Re: [Discuss-gnuradio] How to implement MIMO transmissions

[Josh Blum]

On 02/11/2013 02:51 PM, Lara Deek wrote:
> Hello,
> 
> I have a question about the details of transmitting using gnuradio. I
> have set up a 2x2 MIMO transmitter using 2 USRP2's (or N200's) that
> are connected via a MIMO cable. In C++, I initialize a single USRP
> sink, and set the # channels to 2 (excluding the other settings).
> 
> I am currently using the uhd send() function to transmit data, and my
> first question is: Does issuing a single send() function transmit
> samples on both USRP2's simultaneously, to achieve MIMO spatial
> diversity?
> 
> I also want to send different samples on each USRP2, to achieve MIMO
> spatial multiplexing. Since the buffer that is passed to the send()
> function is a vector, does specifying a vector of size 2, with each
> vector holding different data, do the trick? In that case, to achieve
> MIMO diversity, the 2 vectors would have to carry the same data,
> correct?
> 

Well in gnuradio, you dont have access to the send function. The
scheduler will deliver two streams of equal length (from 2 ports).

Inside of gr-uhd, internally the send() routine takes as an argument a
vector of points, in this case of size 2. If you are curious about the
UHD API usage, there is an example/rx_multi_samples.cpp in uhd. Its RX,
but the usage of the streamer and 2 channels is very similar.

-josh

> Thanks,
> Lara
> 
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