The two device are not clock syncronized.
My end goal is clock syncroniztation & ranging.
The true problem is if it’s possible to compute the time difference between an 
incoming sample and a outgoing sample from USRP. This is critical since i have 
to compute the time elapsed (due to calculation & delays from Linux) between 
the received echo and the outgoing reply. I suggested a method to do this task, 
can it work?
Thanks

From: Colby Boyer 
Sent: Wednesday, July 27, 2011 2:17 AM
To: Mattia Rizzi 
Cc: discuss-gnuradio@gnu.org 
Subject: Re: [Discuss-gnuradio] USRP for two way ranging

This might be possible to do if both devices have access to the same and very 
accurate clock, e.g. GPS.  

What is your end goal?


On Tue, Jul 26, 2011 at 3:59 PM, Mattia Rizzi <mattia.ri...@gmail.com> wrote:

  Hello.
  I need to implent a two way ranging. A device send an “echo”, a second device 
discover the “echo” and send a reply, then the first device can calculate the 
distance. For a correct distance evalutation, the second device must calculate 
the time elapsed between the discover of the first echo and the reply response.
  Let’s assume that the second device is a SDR with gnu radio & USRP1 device.
  The problem is: how to time-correlate the streaming sample received from the 
USRP and the streaming sample transmitted to the usrp.
  If i pre-fill the usrp transmit buffer with dummy data (preventing 
underflows) before starting acquisition&transmission, then i can correlate the 
two streams, right? (Yes, with the hypothesis that i don’t miss data from usb).
  Thank you

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