reportfinal okumura
TRANSCRIPT
Dept. of Electronics & Communication Engg.
ABSTRACT
SIMULATION OF OKUMURA MODEL FOR PROPOGATION LOSS
Propogation models aid in the development of wireless communication networks. A
wireless network can be characterizedby its basic components. A typical network consists
of transmitters, receivers and surrounding environment. Each variable in the network will
affect the propogation model thet can be used or developed for the given network. A model
can be used for certain frequency band to predict with a high degree of accuracy the nature
of surrounding atmosphere.
The primary object of the work reported in this thesis was to simulate the path loss and
signal prediction in urban environment stated by Yoshihisa Okumura in "Field Strength
and its Variability in VHF and UHF Land-Mobile Radio Service", Review of the Electrical
Communication Laboratory, Vol 16, Numbers 9-10, Sep.-Oct, 1968. This model was
named after him. This model is well understood if we have the concept of cellular and
wireless communication .
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CHAPTER: 1
PREAMBLE
1.1GENERAL INTRODUCTION:
Mobile communications is currently at its fastest growth-period in history; due to enabling
technologies, which permit wider deployment. Historically, growth in the mobile
communications field has now become slow, and has been linked to technological
advancements. The need for high quality and high capacity networks, estimating
coverage accurately has become extremely important. Therefore, for more accurate design
coverage of modern cellular networks, signal strength measurements must be taken into
consideration in order to provide an efficient and reliable coverage area. This article
addresses the comparisons between the theoretical and the empirical propagation models. It
was achieved that, the most extensively used propagation data for mobile communications
is Okumura’s measurements and this is recognized by the International Telecommunication
Union (ITU).
The cellular concept was a major breakthrough in solving the problem of spectral
congestion and user’s capacity. It offered high capacity with a limited spectrum allocation
without any major technological change. The cellular concept is a system level idea in
which a single, high power transmitter (large cell) is replaced with many low power
transmitters (small cells). The area serviced by a transmitter is called a cell. Each small
powered transmitter, also called a base station provides coverage to only a small portion of
the service area. The power loss involved in transmission between the base station (BTS)
and the mobile station (MS) is known as the path loss and depends particularly on the
antenna height, carrier frequency and distance. At higher frequencies the range for a given
path loss is reduced, so more cells are required to cover a given area. Base stations close to
one another are assigned different groups of channels. So that all the available channels are
assigned to a relatively small number of neighboring base stations. Neighboring base
stations are assigned different groups of channels so that the interference between base
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stations or interaction between the cells is minimized. As the demand for service increases,
the number of base stations may be increased, thereby providing additional capacity with
no increase in radio spectrum. The key idea of modern cellular systems is that it is possible
to serve the unlimited number of subscribers, distributed over an unlimited area, using only
a limited number of channels, by efficient channel reuse.
1.2 OBJECTIVE OF THE STUDY:
This study of Okumura model helps us to measure the losses occurred during propogation
in urban areas. The simulation results can be used to improve the network coverage issues
in urban environment. Further there are many models were stated, after this okumaura
model was published. But for the basic study of the propagation path loss we have to
understand the Okumura model.
1.3 SCOPE OF THE STUDY:
In this project, have worked on the following
Free space propogation model.
Plane Earth propogation model.
Okumura model.
Simulation of Okumura model using MATLAB.
1.4 REVIEW OF LITERATURE:
(a). Pathloss Determination Using Okumura-Hata Model And Spline
Interpolation For Missing Data For Oman
Imprecise propagation models lead to networks with high co-channel interference and a
waste of power. In this paper, we aim to adapt a propagation model for Salalah (OMAN) as
we examine the applicability of Okumura-Hata model in Oman in GSM frequency band.
The study was carried out for urban area, since measurements provided from OmanMobile
were about the urban areas. The study helped to design better GSM network for the city
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area. We will accomplish the modification by investigating the variation in pathloss
between the measured and predicted values, according to the Okumura-Hata propagation
model for a cell in Salalah city and then finding the missing experimental data with spline
interpolation. Then, we intend to modify the Okumura-Hata model according to the results
obtained in our investigation. We will then verify our modified model by applying it for
other cells and conclude the results. For the purpose the mean square error (MSE) was
calculated between measured path loss values and those predicated on basis of Okumura-
Hata model for an open area. The MSE is up to 6dB, which is an acceptable value for the
signal prediction. Therefore, the model gave a significant difference in an open area that
allowed necessary changes to be introduced in the model. That error was minimized by
subtracting the calculated MSE (15.31dB) from the original equation of open area for
Okumura-Hata model. Modified equation was also verified for another cell in an open area
in Oman and gave acceptable results. Theoretical simulation by Okumura Hata Model and
the obtained experimental data is compared and analyzed further using a piece-wise cubic
spline to interpolate on the set of the experimental data and finding the missing
experimental data points.
(b). Comparison of Empirical Propagation Path Loss Models for Fixed
Wireless Access Systems.
