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Radio Propagation
electricfield
magneticfield
propagation direction
Radio waves are one form of electromagnetic radiation having a
frequency range of about 3Hz to 3000 GHz
Used for indoor and outdoor communication
Can travel in all directions
Can travel long distances
Can penetrate buildings ,foliage etc
Power falls off sharply with distance from source to destination
They are subject to interference from other radio wave
Modeling the radio channel has historically
been one of the most difficult part of mobile
radio system design.
Un-like wired channels that are stationary and
predictable, radio channels are extremely random and
do not offer easy analysis.
It is typically done in a statistical fashion which is based
on measurement made specifically for an intended
communication system or spectrum allocated.
Limitation of Mobile Radio Propagation in
Wireless Communication
The communication between Tx and Rx takes place by simple Line of sight (LOS).
But the path between Tx and Rx may vary from LOS to one that is severely obstructed by buildings, mountains, and foliage.
They generally do this in followig ways:
Directly from one point to another
Following the curvature of the earth
Becoming trapped in the atmosphere and
traveling longer distances
Refracting off the ionosphere back to earth.
Follows contour of the earth
Can propagate considerable distances
Frequencies up to 2 MHz
Example: AM radio
Signal reflected from ionized layer of atmosphere back down to earth
Signal can travel a number of hops, back and forth between ionosphere and earth’s surface
Examples: amateur radio, CB radio,
Tx and Rx antennas must be within line of sight
When wave changes medium, speed changes (Velocity of em wave is a function of the density of the medium)
Attaining good LOS between Tx and Rx antenna is essential in
both Point to Point and Point to Multipoint installations.
Generally there are two types of LOS that are used during
installations:
1. Optical LOS - is related to the ability to see one site
from the other
2. Radio LOS – related to the ability of the receiver to
‘see’ the transmitted signal
Optical line of sight
Radio line of sight
d = distance between antenna and horizon (km)
h = antenna height (m)
K = adjustment factor (earth bulge)to account for refraction, rule of thumb (normal) K = 4/3
hd 57.3
hd 57.3
Maximum distance between two antennas for LOS
propagation:
h1 = height of antenna one
h2 = height of antenna two
2157.3 hh
To quantify(Determine) Radio Line of
Sight(LOS), the Fresnel Zone theory is applied.
The concept of diffraction loss as a function of the path difference around an obstruction is explained by Fresnel zone.
The area around the visual line-of-sight that radio waves spread out into after they leave the antenna.
Fresnel Zone as a football shaped tunnel between the two sites which provides a path for the RF signals
Site A
Site B
d2
d1
The concept of Fresnel zone clearance
may be used to analyze interference by
obstacles near the path of a radio beam .
First determine the RF LoS ,
Zone surrounding the RF LoS is said to
be the Fresnel zone
2nd* 1st*3rd*
* Fresnel Zones
How To Calculate Fresnel zone
radius
?
◦
The general equation for calculating the Fresnel zone radius at any point P is given by
where, Fn = The nth Fresnel Zone radius in meters d1 = The distance of P from one end in meters d2 = The distance of P from the other end in meters λ = The wavelength of the transmitted signal in meters
◦
The strongest signals are on the LOS between Tx and Rx and always lies in the 1st Fresnel Zone.
This area must be clear or else signal strength will weaken.
For minimum Diffraction Loss, clearance of at least 0.6F1+ 3m is required.
Radio Wave Propagation Model
Obstructions in the first Fresnel Zone may create
many issues which affect the performance of the
system.
Also reflection, refrection and scattering create many
issues in LOS
These issues are sorted by many radio propagation
model.
Desert Metro Street Indoor
If the transmitter
- changes transmit power ?
- changes frequency ?
- operates at higher speed ?
What will happen
if the receiver
moves?
What will happen if the medium of
propagation is different types ?
