Communication Paradigm and Interference Katmandu...

8/14/2019 Communication Paradigm and Interference Katmandu July 2008

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PERSPECTIVES IN

COMMUNICATIONPARADIGM

&

INTERFERENCEDr.S.Pal* DFIETE, FIEEE, FNAE, FNASc

ISRO Satellite Centre,

BANGALORE - 560 017

Kathmandu, 11th July 2008

Author is Distinguished Scientist andProgramme Director, SATNAV


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Now a days:

Three things are becoming popular in themodern world Satellite Communication

Personal Communication (Mobile

Communication) Position Location using GNSS

&

There are two buzz words Communication

Information Technology


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If any thing goes wrong generalpublic blames:

Lack of communication or information

&

Technologist blame:

Electromagnetic Interference &Compatibility


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INTERFERENCE

In technological paradigminterference is defined in manyways:

As the signal density of the availablespectrum proliferates, the desiredsignal of one becomes the undesiredsignal or interference of another.

Often, the degree and nature of suchinterferences, including theirfrequency spectra or waveforms, arenot a-priori known.


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An interference could also beintentional, hostile and affecting asystem. These interferences are

not white noise. Even though special means and

technologies are now available toeliminate or mitigate, in view of

the spread of communicationsystems and development of highsensitive systems there is always a

problem.

INTERFERENCE


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Imagine: You are getting interference in your

cordless telephone, TV, radio, musicsystem.

As soon as you switch on your

microwave oven your TV channelchanges (RF to IR). Mobile makes the PChanging. A passing motor cycle causesdisturbance in radio.

In a hospital the sophisticatedmonitoring system goes hay-wirewhenever MRI equipment is switched

on. Pace maker behaves erraticallywhenever mobile is ke t in ocket.


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GPS receiver shows wrong locations Satellites looses lock in orbit. Wong &

spurious command execution

Mobile handset causes problems inaircraft

Blue Tooth and RF LAN

Causes problems in NC Machines

These are a few instances only


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Common Causes

Before you can resolve an interference

problem you must isolate the actualinterference source.

Interference originates from many sourceseven the equipment itself, your residence, orthe neighborhood.

The two most common causes of interferenceare transmitters and electrical equipment.

Communication systems that transmitsignals (transmitters) are capable ofgenerating interference; these includeamateur radios and radio and television

stations.


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Transmitter Interference

Transmitter interference is normally caused bythe actual design of the (interfered with)equipment itself.

Many manufacturers do not protect internal

wiring with adequate shielding or sufficientfiltering, so the interfered with equipment issusceptible to receiving unwanted signals interference.

The source may be as simple as a frayed wirethat connects your speakers to an amplifier.

A faulty wire can act as an antenna that willcarry interfering signals.


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Electrical Interference

Electrical interference appears on theaudio and video portion of televisionprogramming.

There are various patterns: the entirescreen may be covered with rollinghorizontal lines, bars on the TV screenor a series of diagonal dashed whitelines.

Short bursts of interference may be

caused by hair dryers, sewingmachines, electric drills, doorbelltransformers and garage door openers.

If the pattern is on continuously, it may

be caused by equipment that is in use


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If you cannot locate the interference

source in your own house, check withyour neighbours to see if they alsoreceive interference.

The house that has the worst

interference will often be the source ofthe interference.

If you can determine that the electricalinterference is not caused by any device

in your home or a neighbours homeserved by the same transformer,contact the customer servicedepartment of your local powercompany.


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Common Interference modes

& sources Collocated interferences

Remote interference

Cochannel interference Adjacent channel interference

Multipath interference[Best way to correct interference is by locating

the source of interference and mitigate.However it is not always possible to do thesame, hence tight adaptive filtering andinterference cancellation is the option].


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INTERFERENCE PROBLEMS

INTERFERENCE IS A PHENOMINA LIKE NOISEwhich one has to manage & live with.

Mathematically the received signal can be represented as

Rsignal = f( Sw, Dw, Si, Di, )

Where

Rsignal :could be C/N, S/N or Eb/No

under minimum needed ISI, BER

S : The set of parameters specifying the signalcharacteristics (MI, Base band bandwidth, Signal

type, etc.)

subscripts w - indicates wanted

I - indicates interfering

D : Set of network link parameters- eir fre uenc antenna size G/T covera e etc


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INTERFERENCE PROBLEMS

To evaluate Interference one needs:

EIRP of the source, geometrical location BW, signal characteristics, antennapattern etc.,

To evaluate the effect of interference

one needs: Signal characteristics of wanted andunwanted signals ( MI, frequency,filtering, amplification characteristics,etc.)

