[USRP-users] underrun problem in GPS record and replay system with USRP/WBX

Fabrizio Turin fabrizio.turin at rina.org
Mon Nov 27 10:54:39 EST 2017


Thank you for the quick response.
I'm still new to USRP world, I'll try the tests you suggested as soon as I can.
Yes, my flowgraph for the transmission part is just a file source and a usrp sink.
Talk to you soon.




From:	Derek Kozel <derek.kozel at ettus.com>
To:	Fabrizio Turin <fabrizio.turin at rina.org>
Cc:	"usrp-users at lists.ettus.com" <usrp-users at lists.ettus.com>
Date:	27/11/2017 16:42
Subject:	Re: [USRP-users] underrun problem in GPS record and replay system with USRP/WBX



Hello Fabrizio,

Have you tried running the benchmark_rate example included with UHD? That can test if there is any issue sending data at that rate to the USRP. uhd_siggen is also a good test as it uses GNU Radio so can check that the rate continues to work from within GNU Radio.

If both of those work then more information would be needed about your GNU Radio flowgraph. Is it only a file source into a USRP sink?

Regards,
Derek

On Mon, Nov 27, 2017 at 3:19 PM, Fabrizio Turin via USRP-users <usrp-users at lists.ettus.com> wrote:


      Hi all
      for a research project I'm trying to record and replay few seconds of GPS signal. The recording part has been done correctly, a 40 seconds GPS acquisition has been tested against a GPS-SDR receiver obtaining a correct position fix. Now I'd like to transmit the recorded signal through RF cable
      and see if a commercial GPS receiver is able to get the position fix as well. The problem is that, as soon as I start the simple flow graph in GNU radio I get the "U" underrun warning (side note: PC became un-responding too) and it seems I'm not transmitting at all.
      Here's the complete description of the problem:

      Front-end: USRP N210 with WBX

      Recorded file:

      data type: complex float32
      centre freq: GPS L1
      sampling rate: 10 MHz
      acquisition length: 40 seconds
      recorded file size: 3.2 GB

      Host PC:

      OS: Windows 10 Pro (64bit)
      CPU: Intel Core i7-7820HQ
      RAM: 32 GB
      HD: Toshiba THNSNK512GCS8 (545 MB/s write speed)
      network adapter: gigabit capable

      USRP Sink configuration:

      sampling rate: 10 MHz
      input type: complex float32
      wire format: automatic
      centre freq: GPS L1
      Ch0:Antenna TX/RX
      (everything else as default)

      From the numbers I wouldn't say that the bottleneck is the HD (in any case I've already tried loading the recorded file from a RAMdisk with the same problems...) or the network speed.
      Any idea on what I'm doing wrong and how to get rid of the underrun warning?
      Thanks in advance

      Fabrizio




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