Mobile User/Asset Location Finding within a Standard WiFi Environment for RTLS Applications

Microsoft Corporation

This suite of software, network drivers, and algorithms allows determining a transponder’s location within a multi-access point 802.11-based wireless environment, without using special hardware. The 802.11 protocol is also called “WiFi.” The suite is designed for a “hardware-agnostic” implementation; that is, it is not tethered to any specific brand of system hardware. Given a WiFi field of three or more access points, the technology can locate a WiFi-enabled tag, phone, PDA, or computer with an accuracy of about 1.5 meters indoors. The technology complements GPS and RFID technologies, and can operate in environments where neither GPS nor RFID may be appropriate—within a warehouse or office that is not open to the sky, and at distances between reader and transponder (WiFi tag or NIC, for example) that RFID cannot reach. Potential applications range from unique forms of asset location such as farm, construction, or cargo container tracking, to security camera triggering, automated phone forwarding, “smart” security badges, customized advertising displays, and social networking in concert with software on the user’s device. According to the Yankee Group, the real time location service (RTLS) market is expected to climb from a mere $25M USD in 2005, to about $10B USD by 2010.

By making use of the current generation of 802.11 WiFi access points, computers, WiFi-enabled phones, and WiFi tags, the RADAR technology leverages an existing infrastructure investment rather than require new infrastructure investment. RADAR complements GPS and RFID location systems, and works in locations and distances where they cannot. Software that takes advantage of the real time location service (RTLS) provided by RADAR can track movable assets from palettes to cargo containers to equipment at a construction site—anywhere a multi-access point WiFi field can be established. Several cities are currently establishing pervasive public systems. Applications that use the RADAR technology do not have to be recognized as part of a network to triangulate using a network’s access points. The technology is accurate within a few feet when using its calibration techniques. Depending on how often a tag is queried or announces itself to the system, battery life can extend up to three years. RADAR opens mobile computing to a wide range of new location-aware software applications and services that do not currently exist.

Previous in-building location systems generally relied on specialized hardware and technologies that suffer from significant limitations or that require extensive deployment of infrastructure solely for locating tags, transponders, and users. For example, infra-red (IR) wireless technology offers only limited, line-of-sight range. Radio-frequency (RFID) tag systems, like IR, are often built for the sole purpose of establishing location, suffer from short range (approximately 2 feet), and do not provide any data networking services. Specialized hardware can be cost-prohibitive. One wireless LAN-based system estimates a user’s position based on the access point to which he is currently communicating.

RADAR differs from other such work in that it tackles the problem of location and tracking using widely available RF-based wireless LANs. With data networking speeds of 11Mbps or higher, wireless LANs have gained rapid acceptance and are already widely deployed in offices, schools, homes, factories, warehouses, college campuses, and even across whole metropolitan areas. Besides the LANs, the RADAR system does not require any additional hardware and can be enabled using purely software means.

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