Antenna pattern and characteristics ofwanted and unwanted source

The overall effect gives rise tonumber of combinations and a proper

one has to be chosen.


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The Electromagnetic Spectrum


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Communication and

Information Technology


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The word `Communication' comes from Latinword `Communico' - meaning `share'. It iscommunication more than anything else which

has been responsible for the shrinking of timeand distance and with the development of spacetechnology time and distance have lost theirconventional meaning.

The other word `information' which is alsoclosely related to communications means"contents" of message. Claude Shannondefined "information" as "Reduction oUncertainty". Information is also described as

"any difference that makes a difference".Information is a notch on the spectrum withraw data on low end and knowledge/wisdom onthe high end.

The present day society is often referred asinformation society.


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In the past few decades, persons and institutions

have been progressively unsettled by the rapid pace

of social and technological changes brought about

by Communications. In earlier times the world

around us seemed more stable and major changesin values, institutions and technology evolved more

slowly. It took centuries for the Middle Ages to

become the Renaissance, yet many of us have

experienced major technological revolution in onelife time in the last century.


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Many technological reversals have been seen likethe telephone which should have been on the

wired network has become wireless, while the TVwhich was wireless now works on cable. Manyindividual spheres of working have becomealmost universal, like education has come to the

drawing room from school and colleges, sectorslike banking, medicines, hospitals etc which werelocation specific are available on net.

We are presently getting on the crest of the third

wave which is INFORMATION &COMMUNICATION REVOLUTION moreappropriately termed as `IT' -InformationTechnology.


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All the communication services like telephone,

TV, internet, VPN, Electronic Mail, Video TextService MMS, Digital TV, Cellular Mobile

Telephone (PCS), Wireless in Local Loops, Ultra

Broad Band services, extensive use of the spread

spectrum and CDMA services, Video telephones,Interactive Video and Video on demand, Tele-

education, Tele-banking, Tele-health, Tele-

shopping, Global Positioning and Timing system

etc., need either terrestrial or satellite channels toserve the user. The present scenario looks like:


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Cable TV

Television

DVD

VideoCamera

Printer

PDA

Desktop PC

Cellular

Telephone

Fax

Pager

Internet

Cellular

Internet TV

Video on

Demand

Home Banking

Internet

Telephony

Network

Computing

Videoconferencing

Smart Card

Space

World

WideWeb

Terrestrial

Credit Card

A COMMUNICATION SCENARIO

AUDIO SYSTEM


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Space Communication


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In seventies, Communication using satellites in

Geo orbit was done using large 90-95 ft diameter

antennas. Here onboard bandwidth availability

was small and the user always went through PSTNnetwork, never came in contact with the satellite.

The satellite communication was a holy cow

which could be handled and touched with lot o

care. Component technologies both for satellitesas well as ground stations was in its infancy.

SPACE COMMUNICATION


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SOME OF THE SATELLITE COMMUNICATION

SERVICES:

Telephony/TV Broadcasting/Data reception anddistribution/Direct Television broadcasting/Disaster

warning/Continuous weather monitoring/Spacecraft

Vehicle Tracking and Commanding/ Intersatellite

links/ Mail /Internet/Data mining

Position (GPS) and time determination / Moving

motor vehicle tracking etc.

* The commercial communication satellite servicesare rapidly becoming a large & global business

increasing from $11 billion in 1992 to $20 billion in

1996 and $75 billion by year 2005. (Projections have

come down to $$66.5 billion due to iridium failure

and overall slump in the market)

Th t i t t thi hi h h h d


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The most important thing which has happened

in space communication is that the ground

stations are becoming smaller and smaller day

by day reducing to pocket size calculator.


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In my opinion space communication scenario will be:

The future Telecommunication spacecraft will be developedfrom transmission in to Information Satellites (INFOSAT).

They will be given many of the properties of terrestrialtelephone exchanges and signal processing equipments and itwill be possible to integrate them directly into future globalnetworks.

