get time of the first sample transmitted

[Cris8ADC]

Hi everyone,

I´m trying to calculate the time of arrival using 1 usrp x310. I would calculate the time difference between the pulse trasmission start time and when another impulse (sent from another board) is detected by my usrp x310.

The problem that I have is how to find the trasmission start time in labview, the time when I send the first sample. I know that in GRU Radio there is a variable of a class that specified this time (tx_time stream). Is there something similar also in labview? 

Thanks a lot

[psisterhen]

It's not clear from your description exactly how you intend to use those signals to start and end the acquisition.  Is the "pulse transmission" a RF signal coming into the RF input terminals of the device?  What about the other "impulse" is that another RF signal or a digital pulse from the other device.  Please describe these signals in more detail and how you intend to set up your system.

The niUSRP Fetch Rx Data VIs return a timestamp, which corresponds to the first sample of the returned data.  You can use this to help calculate "when" things happen in your signal.  You can set the "clock time" of the device using external signals.  See the niUSRP EX Rx Finite Sync.vi example at <LabVIEW dir>\examples\instr\niUSRP

Perhaps you can have the first signal at the input of channel 0 and the second at the input of channel 1.  You can do a two-channel acquisition and compare the timestamps of when the signal starts in channel 0 and the other pulse arrives in channel 1.  The same timestamps will apply to sample from both channels.

[Cris8ADC]

Hi, thanks you for the reply.

I´m sending a RF signal from the port TX/RX with an antenna (I name it Ant1) of my USRP x310 and I´m receiving this RF signal at the RX2 port of the same USRP through an antenna (I name it Ant2) located 10 metres far to Ant1. So I want to calculate the time difference between the RF signal is sent by Ant1 (named t1) and when it arrives to Ant2 (named t2). I can find t1 in "niUSRP Configure Time Start Trigger.gvi"´s start trigger time (I choose it). For t2 I´m using the constant limit testing and when the result is true I use USRP get time to get the time. Now I have t1 and t2 that are two USRP timestamps. A timestamp has two variables (whole seconds and fractional seconds) and the fractional seconds one has 7 digits next to zero (for ex 0.0000123) and i have a precision of 100 ns. Is there a way to display more digits? I would have a 10 ns precision at least. Is it possible?