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Re: [Discuss-gnuradio] 2 x MIMO Transmitter using USRPN210


From: Josh Blum
Subject: Re: [Discuss-gnuradio] 2 x MIMO Transmitter using USRPN210
Date: Wed, 22 May 2013 02:50:29 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130329 Thunderbird/17.0.5


On 05/22/2013 02:11 AM, Ramcharan M C wrote:
> Hi
> 
> 
>  I am trying to use two USRPN210 to transmit using 2  transmit antennas for
> MIMO,. I have successfully constructed a receiver using 2 USRPs with
> Reciever MIMO with 2 reciever antennas having a daughter board XCVR2450
> using the freely available file multi_sampler.cpp .. I have been able to
> recieve the signals synchronously with zero phase offset on both USRPS
> which are interconnected through the MIMO cable successfully.
>       Now At the transmitter end I have 2 USRPs interconnected through MIMO
> cable having the daughter board XCVR2450 and the USRP connectedd to the
> host PC ... I have been trying to modify the tx_sample_to_file to enable
> MIMO transmitter but I haven't solution as yet
> for 2x MIMO reciever i have reffered mimo_sync_with_usrp.pdf document, but
> is there any similar procedure to achieve 2X MIMO for transmitter
> 

The synchronization procedures are basically agnostic to RX or TX. So
the code for setting up PPS source, REF source, and syncing USRP time is
going to be the same regardless.

The only real difference between RX and TX, is that on RX, you ask for
samples from each stream at a particular time, this aligns the stream.
But on TX, the alignment of transmitted data is caused by the time stamp
in the transmit metadata.

Check out some of the examples using tags to control transmit time:
http://code.ettus.com/redmine/ettus/projects/uhd/wiki/GNU_Radio_UHD#Using-UHD-Software-with-GNU-Radio

Also, you can use gnuradio-companion to do this really easily. You can
make a 2 channel sink block, set the time and ref sources with drop down
menues, click run, and the data alignment is automatically handled.

-josh

> 
> Thanks
> 
> Regards
> 
> RAM
> 
> 
> 
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