The satellite platform will have multiple reconfigurableantennas/transmitters with dynamic power sharing / Receiversin various frequency ranges / large reconfigurable switchingmatrices at baseband and at RF level / intersatellite linkspermitting signals to be exchanged between satellites accordingto changing requirements / complex and efficient analog /optical / digital signal processors / New modulation technique

and multiple access techniques. It will be sufficiently broadband systems & may have even

optical space communication components.

Satellites will be autonomous.


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INTERFERENCE PROBLEMS FOR GEO STATIONARY SATELLITES

Geo Stationary Orbit: It is a natural resource & must be managed efficiently.

Concern - Over crowding of availablespectrum & slots Mitigation: - Frequency Reuse

- Clustering of satellites

- Use of high frequency bands

When all the above options are exhausted, Prioritize the services:i. Mobile services

ii. Remote area Communication

iii. Networking for data transmission

iv. Remote sensing & monitoring (Weather, Pollution etc.,)

v. Broadcast, Quasi Broadcast Services where satellites are particularlyuseful

vi. Disaster managementServices which need to be phased out:

TV, Radio, etc.

Point to point communication with heavy density traffic ( Datatransmission, telephone, internet etc.)

De-orbiting of satellites

Use of optical bands


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INTERFERENCES

INTRA SYSTEM Transponder characteristics

EMI/EMC parameters

Filtering and amplification parameters

LO & IM product management INTER SYSTEM

Geometrical separation

Frequency of operation, G/T, Modulation characteristics, eirp

etc

Antenna Patterns ( Side lobes, polarization discrimination etc.)

System characteristics ( amplification, filtering etc.,)


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Interference in Analog systems: FDM/FM channels ( Gaussian distribution)

Effect : Ghost images

Intelligible cross talks

Mitigation: Look for Protection Ratios

Interference in Digital signals C/I - Degradation of BER for most

popular modulation scheme QPSK

Mitigation: - Use of Spread spectrum & CDMA

Use of new modulation techniques

viz., GMSK

Use of coding /encryption techniques


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MOBILE PHONE & ITS BASE

STATIONS

(Sources of interference & Health Hazards)


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Difference between mobile phonebase station & radio TV transmissions

Mobile phones and radio TV transmissions inVHF/UHF bands in FM mode

Human health hazard from RF radiations ofmobile & video, TV transmissions:

YES & NO

YES : If human beings come in line oftransmission of radio TV transmission

NO: Radio TV transmissions 100 to 5000 times

higher than mobile base station are typicallyhigher transmission times (250-400 meter)

Mobile base station transmission level low .Effect is less.


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Does RF energy from mobile basestation produce ionization radiation like

x-ray?Interaction of EM energy with biologicalmaterial eg. Human cells depends uponfrequency of source:

Electric power 50/60 Hz

AM radio has frequency around 1 MHz

FM radio : 100 MHz

Microwave oven : 2450 MHzX-ray : One million MHz

Cellular phones : 800 2200 MHz


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At extremely high frequencies of x-ray

EM waves have sufficient energy tobreak chemical bonds, therebydamaging the genetic material of cellsleading to cancer or birth defects.

Mobile phones and their base stationshave much lower frequencies. Thereenergy is sufficiently low, its effect oncells is non ionizing.

It does no harm to cells like x ray.However long term effects have notbeen studies.


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Safety guide lines for mobilephone base stations

YES: There are National andInternational safety guide lines formobile phones and base sations

The guiding organizations are: Institute of Electrical and Electronics

Engineers and American National StandardInstitute (ANSI/IEEE)

The International Commission on Non-Ionizing Radiation Protection (ICNIRP)

The National Council on Radiation Protectionand Measurements (NCRP)


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RF Standards

Base stations operating in 1800-2000 MHzANSI/IEEE exposure standard for generalpublic 1.2 mW/cm.sq

For stations operating around 900 MHz

(eg, base stations for analog phones in USA)

ANSI/IEEE exposure standard for general public0.57 mW/cm sq.

Exposure standards apply to power densities

averaged over 30 minutes in case ofANSI/IEEE, NCRP and FCC standards at mobilephone frequencies.


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What are the basis of RF hazard andsafety issues for RF radiation:

Exposure to RF radiation is hazardous ifthe exposure is sufficiently intenseleading to injuries like cataracts, skinburns, deep burns, heat exhaustion andheat strokes.

