Optimizing a Wireless LAN for Location

By Michael McGuinness and Jeffrey Rideout

Placement of Access Points
A second factor that affects location accuracy is the physical environment of the tracking area. The strength of a radio frequency (RF) signal provides location information, and RF characteristics such as reflection, attenuation and multi-path are unique in every environment.

Advanced Wi-Fi tracking systems such as the Cisco Unified Wireless Location Appliance, can account for how building materials, doors, walls and other large objects impact RF signals and location accuracy, effectively tuning the system for the specific environment in which it is operating.

Jeffrey Rideout

To determine the optimum location of all devices in the wireless LAN coverage areas, consider the access points' density and location:

• Most importantly, access points should surround the desired location.
• Roughly one access point should be placed every 50 to 70 linear feet (17 to 20 meters). This translates into one access point every 2,500 to 5,000 square feet (230 to 450 square meters). APs should be separated by 50 to 70 feet.
• Place access points along the periphery and in the center of coverage areas to locate devices close to the exterior of rooms and buildings, while providing reliable data.
• Increasing overall access-point density and moving access points towards the perimeter of the coverage area, location accuracy is greatly improved.
• In long and narrow coverage areas, avoid placing access points in a straight line; instead, stagger them so each access point is more likely to provide a more distinctive snapshot of device location.
• To minimize the degree of co-channel interference, traditional best practice recommends deploying access points on alternating non-overlapping channels, using directional antennas where possible and judiciously limiting access point power levels as necessary.

Making the Case
The investment in a strengthened WLAN, optimized for location tracking, can be rapidly recouped. Hospitals reduce the total cost of ownership of leased or owned equipment, stop the cycle of over-procurement to accommodate theft or loss, and accelerate workflow by locating valuable assets when needed.

In the long term, the standards-based nature of Wi-Fi protects these investments, ensuring that the many users and applications—whether data access, voice or location tracking—will continue to benefit from rapid, cost-effective technology innovation within a common 802.11 framework.

Michael McGuinness is president and CEO of PanGo Networks, a leading provider of a location-aware platforms and applications fueling dozens of leading hospitals' asset-tracking initiatives. Jeffrey Rideout, M.D., is vice president of the Internet Business Solutions Group and chief medical officer at Cisco Systems, a worldwide leader in networking for the Internet.