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GPS is the only functional global navigation
satellite system at the moment. It consists of 24
satellites initially, and after March 2008 of 32
satellites that are in the medium orbit around earth
and they radiate specific microwave signals (1575.42
MHz) by which GPS receivers can determine location,
speed, movement direction and height above sea level
where they are positioned. Their orbit at 20200 km
height (i.e. 26600 km in relation to the earth
center) means that each satellite makes 2 complete
rotations each sidereal day. GPS is developed by The
Ministry of USA Defense under an official name
NAVSTAR-GPS and in the last years there is its great
expansion in civil use. One of its most common
services is various vehicles types, transport
facilities and construction machines monitoring.
Although USA government in certain situations can
cause interruptions in detection of positions by GPS
system (in case of war, military interventions etc.)
American President Bill Clinton renounced this right
in 2000 in order to emphasize the intention of The
Ministry of Defense that this system is mostly
exploited for civil and peaceful purposes.
GPS system operation
GPS receiver calculates position by the messages
from GPS satellite containing very precise time
(moment) when the message is sent from the satellite
to the earth surface. Each satellite keeps sending a
message which, beside the precise time of sending
the message that we mentioned. contains precise
information on satellite orbit (so-called
ephemeris), as well as not so precise information on
the orbit of other satellites in the system
(so-called ephemeris). GPS receiver, according to
the moment when the satellite signal is received,
determines distance from each satellite. With
geometry and trigonometry use GPS receiver
determines according tot these distances its exact
position and represents it in an acceptable form to
the user, i.e. like geographical width and length.
In order to determine precise 2D position the signal
from at least 3 satellites is necessary, and in
order to determine the height above sea level, where
GPS receiver is positioned (i.e. 3D position) signal
from at least 4 satellites is necessary. Since the
total number of satellites is 32, more than 4
necessary satellites are available to GHPS receiver
at each moment. This redundancy the receiver
exploits in order to determine the most precisely
possible the position and to avoid atmosphere and
reflection influence on GPS signal propagation.
In order that GPS system functions the satellites
have to send messages with very precise moment of
sending, i.e. they must have very accurate and
precise real time clocks. That is why atomic clocks
are used for all 34 satellites placed in the orbit.
However, although atomic clocks generate very
precise time (with 1 second mistake in several
million years), due to very high speed of satellites
movement through space, and according to relativity
theory, the clocks are getting slower. This slow
down is approx. 38.6 microseconds for each day of
their operation and after some time this would
surely cause a mistake in determination of GPS
receiver position. That is why the clocks in GPS
satellites are coordinated every few days, by radio
signal, with the reference clock on the earth
surface. GPS system is for the time being the only
practical example that the relativity theory has
influence on the system operation due to the slow
down caused by high speed of satellites movement as
per the earth surface and this makes it especially
interesting for research and its use for scientific
purposes.
Geneko FOX devices
Geneko company has developed a few different devices
for vehicles satellite monitoring and supervision.
All these devices have trademark FOX. In development
of these devices Geneko has employed only local
intelligence and most recent nowadays technology. A
team of engineers, never less than 6 people, has
been working on devices and data collection and
display software for a long time now. Devices
software is written in even 3 program languages
(Java, C and Microchip assembler) so that an optimal
relations achieved between reliability, precision,
development speed and the possibility to fulfill new
desires and needs required by the market and users.
The most recent modules and processors of renowned
companies are used for hardware, like: Siemens,
Microchip and Global Sat. Dimensions of SMD
components and print layers number have surpassed a
long time ago everything that other companies in our
region have been producing and selling.
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