InvestigationoftheAtmosphericAttenuationFactorsinFSO...

Research ArticleInvestigation of the Atmospheric Attenuation Factors in FSOCommunication Systems Using the Taguchi Method

Pelin Demir and Gunes Yılmaz

Electrical- Electronics Engineering Uludag University Bursa 16059 Turkey

Correspondence should be addressed to Pelin Demir pelinsulegmailcom and Gunes Yılmaz gunesyuludagedutr

Received 1 November 2019 Accepted 12 February 2020 Published 12 March 2020

Academic Editor Giulio Cerullo

Copyright copy 2020 Pelin Demir and Gunes Yılmaz +is is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in anymedium provided the original work isproperly cited

In this study Mie and Rayleigh scattering in free space optics (FSO) communication systems were investigated in terms of theatmospheric attenuation Because of the movement of the Earth the communication distance and surrounding gas densities areinconsistent in each region +is change leads to atmospheric attenuation and then data losses and inefficient communication inFSO occur +erefore the density change and distance must be calculated in each communication once the data is transmitted Inthe literature it was observed that the atmospheric attenuation is regarding some FSO communication parameters such astransmission distance visibility and scatter particle size distribution the number of particles per unit volume scatter cross-sectional area and wavelength Besides in real-time communication it is necessary to update FSO parameters simultaneouslyHowever this updating process for all parameter takes a long time to adapt to a new position+is paper proposes the design of theexperiment method (Doe) to determine the severity of the FSO parameters And Taguchirsquos Doe method allows analyzing of FSOcommunication system parameters to avoid long calculation time Results show that the proposed method helps in understandingthe priorities of the parameters in FSO and reducing the updating time

1 Introduction

Recently free space optics (FSO) communication system hasbeen a preferred communication system compared to radiofrequency (RF) +e advances in technology and increasingrequirements have been contributed to the development ofFSO communication system [1]

FSO communication provides high data rate hightransmission security no frequency allocation small size andlow power requirement and easy installation [2] On the otherhand FSO communication systems have some disadvantagessuch as attenuation effects that lead to signal weakness andconsequently limitation of transmission for communication+e attenuation effect of scattering and absorption causes areduction in the performance because of affecting the laserbeam To obtain a better performance the path between thereceiver and the transmitter for FSO communication systemshould have a clean line of sight [3 4] Another attenuationeffect is regarding the turbulence which occurs due to

temperature and pressure fluctuations in the atmosphereFurthermore the weather conditions such as rain snow andfog lead to reducing the performance in the FSO commu-nication system [5] Also the scintillation depending on theturbulence limits the data transmission speed and systemperformance in long-range communication [6]

Absorption and scattering occur due to particles whichreduce both the turbulence and the optical signal and thuslack of laser beam quality occurs [7] Once Gaussian wavepropagates through the atmospheric turbulence the loss byscintillation is considered [8] Due to the dimensions ofparticle scattering types can be ranked as Rayleigh scat-tering Mie scattering and Geometry scattering [9] By usingfundamental modulation techniques simple applicationswith low budget can be realized +en usage of On-Off Key(OOK) switching modulation enables the reduction of thefading effect [10]

While the laser beam propagates through the atmo-sphere it is exposed to attenuation effects To analyse the

HindawiInternational Journal of OpticsVolume 2020 Article ID 9038053 8 pageshttpsdoiorg10115520209038053

attenuation effects many calculations are required +esecalculations are used for updating permeability equationsand this way FSO communication systems are immune tovariable atmospheric conditions However these calcula-tions lead to time losses for data transmission In this paperTaguchirsquos experimental method is proposed to minimize thetime losses and therefore enhance the performance of FSOcommunication systems and suppress the attenuationeffects

2 Atmospheric Properties

+e atmosphere has many layers +ese layers consist ofdifferent and variable gases Figure 1 shows the gasesrsquo dis-tribution in the atmospheric layers [11] +e tropospherelayer shown in Figure 1 is about 15ndash20 km from the Earthand consists of the most intense gases because it is the closestlayer to Earth

