In ITU region 2 there is an ISM and amateur band that overlaps with some of the GSM900
uplink and downlink frequencies. At least in the US, unlicensed "part 15"
operation is also permitted there, though part 15 has strict power limits that make it
mostly useless beyond a few hundred feet.
One could legally implement and test this concept in the US or anywhere else in region 2
with similar laws as long as they can keep it within 902-928 MHz and were either licensed
amateurs or keep the power within part 15 specs.
That said I had a related idea once about the feasibility of an amateur cellular network,
but one of the main questions raised on IRC was about the filtration between TX and RX
since the uplink/downlink spacing would have to be narrowed to fit within the available
window. This would likely have to be done to an even greater extent to support direct
handset to handset communication, thus would be even more of a potential problem.
tl;dr: Legally possible if you're west of the Atlantic, but you may have some notable
technical problems to overcome.
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Sean Harlow
sean(a)seanharlow.info
On Jan 25, 2012, at 9:02 AM, Dave Schmidt wrote:
why should two
phones use uplink frequency to communicate directly
together? why not using downlink frequency?
Because in most if not all counties transmission on downlink frequency requires a
license?
(Sorry and please correct me if this is some obvious nonsense... to me, the original
proposal was looking quite nonsensial because of this, but I'd love to learn if
I'm wrong...)
Dave.