Repeatability of delivery ratios using benchmark_tx/rx

Hi All,

I have two USRP N210 devices connected by an attenuator cable. I set up
the
following experiments.

– BEGIN EXPERIMENT 1

Step 1) Use benchmark_tx on one of the USRPs and send 100 packets. At
the
receiver, I simply record the incoming samples and save them into a file
called samples1.dat. This file is static and does not change from now
on.

Step 2) Run benchmark_rx with the --from-file=samples1.dat option. The
other parameters (modulation, fft-length, occupied-tones, etc) are
identical to those I used at the transmitter in Step 1. Measure the
packet
delivery rate.

Step 3) Repeat Step 2 a bunch of times. Sometimes, I notice differences
in
the packet delivery ratios, even though all runs of the experiment use
the
identical ‘samples1.dat’ file and an identical set of parameters These
differences are small (1-2 packet difference), but I don’t understand
why
they exist.

Is this normal behavior? If so, could someone please let me know what
the
probable causes are?

– END EXPERIMENT 1

The next experiment does not use either of the USRP devices.

– BEGIN EXPERIMENT 2

  1. Use benchmark_tx to generate 100 packets, and write the samples into
    a
    file (samples2.dat) using the --to-file option.

  2. Use benchmark_rx with the --from-file=samples2.dat option and check
    the
    packet delivery rate. The parameters used (fft-length, etc) are
    obviously
    identical to those used to generate the samples in Step 1. I observe
    that
    the delivery rate is never even close to 100%.

  3. Change to a different parameter set and repeat steps 1 and 2. Across
    different runs, I observe that the delivery rate is anywhere between 30%
    and 85%.

This cannot be the expected behavior. Any pointers on what I’m doing
wrong
would be much appreciated!

– END EXPERIMENT 2

Thanks!

Aditya

On Wed, Oct 16, 2013 at 10:22 PM, Aditya D.
[email protected]wrote:

file (samples2.dat) using the --to-file option.
This cannot be the expected behavior. Any pointers on what I’m
doing wrong would be much appreciated!

– END EXPERIMENT 2

Thanks!

Aditya

I should have made a brief mention of my environment:

GNU Radio 3.7.1 installed from source
Ubuntu 12.04 LTS (64-bit)
Thanks!

Aditya

On Wed, Oct 16, 2013 at 10:29 PM, Aditya D.
[email protected]wrote:

in the packet delivery ratios, even though all runs of the experiment use

  1. Change to a different parameter set and repeat steps 1 and 2. Across
    Aditya

Update:

In experiment 1, I began to notice large variations in packet delivery
ratios across different runs of step 3. If I modified benchmark_rx to
just
sleep for a few seconds between tb.start() and tb.wait(), these large
variations disappeared. It seems like once the EOF is reached, it simply
kills all threads that run inside the flow graph.

However, even with the sleep, there are small variations (~1-2 packets)
in
an experiment with a total of 1000 packets being generated. Could anyone
please give me a little hint on why this might be the case?

Thanks.

Aditya

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