In general the percentages of gases in the atmosphere areas follows 78 nitrogen 20 oxygen 9 argon and 004other gases (0004 00018 Ne 0000524 He 000018000055 0000114 Kr) [12] Furthermore each gas in theatmosphere has a different radius size Due to the size ofradius the laser beam is affected in a different way wheninteracting with different gases +e laser beam is exposed tomostly nitrogen and oxygen during propagating in the at-mosphere +e refractive indices and diameters of thesegases for 1064 nm are given in Table 1 Gases such as NeCH4 and Kr do not interact with the wavelength of 1064 nmHowever these gases are affected by different wavelengths

21 Atmospheric Attenuation According to the law of Beerattenuation of laser beam propagation is given as

T I(z)

I0 exp(minus cz) (1)

where T is the permeability c is the attenuation coefficientand z is the transmission length+e refractive index of gasesat a certain wavelength consists of two parts which are realand virtual (r rprime+ rPrime) In the near infrared region (NIR) thevirtual part of the refractive index is small enough so as to beneglected +e virtual part of the refractive index definesscattering +erefore the attenuation due to the scatteringcan be considered +is way the attenuation coefficient forscattering is shown as

c βm + βa (2)

where β is the scattering coefficient and indices of m and arepresent the molecule and aerosol respectively Each co-efficient in (2) depends on the wavelength of the laseremission [13] +ere is no energy loss in case of scatteringhowever the laser beam may be directed to any differentlocation So this situation causes a decrease in beam in-tensity for long-distance transmissions +e physical size ofthe scatterers is a factor that determines scattering

Air molecules lead to Rayleigh scattering in angstromsizes On the other hand aerosols lead to Mie scatteringbecause of scattering the light +e German meteorologist

Gustav Mie found that electromagnetic waves are scatteredby the small dielectric spheres It is calledMie scattering [14]

Electrons which involve the formation of chemicalbonds are called bonding electrons Electronic displacementoccurs when the electrons move towards the other side of themolecule Once the bonding electrons are displaced Ray-leigh scattering occurs +e harmonic field stimulates thedipole in the molecule +erefore polarity of dipole deter-mines where to move them +e propagation is absorbedand the stimulated dipole oscillates at the same frequencywith the laser beam +e radiated energy occurs by thescattering light When a beam collides with a small particlethe area where the particle interacts with the beam is calledthe cross-sectional area Total scattered cross-sectional areais given as [14]

σ 8π3 n2 minus 1( 1113857

2

3N2λ4 (3)

where n is the refractive index and N is the scattered mo-lecular density Besides aerosol scattering is known as Miescattering which is shown as

βa 391V

λ550 nm

1113888 1113889

ρ

(4)

where V is the visibility λ is the wavelength and ρ is the sizedistribution of the scattering particles

Different weather conditions can be specified based ontheir visibility range values According to Kruse model therelationship between the size distribution and visibility isdetermined using [15]

Exosphere

Thermosphere

Mesosphere

Stratosphere

Troposphere

Figure 1 Atmospheric layers with gas distribution

2 International Journal of Optics

p

16 Vgt 50 km

13 6 kmltVlt 50 km

0585V13 Vlt 6 km

⎛⎜⎜⎜⎜⎜⎜⎜⎜⎜⎝⎞⎟⎟⎟⎟⎟⎟⎟⎟⎟⎠ (5)

Rayleigh scattering is also known as molecular scatter-ing For a single molecule it is given as

βm 0827NpApλminus 4

(6)

where Np is the number of particles per unit volume and Ap

is the cross-sectional area of scattering Also Ap is given as[16]

Ap πr2 (7)

where r is the radius of the mass for a molecule In theatmosphere according to the geological location the particlesize distribution and concentration vary Visibility must alsobe taken into account when calculating aerosol scatteringSo they must be known while calculating the aerosolscattering [17]

Also the aerosol size distribution depends on relativehumidity and wind speed Humidity affects the active re-fractive index of the aerosol particle In this case two dif-ferent particle distributions are taken into account ascontinental and maritime air In hazy weather conditionswith 5 km visibility absorption and extinction coefficientsare increased by 487 multiplier factors [18]

