Re: [Discuss-gnuradio] Active Reflector

[Rafael Acurcio]

Hi Marcus,

I'm using the WBX daughter board.

I though the late packages problem could be because of the processing time between receiving a sample and sending it back.  And I have tried to

I used the delay difference like this:

        now = self.uhd_usrp_sink_0.get_time_now()
        self.uhd_usrp_source_0.set_start_time(uhd.time_spec_t(1) + now)
        self.uhd_usrp_sink_0.set_start_time(uhd.time_spec_t(1.001) + now)

And the results are very reasonable.

However in the second USRP sometimes an underflow occurs (U printed in the terminal) followed by a few late packages (Ls printed in the terminal) that I believe that happens because of some queue being filed. It happen apparently in random times (every few seconds).

Thanks a lot for you help Marcus!

On Thu, 18 Jun 2015 at 10:01 Marcus Müller <address@hidden> wrote:

Hi Rafael,

what you're trying to build is not a causal system -- you tell the sink to start transmitting the first sample right at the same moment that your source receives the first sample -- but between that, the samples have to flow through your PC!

Add a bit of delay between rx and tx.

Also, what daughterboard are you using? Unless you use one of the daughterboards that support static phase after tuning, and tune as a timed command, the LO phase between the RX and TX will be random [1]

Best regards,
Marcus

[1] http://files.ettus.com/manual/page_sync.html#sync_phase_lo

On 06/18/2015 06:47 PM, Rafael Acurcio wrote:

Hello all,

I'm trying to do ranging using two USRPs N210.

The idea is that the first USRP sends a signal and then the second USRP recognize it and send the signal back. Looking to the turnaround time I would be able to know the ranging.

Despite some problems that I already had, right now I'm stuck with the second USRP.

To measure the time I'm synchronizing the rx ant tx from the first USRP using the following code:

        now = self.uhd_usrp_sink_0.get_time_now()
        self.uhd_usrp_source_0.set_start_time(uhd.time_spec_t(0.1) + now)
        self.uhd_usrp_sink_0.set_start_time(uhd.time_spec_t(0.1) + now)

Using the fisrt USRP I can do ranging, connecting both (rx and tx) together, with a good precision. However I couldn't make the second USRP work yet. When I try to synchronize the tx and rx like I did in the first USRP I get a bunch of Ls (late packages) in the terminal. The code drop all the packages.

My gnuRadioCompanion blocks for the second USRP looks roughly like

USRP Source -> threshold -> USRP Sink

There's a better way to solve that problem?

Why do I get the late packages?

Thanks in advance,

Rafael.

PS: To analyze the data that I'm sending I'm using File Sink block and analyzing the data after the transmission.

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