Hi Sylvain,
On Thu, Sep 1, 2011 at 10:51 PM, Sylvain Munaut <246tnt(a)gmail.com> wrote:
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).
Most interesting!
Then you have to come up with a protocol that with
those primitives
can build a stable mesh network.
Well, once there is a stable packet transport, then it is fairly easy
to build the mesh on top.
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.
Indeed. The Serval mesh software is being setup so that it can use any
link-layer, including such a GSMish one as you have described. That
part is the easy part from my perspective.
You could probably get some inspiration from the specs
of TETRA DMO
mode since what you want is essentially a DMO mode for GSM.
Yes, in some ways that is what we want. We also need to deal with
bridging to WiFi and some other odd bits and pieces.
Paul.
Cheers,
Sylvain