How GPS works?

GPS(Global Positioning System) is a satellite-based navigation system. It provides time and location-based
information to a GPS receiver, located anywhere on or near the earth surface. GPS works in all weather
conditions, provided there is an unobstructed line of sight communication with 4 or more GPS satellites. GPS is
managed by the US Air Force.

AGPS operates independently of the user's internet connection or telephone signal. However, their presence
increases the effectiveness of GPS positioning. GPS was initially developed by the US government for military
purpose, but currently, anyone with a GPS receiver can receive radio signals from GPS satellites.
Note:

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" Initially when GPS was developed for military use, there were 24 GPS satellites orbiting the earth every 12
hours at a height of 20, 180 km.
" 4 GPS satellites were located in each of the 6 orbits with 60 degree orientation between each other. These
orbital planes do not rotate with respect to any star.
" Later, the number of satellites were increased to 32, to improve location accuracy.
" Localization of any GPS receiver is done through time of flight measurement.
" The greater the number of satellite in line of sight to a GPS receiver, the greater is the accuracy in determining
the position of the receiver.

How GPS works?

Any instant of time, there are at least 4 GPS satellites in line of sight to a receiver on the earth. Each of these
GPS satellites sends information about its position and the current time to the GPS receiver at fixed reqular
instants of time. This information is transmitted to the receiver in the form of signal which is then intercepted by
the receiver devices. These signals are radio signals that travel with the speed of light. The distance between a
GPS receiver and the satellite is calculated by finding the difference between the time the signal was sent fromn
GPS satellite and the time the GPS receiver received the signal.

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Once the receiver receives the signal from at least three satellites, the receiver then points its location using
trilateration process. A GPS requires at least 3 satellites to calculate 2-D position(latitude and longitude on a
map). In this case, the GPS receiver assumes that it is located at mean sea level. However, it requires at least 4
satellites to find receivers 3-D position(latitude, longitude, and altitude).
 What is trilateration?

Trilateration is the process of determining your posi tion based on the intersection of spheres. When a receiver
receivesa signal from one of the satellite, it calculates its distance from the satellite considering a 3-D sphere
with the satellite located at the center of the sphere. Once the receiver does the samne with 3 other GPS
satellites, the receiver then proceeds to find the intersection point of the 3 spheres to calculate it's location.

Once the position of a receiver is calculated, the GPS device can then easily calculate:

" Time of sunrise and sunset

" Speed
" Track
" distance to destination

of the GPS receiver.

Technical challenges face by GPS:

" Time synchronization between individual satellites and the GPS receiver
" Real time update of the exact location of the GPS satellite
" Precise measurement of time of flight
" Interference with other signals

Time synchronization:

" Each of the GPS satellites are equipped with an atomic clock to keep the time updated and accurate. In order
to update and proide precise timing on the receiver, the receiver uses the fourth GPS satellite to keeps it's
timing accurate. With the timing with the receiver and GPS satellites maintained by atomic clocks, the exact
time difference can be calculated by the receiver.
The GPS satellites are constantly managed from groundbased stations to resolve time synchronization.

Significance of ultra precision of time synchronization:

" Electromagnetic radiation propagate with the speed of light. The accuracy in position is directly proportional to
the time measurement, as speed * time = distance, therefore, even a slight deviation in time calculati on can
create huge difference in distance due to large speed of light.

Real time update of exact location of the satellite.

" This is done by monitoring the satellites from a number of widely distributed ground based system.
" Master station analyses all the measurements and transmits the actual position of each satellite.

