# Data Collection Across Multiple Machines and USRPs **URL:** \ **Category:** GNU Radio\ **Created:** [June 3, 2014, 8:25pm UTC](https://www.ruby-forum.com/t/data-collection-across-multiple-machines-and-usrps/230181 "2014-06-03T20:25:28Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![jason\_sam](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/7993a0/32.png) [@jason\_sam](https://www.ruby-forum.com/u/jason_sam)\ **Post date:** [June 3, 2014, 8:25pm UTC](https://www.ruby-forum.com/t/data-collection-across-multiple-machines-and-usrps/230181/1 "2014-06-03T20:25:28Z")
Hey list, this is a question for anyone that has used the USRPs and GNU Radio for synchronized data collection. I need to collect data using USRP N210s across a wireless network for a field test. Basically the USRPs would be connected to laptops running GNU radio and the laptops themselves will be networked over WiFi. My conceptualized collection would work as so: master computer that would control the collection python scripts on remote machines and itself locally (a simple USRP source to throttle to file sink). The caveat is these scripts must start within a second of each other, so I am trying to avoid delays and keep latency under a 1000 ms (preferably somewhere close to 500 ms). My initial testing of my idea at my work desk as been less than spectacular. I was using a bash script that had two lines of code: #!/bin/sh ./home/$USER/Documents/GNU\_radio/data\_collection.py –uhd-addr=addr=10.2.8.104 & ssh -t $USER@Dell1 python ~/Documents/GNU\_radio/data\_collection.py –uhd-addr=addr=10.2.8.105 & It is a very simple script executing a script on local and one remotely via SSH, and according to the saved data files the file creation/modification times are off. If the the save files are created from scratch, the timing is extremely close and meets expectations when it is just two scripts. If the files are already pre-existing then the modification times can range from 1 to 5 seconds. When I add more scripts to the shell script. Like so: #!/bin/sh ./home/$USER/Documents/GNU\_radio/data\_collection.py –uhd-addr=addr=10.2.8.104 & ./home/$USER/Documents/GNU\_radio/data\_collection.py –uhd-addr=addr=10.2.8.102 & ssh -t $USER@Dell1 python ~/Documents/GNU\_radio/data\_collection.py –uhd-addr=addr=10.2.8.105 & ssh -t $USER@Dell1 python ~/Documents/GNU\_radio/data\_collection.py –uhd-addr=addr=10.2.8.103 & The times are even more off and can range from 3 to 10 seconds. Alternatively, I can have dual USRP sources to file sink in the same script to get back down to the original script and I have a 3 to 7 seconds gap between the data files collected in the local script compared to the data files collected by the remote script. Is there a better way to go about collecting data quickly in synchronized fashion? I thought about a timing function built in each GNU radio script that should start the flow graph on any even second (based off a modulus function of current system time in seconds) but I want to weigh all options first. Thanks for your time reading, Jon ---
**Author:** ![jfaulkenberry](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/c2a13f/32.png) [@jfaulkenberry](https://www.ruby-forum.com/u/jfaulkenberry)\ **Post date:** [June 3, 2014, 8:29pm UTC](https://www.ruby-forum.com/t/data-collection-across-multiple-machines-and-usrps/230181/2 "2014-06-03T20:29:35Z")
Hey Jonathan, when you cannot use GPSDOs, you should just sync your Laptops using NTP, and then set the laptop time as device time on the USRPs using set\_time\_now. You can then agree on a specific point in time, use set\_start\_time on the USRP sources and try to estimate how well-coordinated you are by cross-correlating your measurements. Greetings, Marcus ---
**Author:** ![jfaulkenberry](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/c2a13f/32.png) [@jfaulkenberry](https://www.ruby-forum.com/u/jfaulkenberry)\ **Post date:** [June 3, 2014, 8:33pm UTC](https://www.ruby-forum.com/t/data-collection-across-multiple-machines-and-usrps/230181/3 "2014-06-03T20:33:43Z")
On Tue, Jun 3, 2014 at 2:28 PM, Marcus Müller [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Marcus I’ll also recommend the file\_meta\_sink block: > **[GNU Radio Manual and C++ API Reference: gr::blocks::file\_meta\_sink Class...](https://www.gnuradio.org/doc/doxygen/classgr_1_1blocks_1_1file __meta__ sink.html)** This will store a time stamp based on the time info from the USRPs. It should help you realign the data sets afterwards. Tom ---