No biological effects have beenconsistently shown below a certainspecific absorption rate (SAR) of a humanbeing


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Biological effect of RF energy isproportional to the rate of energyabsorption and is less effective in

frequency range of 1 to 10,000 MHz. The safety margin for RF exposure for

public envisaged 5 times more than SAR.

Demonstrated result is 2% of the level

where potentially harmful biologicaleffects have been demonstrated.

What are the basis of RF hazard andsafety issues for RF radiation:


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Mobile phone base linesafety guide lines

With proper design, mobile phone base stationantenna can meet all safety guide lines bywide margin (In India no guideline exist.

Nobody has made a model of city. In a city like

Bombay on the same building 3-4 operatorshave put up their systems)

A mobile phone base antenna at 10 metersheight and operated at maximum power levelmight produce 0.01 mW/cm-sq near theantenna site.

But in publicly accessible area will be in rangeof 0.00001 to 0.0005 mW/cm-sq which is muchbelow safety limit.


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Power density inside a building will belower by a factor of 4 to 20 thanoutside

If antennas are mounted in such a waythat public could gain access to areaswithin 8 meters (horizontal) of the

radiating surface, then it could fail tomeet the standard

If antennas are mounted on hightowers, it may meet the safety

standards



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i i f


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Mobile phone base line safety

guide lines


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RF Energy Levels in Canadian Schools

Near Mobile Phone Base Stations

less than 0.57 mW/cm-sqCanadian Standard

less than 0.00001 mW/cm-sqno antennas nearby4 and 5

0.00022 mW/cm-sqanalog base station across street3

0.0026 mW/cm-sqanalog base station on roof2

0.00016 mW/cm-sqdigital (PCS) base station across street1

Maximum RF LevelBase Station LocationSchool
http://www.mcw.edu/gcrc/cop/cell-phone-health-FAQ/toc.htmlhttp://www.mcw.edu/gcrc/cop/cell-phone-health-FAQ/toc.html


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d


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RF Energy and Cancer

Some 26 reviews & studies till2005 conclude:

Exposure to low level of RFradiation may cause subtlebiological effects. But adversehealth effects remain unproven

Localized exposures from mobile

phones may induce effects as aresult of mild heating ofsuperficial tissues close to head


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Mobile Phones and

Interference


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Mobile phones cause lots of RF interferencesand may interfere with aircraft electronics,

GPS based ITS, GPS based vehicle densitymonitoring system etc.

Use of mobile phones at petrol bunks, inaircrafts ot in ICU units of hospitals and incardiac sections is prohibited.

The intermodulation products (IMs) or passiveintermodulation products (PIM) in thetransmitted signal by mobile phones mayeffect these systems.

It may even effect a pace maker or critical ICUequipment in cardiac section of a hospitalleading to casuality.

The IMs or PIMs can also affect the functioningof VSAT satellite terminals.

Miti ti


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Mitigation

For Health Hazards Prepare a multipath & radiationmodel of the city

Do not increase power

Put the base stations at heights

Do not allow crowding of one placeon account of Base Station

Have continuous monitoring of RFsignal densities.

Miti ti


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For RFI Use of proper filters from mobile

phone base stations

Use of efficient coding andencryption

Use of bandwidth efficientmodulation techniques like QPSKand narrow band GMSK systems

Use of tight filters at the input ofvictim receiving systems

Mitigation


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Mobile phone handset safety

The risk of accident andfatality associated with the

use of mobile phones whendriving has been definitelybeen established beyond

doubt. In current state of knowledge, this

is the only known health risk, ofcourse a serious one.


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GNSS (Global Navigation SatelliteSystem)

Application & Impact of interference(The System is always susceptible to

interference)


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GNSS is the latest technology on

which mankind is likely to dependvery heavily. The system is liable toget interfered by INTENTIONAL &UN-INTENTIONAL sources ofinterference.

The system is extremely low powersystem (Typical receiver sensitivity~-130 dBm) utilizing SS processing

techniques, is vulnerable tointerference particularly the signal& code structure available tocivilian uses of the system


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Availability of GPS to civilian

users After the Korean Airlines flight (KAL

007) President Reagan (1983)

offered free use of GPS for civilianapplications.

