This document summarizes the key components and working of the Global Positioning System (GPS). It discusses the three main segments of GPS - the space segment consisting of 24 satellites, the control segment which monitors the satellites, and the user segment of GPS receivers. It describes how GPS receivers use triangulation of radio signals from four satellites to determine the receiver's precise location, velocity, and time. The document also discusses some challenges with GPS signals and provides an example of how a GPS receiver could be used to navigate and find locations within a city by comparing real-time positional data to coordinates stored in a "location master" database.

1. A Review Paper on Positioning & Navigation
(Global Positioning System)
Er. Shivam Saxena
Department of Electronics & Communication Engineering
Uttar Pradesh Technical University
Lucknow, India
UPTU.nic.in
Abstract— proposed paper presents Working of Such a Navigation Technique Called
GPS Used for tracking an object With respect to its longitudinal and latitudinal axis.
This system is very useful to detect the position of an object in air, water and land.
I. INTRODUCTION
Irrespective of time, location, and weather, Global
positioning system of time provides unparalleled
range of services to commercial military and
consumer applications. Majority of these services
enables airborne, land, and sea users to know their
exact velocity, location, and time whenever and
wherever on Earth. The development and capabilities
of the GPS technology have rendered obsolete and
impractical, other traditional positioning and well-
known navigation systems and technologies such as
magnetic compasses, radio-based devices, and
chronometers among others. Global Positioning
System consists of 24 satellites, 21 of which are active
while three (3) are spares and are located at an altitude
of 10600 miles above the surface of the earth. GPS
receivers on the ground is fitted with computers that
are capable of triangulating its own sense after
obtaining bearings from the other three (3) of the four
(4) GPS satellites located in the same
horizon. GPS segments are categorized into three
distinct segments that include space segment, control
segment, and user segment. Global Positioning
systems perform an array of functions on land, in air,
or at sea. There are specific features that make GPS
systems be attractive. These includes the ability to
provide high positioning accuracies, the capability to
determine accurate time and velocity accuracies,
readily available signals in any part of the world, the
free services at no charge, and all all-weather service
delivery system. Despite the above advantages, a
number of challenges that still impede the
transmission of signals still exist within the limits of
GPS technologies. Majority of these challenges
includes errors such as inaccuracies associated with
the reported location of satellites (orbital errors),
receiver clock errors, signal multipath, and number of
visible satellites, which can affect position reading or
impede signal reception.
II. Structure of GPS
GPS segments are categorized into three distinct
segments that include control segment, user segment,
and space segment. The space segment contains at
least 24 GPS satellites that follow a specific pattern
when orbiting the earth. The satellites travel at an
approximate speed of 7,000 miles per hour, and the
satellites are spaced such that at least four GPS
satellites can send signals to a GPS receiver located

2. anywhere on earth. From each GPS receiver, coded
radio signals are sent to earth and each signal contains
particular information. The information includes the
particular satellite sending the information, the exact
position of the satellite, date and time the signal was
sent, and whether the satellite was performing
properly. Satellites use solar energy, but they are also
powered by backup batteries in the absence of solar
energy. Majority of the satellites have been built to
last for approximately 10 years after which they are
replaced. Monitoring, control, and replacement of
space satellites and GPS technology is done by the US
Department of Defense.
The control segment entails constant monitoring of
the health of satellites, the orbital configuration, and
intensity of signals. The control segment is further
subdivided into ground antennas, monitor stations,
and master control station. There are at least six
unmanned monitor stations all over the earth, each
station is in constantly receiving, and monitoring
information from GPS satellites and at the same time
relays the clock and orbital information to master
control stations (MCS). Similarly, Master Control
Stations make precise corrections of orbital and clock
information received from monitor stations. It sends
the corrected information to ground antennas. Last,
the Ground Antennas are responsible for receiving
corrected clock and orbital information from the
Master Control Station and in turn, relays the
corrected information to appropriate satellites.
Finally, the user segment of the GPS systems is made
up of GPS receivers, which are responsible for
collecting and processing signals received from GPS
satellites that are in the range. It then uses the
collected information to find and display the location,
time, speed, and altitude of the receiver. No
information is transmitted from the receiver to the
satellites.
III. WORKING OF GPS
1. The basic requirement of a satellite navigation
system like GPS is that there must be four
satellites transmitting suitably coded signal from
known position of orbital
2. Three satellites are required to provide the three
distance measurement, and the fourth to remove
receiver clock error.
3. The three satellites provide distance information
when the GPS receiver makes three
measurements of range, Ri, from the receiver to
three known points. Each distance Ri can be
thought of as the radius of a radius of a sphere
with a GPS satellite at its center.
4. A Basic principle of geometry is that “The
interaction of three distances to the receiver
defines the receiver location close to the earth”.
5. Distance from different satellites are measured
in terms of time delay incurred by the satellite
signal in travelling from satellite towards the
receiver for this measurement receiver must
have a clock that is synchronized with atomic
clock at receiver.
6. Signal from satellite travels at speed of light
(C=3×108
m/s), hence distance can be measured
by simple mathematical calculation using
formula (R=C×∆T).
7. Receiver clock have an offset relative to the GPS
satellite atomic clock. Thus when time delay is
measure than measurement will have an error of
clock offset, for this remedy C/A code can
synchronize their internal clock to GPS time
with in 170ns.
8. We need three time measurement to define the
location of receiver in three unknown coordinate
axis x, y & z. when we add the fourth time (The
receiver clock offset τ) time measurement we

