[USRP-users] multiple E310 synchronize

liu Jong jongliu1987 at gmail.com
Mon Oct 16 23:19:32 EDT 2017


Maybe the accuracy of PPS is not enough ?Any suggestion is welcome.
thank you.
best regards
Jon

2017-10-16 17:17 GMT+08:00 liu Jong <jongliu1987 at gmail.com>:

> Hi,all,
>
> I'm using tow E312 to estimate the arrive time difference between received
> signals.The
> program is explained as follows:
>
> uhd::usrp::multi_usrp::sptr UsrpDev = uhd::usrp::multi_usrp::make(“”);
> UsrpDev->set_time_source("gpsdo");
> UsrpDev->set_clock_source("internal", uhd::usrp::multi_usrp::ALL_MBOARDS);
> ...
> uhd::stream_args_t StreamArgs;
> StreamArgs.cpu_format ="fc32";
> StreamArgs.channels.clear();
> StreamArgs.channels.push_back(0);
> uhd::rx_streamer::sptr RxStreamDev = UsrpDev->get_rx_stream(StreamArgs);
> ...
> UsrpDev->set_rx_gain(curGain);
> UsrpDev->set_rx_rate(curRxRates);
> UsrpDev->set_rx_freq(tune_request, 0);
> ...
> UsrpDev->set_time_next_pps(uhd::time_spec_t(GpsTime + 1.0));
> ...
> uhd::stream_cmd_t CapCmdContStart( uhd::stream_cmd_t::STREAM_MODE_START_CONTINUOUS
> );
> CapCmdContStart.stream_now = false;
> CapCmdContStart.num_samps = IQ_NUMS;
> CapCmdContStart.time_spec
> = uhd::time_spec_t((double)nextBoardTime);
> RxStreamDev->issue_stream_cmd(CapCmdContStart);
> ...
> size_t RxNums = RxStreamDev->recv( RecvBuffVec, RecvNums, RxMetaData,
> timeoutD, false );
> ...
>
>
> Right now, the data blocks received from the two receivers have strictly
> aligned time stamps:
>
> [image: 内嵌图片 1]
>
> However, the time difference between IQ data is irregular. In repeated
> tests, the range of thetime difference of the signal at the same location
> may reach thousands of sampling points.
> For example, the IQ data of the two data blocks are shown in the following
> figure. These two blocks are captured from the GSM downlink by two E312 in
> same location, and the blocks
> have the same start timestamps. In the figure, the red line is I, and
> yellow line is Q.According to the GSM frequency correction burst, we can
> see that the TDOA error of the two data
> blocks is very large. There is no GSM frequency correction burst in the
> first data block, but there is a GSM frequency correction burst in the
> second data blocks(2200~2500).
>
>
> [image: 内嵌图片 2]
>
>
> On the other hand, we use “STREAM_MODE_NUM_SAMPS_AND_DONE” commands
> to collect data, and the time difference is equally large and irregular.
> We use Linux ppstest command to test the PPS of the GPS, and the display
> is normal.
>
> Our problem is that ,
> 1) does the E312 of the GPS have a dedicated 1PPS output pin available to
> the FPGA?;
> 2) can E312 be used for TDOA measurement and, if possible, how to
> implement it in the
> program?
> We should appreciate an early reply, a prompt reply would help us greatly.
>
> best reagrds
> Jon
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/attachments/20171017/1e189914/attachment-0002.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image.png
Type: image/png
Size: 621463 bytes
Desc: not available
URL: <http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/attachments/20171017/1e189914/attachment.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image.png
Type: image/png
Size: 73195 bytes
Desc: not available
URL: <http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/attachments/20171017/1e189914/attachment-0001.png>


More information about the USRP-users mailing list