USRP's not Communicating

GNU Radio
1

Hello,

I want to transmit the data between two USRP’s and make them communicate
with each other. But I guess the packets are not being received
properly.
I am connected the two USRP’s to the same laptop and trying it. Is that
applicable? I mean, will it work if I do that? Or should I connect to
two computers and perform that? I have been receiving this error.

Code:
./benchmark_rx.py -f 2.435G
./benchmark_tx.py -f 2.435G

linux; GNU C++ version 4.8.4; Boost_105500;
UHD_003.009.git-144-g407e3086

Using Volk machine: avx_64_mmx
– Opening a USRP1 device…
– Using FPGA clock rate of 64.000000MHz…

No gain specified.
Setting gain to 56.250000 (from [0.000000, 112.500000])

UHD Warning:
The hardware does not support the requested RX sample rate:
Target sample rate: 0.050000 MSps
Actual sample rate: 0.250000 MSps

Symbol Rate: 25000.000000
Requested sps: 2.000000
Given sample rate: 250000.000000
Actual sps for rate: 10.000000

Requested sample rate: 50000.000000
Actual sample rate: 250000.000000
ok = False pktno = 53034 n_rcvd = 1 n_right = 0
ok = False pktno = 24 n_rcvd = 2 n_right = 0
ok = False pktno = 35 n_rcvd = 3 n_right = 0
ok = False pktno = 44 n_rcvd = 4 n_right = 0
ok = False pktno = 46 n_rcvd = 5 n_right = 0
ok = False pktno = 46 n_rcvd = 6 n_right = 0
ok = False pktno = 3872 n_rcvd = 7 n_right = 0
ok = False pktno = 12304 n_rcvd = 8 n_right = 0
ok = False pktno = 49 n_rcvd = 9 n_right = 0
ok = False pktno = 50 n_rcvd = 10 n_right = 0
ok = False pktno = 54 n_rcvd = 11 n_right = 0
ok = False pktno = 200 n_rcvd = 12 n_right = 0
ok = False pktno = 63 n_rcvd = 13 n_right = 0

Please suggest. Thank you

Regards,
Ravi

2

You can have each USRP on the same computer or not, that shouldn’t
matter.

I’ve done this test with some USRP2’s and I remember what we did was
transmit a CW tone from one to another and measure a frequency offset
(maybe 10s of kHz?). Basically, transmit a tone at some known frequency
(like 200 MHz) and measure the received frequency (maybe something like
200.02 MHz) and then add the 0.02 into you center frequency for this
test.

You can also just synchronize the USRPs with a 10MHz reference and 1PPS.

Devin

3

On 08/25/2015 10:17 PM, devin kelly wrote:

You can also just synchronize the USRPs with a 10MHz reference and 1PPS.

Devin
The USRP2 uses a 2.5PPM master on-board clock, so at 200Mhz tuned
frequency, the max it can be off is about 500Hz. For narrowband
transmission,
that may be too much, but I’d be very surprised to see 20kHz offset
with a 200MHz carrier.

4

Ah sorry I wasn’t specific. This was from years ago, the numbers I used
were just meant to be an example, not accurate.

5

Dear Ravi,

this is no good. We’ve told you several times now that you need to fix
things, and you just come back with your same broken configuration and
ask the same question. It’s totally OK if you just say “hi, sorry, I did
not understand your answer, could you explain this and that”, but not
addressing what we wrote is really getting frustrating, for me at least.

Let me repeat what Tom and others have tried to explain to you: There’s
no single “switch” you can flip so that your transmission works. We have
pointed out methods to help you optimize your transmission, for example
looking at the RX spectrum and adjusting gains until it looks “good”. We
can’t, just by looking at the problems the receiver script has, tell you
what you need to do. Really. Please stop asking the same question over
and over again, and ask different questions. A clever one would, for
example, be: I’ve got this spectrum (screenshot), and it doesn’t look
like <modulation I’m expecting>. Increasing the gain just made things
worse."

I hope this leads you to a path that promises more success than what
you’re currently doing.

So: You’ve gotten /a lot/ of responses. You might need to consider how
much consultation costs you would have caused if we weren’t doing this
out of interest but for money – so please explain what you did not
understand in our answers, we really want to help!

Here’s my rather comprehensive answer from last time:

You should really specify the gain. That defines how much power comes

250kS/s. The effect of you not correcting your flow graph is that the
doing something else on it? Or are you running in a virtual machine?

No gain specified.
Actual sample rate: 0.250000 MSps
effect kind of cancels itself out – still, fix that!

to me as “John”, so I’d suggest you pick one and stick with that,
because it’s less confusing.

[1] “Communication Problems between 2 USRP” email thred

Best regards,

Marcus