3 Taguchi Optimization Method

Taguchi method is useful in determining the optimumcombination results for any system [19] +is method wasfirstly used in quality engineering and product designstudies and today it is used in various studies which aretrying to reach the result by doing less experimentation oranalyses [20] +e difference between the Taguchi methodand other statistical methods is that it allows groupingcontrolled and uncontrollable parameters and therefore itprovides analyzing for multiple parameters in the case ofmore than two levels Furthermore it minimizes the vari-ance in the target area while bringing the average of per-formance value to the desired level [21]+e Taguchi methodis based on the orthogonal arrays [22] And it is widely usedto design experimental studies +e optimal number of

experiments can be achieved by Taguchi optimizationmethod and the control parameters are determined by usingorthogonal arrays (OA) [23 24] Figure 2 shows the flowchart for Taguchirsquos method which consists of five steps ingeneral approach +ese steps are concerning defining theparameters and its level of system selection of orthogonalarray creating your experimental table calculating the resultand ranking priority of parameters and finally eliminatingthe unnecessary parameters with low severity

Each system or embodiment consists of some parameterswhich have some values+e value of parameter is called levelin Taguchirsquos method +e right design of experiment must bedefined for a suitable solution +e selection matrix inTaguchirsquos method is given in Table 2 According to thenumber of parameters and the level of each parameter asuitable experiment table can be selected by using Table 2 [23]

31 eoretical Method In the theoretical study wave-lengths of 850 nm and 1064 nm were used for analysisVisibility value was used as 6 km in calculations For eachwavelength Mie and Rayleigh attenuation were calculatedby using (6) and (7) and Np and Ap are calculated for eachgas as shown in Table 3

While calculating the Ap value r parameter is obtained[26]

r r0A13

(8)

where r is the radius of the nucleus of mass number A andthe parameter r0 is constant and its value is 12 times 10minus 15 m

Considering Table 3 the calculated Rayleigh scatteringvalues for 850 nm and 1064 nm are shown in Table 4

As shown in Table 4 the scattering values were calcu-lated for each gas in the troposphere as the value of visibilityis to be considered 6 km for the troposphere +e ratio of gasand diversity of gas are more at the troposphere +escattering behaviour at two different wavelengths was ob-served for wavelength of 850 nm and 1064 nm Rayleighscattering occurs more under the same conditions which is850 nm wavelength

+e shorter end of the visible spectrum is closer tooxygen and nitrogen gases as an atom and they interactmore and scatter to a higher degree +erefore a shorterwavelength of light scatters more than longer wavelengths

Table 1 Refractive indices and diameters of atmospheric gases

Gas Refractive index (λ 850 nm) Refractive index (λ1064 nm) Refractive index (λ1550 nm) Diameter (pm)N2 100029596 10002952 100029442 112O2 100024932 10002484 100024763 96Ar 100027950 10002820 100027808 142CO2 100044397 10004419 100043822 23242Ne 100006610 (05462 μm) 100006610 (05462 μm) 100006610 (05462 μm) 76He 1000034787 100003475 1000034708 62CH4 10004365 (168 μm) 10004365 (168 μm) 10004365 (168 μm) 398H2 100013718 10001367 100013617 102Kr 10004266 (06234 μm) 10004266 (06234 μm) 10004266 (06234 μm) 170H2O 13290 13260 13180 942

International Journal of Optics 3

As shown in Table 5 the Mie scattering values arecalculated by (4) with different visibilities

+e result of the obtained values can be evaluated with thegraphs as given in Figures 3 and 4 Figure 3 shows the at-tenuation values of each gas molecule for 850 nm at a distanceof 6 km from the Earth It is seen that the nitrogen value hasthe highest value and then comes oxygen +e attenuationrates of other gases are close to each other Figure 4 shows the

attenuation values for 1064nm Oxygen and argon were theprominent gas molecules at 1064 nm with respect to 850 nm

As a result total attenuation is increased at largerwavelengths in the case of low-visibility weather conditions

Table 2 Taguchi orthogonal array selection matrix [23]

Parameter number4 5 6 7 8 9 10 11 12 13 14 15

Level number2 L8 L8 L8 L8 L12 L12 L12 L12 L16 L16 L16 L163 L9 L18 L18 L18 L18 L27 L27 L27 L27 L27 L36 L364 Lprime16 Lprime16 Lprime32 Lprime32 Lprime32 Lprime32 Lprime32

