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A STUDY OF METHODS FOR
ELECTROMAGNETIC EVALUATION OF A
LARGE AIRCRAFT IN-CABINENVIRONMENT
SUBMITTED BY:- SOUMYA TEJAS
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ABSTRACT
Electromagnetic (EM) field mapping inside the aircraft cabin area is
required for commercial applications for the passenger area (wireless
communication, Wi Fi WLAN etc.)
It is done using 3-D ray tracing. However, computations become highly
complex due to the presence of passenger seats, partitions, flooring
material, apertures etc. in the passenger area.
A literature survey is done with focus on EM scattering, diffraction, and
absorption mechanisms in a closed lossy cavity.
Methods that make computations numerically efficient have been
discussed.
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ORGANIZATION PROFILE
National Aerospace Laboratories
NAL is a government organization under Council of Scientific and
Industrial Research (CSIR) established in 1959 in Bangalore.
It is a high technology oriented institution concentrating on
advanced topics in aerospace and related disciplines.
NAL has developed HANSA trainer aircraft and another light
transport aircraft SARAS is undergoing flight testing.
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RAY TRACING
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Forms of Interaction of EM rays WithSurface
Reflection Transmission (Refraction)
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o Geometrical Optics (GO): It is suitable for direct and line-of-sight (LOS) path GO considers only direct and reflected paths
o
Physical Optics (PO): It also considers scattered field strengthso Physical Theory of Diffraction (PTD):
It is an extension of PO It includes the consideration of edge currents
o Geometrical Theory of Diffraction (GTD):
It is an extension of GO GTD considers diffraction It tends to give erroneous results in shadowed regions
o Uniform Theory of Diffraction (UTD): It is an improved version of GTD UTD considers multiple diffractions and scattering This theory tends to give good results for shadowed regions
Theories for Interaction of EM raysWith Surface
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PATH LOSS
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Definition : Path loss is the power lost during transmission of
electromagnetic radiation from transmitter to thereceiver.
Models : Two categories of models are there for path loss models(i) Empirical(ii) Site-specific
Empirical model : Considers only the parameters of the communication system Simple calculations Approximate results
Site-Specific model : Considers details of the environment Complex calculations Accurate results
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EMPIRICAL MODELS1. Okumura Model Applicable for:
Frequencies from 150-1920 MHz Radio path length of 1 100 km
Transmitter antenna height from30 1000 m
Outdoor environment
Model equation:
L50(dB): median propagation path loss A mu : median attenuation relative to free spaceG: gain factors
1. Hata Model Applicable for:
Frequencies from 150 - 1500 MHz Radio path length of 1 100 km Receiver antenna height from 1 - 10
m Outdoor environment
Model equation:
h re: receiver antenna effective heighth te: transmitter antenna effective height
AREAretemu F GhGhGd f A LdB L +=++=
retec hah f dBurban L
d hte
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EMPIRICAL MODELS1. Cost-231-Walfisch-Ikegami
Model Applicable for:
Frequencies from 800 2000MHz
Transmitter antenna height 4 50m
Receiver antenna height 1 3 m Urban environment
Model equation:
Lo: free space lossLrts : roof-top to street scattering and diffraction
lossLmsd : multi-screen diffraction loss
1. Dual Slope Method
Applicable for: Line-of-sight (LOS) condition Outdoor environment
Model equation:
d brk : turning point or break-point distancen
1: slope of best fit line before break-point
n 2: slope of best fit line after break-point
+>+++=
msd rts
msd rtsmsd rtsb L L L
L L L L L L ++
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EMPIRICAL MODELS1. Power/Distance Model
Applicable only for indoor environment.
Model equation:
FAF: floor attenuation factor WAF: wall attenuation factord: radio-path lengthd o: reference radio-path length
== +++= P
p
Q
q pWAF q FAF d d nd PLd PL
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SITE-SPECIFIC MODELS1. Ray-tracing technique2. Finite difference time domain (FDTD)
3. Method of Moments4. Artificial Neural Networks (ANN)
FDTD and MoM are numerical methods ANN includes usage of specifically trained neural networks
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SMALL-SCALE FADING
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MODELS:1. Ricean (Rice) Distribution
This model is applicable only forLOS paths.
Probability distribution function:
r: amplitude of received signal envelope2 2: predicted mean power of multipath signal A: amplitude of dominant signalI0(.): Bessel function, first kind, zero order
1. Rayleigh DistributionThis model is applicable only forNon-Line-of-Sight (NLOS) paths.
Probability distribution function: