eele 5414 wireless communications -...
TRANSCRIPT
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