RADIO PROPAGATION

Electromagnetic Spectrum EM bunch of types of radiation. Radiation is energy that travels and spreads

out. E.g. visible light that comes from lamp and

radio waves comes from radio station. Electromagnetic radiation can be described in

terms of stream of photons. Mass less particles traveling and moving at the

speed of light. Each photon contain certain amount of energy,

and all ER consists of these photon.

Types of ER

Radio Microwave Infrared Visible Ultraviolet X-rays Gamma Rays

Contd.

Types of ER Radio has the lowest frequency and longest

wavelength. Wavelengths from few millimeters to about

twenty meters. Microwaves has longer wavelength between

1 mm and 30 cm than visible light. Infrared wavelengths longer than the red

end of visible light and shorter than microwaves.

Types of ER Visible wavelength which the human

eye can see colors ranging from red 700 nm to violet 400 nm.

Ultraviolet wavelengths shorter than the violet end of visible.

X-rays has very short wavelength and very high energy.

Gamma rays highest energy, shortest wavelength, energies greater than about 100 keV.

Radio Propagation Modes VLF: Very low frequency 3 to 30 KHz

guided between the earth and the ionosphere.

LF: Low Frequency 30 to 300 KHz guided between the earth and the ionosphere, Ground Waves.

MF: Medium Frequency 300 to 3000 KHz Ground waves, E layer ionospheric refraction at night, when D layer absorption disappears.

Contd.

HF (Short Wave): High Frequency 3 to 30 MHz E layer ionospheric refraction, F layer ionospheric refraction.

VHF: Very High Frequency 30 to 300 MHz Line of Sight.

UHF: Ultra High Frequency 300 to 3000 MHz Line of sight.

Propagation Ways

Antenna Ground ways Line of sight propagation Sky wave propagation Diffraction Absorption

Antenna Beginning and end of

communication. Provide gain and directivity on both

end. Take off angle depends on:

Type of antenna Height of antenna Terrain

Ground Ways Follows the curvature of the earth. Waves are attenuated because

ground is not a good conductor. VLF and LF frequencies are used

for military communication. Radio services relied exclusively

on long wave.

Line of Sight Propagation Direct propagation that are visible. signal can travel through many non-

metallic objects. Example Satellite and reception of

television signals. Ground plane reflection effects are an

important factor. Interference between direct beam and

ground reflected beam.

Sky Wave Propagation Sky waves also referred as skip. Refraction of radio waves in the

ionosphere. F2 layer most important layer for HF

propagation. Layers directly affected by the sun. Sky wave modes used in amateur radio

operators, commercial marine and aircraft communication.

Diffraction Radio waves are bent around sharp edges. Used over a mountain range. Line-of-sight path is not available. Diffraction mode requires increased signal

strength. Signals for urban cellular telephony. Where multi-path propagation, absorption

and diffraction phenomena dominent.

Absorption Low frequency radio waves travel easily

through brick and stone. VLF even penetrates sea-water. Shows frequency rises absorption effects. Microwave and high frequencies absorption

is major factor in radio propagation. 58 to 60 GHz band major absorption peak,

so band is useless for long distance use.

Radio Wave Propagation Term used to explain how radio waves

behave when they are transmitted. Mechanism are diverse, but

characterized by reflection, diffraction and scattering.

In free space all electromagnetic waves obey inverse-square law.

Which states electromagnetic wave’s strength in proportional to 1/(x)2.

Inverse Square Law

Large Scale Propagation

Propagation models that predict the mean signal strength for an arbitrary transmitter-receiver separation distances are useful in estimating the radio coverage area of a transmitter and are called Large-Scale propagation.

Small Scale Fading

Propagation models that characterize the rapid fluctuations of the received signal strength over very short travel distances (a few wavelength) or short time durations (on the order of seconds) are called Small-Scale Fading.

Small Scale and Large Scale Fading

Free Space Propagation Model

Predict received signal strength. Transmitter and receiver are in line-of-

sight. Satellite communication and Microwave

radio links undergo free space propagation. Large-Scale radio wave propagation

models predicts the received power decays as a function of T-R distance.

Friis Free Space Equation

Pt is the transmitted power. Pr (d) is the received power. Gt is the transmitter antenna gain. Gr is the receiver antenna gain. d is the T-R separation distance in meters. L is the system loss factor. λ is the wavelength in meters.

Numerical If a transmitter produces 50W of

power, express the transmitter power in units of (a) dBm (b) dBW. If 50W is applied to unity gain antenna with a 900 MHz carrier frequency, find the received power in dBm at a free space distance of 100m from the antenna. What is Pr(10 Km). Assume unity gain for the receiver antenna.

Radio Propagation Models Also known as Radio Wave or Radio Frequency

Propagation Model. Empirical mathematical formulation which

includes: Characterization of radio wave propagation Function of frequency Distance Other condition

Single model developed to: Predict behavior of propagation Formalizing the way radio waves are propagated Predict path loss in the coverage area

Characteristics Path loss is dominant factor. Models typically focus on path loss realization. Predicting:

Transmitter coverage area. Signal distribution representation.

