Benchmark test between two USRPs have different performances in two directions

GNU Radio
1

I run benchmark_tx in USRP A, and benchmark_rx in USRP B:
A: ./benchmark_tx.py -f 2.46G -r 0.5M --tx-gain=-30
B: ./benchmark_rx.py -f 2.46G -r 0.5M
The n_right/n_recvd is 549/628.
But when I rx in USRP A and tx in USRP B with the same parameters, the
n_right/n_recvd is always pretty bad: 0/275.
What might be the reasons?
I am using USRP N210 and XCVR2450.

2

On 08/03/2012 03:45 PM, Weixian Z. wrote:

I run benchmark_tx in USRP A, and benchmark_rx in USRP B:
A: ./benchmark_tx.py -f 2.46G -r 0.5M --tx-gain=-30
B: ./benchmark_rx.py -f 2.46G -r 0.5M
The n_right/n_recvd is 549/628.
But when I rx in USRP A and tx in USRP B with the same parameters, the
n_right/n_recvd is always pretty bad: 0/275.
What might be the reasons?

0/275 doesnt sound like a performance difference. Something is just not
working, or incorrect setup, antenna issues.

Before experimenting with the mac layer examples in gnuradio, it might
be good to verify setup connectivity and signal integrity, etc.

have you verified functionality of your setup with a simple test tone?
Check the the correct antennas are used. correct frequency comes out,
reasonable power level.

cheers,
-josh

3

Hi Josh,
The tone test works. And I have tried to use different antennas. The
following is the result:

The results are very different even with same antennas. The
n_rcvd/n_right
is 626/623, and 289/0 sometimes. What might be the reason?

4

Hi Josh,
I was testing benchmark_tx.py at tx end and uhd_fft at rx end at 5.0GHz
frequency:
./benchmark_tx.py -f 5.0G -r 0.5M -A J1 --tx-gain=-30
And the received spectrums don’t look like have frequency offset, check
the
attached.

5

On 08/08/2012 10:31 AM, Weixian Z. wrote:

Hi Josh,
The tone test works. And I have tried to use different antennas. The
following is the result:

The results are very different even with same antennas. The n_rcvd/n_right
is 626/623, and 289/0 sometimes. What might be the reason?

There will be a slight frequency offset between devices. Often with some
of the example apps, this offset will cause the signal to be outside of
the filter pass band. It would be good to make sure that the received
spectrum appears at the expected frequency:

some faq on this:
http://gnuradio.org/redmine/projects/gnuradio/wiki/FAQ#I-have-two-USRPs-and-when-I-transmit-on-one-and-receive-on-the-other-at-the-same-frequency-I-get-an-offset

In general, it looks like you are seeing a lot of dropped packets or
checksum errors. You have to diagnose the issue at a lower level. How
does the received spectrum look? How-about the received constellation?
Any obvious distortions, etc?

-josh