Path loss & Path loss & shadowing shadowing

By eng : mahmoud By eng : mahmoud abdel azizabdel aziz

OUTLINE

Ray Tracing Path Loss Models

Free Space Model

2 Ray Model

General Ray Tracing

Empirical measurementLog Normal Shadowing

Propagation Characteristics

Path Loss (includes average shadowing)Shadowing (due to obstructions)Multipath Fading

Pr/Pt

d=vt

Pt Very slow

SlowFast

PrPt

v

d=vt

Path Loss Modeling

Maxwell’s equations- Complex and impractical

Free space path loss model - Too simple

Ray tracing models - Requires site-specific information

Empirical ModelsDon’t always generalize to other environments

Simplified power falloff modelsMain characteristics: good for high-level analysis

Free Space path loss (LOS) Free Space path loss (LOS) ModelModel

Path loss for unobstructed LOS pathPower falls off:

inversely Proportional to d2

Proportional to 2 (inversely proportional to f2)

d=vt

the signal propagates along a straight line &The channel model called a line-of-sight (LOS)

Ray Tracing ApproximationRay Tracing Approximation

1 -In ray tracing we assume a finite number of reflectors with

known location and dielectric properties. 2 -Represent wavefronts as simple particles

3 -Typically includes reflected rays, can also include scattered and defracted rays.

4-Requires site parameters * Geometry

*Dielectric properties

Two Path ModelTwo Path Model

1-Path loss for one LOS path and 1 ground (or reflected) bounce

2 -path loss has alternate min & max as d is increase 3 -Power falls off

Proportional to d2 (small d)Proportional to d4 (d>dc=4hrht\ )

General Ray TracingGeneral Ray Tracing

1-Models all signal components

ReflectionsScatteringDiffraction

1-Requires detailed geometry and dielectric properties of site

2 -GRT method uses geometrical optis3 -Computer packages often used

Different types of cellsDifferent types of cells: :

1 -each model is define for a specific environement

Empirical ModelsEmpirical Models1-A number of path loss models have been developed

over the years to predict path loss in typical wireless environments such as large urban macrocells, urban microcells, and, more recently, inside buildings These models are mainly based on empirical measurements over a given distance in a given frequency range and a particular geographical area or building .

2 -Analytical models characterize Pr/Pt as a function of distance, so path loss is well defined. In contrast, empirical measurements of Pr/Pt as a function of distance include the effects of path loss, shadowing, and multipath.

Okumura-Hata modelOkumura-Hata model

Most popular modelBased on measurements made in and around Tokyo in 1968.

between 150 MHz and 1500 MHz 1 -Output parameter : mean path loss (median path

loss) LdB2 -Validity range of the model:

• Frequency f between 150 MHz and 1500 Mhz •TX height hb between 30 and 200 m

•RX height hm between 1 and 10 m •TX - RX distance r between 1 and 10 km

Okumura-Hata model contOkumura-Hata model cont..

3 types of prediction area: •Open area : open space, no tall trees or building

in path

•Suburban area : Village Highway scattered with trees and house Some obstacles near the mobile

but not very congested

•Urban area : Built up city or large town with large building and houses

Village with close houses and tall

Okumura-Hata model contOkumura-Hata model cont.Definition of parameters:

hm : mobile station antenna height above local terrain height [m]

dm: distance between the mobile and the buildingh0 : typically height of a building above local terrain height [m]hb: base station antenna height above local terrain height [m]r :great circle distance between base station and mobile [m]R=r x 10 great circle distance between base station and mobile [km]f: carrier frequency [Hz]fc=f x 10 carrier frequency [MHz]λ: free space wavelength [m]

6

3

•Okumura takes urban areas as a reference and applies correction factors

COST 231- extension to Hata modelCOST 231- extension to Hata model

Okumura-Hata model for medium to small cities has been extended

to cover 1500 MHz to 2000 MHz (1999)

LdB = F + B log10 R – E + G

F = 46.3 + 33.9 log10 fc – 13.82 log10 hb

E designed for medium to small cities 0 dB medium sized cities and suburban areas

G = 3 dB metropolitan areas

Indoor Attenuation FactorsIndoor Attenuation Factors

1 -Indoor environments differ widely in the materials used.

2 -Thus, it is difficult to find generic models that can be accurately applied to determine empirical path loss .

3 -Indoor path loss models must accurately capture the effects of attenuation across floors

4 -the attenuation per floor is greatest for the first floor that is passed through and decreases with eachsubsequent floor passed through.

Simplified pathSimplified path loss modelloss model when tight system specifications must be met or the best locations for base stationsor access point layouts must be determined.

•the following simplified model for path loss as a function of distance is commonly used for system design:

K :depends on the antenna characteristics and the average channel attenuation,

do: is a reference distance for the antenna far-field

assumed to be 1-10 m indoors and 10-100 m outdoors

γ: is the path loss exponent

Thanks