[USRP-users] usrp b210 and mimo

Juha Vierinen x at mit.edu
Fri Dec 5 08:50:17 EST 2014


I've slowly gathered the courage to try out the B210 devices. I was
impressed by the fact that I could get 50 MHz of bandwidth out of it.
However, I immediately ran into problems with absolute timing.

I've been using the B210 for mimo with USRP N200 devices for testing. The
N200 devices all nicely synchronize themselves to the external PPS and
after multiple restarts, their timing will be accurate. However, the
starting time of the B210 seems to have a random component with a standard
deviation of about 100 microseconds. Every time I restart sampling, the
offset between the N200 and the B210 is slightly different. There is no
change in the timing offset between the N200 devices.

Is this a known issue, or am I doing something wrong?

This is how I configure the devices:

u.set_clock_source("external")
u.set_time_source("external")
tt = time.time()
while tt-math.floor(tt) < 0.2 or tt-math.floor(tt) > 0.3:
    tt = time.time()
    time.sleep(0.01)
print("Latching at "+str(tt))
u.set_time_unknown_pps(uhd.time_spec(math.ceil(tt)+1.0))
time.sleep(1)
u.set_start_time(uhd.time_spec( starttime ) )

juha
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