Channel effects
Effect of mobility
Transmit power, data rate,
signal bandwidth, frequency
tradeoff
Tx
Rx
Radio Propagation Models are used to predict
received power or path loss based on refraction,
reflection, diffraction and scattering
• Large Scale Models
• Small scale (Fading) Models
Propagation models that characterized signal strength over a large Tx-Rx separation
Large scale models predict behavior averaged over distances >>
Function of distance & significant environmental features, independent of frequency◦ Breaks down as distance decreases◦ Useful for modeling the range of a radio system and rough
capacity planning
Large scale
Model that characterize the rapid fluctuations over the received signal strength at very short distance travelled or short time duration ◦ Multipath effects dominate◦ Frequency and bandwidth dependent
Small scale
Radio Wave Propagation Model
Free Space Propagation Model
• It is Used to predict received signal strength when the transmitter and receiver have a clear line-of-sight path
– satellite communication
– microwave line-of-sight radio link
• Friis free space equation
: transmitted power : T-R separation distance (m)
: received power : system loss
: transmitter antenna gain : wave length in (m)
: receiver antenna gain
Note :The friis free equation shows that the received power fall off as the square with Tx-Rx separation.
Ld
GGPdP rtt
r 22
2
)4()(
tP
)(dPr
tG
rG
d
L
• The gain of the antenna
: effective aperture is related to the physical size of the antenna
• The wave length is related to the carrier frequency by
: carrier frequency in Hertz
: carrier frequency in radians
: speed of light (m/s)
• The losses are usually due to transmission line attenuation, filter losses, and antenna losses in the communication system. A value of L=1 indicates no loss in the system hardware.
2
4
eAG
eA
c
c
f
c
2
f
cc
L )1( L
• Path loss is the difference between transmitted power and received power and may or may not include antenna gain effect
• When antenna gains are included
• When antenna gains are excluded
• The Friis free space model is only a valid predictor for for values of d which is in the far-field (Fraunhofer region) of the transmission antenna.
22
2
)4(log10log10)(
d
GG
P
PdBPL rt
r
t
22
2
)4(log10log10)(
dP
PdBPL
r
t
rP
• The far-field region of a Tx is defined as the region beyond the far-field distance
where D is the largest physical linear dimension of the antenna.
• To be in the far-filed region the following equations must be satisfied
and
• The following equation does not hold for d=0.
• Use close-in distance and a known received power at that point
or
22Dd f
Dd f fd
Ld
GGPdP rtt
r 22
2
)4()(
0d)( 0dPr
2
00)()(
d
ddPdP rr
fddd 0
d
ddPdP r
r00 log20
W 001.0
)(log10dBm )(
fddd 0
Given
A transmitter produces 50W of power.
If this power is applied to a unity gain antenna with
900 MHz carrier frequency, find the received power
at a free space distance of 100 m from the antenna.
What is the received power at 10 km?
Assume unity gain for the receiver antenna.
Pr = Pt Gt Gr 2/(4)2 d2 L
Pt = 50 WFc = 900 MhzGt = 1Gr = 1 = (3 • 108) / (900 • 106) = 0.33 mL = 1d = 100 m
Pr = 3.5 • 10-3 mW
Pr (10 km)= Pr (100 m) • (100m/10km)2
= 3.5 • 10-3 mW • 1/100
= 3.5 • 10-6 mW
Free space propagation model is in most cases inaccurate
when used alone
Because ,hardly there is LOS between Tx and Rx in mobile
communication
2- Ray model has been found to be reasonably
accurate for predicting the large scale signal strength
over distance of tens of Km that uses tall towers(50m
high) as well as for LOS microcell channel in urban
areas.
2 Ray ground Reflection model assumes one direct
LOS path and one reflected path reached receiver
with significant power Intuition: ground blocks 1st Fresnel zone
RT
ht hrp1
p0
hr
ht
d
ELOSETOT = ELOS + Eg
Eg (d’’)
(q q)
(d’)
If E0 is the free space E-Field at a reference distance d0 from transmitter then for d≥d0 ,the free space propagation E Filed is given by
= Fresnel reflection coefficient as a function of: material properties, polarization of wave angle of incidence signal
frequency
))''
(cos(''
),"(
))'
(cos('
),'(
c
dtw
d
dEtdE
c
dtw
d
dEtdE
coo
g
coo
LOS
is the amplitude of the electric field at distance d
ωc = 2πfc where fc is the carrier frequency of the signal
Γ = −1
Path difference depends on the phase difference between direct and reflected wave.
