Site surveys are no longer needed

In reviewing proposals for enterprise wireless LAN installations, I’m amazed at how often I find a hefty sum quoted for a site survey. Much to the dismay of the installer, I almost always recommend deleting this item, because it’s usually a waste of time. Site surveys have no relation to real-world performance. They’re relics of a time when access points were expensive, so it made sense to optimize for coverage. But a site survey provides a moment-in-time snapshot of the radio environment; it doesn’t consider the number of users, their traffic patterns and data loads, overall throughput requirements, interference or network changes.

Given that today’s access points are much less expensive and still declining in price, while installation labor costs are rising, site surveys in effect convert inexpensive access points into an expensive, labor-intensive activity that ultimately yields sub-optimal results. Why do we still assume a philosophy of scarcity, optimizing for the minimum number of access points required for basic coverage, instead of providing the abundance of capacity that leads to happier users, more productivity and the bandwidth that ultimately will be needed to support VoIP over Wi-Fi?

The philosophy I recommend is not unlike that used to develop software. Attempting to optimize the performance of an application before it’s written is usually futile. It’s better to get something working, measure where the bottlenecks are and then optimize those modules that need it. The same holds true for WLAN installations: It’s best to deploy – taking into consideration user locations, traffic patterns and throughput requirements – and then use additional fill-in access points to compensate for any errors in initial assumptions. Proponents of site surveys will counter that it’s preferable to understand the radio propagation characteristics of a site, and any potential sources of interference, upfront. However, site surveys cannot address these concerns – radio propagation is so nonlinear that no great truths usually emerge from the survey, and interference is best addressed via a spectrum analyzer, not a WLAN.

Finally, two important technologies are further nailing the site survey coffin shut. One is radio frequency spectrum management (RFSM) tools, available from many WLAN vendors. These automatically configure (and re-configure) parameters such as radio channel and transmit power dynamically, and often can point out holes in coverage and under-capacity in a given location. Second, as we enter the era of dense deployments, as opposed to the sparse deployments resulting from the cult of scarcity that site surveys reinforced, we can now attach access points directly to wiring in the walls and essentially over-provision an installation while minimizing installation costs. Density, coupled with centralized management and RFSM tools, is the key to successful WLAN installations as the WLAN evolves to be the default network connection for many companies. So skip the site survey and buy a few more access points. You’ll be glad you did.

Mathias is a principal at Farpoint Group, a consultancy specializing in wireless communications and mobile computing. He can be reached at craig@farpointgroup.com.