This document discusses a Free Space Optical (FSO) communication system and proposes addressing atmospheric attenuation for the LaserFire FSO system. It begins with an abstract and table of contents. It then provides background on FSO communication, advantages over other systems, and how FSO works. The document proposes using wavelength selection and good light sources to minimize scattering and absorption effects to compensate for atmospheric challenges over long ranges.
Comparative Investigation Ofinter-Satellite Optical Wireless Communication By...theijes
The optical wireless communication systems have got greater popularity in the previous couple of years because of its benefit over conventional radio frequency conversation structures. This paper reviews the effect of the usage of NRZ ,RZ and Gaussian pulse generator modulation codecs on the performance of the optical wireless communique (OWC) channel in terms of Quality factor aspect and Minimum BERat bit rate of 10 Gbps. It has been watched that NRZ function generator gives better execution for optical wireless association conversely with RZ and Gaussian association for different values of aperture diameters and range.
Free Space Optics is a medium with high bandwidth which has maximum data rate. Demand for
large data speed capacity has been increasing exponentially due to the massive spread of internet
So with the growing transmission rate and demand in the field of optical communication, the electronic
regeneration has become more expensive. With the introduction of power optical amplifiers the cost of
converting optical signals to electronic
combinations of hybrid amplifiers have been studied and emerged in FSO system. Their performances
have been compared on the basis of transmission distance
Comparative Investigation Ofinter-Satellite Optical Wireless Communication By...theijes
The optical wireless communication systems have got greater popularity in the previous couple of years because of its benefit over conventional radio frequency conversation structures. This paper reviews the effect of the usage of NRZ ,RZ and Gaussian pulse generator modulation codecs on the performance of the optical wireless communique (OWC) channel in terms of Quality factor aspect and Minimum BERat bit rate of 10 Gbps. It has been watched that NRZ function generator gives better execution for optical wireless association conversely with RZ and Gaussian association for different values of aperture diameters and range.
Free Space Optics is a medium with high bandwidth which has maximum data rate. Demand for
large data speed capacity has been increasing exponentially due to the massive spread of internet
So with the growing transmission rate and demand in the field of optical communication, the electronic
regeneration has become more expensive. With the introduction of power optical amplifiers the cost of
converting optical signals to electronic
combinations of hybrid amplifiers have been studied and emerged in FSO system. Their performances
have been compared on the basis of transmission distance
A STRUCTURED DEEP NEURAL NETWORK FOR DATA-DRIVEN LOCALIZATION IN HIGH FREQUEN...IJCNCJournal
Next-generation wireless networks such as 5G and 802.11ad networks will use millimeter waves operating
at 28GHz, 38GHz, or higher frequencies to deliver unprecedentedly high data rates, e.g., 10 gigabits per
second. However, millimeter waves must be used directionally with narrow beams in order to overcome the
large attenuation due to their higher frequency. To achieve high data rates in a mobile setting,
communicating nodes need to align their beams dynamically, quickly, and in high resolution. We propose a
data-driven, deep neural network (DNN) approach to provide robust localization for beam alignment,
using a lower frequency spectrum (e.g., 2.4 GHz). The proposed DNN-based localization methods use the
angle of arrival derived from phase differences in the signal received at multiple antenna arrays to infer the
location of a mobile node. Our methods differ from others that use DNNs as a black box in that the
structure of our neural network model is tailored to address difficulties associated with the domain, such as
collinearity of the mobile node with antenna arrays, fading and multipath. We show that training our
models requires a small number of sample locations, such as 30 or fewer, making the proposed methods
practical. Our specific contributions are: (1) a structured DNN approach where the neural network
topology reflects the placement of antenna arrays, (2) a simulation platform for generating training and
evaluation data sets under multiple noise models, and (3) demonstration that our structured DNN approach
improves localization under noise by up to 25% over traditional off-the-shelf DNNs, and can achieve submeter
accuracy in a real-world experiment.
ULTRA WIDE BAND TECHNOLOGY
BODY AREA NETWORKS
BW ³ 500 MHz regardless of fractional BW
UWB is a form of extremely wide spread spectrum where RF energy is spread over gigahertz of spectrum
Wider than any narrowband system by orders of magnitude
Power seen by a narrowband system is a fraction of the total UWB power
UWB signals can be designed to look like imperceptible random noise to conventional radios
The attached narrated power point presentation attempts to explain the block diagram, working principle, different architectures, advantages, disadvantages and applications of free space optical communications apart from the comparison of free space optics with fiber optics and other counterparts such as RF and metallic cables. The material will be extremely useful for KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.
