12pt"><div><span>Hi</span></div><div><br><span></span></div><div><span>Thank you so much Thomas, I learned too much from you.</span></div><div><br><span></span></div><div><span>Is there a good sample for UHD USRPs like USRP N210 which can send and receive file in other side?</span></div><div><br><span></span></div><div><span>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?</span></div><div><br><span></span></div><div><span>I heard that USRPs need hardware modification to be able to capture GSM signals, is it correct for N210?</span></div><div><br><span></span></div><div><span>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.</span></div><div><br><span></span></div><div><span>Thank you once again</span></div><div><br></div> <div style="font-family: times new roman, new york, times, serif; font-size: 12pt;"> <div style="font-family: times new roman, new york, times, serif; font-size: 12pt;"> <font face="Arial" size="2"> <hr size="1"> <b><span style="font-weight:bold;">From:</span></b> Thomas Tsou <ttsou@vt.edu><br>
<b><span style="font-weight: bold;">To:</span></b> Avner Ezra <avner.ezra@yahoo.com> <br><b><span style="font-weight: bold;">Cc:</span></b> "baseband-devel@lists.osmocom.org" <baseband-devel@lists.osmocom.org> <br> <b><span style="font-weight: bold;">Sent:</span></b> Tuesday, January 3, 2012 10:41 PM<br> <b><span style="font-weight: bold;">Subject:</span></b> Re: Newbie DSP Questions<br> </font> <br>
On Sat, Dec 31, 2011 at 5:16 PM, Avner Ezra <<a ymailto="mailto:avner.ezra@yahoo.com" href="mailto:avner.ezra@yahoo.com">avner.ezra@yahoo.com</a>> wrote:<br>> A) Sometimes when I scan a network bandwidth like GSM1800 using kalibrate, I<br>> see some channels like 820, 538, etc. When I re-scan, I cannot find them.<br>> Does this mean that kalibrate finds a channel when a mobile handset has a<br>> live conversation or sms send or receive in progress? or what?<br><br>No, it most cases it means a weak signal. Kalibrate performs<br>per-channel energy detection prior to offset calculation against the<br>FCCH, which is always active. The variance is probably just noise.<br><br>> B) I want to wideband capture for example 125 ARFCN. It needs 25MHz<br>> bandwidth which USRP N210 can handle and stream it easily. Even AFAIK I can<br>> double this number and capture 250 ARFCN using single N210 (50MHz, in<br>> USRPN210 data sheet it says
it's capable of streaming 50MHz wide signals).<br><br>To capture 50MHz you need to 8-bit samples to avoid saturating the<br>Ethernet bus. So yes it's possible, though I'm not sure about the<br>current state of device or API support for the feature.<br><br>> How can I wideband capture 125 ARFCNs? I tried to do it using:<br>> ./uhd_rx_cfile.py -f `arfcncalc -a 512 -b 1800 -d` --samp-rate=25000000 -N<br>> 200000000 -g 70 b1.cfile<br>><br>> What I understood and decided to write such command above:<br>><br>> B-1) arfcncalc calculates frequency of first GSM1800 channel (512 ARFCN)<br>> which is start point (in above command)<br>> B-2) Sampling Rate is the bandwidth I want to capture, in our case it's<br>> 25MHz means 125 ARFCN which each ARFCN has 200kHz bandwidth<br>> B-3) 200M samples will be received (-N parameter)<br>> B-4) Gain value is 70, means it will boost antennas to maximum power to<br>> receive signals, I
think USRPN210 max. gain is 80<br>> B-5) My decimation rate here using 25M sampling rate and USRP N210 which has<br>> 100MHz ADC, will be 4. So if I decided to read cfile I have to use 4 as<br>> decimation rate.<br><br>You want the centre frequency of the spectrum you want to capture -<br>not the start point. Also, the maximum gain value will also vary<br>depending on the daughterboard. Otherwise, you are correct.<br><br>> C) How can I seperate and process 200khz by 200khz channels in wideband<br>> captured file?<br><br>The brute force approach is to individually frequency translate each<br>channel down to baseband, low-pass filter, and perform sample rate<br>conversion. The more efficient method it to construct a multirate<br>channelizer. GNU Radio has blocks for either approach, though<br>construction may not be straightforward.<br><br> Thomas<br><br><br> </div> </div> </div></body></html>