Location Tracking, Performing a Calibration

lightweight access points. This appliance tracks any Wi-Fi device, including Wi-Fi clients, standards-based Wi-Fi active RFID tags, rogue access points, and clients. It was designed with the following requirements in mind:

•Manageability—The same browser-based interface that is used for the Cisco WCS is also used for the appliance. Moreover, the location appliance integrates directly into the wireless LAN architecture, providing one unified network to manage instead of multiple disparate wireless networks.

•Scalability —The appliance was built to simultaneously track up to 1500 wireless devices. WCS can manage multiple location appliances for greater scalability.

•Security—The controller, WCS, and the location appliance were separated to deliver the most secure architecture possible. The appliance records historical location information that can be used for audit trails and regulatory compliance.

•Open and standards based—The appliance has a SOAP/XML API that can be integrated by partners with other business applications and can track any standards.

•Easy deployment of business applications—The appliance can be integrated with new business applications such as asset tracking, inventory management, location-based security, or automated workflow management.

Location Tracking

The location appliance calculates the location of tracked devices using RF fingerprinting. This technique uses RF characteristics such as reflection, attenuation, and multi-path to impact signal strength readings of devices in specific environments.

To detect the RF signal at each location in an enterprise, the system must first understand how the RF interacts with an installation's environmental variables, such as building materials, walls, doors, and furniture. As such, an RF calibration is required (post wireless LAN installation) to determine the characteristics of that specific RF environment.

When an RF calibration is performed, the attenuation of walls and other building characteristics is taken into account. The extent of RF reflection and multi-path is also calculated for every coordinate, or grid, on a floor map in the management system for each access point. For a single point on the grid, many different access points detect devices; however, each access point detects these devices at different signal strengths.

At the conclusion of calibration, a database is populated inside of the management system. That database contains each coordinate and how each access point views that coordinate from the standpoint of signal strength.

When devices' locations are requested by the management system, each controller replies on behalf of its access points with the signal strengths at which they detect them. The management system then matches the information it gathers from the controllers against its database of location RF fingerprints. Devices' locations are then plotted visually on a floor map.

Performing a Calibration

You can generate the location of coordinates of tracked devices by using prediction. The location coordinates generated in this case are predicated from RF models that the engine already has in its knowledge base. However, if the location resolution is not within specifications, it can be further tuned using a technique known as calibration.

Cisco 2700 Series Wireless Location Appliance Deployment Guide

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