∆ = d”− d’
The phase difference θ∆ is due to Path difference ,
The mirror images mehtod is used to find out the difference between the LoS and Eg
if d >> (ht + hr),
Then and will be very small
Assuming “d” very very large then the difference between d’ and d’’ becomes very small and the amplitude of E los and Eg are virtually indentical and differ only in phase
= =
By putting various values we have
where k is a constant related to E0,antenna height and the wavelenght
for large distances it can be shown that the received
power falloff with distance raised to the fourth power
dhhG
GdBPdBdP
d
hhGGPdP
rtr
ttr
rtrttr
log40log20log20log10
log10)(
)(4
22
So Two-ray model has power fall off with d4 (40dB/decade) Because of Pr 1/d4
A mobile is located 5 km away from a base station, and uses a vertical /4 monopole antenna with a gain of 2.55dB to receive cellular radio signals. The electric field at 1 km from the transmitter is measured to be 10-3 V/m. The carrier frequency used is 900 MHz.
(a) Find the length and the effective aperture of receiving antenna.
(b) Find the received power at the mobile using the 2-way ground model assuming the height of the transmitting antenna is 50 m and receiving antenna is 1.5 m above the ground.
d0 = 1 km
E0 = 10 -3 V/m
ht=50 m
hr = 1.5 m
d = 5 km
(a)
f = 900 MHz
= (3 * 108) / (900 * 106) = 0.33 m
Length of receiving antenna,
L = / 4 = 0.33/4 = 0.0833 m = 8.33 cm
(b)
Gain of antenna = 2.55 dB = > 1.8
Er (d) = (2 E0 d0 2 ht hr ) / ( d2 )
= 2•10-3•1•103•2 •50 •1.5/(5 • 103)2 • 0.333
= 113.1 • 10-6 V/m
Pr (d)
= I Er I2 2 Gr
4
= (113.1 • 10-6) 2 • (0.333) 2 • 1.8
377 4
= 5.4 • 10-13 W
= -92.68 dBm
… Very Good Morning
Small scale Propagation models describe signal variability on a scale of
Multipath effects dominate
Frequency and bandwidth dependent
Time variation of received signal power caused by
changes in the transmission medium and path(s).
Caused by interference between two or more versions
of the transmitted signal which arrive at the receiver at
slightly different times.
Combine at the receiver antenna to give a resultant
signal which can vary widely in amplitude and phase
Fading may cause disruptions in the communication
In fixed environment is caused by atmospheric
conditions.
In mobile environment creates more complex effects
Rapid fluctuations of the amplitude, phase or
multipath delays of a radio signal over short
period of time or travel distance
Speed of mobile
◦ Cause Doppler shift at each multipath component
◦ Causes random frequency modulation
Multipath propagation
◦ Presence of reflecting objects and scatterer cause
multiple versions of the signal to arrive at the
receiver
When a transmitter or receiver is moving, the frequency of
the received signal changes,
The change in frequency is called Doppler Shift
If the mobile is moving toward the direction of arrival of the
wave is called positive Doppler shift.
If the mobile is moving away from the direction of arrival of the
wave is called negative negative shift
The frequency of the signal
that is received in front of the
transmitter will be bigger
The frequency of the signal
that is received behind the
transmitter will be smaller
At a receiver point ,radio waves
generated from the same transmitted
signal may come
from different directions
with different propagation delays
with different amplitudes (random)
with different phases (random)
with different angles of arrival (random).
Obstacles reflect signals so that multiple copies with varying delays are received
Reasons Behind
Reflection
Diffraction
Refrection
Scattering
Multiple copies of a signal may arrive at different phases◦ If phases add destructively, the signal level relative to
noise declines, making detection more difficult
Intersymbol interference (ISI)◦ One or more delayed copies of a pulse may arrive at the
same time as the primary pulse for a subsequent bit
transmitted
signal
received
signal
Ts
tmax
Based onMulti path time delay
Based on Doppler spread
Flat fading
BC
BS
Frequency selective fading BC
BS
TC
TSSlow fading
Fast fading
TC
TS
fading
In order to compare different multipath channels we
need parameters which quantify the multipath channel,
which are as follows
1. Delay spread
2. Coherence bandwidth
3. Doppler spread
4. Coherence time
The time delay spread is the total time interval
during which reflections with significant energy
arrive. Types of Delay Spread
- Mean excess delay
- RMS delay spread
- Maximum Excess delay
Mean excess delay is the first moment of the power
delay profile and is defined by the equation
h
k
h
kk
k
k
k
kk
P
P
a
a
)(
)(
2
2
t
ttt
t
Defined as the time delay value after which the multipath energy falls to
X dB below the maximum multipath energy (not necesarily belonging to
the first arriving component).
