Different vendors take different approaches to tracking people, places and things in wireless networks.Some location-tracking technology suppliers are makers of wireless LAN communications systems that layer location services onto their systems. Others are third-party location specialists that provide overlay wireless tracking systems.Several fall into the \u201cRF fingerprinting\u201d category, using intelligent algorithms to account for environmental effects on wireless signals. Calculations used to build a wireless \u201cfingerprint\u201d of the radio environment are gathered by a physical walk-around using a handheld spectrum analyzer (or are auto-calibrated in some systems). They are then compared to deviations in the real-time environment to locate the client.Below is a sampling of vendors that fall into the RF fingerprinting category (companies are Wi-Fi communications systems vendors unless otherwise noted):* AirTight (overlay)Auto-calibrates the fingerprint. Claims precision of less than 12 feet depending on access point (AP) vendor. Primarily focused on security applications.* Cisco\/AirespaceAuto-calibrates the fingerprint. Claims precision of \u201cwithin a few meters.\u201d Requires Cisco lightweight APs, controllers, and Cisco 2700 Wireless Location Appliance. Uses technology for many applications.* Cognio (overlay)Performs manual fingerprinting using handheld spectrum analyzer. Focused on troubleshooting and security applications, locates any device sharing the 2.4GHz or 5GHz unlicensed WLAN spectrum that could cause interference. Among them: 802.11 devices, microwave ovens, cordless phones and Bluetooth devices.* Newbury Networks (overlay)Holds a patent for its particular RF fingerprinting algorithm (U.S. Patent No. 6,674,403 B2). Last week, Newbury announced that it has expanded its 802.11-centric Newbury Location Platform, adding asset tracking and content delivery applications to its existing WLAN security application. It also said it intended to open up the platform to third-party partners.* Trapeze NetworksUses fingerprinting technology of partner Ekahau. Also uses internally developed Received Signal Strength Indicator (RSSI), triangulation, nearest AP technology. Focused on site-survey applications.Among the companies that don\u2019t use fingerprinting:* Aruba Wireless NetworksAdvocates deploying a very dense grid of its 802.11 sensors, which continually communicate with one another, so that changes in the environment are always accounted for.* Network Chemistry (overlay)Creates a \u201csignal propagation model\u201d for each sensor showing what signal would be expected to be received at the sensor from every possible floor plan location. Then compares model with actual sensor readings, computes error between actual and model, and determines location based on where error is lowest.