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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: