Boosting the signal from a city-wide Wi Fi network?

In Wilkes-Barre PA, we have a city-wide Wi Fi network through Frontier Communications. I have a business in the downtown area where the signal should be strong but cannot get it in my brick building. What can I do to boost the signal so I can get on the network in my cafe? Will a Belkin or Netgear Range Extender work? What if there are multiple wireless networks?