Table 3 Number of gas molecules in the atmosphere

Gas Number of molecules per unitvolume Np

Cross-section areaAp

N2 33 times 1021 4162 times 10minus 23

O2 88 times 1020 4441 times 10minus 23

Ar 42 times 1019 5178 times 10minus 23

CO2 17 times 1018 5621 times 10minus 23

Ne 81 times 1015 3318 times 10minus 23

He 22 times 1017 1138 times 10minus 23

CH4 81 times 1015 2870 times 10minus 23

H2 22 times 1015 7172 times 10minus 24

Kr 45 times 1015 8593 times 10minus 23

Table 4 Rayleigh scattering values for 850 nm and 1064 nm

Gas 850 nm Rayleigh scattering 1064 nm Rayleigh scatteringN2 02169 00886O2 00617 002521Ar 3435 times 10minus 3 14010 times 10minus 3

CO2 1509310minus 4 61655 times 10minus 5

Ne 424 times 10minus 7 17340 times 10minus 7

He 39546 times 10minus 6 16153 times 10minus 6

CH4 36720 times 10minus 7 1499 times 10minus 7

H2 24923 times 10minus 8 10180 times 10minus 8

Kr 61079 times 10minus 7 24949 times 10minus 7

Table 5 Mie scattering values for 850 nm and 1064 nm

Visibility (km) 850 nm Mie scattering 1064 nm Mie scatteringVgt 50 04724 426ltV (15)lt50 02243 13855Vlt 6 00506 04784

Define number ofparameters and levels

Select a suitableorthogonal array

Create design ofexperiment table

Reduceoptimization range

End

Definingcriteriamet

No

Yes

Calculate results and ranking of

parameters

Figure 2 General Taguchirsquos method approach [25]


(V 6 km) Besides total attenuation for larger wavelengthincreases in the case of high visibility clean air conditions(V 50 km)

Once any visibility condition is concerned it is un-derstood that increasing of the total attenuation is inde-pendent from the wave length

By using a different wavelength the total attenuationvalue of N2 at 1550 nm is sim206 and this value is greater thanthe attenuation values for the wavelengths of 980 nm and1064 nm +e selection of wavelength happens according tothe material which produces laser 1550 nm 1064 nm and980 nm wavelengths are obtained by VCSEL solid statepulsed type laser Nd YAG type laser and InGaAs type laserrespectively +e data rate of the 1550 nm and 1064 nmwavelength laser is about 10Gbps and for 980 nm it is 1-2Gbps [27]

+e data rate of wavelength with maximum attenuation ishigher than the other wavelengths However this requires thedetermination of the severity for the attenuation parameters

Because the attenuation at 1550 nm leads to transmit-ting more power to overcome the attenuation due to fogsmoke cloud and so on In this case the severity for theparameters for attenuation must be determined by usingTaguchi method

32 Taguchirsquos Design of Experiment in Free Space OpticsCommunication Firstly the orthogonal array has beenselected and then the other step is to determine the inputparameters Response table is formed by the values obtainedas a result of the iteration When the experiments are carriedout and the iteration is completed a test chart is created withthe results obtained Figure 5 shows the diagram of theproposed method

In this section lower and upper limits were determinedfor the six parameters related to attenuation values due toRayleigh andMie scattering which are atmospheric effects infree space optics communication as shown in Tables 4 and 5+e values of the two levels for upper and lower limits aregiven in Table 6

+e selected parameters are directly related to the at-tenuation coefficient

Considering the six parameters and two levels for at-mospheric attenuation appropriate orthogonal array is L8experiments in Table 2 Experimental design chart for L8 iscreated by using Table 6 and orthogonal sequence selectionmatrix of Taguchi method is shown in Table 7

4 Results and Discussion

+is paper proposes to use Taguchirsquos design of experimentalmethod In this context six parameters and their two levels(considering the minimum and maximum values) wereconsidered to define orthogonal experiment array which issuitable for L8 shown in Table 2 So L8 orthogonal array haseight experiments shown in Table 7 By using the attenuationequations for the atmosphere Rayleigh and Mie the ex-periments (calculations) shown in Table 7 were performed+e obtained results for attenuation are shown in Table 8

Another step is the calculation of the signal noise ratio(SNR) in Taguchirsquos method SNR values are calculated for alllevels of defined parameters so as to get absolute delta be-tween minimum and maximum SNR values for these pa-rameter levels +is way the parameters effect on theattenuation can be ranked according to their priority levels+erefore it allows having a chance to eliminate an un-necessary parameter or a parameter with low effect on at-tenuation SNR values for the obtained values are shown in

