But the rest of the world and considering illegal frequencies being used around the US will make this problem harder than one thinks.
So you come up with a great solution for 900Mhz, problem is you can't use it in the EU or Asia. Or how about 433? nope, more conflicts outside the US.
Then there's the 1W vs 25mW (rest of the world) requirement....
Not only is this a tech and regulation problem, it's a frequency management and standards nightmare.
At least you can drive a DARPA challenge car or a biped robot in pretty much any country without conflicting tech (but conflicting regs).