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. <[email protected] <mailto:[email protected]>> > > 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
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