005

0650

024

005

0653

9

005

0650

36

005

0650

4

026

755

011

235

005

4085

005

08

005

0656

1

0

01

02

03

H2 He CH4 Ne N2 O2 Ar CO2 Kr

850n

m at

tenu

atio

nva

lues

Atmospheric gases

Figure 3 Attenuation values for 850 nm0

4784

047

84

047

84

047

846

047

84

056

7

050

361

047

98

047

84

042

047

052

057


1064

nm at

tenu

atio

nva

lues

Atmospheric gases

Figure 4 Attenuation values for 1064 nm


Table 8 Absolute delta values between minimum andmaximum parameter levels and parameters ranking aregiven in Table 9

According to Table 9 the scatter cross-sectional area isthe most important parameter Visibility and scatter particlesize distribution then follow

+e analysis result shows that the most important pa-rameter is the scatter cross-sectional area Ap which directlyaffects Rayleigh scattering +e effect of Rayleigh scatteringto the attenuation parameter appears to be bigger than Mie

Table 6 Free space optics communication scattering and absorption parameters experimental design levels

Parameters Level I Level IITransmission distance (L) 1 km 12 kmVisibility (V) 6 km 50 kmScatter particle size distribution (p) 13 16Number of particles per unit volume (Np) 22 times 1015 (H2) 33 times 1021 (N2)Scatter cross-sectional area (Ap) 7172 times 10minus 24 8593 times 10minus 23

Wavelength (λ) 850 nm 1064 nm

Table 7 Free space optics attenuation experiment design chart for L8

Experiments Transmissiondistance (km)

Visibility(km)

Scatter particlesize distribution

Number of particlesper unit volume Scatter cross- sectional area Wavelength (nm)

1 1 6 13 22 times 1015 (H2) 7172 times 10minus 24 8502 1 6 13 33 times 1021 (N2) 8593 times 10minus 23 10643 1 50 16 22 times 1015 (H2) 7172 times 10minus 24 10644 1 50 16 33 times 1021 (N2) 8593 times 10minus 23 8505 12 6 16 22 times 1015 (H2) 8593 times 10minus 23 8506 12 6 16 33 times 1021 (N2) 7172 times 10minus 24 10647 12 50 13 22 times 1015 (H2) 8593 times 10minus 23 10648 12 50 13 33 times 1021 (N2) 7172 times 10minus 24 850

Define the each gas ratio in atmospheric layers

Calculate the cross-sectionarea value of each gas

Calculate the total attenuation values

Calculate Rayleigh and Mie scattering for 850nmand 1064nm wavelength

Apply the Taguchi method with the selectedparameters

Determine the importance of the parameters at theend of the analysis

Figure 5 +e diagram of the proposed method

Table 8 Results using Taguchi analysis

Experiments Results1 03192 330E minus 803 167E minus 064 100E minus 1505 01516 253E minus 897 01098 100E minus 100


scattering +is analysis may indicate that Mie scattering canbe neglected for a satellite placed on the troposphere

Considering the wavelength together with visibility itcan be neglected in low visibility In the low-visibility forcommunication at the troposphere distance compared tothe selected wavelengths such as 850 nm 1064 nm and1550 nm the best result is taken for 850 nm

While designing FSO communication system atmo-spheric events can be estimated and the wavelength to betransmitted can be selected +us more efficient and fastcommunication will be ensured

Under these conditions the number of experiments isreduced by using the selected ldquosixrdquo parameters Taguchimethod allows the elimination of the parameters with lowimportance and therefore the approximate result would beobtained in a shorter time

5 Conclusions

According to the analysis the scattering cross-sectional areaof the gas particles directly affects the attenuation

+e results of analysis show that N2 gases at 850 nmwavelength and O2 gases at 1064 nm wavelength affectsignificantly the scattering +e reason for these obtainedfindings depends on the particle dimension of N2 and O2gases +erefore Taguchi analysis was used for investigatingthe effect of these gases on the scattering

Taguchi method allowed the reduction of the number ofexperiments and saving analysis time +e Taguchi methodhas shown that eight experiments for assessment are sat-isfactory compared to 64 experiments in the case of sixparameters and two levels

Due to the movement of the Earth the communicationdistance and surrounding gas densities are changeable in eachregion From this change the density change and distanceshould be calculated in each communication when the data istransmitted +ese calculations lead to too many experimentsto determine the desired parameters Taguchi method reducesthe number of experiments by calculating the most importantparameters and thus saves time Taguchi method for FSOsystems was found to be a useful method for analysis

