Phone acting as a BTS

[Sylvain Munaut]

Hi,

Since the beginning, I'm wondering if it would be possible to turn one
of those cheap phone into a BTS. I'm n ot talking a full featured BTS
and the mod will involve hardwares changes obviously.
The more I look at it and the more I think it might work. No, I'm not
crazy, please bear with me until the end of this post :)

So, what are the obstacles (taking the C118 as an example):

* 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).

* RX/TX switch

Those have ports that have frequency bands ... but .. do they really
filter that much ?


* 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 ...


But this can still be a battery powered handheld BTS :)


     Sylvain