Self-contained module
concealed on person, or chipset embedded in object.
Reports location upon remote request.
GPS-equipped devices: e.g.: cell phones. When user dials 911 his location is sent to the
emergency call center.
Same as GPS except that the cell phone
calculates its location by triangulating three
cell towers.
ID tag attached to an object is
activated by strong radio field, then
sends a message to a nearby reader.
WiFi access points transmit an ID.
Some are informally logged by volunteers with approximate location.
Nominal
Accuracy
3 to 10m indoors and outdoors in both
horizontal and vertical planes
3 to 10m outdoors horizontal plane, 50m or
poorer vertical plane
10m to 5km outdoors in horizontal plane,
poorer in vertical
Typical 1 to 5m in very small areas both
indoors and outdoors
Typical 30m in small areas both indoors
and outdoors
Location
Reference
Locator computes
its location using existing local commercial broadcast signals as
beacons.
Cell phone computes its location
if
it can receive GPS signal.
Cell phone computes its location
if
it can receive signals from three cellular towers.
Reader location is considered the tag's location. Triangulation
also possible with multiple readers.
Only approximate access point proximity sensing is
possible.
Operator
Interface
Authorized person requests location
remotely online or via telephone.
User must initiate a call for help to
public emergency call center.
User must initiate a call for help to
public emergency call center.
Tag must be carried close to a reader.
None. WiFi is unmanaged and ad hoc.
Coverage
Coverage indoors and
out throughout metropolitan areas served by broadcast signals.
Only locations with both
GPS and cellular coverage. Poor or no service indoors.
Only locations with multi-site
cellular service. Limited service/poor accuracy indoors.
Immediate proximity to
the reader.
Immediate proximity to the WiFi access
point.
Service
Area
Metropolitan areas
in most countries.
Areas with both GPS and
suitable cellular service.
Areas with
service from multiple cell towers.
Typically several foot radius from
the reader.
Typically
30-50 meters from access point.
Security
Broadcasts resist jamming. No
single-point vulnerabilities.
Easily spoofed or jammed. Vulnerable
to disruption.
Easily spoofed or jammed. Vulnerable
to disruption.
Can be spoofed or jammed. Vulnerable
to disruption.
Unlikely to be spoofed or jammed, but
easily disrupted.
Ease of
Use
No user interaction required, making it ideal for
small children and infirm adults.
Cell phones are too complex for many children and
disabled persons to use.
Cell phones are too complex for many children and
disabled persons to use.
Reader infrastructure is complex to set up. Major
investment.
No setup needed. Access points are
unmanaged and poorly documented.
Operating Cost
Free broadcast signal infrastructure.
Free GPS, costly cellular.
Free GPS, costly cellular.
Costly infrastructure, custom build-out.
Free but undependable WiFi.
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Just how powerful IS
SafeLink?
Signal Power
Levels Compared.*
SafeLink
(VHF)
~30 miles
Cellular
(900 MHz)
~4 miles
GPS
(1.6 GHz)
~11,000 miles
Effective Radiated Power
+45 dBW
+10 dBW
+30 dBW
Path
Loss Unobstructed
106 dB
108 dB
183 dB
Received Signal Power
-61 dBW
-98 dBW
-153 dBW
SafeLink is Stronger by:
37 dB (5,000 times)
92 dB (2 billion times)
*SafeLink's signal power and robust frequency reach indoors like no
other positioning technology.
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A More Reliable Wireless
Positioning Solution
Location-Based
Services (LBS) are in their infancy. Initially they used GPS because
it was available at the time.
However, GPS will not ultimately succeed in the LBS market because it does
not work in places where most people spend their time on a daily basis -
indoors and in dense urban environments.
According to research, people in
developed countries on average spend over 50 percent of their time in
urban areas (cities) or indoors (office buildings, homes, schools, malls).
GPS services work poorly or not
at all indoors. Errors
of hundreds of meters horizontally, and even larger errors vertically, are
common due to weak satellite signals that are
attenuated and reflected by buildings and walls.
Given these inherent drawbacks
of GPS, LBS manufacturers have experimented with hybrid solutions in which GPS is
augmented by cellular, WiFi access point (AP), and U-TDOA signals.
But these additional signals
bring their own sets of problems. Cellular triangulation is
frustrated by small cell sizes and poor signal penetration. WiFi AP
service radius is
tiny. Many APs are unknown; relatively few are accurately logged.
Unlicensed, undocumented, and movable APs cause serious AP database errors. A
disorganized infrastructure such as this is unacceptable for LBS and Public
Safety uses. Further, achievable measurement accuracy with WiFi is poor:
volunteers log AP locations casually at best, and location measurement is performed
using coarse proximity sensing. U-TDOA augmentation also is inherently inaccurate, and
in addition may
require costly cellular network hardware upgrades.
These hybrid designs essentially are
an attempt to improve GPS accuracy through use of additional location
information obtained from other signal sources. Unfortunately, hybrid
designs are fragile since they are only as strong as the weakest link; all
elements of a hybrid design must work in order to improve upon raw GPS
accuracy. And, of course, hybrid designs are still dependent upon reception
of at least some GPS satellite signals which, as stated previously, can be a
significant challenge indoors. Even under clear-sky outdoor reception
conditions, GPS receivers typically operate with only a very small 5-8 dB
signal margin.
In addition to its indoor and
urban service limitations, GPS is known to be vulnerable to
spoofing, jamming and service disruptions. Cellular service is also
considered vulnerable to disruption from natural disasters and terrorist-type
attacks directed against its single-point failure weaknesses. For
these and other reasons, the United States government considers GPS and
cellular networks to be secondary, rather than primary, systems for use
under emergency conditions.
SafeLink is a far simpler and
far more robust solution to the challenges of accurate urban and indoor
location measurement. It is based on use of the strongest signals in
existence anywhere in the world - commercial broadcasts. Broadcast
signals are known to penetrate dense concrete buildings and
urban canyons in population centers worldwide, providing unequalled coverage
virtually everywhere throughout the populated world. And with no
single-point failures like those of GPS and cellular networks, SafeLink can
be counted on to deliver critical LBS and Public Safety services when they
are needed.
Location-Based
Services (LBS) are in their infancy. Initially they used GPS because
it was available at the time.
However, GPS will not ultimately succeed in the LBS market because it does
not work in places where most people spend their time on a daily basis -
indoors and in dense urban environments.