a) Loran
In order to be able
to locate E 911 wireless callers, there are three
types of location systems. The first type of
location system, employed by Code Alarm, involved
the use of Loran, which is a hyperbolic navigation
system. The hyperbolic navigation system is one
involving a base station transmitter and two slave
transmitters, with time difference of arrival of
the signals from the base and slave stations
providing a fix for the individual receiving the
signals. Aside from the Loran system being
relatively low-frequency and requiring long whip
antennas, Loran-based systems suffer from the
problem of the degradation of position when these
signals travel over land. In short, the hyperbolic
lines of propagation are skewed by land-based
objects, making the Loran system more suitable for
use away from land, e.g., in the ocean.
b) Triangulation
The second type of
solution requires triangulation. Triangulation is
used to locate the wireless transmitter, in which
either direction-finding techniques,
time-difference of arrival techniques, or
repeater-type beacons are utilized in order to
calculate the position through the utilization of
one or more cell sites. While triangulation systems
address the embedded base issue, they are
relatively unusable in rural areas in which the
towers are along a line making the geometry
difficult. Also, lack of cell sites leave some
areas uncovered.
c) GPS
This leaves the GPS
solutions. For in-vehicle tracking and signaling,
GPS receivers have been located within the cars and
GPS antennas are placed on the outside of the car
body to provide the location information to be
modemed to a central dispatch office. As will be
described, such systems are employed in the
Motorola RESCU-type system, and systems from ATX,
BART, Car Cop and others. A second type of GPS-type
system employs modeming raw GPS data to a central
processing location at a cell site, in which GPS
signals are detected at an individual phone and are
presented to a GPS receiver at a cell site for
processing. These type of systems require a modem
for the transmission of the locally generated
information to the cell site and while providing
accurate location, suffer from the power
consumption of the modem and the deployment and
cost of the apparatus at each cell site to
calculate position. Such systems include the Tiget
system from NAVSYS and the SnapTrack system.
Costs
With respect to the
cost of the above systems, the cost for the
original Code Alarm/Loran system was $35 per month
for a dedicated cellular phone, plus $40 per month
for the dispatch operation. This type of solution
proved to be too costly, at least as far as
consumers were concerned.
As to the cost of
triangulation-type systems, it was reported
originally that the beacon-based Teletrack system
cost upwards of $500K per cell site, which was
prohibitively expensive. KSI was first with the
suggestion of triangulation using a
direction-finding (angle of arrival) system at a
cost of approximately $50K per cell site, followed
by the Sanders Associates solution at $90K per cell
site, and finally by a time difference of arrival,
or TDOA-type solution from the Associated Group in
the form of the True Position system. This system
is nominally pegged at $50K per cell site, or at
$35 per user, assuming 1500 users per cell site.
Building a GPS
receiver into a cell phone as a unitary device is
proposed by the FoneFinder system from Tendler
Cellular, in which the entire phone/GPS/FoneFinder
chip set brings the cost of the phone to
approximately $400 per phone. Associated revenue
streams not only pay for the additional FoneFinder
functions, but also offset infrastructure costs or
provide other profit centers.
The GPS Solution
What constitutes the
GPS solution is the provision of 26 satellites
operated by the United States Air Force from a
command center in Colorado in which at any given
time at minimum four satellites are viewable from
any position on the surface of the earth and
oftentimes as many as seven to eight satellites. On
occasion, it has been reported that upwards of
twelve satellites are viewable, which is the reason
why one of the GPS manufacturers, namely Garmin,
produces a twelve-channel parallel receiver.
The GPS system
employs 40-watt spread-spectrum transmitters, which
results in 150 dB down uncorrelated signals at the
surface of the earth. Because of the low-power
transmission, acquiring the satellites at the
surface of the earth is not an easy problem.
Nonetheless, various GPS manufacturers have been
able to acquire the satellites in as little as ten
seconds for a so-called "hot start," which will be
defined hereinafter. The GPS satellite system at
present provides the information free to a user
anywhere in the world, as the 26 GPS satellites
provide universal coverage.
