Forum: GNU Radio [ USRP configuration with/without MIMO in unshared Ethernet mode ]

*Hi all,

Recently, I tried testing how the data flows from one USRP to another in 
a
2x2 setup. My configurations went as follows:

2 USRPs were connected via a MIMO. Each USRP was connected to an 
Ethernet
cable and so both of them were in two different subnets. Now when I set 
one
of the USRPs clock source and time source to MIMO, I observed that both 
of
them were synchronized and believe that its acting as a slave for the
Master's clock and time source.
What I'm not able to understand is whether the slave is receiving its 
data
via the MIMO (from the Master) or via its own RF input i.e whether . I
thought that modulating the RF input to both the USRPs would show some
difference on the FFT plot but both were identical. Could any one please
tell me how the data flow occurs by suggesting a good test case?

My second question is:
In a 4X4 USRP setup, how can we synchronize all the 4 USRPs without a 
MIMO
connection (between 2 USRPs within a pair), using a 10MHz reference 
given
to each of the USRP and a PPS source?
Please not that I'm using USRP N210 for my experiments.

Looking forward to your reply.
*

On 10/10/2012 08:53 PM, Ashish Raste wrote:
> What I'm not able to understand is whether the slave is receiving its data
> via the MIMO (from the Master) or via its own RF input i.e whether . I
> thought that modulating the RF input to both the USRPs would show some
> difference on the FFT plot but both were identical. Could any one please
> tell me how the data flow occurs by suggesting a good test case?

If both usrps are attached to an ethernet cable, the data does not
travel over the mimo cable.

If only one usrp is attached to an ethernet cable, the mimo cable acts
like a network switch.

>
> My second question is:
> In a 4X4 USRP setup, how can we synchronize all the 4 USRPs without a MIMO
> connection (between 2 USRPs within a pair), using a 10MHz reference given
> to each of the USRP and a PPS source?

You will want to share a 10MHz ref and PPS signal to the two master
devices. The other two devices in the configuration can get reference
and time, each from a mimo cable.

http://files.ettus.com/uhd_docs/manual/html/sync.html

CHeers,

-josh

*I made some refinement to my previous question, as follows, for you to 
get
a better view of my problem:

**2 USRPs were connected via a MIMO. Each USRP was connected to an 
Ethernet
cable and so both of them were in two different subnets (This is the
commonly known unshared Ethernet Mode) . I have a host PC which runs the
GRC design. Now when I set one of the USRPs clock source and time source 
to
MIMO, and the other USRPs clock source and time source to default, I
observed that both of them were synchronized and believe that one is 
acting
as a slave for the Master's clock and time source.. What I'm not able to
understand is the baseband data path  between the USRPs and the host PC. 
That
is, whether the slaves baseband date within the GRC design  is
received/transmitted via its own Ethernet interface  and the masters
basedband data within the GRC design is received/transmitted  via its 
own
Ethernet interface? So, this means that the MIMO cable is only used for
 sending the clock and time signals from the Master to the Slave ?*

* *

*Next, I retained the MIMO cable, set the Master USRPs clock source to
external  and have a 10MHz source connected to the Reference input. The
slave USRPs clock source and time source remained as MIMO mode.  So my
question is would the Slave USRP received the 10MHz Reference via the 
MIMO
cable  ? *

* *

*My second question is:
In a 4X4 USRP setup, how can we synchronize all the 4 USRPs without a 
MIMO
connection (between 2 USRPs within a pair), using a 10MHz reference 
split
to each of the USRP and a PPS source?
Please not that I'm using USRP N210 for my experiments.

Best Regards,

*

> received/transmitted via its own Ethernet interface  and the masters
> basedband data within the GRC design is received/transmitted  via its own
> Ethernet interface? So, this means that the MIMO cable is only used for
>  sending the clock and time signals from the Master to the Slave ?*

Thats correct. When each USRP has its own ethernet link, the MIMO cable
is only used for clock and time signals.

>
> * *
>
> *Next, I retained the MIMO cable, set the Master USRPs clock source to
> external  and have a 10MHz source connected to the Reference input. The
> slave USRPs clock source and time source remained as MIMO mode.  So my
> question is would the Slave USRP received the 10MHz Reference via the MIMO
> cable  ? *
>

Yes. The slave device will still get 10MHz over the MIMO cable. This is
regardless of how the master gets his reference.

> * *
>
> *My second question is:
> In a 4X4 USRP setup, how can we synchronize all the 4 USRPs without a MIMO
> connection (between 2 USRPs within a pair), using a 10MHz reference split
> to each of the USRP and a PPS source?

Yes, you can split 10MHz and PPS signal to all 4 units.

-josh