Data Availability

+e data used to support the findings of this study are in-cluded within the article

Conflicts of Interest

+e authors declare that they have no conflicts of interest

References

[1] A Malik and P Singh ldquoFree space optics current applicationsand future challengesrdquo International Journal of Opticsvol 2015 Article ID 945483 7 pages 2015

[2] M H Mahdieh and M Pournoury ldquoAtmospheric turbulenceand numerical evaluation of bit error rate (BER) in free-spacecommunicationrdquo Optics amp Laser Technology vol 42 no 1pp 55ndash60 2010

[3] A K Majumdar and J C Ricklin Free Space Laser Com-munications John Wiley and Sons New York NY USA2008

[4] G Alnwaimi H Boujemaa and K Arshad ldquoOptimal packetlength for free-space optical communications with averageSNR feedback channelrdquo Journal of Computer Networks andCommunications vol 2019 Article ID 4703284 8 pages 2019

[5] H Yuksel Studies of the effects of atmospheric turbulence onfree space optical communications Department of Electricaland Computer Engineering University of Maryland CollegePark MD USA PhD dissertation 2005

[6] S Navidpour M Uysal and M Kavehrad ldquoBER performanceof free-space optical transmission with spatial diversityrdquo IEEETransactions on Wireless Communications vol 6 no 8pp 2813ndash2819 2007

[7] A K Majumdar Advanced Free Space Optics (FSO) a SystemsApproach Springer Atlanta GA USA 2015

[8] A ElHelaly A H Mehana and M M Khairy ldquoReduced-complexity receiver for free-space optical communicationover orbital angular momentum partial-pattern modesrdquo In-ternational Journal of Antennas and Propagation vol 2018Article ID 8514705 11 pages 2018

[9] A S El-Wakeel N A Mohammed and M H Aly ldquoFreespace optical communications system performance underatmospheric scattering and turbulence for 850 and 1550 nmoperationrdquo Applied Optics vol 55 no 26 pp 7276ndash72862016

[10] K O Odeyemi P A Owolawi and V M Srivastava ldquoPer-formance analysis of free space optical system with spatialmodulation and diversity combiners over the gamma gammaatmospheric turbulencerdquo Optics Communications vol 382no 1 pp 205ndash211 2017

[11] D R Lide Handbook of Chemistry and Physics CRC PressBoca Raton FL USA 84th edition 2003

[12] F Moller ldquoOptics of the lower atmosphererdquo Applied Opticsvol 3 no 2 pp 157ndash166 1964

[13] A Bucholtz ldquoRayleigh-scattering calculations for the terres-trial atmosphererdquo Applied Optics vol 34 no 15pp 2765ndash2773 1995

[14] O Bouchet H Sizun C Boisrober F Forne andL P N Favennec Free-Space Optics Propagation and Com-munication ISTE Ltd London UK 2006

[15] X Chen X Gao X Qu et al ldquoQualitative simulation ofphoton transport in free space based on monte carlo methodand its parallel implementationrdquo International Journal of

Table 9 Analysis result and importance level

Parameters Level 1 Level 2 Delta RankingTransmission distance minus 1083910 minus 1009626 74284 600Visibility minus 746870 minus 1596119 849249 200Scatter particle size distribution minus 1533185 minus 784631 748554 300Number of particles per unit volume minus 1199851 minus 984631 215220 500Scatter cross-sectional area minus 681433 minus 1705182 102374 100Wavelength minus 786180 minus 1344497 558317 400


Biomedical Imaging vol 2010 Article ID 650298 9 pages2010

[16] H Weichel ldquoAtmospheric propagation of laser beamsrdquo SPIEvol 547 no 1 pp 1ndash15 1985

[17] G Taguchi and Y W S Chowdhury Taguchirsquos Quality En-gineering Handbook Architecture Wiley New York NY USA2005

[18] B Gokccedile and S Tasgetiren ldquoA system development for thedesign and optimization of metallurgical experiments byusing genetic algorithms and taguchi methodsrdquo Journal ofScientific and Industrial Research vol 73 pp 219ndash224 2014

