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Re: [Discuss-gnuradio] Time syncing between SDRs on different computers

From: Derek Kozel
Subject: Re: [Discuss-gnuradio] Time syncing between SDRs on different computers
Date: Wed, 16 Aug 2017 16:57:05 +0100

It should be pointed out that the hardware based timestamping is only needed if you need time alignment better than a half second or so. With USB transfers, various buffers, NTP based alignment of the host computer's time, and some extra code on the host side you could do a coarse time alignment, probably with less than a half second of error.

You could also time align the streams if both radios receive the same signal and you know the distance (and other details depending on the precision needed) between the transmitter and your two receivers. This is done by many protocols like the cellular standards to create a distributed timebase, but quickly becomes non-trivial.

The B200 does timestamping in the FPGA and can use a 1PPS signal to align to GPS time. It is more expensive than the HackRF, but much less than the $3000 mentioned above.

On Wed, Aug 16, 2017 at 4:20 PM, Sylvain Munaut <address@hidden> wrote:
On Wed, Aug 16, 2017 at 5:11 PM,  <address@hidden> wrote:
> What type of hardware? I thought from hardware point of view only precise clock is required and all the other things in
> firmware. I've naively thought i could modify hackrf firmware to get this feature.

Mostly a FPGA and a PPS input from a GPS receiver.

Each individual sample has a timestamp of when it has been received.
And you can also reset the timestamp on the next  PPS edge.

Technically it would be possible to modify the hackrf firmware and
repurpose some GPIOs and have all samples transmitted to the host be
in timestamped packets and implements timestamping in the on-board
For additional hardware you'd only need an external GPS receiver (or
some other way to have both a single freq reference + single sync



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