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

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

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

.

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