**Author:** ![jfaulkenberry](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/c2a13f/32.png) [@jfaulkenberry](https://www.ruby-forum.com/u/jfaulkenberry)\ **Post date:** [June 3, 2014, 9:12pm UTC](https://www.ruby-forum.com/t/data-collection-across-multiple-machines-and-usrps/230181/4 "2014-06-03T21:12:02Z")
From: discuss-gnuradio-bounces+sean.nowlan=removed\_email\_address@domain.invalid [[mailto:discuss-gnuradio-bounces+sean.nowlan=removed\_email\_address@domain.invalid](mailto:discuss-gnuradio-bounces+sean.nowlan=removed_email_address@domain.invalid)] On Behalf Of Tom R. Sent: Tuesday, June 03, 2014 2:32 PM To: GNURadio D.ion List Subject: Re: [Discuss-gnuradio] Data Collection Across Multiple Machines and USRPs On Tue, Jun 3, 2014 at 2:28 PM, Marcus Müller \ wrote: Hey Jonathan, when you cannot use GPSDOs, you should just sync your Laptops using NTP, and then set the laptop time as device time on the USRPs using set\_time\_now. You can then agree on a specific point in time, use set\_start\_time on the USRP sources and try to estimate how well-coordinated you are by cross-correlating your measurements. Greetings, Marcus I’ll also recommend the file\_meta\_sink block: [http://gnuradio.org/doc/doxygen/classgr\_1\_1blocks\_1\_1file\_\_meta\_\_sink.html](http://gnuradio.org/doc/doxygen/classgr_1_1blocks_1_1file __meta__ sink.html) This will store a time stamp based on the time info from the USRPs. It should help you realign the data sets afterwards. Tom If you don’t have GPSDOs but need near-GPS accuracy, one option is to get cheap USB GPS pucks and configure your GPSD instance to run an NTP server, and point your system ntpd client at it. Then use the “set\_time\_now” UHD/gr-uhd command to set the time register on multiple radios. Finally, use the “set\_start\_time” command mentioned above to schedule RX captures. [GPSD redirection page](http://www.catb.org/gpsd/gpsd-time-service-howto.html)[http://www.catb.org/gpsd/gpsd-time-service-howto.html](http://www.catb.org/gpsd/gpsd-time-service-howto.html) Sean On 03.06.2014 20:24, Jonathan F. wrote: Hey list, this is a question for anyone that has used the USRPs and GNU Radio for synchronized data collection. I need to collect data using USRP N210s across a wireless network for a field test. Basically the USRPs would be connected to laptops running GNU radio and the laptops themselves will be networked over WiFi. My conceptualized collection would work as so: master computer that would control the collection python scripts on remote machines and itself locally (a simple USRP source to throttle to file sink). The caveat is these scripts must start within a second of each other, so I am trying to avoid delays and keep latency under a 1000 ms (preferably somewhere close to 500 ms). My initial testing of my idea at my work desk as been less than spectacular. I was using a bash script that had two lines of code: #!/bin/sh ./home/$USER/Documents/GNU\_radio/data\_collection.py –uhd-addr=addr=10.2.8.104 & ssh -t $USER@Dell1 python ~/Documents/GNU\_radio/data\_collection.py –uhd-addr=addr=10.2.8.105 & It is a very simple script executing a script on local and one remotely via SSH, and according to the saved data files the file creation/modification times are off. If the the save files are created from scratch, the timing is extremely close and meets expectations when it is just two scripts. If the files are already pre-existing then the modification times can range from 1 to 5 seconds. When I add more scripts to the shell script. Like so: #!/bin/sh ./home/$USER/Documents/GNU\_radio/data\_collection.py –uhd-addr=addr=10.2.8.104 & ./home/$USER/Documents/GNU\_radio/data\_collection.py –uhd-addr=addr=10.2.8.102 & ssh -t $USER@Dell1 python ~/Documents/GNU\_radio/data\_collection.py –uhd-addr=addr=10.2.8.105 & ssh -t $USER@Dell1 python ~/Documents/GNU\_radio/data\_collection.py –uhd-addr=addr=10.2.8.103 & The times are even more off and can range from 3 to 10 seconds. Alternatively, I can have dual USRP sources to file sink in the same script to get back down to the original script and I have a 3 to 7 seconds gap between the data files collected in the local script compared to the data files collected by the remote script. Is there a better way to go about collecting data quickly in synchronized fashion? I thought about a timing function built in each GNU radio script that should start the flow graph on any even second (based off a modulus function of current system time in seconds) but I want to weigh all options first. Thanks for your time reading, Jon * * * Discuss-gnuradio mailing list removed\_email\_address@domain.invalid[mailto:removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) [https://lists.gnu.org/mailman/listinfo/discuss-gnuradio](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio)