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Simultaneous Tx and Rx when in MIMO
cochenob
05-19-2014 09:02 AM
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I've got an application where I want to time synchronize Rx channels across two devices, so I'm using a MIMO cable and programming things accordingly. No problems there.
I also need an RF source to drive another device. This source doesn't need to be time synchronized or phase locked to anything...I just need a source. I could use/buy another one...but why do that when I already have two perfectly fine RF sources on the other channel of each USRP? Problem is...it doesn't seem to work. If initiate a Tx process...then configure and initiate a MIMO'd Rx process...the Tx process stops. Same thing if I try it the other way around. Is this to be expected? If I configure things for MIMO, does this essentially "block out" the other channel?
Or...do I have to set up synchronous processes on both the Tx and Rx, even if I don't require them on both?
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Brandon
05-20-2014 02:09 PM
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Brandon,
You are correct. When using a MIMO connect the USRP can only receiver or transmit but cannot do both. As stated in the NI-USRP help documentation:
"A MIMO communication testbed requires all Rx channels to act as a single receiver, and all Tx channels to act as a single transmitter."
06-03-2014 06:49 AM
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Noah-
I was just downloading v1.3 this AM and was reading about the changes and came across this...
| 460052 | Fixed an issue that caused the local oscillator to fail to lock when two devices connected by the MIMO connector transmit synchronously while one device also receives. |
If I read this correctly, this is basically what I wanted to do (only the other way around...2 MIMO'd devices receiving, with on also transmitting. Am I interpreting this fix right?
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Brandon
06-03-2014 10:31 AM
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Yes, this should work in the 1.3 driver.
What you'll want to do is have two NI-USRP sessions (one Rx and one Tx), each opened to BOTH devices. Even if you only want to use one of the devices for the Tx session, open it to both. Then you can disable the channel you don't want to use. That may seem a little strange, but that's what the driver expects at the moment.
Glad you found the bugfix in the documentation!
Patrick