In 1993 the constellation was

declared operational while in 1997the uninterrupted use of GPScivilian frequency was announcedwhile in May 2000 S/A was

GPS Applications & Uses


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Civil Aviation Ocean, En-Route, Terminal NPA, PA

Target 3D guidance for all terminals &precision approach-CAT-3

Maritime Operations

Vessel navigation

Ocean Coastal

Harbor and Harbor (HHA)

Inland waterway and constructed channel



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Vessel Traffic Services (VTS) Surveillance

Search & Rescue Mission

Resources Exploration

Aids to Navigation Positioning

Transportation

PTC Positive train control [Anticollision,

speed control Automatic Train Control etc.] ITS (Intelligent Transportation System)

Travel management, Fleet managementetc.



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Other Vital Applications

Power grid synchronization,Banking Time Standards, Survey,

GIS, Scientific research, earthmovement monitoring, spacecrafttracking etc.

Military target identification behindflying, Mobile Communication,Farming etc.


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Vulnerability of SystemsBased on GPS


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GPS Vulnerability

Unintentional Sources

Ionospheric interference

Radio frequency interference

L1(1575.42MHz) gets interfered fromVHF-TV (23,66,67),MSS, UWB, Over thehorizon (OTH) Radars, Cellphones

L2 (1227.6 MHz) get affected byPersonal Electronic Devices (eg. cell

phone) & Radars (Systems have co-primary allocations)

L5 (1176.45MHz) overlaps to military Joint Tactical Information Distribution

Systems


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Wide spread digital TV,

VHF,transmissions Airport,Surveillance Radars etc.

MSS (1610-1660.5 Hz)

Spurious & Harmonic Emissionfrom GSO [1525-1559 MHz) (These are unregulated by ITU.

MSS space to Earth is 1559-1567MHz)

Human factors

GPS V l bilit t I t ti l


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GPS Vulnerability to Intentionalsources

The P(Y) code has got a better accuracyintegrity & antijamming capabilitiesthan C/A code. Y code jammers affectthe C/A code. International sources

could by GPS like signal transmitters(1W to 1000 watts)

Depends on the duration, location &type of intention for causinginterference.

Main methord could

JAMMING (CW or GPS like PN-interfering

signal


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Protecting

the

GLOBAL POSITIONING SYSTEM


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WHAT HAPPENS IF THE GPS SYSTEM

IS

INTERRUPTEDOR

INTERFERE WITH


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GPS System will act as confused

Banking system, Power Grid,Cellular systems, communicationlinks and other systems using

accurate time of GPS will geteffected, may not be instantly.

Systems such as weather balloons,

uninhabited Ariel Vehicles andvarious other GPS equippedplatforms using position data maybecome unusable on the onset of

the anomal .


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Since GPS service is free and easy touse, because of the low power of the

signal interference whetherunintentional or intentional may causelarge outrages

Vulnerability cannot be completelyeliminated on account of it being a lowpower system in a crowded spectrummultiple sources of noise, no control onuse of counterfeit signature

GPS threats are proliferating productsare appearing on the market includingdesign on the internet.


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Possible Solutions

SPECTRUM MANAGEMENT & LEGALACTION

DETECTION & LOCATIONCAPABILITY

Locate interference & deployinterference location equipment

Detect anomalies, noise, loss ofaccuracy (DOP Spikes), or ifsomething is wrong with the GPS

si nal

Possible Solutions contd


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Possible Solutions contd.

GPS Modernization Programme

Higher EIRP, Longer, Robust Code andwide separation of L1,L2 & L5

JAM RESISTANT USER EQUIPMENT(Adaptive signal reception etc. withmulti-element antenna, adaptiveantenna array, polarizationdiscrimination)Amplitude, time of arrival, angle ofarrival etc

Cryptographic Authentication


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Possible Solutions contd.

Predict what the anomaly will do tothe use of GPS by gathering data,

analyzing and determiningpotential impacts

Determine how to mitigate the

anomaly: for example, by reportingsatellite errors to local receiversand locating the interferencesource

CONCLUSION


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Presently man is in a shrinking globe and

also in expanding universe with lots oftechnological surprises for thetechnological pundits.

We are becoming increasingly networked

thereby our world is growing smaller &bigger simultaneously.

Communication in all its forms isaffecting our life and so is interference.

A synergy has to be worked out intodesired-undesired intentional and un-intentional signals and interferences.

Proper identification and mitigationtechniques will be the need of the day.

CONCLUSION


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THANK YOU

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