Ok, there are a number of variables here:

Type of transmission:
Broadcast (aanybody in range can receive it)
"beamcast" (directional, but anybody in the right direction can
recioeve it)
point to point (either you have to be near the destination point to
receive it, or *only* the destination unit can recieve it)

Range
does it obey the inverse square law or some other function of range
if not, does it just "chop off" at range?

speed (how fast does the signal move)

bandwidth (how many symbols per second?)

"symbol set" (how many different "states" does the signal have?)

Then we get into things like size of unit, of antenna, etc. Powerr
requirements. And more.

Oh yeah, special conditions. Does it require a strong gravity field?
A weak one? Or some other thing that limits the location of
transmitters/receivers.

--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com