Benefits
The immediate
benefit of the utilization of global position
satellites is that the coverage is universal. While
in Argentina as few as four satellites are viewable
at one time, in the United States eight to ten
satellites are viewable at one time, making the
coverage universal, absent blocking, which will be
described below. Also, there is no infrastructure
necessary to receive the signals from the
satellites. Note, three satellites give a
two-dimensional fix, with four satellites giving a
three-dimensional fix (including altitude). At
present the U.S. government does not charge for the
operation of the GPS system, as it is recognized
that the taxpayers have paid for this system
initially in the form of funding of the Department
of Defense.
The positional
accuracy available with the global position
satellite system varies depending upon whether
selective availability, or S/A, has been switched
on or not. Selective availability is provided by
the Department of Defense to purposely degrade the
accuracy of the location information by altering
the pseudo range value and in essence skipping the
position around at random. With S/A engaged (the
normal mode of operation), GPS accuracy is within
100 meters 98% of the time and 50 meters 75% of the
time. With selective availability turned off by the
"National Command Authority" (read President
Clinton), the accuracy available is 10 meters 100%
of the time. In terms of the Report and Order, the
GPS solution satisfies the accuracy of 125 meters
67% of the time.
Both Senator Kennedy
and variety of groups have urged the President to
turn off selective availability, in part because
so-called differential GPSs which work on a
correction signal from a beacon receiver completely
cancel out the protection of selective
availability. Originally, differential beacons were
manufactured by Magnavox, which sold the business
to Leica. In point of fact, one can defeat
selective availability by buying a beacon receiver
from Leica for about $3,000 and placing it on the
White House lawn, thereby eliminating any kind of
protection that selective availability would
afford.
An unexpected
benefit of the GPS is that is works even in urban
canyons and in the presence of dense foliage. It
also provides tracking updates every second so that
the position of a mobile caller can be ascertained
in real time.
Disadvantages
As will be
appreciated, since the GPS satellites must be in
direct view of the GPS receiver, the receiver in
general will not work inside buildings, tunnels, or
around other obstacles, such as overpasses, etc.
Moreover, satellites will not be acquired in the
presence of strong electromagnetic interference, or
EMI, with long times to first fix being associated
with use in the so-called "urban canyons" of cities
and dense foliage.
It has, however,
been the experience of Tendler Cellular through
much testing that with eight or more channel
parallel receivers enough satellites are in view to
minimize the effects of the urban canyons, dense
foliage, or anything other than complete blockage
of the signal. It is noted that SnapTrack's company
indicates receipt of signals within buildings.
It is also noted
that time to first fix is significantly lengthened
in massive downpours or black cloud cover.
Moisture, in general, absorbs the microwave energy
as does snow on rooftops.
Time to first fix is
also elongated in a moving vehicle due to the
multi-path distortions involved when the physical
geometry changes as the vehicle moves. However,
once a fix has been obtained and the correlators
lock onto the signals, the 150 dB down situation
translates into a 120 dB down situation in which
most GPS receivers, when locked up and tracking, do
not lose lock very frequently.
GPS Requirements
In order to obtain a
fix and output the result, the GPS receiver
requires the Time of Day, Almanac, and Ephermis, as
well as approximate position on the surface of the
earth. The Time of Day is set by atomic clocks,
both within the satellites and upgraded through
signals from the United States Air Force in
Colorado. It is noted that Einstein's Special
Theory of Relativity applies because the time
associated with a clock on a satellite differs from
the time at the surface of the earth. If Einstein's
Theory of Relativity were not taken into account,
the location would be off by as much as 20 miles.
The satellites each
broadcast the time of day so that atomic clocks are
not necessary at the GPS receiver. Also broadcast
is the Almanac, which is the position of the
satellites within about two miles. The Almanac is
uploaded to the GPS satellites and in essence does
not change over a six-month period of time.
The third piece of
information which is essential to the obtaining of
a position is called the Ephermis, which is the
position of the satellite to within ten feet. This
position is uploaded every two hours by the United
States Air Force from Colorado. Without the
Ephermis, accuracies would be significantly
degraded. It is therefore the requirement that the
Time of Day, Almanac, and Ephermis be obtained by
the GPS receiver in order for it to do its own
location calculation and output the results.
