Global Positioning System (GPS) Technology in Satellite Communications
University of Diyala
College of Engineering
Department of Communications
Engineering
Satellite Communications
By:
Dr. Majidah Hameed
Majeed
Lecture # 8
CHAP
T
ER 4
GLOB
A
L POS
I
TIONI
N
G SYS
T
EM
GPS
4.
1
Introduction
At
the
beginning
of
the
1970s,
a
new
proje
c
t
was
proposed
GPS.
This
concept
pro
m
ised
to
fulfill
all
the
requirements
of
the
US
governm
e
nt,
na
m
ely
that
one
should
be able
to
deter
m
ine
ones
p
osition
a
c
curately,
at
any
point
on the e
a
rth’s
surfac
e
, at
any
time,
in
any
weather conditions.
GPS
is
the
shortened
form
of
NAVSTAR
GPS.
This
is
an
a
c
ronym
for
NAVigation
System
with Time
And
Rangi
n
g
Global
Positioning
S
y
ste
m
.
The
first satellites
were
l
aunched
into space
in
1978.
The
System
was
declared
fully
operational
in
April
1995.
The
Global
Positioning
System consists
of 24
satellites,
that circle
the
globe
once
every
12
hours,
to
provide
worldwide
position,
ti
m
e
and
velocity infor
m
ation.
GPS
m
a
kes
it p
ossi
ble
to pre
c
isely identify
lo
c
ations
on
t
he
earth by measuring
distance
from
the
satellites. G
PS
a
llows
you
to re
c
ord
or
cre
a
te
locations
from
plac
e
s
on
the
e
a
rth
a
nd
help you
n
a
vigate
to and
from those
places.
The
total
GPS
configuration
is
co
m
prised
of
three
distinct
se
g
m
ents:
.
The
S
p
a
c
e
Segment
.
Satellites
orbiting
the
e
a
rth.
.
The
Control
Seg
m
ent
.
S
tations
positioned
on
the
e
a
rth
‘
s
equator
to
control
the
satellites
.
The
User
Seg
m
ent
.
Anybody
that
rec
e
i
v
e
s
and
uses
the
GPS
s
i
gnal
a
s
shown in
fig
(4.1).
3
Fi
g
ure
4.
1
:
GPS
segm
e
nts
4.2 The
Space Se
g
ment
The
Spa
c
e
Se
g
me
nt
is
desi
g
ned
to
consist
of
24
satellite
s
orbiting
the
earth
at
approxi
m
ately
20200
km
,
Each
satellite
co
m
pletes
one
e
a
rth
orbit
every
twelve
hours
(two
orbi
t
s
every
24
hours).
At
time
of
writing
there
are
26
operat
i
onal
satellites
orbiting
the
earth
as shown in
fig
(
4.2).
Fig (4.2)GPS
S
atellite
Constellation
4
The
spa
c
e
segment
is
so
designed
that
th
e
re
will
be
a
m
in
i
m
u
m
of
4
sa
t
ellites
visible
above
a
15°
cu
t
-off
angle
at
any
p
o
int
of
the
e
a
rth’s
surface
at
any
one
time.
F
our
satellites
are
the
m
in
i
m
u
m
that
m
ust
be visible
for most
applications.
Each GPS
satellite
has several very a
c
curate
ato
m
i
c
cloc
k
s on board.
The
clocks
operate
at
a
funda
m
ental
frequ
e
ncy
of
10
.
23MH
z
.
T
his
is
used
to
generate
the
sig
n
a
l
s
that
a
re
b
r
oadcast
from
th
e
sa
t
ellite.
The
sa
t
ellites
broadcast
two
carrier
waves
constantly.
These
c
arrier
waves
are
in
the
L
-
B
a
nd (used for
radio),
and
travel
to
earth
at
the
sp
e
ed of
light.
These
c
a
r
r
ier
waves
are
deri
v
ed
from
the
funda
m
ental
frequency,
gener
a
ted
by
a
v
e
ry
pre
c
ise ato
m
i
c
clock:
Each
satel
l
ite
has
a
design
life
of
a
pprox
ima
tely
10
years,
we
i
ghs
abo
ut
2,000 po
u
nds,
and
is
a
bout 17 fe
e
t
a
c
ross with
its
solar
panels
exten
d
ed.