It is also called excess delay spread.
RMS delay spread is the square root of the second
central moment of the power delay profile and is defined
by the equation:
where
22 )(tt t
h
k
h
kk
k
k
k
kk
P
P
a
a
)(
)(2
2
22
2
t
ttt
t
Delay spread figures
at 900 MHz
Delay in
microseconds
Urban 1.3
Urban, worst-case 10 - 25
Suburban, typical 0.2 - 0.31
Suburban, extreme 1.96 - 2.11
Indoor, maximum 0.27
Delay Spread at 1900 MHz
Buildings, average 0.07 - 0.094
Buildings, worst -
case
1.47
◦ Range of frequencies over which the channel can
be considered flat (i.e. channel passes all spectral
components with equal gain and linear phase).
Effect of frequency selective fading on the received signal spectrum
Signal bandwidth Bs
Freq.
Power
Describes
frequency
selective
phenomenon of
fast fadingCoherence
Bandwidth Bc
50
1CB
5
1CB
CS 515© İbrahim Körpeoğlu
107
Coherence Bandwidth (BC) is the range of frequencies over which the
frequency correlation is above 0.9, then
If we define Coherence Bandwidth as the range of frequencies over which the frequency correlation is above 0.5, then
is rms delay spread.
This is called 50% coherence bandwidth.
Coherence time is the time duration over which the channel impulse responseis essentially invariant.
If the symbol period of the baseband signal is greater then coherence time, than the signal will distort, since channel will change during the transmission of the signal .
mfCT 1
Coherence time (TC) is defined as: TS
TC
Dt=t2 - t1t1 t2
f1f2
mfC
fT
m
423.0216
9
Coherence time is also defined as:
Coherence time definition implies that two signals arriving with a time separation greater than TC are affected differently by the channel.
Multipath Time delay spread causes the
transmitted signal to undergo two types of
fading
Flat Fading
Frequency selective fading
Occurs when the amplitude of the received signal
changes with time
Occurs when symbol period of the transmitted signal is
much smaller than the Delay Spread of the channel
May cause deep fades.
Increase the transmit power to combat this situation.
BS << BC
TS >> t
CS 515© İbrahim Körpeoğlu
115
h(t,ts(t) r(t)
0 TS 0 t 0 TS+t
t << TS
Occurs when:BS << BC
andTS >> t
BC: Coherence bandwidthBS: Signal bandwidthTS: Symbol periodt: Delay Spread
Occurs when channel multipath delay spread is greater than the symbol period.
Bandwidth of the signal s(t) is wider than the channel impulse response.
◦ Symbols face time dispersion
◦ Channel induces Intersymbol Interference (ISI)
BS > BC
andTS < t
h(t,ts(t) r(t)
0 TS 0 t 0 TS+t
t TS
TS
Causes distortion of the received baseband signal
Causes Inter-Symbol Interference (ISI)
Due to Doppler Spread
Rate of change of the channel characteristic is largerthan the Rate of change of the transmitted signal
The channel changes during a symbol period.
The channel changes because of receiver motion.
Coherence time of the channel is smaller than the symbol period of the transmitter signal
CS 515© İbrahim Körpeoğlu
119
Occurs when:BS < BD
andTS > TC
BS: Bandwidth of the signalBD: Doppler SpreadTS: Symbol PeriodTC: Coherence Bandwidth
Due to Doppler Spread
Rate of change of the channel characteristicsis much smaller than the Rate of change of
the transmitted signal
Occurs when:BS >> BD
andTS << TC
BS: Bandwidth of the signalBD: Doppler SpreadTS: Symbol PeriodTC: Coherence Bandwidth
There are Several Methods to measure small scale fading◦ Direct RF Pulse System
◦ Spread Spectrum Sliding Correlator Channel Sounding
◦ Frequency Domain Channel Sounding
These techniques are also called channel sounding techniques
CS 515© İbrahim Körpeoğlu
123
125
Pulse Generator
BPF DetectorDigital
Oscilloscope
RF Link
fc
Tx
Rx
A simple channel sounding approach is the direct RF pulse
system as shown in the figure.
