1. Wireless Communication Channels: Large-Scale Pathloss

2. The Three Basic Propagation Mechanisms
Three basic mechanisms that impact propagation in a mobile communication system
Reflection
A propagating electromagnetic wave impinges upon an object which has very large dimension compared to the wavelength
Reflection occurs from surface of earth and from buildings and walls
Diffraction
The radio path between the transmitter and receiver is obstructed by a surface that has sharp irregularities
Scattering
When the medium consists of objects with dimensions that are small compared to the wavelength

3. Reflection

4. Reflection from Dielectrics
Normal Incidence
Parallel Incidence Er Ei Ei Er Hi Hr Hr Hi Et Et
Snell’s Law

5. Reflection from Dielectrics
Normal Incidence
Parallel Incidence Er Ei Ei Er Hi Hr Hr Hi Et Et
First Medium is Free space and μ1 = μ2

6. Reflection from Dielectrics
Normal Incidence
Parallel Incidence Er Ei Ei Er Hi Hr Hr Hi Et Et
First Medium is Free space and μ1 = μ2 , θi approaches 0
This shows that the ground may be modeled as a perfect reflector with a reflection coefficient of unit magnitude when an incident wave grazes the earth regardless of the polarization or dielectric properties

7. Ground Reflection (Two-Ray) Model
Transmitter
ETOT=ELOS+Eg
ELOS
Receiver Ei ht
Er= Eg hr d
A single direct path between the base station and a mobile is seldom the only means for propagation
Friis equation is most likely inaccurate
Two ray ground reflection model has been found to be reasonably accurate for predicting large scale strength over distances of several Kms for mobile radio systems that use tall towers
Power Flux Density

8. Ground Reflection (Two-Ray) Model
Assuming grazing incidence Γ=-1 for normal incidence

9. Ground Reflection (Two-Ray) Modelht
ELOS Ei
Er= Eg
Transmitter
Receiver
ETOT=ELOS+Eg d hr d’
d’’

10. Ground Reflection (Two-Ray) Model
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11. Ground Reflection (Two-Ray) Model
Slide 9
Let evaluate ETOT at t=d’’/c
ETOT

12. Ground Reflection (Two-Ray) Model
Assume for large d
Note that rather than using phasors, we could also use
Important Note:
The significance of the path difference Δ appears in the phase difference θΔ between the two waves (LOS and Reflected Wave)

13. Ground Reflection (Two-Ray) Model
Under the assumption

14. Ground Reflection (Two-Ray) Model
But from LOS analysis

15. Ground Reflection (Two-Ray) Model Notes
The received power falls off with distance raised to the fourth power, 40 dB/decade
Much rapid than free space
The received power and path-loss are no longer dependent on frequency
PL(dB)=40logd-(10logGT+10logGR+20loght+20loghr)