4.
2
The
Co
n
trol
Segment
The
Contr
ol
Segme
nt
consists of one
master
c
ontrol
station
(
MCS)
,
5
m
onitor
stations
and
4 gr
o
und
anten
n
as
distributed
A
m
on
gst
5 locations
roughly
on the
earth’s
e
qua
t
or
as
shown
in fig
(
4.
3).
fig
(
4.3
).
5
The
Contr
ol
Segme
nt
tracks as sh
o
wn
in
(fig
4.4
)
the
GPS
satellites,
updates
their
orbiting
position
and
c
alibrates
and sy
n
chroniz
e
s
their
clocks.
A
further
i
m
portant
function
is
to
dete
r
m
i
ne
the
orbit
of
e
ach
satellite
and
Predict
it’s
path
for
th
e
following
24 hours.
This
infor
m
ation
is
u
p
loaded
t
o
e
ach
satellite
a
nd su
b
sequently
br
o
adc
a
st
from
it.
This
e
nables
the
GPS
Receiver
to
know
where
each
satellite
can be
expected to be
found.
Fig
(
4.4)
The
MCS
uplinks data
to
GPS
satellites
which
includes:
•
A
l
m
anac,
which
is
a
log
of
all
GPS
satellite
positions
and
he
a
lth,
a
nd allows
a
GPS
rec
e
iver
to
identify
which
satellites
are
in
its
he
m
isp
here,
and
a
t
what
t
i
me
s.
•
An
almanac
is
like
a
schedule
telling
a
GPS
rece
i
ver
w
h
en and
where
satellites
will
be
overhea
d.
T
ran
s
m
i
tted
continuously
by
all
s
a
t
ellites,
the alm
a
nac
allows
GPS
rec
e
ivers
to
c
hoose
the
best
satellite
signals
to use
to dete
r
m
ine
position.
•
Ephe
m
eris
data
is u
nique
to
e
a
c
h
sa
t
ellite,
and
provides highly a
c
cura
t
e
satellite
posit
ion
(orbit)
infor
m
ation for
that
GPS
satellite alo
ne.
It
does
not include
inf
or
m
ation
about the
GPS
constellati
o
n
as a
whole.
Ephe
m
eris
infor
m
ation
is
also
tran
s
m
itted
as
a
part
of
e
a
ch
satellite’s
time
signal.
6
•
By
using
the
in
f
orm
a
tion
f
r
om
the GPS
satellite c
onstellation
a
l
m
anac in
conju
n
c
tion
with the
ephemeris
data
from
each
satellite,
the position
of
a
GPS
satellite
can
be very
pre
c
isely deter
m
ined for
a
given time.
•
Cloc
k
-corre
c
tion
factors
for
e
a
ch
satellite;
necessary
to
e
nsure
that
all satellites
a
r
e
operating
at
the
same pr
e
cise
t
ime
(known
as
“GPS
Ti
m
e”).
•
A
t
m
ospheric
data
(to
help
correct
m
ost
of the
distortion
c
aused
by
the
GPS
satellite
sig
nals
pa
s
sin
g
through
the
ionosphere
layer
of
th
e
at
m
osphere).
4.4 The
U
ser
S
egment
The
U
s
er Segment
co
m
prises
of
anyone using
a
GPS
rec
e
iver
to
rec
e
ive
the
GPS
sig
nal
and
deter
m
in
e
their
position
and/
or
time.
Typical
applications
within
the
user
segment
are
land
navigation
for
hikers,
vehicle
l
ocation,
surveying,
ma
rin
e
navigation,
a
e
rial
navigation,
ma
chine
con
t
rol
et
c
,
fig
(4.5)
sh
o
ws
a
kind of
GPS re
c
eiv
er
Fig
(4.5)
7
Introduced in the 1970s, the Global Positioning System (GPS) revolutionized location tracking worldwide. Consisting of 24 satellites in the space segment, GPS allows precise positioning on Earth by measuring distances from these satellites. The control segment, including master control stations and monitor stations, ensures the accuracy and functionality of the GPS system. Learn about the technology behind GPS and its essential segments in satellite communications.