[19] T T K Elfarah Magnezyum matrisli karbur takviyeli kom-pozitlerin toz metalurjisi yontemi ile uretiminin Taguchimetodu ile optimizasyonu Dept of Mate And Scien EngKastamanu Univ Kastamonu Turkey PhD dissertation2018

[20] C R Rao ldquoFactorial experiments derivable from combina-torial arrangements of arraysrdquo Supplement to the Journal ofthe Royal Statistical Society vol 9 no 1 pp 128ndash139 1947

[21] W Weng F Yang and A Elsherbeni Electromagnetics andAntenna Optimization Using Taguchirsquos Method Morgan ampClaypool Pub San Rafael CA USA 1st edition 2007

[22] U Demir and M C Akuner ldquoUsing Taguchi method indefining critical rotor pole data of LSPMSM considering thepower factor and efficiencyrdquo Tehnicki VjesnikmdashTechnicalGazette vol 24 no 2 pp 347ndash353 2017

[23] U Demir and M C Akuner ldquoDesign and optimization of in-wheel asynchronous motor for electric vehiclerdquo Journal of theFaculty of Engineering and Architecture of Gazi Universityvol 33 no 4 pp 1517ndash1530 2018

[24] H Haroon H A Razak S S Khalid N Nadia and A AzizldquoOn the effectiveness of Taguchi method in optimizing theperformance of parallel cascaded MRR array (PCMRRA)rdquoOptoelectronics and Advanced Materials vol 11 no 7-8pp 393ndash397 2017

[25] W-C Weng F Yang and A Z Elsherbeni ldquoLinear antennaarray synthesis using Taguchirsquos method a novel optimizationtechnique in electromagneticsrdquo IEEE Transactions on An-tennas and Propagation vol 55 no 3 pp 723ndash730 2007

[26] Nuclear Size and Density CR Nave USA 2000 httphyperphysicsphy-astrgsuedu

[27] H Kaushal V K Jain and S Kar ldquoFree space opticalcommunicationrdquo in Optical Networks Springer BerlinGermany 2017


attenuation effects many calculations are required +esecalculations are used for updating permeability equationsand this way FSO communication systems are immune tovariable atmospheric conditions However these calcula-tions lead to time losses for data transmission In this paperTaguchirsquos experimental method is proposed to minimize thetime losses and therefore enhance the performance of FSOcommunication systems and suppress the attenuationeffects

2 Atmospheric Properties

+e atmosphere has many layers +ese layers consist ofdifferent and variable gases Figure 1 shows the gasesrsquo dis-tribution in the atmospheric layers [11] +e tropospherelayer shown in Figure 1 is about 15ndash20 km from the Earthand consists of the most intense gases because it is the closestlayer to Earth

In general the percentages of gases in the atmosphere areas follows 78 nitrogen 20 oxygen 9 argon and 004other gases (0004 00018 Ne 0000524 He 000018000055 0000114 Kr) [12] Furthermore each gas in theatmosphere has a different radius size Due to the size ofradius the laser beam is affected in a different way wheninteracting with different gases +e laser beam is exposed tomostly nitrogen and oxygen during propagating in the at-mosphere +e refractive indices and diameters of thesegases for 1064 nm are given in Table 1 Gases such as NeCH4 and Kr do not interact with the wavelength of 1064 nmHowever these gases are affected by different wavelengths

21 Atmospheric Attenuation According to the law of Beerattenuation of laser beam propagation is given as

T I(z)

I0 exp(minus cz) (1)

where T is the permeability c is the attenuation coefficientand z is the transmission length+e refractive index of gasesat a certain wavelength consists of two parts which are realand virtual (r rprime+ rPrime) In the near infrared region (NIR) thevirtual part of the refractive index is small enough so as to beneglected +e virtual part of the refractive index definesscattering +erefore the attenuation due to the scatteringcan be considered +is way the attenuation coefficient forscattering is shown as

c βm + βa (2)

where β is the scattering coefficient and indices of m and arepresent the molecule and aerosol respectively Each co-efficient in (2) depends on the wavelength of the laseremission [13] +ere is no energy loss in case of scatteringhowever the laser beam may be directed to any differentlocation So this situation causes a decrease in beam in-tensity for long-distance transmissions +e physical size ofthe scatterers is a factor that determines scattering

Air molecules lead to Rayleigh scattering in angstromsizes On the other hand aerosols lead to Mie scatteringbecause of scattering the light +e German meteorologist

