Re: [Discuss-gnuradio] Re: Cellular relay

[a3seth]

Quoting David Young <address@hidden>:

> Aaditeshwar,
> 
> It is a shame if I have to buy or build a basestation to get any use
> out of old cell phones in my home, even if I can use a USRP and GNU
> Radio to do it. :-) Are any cellular modes more symmetric than CDMA?
> Is direct phone-to-phone communication possible, even without WiFi?
> 
> Do you know whether or not it is possible to get instructions for
> re-programming the old phones?
> 
> Dave

Dave,

I agree that the idea of having a thin SDR relay for networking old cellphones
might not have been the brightest of all ideas, but it is not altogether
impractical for the following reasons:

- There are companies like Clariton that tie up with cable modem ISPs and
provide a celluar RF to fibre conversion at the modems, and a reconversion to RF
at tap points closer to cellular base stations. This helps alleviate the problem
of poor cellular coverage inside buildings. The SDR relay could simply be
integrated with their solution.

- Hardly any phones discarded today have WiFi on them. Some do have bluetooth
radios but the range is very small. Hardware hacks inside phones will be needed
to increase the range.

- The SDR relay does not have to be a full fledged base station at all. The idea
here is to have some cheap device that just understands 3 channels, can be
plugged anywhere inside homes, and can link together old cellphones that do not
even have a SIM card.

To further answer your questions:

- Symmetric communication in CDMA: It is actually completely asymmetric. I also
couldn't find anything better than to use the paging and access channels given
that the entire CDMA digital processing, MAC, and link layer protocols are built
right into the chipsets which cannot be modified. Therefore, even the CDMA data
channels cannot really be used.

- Reprogramming cellphones: Most cellphones support a J2ME or BREW virtual
machine with downloadable apps, and that is all that is needed on cellphones to
enable this solution. In fact, this was a major reason to use simple
out-of-the-box mechanisms because the J2ME or BREW app on cellphones only needs
to send and receive SMSes now.

I'll also add that putting this SDR relay inside homes may not be the best
application at all. What might instead be feasible is to include relay
functionality in the cellphones itself. This will be a move towards cognitive
radio where cellphones will sense the environment so as not to create any
interference, and yet be able to communicate with peer cellphones directly. What
seemed cool to me was that such relayed communication was indeed possible.

Regards,
Aaditeshwar.


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