A STRUCTURED DEEP NEURAL NETWORK FOR DATA-DRIVEN LOCALIZATION IN HIGH FREQUEN...IJCNCJournal
Next-generation wireless networks such as 5G and 802.11ad networks will use millimeter waves operating
at 28GHz, 38GHz, or higher frequencies to deliver unprecedentedly high data rates, e.g., 10 gigabits per
second. However, millimeter waves must be used directionally with narrow beams in order to overcome the
large attenuation due to their higher frequency. To achieve high data rates in a mobile setting,
communicating nodes need to align their beams dynamically, quickly, and in high resolution. We propose a
data-driven, deep neural network (DNN) approach to provide robust localization for beam alignment,
using a lower frequency spectrum (e.g., 2.4 GHz). The proposed DNN-based localization methods use the
angle of arrival derived from phase differences in the signal received at multiple antenna arrays to infer the
location of a mobile node. Our methods differ from others that use DNNs as a black box in that the
structure of our neural network model is tailored to address difficulties associated with the domain, such as
collinearity of the mobile node with antenna arrays, fading and multipath. We show that training our
models requires a small number of sample locations, such as 30 or fewer, making the proposed methods
practical. Our specific contributions are: (1) a structured DNN approach where the neural network
topology reflects the placement of antenna arrays, (2) a simulation platform for generating training and
evaluation data sets under multiple noise models, and (3) demonstration that our structured DNN approach
improves localization under noise by up to 25% over traditional off-the-shelf DNNs, and can achieve submeter
accuracy in a real-world experiment.
ULTRA WIDE BAND TECHNOLOGY
BODY AREA NETWORKS
BW ³ 500 MHz regardless of fractional BW
UWB is a form of extremely wide spread spectrum where RF energy is spread over gigahertz of spectrum
Wider than any narrowband system by orders of magnitude
Power seen by a narrowband system is a fraction of the total UWB power
UWB signals can be designed to look like imperceptible random noise to conventional radios
The attached narrated power point presentation attempts to explain the block diagram, working principle, different architectures, advantages, disadvantages and applications of free space optical communications apart from the comparison of free space optics with fiber optics and other counterparts such as RF and metallic cables. The material will be extremely useful for KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.
Free Space Optics (FSO) communications, also called Free Space Photonics (FSP) or Optical Wireless, refers to the transmission of modulated visible or infrared (IR) beams through the atmosphere to obtain optical communications. Like fiber, Free Space Optics (FSO) uses lasers to transmit data, but instead of enclosing the data stream in a glass fiber, it is transmitted through the air. Free Space Optics (FSO) works on the same basic principle as Infrared television remote controls, wireless keyboards
DATA RATE ANALYSIS AND COMPARING THE EFFECT OF FOG AND SNOW FOR FREE SPACE OP...IJEEE
In this paper the combined effect of specific attenuation due to Fog and Snow on FSO and RF links is considered. Optical wave attenuation due to low atmospheric visibility conditions causes a performance degradation of free space optical (FSO) communication systems.
Digital technology is evolving rapidly, leading to the
emergence of new services and applications that
are transforming the way people live, work, play and
communicate. Beyond basic web browsing, which
revolutionised the way people accessed and shared
information in the 1990s, the emerging digital
era is based on the interconnection of multiple
devices over intelligent networks, enabling users to
seamlessly interact with a variety of interoperable
services. The large-scale societal adoption and
utilisation of digital technologies is a key driver
of measurable economic, social and cultural
value, including increased productivity, a rise in
employment rates, improved security, and greater
capacity to tackle social and environmental issues.
Disruptive Technologies: International Economic Development Council (IEDC) 20...amberguitrau
As part of the 2014 IEDC Leadership Summit, Jon Roberts, TIP's Principal & Managing Director of TIP Strategies, presented an analysis of disruptive technologies and how economic developers might benefit from considering the affect that such technologies have on the labor pool, the supply chain, and social norms.
