As you might imagine, the ability to tie a user's or system's data to the current position of the mobile device creates a host of potential new applications. To steal a phrase from The Twilight Zone, "Imagine, if you will..."
Automatic routing of your company's field repair fleet to the next nearest job site, based on their current location
Elimination of automobile theft due to the fact that police can instantly track a car the second it's stolen
Quickly scanning a bar code on a new DVD player and locating the best price within a 15-mile radius
Finding the sushi restaurant nearest to you in a strange city
Being notified that your favorite clothing store is offering you a 20% off coupon when you're within a mile of the storefront
Software routing of emergency response vehicles to the scene of an accident
While the concept of mobile positioning may sound somewhat futuristic, it may surprise you to learn that many of the items in the list above (particularly the 1st, 2nd, and 6th items) are approaching reality today. Thanks to the Global Positioning System (GPS), vehicle-mounted GPS receivers enable a wide variety of public safety, automated vehicle location (AVL), and asset-management applications in use today by large police/fire forces and trucking/delivery companies. Wireless Week magazine also recently reported on the use of LBS in the aftermath of the World Trade Center tragedy to aid in the location of wireless devices at Ground Zeroanother use of this technology to enhance public safety.
While these solutions have become increasingly popular in targeted vertical markets, the general public's experience with LBS has been limited to the use of GPS devices for use in personal navigation (car, plane, boat, hiking, and so on). The integration of a user's position with other information within an application could clearly be of great value, so what's holding things up? Like many other wireless technologies, location-based services are not commonplace for the general public yet due to concerns over receiver size, pricing, device processing power and battery life, communications coverage and bandwidth, data security, and user privacy. While all of these barriers are being addressed on a variety of fronts, I'll discuss the technical issues here.
There are a wide variety of techniques for pinpointing a device's location on a wireless network. At their most basic, the primary techniques used can be broken down into three categories: the network-based, device-based, and hybrid approaches.
Network-based techniques combine a number of parameters to determine the location of a device on a wireless radio network. These parameters include things like signal strength, antenna triangulation, and signal direction. Two leading network-based technologies are the Time Difference of Arrival (TDOA) and Angle of Arrival (AOA) techniques. According to wireless location company Geometrix,
TDOA calculates a location by "measuring the exact time of arrival of a handset radio signal at three or more separate cell sites. Because radio waves travel at a fixed and known rate (the speed of light), by calculating the difference in arrival time at pairs of cell sites, it is possible to calculate hyperbolas on which the transmitting device is located."
AOA determines a caller's location by "[determining] the direction of arrival of a handset's signal at the cell site. The phase difference of the signal on elements of a calibrated antenna array mounted at the cell site provides the angle of arrival. The intersection of the angles from two or more sites provides the location."
As you might suspect, network positioning has its pros and cons. On the positive side, no special hardware or software is required on the user's handset. Instead, a carrier (such as Sprint PCS, Cingular, and so on) must install specialized hardware and software at the tower base station, which can result in significant capital expenses during the initial deployment. In addition, network-based positioning techniques are not as accurate as their device or hybrid counterparts (discussed shortly). For more information, visit any of the following companies that offer network positioning products:
Device-based techniques make use of specialized hardware and software located on a device to accurately determine a user's location. Due to the global availability of the U.S. Department of Defense Global Positioning System, the device hardware almost without fail consists of an inexpensive GPS receiver or GPS chipset built into the device. Until 2000, GPS "Selective Availability" was not available to the general public, limiting device accuracy to approximately 30 meters. With selective availability turned off due to an executive order signed by then-President Clinton, GPS devices can now accurately determine location to 5 meters. Differential GPS (DGPS) units can be accurate down to 12 meters, certainly good enough to locate the nearest coffee shop on a cold winter morning!
GPS receivers are available for a wide variety of mobile platforms (including Palm OS and Windows CE/Pocket PC devices), are relatively inexpensive, and are very easy to set up and begin using. In addition, a wide variety of software applications (for logistics, GIS, tracking, and so on) include integrated GPS support. On the down side, GPS devices tend to be a bit large and power-hungry. To date, no one has integrated a GPS receiver into a PDA hardware architecture, although Sprint PCS announced at the end of September 2001 that they would begin offering Samsung's GPS-equipped SPH-N300 phone for $149.99. Other companies offering GPS receivers for mobile devices include the following:
Hybrid techniques make use of a combination of handset-based hardware and software and network/server-based hardware and software. This approach has the advantage of producing very accurate results at a low cost and with minimal impact to the device user. Leading with this approach are QUALCOMM-owned SnapTrack and SiRF Technologies.
While mobile commerce has been the "next big thing" for nearly two years now, it's clear that it will take some time for truly immersive mobile commerce experiences to become commonplace. Instead, you may be surprised to learn that the U.S. federal government is currently driving adoption of wireless location services! The FCC's E911 mandate requires that mobile operators implement location services with all 911 (emergency) calls in a two-phased approach. Phase I requires that all 911 call centers be able to identify incoming calls so that the calls can be returned should they be disconnected. Phase II requires that 67% of calls be located to within 100 meters for network approaches and that 67% of calls be located to within 50 meters for handset approaches. The deadline for this implementation was to be within six months of October 2001, but already wireless carriers are lining up to obtain waivers and/or extensions for compliance. To be sure, the future of E911 will be very interesting to watch, as it affects all future location services!