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
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William Thompson Ph.D.
Research Engineer
Toshiba Research Europe Limited
32 Queen Square, Bristol, BS1 4ND, UK
Tel: +44 (0) 117 906 0734