Empirical propagation models have found favour in both research and industrial
communities owing to their speed of execution and their limited reliance on detailed
knowledge of the terrain. Although the study of empirical propagation models for mobile
channels has been exhaustive, their applicability for FWA systems is yet to be properly
validated. Among the contenders, the ECC-33 model [1], the Stanford University Interim
(SUI) models [2] and the COST-231 Hata model [3] show the most promise. In this paper,
a comprehensive set of propagation measurements taken at 3.5 GHz in Cambridge, UK is
used to validate the applicability of the three models mentioned previously for rural,
suburban and urban environments. The results show that in general the SUI and the COST-
231 Hata model over-predict the path loss in all environments. The ECC-33 models shows
the best results, especially in urban environments.
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1.7 LIMITATIONS OF THE PROJECT:
This simulation has a slow response to the rapid changes in the terrain,
therefore the model is fairly good in urban and suburaban areas, but not as good in rural
areas.
As the external environment changes the path loss calculated changes and
hence some correction factors should be added to the actual formula to compensate to
this effects.
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CHAPTER: 2
2.1 Propogation Models
A radio propagation model, also known as the Radio Wave Propagation Model or the
Radio Frequency Propagation Model, is an empirical mathematical formulation for the
characterization of radio wave propagation as a function of frequency, distance and other
conditions. A single model is usually developed to predict the behavior of propagation for
all similar links under similar constraints. Created with the goal of formalizing the way
radio waves are propagated from one place to another, such models typically predict the
path loss along a link or the effective coverage area of a transmitter.
As the path loss encountered along any radio link serves as the dominant factor for
characterization of propagation for the link, radio propagation models typically focus on
realization of the path loss with the auxiliary task of predicting the area of coverage for a
transmitter or modeling the distribution of signals over different regions. Because each
individual telecommunication link has to encounter different terrain, path, obstructions,
atmospheric conditions and other phenomena, it is intractable to formulate the exact loss
for all telecommunication systems in a single mathematical equation. As a result, different
models exist for different types of radio links under different conditions. The models rely
on computing the median path loss for a link under a certain probability that the considered
conditions will occur.
The theoretical propagation models are divided into two basic types namely:
Free space propagation.
Plane earth propagation model.
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2.2 Free space propogation model
In free space, the wave is not reflected or absorbed. Ideal propagation implies equal
radiation in all directions from the radiating source and propagation to an infinite distance
with no degradation. Spreading the power over greater areas causes the attenuation.
Equation (1) illustrates how the power flux is calculated.
Pd = Pt / 4π d ² --(1)
Where Pt is known as transmitted power (W/ m² ) and Pd is the power at a distance d from
antenna. If the radiating element is generating a fixed power and this power is spread
over a ever-expanding sphere, the energy will be spread more thinly as the sphere expands.
By having identified the power flux density at any point of a given distance from the
radiator, if a receiver antenna is placed at this point, the power received by the antenna can
be calculated. The formulas for calculating the effective antenna aperture and received
power are shown in equations (2) and (3). The amount of power ‘captured’ by the antenna
at the required distance d, depends upon the ‘effective aperture’ of the antenna and the
power flux density at the receiving element. Actual power received by the antenna depends
on the following:
The aperture of receiving antenna (Ae).
The wavelength of received signal (λ).
The power flux density at receiving antenna (Pd).
Effective area Ae of an isotropic antenna is:
Ae = λ ² / 4 --(2)
While power received is:
Pr = Pd × Ae = Pt ×λ ² /(4πd²) --(3)
While equation (4) illustrates the path loss (Lp):
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Lp = Power transmitted (Pt ) - Power received (Pr ) --(4)
2.3 Plane earth propogation model
The free space propagation model does not consider the effects of propagation over
ground. When a radio wave propagates over ground, some of the power will be reflected
due to the presence of ground and then received by the receiver. Determining the effect
of the reflected power, the free space propagation model is modified and referred to as
the ‘Plain-Earth’ propagation model. This model better represents the true characteristics
of radio wave propagation over ground. The plane earth model computes the received
signal to be the sum of a direct signal and that reflected from a flat, smooth earth. The
relevant input parameters include the antenna heights, the length of the path, the
operating frequency and the reflection coefficient of the earth. This coefficient will vary
according to the terrain type (e.g. water, desert, wet ground etc).
2.4 Okumura Model
Okumura's model is one of the most widely used models for signal prediction in urban
areas. This model is applicable for frequencies in the range 150 MHz to 1920 MHz
(although it is typically extrapolated up to 3000 MHz) and distances of 1 km to 100 km.
It can be used for base station antenna heights ranging from 30 m to 1000 m.