Single Mode Optical Fiber in Rof System Using DWDMIJERA Editor
Performance analysis was carried out to find the effect of crosstalk in a WDM system. Firstly, analysis of BER
was carried out without crosstalk. Then analysis of BER with crosstalk was done. Using equation for crosstalk,
number of channels was plotted using matlab. System parameters were optimized for a particular crosstalk.
Objective of the thesis work
Performance Analysis is carried out to find the effect of crosstalk due to optical cross connect in a DWDM
system considering a WDM based optical cross connect (OXC). An analysis is carried out to find the amount of
crosstalk due to OXC. The bit error rate performance degradation due to crosstalk is evaluated for OXC
parameter and number of wavelengths per fiber. The optimum parameters such as optimum number of channels
and hops are determined.
525Optimization of Inter-satellite Link (ISL) in Hybrid OFDM-IsOWC Transmissi...idescitation
Inter-satellite optical wireless communication
system (IsOWC), one of the important applications of FSO
(Free Space Optics) technology, will be deployed in space in
the near future because of providing power efficient and high
bandwidth allocation facilities unlike present microwave
satellite systems. In this paper, we have deliberated a novel
model of OFDM-IsOWC system using OPTISYSTEM T M
simulator to optimize an inter-satellite link (ISL) between
satellites with acceptable SNR and BER, which is not reported
in previous investigated work.
This report gives the viewers a broad description about using a light wave generated from a typical LED's or LASER source for an effective communication.
Optical communication, also known as optical telecommunication, is communication at a distance using light to carry information. It can be performed visually or by using electronic devices. The earliest basic forms of optical communication date back several millennia, while the earliest electrical device created to do so was the photophone, invented in 1880.
An optical communication system uses a transmitter, which encodes a message into an optical signal, a channel, which carries the signal to its destination, and a receiver, which reproduces the message from the received optical signal. When electronic equipment is not employed the 'receiver' is a person visually observing and interpreting a signal, which may be either simple (such as the presence of a beacon fire) or complex (such as lights using color codes or flashed in a Morse code sequence).
Modern communication relies on optical networking systems using optical fiber, optical amplifiers, lasers, switches, routers, and other related technologies. Free-space optical communication use lasers to transmit signals in space, while terrestrial forms are naturally limited by geography and weather. This article provides a basic introduction to different forms of optical communication.
Visual forms
Visual techniques such as smoke signals, beacon fires, hydraulic telegraphs, ship flags and semaphore lines were the earliest forms of optical communication.[1][2][3][4] Hydraulic telegraph semaphores date back to the 4th century BCE Greece. Distress flares are still used by mariners in emergencies, while lighthouses and navigation lights are used to communicate navigation hazards.
The heliograph uses a mirror to reflect sunlight to a distant observer.[5] When a signaler tilts the mirror to reflect sunlight, the distant observer sees flashes of light that can be used to transmit a prearranged signaling code. Naval ships often use signal lamps and Morse code in a similar way.
Aircraft pilots often use visual approach slope indicator (VASI) projected light systems to land safely, especially at night. Military aircraft landing on an aircraft carrier use a similar system to land correctly on a carrier deck. The coloured light system communicates the aircraft's height relative to a standard landing glideslope. As well, airport control towers still use Aldis lamps to transmit instructions to aircraft whose radios have failed.
Comprehensive investigation of coherent optical OFDM-RoF employing 16QAM exte...IJECEIAES
Given the growing need for long haul transmission that requires a high rate of data, the orthogonal frequency division multiplexing scheme (OFDM), is regarded as a technique with high potentials for high-capacity optical networks. OFDM transmits over both optical and wireless channels, with the data distributed over a huge amount of the subcarrier, and the data is distributed over a huge number of subcarriers. OFDM achieves RF signal for a long-haul transmitting by utilizing Radio over Fiber (RoF) system, which is known to produce higher orthogonality of the OFDM modulated signal designed for the wireless network. RoF systems comprise of heterogeneous networks designed through the use of wireless and optical links. The aim of this paper is to carry out an investigation of the performance of the external modulation in RoF links, while analyzing the shortcomings caused by the various elements of the optical system. The Mach–Zehnder modulator (MZM) can be applied in external modulation, and exhibits a more robust performance when implemented with the OFDM modulation technique.