This technique allows engineers to determine rapidly the
power delay profile of any channel, essentially a wideband
pulsed.
This system transmits a repetitive pulse of width Tbb , and
uses a receiver with a wide band-pass filter (BW=2/Tbb Hz).
The signal is then amplified, detected with an envelope
detector, and displayed and stored on a high speed
oscilloscope.
This gives an immediate measurement of the square of the
channel impulse response convolved with the probing pulse .
If the oscilloscope is set on averaging mode, then this system
can provide a local average power delay profile.
Another attractive aspect of this system is the lack of
complexity, since off-the shelf equipment may be used.
The minimum resolvable delay between multipath
components is equal to the probing pulse width Tbb.
The main problem with this system is that it is subject to
interference and noise, due to the wide pass-band filter
required for multipath time resolution.
Also, the pulse system relies on the ability to trigger the
oscilloscope on the first arriving signal.
If the first arriving signal is blocked or fades, severe fading occurs, and it is possible the system may not trigger properly.
Another disadvantage is that the phases of the individual multipath components are not received, due to the use of an envelope detector.
However, use of a coherent detector permits measurement of the multipath phase using this technique.
Indoor Propagation model
?
Indoor channels are different from
traditional mobile radio channels in two
different ways:
The distances covered are much smaller
The variablity of the environment is much greater
for a much smaller range of T-R separation
distances.
The first home in which the units were tested was built
in 1910.
It was a 24’x50’ two-story home with a basement.
Two units were placed at various locations within the
home and tested to see if they could communicate with
one another.
In this test, the two link failures occurred in only
one direction.
In the first failure, one unit was placed on top of a
bookcase in bedroom #3, while the other unit was
positioned in the master bedroom.
The link was successful in both directions when just
the master bedroom door was open and when both
bedroom doors were open.
However, if either the master bedroom door or both
bedroom doors were closed, the link from the master
bedroom to bedroom #3 was unsuccessful.
In this scenario, the additional attenuation
provided by the doors was just enough to prevent
the units from working correctly.
The second failure occurred when the unit in
the master bedroom was moved to a shelf in
the storage room in the basement.
In this case, the link from the storage room to
the master bedroom was successful, while the
opposite link was not.
So we can say that the propagation
inside a building is influenced by:
Layout of the building
Construction materials
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 stores
Retail stores
Sport arenas
Indoor propagation is dominated by the same mechanisms as outdoor:-
Reflection,
Diffraction
Scattering,
◦ However, conditions are much more variable
The level of floors
Doors/windows open or closed
◦ Line-of-sight (LOS)
◦ Obstructed (OBS) with varying degrees of clutter
Fading for fixed and moving terminals Motion of people inside building causes
Ricean Fading for the stationary receivers Portable receivers experience in general Rayleigh fading for OBS propagation paths Ricean fading for LOS paths.
Delay spread is the total time interval during which reflections with significant energy arrive at the recevier.
Buildings with fewer metals and hard-partitions typically have small delay spreads: 30-60 ns.
Larger buildings with great amount of metal and open aisles may have rms delay spreads as large as 300ns.
Despite many acceleration techniques being applied,
the use of accurate propagation modeling for indoor
scenarios remains limited due to the complex indoor
propagation environment.
We have following approaches
Empirical models are mainly based on empirical factors such
as distance or frequency. Mean received signal power is attenuated as a function of the
distance.
For indoor propagation this mechanism is less relevant, but effects a wave guidance through corridors can occur
They are computationally fast but they do not consider a great
deal of environmental information so their accuracy is limited.
Deterministic approaches take into account the
environmental information such as object positions and
the corresponding materials.
Although these approaches are more time-consuming
when compared to empirical models but allow for a
higher level of accuracy to be obtained.
Existing Indoor Propagation Models
The log-distance path loss model assumes that path
loss varies exponentially with distance.