Gustav Mie found that electromagnetic waves are scatteredby the small dielectric spheres It is calledMie scattering [14]

Electrons which involve the formation of chemicalbonds are called bonding electrons Electronic displacementoccurs when the electrons move towards the other side of themolecule Once the bonding electrons are displaced Ray-leigh scattering occurs +e harmonic field stimulates thedipole in the molecule +erefore polarity of dipole deter-mines where to move them +e propagation is absorbedand the stimulated dipole oscillates at the same frequencywith the laser beam +e radiated energy occurs by thescattering light When a beam collides with a small particlethe area where the particle interacts with the beam is calledthe cross-sectional area Total scattered cross-sectional areais given as [14]

σ 8π3 n2 minus 1( 1113857

2

3N2λ4 (3)

where n is the refractive index and N is the scattered mo-lecular density Besides aerosol scattering is known as Miescattering which is shown as

βa 391V

λ550 nm

1113888 1113889

ρ

(4)

where V is the visibility λ is the wavelength and ρ is the sizedistribution of the scattering particles

Different weather conditions can be specified based ontheir visibility range values According to Kruse model therelationship between the size distribution and visibility isdetermined using [15]

Exosphere

Thermosphere

Mesosphere

Stratosphere

Troposphere

Figure 1 Atmospheric layers with gas distribution


p

16 Vgt 50 km

13 6 kmltVlt 50 km

0585V13 Vlt 6 km

⎛⎜⎜⎜⎜⎜⎜⎜⎜⎜⎝⎞⎟⎟⎟⎟⎟⎟⎟⎟⎟⎠ (5)



(6)



Ap πr2 (7)









r r0A13

(8)









































End

Definingcriteriamet

No

Yes


parameters















005

0650

024

005

0653

9

005

0650

36

005

0650

4

026

755

011

235

005

4085

005

08

005

0656

1

0

01

02

03


850n

m at

tenu

atio

nva

lues

Atmospheric gases


4784

047

84

047

84

047

846

047

84

056

7

050

361

047

98

047

84

042

047

052

057


1064

nm at

tenu

atio

nva

lues

Atmospheric gases











Visibility(km)


















5 Conclusions





Data Availability




References

































p

16 Vgt 50 km

13 6 kmltVlt 50 km

0585V13 Vlt 6 km

⎛⎜⎜⎜⎜⎜⎜⎜⎜⎜⎝⎞⎟⎟⎟⎟⎟⎟⎟⎟⎟⎠ (5)



(6)



Ap πr2 (7)









r r0A13

(8)









































End

Definingcriteriamet

No

Yes


parameters















005

0650

024

005

0653

9

005

0650

36

005

0650

4

026

755

011

235

005

4085

005

08

005

0656

1

0

01

02

03


850n

m at

tenu

atio

nva

lues

Atmospheric gases


4784

047

84

047

84

047

846

047

84

056

7

050

361

047

98

047

84

042

047

052

057


1064

nm at

tenu

atio

nva

lues

Atmospheric gases











Visibility(km)


















5 Conclusions





Data Availability




References


































































End

Definingcriteriamet

No

Yes


parameters















005

0650

024

005

0653

9

005

0650

36

005

0650

4

026

755

011

235

005

4085

005

08

005

0656

1

0

01

02

03


850n

m at

tenu

atio

nva

lues

Atmospheric gases


4784

047

84

047

84

047

846

047

84

056

7

050

361

047

98

047

84

042

047

052

057


1064

nm at

tenu

atio

nva

lues

Atmospheric gases











Visibility(km)


















5 Conclusions





Data Availability




References













































005

0650

024

005

0653

9

005

0650

36

005

0650

4

026

755

011

235

005

4085

005

08

005

0656

1

0

01

02

03


850n

m at

tenu

atio

nva

lues

Atmospheric gases


4784

047

84

047

84

047

846

047

84

056

7

050

361

047

98

047

84

042

047

052

057


1064

nm at

tenu

atio

nva

lues

Atmospheric gases











Visibility(km)


















5 Conclusions





Data Availability




References









































Visibility(km)


















5 Conclusions





Data Availability




References





































5 Conclusions





Data Availability




References

































InvestigationoftheAtmosphericAttenuationFactorsinFSO...

Documents

Transcript of InvestigationoftheAtmosphericAttenuationFactorsinFSO...