900MHz packet radio?

Paul Gardner-Stephen paul at servalproject.org
Thu Sep 1 21:16:11 UTC 2011

Hello Mad,

On Fri, Sep 2, 2011 at 2:10 AM, mad <mad at auth.se> wrote:
> Hi Paul,
> another point to assess is if it is feasible at all to use these devices with a to-be-developed p2p protocol in terms of practicability to operate them in the field as you intend.
> Because there is still the issue of power consumption you can not get around so easily.
> GSM phones can maintain their high standby-times only by relying on stable basestations to be able to switch off their transceivers for most of the time.
> As Sylvain stated there has to be a master kind of imitating the BS for its neighbours to sync on. This master most certainly had to send a beacon all the time so its battery would drain quickly. The operation time in master mode would be significantly less than the usual speech-time of that phone, so not much more than very few hours.
> As there is only a short radio range, all participating devices had to act as a master for some time of their operation and suffer from this energy consuming mode, especially in loosely covered areas where are no or few other devices reachable.
> It's just my view that this should be considered, too, before making huge efforts to implement sth. like this for the intended purpose.

You're absolutely right about energy consumption. In fact, this is a
big problem for WiFi too, as there it is difficult to disable the 10Hz
beaconing in ad-hoc mode.

Our view is that the right technology for other occasions, e.g.,, GSM,
exists, but we want to at least provide the possibility of
communications in the other situations, which it turns out happens
fairly often (disaster, remote, developing countries).

We will also look into tricks like using the beacons from a nearby
cell to synchronise ourselves if it is available, as that should
enable us to save a lot of power, and only resort to beaconing
ourselves if we really have to.

Your point about sharing around the being master is an important
point, and certainly one that would need to implement.

> Of course it would be a cool addon to osmocom-bb and this shouldn't keep anybody from doing this for the sake of rising to the challenge. ;-)

Well, if it looked like it was sensible, then someone else would
probably have done it ;)
Anyway, I am committed to at least try, and intend to throw some
resources (including financial) behind the effort.
Besides, the more this conversation continues, the more convinced I am
that it is possible, even if the solution might be a conglomeration of
rather interesting work-arounds.

The point is that there is every possibility that it will work, and if
it does, then one of the eventual side-effects should be the gaining
of access to material that will enable the reprogramming of more
modern baseband processors to positive ends, which will be much more
interesting for everyone.


> Regards,
>  Mad

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