You're probably just seeing the group delay of the interpolation filters on the N210, which for a given configuration, should be of a fixed and predictable duration.
On 2015-11-13 11:18, Will Thompson wrote: > Hi > > I have question about the latency of transmissions in the N210 USPR. > > A bit of back ground in my system: > > I have three nodes. > > One (Node1) that periodically transmits a signal. > > The one of the other nodes (Node2) tries to synchronise its transmission with > that of Node 1. > > Node3 is simply used to record the transmissions and check that they align. > > When Node2 starts up, it saves the rx_time of the initial stream item Tag > from the USRP source. > > It then listens for the periodic transmission from Node1. Node2 then > estimates the timing offset of Node1's transmission and starts to transmits > its signal that should be synchronised with Node1's. > > It adds a tx_time tag to its burst which is based on the rx_time tag of its > first arriving sample and a multiple of the sample time and then number of > sample bins needed to align with Node1's transmissions. > > (the system is working with a sample rate of 1Ms, centre frequency of > 2.48GHz, and using N210 with XCVR2450) > > The issue I'm having is that the actual transmission of Node2 is about 26us > behind that of Node1, and I'm wondering why this might be… is this a > predictable delay, or might it change with other systems? > > Possible issues might be that it is the delay between the Tx burst being > released from the buffers and actually being transmitted, but I feel that > 26us is quite a long time really. > > Or it might be from the original rx_time tag somehow. > > Any advice or insight into this would be greatly appreciated. > > Thanks. > > Will > > -- > > William Thompson Ph.D. > > Research Engineer > > Toshiba Research Europe Limited > > 32 Queen Square, Bristol, BS1 4ND, UK > > Tel: +44 (0) 117 906 0734 > > ------------------------- > > NOTE: The information in this email and any attachments may be confidential > and/or legally privileged. This message may be read, copied and used only by > the intended recipient. If you are not the intended recipient, please destroy > this message, delete any copies held on your system and notify the sender > immediately. > > Toshiba Research Europe Limited, registered in England and Wales (2519556). > Registered Office 208 Cambridge Science Park, Milton Road, Cambridge CB4 0GZ, > England. Web: www.toshiba.eu/research/trl > > ------------------------- > This email has been scanned for email related threats and delivered safely by > Mimecast. > For more information please visit http://www.mimecast.com [2] > ------------------------- > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio [1] Links: ------ [1] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio [2] http://www.mimecast.com
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