1. Free Space Optical (FSO)
Communication Systems
E E 421 FinalProject
ThisdocumentcontainsinformationonFSOcommunication
as well assome of the challengesmetwhendesigningsuch
systems. Furthermore,thisdocumentproposestoaddress
the atmosphericattenuationproblemforthe Space Photonic
proprietaryLaserFire FSOcommunicationsystem.
Chad Weiss
JosephCourtright
5/2/2016
2. 1
Abstract:
Free space optical (FSO) communicationisaformof communicationthathasbeeninuse since the dawn
of earlyhumancivilization. Fire signalswereusedinordertosendalertmessagesorsignalsof warover
verylongdistanceswithverylittletime oreffortinvolved. Now,communicationhasevolvedtoits
presentdayform;i.e.a meshnetworkof interconnecteddevicesenablinglongdistance communication
overguided/unguidedmedia.
Although presentdayFSOcommunicationtechnologyallowsforeffortlesscommunication,designing
such systemsisanythingbuttrivial. Engineersare facedwiththe huge problemthatisatmospheric
attenuationwhendesigningFSOcommunicationsystems. ManufacturerslikeSpace Photonicshave
beenable toachieve wirelessoptical communicationatdistancesupto5 km but remainvulnerable to
adverse weatherconditionslike fog,rainorsnow.
Thispaperseeksto addressthe vulnerabilitiesthatSpace Photonicsface regardingFSOcommunication
systems. Furthermore,thispaperproposesasolutiontothe problemthatisatmosphericattenuation
on the LaserFire FSOcommunicationsystem(Space Photonicsproprietary). Finally,the paperwill
conclude withashort discussionabout the future of FSOcommunication.
3. 2
Table of Contents
Section Page
i.Abstract 1
ii.Contents 2
I. Introduction 3
II.Advantages 3
III.Last Mile Problem 4
IV.How itWorks 4
V.SystemSolution 5
VI.Proposal 8
VII.Future 8
VIII.WorksCited 10
List of Tables
Table Page
Table 1: MitigationTechniques 7
4. 3
Introduction
Free space optical communication(FSOCommunication) islaserbasedcommunicationsystem. Similar
to fiberopticscommunication, FSOcommunication hasaveryhighdata rate whencomparedwithradio
transmissionorcopperlines. Since complicatedcableinstallationsare unnecessaryforFSOsystems,the
systemsare much cheaper.Itisthe combinationof highspeedandlow costwhichmakesFSO
technologysouseful.
Optical signalsare one of the earliestformsof longdistance communication.In800 BC and perhaps
earlier,fire beaconswouldbe flashedbythe Romanstosendmessagesoverlongdistances. OnJune 3,
1880 AlexanderGrahamBell testedthe Photophone.The Photophonemodulatedvoice signalswitha
mirrorusedto direct sunlight.The systemhada range of about 700 feet,butfailedtoworkwhenitwas
cloudyor at night.
Free space optical communicationsystemsintheirmodernformoriginatedinthe late 60s,withthe
inventionof laser. Dr.Erhard Kube is consideredone of the founders of fibersopticnetworks.InJune of
1968, Dr. Kube published"Informationtransmissionbylightbeams throughthe atmosphere"the first
journal article proposingoptical transmissionwith lasersystems [1] [2].
Early applicationsinvolvedmilitarysatellitesandNASA.Thesespace basedapplications rallied
communicationsbetweensatellites. Because atmosphericinterference isthe primaryobstacle toFSO
systems, space providesanexcellent environmentforapplication. FSOhas beenwidelyreplacingother
formsof wirelesscommunication.Somebusinesseshave found FSOsystems tobe a suitable
replacementforEthernetnetworkingcables. Furthermore, FSOsystems are beingusedtotransmitlive
television andcell signals.Ashigherresolutionsof videobecome more commonplace,the needto
switchto higherspeedscausesgroupstorely more andmore on optical communicationsystemssuchas
free space optics.
Advantages
One of the primaryadvantagesof the FSO communicationsystem isthe highspeed atwhichthe system
transmitsdata. All FSOsystems are guaranteedtohave a data rate of at least2.5 Gbps.Some newer
systemsevenhave speedsof upto160 Gbps [1] [3]. Comparatively, radiowaves tendtofunctionata
maximumof only15Kbps. Signal modulation isusedto encode the datawithinthe waves.Dependingon
the type of modulation,the numberof bit sentina single wave canbe varied.However, datarate is
alwaysinverselyproportional tothe wavelength. FSOprimarily usesinfraredlightasa carrierwhichhas
a smallerwavelengththanRadioorTV waves.
