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/$USER/Documents/GNU_radio/data_collection.py --uhd-addr=addr=10.2.8.104 &
ssh -t address@hidden python ~/Documents/GNU_radio/data_collection.py --uhd-addr=addr=10.2.8.105 &
It is a very simple script executing a script on local and one remotely via SSH, and according to the saved data files the file creation/modification times are off. If the the save files are created from scratch, the timing is extremely close and meets expectations when it is just two scripts. If the files are already pre-existing then the modification times can range from 1 to 5 seconds. When I add more scripts to the shell script. Like so:
#!/bin/sh
./home/$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 address@hidden python ~/Documents/GNU_radio/data_collection.py --uhd-addr=addr=10.2.8.105 &
ssh -t address@hidden 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