Phase-lock across USRP-2 boxes and radar receiver development

Mr. Josh B., Mr. Matt E.,

I think that you are following discussion on the mailing list
that is “phase-lock problem across USRP-2 boxes”.
Mr. Juha V. kindly helped us with the information that

– USRP-2 FPGA with GNU Radio original does not support “phase-lock
across USRP-2 boxes”.
– USRP-2 FPGA with UHD supports that.
– The “phase-lock across USRP-2 boxes” is the “NCO phase reset at PPS

Are these true? We are developing a radar receiver, and already
have a working program with GNU Radio original FPGA. For us, easiest
way is to use a revised FPGA with “NCO reset at PPS” over GNU Radio.
Is there such version of the FPGA image? The other way may be for us
to switch to the UHD.

What do you suggest?

As our application is a radar receiver. Then in our program,
we apply the TX pulse to PPS input, and reset the time counter
at the TX pulses. Is this possible with UHD? This is
one critical point for us to move to UHD.

I hope your help. Thanks.


Mamoru Y. / RISH, Kyoto University
[email protected]
Phone +81-774-38-3814, Cell +81-90-5653-7555

In the case of the gnuradio-USRP2 driver, the CORDIC is always spinning,
and this guarantees that the phase between CORDICs will always be
different among multiple USRP2s.

In the case of the UHD USRP2 driver, the CORDIC only spins when samples
are being processed through it. In this manner, as long as all USRP2s
are told to stream RX samples at the same time, the phase will be the
same across all USRP2s. Also, the USRP MIMO interface automates the
synchronization and synchronized streaming among multiple USRP2s.


Am Fr 08.10.2010 14:57, Mamoru Y. [email protected]

– The “phase-lock across USRP-2 boxes” is the "NCO phase reset at PPS
As our application is a radar receiver. Then in our program,
[email protected]
Phone +81-774-38-3814, Cell +81-90-5653-7555

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Hello Mamoru,

you can find the code of UHD under the following link:

The main advantage of the driver (for me) is that it uses UDP as the
transport layer protocol, and thus the USRP2 is not Linux-only. There
are some announcements from Josh B. on all the features, and recently
there were some posts that it works well with MIMO systems; it should
have all the features of the “legacy” version.

In practice, the only change you need in your code is to use UHD sinks
and sources instead of the old USRP2 ones (and of cause install the
driver and update the FGPA bitstream and firmware on the SD card, as
well as gnuradio on the “next” branch).

I have not attempted to use the MIMO capabilities, but I would recommend
the switch to UHD.

There is some information on how to install the driver in the manual

[currently in (rainy) Kyoto]