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Presentation Transcript
University of Diyala College of Engineering Department of Communications Engineering Satellite Communications By: Dr. Majidah Hameed Majeed
CHAPTER 4 GLOBAL POSITIONING SYSTEM GPS 4.1Introduction At the beginning of the 1970s, a new project was proposed GPS. This concept promised to fulfill all the requirements of the US government, namely that one should be able to determine ones position accurately, at any point on the earth s surface, at any time, in any weather conditions. GPS is the shortened form of NAVSTAR GPS. This is an acronym for NAVigation System with TimeAnd Ranging Global Positioning System. The first satellites were launched into space in 1978. The System was declared fully operational inApril 1995. The Global Positioning System consists of 24 satellites, that circle the globe once every 12 hours, to provide worldwide position, time and velocity information. GPS makes it possible to precisely identify locations on the earth by measuring distance from the satellites. GPS allows you to record or create locations from places on the earth and help you navigate to and from those places. The total GPS configuration is comprised of three distinct segments: . The Space Segment . Satellites orbiting the earth. . The Control Segment . Stations positioned on the earth s equator to control the satellites . The User Segment . Anybody that receives and uses the GPS signal as shown in fig (4.1). 3
Figure 4.1: GPS segments 4.2 The Space Segment The Space Segment is designed to consist of 24 satellites orbiting the earth at approximately 20200 km , Each satellite completes one earth orbit every twelve hours (two orbits every 24 hours). At time of writing there are 26 operational satellites orbiting the earth as shown in fig (4.2). Fig (4.2)GPS Satellite Constellation 4
The space segment is so designed that there will be a minimum of 4 satellites visible above a 15 cut-off angle at any point of the earth s surface at any one time. Four satellites are the minimum that must be visible for most applications. Each GPS satellite has several very accurate atomic clocks on board. The clocks operate at a fundamental frequency of 10.23MHz. This is used to generate the signals that are broadcast from the satellite. The satellites broadcast two carrier waves constantly. These carrier waves are in the L- Band (used for radio), and travel to earth at the speed of light. These carrier waves are derived from the fundamental frequency, generated by a very precise atomic clock: Each satellite has a design life of approximately 10 years, weighs about 2,000 pounds, and is about 17 feet across with its solar panels extended. 4.2The Control Segment The Control Segment consists of one master control station ( MCS) , 5 monitor stations and 4 ground antennas distributedAmongst 5 locations roughly on the earth s equator as shown in fig ( 4.3). fig ( 4.3 ). 5
The Control Segment tracks as shown in (fig 4.4 ) the GPS satellites, updates their orbiting position and calibrates and synchronizes their clocks.Afurther important function is to determine the orbit of each satellite and Predict it s path for the following 24 hours. This information is uploaded to each satellite and subsequently broadcast from it. This enables the GPS Receiver to know where each satellite can be expected to be found. Fig ( 4.4) The MCS uplinks data to GPS satellites which includes: Almanac, which is a log of all GPS satellite positions and health, and allows a GPS receiver to identify which satellites are in its hemisphere, and at what times. An almanac is like a schedule telling a GPS receiver when and where satellites will be overhead. Transmitted continuously by all satellites, the almanac allows GPS receivers to choose the best satellite signals to use to determine position. Ephemeris data is unique to each satellite, and provides highly accurate satellite position (orbit) information for that GPS satellite alone. It does not include information about the GPS constellation as a whole. Ephemeris information is also transmitted as a part of each satellite s time signal. 6
By using the information from the GPS satellite constellation almanac in conjunction with the ephemeris data from each satellite, the position of a GPS satellite can be very precisely determined for a given time. Clock-correction factors for each satellite; necessary to ensure that all satellites are operating at the same precise time (known as GPS Time ). Atmospheric data (to help correct most of the distortion caused by the GPS satellite signals passing through the ionosphere layer of the atmosphere). 4.4 The User Segment The User Segment comprises of anyone using a GPS receiver to receive the GPS signal and determine their position and/ or time. Typical applications within the user segment are land navigation for hikers, vehicle location, surveying, marine navigation, aerial navigation, machine control etc, fig (4.5) shows a kind of GPS receiver Fig (4.5) 7
