PROPAGATION MODELS

Presented ByAYUSHI GAGNEJA

M.E ScholarElectronics & Communication

EngineeringNITTTR-CHANDIGARH

Introduction to Radio Wave Propagation

• The mobile radio channel places fundamental limitations on the performance of wireless communication systems.

• Radio channels are extremely random and do not offer easy analysis.

• Modeling radio channel is important for:–Determining the coverage area of a

transmitter–Finding modulation and coding

schemes to improve the channel quality

Radio Propagation Models• Transmission path between sender and

receiver could be –Line-of-Sight (LOS) –Obstructed by buildings, mountains and

foliage • Even speed of motion effects the fading

characteristics of the channel

BASIC DIVISION OF PROPAGATION MODELS• Different models have been developed to

meet the needs of realizing the propagation behavior in different conditions.

• Types of models for radio propagation include:– Models for Outdoor Applications– Models for Indoor Applications

Outdoor Propagation Model• Radio transmission in mobile communication

takes place over irregular terrain

• There are different propagation models available to predict the signal strength, Pr(d), by estimating the path loss at a particular sector.

• Irregular terrain such as simple curved earth profile, highly mountainous or trees, building etc.

• Models used are based on systematic interpretation of measurement data obtained in the service area.

• They may vary in complexity and accuracy.

- Longely Rice- Durkins Model- Okumura Model- Hata Model- Wideband PCS Microcell- PCS Extension to Hata Model- Walfisch – Bertoni Model

TYPES OF MODELS

Okumura ModelIt is wholly based on measured data, no analytical explanation

• among the simplest

• best in terms of path loss accuracy in cluttered mobile environment

Okumura developed a set of curves in urban areas with quasi-smooth terrain

• It is one of the most widely used models for signal prediction in urban areas.

• Applicable for the frequencies in the range 150MHz to 1920MHz

• Distances of 1km to 100km• Antenna heights from 30m to 1000m.

• Okumura developed a set of curves giving the medium attenuation relative to free space (Amu), with base station effective antenna height (hte) of 200m and a mobile antenna height (hre) of 3m

• Curves are developed using vertical omnidirectional antennas at both base and mobile.

Estimating path loss1. Determine free space loss, Amu(f,d),

between points of interest

2. Add Amu(f,d) and correction factors to account for terrain

L50(dB)= LF + Amu(f,d) – G(hte) – G(hre) – GAREA

L50 = 50% value of propagation path loss

LF = free space propagation loss

Amu(f,d)= 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 environment

70

60

50

40

30

20

10

A mu(f

,d) (

dB)

70 100 200 300 500 700 1000 2000 3000

f (MHz)

100

8070605040302010521

d(km)

Urban Areaht = 200mhr = 3m

Median Attenuation Relative to Free Space = Amu(f,d) (dB)

Amu(f,d) & GAREA have been plotted for wide range of frequencies Also G(hte)varies at rate of 20dB/decade and G(hre)varies at a rate of 10dB/decade

G(hte) = 10m < hte < 1000m

G(hre) = hre 3m

G(hre) = 3m < hre <10m

model corrected for• h = terrain undulation height• isolated ridge height• average terrain slope• mixed land/sea parameter

16

35

30

25

20

15

10

5

0

GA

REA

(dB

)

100 200 300 500 700 103 2103 3 103

frequency (MHz)

suburban area

quasi open area

open area

Correction Factor = GAREA(dB)When terrain related parameters are calculated, correction parameters are added/subtracted. These are available as Okumura curves.

• Extrapolations of the derived curves can be made

to obtain values outside the measurement range.

• Simplest and best in accuracy in path loss

prediction for cellular and land mobile radio

systems.

DISADVANTAGE: •slow response to rapid terrain changes, so not so

good in rural areas.

•common standard deviations between predicted

& measured path loss 10dB - 14dB

Hata Model It is an empirical model of graphical path loss

data from Okumura• Its range is valid from150 MHz to 1500

MHz• Hata represented urban area propagation

loss as a standard formula and supplied for correction equations for application to some situations

• Okumura predicts median path loss for different channels

• Propagation losses increase• with frequency• in built up areas

Parameter

Comment

L50 50th % value (median) propagation path loss (urban)

fc frequency from 150MHz-1.5GHzhte, hre Base Station and Mobile antenna height (hre) correction factor for hre , affected by

coverage aread Tx-Rx separation

Standard formula for Median Path Loss

For small to medium sized city, mobile antenna correction factor is given by:

(hre) = (1.1log10 fc - 0.7)hre – (1.56log10 fc - 0.8) dB

For a large city, it is given as (hre) = 8.29(log10 1.54hre)2

– 1.1 dB for (fc 300MHz)

(hre) = 3.2(log10 11.75hre)2 – 4.97 dB

for (fc > 300MHz)

To obtain path loss in a suburban area, the standard Hata formula is

modified as:

L50 (dB) = L50 (urban) - 2[log10 (fc/28)]2 – 5.4

For path loss in open rural areas, the formula is modified as

L50 (dB) = L50 (urban) - 4.78(log10 fc)2 - 18.33log10 fc - 40.98

Path

Los

s (dB

)

hte (m)

160155150145140135130125120

20 60 100 140 180

20km

10km

5km

fc = 700MHz

Path

Los

s (dB

)

Range (km)0 4 8 12 16 20

180170160150140130120110100

900 MHz700 MHz

• hte = 30m• hre = 1m

Example Tables for Okumura-Hata Model

Terrain Legend• Urban• Suburban• Open

HATA Model• Mostly used in Radio frequency• Predicting the behavior of cellular

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

communication.

