Have a look, just for example, at Motorola's LANPlanner and Trapeze's RingMaster, which are good examples of this capability. But also have a look at Meru Network's Wireless Virtual reality app, which obtains performance data in an operating network.
Planning, after all, isn't enough; you need to use available management tools to determine what's really working -- and what still needs attention. Keep in mind, again, that RF planning is only as good as the data fed into the system. I've found that absolutely every detail relating to RF propagation, user traffic loads (and time-boundedness requirements), and location-specific demand can't always be determined in advance. Plus, these variables can and will change over time.
And, finally, it's increasingly becoming a good idea to use a spectrum analyzer to do an "RF sweep" of a given area, looking for potentially harmful interference; planning tools can't take this into account. Some WLAN products will eventually build this functionality in, eliminating (or, at least, managing) this additional variable.
I've yet to do a side-by side comparison of different installation techniques, but I'm itching to do so -- that's the only way we'll know whether RF planning, site surveys or simple trial and error yield the best and/or most cost-effective results. But no matter how much up-front simulation and analysis you do, plan on stepwise, incremental refinements and on buying additional equipment over time. Hey, it's radio, and no simulation or analysis will ever be perfect.
Craig J. Mathias is a principal at Farpoint Group, an advisory firm specializing in wireless networking and mobile computing. He can be reached at firstname.lastname@example.org.