Differential GPS[DGPS]
DGPS is an improvement over GPS that provides enhanced location accuracy
Working:
" The GPS receiver also called as the base station must be set up at a precisely known location
" The base station receiver calculates it's position based on the satellite signals and compares it's location to the
known location

" The difference between the two locations is applied to the data recorded by the GPS receiver
" Provides position accuracy in sub-meter to cm range

DGPS uses a network of fixed ground-based stations to broadcast the difference between the positions indicated
by the GPS satellite systems and the known fixed positions. These stations broadcast the difference between the
measured satellite pseudo-ranges and actual pseudo-ranges and the receiver stations may correct their pseudo
ranges by the same amount.
GPS Full Form
GPS stands for Global Positioning System. GPS isa satellite-based navigation system that allows ground users to
provide their exact location, velocity, and time 24 hours a day, in all weather conditions, all over the world. GPS
developed by the U.S. Department of Défense. It was basically designed to assist soldiers and military

vehicles but after some years it's available to anyone having a GPS receiver. GPS is a common system that most
of us are using to reach from one location to Another location.

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The GPS systems are a Combination of a network of satellites that are constantly sending coded information in
the form of radio signals. After that receiver received the signals and interprets the transmitted information from
the satellites to locate the position on earth accurately. This satellite system is congestive of 29 satellites
situated at almost 20,000 kilometers above the Earth's surface. The GPS satellites are located at 6 earth
centered orbital planes and travel at a speed of 14,000 km/hr. The GPS was first time used in combat during the
Gulf wars.

Space Segment

User Segmens
Control Segment

Global Positioning System

Functionality of GPs:
The GPS device will first establish a connection with 3 to 4 satellites. After that GPS satellite broadcasts a
message including the location of the receiver. If the GPS receiver receives a Group of messages from different
satellites to calculate the exact position using the process called triangulation.
Architecture of GPS:

GPS Architecture is basically divided into three segments.

1. Space segment: The GPS satellites fly in circular orbits at an altitude of 20000 km and with a period of 12
hours. It's powered by Solar cells. The GPS satellite Continuously orients themselves to point their solar panels
toward the sun and their antenna. Towards the earth. Orbital planes are centered on the earth. Orbits are
designed so that, at least, Six satellites are always within a line of sight from any location on the Planet. The
GPS System Consist of 24 satellites (in present 32) Established in near-circular orbits arranged in 6 orbitals
Placed at 55 Degree Inclination to the Equator at 20200 km height and 26600 km orbital Radius. The Period of
Revolution is 12 Hours. So that at least 4 Satellites are available for observations at any time throughout the
year anywhere in the World.
2. Control Segment: The second component of GPS is the Control segment. It's further divided into three sub
components.
Master Control System
o Monitor Station: The monitor station checks the exact latitude, Position, Speed, and overall health of the
orbiting satellites. The control segment ensures that the GPS and Clocks remain within acceptable limits. A
station can track up to 11 satellites at a time. This "check-up" is performed twice a day, By each station.
Ground Antennas: The ground Antennas monitor and track the satellites from horizon to horizon. They also
transmit correction information to individual satellites. Communication with the GPS satellites for command
and control purposes.

3. User Segment: The Master Control Station is located at Falcon Air Force base in Colorado Springs.
Responsible for the overall management of remote monitoring and transmission sites. Checkup is performed
twice a day, by each of the 6 stations as satellites Complete their Journey around the earth. Master Control can
reposition satellites to maintain an optimal GPS Constellation. It also includes a display for showing location
and speed information to the user. Areceiver is often described by its number of channels ( this signi fies how
many satelli tes it can monitor simultaneously). As of recent, receivers usually have between twelve and twenty
channels. There are five stations for satellites signal Receivers:
o Colorado (Main Station)
o Hawaii
o Ascension
o Diego Garcia
o Kwajalein
oCape Canaveral

GPS receiver basically consists of three components:

" An Antenna ( tuned to the frequencies tran smitted by the satellites).

" Receiver processor.
" Highly Stable Clock(Commonly a Crystal oscillator).

Usage of GPS:
There are five most uses of the GPS.

