USRP Delays


#1

Hi everyone,
I am interested in knowing the delay jitter of the
total
transmission time of a packet/waveform. Specifically, I want to know the
time between the time the flowgraph is tsarted in python (tb.run or
tb.start) and the time that the first sample is transmitted into the air
from the USRP hardware. I want to know if I can reduce the jitter in
this
time (across runs) to as low a value as possible.

I use usrp_siggen.py with gnuradio-3.1.2 to transmit a square waveform
.I
try to start the flowgraph at a precise time x (in microseconds) by
using
y=x-time.time() and time.sleep(y) and then tb.start(),time.sleep(0.1)
and
tb.stop(). I also use an interp of 32 at the Tx. I have a receiver that
logs
all data (with -d 64). I observe the samples just out of the usrp
source.

For transmissions that are precisely spaced in time using appropriate
values
x, the inter transmission delay measured at the receiver is off by a
value

than 2 ms.
(despite using nice to increase the priority of this process).

  1. Is it possible to reduce the jitter between successive Tx.delay
    measurements to be few 10’s of microseconds or lesser?

  2. Is there a way to run the usrp_siggen code as a kernel module to
    improve
    the delay jitter performance?

Thanks in advance for your help,
Sri