Critical to GPS
operation is the so-called "time to first fix," or
TTFF. While this is not critical when battery life
is unlimited such as when using a car battery, it
is critical in handheld operation when, in order to
conserve battery power, the GPS is only turned on
when required. GPS architecture and technology has
improved over the past years such that at the
present date, for a "cold start" in which none of
the above information has been obtained, a time to
first fix has been reported in as few as two
minutes, and as much as 30 minutes for the
"out-of-box" situation.
A "warm start" is
one in which the Time of Day, Almanac and location
are at hand, but in which the Ephermis is stale.
This occurs if the GPS receiver has not seen the
satellites within the past two hours. Warm starts
typically now range from 30-60 seconds, an
improvement over the early GPS units of two to six
minutes.
Finally, for a "hot
start", in which the GPS has seen the satellites
within the last two hours, hot starts range from 10
to 22 seconds.
Time to first fix,
as mentioned above, is dependent upon a clear view
of the satellites, little if any cloud cover, and
no EMI interference along with no blockage.
Surprisingly, with the modern GPS receivers the
time to first fix is not significantly degraded by
cloud cover or, in fact, EMI with proper
filtration. Also, due to the eight channel or
better parallel operation, dense foliage is not the
problem originally thought.
Size of GPS Receivers
In order for GPS
receivers to be incorporated into handsets, it is
important that their size not be a limiting factor.
To date, this has been the case, with the smallest
size presently available at a reasonable price
being the Garmin 12-channel at three inches by two
inches. The original Motorola Encore unit, which is
an eight-channel device, was originally five inches
by three inches. In an effort to miniaturize these
receivers for the Department of Defense, Motorola
provided a so-called "MCM" version of the receiver,
which was only 1.25 inches by 1.25 inches. Yield
problems in the manufacture of these ultra-small
GPS receivers has increased the price, as will be
seen, to about $500. The following is a list of GPS
manufacturers and the sizes of their current
receivers.
|
-Motorola Encore:
|
8 channel
|
5" x 3"
|
|
-Garmin:
|
12 channel
|
3" x 2"
|
|
-Motorola:
|
MCM 8 channel
|
1.25" x 1.25"
|
|
-Magellan:
|
10 channel
|
3.25" x 1.7"
|
|
-Rockwell:
|
Jupiter 8 channel
|
2.8" x 1.6"
|
|
-JRC:
|
CC8-290 8 channel
|
3.4" x 1.6"
|
|
-Trimble:
|
ACE - 8 channel
|
3.25" x 1.83"
|
|
-Ashtech:
|
G8 - 8 channel
|
2.44" x 1.57"
|
As to the price of a
GPS receiver, it should be noted that while several
companies offer so-called "chip sets," the
incorporation of a chip set into a workable product
requires low noise amplifiers, a printed circuit
board with isolated ground planes and much
shielding. The receiver should also have adequate
three-pole front end filtering and accommodate
active antennas. The following table lists current
board-level GPS receivers available for OEM use.
|
-Motorola MCM:
|
$500
|
|
-JRC:
|
$90 - $100
|
|
-Motorola/Encore:
|
$90 - $110
|
|
-Garmin:
|
$110 - $125
|
|
-Ashtech/Phillips:
|
$80 - $100
|
|
-Trimble:
|
$90 - $100
|
|
-Magellan:
|
$90 - $100
|
As can be seen, the
price of the board-level GPS receivers has come
down significantly, but, due to the physical parts
on the board, including shielding, the price is
likely to remain relatively in the same ball park
of between $80 and $100 for at least the next two
years. There are quality differences between the
receivers, mainly having to do with the algorithms
that the receivers use and more importantly, the
board layout configuration which minimizes RF
interference problems while at the same time making
the receivers more sensitive and reliable. When
developed for handset use, EMI rejection and
filtering is of paramount importance in the
selection of a receiver. It has been found that
routing of antenna wires, placement of antennas,
antenna tuning, and shielding between the cell
phone motherboard and the GPS are critical. It is
also noted that antennas must be tuned for the
cases in which they are assembled, with the tuning
at 1.57542 gigahertz, requiring an offset of no
more than 5-10 megahertz. It has been found that
antenna tuning is the most critical element to
exceedingly low time to first fix ratings.
