Cellular and Mobile Communications
20EC1158
Unit-4 :
Mobile Propagation Environment
1
Unit-4 : Mobile Propagation Environment
SYLLABUS :
Introduction, Signal reflections in flat and hilly terrain, Mobile
Point-to-Point Model (Lee model) – standard condition, area-area
prediction curves for human - made structures, phase difference
between direct and reflected paths, general formula for mobile
radio propagation, Propagation over water or flat open area,
Foliage loss, near and long distance propagation, Path Loss from
a Point to Point Prediction Model in different Conditions.
2
INTRODUCTION
INTRODUCTION
INTRODUCTION
Cell Coverage
• Cell Coverage can be based on signal coverage or
on traffic coverage.
• Signal coverage can be predicted by coverage
prediction models. i.e how the area is covered
with a minimum number of cell sites.
• The cell sites must be engineered so that the
holes are located in the no-traffic locations.
• Ex : point-to-point prediction model ( lee model )
• The results generated from the predicted model
differs on the type of service area used.
Service area
• Service area encounters one of the following
environments:
Ground incident angle, Elevation angle
• Incident angle : The angle of wave arrival
incidently pointing to the ground.
• Elevation angle : The angle of wave arrival at
the mobile unit.
Ground Reflection angle
• Reflection angle : The angle of wave reflected
from the ground.
• Based on Snell’s law;
Angle of Incidence = Angle of Reflection
Example : Flat Terrain
Example : Hilly Terrain
point-to-point Lee prediction model
• Point-to-point lee model is obtained in 3 steps
1. Generate a standard condition
2. Obtain an area-to-area prediction model
3. Obtain a point-to-point model using the area-
to-area model as a base.
point-to-point Lee prediction model
A standard condition :
• To generate a standard condition the following
table is used.
point-to-point Lee prediction model
Area-to-Area prediction curves for man-made
structures
• Assumption : Areas are considered flat even though the data
may be obtained from non-flat areas.
• Area-to-Area prediction curves are different in different areas.
Different man-made structures gives different Area-to-Area
prediction curves.
• Measurements made in urban areas is different from sub-
urban and open or rural areas.
• Signal strength is measured at high spots and at low spots
surrounding the cell-sites.
• Area-to-Area prediction is an average process.
• The standard deviation of the average value indicates the
degree of terrain roughness.
Path Loss for Human-made structures
a) Measurement area selection b) Pathloss Phenomena
1-mile intercept is considered as a starting point for obtaining the path loss curves.
point-to-point Lee prediction model
Area-to-Area prediction curves for man-made
structures
• Area-to-Area prediction model can be represented by two parameters:
1. 1-mi intercept point: the power received at a distance of 1 mile from the
transmitter.
2. The path loss slope.
• Two general approaches to find these values experimentally are
1. Compare the area of interest with an area of similar human-made
structures whose path loss is already measured for certain cities.
2. If the human-made structures of a city are different from the cities listed,
- set up a transmitting antenna at the center of the general area.
- take 6 or 7 measured data points around 1-mi intercept and around the
10-mi boundary based on the high and low spots.
- Then compute the average of the 1-mi data points and of the 10-mi data
points.
- By connecting the two values, the path-loss slope can be obtained.
Propagation Path Loss in different
Areas
• If the terrain of the hilly area is generally sloped,
then data points measured have to be converted.
Path-loss phenomena
with different 1-mi intercept and different slopes
BS antenna is located in the city
BS antenna is located outside the city
Structures are uniformly distributed
Two-Ray Ground Reflection Model
Two-Ray Ground Reflection Model
Assumption :
d >> (ht + hr)
Two-Ray Ground Reflection Model
• Received Power considering Gain of
transmitting and receiving antennas :
• Pathloss in dB:
General path loss formula for mobile
propagation
• Considerations :
– Sub-urban area
– Power at 1-mi intercept level under standard conditions as
per the table is P = -67.1 dBm and
Propagation Over Water
Two Cases
1. Fixed point-to-point transmission over a water
2. Land-to-mobile transmission over a water
Fixed point-to-point transmission
over a water
• Received power at a distance ‘d’ is estimated
by using the formula
Fixed point-to-point transmission
over a water
• Received power at a distance ‘d’ is estimated
by using the formula
Fixed point-to-point transmission
over a water
• h1 and h2 are
actual heights of the
antennas.
•H1 and H2 are
height of the hills.
over water
Path difference
Phase Difference
• Substituting in the received power
equation,
Numerical-1
Numerical 1- Solution
Numerical -2
Land – to-mobile transmission
over a water
Fixed
antenna
Mobile
user
Land – to – mobile transmission model over a water
Path Loss from point-to-point Lee
model in different conditions
• Line-of-sight path : un-obstructed by both terrain
contour and man-made structures.
• Non-obstructive direct path : un-obstructed by the
terrain contour and obstructed by man-made
structure.
• Obstructive path : obstructed by the terrain contour
Finding antenna height gain
Illustration of the terrain effect on the effective
antenna height gain at each position.
Illustration of the terrain effect on the effective
antenna height gain at each position.
Obstructive path condition: obstructed by
the terrain contour
Diffraction
Phenomena of diffraction:
Diffraction Gain
Merit of Point-to-Point Lee Model
Applications of Point-to-Point Lee
Model
Foliage Loss
67
Foliage Loss
68
Propagation in Near-in Distance
Why use 1-mi intercept?
69
Propagation in Near-in Distance
Why use 1-mi intercept?
70
Curves for Near-in Propagation
71
Curves for Near-in Propagation
72
Curves for Near-in Propagation
73
Long DistancePropagation: Within
50mi radius
74
