# Transmit time synchronization

**URL:** <https://www.ruby-forum.com/t/transmit-time-synchronization/233358>\
**Category:** GNU Radio\
**Created:** [December 7, 2014, 4:11pm UTC](https://www.ruby-forum.com/t/transmit-time-synchronization/233358 "2014-12-07T16:11:12Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [December 7, 2014, 4:11pm UTC](https://www.ruby-forum.com/t/transmit-time-synchronization/233358/1 "2014-12-07T16:11:12Z")

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Hello all,

Ive been trying to achieve transmit time synchronization for over a  
month  
now using GNURadio and USRP B200, and so far i have had limited success.  
I  
could not find alot online. My question is simple. Is it possible to  
achieve synchronization between two USRPs without using an external  
signal  
or the GPSDO?

If so a little guidance would be much appreciated. Thanks.

---

<div class="post-metadata">

**Author:** ![Muhammad\_Shahmeer\_O](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/76d3ee/32.png) [@Muhammad\_Shahmeer\_O](https://www.ruby-forum.com/u/Muhammad_Shahmeer_O)\
**Post date:** [December 7, 2014, 4:22pm UTC](https://www.ruby-forum.com/t/transmit-time-synchronization/233358/2 "2014-12-07T16:22:52Z")

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Hello Muhammad Shahmeer Omar,

with neither an external signal or a GPSDO, this is physically  
impossible.

I think with external signal you mean the PPS signal; you can of course  
use a reference signal and build synchronization in software. That is a  
problem equivalent to synchronization in communication systems, e.g.  
synchronization of mobile phones to a base station.

Best regards,  
Marcus M?ller

---

<div class="post-metadata">

**Author:** ![Muhammad\_Shahmeer\_O](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/76d3ee/32.png) [@Muhammad\_Shahmeer\_O](https://www.ruby-forum.com/u/Muhammad_Shahmeer_O)\
**Post date:** [December 7, 2014, 7:05pm UTC](https://www.ruby-forum.com/t/transmit-time-synchronization/233358/3 "2014-12-07T19:05:24Z")

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Thanks Marcus!

Is it possible to synchronize the usrps using individual gpsdo modules  
for  
each board or is a central distribution system (like the octoclock)  
necessary?  
Hello Muhammad Shahmeer Omar,

with neither an external signal or a GPSDO, this is physically  
impossible.

I think with external signal you mean the PPS signal; you can of course  
use  
a reference signal and build synchronization in software. That is a  
problem  
equivalent to synchronization in communication systems, e.g.  
synchronization of mobile phones to a base station.

Best regards,  
Marcus Müller

On 12/07/2014 04:09 PM, Muhammad Shahmeer Omar wrote:

Hello all,

Ive been trying to achieve transmit time synchronization for over a  
month  
now using GNURadio and USRP B200, and so far i have had limited success.  
I  
could not find alot online. My question is simple. Is it possible to  
achieve synchronization between two USRPs without using an external  
signal  
or the GPSDO?

If so a little guidance would be much appreciated. Thanks.

* * *

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