Knowing where you are is a key piece of information. And like just about every other technology-related development...
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in the past decade, the science behind indoor location tracking has improved dramatically.
Initially available to consumers in standalone navigation units, then used in basic cellphones to provide precise location, the Global Positioning System (GPS) is now a critical feature of many smartphone functions. GPS devices determine location through a process known as trilateration, using precise timing information transmitted from a constellation of satellites. As efficient as that process is, however, the nature of the satellite system limits its indoor capabilities. But we have become so accustomed to knowing where we are that pinpointing a person's indoor location is becoming a necessary -- not merely a nice-to-have -- feature. Luckily, advances in wireless technology are filling this gap.
Ubiquity of Wi-Fi enables indoor location tracking
802.11 Wi-Fi networks are ubiquitous. As wireless technology matures from networks of convenience to networks of primary access, additional services are rolling out every day. As a result, Wi-Fi-anchored indoor location identification has become essential.
Wi-Fi location differs from satellite navigation in several important ways. First, GPS provides location information in a globally agreed-upon system of latitude, longitude and altitude. No such system exists for indoor location tracking. Secondly, and relatedly, Wi-Fi location is a network-side service, not a client-side function. Because access points (APs) can be placed anywhere, there is little use in a client triangulating itself. After all, there is no reference point from which to base the calculation. Rather, the network locates the clients. This results in clients not "knowing" where they are. Additional steps must be taken to inform the client where it is.
Operationally, Wi-Fi location tracking services are fairly straightforward. Clients send probes to investigate what networks are available. Multiple APs may be in range of the probing client. The APs determine the receive signal strength indication, or RSSI, of these probes. Systems and applications attached to the core Wi-Fi network (for example, AeroScout, Cisco's Mobility Services Engine or Meru's E(z)RF Location Manager) collect and process this information to determine each client's location relative to the APs.
AP placement and density key to making Wi-Fi location work
In order for this system to work, consider these features during network design and implementation. First, AP placement and density are critical. Ensure there are enough APs to provide multiple detection points. Ideally, they should not be placed in a straight line, such as down a hallway. Second, APs must be placed on floor plans that accurately reflect not just the obvious obstacles such as walls, but also mechanical and other features (such as large HVAC structures) that can greatly affect RF performance. These maps are a foundational element of the location service. They act as the location authority for a network operator in the same way latitude and longitude do on a global scale.
There are many advantages to a business running location services on its Wi-Fi network. Hospitals, for example, use Wi-Fi location services to perform a variety of tasks, from tracking expensive mobile assets to monitoring the temperature and humidity of sensitive drugs. Additionally, some healthcare providers track people and the time they spend in different areas to monitor patient care (for example, how long a nurse stayed in a patient room). One company even uses location services to monitor hand washing.
Indoor way finding generates benefits, challenges
Indoor way finding in large establishments is not just a convenience to visitors, but it can also be used in times of emergency. At airports, tracking the number and movement of devices can be used to gauge how many people are in an area and how quickly they are moving -- information the Transportation Security Administration might use to monitor lines and thus add staff as needed. Museums and other attractions are also using this technology to provide self-guided tours.
Aggregate (and anonymous) data may be used by facility planners to monitor how many people are in different parts of a building or campus at different times of the day. Retailers, meantime, would love to know how many people spend how much time in various areas of their establishments.
Yet this level of collecting data raises privacy concerns and fuels the next critical piece of enterprise-based location services -- policy.
Simply operating a Wi-Fi network means collecting information about client location, even if additional location services aren't added to the network. When they run location services and collect this information, operators need to establish data retention and data use policies. By their nature, location services track all Wi-Fi devices and devices transmitting in Wi-Fi bands (such as Bluetooth); it may not be possible to segregate populations, such as, say, employees as opposed to visitors. If devices not owned or associated with the business are being tracked, what are the notification requirements?
Location-based services provide a rich set of features to both network users and network operators. Enabling such services by extending the location tracking of a Wi-Fi network is a natural progression in the maturity of this service. Technical challenges are easily overcome, but operators should not let the technology proceed faster than the establishment of policies surrounding data use.
About the author:
Andrew Gallo is a Washington, D.C.-based senior information systems engineer and network architect, responsible for design and implementation of the enterprise network for a large university.
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