900MHz packet radio?

Sylvain Munaut 246tnt at gmail.com
Thu Sep 1 13:21:51 UTC 2011


You have to essentially stick with GSM mostly so:

 - Same modulation GMSK
 - Same frame structure of 4.615ms
 - Same bursts : 156.25 bits
 - Same channel coding for CCH and TCH
 - Same channel spacing of 200kHz

This way you can mostly reuse the GSM primitives offered by the baseband DSP.

Then you have to create new primitives so that phones can do between
them what they would do with a BTS
 - Transmit a FCCH / SCH ( so that a phone can become 'local master'
and provide sync to other phones )
 - RX RACH requests ( so that a phone that's 'local master' can answer
incoming requests for channels )

Both of theses actually already exist (I coded them).

Then you have to come up with a protocol that with those primitives
can build a stable mesh network.

And this latter part doesn't actually require any messing with
osmocom-bb at first, you should design and simulate it fully _first_.
And then once you have it you can start implementing it on real
hardware.

You could probably get some inspiration from the specs of TETRA DMO
mode since what you want is essentially a DMO mode for GSM.

Cheers,

    Sylvain




More information about the baseband-devel mailing list