Re: [Discuss-gnuradio] How to synchronize two transmitters

[Marcus D. Leech]

On 27/01/12 01:16 PM, André Selva wrote:

What I think that might be a solution is using only one computer with two USRPs. In the flowgraph, you will have two sinks. If your network card are both identical and the distance between the USRPs are not large enough to be considered, I don't see why the signals would not be syncrhonized (or, at least, very similar to each other).

Att, 

2012/1/22 yend B. <address@hidden>

I was wondering if there is a way to syncrhonize two transmitters running on two machines.

Both transmitter use OFDM. I could use a shared reference clock, but the problem is that

I don't know how exactly I can send packets SIMULTANEOUSLY from both transmitters.

I want to measure co-channel interference and study multiuser detection alogorithms.

 

Regards!

If you have a USRP that can take external synchronization signals (1PPS and 10Mhz clock), then
  you can use the raw UHD primitives to have transmit streams start at a particular time.  You'd
  first do a "setup" where you'd use set_time_at_next_pps(), and have the two hosts agree on what
  time to set on the two USRP units.  Then both hosts would start a TX stream at a particular time
  in the future--some point *past* where the set_time_at_next_pps() is set.


Or if you run on a single host, you can use a uhd_usrp_sink block with multiple channels--one for
  each USRP, and set it up for PPS synch, etc.  I believe UHD will arrange to time-align all the channels
  when they're inside a single block.  UHD source/sink block can be used to talk to multiple USRP
  units, and conceptually form a "synchronization domain", when the appropriate synch hardware is
  in use.

-- 
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org