Outputs
The primary output
format for the GPS receiver was developed in the
marine community some ten years ago and is the
so-called "NMEA 0183 standard." This was developed
by the National Marine Electronics Association with
the latest revision being the version 2.1. The
majority of the GPS receivers output the
information in the 2.0 version, which has been
relatively static for a number of years. The output
sentences such as GGA, GLL and others provide a
latitude and longitude, the time of day, velocity,
course over ground, direction, satellite strength,
and other useful data. The NMEA 0183 format is
designed to be transmitted over a two-wire bus and
is extremely robust as would be necessary for
marine environments.
Recently, the output
of the GPS has been available in an RS 232 format,
which is useful in driving map displays, but
somewhat less useful in view of the fact that most
map displays are capable of being driven by the
NMEA 0183 format, mostly for historical reasons.
GPS Solutions, Interposed
Dispatcher
For a number of
GPS-based systems finding stricken individuals,
especially in mobile applications, has relied on
the interposition of an intermediate dispatch
operation between the 911 caller and the PSAP, or
Public Safety Answering Point. The first of such
systems was developed by Motorola as the Motorola
RESCU System, followed by systems such as the
CarCop system, being developed for ADT, the BART
system, which utilizes the Motorola GPS receiver,
Highway Master and ATX. These systems modem the
information relating to the location of the
vehicle, its tag number, the type of problem, and
other information directly to a third-party
dispatch operation. Upon receipt of an emergency
call, the third-party dispatch operation telephones
the nearest PSAP given the location and provides
the information to the backline of the PSAP.
Currently, according to APCO, the Association of
Public Safety Communications Officers, there are
7,000 PSAPs in the United States. According to
NENA, the National Emergency Number Association,
there are 4,800 PSAPs. One problem with the above
solutions is routing of the 911 call based on
detected location.
As a result,
contacting the appropriate PSAP is a problem. The
routing to the appropriate PSAP, while on the local
level is currently handled via local politics, is
handled by the intermediate dispatch operation type
system by calling the PSAP which is closest to the
position detected by the on-board GPS. While in
many cases this works satisfactorily, misrouting of
calls has been reported, especially where the
location is near a state line, county line or city
line. Local preferences as to the routing are in
general handled by the state police or
telecommunications unit of the particular state,
with calls being routed from a primary PSAP to a
regional PSAP based on a one-touch transfer
operation from the central or primary PSAP. It is
thus the local preference which governs to which
entity the call is transferred, rather than the
particular location of the E-911 caller.
GPS Solutions, Automatic Feed
Direct to PSAP
The first GPS-based
solution which routed the calls to the appropriate
PSAP involved NAVSYS and the Tigit system, in which
raw GPS data is modemed to a centralized processing
point within the state which determines the
location of the E-911 caller and automatically
routes the call in accordance with locally
developed rules or principles. The Tigit system
requires a GPS front end mounted on the handheld
cellular phone and requires modeming of the
information for processing to a full-up GPS
receiver at the recipient site. This system
requires that each state have infrastructure to
accommodate the incoming calls and calculate
positions of the E-911 callers as well as routing
based on the location of the call. The state of
Colorado has implemented such a system, which has
been in use for approximately two years at an
initial cost of $5 million for the statewide
infrastructure.
Most recently, a
system which provides automatic direct feed to the
PSAP is the SnapTrack system, which improves upon
the Tigit system by providing infrastructure at the
recipient site to more accurately locate the
stricken individual by providing a differential
correction due to the close location of the cell
site to the transmitting source, that being the 911
caller. Correlators within the GPS receiver may be
preset due to pre-knowledge of location, ephermis,
almanac, and time of day so that the correlators
will more quickly lock up to the GPS signal. The
GPS receiver may either be at the recipient site,
or the correlators on the handset may be preset
through communication between the recipient site
and the handset. It is reported by SnapTrack that
the SnapTrack system permits location within
buildings and even within desk drawers within
buildings, with the system having been demonstrated
at the offices of SnapTrack.
FoneFinder
Presently, the only
handset solution in which the GPS is carried by the
cell phone is provided by Tendler Cellular and is
called the FoneFinder.