Anotherimportantadvantage of FSOsystemsiscost.Fiberopticcablesare able to rival FSOwithspeed.
However, fiberopticscable networkscanbe expensive.Anysignificantinfrastructure of fiberoptic
cableswill require timeandmanpowertoinstall. Howeverfree space optical systems onlyrequiresa
transmitteranda receiver.Finallyradioandtelevisionwavesare regulatedandspecifictransmission
frequenciesare owned.Because infraredtransmissionsare unregulatedone wouldnotneedtoowna
sectionof the radiospectrum[3].
5. 4
The beam divergenceisproportionaltowavelength asindicatedbythe equationbelow.
θdiv =
2.44λ
Dr
FSO useswavelengthsbetween700nmand 1600nm whichissignificantlysmallerthanthe 30mm to 3m
whichisusedinRF communications.The FSOsignal propagatesata much smallerangle. The signal
takeslesspowertotransmitovera longer distances,because the powerismore focused overasmaller
area at the same distance.
Generally,wirelesstechnologyisasecurityrisk,because itpropagateswithinalargerfield.However,
FSO propagatesata muchsmallerangle thanradioor televisionwaves. Thissmall fieldof propagation
makesitnearlyimpossible totapintoa communicationwithoutalsocuttingthe communication.
Additionally,FSOsignalscannotbe detectedusing aspectrumanalyzerorRF meter.
Finally,FSOsystemsare notsubjecttointerference fromotherFSOsystems. FSOoperatesona narrow
beamunlike RF.Itusesa highlydirectionalbeamandtherefore manyFSOsystemscanoperate onthe
same frequencywithinclose proximityandnothave to worryabout interferingwitheachother.
Last Mile Problem
Since the 1960s the worldhasbuiltup a massive networkof highspeedfiberopticcablesbetweencities
and majorcenters;however,installingfiberopticcables, especiallyinurbanareas,posesmany
problems. There are several obstacles regardingthe costsandpermits required toinstall fiberoptic
cables. Inthe UnitedStatesonlyaboutfive percentof all buildings have adirectconnectiontofiber
opticsinternet.Whileatthe same time 75% of all businessesexistwithinone mileof one of these
centers[4].Many of these businessesare connectedwith slowerEthernetcables. The speedof any
connectionisonlyasfast as the slowestpart,sothese corporationsdonotreceive the speedbenefits
associatedwithfiberopticsandinsteadrelyonmuchslowerconnectionspeeds;thisisknownare the
lastmile problem. One of the majorapplications of FSOsystemsistosolve the lastmile problem,
because theymaintainahighspeedconnectionwithoutthe needforexpensive,highcostinstallations.
By creatinga FSO network, otherbusinessesinthe regioncanbenefit fromhighspeedconnections
withoutneedingtobuildupexpensive infrastructure.
How It Works
Like manyfiberopticssystemsFSOusespulsesof lighttocarrydata. However,unlikefiberoptics
systems, FSOsystemseliminate the needfora guidingmedium suchthatthe lightsignal canpass safely
fromthe transmittertothe receiver.Instead,the message isdirectedthroughthe openairbyusing
unguided line of sighttoreachthe receiver.
The data transmissioninfree space opticssystemsisdone entirelybylaser. The energyof electronsis
quantized,meaningthatitcan onlyexistatparticularevery level. A laseriscreatedbygettingan
electrontoabsorb an electriccharge movingupto a higherenergylevel. Ina shortperiodof time the
electronwill rerelease the energyasa wave of lightat a specificfrequency. The frequencycanbe found
6. 5
by the RydbergequationshownbelowwhereRisthe Rydbergconstantand n1 and n2 are propertiesof
the atom.
f = c × R(
1
n1
2
+ n2
2)
The lasercan be modulatedbycontrollingthe amountof currentusedto create the laser.By usinga
largercurrent,the laserwill be more intense.However,since thisrelationshipisnon-lineardigital
modulationispreferred [5]. The wavelength of the lightisanimportantfactorin determininghow
much isscatter or absorbedinthe atmosphere.