" Location:- with the help of GPS we can find the exact position of the object.
" Navigation:- we can navigate one location to another with the help of GPS.GPS technology is also useful for
Transportation Management and breathing of Ship at docks.
Tracking: with the help of GPS we can Monitor object movement like speed, distance, position.
Mapping:- GPS also helps in creating maps of the World.
" Timing- GPS also provides the estimated time for reaching destination measurement its depend on speed and
object movement.

For Example, GPS technology is also useful for Monitoring Vehicles and Persons. Tracking is useful in the
following services:

" Mass Tracking

" Ship Tracking
" Vehicle Tracking

GPS tracking is Mostly used by Police, Ambulance, Fire Department Service, and Mass delivery man. AGPS
tracking device is a portable device. GPs device allows users to monitor and track the exact location of an
object. These devices are most commonly used in Ambulance, train airplane tracking systems. While tracking
devices are used in-car navigation systems, then GPS navigation systemns show the drivers their location on a
digital map and also provide driving instructions and direction for a destination. Advanced feature GPS trackers
use GPS technology to track a vehicle's current location and trip history. We can broadcast GPS data to a
computer, smartphone, or tablet.
GSM in Wireless Communication
GSM stands for Global System for Mobile Communication. GSM is an open and digital cellular technology used
for mobile communication. It uses 4 different frequency bands of 850 MHZ, 900 MHZ, 1800 MHz and 1900 MHz.
It uses the combination of FDMA and TDMA. This article includes all the concepts of GSM architecture and how
it works.

GSM is having 4 different sizes of cells:

1. MacrO: In this size of cell, Base Station antenna is installed.

2. Micro: In this size of cell, antenna height is less than the average roof level.
3. Pico: Small cells' diameter of few meters.
4. Umbrella: It covers the shadowed (Fill the gaps between cells) regions.
Features of GSM are:

1. Supportsinternationalroanming
2. Clear voice clarity
3. Ability to support multiple handheld devices.
4. Spectral / frequency efficiency
5. Low powered handheld devices.
6. Ease of accessing network
7. International ISDN compatibility.
8. Low service cost.

9. New features and services.

GSM is nothing but a larger system which is divided into further 3 subsystems.

1. BSS: BSS stands for Base Station Subsystem. BSS handles traffic and signaling between a mobile phone and
the network switching subsystem. BSS having two components BTS and BSC.
2. NSS: NSS stands for Network and Switching Subsystem. NSS is the core network of GSM. That carried out
call and mobility management functions for mobile phone present in network. NSS have different components
like VLR, HLR and EIR.
3. OSS: 0SS stands for Operating Subsystem. OSS is a functional entity which the network operator monitor and
control the system. OMC is the part of Oss. Purpose of OSS is to offer the customer cost-effective support
for all GSM related maintenance services.

Radig Ai Abis Interface- Ainterface

BIS HLR AUC

MS
BIS

BIS

MSC OMC

Oper ational Suppart Subsysten

BIS

BIS
EIR: PSTN

BIS

Mobile Station Base Station Neteor k Suaitching

Suppose there are 3 Mobile stations which are connected with the tower and that tower is connected to BTS
through TRX, then further connected to BSC and MSC. Let's understand the functionality of different
components.

1. MS:MS stands for Mobile System. MS comprises user equipment and software needed for communication
with a mobile network. Mobile Station (MS) = Mobile Equipment(ME) + Subscriber ldentity Module (SIM). Now,
these mobile stations are connected to tower and that tower connected with BTS through TRX. TRX is a
transceiver which comprises transmitter and receiver. Transceiver has two performance of sending and
receiving.
2. BTS:BTS stands for Base Transceiver Station which facilitates wireless communication between user
equipment and a network. Every tower has BTS.

3. BSC : BSC stands for Base Station Controller. BSC has multiple BTS. You can consider the BSC as a local
exchange of your area which has multiple towers and multiple towers have BTS.

4. MSC: MSC stands for MobileSwitching Center. MSC is associated with communication switching functions
such as call setup, call release and routing. Call tracing, call forwarding all functions are performed at the MSC
level. MSC is having further components like VLR, HLR, AUC, EIR and PSTN.

