Hello,
we have implemented a 2 TX x 1 RX MISO testbed with GNU Radio 3.4 and
USRP1 . Both transmitters are using at 2.4GHz ( actually tx1 uses
2.401GHz and tx2 uses 2.403GHz ) , and are sending data ( BPSK
modulated ) at the same time ( in the same time slot ).
The summation of both transmissions is causing problems at the receiver
:
1 - the Costas PLL does not appear to lock to a single frequency
2 - the MM bit-synchronizer does not appear to work
Has anyone attempted this type of MISO system with the default GNU
Radio 3.4 and USRP1 distribution ?
Our goal is to plot the constellation of all superimposed received
symbols but to achieve this we need a frequency-locked receiver and a
recovered ( bit-synchronous ) clock.
Han and Nick
UIC Wireless Lab
On Sat, 2 Jun 2012 17:47:50 -0400, Nick Iliev wrote:
Hello,
we have implemented a 2 TX x 1 RX MISO testbed with GNU Radio 3.4 and
USRP1 . Both transmitters are using at 2.4GHz ( actually tx1 uses
2.401GHz and tx2 uses 2.403GHz ) , and are sending data ( BPSK
modulated ) at the same time ( in the same time slot ).
What is the frequency setting at the receiver side? Do you use two
daughter boards at the receiver? If there’s only one daughter board
I think the receiver can only lock to one frequency and the transmitter
of the different frequency might just create interferce. Also you should
consider to compensate the possible frequency offset between tx and rx
in real world. [1] I think you can use two daughter boards at the
receiver and make them to receive signals from two frequencies, but
that’s not typical MIMO setup.
IMHO setting up MIMO with USRP1 is not very easy. You need to make
hardware modification to make two USRPs synchronize with one master
device or an external clock. You can find some more info from [2].
[1]
http://gnuradio.org/redmine/projects/gnuradio/wiki/FAQ#Why-is-there-always-a-frequency-offset-when-transmitting-from-one-USRP-to-another
[2] http://gnuradio.org/redmine/projects/gnuradio/wiki/USRPClockingNotes
Alick