The FoneFinder unit
operates by receiving satellite signals at the
handset, calculating position at the handset and
providing these signals to a speech synthesizer
which modulates the cell phone transmitter to
verbally report position in English. The salient
feature of this system is that there is no
additional infrastructure required at the cell site
or at the PSAPs to be able to obtain location
information. Additionally, the FoneFinder system
also reports the mobile identification number, or
MIN (e.g. cell phone number), at the same time it
reports the latitude and longitude. Also verbally
reported is the time since last fix, such that if
the phone is activated in a building, the phone
remembers its last fix and reports that along with
how long ago the fix was obtained so that EMTs can
ascertain the validity of the incoming data.
The advantages of such a system
are as follows:
1) FoneFinder meets the ANI and ALI requirements
now.
2) The transmission of the latitude and
longitude goes directly to the PSAP upon dialing of
911 by the FoneFinder phone.
3) This dialing is done automatically with the
press of a protected 911 button.
4) The information is sent along the voice
channel such that there is no additional
infrastructure required along the transmission path
or at the PSAP, where the information is taken down
by pencil and paper and is placed on audiotape for
future reference.
5) Inexpensive electronic maps may be provided
at the PSAP such as the Delorme Street Atlas which
is addressable by latitude and longitude at a cost
of $40 for the entire United States. A specialized
version of the Street Atlas is available from
Delorme as MapExpert for approximately $300 per
CD-ROM.
6) In addition to there being no additional
infrastructure with the FoneFinder system due to
its verbal enunciation format, the system is, as
with all GPS systems, universal, and
7) is instantly deployable with the provision of
the phone. This means that there are no changes to
cell site switches and no additional infrastructure
in order to be able to obtain the information at
the PSAP.
8) One large advantage with respect to all GPS
systems, as opposed to triangulation, is that there
is no "Big Brother is watching you" scenario.
People are found only when they want to be found
and that is with the depression of the 911 button.
9) With respect to the FoneFinder system, the
cost of the phone and the additional
GPS/antenna/PCB is on the order of $400, which
makes the entire system relatively inexpensive in
its entirety.
Revenue Streams
There are a number
of revenue streams possible with the FoneFinder
phone to not only offset the cost of the phone, but
also to provide enough significant revenue to
offset the costs of infrastructure solutions should
they be desirable for any given carrier. One
cost-recovery mechanism is a $4 per month charge
for a three-year no-cut contract. This provides
$144 which is the approximate cost of the
additional FoneFinder apparatus necessary for the
phone. The Strategis Group estimates that the
public would pay an additional $4 per month for the
location of the 911 call to be identified to the
rescuing entity.
The second revenue
stream associated with the FoneFinder phone has to
do with a National Concierge Service function, in
which upon depression of a separate button, a
dispatch agency is called to be able to answer
those types of questions which a concierge would
normally answer. Restaurants, directions, and all
manner of assistance are contemplated to be part of
this service. It has been estimated that a $2.00
per month revenue stream back to the carriers can
be associated with such a service, or $0.25 per
minute, based on either a $7.00 per month charge or
a $1.50 per minute charge.
A third revenue
stream has to do with a 911 Back-up Service which
is provided at the user's option, such that when a
call is terminated to the PSAP, an identical call
goes to a dispatch agency, which inquires as to
whether or not the individual has been helped. If
not, the dispatch service calls the PSAP on its
backline to make sure that ambulances, police,
EMTs, etc. are on the way. The revenue stream back
to the carrier to offset the cost of the handset is
approximately $20 per call out of a total $50
one-time charge for such a service.
Summary
FoneFinder provides
for ANI and ALI now. Moreover, the above revenue
streams permit the FoneFinder units to be provided
"free" to the public and permit swap-outs of the
embedded base. Regardless, currently the embedded
base is swapped out every three years, and with
there being no significant embedded base for PCS
carriers, there is a revenue stream associated with
FoneFinder phones which can be used for other
purposes. Thus, with the utilization of the
FoneFinder phone, there is a diversion of revenue
possible to fund the so-called "infrastructure
solution." As a result the FoneFinder phone can be
utilized along with triangulation to provide a
"belt and suspenders" solution. It is recognized
that neither the GPS solution nor the
infrastructure solution results in absolute
certainty of rescue. In point of fact, both types
of systems have inherent limitations. However, the
above mentioned "belt and suspenders" approach with
signaling at two different levels can increase
reliability of rescue.
Types of
Solutions