Hello Hojoon, You will have to profile your system to determine the minimum delta that works reliably on your system, as well as choosing a definition for reliable. Networking stacks nearly always have stochastic delays due to the various context switches and scheduling issues with transferring data to and from a user program and the actual network hardware. On the USRP side the FPGA provides a much more deterministic behavior because the logic is exclusively serving the network traffic. The DRAM buffer on the transmit side is there to absorb some of the variability of the host computer network stack, but it can only do that if there is enough time delay between samples being sent by the program and when the DAC must be producing the associated analog signal.
In practice I have always used a few (5-20) ms and found it to be reliable for transmissions lasting up to an hour, but you will have to test your specific setup. Different OS network stacks have different options for tuning to reduce both the average and peak latency of the network drivers. I'm not an expert in them but there are a variety of good resources online. In applications demanding both small latency and high reliability moving to a realtime Linux environment can help in meeting those hard deadlines. I believe that some of the LTE and GSM projects have been successful with that approach. Regards, Derek On Thu, Jul 5, 2018 at 12:34 PM, Hojoon Yang via USRP-users < usrp-users@lists.ettus.com> wrote: > Hi, > > > > I am using USRP X310 with two UBX-160 daughterboards. > > > > In my application, I am using timed transmission, for example, > > > > start transmission at (usrp_get_time_now() + delta) > > > > My question is, what is the smallest delta value that can be successful in > the *real world*? Theoretically, the delta can be any value, if the host > can send the packet to the USRP fast enough. > > > Suppose we have a PC which have i7-8700k CPU and the PC only runs this > application. when I set the delta 1ms, Can I avoid late 'L'? > > > Best regards, > > Hojoon > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > >
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