Telecommunication link encounter these conditions. Terrain Path Obstructions Atmospheric conditions

Different model exist for different types of radio links.

Model rely on median path loss.

Development Methodology Radio propagation model practical in nature. Means developed based on large collection

of data. In any model the collection of data has to be

sufficient large to provide enough likeliness. Radio propagation models do not point out

the exact behavior of a link. They predict most likely behavior.

Variations

Different models needs of realizing the propagation behavior in different condition.

Types of Models for radio propagation: Models for outdoor attenuations. Models for indoor attenuations. Models for environmental attenuations.

Models For Outdoor Attenuations

Near Earth Propagation Models Foliage Model

Weissberger’s MED Model Early ITU Model Updated ITU Model

One Woodland Terminal Model Single Vegetative Obstruction Model

Contd. Terrain Model

Egli Model ITU Terrain Model

City Model Young Model Okumura Model Hata Model For Urban Areas Hata Model For Suburban Areas Hata Model For Open Areas Cost 231 Model Area to Area Lee Model Point to Point Lee Model

Models For Indoor Attenuations

ITU Model For Indoor Attenuations Log Distance Path loss Model

Models For Environmental Attenuations

Rain Attenuation Model ITU Rain Attenuation Model ITU Rain Attenuation Model For

Satellites Crane Global Model Crane Two Component Model Crane Model For Satellite Paths DAH Model

Weissberger’s Model Formulated in 1982. Calculate path loss if one or more trees in

a point-to-point link. This models belongs Foliage or

Vegetation model. Only applicable when an obstruction

made by Foliage between transmitter and receiver.

Coverage area frequency is 230 MHz to 95 GHz and depth of foliage up to 400m.

Weissberger’s Formulae

L = Loss due to foliage. (decibel) f = Transmission frequency. (GHz) d = Depth of foliage. (meter) Example: Bunch of foliage between

transmitter and receiver. Find path loss, if base station carrier frequency are 845 MHz and 70 GHz and depth of foliage are (a) 9 m (b) 300 m.

Early ITU Model

Adopted in late 1986. Model is applicable where some obstructions made by trees

along its way. Path loss calculate point-to-point links. Suitable for point to point microwave links. Frequency range and depth of foliage are not specified.

f = Transmission frequency MHz d = Depth of foliage meter L = Path loss Decibel Numerical: Transmission frequency are 900 MHz and 1900

MHz and distance of foliage is 20m and 300m, Find Path loss.

Updated ITU Model

One Woodland Model Woodland model belonging to the

class of foliage model. Applicable where one terminal of link

is inside foliage and the other end is free.

Frequency range of this model 5 GHz. Depth of foliage is unspecified.

Formulae

Av = Attenuation due to vegetation. Decibel A = Maximum attenuation for one terminal

caused by certain foliage. d = Depth of foliage. Ɣ = Specific attenuation for short vegetation. Numerical: Find attenuation due to

vegetation when Maximum attenuation is 14.3 dB, depth of foliage 200m or 10m and specific attenuation is 1.8 dB/m or 8 dB/m.

UHF (870 MHz) Measurements of Single Trees

L-Band (1.6 GHz) Measurements of Single

Trees

Single Vegetative Model Both ends are completely outside foliage. But a single plant or tree stands in the

middle of the link. Frequency range below 3 GHz and over 5

GHz. Depth of foliage is not specified. Numerical: Operational frequency are

850 MHz and 1800 MHz and depth of foliage are 10m and 100m, Find path loss.

Formulae

A = Attenuation due to foliage. Decibel Ɣ = Specific attenuation. Ri = Initial slope of the attenuation curve. Rf = Final slope of the attenuation curve. f = Operational frequency. k = Empirical constant.

Contd. Calculation of Slopes

Initial slope

Final slope

Calculation of k

ko = Empirical constant Rf = Empirical constant for frequency dependent

attenuation Ao = Empirical attenuation constant Ai = Illumination area (1m < Ai < 50m)

Empirical Constant

Empirical constants a, b, c, k0, Rf and A0 are used as tabulated below.

Parameter Inside Leaves Out of Leaves

a 0.20 0.16

b 1.27 2.59

c 0.63 0.85

k0 6.57 12.6

Rf 0.0002 2.1

A0 10 10

Terrain Model Egli Model

Predict the total path loss a point to point link. Typically suitable for cellular communication

where one antenna is fixed and another is mobile.

Egli Model is applicable where the transmission has to go over an irregular terrain.

Not applicable where some vegetation obstruction is in the middle of the link.

Frequency is not specified in this model.

Formulae

A = Attenuation. Decibel D = Path Distance. Miles F = Frequency. MHz HT = Transmitter Antenna Height. Feet HR = Receiver Antenna Height. Feet Numerical: Find Path loss, if path distance is

0.0186 miles (30m) and transmitter antenna height and receiver antenna height are 328 feet's (100m) and 19.68 feet’s (6m) respectively.