" VLR:VLR stands for Visitor Location Register. VLR is a database which contains the exact location of all
mobile subscribers currently present in the service area of MSC. If you are going from one state to another
state then your entry is marked into the database of VLR.
" HLR: HLR stands for Home Location Register. HLR is a database containing pertinent data regarding
subscribers authorized to use a GSM network.. If you purchase SIM card from in the HLR. HLR is like a home
which contains all data like your ID proof, which plan you are taking, which caller tune you are using etc.
" AUC: AUC stands for Authentication Center. AUCauthenticates the mobile subscriber that wants to connect
in the network.
" EIR:EIR stands for Equipment ldentity Register. EIR is a database that keeps the record of all allowed or
banned in the network. If you are banned in the network then you can't enter the network, and you can't make
the calls.

" PSTN :PSTN stands for Public Switched Telephone Network. PSTN connects with MSC. PSTN originally a
network of fixed line analog telephone systems. Now almost entirely digital in its core network and includes
mobile and other networks as well as fixed telephones. The earlier landline phones which places at our home is
nothing but PSTN.

5.0MC: OMC stands for Operation Maintenance Center. OMC monitor and maintain the performance of each
MS, BSC and MSC within a GSM system.

Three subsystem BSS, NSS and OSS are connected with each other via some interfaces. Total three interfaces
are there:

1. Air Interface: Air interface is also known as UM interface. Interface between MS and BTS is called as UM
interface because it is mobile analog to the U interface of ISDN.
2. Abis Interface:Itis a BSS internal interface linking with BTS and BSC.
3. A interface: It provides communication between BSS and MSC.

Services of GSM:

1. Bearer services/ data services:

GSM specifies different mechanism for data transmission, The original GSM allowing for data rates of up to 9600
bits/s

Bearer services permit transparent or non transparent data transmission.

" Transparent bearer services:

Transparent bearer services only use the physical layer to transmit data. Data tran smission has a constant delay
at throughput if no transmission error occurs.

" Non-transparent bearer services:

Non-transparent bearer services use protocols of layer two and three two three to implement error correction and
flow control. (data link layer and network layer).
 2. Tele services:

Tele services are nothing but we use now as at also.

. Video calls.

" Video text and face emoji.

" short text message(SMS).

3. Supplementary services:

Supplementary services it means advanced services.

"Conference calls.
" Call waiting.
. Call forwarding.

GSM security:

" GSM offers several security using confidential information stored in the AUC and in the individual SIM.
" The SIM stores personal secret data and is protected with a pin against unauthorized use.

Advantages:
Compatibility: GSM is widely used around the world, so it is compatible with many different networks and
devices.

Security: GSM offers enhanced security features such as authentication, encryption and confidentiality, which
helps to protect the user's privacy and data.

Efficient use of bandwidth: GSM uses a time-division multiplexing (TDM) technique which enables many users to
share the same frequency channel at different times, making it an efficient use of the available bandwidth.
Roaming: GSM allows users to roam internationally and use their mobile phones in other countries that use the
sarne GSM standard.

Wide range of features: GSM supports a wide range of features, including call forwarding, call waiting, voicemail,
conference calling, and more.

Disadvantages:
Limited coverage: GSM networks may have limited coverage in some remote areas, whi ch can make it difficult for
users to make calls or access the internet.

Network congestion: GSM networks may become congested during peak hours, which can lead to dropped calls
or poor call quality.

Security vulnerabilities: Although GSM offers enhanced security features, it is still vulnerable to certain types of
attacks, such as eavesdropping and spoofng.

Data transfer speed: GSM networks offer relatively slow data transfer speeds compared to newer technologies
such as 3G and 4G.

Limited capacity: GSM networks have a limited capacity for handling large volumes of data, which can be a
disadvantage for users who require high-speed internet access or other data-intensive applications.

Hence, this is the complete architecture and functionalities of GSM components.