The lightfromthe laseristo be focusedontoa beamusingsurroundingmirrorsandlenses. Thenthe
selectionof the lenswill determine the diversionof the beam andthe laser‘sfocuslength.A more
focusedbeam hasa higherpowerconcentration andthe focuslengthcanbe carefullychosenbasedon
howfar the lightisto travel.
The unguided laserlightwillneedtobe aimed atthe receiveroverthe openair. Inthe openair the
signal can be scattered,absorbedorblocked. Once atthe receiveranotherlenswillfocusinontoa
photodetector. The selectionof the lenscandeterminethe acceptance angle intoreceiver.The
combinationof the acceptance angle andthe size of the aperture openingdeterminethe amountof
lightwhichentersthe photoreceptor. The photoreceptorthenconvertsthe signal backintoan
electronicsignal andsendsthe communication.
System Solution
The primarychallenge whendesigningaFSOcommunicationsystemisthe abilitytocompensate for
atmosphericattenuationsandatmosphericdisturbances,especiallywhendesigningforlongrange and
highspeed. Toaccomplishthis,one musttake intoaccount the effectsof atmosphericabsorption,
scatteringandturbulence,whichleadtoahigherattenuationfactor. Due tothe interactionbetween
lightandmatter,atmosphericabsorptionandscattering canbe minimizedbychoosingasource of
propagatinglightwithanappropriate wavelength. Furthermore,itisimperative tochoose agoodlight
source,suchas a laserdiode andnota poorsource such as a LED. Otherfactors that affectthe overall
performance of FSOsystemsinclude:atmosphericattenuation,scintillation,buildingalignment,
vibrations,solarinterference andline-of-sightobstructions.
In orderto minimize the scatteringandabsorptioneffectof the atmosphere hasonthe propagatinglight
signal,one mustselectthe wavelengthwisely. If the wavelengthistooshort,toomuch of the signal will
scatter duringtransmission,causingthe biterrorrate (BER) to become increasinglydetrimentaltothe
fidelityof the signal. Asforthe absorption,one mustchoose awavelengththatfallswithinthe
appropriate atmospherictransmissionwindow,i.e.the range of wavelengthvaluesthatwill minimize
absorption. The absorptionvaluesfordifferentwavelengthscanbe foundindatabaseslike HITRAN
(HighResolutionTransmission) orwithcomputerprogramslike MODTRAN (Moderate Resolution
AtmosphericTransmission). MODTRAN simulatesvariouswavelengthsof the electromagneticspectrum
as theypropagate throughthe atmosphere undersetatmospheric conditionssuchasfog,rain or snow.
7. 6
These simulationsprovidesystemengineerswiththe informationtomake decisionsaboutthe overall
design. Itisimperative thatone alsoconsidersthe probabilityandstatisticsof weatherphenomena
withinthe natural environmentwhere the FSOcommunicationwilloperate.
Aside fromatmosphericattenuation,additionallyone mustconsideratmosphericturbulence asamajor
systeminterrupt. Turbulentcells,alsoknownaseddies,ultimatelyensuesconstructive and
deconstructive interferencesonthe propagatinglightthatpassesthroughthem. Due tocorrelations
betweenpressure,temperature andindex of refraction,highertemperaturesandgreaterpressures
pocketshave a higherindex of refractionthanlowerpressure andlowertemperature pockets. Asthe
propagatinglightpassesthroughthe non-uniformmedium,constructiveordeconstructiveinterference
may occur. The resultof thisinterference isaredirectionof the propagatingsignalwhichleadsto
fluctuations inintensity,alsoknownasscintillation. Turbulence inducedbeamwanderingand
turbulence inducedbeamspreadingalsooccurs. Engineersare facedwithahuge dilemmabecause the
effectsof turbulence cannotbe avoided. Turbulence inducedbeamspreadingoccurswhenthe beam
size islargerthan the eddies,whenthe beamsizeissmallerthanthe eddiesandwhenthe beamsize is
approximatelythe same size of the eddies.
