Re: [Discuss-gnuradio] Time synchronization between two USRPs without external signal

[Miklos Maroti]

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.
>
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