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Deploying Indoor WLAN Positioning Systems

Most of us are familiar with Global Positioning System (GPS) products that help us navigate while driving, hiking, boating, and flying. GPS uses a combination of orbiting satellites to determine position coordinates. This works great in most outdoor areas, but the satellite signals are not strong enough to penetrate inside most indoor environments. As a result, a new strain of indoor positioning technologies that make use of 802.11 wireless LANs is beginning to appear on the market.

Awesome Applications

The idea of combining positioning information with wireless LAN applications has always been interesting to me. A central server can monitor the coordinates of wireless tags and users and feed position information to various types of application software. Warehouse location systems make it faster to find items and hospitals can track the location of doctors and nurses to dispatch the right person who's closest to an emergency.

The usage of location-aware systems over wireless LANs, however, is now moving toward the consumer market. For example, the ability to track children is extremely valuable. Imagine being in a theme park and your toddler wanders off without your knowledge. With a location system, you can easily find them among a large crowd. Through the use of a concealed wireless tracking tag, this type of system can aid tremendously if someone takes a child without permission.

The use of location-aware applications in retail environments is pretty exciting. You can deploy this type of system in a shopping mall or large retail store and implement electronic flyers and advertisements. The system takes into consideration the physical location of shoppers within the facility and customizes content appropriately.

For example, users can receive an electronic directory and advertisement flyer on their wireless PDA after entering the mall. The directory would include a map of the facility that identifies the person's exact position on the map. As the shopper clicks on a store, restroom, or ATM machine in the directory, the map indicates directions that take them to the desired selection. If your spouse or shopping friend is carrying a wireless device, then you can also keep track of each other's whereabouts.

To take this further, retailers can push sales information out to shoppers that come within range of the store. If the user selects one of the advertisements, their PDA can lead them to the applicable merchandise. Of course, this can result in electronic competition. For example, you can be shopping for tools in one store, and a competing store can pop up an advertisement for a better deal in an attempt to steal the business.

These are all pretty thrilling applications for a gadget guy like me. Anything that beeps and displays stuff captures my interests. The problem with expanding this market, though, is that most people just want to shop traditionally, which is why Internet-based shopping has yet to overtake a trip to the mall.

Proprietary Technologies

Indoor positioning requires the deployment of specialized equipment that integrates with a wireless LAN. Vendors are not too open about discussing how their products determine the user's position, but they likely monitor propagation delays among the wireless nodes (access points and users) to triangulate and calculate relative position. An issue with these systems, however, is that there are no standards. All solutions are vendor-specific.

For example, Ekahau offers the Ekahau Positioning Engine (EPE) that locates laptops or PDA devices within 1 meter (3.5 feet) in less than a second. EPE is a software-only solution based on Java 2 that runs on Windows NT/2000/XP, WinCE 3.0 and Pocket PC 2002. An Ekahau Manager application records site data and tracks devices, with the ability to show a floor plan that displays the location of each wireless nodes.

WhereNet is another company that offers a line of positioning solutions. The WhereLAN Access Point supplies an 802.11b wireless LAN that makes available a positioning infrastructure capable of supporting various types of location-based applications. WhereNet's Visibility Server Software is a software package that provides tools necessary to manage the assets and resources.


As I mentioned, there are no standards for indoor positioning systems. As a result, carefully analyze each vendor's offering before making a decision. Some offer network agnostic solutions, which minimizes the use of proprietary components. At least in those cases, you can utilize off-the-shelf access points and network cards.

Before implementing a location system that tracks people, be sure to consider privacy issues. Of course these systems are meant to help people, but unethical operators (or hackers) may take advantage. For example, a system tracking people belonging to a particular group could provide information on when individuals are far enough away from the group to be victimized. Think about implementing security mechanisms.

Before tracking employees, be sure to discuss the system with an attorney to ensure that you're not violating employee's rights. In some cases, you might need to have employees sign an agreement to relinquish privacy act rights. It's best to investigate these issues early on before asking employees to use the system.

As with any wireless LAN application, take into account potential performance degradation. Location-based systems invoke the transmission of overhead packets over the wireless LAN in order to implement positioning algorithms. This additional overhead can significantly lessen throughput available to users. Thus, choose a solution that minimizes the transmission of packets. In fact, it doesn't hurt to ask the vendor for test results related to overhead and throughput. If the positioning engine requires most of the usable bandwidth of the WLAN, then there won't be much left for other applications.

Jim Geier provides independent consulting services to companies developing and deploying wireless network solutions. He is the author of the book, Wireless LANs (SAMs, 2001) and offers computer-based training (CBT) courses on wireless LANs.

Join Jim for discussions as he answers questions in the 802.11 Planet Forums.

802.11 Planet Conference Have you got a position on positioning systems? Join us at the 802.11 Planet Conference & Expo, Dec. 3-5 in Santa Clara, CA. One of our sessions will cover The Location-Aware WLAN.