INDOOR PROPAGATION

MODEL

• With the advent of Personal Communication Systems (PCS), we need to characterize radio propagation inside the buildings.

• Indoor radio channels are different because– The distances covered are much smaller– The variability of the environment is much

greater

• Smaller Tx-Rx separation distances than outdoors• Higher environmental variability for much small

Tx-Rx separation, conditions vary from: • Doors/windows open or not• The mounting place of antenna: desk, ceiling, etc.

• The level of floors

• Propagation inside the building is strongly influenced by various features like– layout of the building– construction materials– building type– where the antenna mounted, …etc.

• Indoor radio propagation is dominated by 3 mechanisms– Reflection– Diffraction– Scattering

• In general, indoor channels may be classified either as Line of Sight, LOS or Obstructed Sight, OBS with varying degree of clutter

• The losses between floors of a building are determined by the external dimensions and materials of the building, as well as the type of construction used to create the floors and the external surroundings.

Building types • Residential homes in suburban areas• Residential homes in urban areas• Traditional office buildings with fixed walls (hard partitions) • Open plan buildings with movable wall panels (soft

partitions) • Factory buildings • Grocery or Retail stores • Sport arenas

Some Key Models - Partition Losses – Same Floor- Partition Losses – Different Floor- Log-distance path loss model- Ericsson Multiple Breakpoint Model- Attenuation Factor Model

Partition Losses – Same Floor• Buildings have a wide variety of

partitions and obstacles which form the internal and external structure.

• There are mainly 2 types of partitions:– hard partitions: immovable, part of building– soft partitions: movable, lower than the

ceiling

• Partitions vary widely in their physical and electrical properties.

• Path Loss depends upon the type of partition

Average signal loss measurements for radio paths obstructed by common building material

Partition Losses – Different FloorLosses between floors of the building are determined by •External building dimensions•Type of construction used to create the floor •External surroundings•Number of windows•Presence of tinting on windows

Total Floor Attenuation Factor and Standard Deviation for 3 Buildings

Average Floor Attenuation Factor in dB for 4 different floors in 2 office buildings

Indoor path loss obeys the distance power law given by equation:

• n depends on surroundings and building type, for free space it is 2

• = normal random variable in dB having standard deviation dB

Log-distance Path Loss model

Path Loss Exponent for Different Environments

Ericsson Multiple Breakpoint Model

• It was obtained by measurements in a multiple floor office building.

• It has 4 breakpoints and considers both an upper and lower bound on path loss.

• It assumes that there is 30dB attenuation at d0 =

1m which is accurate for f = 900MHz & unity

gain antennas.

• Also it provides a deterministic limit on range of path loss at given distance

• It used a uniform distribution to generate path loss values within minimum &maximum range, as a function of distance for in-building simulation.

Path Loss Exponent and Standard Deviation for different buildings

Ericsson’s in-building path loss model

Attenuation Factor Model• It includes effect of building type & variations

caused by obstacles.• It provides flexibility and reduces standard

deviation between measured and predicted path loss to 4dB

• Compared to standard deviation for path loss with log-distance model i.e. 13dB for 2 different buildings

nSF = exponent value for same floor measurement – must be accurate

FAF = floor attenuation factor for different floor PAF = partition attenuation factor for obstruction

encountered by primary ray tracing

Attenuation Factor Model is given by:

Primary Ray Tracing = single ray drawn between Tx & RxIt yields good accuracy with good computational efficiency

FAF

PAF(1)

PAF(2)

Rx

Tx

decreases as average region becomes smaller-more specific

Replace FAF with nMF = exponent for multiple floor loss

Path Loss Exponent and Standard Deviation for different buildings

Standard Deviation decreases as average region becomes smaller and more site specific.

Scatter plot illustrating actual measured path loss in multi floored building 1

Scatter plot illustrating actual measured path loss in multi floored building 2

In-Building Path Loss obeys free space + loss factor ()

• loss factor increases exponentially with d (dB/m) = attenuation constant for channel

f 850MHz 0.621.7GHz 0.57

4-story bldgf

850MHz 0.481.7GHz 0.35

2-story bldg

EXAMPLECalculate the mean path loss using Okumara’s model for d=50km, hte =100m, hre =10m in a suburban environment. If the base station transmitter radiates an EIRP of 1kW at a carrier frequency of 900 MHz, find EIRP(dBm) and the power at the receiver where gain at receiving antenna is 10dB.

G(hte) =

G(hre) =

= = -6 dB

= = 10.46 dB

Total mean path loss is

= 125.5 dB + 43 dB –(-6) dB – 10.46 dB - 9 dB=155.4 dB

L50(dB)= LF + Amu(f,d) – G(hte) – G(hre) – GAREA

EXAMPLEFind the mean path loss 30m from the transmitter, through 3 floors of the Office building 1. Assume 2 concrete block walls are between the transmitter and receiver on the intermediate floors. Mean path loss exponent for same-floor measurements in a building is n=3.27, mean path loss exponent for three-floor measurements in a building is n=5.22, while floor attenuation factor FAF=24.4 dB.

Mean path loss for same floor measurement is

= PL(1m) + 10*3.27*log(30) + 24.2 + 2*13= 130.2 Db

Mean path loss for different floor measurement is

= PL(1m) + 10*5.22*log(30) + 2*13= 108.6 dB

Thanks