The last three thingsthatcan affectthe overall performance of FSOcommunication systemsare:Beam
divergence,ambientlightandmisalignment/buildingsway. Beamdivergence occurswhenthe length
of the linkisverylarge incomparisontothe aperture of the receiver. Divergence occursatthe receiving
endwhichleadstosome geometriclossof light. Again,thislossincreasesasthe lengthof the link
increasesanddecreasesasthe size of the receiveraperture isincreased. Ambientlightreferstothe sun
or moonlightthatinterfereswiththe signal byaddingsomethingcalledshotnoise. Shotnoise canbe
avoidedif the wavelengthisincreased. Increasingthe wavelengthreducesthe probabilitythatnoise will
be addedto the system. Lastly,there isbuildingswayormisalignment. Thiscancause serious
problems,especiallyif the beamcannotsee the receiver. Buildingswaycanoccur formany reasons.
Thermal linearexpansionof materialsinhightemperature environmentsmaycause the buildingto
expandorcontract in coldweatherenvironments. Also,tremorsandearthquakes maycause vibrations
inthe superstructure of the buildingwhichwouldultimatelyrattle the signal transmitter. Additionally,
there isa chance that highwindspeedscouldshake the FSOcommunicationsystemanddisruptthe link
also.
Systemengineershave manyobstaclestoovercome whendesigningaFSOcommunicationsystemand
despite all the effortstomaintainaviable linkbetweentwolocations,thereisalwaysthe chance that
something,whetheritisabird,a plane orSuperman,will obstructthe signal pathbyblockingthe line-
of-sight(LOS). Engineershave tocome upwitha way to mitigate the effectsof all these nuances.
Moreover,itisimperative todevelopasystemthatisadaptable toany situationimaginable;otherwise
the system’sexecution isextremelylikelytofail. Thatiswhymuch thoughtisinvolvedwhendesigninga
FSO system. FSOcommunicationsystemsare veryvulnerableandneedtobe as strongas Mother
Nature itself.
Some of the designparametersconsideredwhendesigningaFSO communicationsysteminclude the
beamdivergence,transmitterpower,operatingwavelength,andtransceiverfield-of-view (FOV). For
8. 7
Space Photonics,anadvancedtracking,acquisitionandpointingsystem(TAP) isusedtocompensate for
all the adverse weathereffectsandlongdistance challenges. The subjectof interestisthe LaserFire FSO
communicationsystem. Thissystemisahighlysecure communicationsystemthatprovides
uninterrupted,secure wirelesscommunicationwithultra-highwirelessbandwidth. Ithas an automatic
tracking,acquisitionandpointingsystemwhichallowsforsmallerspotsize transmissionbeamswhich
make it virtuallyimpossibletodetectorintercept. The LaserFire systemoperatesinthe nearinfrared
spectrumandprovidesafast continuouslinksynchronizationthatcorrectsforatmosphericturbulence
and beamfading. Forextrasecurity,if the beamisblockedforany reason,the transmitterwill
automaticallystopsendingdataas to ensure informationsecurity. The highfidelitysystemcanprovide
up to 1.0 Gbpsat distancesupto5 km; furthermore,the systemhasbeendesignedtobe compatible
withcommerciallyavailable wavelengthdivisionmultiplexing(WDM) componentsformuchhigher
aggregate bandwidths. LaserFirehasa low mass, low powerrequirementandcanbe deployedrelatively
easyinpoint-to-pointandmultimode configurations. Itusesa small,highlycollimated,infraredbeam
and GUI to assure a reliable connection.
Despite all of the greatthingsaboutLaserFire,itisstill mildlysusceptible toadverse weatherconditions
such as snow,heavyrain,fogor dust. Much researchhasbeendone totry and mitigate the effectsof
such impairments. Developmentsonthe actual physical layeraswell assome of the upper layersinthe
system,like the linkornetworklayerare pushingthe limitsforFSOcommunicationsystems.
Here is a table thatincludessome of the alreadyexistingmethodsforaddressingFSOcommunication
systemdesignchallenges:(Redreferstophysical layertechniques,bluereferstothe upperTCP layers)
Table 1: Mitigation Techniques
MitigationTechnique DesignChallenge Justification
Aperture Averaging AtmosphericTurbulence Increasingthe receiveraperture
createsa largeracceptance
angle whichcan helpaverage
out the fastfluctuations,or
scintillations,causedbyeddies,
thusreducingchannel fading.
Adaptive Optics AtmosphericTurbulence A closedloopfeedbacksystem
compensatesforthe beam
misalignmentdue toturbulence.