ITU Terrain Model Predicts the median path loss for a

link. Developed on the basis of diffraction

theory. Applicable on any terrain. Suitable to be used inside cities as

well as in open fields. Ideal for modeling line of sight link in

any terrain.

Formulae

A = Empirical Diffraction loss Decibel. CN = Normalized Terrain clearance. h = The height difference. Meter hl = Height of the line of sight link. ho = Height of obstruction. Meter F1 = Height of first fersnel zone. Meter d1 = Distance of obstruction from one terminal. Meter d2 = Distance of obstruction from another terminal. Meter f = Transmission frequency. d = Distance form transmitter to receiver. Numerical: Self practice.

Longley-Rice Model Applicable point-to-point communication

system. Frequency range 40 MHz to 100 GHz. Now available as computer program. Operates in two modes:

Point-to-point mode prediction. Area mode prediction.

Important modification is introduce urban factor.

Not suitable due to environmental factors and multi path propagation.

Okumura Model Used for signal prediction in Urban areas. Frequency range 150 MHz to 1920 MHz and

extrapolated up to 3000 MHz. Distances from 1 Km to 100 Km and base station

height from 30 m to 1000 m. Firstly determined free space path of loss of link. Model based on measured data and does not

provide analytical explanation. Accuracy path loss prediction for mature cellular

and land mobile radio systems in cluttered environment.

Formulae

L50 = Percentile value or median value. LF = Free space propagation loss. Amu = Median attenuation relative to free

space. G(hte) = Base station antenna height gain

factor. G(hre) = Mobile antenna height gain factor. GAREA = Gain due to the type of

environment.

Correction Factor GAREA

Numerical

Find the median path loss using Okumura’s model for d = 50 Km, hte = 100 m, hre =10m in a suburban environment. If the base station transmitter radiates an EIRP of 1 kW at a carrier frequency of 1900 MHz, find the power at the receiver (assume a unity gain receiving system).

Hata Model Urban Areas Most widely used model in Radio frequency. Predicting the behavior of cellular

communication in built up areas. Applicable to the transmission inside cities. Suited for point to point and broadcast

transmission. 150 MHz to 1.5 GHz, Transmission height up

to 200m and link distance less than 20 Km.

Formulae

For small or medium sized city

For large cities

Numerical

Find the median path loss using Hata model for d = 10 Km, hte = 50 m, hre = 5 m in a urban environment. If the base station transmitter at a carrier frequency of 900 MHz.

Hata Model For Suburban Areas

Behavior of cellular transmission in city outskirts and other rural areas.

Applicable to the transmission just out of cities and rural areas.

Where man made structure are there but not high.

150 MHz to 1.5 GHz.

Formulae

LSU = Path loss in suburban areas. Decibel

LU = Average path loss in urban areas. Decibel

f = Transmission frequency. MHz

Hata Model For Open Areas Predicting the behavior of cellular

transmission in open areas. Applicable to the transmissions in

open areas where no obstructions block the transmission link.

Suited for point-to-point and broadcast links.

150 MHz to 1.5 GHz.

Formulae

LO = Path loss in open areas. Decibel

LU = Path loss in urban areas. Decibel

f = Transmission frequency. MHz

ITU Model For Indoor Attenuation

Path loss inside a room. Closed area inside a building

delimited by walls. Frequency Range 900 MHz to 5.2

GHz. Floors are 1 to 3.

Formulae

L = path loss. Decibel f = Transmission frequency. MHz d = Distance. Meter N = Distance power loss coefficient. n = Number of floors between transmitter and

receiver. Pf(n) = Floor loss penetration factor. See Next Slide Tables.

Distance Power Loss Coefficient N and Penetration Loss Factor n Values

Frequency Band Residential Area Office Area Commercial Area

900 MHz N/A 33 20

1.2 GHz N/A 32 22

1.3 GHz N/A 32 22

1.8 GHz 28 30 22

4 GHz N/A 28 22

Frequency Band Number of Floors Residential Area Office Area Commercial Area

900 MHz 1 N/A 9 N/A

900 MHz 2 N/A 19 N/A

900 MHz 3 N/A 24 N/A

1.8 GHz n 4n 15+4(n-1) 6 + 3(n-1)

2.0 GHz n 4n 15+4(n-1) 6 + 3(n-1)

5.2 GHz 1 N/A 16 N/A

Log Distance Path Loss Model Path loss a signal encounters inside a

building over distance. Model applicable to indoor attenuation.

L = Path loss inside building. Decibel Lo = Path loss at reference distance.

Decibel Ɣ = Path loss distance exponent. See table Xg = Gaussian random variable. See table

Coefficient 10Ɣ and σ in dB

Building Type Frequency of Transmission 10γ σ

Retail store 914 MHz 22 8.7

Grocery store 914 MHz 18 5.2

Office with hard paritition 1.5 GHz 30 7

office with soft partition 900 MHz 24 9.6

office with soft partition 1.9 GHz 26 14.1

Textile or chemical 1.3 GHz 20 3.0

Textile or chemical 4 GHz 21 7.0, 9.7

Metalworking 1.3 GHz 16 5.8

Metalworking 1.3 GHz 33 6.8