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Re: [Discuss-gnuradio] USRP for two way ranging

From: Colby Boyer
Subject: Re: [Discuss-gnuradio] USRP for two way ranging
Date: Tue, 26 Jul 2011 17:49:36 -0700

You would need a very very accurate real time guarantee on how long it would take to process/detect an echo, and then to respond to it. To my knowledge the GNURadio framework cannot make that guarantee, in general. I would not try to depend on getting an accurate time for signal processing delay and Linux delay.

Look at the UHD driver and see if you can be creative with the driver calls. That is your best bet, honestly. With UHD you can schedule clock accurate transmit bursts and receive bursts.


On Tue, Jul 26, 2011 at 5:33 PM, Mattia Rizzi <address@hidden> wrote:
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?
Sent: Wednesday, July 27, 2011 2:17 AM
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 <address@hidden> wrote:
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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