wireless communication

1. 19EC61C – WIRELESS COMMUNICATION
B. Ganapathy Ram
Assistant Professor (SG)
Department of ECE
National Engineering College

2. UNIT – 2
MOBILE RADIO WAVE PROPAGATION - LARGE
SCALE FADING
COURSE OUTCOME (CO)
CO 2: After completing this course you can able to analyze the propagation
models for large scale fading. (K2)
LECTURE 4
PATH LOSS MODELS

3. SIMPLIFIED PATH LOSS MODEL
 Accurate path loss models can be obtained from empirical
measurements to met system specifications and to determine
 the best locations for base stations.
 A simple model of signal propagation can be used instead of complex
one to approximate real channel.
 Simplified model for path loss as a function of distance is commonly
used for system design
d0 - reference distance for
the antenna far-field
γ - is the path loss exponent
K - constant which depends
on the antenna charac-
teristics and the average
channel attenuation

4. EMPIRICAL PATH LOSS MODELS
 Several path loss models are developed to predict path loss in typical
wireless environments such as large urban macrocells, urban microcells, and
inside buildings.
 These models are mainly based on empirical measurements over a given
distance in a given frequency range and a particular geographical area or
building.
 Many wireless systems use these models as a basis for performance
analysis.
1. Okumura’s Model
2. Hata Model
3. COST231 Extension to Hata Model
4. Walfisch/Bertoni Model
5. Piecewise Linear (Multi-Slope) Model
6. Indoor Propagation Models

5.  Okumura’s model is for signal prediction in large urban macrocells.
 It is applicable over distances of 1-100 Km and frequency ranges of 150-
1500 MHz.
 Okumura used extensive measurements of base station-to-mobile signal
attenuation throughout Tokyo to develop a set of curves giving median
attenuation relative to free space of signal propagation in irregular terrain.
 The base station heights for these measurements were 30-100 m, the
upper end of which is higher than typical base stations today.
OKUMURA’S MODEL

6. The path loss formula of Okumura is given by
d - distance between transmitter and receiver
L50 - median (50th percentile) value of propagation path loss
Lf - free space path loss
Amu - median attenuation in addition to free space path loss across
all environments
G(ht) - base station antenna height gain factor,
G(hr) - mobile antenna height gain factor
GAREA - gain due to the type of environment.

7. Okumura derived empirical formulas for G(ht) and G(hr) as
Okumura’s model has a 10-14 dB empirical standard deviation between
the path loss predicted by the model and the path loss associated with
one of the measurements used to develop the model.

8. HATA MODEL
 The Hata model is an empirical formulation of the graphical path loss data
provided by Okumura
 It is valid over roughly the same range of frequencies, 150-1500 MHz.
 This empirical model simplifies calculation of path loss.
 The standard formula for median path loss in urban areas under the Hata
model is
a(hre) - correction factor for mobile antenna height based on the size of the
coverage area.
For small to medium sized cities
For larger cities at frequencies fc > 300 MHz

9. The standard formula for median path loss in suburban areas
The standard formula for median path loss in rural areas
where K ranges from 35.94 (countryside) to 40.94 (desert).
 Hata’s model does not provide for any path specific correction factors, as is
available in the Okumura model.
 The Hata model well-approximates the Okumura model for distances d > 1
Km.
 It is a good model for first generation cellular systems.
 It does not model propagation well in current cellular systems with smaller
cell sizes and higher frequencies.
 Indoor environments are also not captured with the Hata model.

10. COST231 EXTENSION TO HATA MODEL
The Hata model was extended by the European cooperative for scientific and
technical research (EUROCOST) to 2 GHz as follows.
a(hr) - correction factor
CM is 0 dB for medium sized cities and suburbs and 3 dB for metropolitan
areas.
This model is restricted to the following range of parameters:
1.5GHz < fc < 2 GHz
30m < ht < 200 m,
1m < hr < 10 m
1Km < d < 20 Km.

11. WALFISCH/BERTONI MODEL
 A model for the impact of diffraction from rooftops and buildings was
developed by Walfisch and Bertoni .
 This model uses diffraction to predict average signal strength at street
level.
 The model considers the path loss to be the product of three factors:
P0 is the free space path loss for omnidirectional antennas
Q2 reflects the signal power reduction due to buildings that block the
receiver at street level
P1 is based on the signal loss from the rooftop to the street due to
diffraction.
The model has been adopted for the IMT-2000 standard.

12. PIECEWISE LINEAR (MULTI-SLOPE) MODEL

13. INDOOR PROPAGATION MODELS