Where
n =s the path loss exponent,
d = T-R separation in meters,
d0 = close-in reference distance in meters.
PL(d0) is computed using the free space path loss equation
Building Type Path loss Exponents
Free Space 2.0
Retail store 2.2
Grocery store 1.8
Urban cell 2.7-3.5
Urban cell shadowed 3-5
In building, Line of sight 1.6-1.8
Obstructed In building,4-6
Obstructed in factories 2 - 3
If there is any obstacles between Tx and Rx
Then
log –Distance Formula is applicable or Not
?
One downfall of the log-distance path loss model is that
it does not account for shadowing
Effects that can be caused by varying degrees of clutter
between the transmitter and receiver.
The log-normal shadowing model attempts to compensate for this.
PL(dB] = PL(d0) + 10nlog(d/d0) + X
Where X is a zero-mean Gaussian random
variable with standard deviation
Building Frequency (MHz) n (dB)
Retail Stores 914 2.2 8.7
Grocery Store 914 1.8 5.2
Office, hard partition 1500 3.0 7.0
Office, soft partition 900 2.4 9.6
Office, soft partition 1900 2.6 14.1
Factory LOS
Textile/Chemical 1300 2.0 3.0
Textile/Chemical 4000 2.1 7.0
Paper/Cereals 1300 1.8 6.0
Metalworking 1300 1.6 5.8
Suburban Home
Indoor Street 900 3.0 7.0
Factory OBS
Textile/Chemical 4000 2.1 9.7
Metalworking 1300 3.3 6.8
Several researchers have attempted to modify the
log-distance model by including additional
attenuation factors based upon measured data.
One example is the attenuation factor model
proposed by Seidel and Rappaport .
The attenuation factor model incorporates a
special
path loss exponent and a floor attenuation factor to
provide an estimate of indoor path loss
where nsf is the path loss exponent for a same floor
measurement and FAF is a floor attenuation factor
based on the number of floors between transmitter
and receiver.
Partition losses (same floor)
Partition losses between floors
Signal Penetration into Buildings
The path loss depends on the type of the partitions
There are two kind of partition at the same
floor:
◦ Hard partions: the walls of the rooms
◦ Soft partitions: moveable partitions that does not
span to the ceiling
The losses between floors of a building are
determined by
External dimensions and materials of the building
Type of construction used to create floors
External surroundings
Number of windows
Presence of tinting on windows
Building FAF (dB) (dB)
Office Building 1
Through 1 Floor 12.9 7.0
Through 2 Floors 18.7 2.8
Through 3 Floors 24.4 1.7
Through 4 Floors 27.0 1.5
Office Building 2
Through 1 Floor 16.2 2.9
Through 2 Floors 27.5 5.4
Through 3 Floors 31.6 7.2
Average Floor Attenuation Factor in dB for
One, Two, Three and
Four Floors in Two Office Buildings
Material Type Loss (dB) Frequency (MHz)
All metal 26 815
Aluminim Siding 20.4 815
Concerete Block Wall 3.9 1300
Loss from one Floor 20-30 1300
Turning an Angle in a Corridor 10-15 1300
Concrete Floor 10 1300
Dry Plywood (3/4in) – 1 sheet 1 9600
Wet Plywood (3/4in) – 1 sheet 19 9600
Aluminum (1/8in) – 1 sheet 47 9600
Average signal loss measurements reported by
various researches for radio paths obscructed
by some common building material.
RF signals can penetrate from outside
transmitter to the inside of buildings
However the siganls are attenuated
The path loss during penetration has been found
to be a function of:
Frequency of the signal
The height of the building
Frequency (MHz) Loss (dB)
441 16.4
896.5 11.6
1400 7.6
Penetration loss decreases with increasing frequency
Penetration loss decreases with the height of
the building up-to some certain height
At lower heights, the urban clutter induces
greater attenuation
and then it increases
Shadowing affects of adjascent buildings
The indoor channel typically behaves as a Rician
channel.
If the line-of-sight is blocked.
Rayleigh fading becomes an appropriate model
Rician fading is similar to that for Rayleigh, except that in Rician fading a strong dominant component is present.
This dominant component can for instance be the line-of-sight wave.
Refined Rician models also consider that the dominant wave can be a phasor sum of two or more dominant signals, e.g. the LOS, plus a ground reflection.
