|Subject:||Re: [Discuss-gnuradio] Time synchronization between two USRPs without external signal|
|Date:||Sat, 12 Oct 2013 16:10:19 +0800|
|User-agent:||Mozilla/5.0 (Windows NT 6.1; rv:17.0) Gecko/20130801 Thunderbird/17.0.8|
I'm glad to hear from you.
The idea of this experiment is quite similar to the core of your honored paper "The flooding time synchronization protocol". It's a transmitter-receiver sync method using precious tx/rx timestamp to synchronize transmitter's and receiver's local timer.
On the transmitter side, sync message is transmitted every 1 sec. Using rx tags, it's easy to get the average receive interval is 1.0003sec and the jitter is around 320us. Considering the interval jitter is 2*(rx jitter+rx jitter), the sync accuracy is 160us.
I wanna break into USRP FPGA to achieve 1us or less accuracy. And I don't understand your "continuously transmission". Could give me some details.
2013/10/12 9:03, Miklos Maroti wrote:
Hi Harrz, What do you mean by 160us precision? How did you measure it or compute it exactly? I do not understand your goal, but it is quite simple to synchronize two usrps with continuous transmission to within one sample and if you continuously receive the transmitted signal on the transmitter side, then you can avoid all time stamping problems and effectively synchronize the tx and rx chains of a single usrp. Miklos On Thu, Oct 10, 2013 at 3:51 PM, Harry Zhang <address@hidden> wrote:Hi, I have implemented time synchronization between two USRPs without GPSDO, MIMO cable or referring to computer's time.It's a sender-receiver method based on message exchange. It will be included in my next paper soon. I use the tx_time and tx_sob tag to transmit the message at the planned time. When this message researches the receiver, I can get the receive time via rx_time tags. The transmit and receive time of tx tags and rx tags are recorded in USRP motherboard without the jitter of Ethernet cable or operating system. So I think it could achieve the best accuracy without modifying FPGA. The experiment shows the accuracy is around 160us. I think it's mostly caused by the jitter of the tx tag's time. I wanna achieve better accuracy than this and the best way is adding a hardware timestamp module in FPGA. Is this way feasible? As for now, I wanna get a depth understanding of the implementing of tx tag,so I will know the accuracy limit of this method. But I'm not familiar with the FPGA, so could anyone describe how tx_time tag implemented or give me some documents about this? Thanks in advance. _______________________________________________ Discuss-gnuradio mailing list address@hidden https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
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