CalypsoBTS timeslots allocation

Sylvain Munaut 246tnt at gmail.com
Wed Sep 9 14:12:52 UTC 2015


> as->l1l[0].tx_mask = 0xe3; /* TS 5,6,7,0,1 */
> as->l1l[0].rx_mask = 0x01; /* TS 0 */
> Why 2, 3, 4 timeslots is not used?

In GSM the UL and DL timeslot are shifted by 3 time slot periods. So
the UL timeslot 0 happens at the same time at the DL timeslot 3. BTS

In this case the phone works at the BTS, so TX is DL and RX is UL.

So RX timeslot 0 happens at the same time as TX timeslot 3.

And :
 * the phone cannot both TX and RX at the same time => That's why 3 is
not in the TX mask because it is in the RX mask.
 * the phone needs some time to switch/retune from RX to TX
frequencies => That's why 2 & 4 are not in the TX mask
 * phone [0] needs to both TX at TS0 ( to send the BCCH/CCCH infos of
the cell ) and RX at TS0 ( to receive the RACH requests )
 * It's also biased toward TX because to be detected more reliably, it
needs to fill the channel with power ( in theory all timeslots are
filled ... here 3 of them are not because that's the best one phone
can do )


> And how to connect more than two phones to the transceiver? Should I add a
> new TRX in OpenBSC config and/or modify source code of the transceiver app?

No idea about that, Andreas did the multiphone stuff, I never used it ...


Cheers,

   Sylvain



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