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Harald Welte laforge at gnumonks.orgHi Domi,
On Sun, Jan 13, 2019 at 11:17:33AM +0100, Tomcsányi, Domonkos wrote:
> Just a fun fact: afaik current commercial multi-purpose (2G/3G/4G) base stations use generic SDRs to accomplish support for all technologies in a compact package.
Sure. I think it's not so much the size of the package, but mostly the
software reconfiguration part for so-called "spectrum re-farming". This
allows you to scale down the number of GSM carriers and scale up the
number/width of LTE carriers without any on-site visits.
> Of course those SDRs are in a completely different league in terms of
> accuracy, calibration and price :).
When I said "general-pursose SDR" I was referring to a USRP-style or LimeSDR-style
device. This means, basically
1) wide-band radio front-ends without band filters
2) IF or baseband filters that are muhc wider than GSM channels
3) all processing on general-purpose CPUs (as opposed to ASICs, DSPs or FPGAs)
4) no calibration of the RF output power over frequency and temperauture
5) no calibration of the Rx signal level over frequency and temperature
6) no clock that conforms even remotely to 3GPP accuracy requirements
Of course not all of those topics are realted to the original discussion, and
of course you can still use a general-purpose SDR as one element of a real-world
base station. But then you have to add at least some of the missing elements
I described above.
For the calibration part: This could all be done in [open source
software], if you have a signal generator with known/defined signal
level. It would be a great project to define a calibration setup to
determine calibration tables for Rx and Tx levels over (at least)
frequency.
OsmoBTS already has support for applying calibration tables on the
transmit side, which were originally intended in case you add an
external, non-linear-gain PA to a previously calibrated BTS. That could
possibly be extended? For the receive side, no support exist.
Regards,
Harald
--
- Harald Welte <laforge at gnumonks.org> http://laforge.gnumonks.org/
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