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8/14/2019 INCEMIC Feb 2006-Interference Lecture
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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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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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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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The situation changed considerably in eighties and the
communications requirements became really nerve-
racking. Imagine the transmission reception of signals
to satellites from:A ship pitching and rolling on the high seas
An aero-plane flying at a speed of >800 kms per
hour
An orbiting space vehicle/satellite with speeds >7to 8 kms per second
An aero-plane or a ship in distress
A mountaineer/A trekker/A forest guard/An
elephant/A tiger/A bird/A turtle/a dolphinA man always on move / A motor vehicle.
If using satellites to communicate is a great marvel,
doing the same without stopping or even slowing down
is almost miracle.
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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.
In the foreseeable f t re ne eq ipments and techniq es
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In the foreseeable future new equipments and techniques
will be used in space borne technology which will extend
and improve the possibilities of satellite communications
beyond our present imaginations. Some of these we
discuss today:
The size of Geo satellite will continue to
increase . Incremental improvements are
foreseen in intelligent bus design which takescare of the spacecraft control traffic control
and particularly the thermal control to
allow the use of prime power beyond 10 to
15 KWS.
Small GEOs for smaller capacity routes will
also be used.
Emphasis will be more on using digital
bandwidth and simpler ground stations
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Greater Transmit
power and more
complex antennas onthe satellites will
make operations
possible with a large
number of very small
Earth stations.
DBS/DTH services
with 300 - 500
channels.The servicemay broadcast
multimedia &
internet .
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Phased array - orbit
re-configurable
antennas with digital
beam forming capable
of dynamically sharing
RF power, controlling
EIRPs and generating
large number of spotbeams will be used
extensively. This may
call for large
deployable antennas (>25 meter in diameter),
complex feed systems.
The similar systems
may be even needed
for ground networks.
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Use of efficient signal processors and switching
equipment.
Networking technology for the seamless integration ofhigh data rate communication satellites & terrestrial
facilities.
Direct connections between satellites (Inter satellite links).
The use of higher frequency bands (Ka band and V band)
& frequency reuse by multiple beams.
Miniaturization of electronics will enhance the launch
capabilities & reduce the cost.
High speed two way INTERNET - through VSAT
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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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INTERFERENCE PROBLEMS FOR GEO STATIONARY SATELLITES
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 PROBLEMS FOR GEO STATIONARY SATELLITES
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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INTERFERENCE PROBLEMS FOR GEO STATIONARY SATELLITES
More Tips for mitigation:
Antenna Pattern ( Tighter
pattern ) & narrow beams
(Both onboard as well as
ground)
[ E = 32 25 log10dBi ]- needs re-look
INTERFERENCE PROBLEMS FOR GEO STATIONARY
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INTERFERENCE PROBLEMS FOR GEO STATIONARYSATELLITES
More Tips for mitigation:
Development of tight filtering techniques &almost linear phase filters
Development of GMSK modulation techniques Development of adaptive antenna systems
Maximum use of digital modulationtechniques
A cautious approach towards use ofregenerative transponders.
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INTERFERENCE PROBLEMS FOR GEO STATIONARY SATELLITES
More Tips for mitigation
(contd..): Better satellite station keeping
Carrier energy dispersal
Standardized frequency band pairing Standardization of frequency translation
in satellites
Adoption of a graduated scale of singleentry interference allowances
The adoption of guidelines for themaximization of service arc
Classification and segregation of
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INTERFERENCE PROBLEMS FOR GEO STATIONARY SATELLITES
More Tips for mitigation
(contd..): Dual polar feeds
Antenna systems of good polarization
purity Additional earth station high power
amplifiers and low noise amplifierswhere access is needed to both
polarization modes. Adaptive interference suppressors if
needed to deal with rain depolarization.
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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 public
0.57 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:
bil h b li
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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.
M bil h b li
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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
Mobile phone base linesafety guide lines
M bil h b li
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Mobile phone base linesafety guide lines
M bil h b li f t
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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.html8/14/2019 INCEMIC Feb 2006-Interference Lecture
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RF E d C
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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
RF Energ and Cancer
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Canadian study indicate that theeffect of exposures from mobilephones in thousand times lower
than the recommended safe levelThe EM field of a mobile phone
does not constitute health hazard
according to present state ofscientific knowledge
RF Energy and Cancer
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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.
Mitigation
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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.
Mitigation
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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 QPSK
and narrow band GMSK systems Use of tight filters at the input of
victim 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, thisis 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 onwhich 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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GPS Applications & Uses
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GPS Applications & Uses
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
GPS Applications & Uses
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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.
GPS Applications & Uses
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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 Systems
Based 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 Vulnerability to Intentional
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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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The civil transportation infrastructureseeking the increased efficiency madepossible by GPS is developing a relianceon GPS that can lead to seriousconsequences if the service isdisrupted, and the users are not
prepared with mitigating equipment &operational procedures.
Systems and procedures to monitor,report and locate intentional &unintentional interference should beimplemented or utilized in anyapplication for which loss of GPS is nottolerable.
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WHAT HAPPENS IF THE GPS SYSTEM
IS
INTERRUPTEDOR
INTERFERE WITH
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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, polarization
discrimination)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
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GPS Interference Location System (GILS)
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GPS Interference Location System (GILS)
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Central WEB Server for GILS
Central
WEB
Server
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Some of the characteristics at each
site examined are:
Satellite in view
Satellite orientation & plane
S/N
Health status / Ephemeris data
Position estimation error
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The measured characteristics areevaluated with the bounding
parameters on an epoch (eachmeasurement) by epoch basis indetermining the error source.Sources for error could include anyor all of the following:
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User segment error (No goodcheck)
Control/space segment
Invalid data (position/Almanac
error)Clock error (position error)
SV Health problem (Almanac error)
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Environment:
Interference (S/N Check) Spoofing (S/N change rate, SV
selection)
Ionospheric error (Position error) Multipath (Position error)
If an error is reported, the server willsend an alert to local area point ofcontact.
Such a system will be useful atairports.
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 networkedthereby 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.
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THANK YOU