This combined signal is then mostly treated as a deterministic (fully predictable) process, and that the dominant wave can also be subject to shadow attenuation.
Besides the dominant component, the mobile antenna receives a large number of reflected and scattered waves
Rayleigh fading is caused by multipath reception.
The mobile antenna receives a large number, say N,
reflected and scattered waves.
Because of wave cancellation effects, the
instantaneous received power seen by a moving
antenna becomes a random variable, dependent on
the location of the antenna.
1- Describe fading and its classification ?
2-Discuss impulse response Model of a multipath
channel ?
3-Explain small scale multipath measurement?
4-what is shape factor ? Discuss
5- Describe different types of diversity ?
Radio communication in a mobile systems often takes place over
a irregular terrain
The terrain profile vary from plan to highly mountainous and
dessert
That terrain help for estimating the path loss
The presence of trees, building, and other obstacle also must be
taken into account.
A number of propagation models are available to predict path loss
over irregular terrain.
Varies widely in their approach, complexity and accuracy.
These models are based on systematic interpretation of
measurement data obtained in the service area.
Longley-Rice Model
Durkin’s Model
Okumura’s Model
Hata Model
PCS extension to Hata Model
Walfisch and Bertoni
The Okumura model is a Radio propagation model
Built using the data collected in the city of Tokyo.
Ideal for using in cities with many urban structures but not
many tall blocking structures.
The model served as a base for the Hata Model.
Built into three modes
◦ Urban,
◦ Suburban
◦ Open areas.
Wholly based on measured data , no analytical explanation◦ Among the simplest & best for in terms of path loss
accuracy in cluttered mobile environment
◦ useful for
frequencies ranging from 150MHz-1920MHz
distances from 1km to 100km
base station antenna heights from 30m-1000m
◦
◦ Slow response to rapid terrain changes
◦ Common standard deviations between predicted & measured path loss 10dB - 14dB
◦ widely used for urban areas
Estimating path loss using Okumura Model
1. Determine free space loss, 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 (median)
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
Am
u(f
,d)
(dB
)
70 100 200 300 500 700 1000 2000 3000 f (MHz)
100
807060
50
40
30
2010521
d(km
)
Urban Areaht = 200mhr = 3m
Median Attenuation Relative to Free Space = Amu(f,d) (dB)
35
30
25
20
15
10
5
0
GA
RE
A(d
B)
100 200 300 500 700 103 2103 3 103
frequency (MHz)
suburban areaquasi open areaopen area
Correction Factor = GAREA(dB)
An empirical model based on Okumura
Predicts median path loss for different channels
Valid over UHF/VHF band from 150MHz-1.5GHz
Charts used to characterize factors affecting mobile land propagation
Standard formulas for approximating urban propagation loss
L50 (urban)(dB) = A + B log10d
A= 69.55 + 26.16 log10(fc) – 13.82 log10(hte) – (hre)
• represents fixed loss – dependence on fc
• dependence on antenna heights
B= 44.9 - 6.55 log10(hte)
• represents path loss exponent, worst case ≈ 4.5
L50 (urban)(dB) = 69.55 + 26.16log10 fc – 13.82 log10 hte – (hre)
+ (44.9-6.55hte)log10 d
Mobile Antenna Height Correction Factor for Hata Model
(hre) Comment(1.1log10 fc - 0.7)hre – (1.56log10 fc - 0.8)dB Medium City 3.83
8.29(log10 1.54hre)2 – 1.1 dB Large City (fc
300MHz)
3.84
a
3.2(log10 11.75hre)2 – 4.97 dB Large City (fc >
300MHz)3.84
b
L50 (dB) Comment
L50 (urban) - 2[log10 (fc/28)]2 – 5.4 Suburban Area 3.85
L50 (urban) - 4.78(log10 fc)2 - 18.33log10 fc -
40.98
Rural Area 3.86
• represent reductions in fixed losses for less demanding environments
Hata Model for Rural and Suburban Regions
Valid Range for Parameters
• 150MHz < fc < 1GHz
• 30m < hb < 200m
• 1m < hm < 10m
• 1km < r < 20km
Propagation losses increase
• with frequency
• in built up areas
