To many people, "location-based services" (LBS) is just one long buzzword. The average American consumer is probably familiar with some of the capabilities of the FCC-mandated e-911 initiative. But he or she has had little real exposure to LBS products. That scenario is about to change, however. Location-aware hardware and software are now being designed into a growing variety of wireless products.

What is fueling the increase of LBS products in the United States? The e-911 mandate has spawned a lot of this growth. It requires wireless carriers be able to locate a cell phone if it is used to dial 911. The carrier can then give the user's location information to emergency dispatchers.

In addition to e-911, some vertical markets have been driving LBS. They include fleet-management for transportation, corrections services, and personal-locator systems. According to Sal Dhanani, Senior Director of Marketing for Televigation, Inc. (www.televigation.com), there is strong growth in the U.S. LBS market. Some recent announcements are feeding this growth. For example, Televigation has launched a service with Nextel that provides voice-enabled turn-by-turn directions to specially equipped cell phones.

Traditionally, location-based applications have included resource finders, roadside assistance, and asset tracking. Now, personal-locator applications are also gaining popularity. Their success is largely due to the early introduction of pure LBS devices like Wherify's (www.wherifywireless.com) Global Positioning System (GPS) Locator for Kids. This device is neither a cell phone nor a PDA. Rather, it is a wristwatch that provides two-way personal-location services (FIG. 1). Using such a device, the wearer's location and direction can be quickly and easily determined via the Internet.

Though the platforms vary, it's clear that more wireless engineers are incorporating some form of LBS technology into their designs. What does a designer need to know in order to ensure a successful LBS implementation? To some extent, the answer to this question depends on whether the engineer is designing for the U.S. or the European market. Many U.S. designs have focused on e-911 compliance. In contrast, the European markets have worked to develop a more diverse and commercially viable LBS strategy. In either case, it's critical for the designer to understand a few basic terms and concepts.

BACK TO BASICS
To gather information about the geographic location of a device/user, location-based services use a variety of technologies. Each technology is best suited for a particular environment—for example, indoor versus outdoor use. Locating a device/user indoors might well be done with WLAN technology. Once that same user walks outdoors, however, position location can be best accomplished with a GPS-based approach (See Table).

The two most prominent position-location technologies are cell-phone triangulation and the use of GPS satellites. Other emerging technologies include digital television (DTV), ultra wideband (UWB), and WLANs.

To a large extent, the underlying cell-phone network determines which location technology should be implemented. For example, the Global System for Mobile Communication (GSM) is the most common cellular standard in Europe. GSM networks have unique timing capabilities. As a result, location data can be calculated using Enhanced Observed Time Difference (E-OTD) techniques. By utilizing at least three cellular base stations, these techniques calculate the differences in a signal's arrival time at each base station.

With this approach, customers needn't buy new handsets. In addition, the calculations don't significantly affect the network's performance. Of course, a drawback does exist: Each base station must be outfitted with location-measurement units.

In the U.S., many GSM networks are now appearing. So far, the most dominant network system is based on Time Division Multiple Access (TDMA). Like the European systems, TDMA relies on the E-OTD method for determining handset location.

For 2.5G and 3G, those TDMA networks are expected to be replaced by Code Division Multiple Access (CDMA) and Wideband CDMA (W-CDMA) networks. To calculate location data, a CDMA network uses a location technique known as assisted-GPS (A-GPS). As the name implies, A-GPS relies on both the cellular network and satellites for position triangulation. Compared to GSM-only solutions, it offers the advantages of accuracy and altitude calculations. The only drawback is that cellular handsets must be equipped with a separate receiver. Typically, they take the form of an RF front-end chip, a baseband chip, a patch antenna, and software.

Wideband-CDMA networks, on the other hand, use a different mechanism to determine position. Charles Murphy, Senior Staff Systems Engineer for Motorola's WBSG Systems Group (www.motorola.com), points out that W-CDMA systems are moving to a location-service standard called Observed Time Difference Of Arrival (OTDOA). These 3G networks face many technical challenges in order to provide adequate location accuracy.