> The default maximum bandwidth is 8MHz (16-Bit I/Q samples, only 12-bit
> are used), it might be possible to switch to 8-bit, but I have not
> tried it yet. If you use the full USB bandwidth for one channel, you
> need two units for downlink and uplink.
One thing I'd like to add : When using the full USB bandwidth, there
is the occasional packet dropped. And currently we don't use the
inband signalling firmware so that's not ideal because we can loose
sync.
It'd be pretty great if someone used the latest inband firmware and
integrated that into the UHD driver and then used that as a source for
airprobe.
This way we get:
- Transparent USRP/USRP2 support with timestamping
- No need to resync all the time, progressive TOA adjustement would
be enough (like in a real phone).
We would also get the function available in the inband firmware which
is timestamped register write (IIRC), so this would allow to change
the DDC offset near instantly (e.g. between bursts).
With those software only changes, a USRP with a single DBSRX would be
capable of covering a big part of GSM900 (UL&DL), using only DDC
shifts for tuning. (Use two DBSRX to cover it all). Furthermore, if
you remove the TX path, the USRP can get 4 RX DDC path, so it would
provide 4 * 2MHz located anywhere you want.
To me, we're far from having reached the limitation of the USRP HW ...
Cheers,
Sylvain
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