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costs due to the need for hardware changes to their network infrastructure. At the same
time, many businesses were quick to recognize the market potential of location-aware
wireless terminals for applications as diverse as fleet management and social network-
ing.
The first commercial launch of LBS services was in Japan by KDDI in 2001; early
offerings in Japan met with wide acclaim and rapid adoption. Elsewhere, adoption has
been slower but is now reaching critical mass as mobile platforms, including Java ME,
Qualcomm's Binary Runtime Environment for Wireless (BREW ), Apple's iPhone, and
Google's Android, provide APIs for LBS applications. In addition, carriers have made the
service available for applications on their networks.
Today, several commercially available systems permit wireless devices to determine
their location with great precision, provided they have access to one or more Wide Area
Network (WAN) services. The most well known is GPS, in which a device triangulates its
position using information derived from radio signals received from orbiting satellites.
While commercial GPS receivers have been available at low cost for industry and per-
sonal purposes for more than a decade, commercial GPS has two major disadvantages
that make it ill-suited to be the only means of mobile device positioning. First, GPS
receivers require a clear view of the sky in order to be able to receive the radio signals
from the satellites that the service uses. Second, GPS accuracy is somewhat variable due
to a combination of atmospheric effects and a specific GPS feature named Selective
Availability (SA), which permits the US government to compromise the accuracy of civil-
ian GPS in times of war. Fortunately, SA is presently deactivated, and with the widespread
civilian adoption of GPS, it is unlikely to be reintroduced, but other errors can lead to an
error of several meters. Today, there are ongoing efforts around the world to develop
other global navigation assistance systems for political and economic reasons, providing
international alternatives to GPS (which works anywhere on the globe).
To address the inherent problems with GPS, several other schemes have been pro-
posed, including A-GPS and various forms of network triangulation. A-GPS works by
using additional hints about the device's position gleaned from data about which cell
sites it may be using, and it delegates much of the mathematical processing that deter-
mining your position requires to network resources. Triangulation techniques rely on
determining a device's position based on received signals from local cell towers, and
more recently local Wi-Fi base stations as well. To ensure rapid position determination
time, as well as high accuracy and availability, today's wireless handsets usually incorpo-
rate several schemes for position location.
While the means of determining a device's position may vary under the hood, the
result that the positioning system provides is the same: the device's coordinate, which is
usually the latitude and longitude computed at a specific time fixed to a
datum
—a math-
ematical model of the earth's surface. Because the positioning system is approximate—
atmospheric effects, radio propagation effects such as multipath, and other factors intro-
duce error into even the best positioning systems—the position that the system provides
is a notion of the position's
accuracy
, usually a radius. The coordinates and radius define
