On Tue, Jun 3, 2014 at 2:28 PM, Marcus Müller <[email protected]> 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 This will store a time stamp based on the time info from the USRPs. It should help you realign the data sets afterwards. Tom > On 03.06.2014 20:24, Jonathan Fox 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 > [email protected]https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
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