Hi Sylvain,
On Wed, Feb 24, 2010 at 12:06:54AM +0100, Sylvain Munaut wrote:
* RX filters :
Obviously you would need to remove one and replace it with one for the
good band. I would only replace one of them so that you can use the
900 band for BTS and the 1800 band for MS for example (so that you can
still listen to a official bts and calibrate the clock).
One problem is physical: All the BTS type SAW filters I've been able to
find (and there are very few on the market) are a number of times larger
than the MS type filters, i.e. you won't be able to mechanically fit them.
* RX/TX switch
Those have ports that have frequency bands ... but .. do they really
filter that much ?
no, they're really just switches. The only difference is Rx/Tx outputs.
* MS can't TX/RX simultaneously.
I think you can take advantage of the fact. Imagine that you only ever
allocate channels on TS0,1 & 2. ( BCCH+SDCCH/4 + 2*TCH/F ), you could
divide your time like this :
TS0 - Capture FCCH of a nearby station to calibrate local vcxo
TS1 - Our BTS TS0 TX
TS2 - Our BTS TS1 TX
TS3 - Our BTS TS2 TX
TS4 - Our BTS TS0 RX
TS5 - Our BTS TS1 RX
TS6 - Our BTS TS2 RX
TS7 - nothing ...
Interesting idea, but I doubt it would work all that well. A C0 of a BTS is
required to transmit continuously on all timeslots. The first step when
scanning for BTS's is a power scan. So if a MS does a power scan, it might
do that at a time when your poor-mans-BTS is not transmitting and thus not find
it.
There might be other reasons why a MS is having problems with a
'discontinuously trasmitting' C0 of a BTS, as it is required by the spec.
David Burgess might know more about it. Also, this behavior could be
simulated with OpenBTS, just to see how phones react to it.
But I'd say definitely worth a try...
--
- Harald Welte <laforge(a)gnumonks.org>
http://laforge.gnumonks.org/
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