[USRP-users] 4*4 MIMO

Farrukh Aziz farrukh59th at yahoo.com
Thu Sep 13 18:03:52 EDT 2012


Hi Ben, I am sorry for not being very precise initially. Yes I am doing a synchronized receiver only. I am trying to receive 4 synchronized complex data streams. In doing this I only require time and frequency synchronization whereas phase synchronization is not required. I want to clarify further on how this is done inside. USRP (N210) has two ADCs, so this feeds two real signals into the FPGA at 12.5 MHz IF. Downcoversion to baseband is performed inside the FPGA, where a cos(2*pi*f*t) and sin(2*pi*f*t) generated from NCO are multiplied, thus generating two IQ pairs at baseband. 1) What is the sampling interval 't'2) Which chip is used in ADC?  This link shows my question.http://tinypic.com/view.php?pic=35bihi0&s=6

Farrukh Aziz Bhatti
PhD Candidate
Department of Electrical & Computer Engineering
University of Auckland+64 21 02973964



--- On Thu, 13/9/12, Ben Hilburn <ben.hilburn at ettus.com> wrote:

From: Ben Hilburn <ben.hilburn at ettus.com>
Subject: Re: [USRP-users] 4*4 MIMO
To: "Farrukh Aziz" <farrukh59th at yahoo.com>
Cc: "USRP user forum" <usrp-users at lists.ettus.com>
Received: Thursday, 13 September, 2012, 10:32 PM

Hi Farrukh -
I had originally interpreted your question to mean you wanted to use only TVRX2s to achieve a full 2x2 MIMO system.  After re-reading your question, however, I just realized that you may have been asking if you could use TVRX2s for the receive portion of a full MIMO setup, while using a different radio / USRP / daughterboard / etc for the transmit portion.


If this is your question, then YES, you are correct in your understanding. Please pay careful attention to the synchronization notes I linked to you before, as they will be critical to using the TVRX2s appropriately.


Sorry for the confusion!
Cheers,Ben
----------------------------Ben Hilburn @ Ettus Research, LLC   |   USRP





On Thu, Sep 13, 2012 at 10:20 AM, Ben Hilburn <ben.hilburn at ettus.com> wrote:


Farrukh -
You cannot do MIMO, of any size, with the TVRX2, because the TVRX2 is receive-only.
You can receive synchronized samples across two boards, although the boards will not maintain relative phase after a tune.



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


Cheers,
Ben
----------------------------Ben Hilburn @ Ettus Research, LLC   |   USRP






On Tue, Sep 11, 2012 at 3:35 PM, Farrukh Aziz <farrukh59th at yahoo.com> wrote:



Hi, I was looking at this (new) document that shows different ways of making a MIMO system.
http://www.ettus.com/content/files/kb/mimo_and_sync_with_usrp.pdf 




Since it did not discuss one of the options that I have used, so I thought to clarify myself. Can we implement a 2*2 MIMO by using a TVRX2 daughterboard on a USRP N210 without using any external reference signals?



Secondly can we implement a 4*4 MIMO by using 2 USRPs (N210) each fitted with a TVRX2 daughterboard. The USRPs are inter linked with a MIMO cable. The 1 PPS and 10 MHz synch signals are provided using a GPSDO (to the master node). However the GPSDO is not connected with a GPS antenna.



Please let me know if my approach is correct.
Farrukh Aziz Bhatti
Department of Electrical & Computer Engineering



University of Auckland+64 21 02973964





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