QUESTION: How can I compute the sub-groups of nodes that can communicate based on signal strength and print the lists? I don't necessarily need to know "full adjacencies"; rather, just like the example above, if 1-2 and 2-3, then 1,2,3 are in a "group".
What you want is called a Transitive Closure, which is a well known problem from graph theory. There are simple algorithms that run in cubic time worst case, but IIRC, an n2.5
algorithm exists as well. Search on CPAN for "Graph" and "Transitive Closure" should give you a few pointers.