3. can solve basic equation for fourth unknown.
GPS satellite in rectangular coordinate system
with its origin at the center of earth this
coordinate system is called earth centered earth
fixed (ECEF). The z-axis is directed through the
earth North Pole and x-axis pass through the line
of zero longitude on earth surface and y-axis
passes through the 900
east meridian.
9. If receiver coordinates are (Ux ,Uy, Uz) and four
satellite have coordinates (Xi, Yi, Zi) where
(i=1,2,3,4………).we can calculate the pseudo
range (PRi=Ti×C) between satellite and receiver.
the equations that relate pseudo range to time
delay are called ranging equation and given by
(X1-Ux)2
+(Y1-Uy)2
+(Z1-Uz)2
= (PR1-τC)2
(X2-Ux)2
+(Y2-Uy)2
+(Z2-Uz)2
= (PR2-τC)2
(X3-Ux)2
+(Y3-Uy)2
+(Z3-Uz)2
= (PR3-τC)2
(X4-Ux)2
+(Y4-Uy)2
+(Z4-Uz)2
= (PR4-τC)2
After calculate the coordinates of the satellite
Relative to the COE, Receiver can solve the
ranging equation to find the position.
IV. Case study of Magellan
GPS 310
Designing a Location Master to
Accommodate the mapped Data
The GPS system uses master backend file for
processing and comparing of the real time data
outputted by GPS with that of static mapped positional
coordinates design in it. It is design in such a way for
easily updating, marking, viewing of mapped
coordinates present in the location master.
For instance if say user finds a important place in the
city which is not present in the location master file,
then the user has got an option to view the current
location master file and then add a new entry on to it.
Location master maintains the location position
coordinates in the following format with the location
code acting as a primary key to use other additional
file as shown below.
ID Latitude Longitude Area City Country
1139 07807.30, 4 road saleem India
2345 00E
N
21139. 07807.2000, Shop saleem India
1789 E
N
31141. 07806.36 GH saleem India
0023 53E
N
41123. 07807.23 5Road saleem India
4533 22E
Location Master Data
Id Latitude Longitude
1 1139.2345,N 07809.3000,E
1 1139.1789,N 07809.2000,E
2 1141.0023,N 07806.3653,E
2 1139.2315,N 07803.1200,E
3 1123.2322,N 07923.5454,E
3 1125.5454,N 07803.2332,E
Location master allows the GPS System users to
perform ADD, DELET, VIEW and UPDATE on it.
Moving Compass and precise positioning
This section of the paper portrays the task done in
moving compass module of the GPS system as it holds
Important Features
1. NMEA data output for PC interface
2. DGPS ready
3. Powerful 12-parallel channel receiver
4. Displays distance, bearing, heading,
Direction, Steering Speed, Time to go,
Elevation, Satellite Directions.

4. the precise positioning and navigation across the city
with relative ease. It basically is used for precise
positioning by comparing the mapped positional
coordinates present in the location master with that of
the newly acquired positional
current location of the user while traveling across
the city. With respect to the difference it finds with the
existing mapped positional coordinates in the location
master, their current locations is found when it is
approximately zero and From the sets of NMEA data,
the GPS system filters for GLL, then for difference
exceeding but relatively of certain small margin are its
nearby places. This information computed after
acquiring continuous NMEA messages every one
second and then comparison done with that of the
mapped positional coordinates present in the location
master yields the user about all necessary information
that is required. But the accuracy of the computed fix
about the current location and nearby places, distance
for steering to destination, direction and speed etc. are
entirely dependent on the mapped positional
coordinates present in the location master and other
modules.
V. GPS RECEVIER
In developing a design of receiver, two possibility
exist-
1. Hardware- based design
- Hardware chipsets are available from a number
of suppliers including SiRF and Magellan. The
hardware chipset perform a correlation and
signal acquisition. Most chipsets use an RS-
232 interface supporting the NMEA command
set.
2. Software-based design
- Recently chipsets have become readily
available which sample and down
convert the C/A (Coarse/Acquisition)
code. The sampled can then be proceed in software
using different techniques.
VI. CONCLUSION
This system developed is a miniature of what can
be done with the usage of GPS technology, since cost
being a constraint for further advancement, it provides
the users a wide variety of applications by using a
basic GPS receiver which is costing less Thus the
implemented system can pave way for developing
other systems using high end GPS receivers with lot of
new features and advancements, so that applications
such as vehicle tracking, tourist guide software etc. can
be developed for the Users.
VII. Reference
Reference from book-
[1] Satellite communication 2nd
Edition, Timothy pratt,
Charles Bostian, Jeremy allnutt, John Wiley & Sons
[2] Global Positioning System: Signals, Measurements
and Performance By Pratap Misra and Per Enge.
[3] GPS Positioning Guide Geodetic Survey Division,
Natural Resources Canada, 1993.
[4] The Global Positioning System and GIS Michael
Kennedy, Ann Arbor Press, 1995.
[5] GPS Satellite Surveying 2nd Edition, Alfred
Leick, John Wiley & Sons, 1995
Reference from Web-
1. http://gauss.gge.unb.ca/gpsworld.com
2. https://www.watereuse.org
3. http://en.wikipedia.org
4. http://www.gpsy.com
5. http://www.magellangps.com
6. http://www.joemehaffey.com
7. http://www.rlageosystems.com