EELE 5414 Wireless

Communications

Chapter 4: Mobile Radio Propagation:

Large-Scale Path Loss

In the last lecture

Outline

• Diffraction.

• Scattering.

• Practical link budget design.

– Log-distance model

– Log-normal shadowing model

• Outdoor propagation models.

– Durkin’s model – Case study.

– Okumura model.

Diffraction

• Diffraction: allow the radio signal to propagate behind

obstruction.

• Occurs when the radio path between sender and receiver is

obstructed by a surface with sharp irregularities (edges)

• The received field strength decrease rapidly as the receiver

moves deeper into the shadowed region.

Fresnel Zone Geometry and knife edge model

Δ ������ � ��

2����� �

2 Δ

��

2 ����� � ��

2�����

Using the small-angle approximation � � � � � � ��� � ��

����

Using Fresnel-Kirchoff diffraction parameter

� � ��������

�����= � �

�����

�������� �

2��

Diffraction Loss

The diffraction due to

the presence of a knife

edge, as compared to

the free space E-field

is given by:�� �� � 20 !" #��

Where #�� is the

Fresnel integral.

Tables are used to find

the results or

approximated by Eq.

(4.61)

Fresnel Zone Geometry and knife edge model

Receiver and Transmitter do

not have the same height

Example 4.8

Multiple knife-edge diffraction

Rough Surface Scattering

• Generally difficult to model because the environmental

conditions that cause it are complex.

• Modeling “position of every street sign” is not feasible.

• When is a surface considered rough?

– When the maximum height from the surface, h, is greater than

�$ ��

%&'()*where Θ' is the angle of incidence.

• Scattering has two effects important to us:

1. Rough surface scattering reduces the power in the reflected wave.

2. Scattering causes additional multipath to be received in directions

other than the specular direction (recall -' � -.).

Practical Link Budget Design

• Log-distance Path loss model

– The average received decreases logarithmically with

distance

/0 � � /0 �12

23

(

where d is the distance, �1 is

the reference distance and n is the pathloss exponent.

– Pathloss exponent indicates the rate at which the

pathloss increase with distance and depends on the

environment.

– Reference distance: Large system (1km) , small (1m)

Log-distance Path loss model

Log-normal Shadowing

• The log-distance model does not include the difference in the surrounding environments at two points with the same T-R separation.

• /0 � � /0 �1 � 105 !" 2

26� 78 where 9: is a

zero-mean Gaussian distribution random variable with standard deviation :.

• : and n are computed from measured data to reduce the difference between the measured and the estimated path losses.

• Probability the received signal level will exceed </. � ��= � /> ��= − /0 � [��= �

Log-normal Shadowing

• Probability the received signal level will

exceed <

Pr /. � > < � D�EFGH��8

• Probability the received signal level will

bebelow<

Pr /. � < < � D�FE�GH��8

Log-normal Shadowing

Example 4.9

Outdoor Propagation Models

• Durkin’s Model is a simulator consists of two

parts

1. Access to a topographic data base of the area.

2. Simulation of the received power at a different

receiver location.

Durkin’s Model – Profile construction

Durkin Model – LOS decision

Durkin Model – Non LOS case

“Epstein and Peterson method”

Okumura Model

• One of the most widely used models in urban areas.

• Applicable for frequency ranges from 150-1920 MHz, distances from 1km to 100 km and tower heights from 30m to 1000m.

• Wholly based on measured data and does not provide any analytical explanation.

• Used by many standards for system planning in Japan.

• Bad performance in rural area.

• Empirically formulated by HATA model (refer to section 4.10.4)

Okumura Model (2)

• O �P � OQ � RST U, � − W XYZ − W X[Z − WR\]R

• Where

– 0^: free space propagation losses. ????

– _`a b, � : the median attenuation relative to the

free space (given by a curve).

– � �cd : Base station antenna height gain factor.

– � �.d : Mobile antenna height gain factor.

– � �.d and � �.d are functions of the height but

with antenna pattern (refer to Eq. 4.81).

Okumura Model (3)

Okumura Model (4)

The major disadvantage with the model is its low response to

rapid changes in terrain, therefore the model is fairly good in

urban areas, but not as good in rural areas.

Common standard deviations between predicted and measured

path loss values are around 10 to 14 dB.

m30m1000200

log20)( >>

= tete

te hh

hG

m33

log10)( ≤

= rere

re hh

hG

m3m103

log20)( >>

= rere

re hh

hG

Hata Model (1)

Empirical formulation of the graphical data in the Okamura model.

Valid 150MHz to 1500MHz, Used for cellular systems

The path loss given by Hata is:

fc is the frequency in MHZ (150 MHz-1500 MHz)

hte is the effective base station height.

hre is the effective mobile station height

a(hre ) is correction factor given by

1) For small to median city

2) For large cities

( ) ( ) ,loglog511.69.4482.13log16.2655.6950 dhhahfL teretec −+−−+=

( ) ( ) ( ) dB8.0f log56.1 0.7-f log1.1 cc −−= rere hha

oo

( ) ( ) MHz300for dB1.1 1.54 log29.8 2 ≤−= crere fhha

( ) ( ) MHz300for dB97.4 11.75 log2.3 2 ≥−= crere fhha

Hata Model (2)

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

modified as

And the path loss for open rural area

Hata model is accurate for cell with radius larger than 1 km.

( ) ( )[ ] ,4.528/log2 25050 −−= cfurbanLL

( ) ( )[ ] ( ) ,94.40log33.18log78.4 25050 −+−= cc ffurbanLL

PCS Extension of Hata Model

COST-231 Hata Model, European standard

Higher frequencies: up to 2GHz

Smaller cell sizes

Lower antenna heights

( ) ( ) MretedB ChadhFL +−−+= loglog55.69.44

tec hfF log82.13log9.333.46 −+=

0

3=MC

Metropolitan centersMedium sized city and suburban areas

Indoor Propagation Model

The distances covered are much smaller

The variability of the environment is much greater

Key variables: layout of the building, construction materials,

building type, where the antenna mounted, …etc.

In general, indoor channels may be classified either as LOS or

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.

Floor attenuation factor (FAF)

Log-distance Path Loss Model

Signal Penetration into Buildings

RF penetration has been found to be a function of

frequency as well as height within the building. Signal

strength received inside a building increases with

height, and penetration loss decreases with increasing

frequency.

Walker’s work shows that building penetration loss

decrease at a rate of 1.9 dB per floor from the ground

level up to the 15th floor and then began increasing

above the 15th floor.

Some devices to conduct the signals into the buildings

Homework

• Due to 27/10/2014 (there will be quiz on he same day covering chapter 4)

• 4.9 (Ground Reflection model)

• 4.19 (Diffraction)

• 4.20 (Diffraction)

• 4.25 (Handoff + Log-normal shadowing)

• 4.29 (Link budget Calculation)

• Next Lecture : Small scale fading and multipath