Adaptive Thresholding AtmosphericTurbulence Codingandmodulation
techniquescanbe usedto
simplifythe detectionof a1 or 0
at the receiver. If dispersionor
scintillationwere tooccur,
adaptive thresholdingcould
cleanup the BER of the system.
BackgroundNoise Rejection SolarInterference Spatial filters,polarizingfilters
and modulatingtechniqueswith
highpeak-to-average power
9. 8
couldeliminateanynoise
enteringthe receiver.
HybridRF/FSO AtmosphericAttenuation If weatherconditionsmake it
impossible forFSO
communication,the system
couldswitchto a backupRF.
PacketRe-transmission IncreasedBER,single-biterrors
and bursterrors
Re-transmissionprotocolssuch
as automaticrepeatrequest
(ARQ) can improve the overall
performance of the link.
ReconfigurationandRerouting LOS obstructions,faulty
equipment
Path configurationanddata
reroutingisissuedinorderto
increase the reliabilityand
availabilityof the link.
Qualityof Service Control AtmosphericAttenuation,
Distortion,Turbulence,Solar
Interference,Scattering,
Absorption,Hardware Failure,
LOS obstructions,FOV
limitations,misalignmentand
weather
Implementationof routing
protocolsandcontrol algorithms
can be usedtoimprove the
overall qualityof the service
beingprovidedbymeasuringthe
data rate,latency,delayjitter,
data loss,energyconsumption,
reliabilityandefficiency.
Proposal
Regardingall of the mitigationtechniqueslistedinTable 1onlyone addressesthe atmospheric
attenuationfactorsuch,i.e.the hybridRF/FSOsystem. UponthoroughlyinvestigatingSpace Photonics’
LaserFire,itwasdiscoveredthatthe systemwasvulnerable toadverse weatherconditionslike fog,rain
and snowwithabsolutelynobackupavailable. Therefore,itissuggestedtoimplementahybridRF/FSO
systeminorderto compensate forthe effectsof atmosphericattenuation. Increasingthe datarate will
involve researchinvestigatingthe propertiesof semi-conductormaterialsinrelationtothe fastforward
recombinationtimesaswell asmanyothersubjects. Inorderto improve the range of currentFSO
systems,largerbeamsandmore advancedtransmitterreceiverswill have tobe researchedand
developed. Since the definitionof aFSOcommunicationsystemincludesthe factthatitis an unguided
transmissionlink,one wouldhave tocreate avacuum or rarefactioninthe transmissionpath. One
mightbe able to accomplishrarefactionusingsoundwavesbut,itisstill very unlikelythatitwill actually
increase the range of the FSO system. Sounddoesn’ttravel veryfarbefore attenuatinganditisvery
difficulttocontrol. Laserpoweramplifierswouldhave tobe integratedinordertoachieve further
distances.
Future
The future for FSOcommunicationisverypromising. Itprovidesuserswithhigherbandwidths,greater
securityandincreaseddataratesfor lessmoney,lesspowerandlesspermissionwhichmakessetup
10. 9
easyand quick. The applicationsforFSOtechnology are endless;theycanbe usedindevelopingthird
worldcountries,establishingsecure communicationincombatsituations,promotingsustainabilityand
much more. The main challenge iscontrollingthe atmospherictransmissionchannel. Until weathercan
be controlledandlossymediaeradicatedfromthe transmissionchannel,FSOcommunicationsystems
will remainlimited.
11. 10
Works Cited
[1] Laseroptronics,"FSOHistoryandTechnology,"Laseroptronics,2016.[Online].Available:
http://www.laseroptronics.com/index.cfm/id/57-66.htm.[Accessed16April 2016].
[2] LightPointe,2006.[Online].Available:http://www.freespaceoptics.org/freespaceopticshome.html.
[Accessed16 April 2016].
[3] Sona Optical,"FSOGuide,"SonaOptical,[Online]. Available:
http://www.fsona.com/technology.php?sec=fso_guide. [Accessed17April 2016].
[4] P. S.J. Rajput,Director, Free SpaceOptical Communication. [Film].EandC Engg Dept.,2015.
[5] M. Carter,"LaserBeam Modulation,"October2015. [Online]. Available:
http://www.maxmcarter.com/lasrstuf/lasermodulator.html.[Accessed19April 2016].