How can I improve the range of a an Airport Extreme Router (2011)?
I live in an apartment building, and I am trying to share the cost of internet with a neighbor just a few doors down. She recently got an Airport Extreme (b/g/n) router with the expectation that it would provide a bit more range than other models and allow me to connect my Macbook Pro (N enabled) in my apartment, but so far the results are not great. I live in an older stone building, but there aren't too many walls between my apartment and hers, and we are connected by a main corridor.
At this point, I have experimented with switching the 2.4ghz channel as there are many other wireless networks in my building. However, that hasn't resolved the problem. Connectivity, signal, and link strength are all underwhelming, and frankly are inadequate for most of my needs.
What's the best way to improve the range? Is there software that can help identify/quantify a better channel/signal strength? What are other alternatives? I know that it is possible to run ethernet through power lines, but since we don't share an apartment, just an apartment building, would that work?