Okumura developed a set of curves giving the median attenuation relative to free space
(Arnu), in an urban area over a quasi-smooth terrain with a base station effective antenna
height (hte) of 200 m and a mobile antenna height (hre) of 3 m. These curves were
developed from extensive measurements using vertical omni-directional antennas at both
the base and mobile, and are plotted as a function of frequency in the range 100 MHz to
1920 MHz and as a function of distance from the base station in the range 1 km to 100
km. To determine path loss using Okumura's model, the free space path loss between the
points of interest is first determined, and then the value of Amu(f, d) (as read from the
curves) is added to it along with correction factors to account for the type of terrain. The
model can be expressed as
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L50(dB) = LF + Amu(f, d)- G(hte) — G(hre) — Garea --(5)
where L50 is the 50th percentile (i.e., median) value of propagation path loss, LF is the
free space propagation loss, Amu is the median attenuation relative to free space, G(hte)
is the base station antenna height gain factor, G(hre) is the mobile antenna height gain
factor, and GAREA is the gain due to the type of environment. In here the antenna height
gains are strictly a function of height and have nothing to do with antenna patterns.
Plots of Amu(f, d) and GAREA for a wide range of frequencies are shown in Figure
below:
Fig 1: Median attenuation relative to free space (Amu) Fig 2: correction factor Garea for different
terrain
Okumura found that G(hte) varies at a rate of 20 dB/decade and G(hre) varies at a rate of
10 dB/decade for heights less than 3 m.
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Other corrections may also be applied to Okumura's model. Some of the important terrain
related parameters are the terrain undulation height (Δh), isolated ridge height, average
slope of the terrain and the mixed land-sea parameter. Once the terrain related parameters
are calculated, the necessary correction factors can be added or subtracted as required.
All these correction factors are also available as Okumura curves.
Okumura's model is wholly based on measured data and does not provide any analytical
explanation. For many situations, extrapolations of the derived curves can be made to
obtain values outside the measurement range, although the validity of such extrapolations
depends on the circumstances and the smoothness of the curve in question.
Okumura's model is considered to be among the simplest and best in terms of accuracy in
path loss prediction for mature cellular and land mobile radio systems in cluttered
environmehts. It is very practical and has become a standard for system planning in
modern land mobile radio systems in Japan. The major disadvantage with the model is its
slow response to rapid changes in terrain, therefore the model is fairly good in urban and
suburban areas, but not as good in rural areas. Common standard deviations between
predicted and measured path loss values are around 10 dB to 14 dB.
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CHAPTER 3:
3.1 Implementation of Okumura model
The calculation of path loss and the received power at a point, the model predicts that the
received power decays as a function of Tx-Rx separation distance.This implies that
received power decays with distance at a rate of 20 db/decade. The path loss for free space
model when antenna gains are included is given by
PL(dB) = 32.44+20log(d) +20 log(f ) -Gt -Gr .
Where
Gt is the transmitted gain of the antenna(dB).
Gr is the receiver antenna gain(dB).
D is the Tx-Rx separation distance in kilometers.
F is the frequency in Megahertz.
In here the MATLAB is used as a simulator. This code can be used for calculating
propogation loss with different operating frequency of the carrier and different Tx-Rx
distances. This code can be used for theoretical calculation of received power at a point if
the transmitted power is known.
3.1 Matlab code
clc;clear all;close all; Hte=30:1:100; Hre=input('Enter the receiver antenna height 3m<hre<10m : ');d =input('Enter distance from base station 1Km<d<100Km : '); f=input('Enter the frequency 150Mhz<f<1920Mhz : ');Pt=input('input transmitted power in kW : ');
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P=10*(log(Pt*10^6)/(log(10))); c=3*10^8;lamda=(c)/(f*10^6);Lf=32.5+ (20*((log(d))/(log (10))))+(20*((log(f))/(log (10))));%%Lf=Lf1/(log (10));%%Lf =10*log((lamda^2)/((4*pi)^2)*(d*1000)^2); Amu = 43; Garea = 9; Ghte = 20*(log(Hte/200)/(log (10)));if(Hre>3)Ghre = 20*(log(Hre/3)/(log (10)));elseGhre = 10*(log(Hre/3)/(log (10)));end L50 = Lf+Amu-Ghte-Ghre-Garea;Pr=P-L50; display('Propagation pathloss is : ');disp(L50); display('Power recieved : ');disp(Pr); plot(Hte,L50,'LineWidth',1.5);title('Okumura Model Analysis');xlabel('Transmitter antenna Height ');ylabel('Propagation Path loss(dB) Km');grid on;
3.3 Simulation Results
Case1:
Enter the receiver antenna height 3m<hre<10m : 10
Enter distance from base station 1Km<d<100Km : 50
Enter the frequency 150Mhz<f<1920Mhz : 900
input transmitted power in kW : 1
Propagation pathloss is :
155.0690
Power recieved :
-95.0690
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CASE 2:
Enter the receiver antenna height 3m<hre<10m : 5
Enter distance from base station 1Km<d<100Km : 50
Enter the frequency 150Mhz<f<1920Mhz : 900
input transmitted power in kW : 1
Propagation pathloss is :
161.0896
Power recieved :
-101.0896
Plot that states the propogation loss decreases if the antenna height is increased keeping
other parameters constant.
Fig 3: Propogation path loss v/s transmitter antenna height.
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CONCLUSION
In this report, Okumura Model for determination of path loss in urban areas is simulated.The
calculated path loss can be compared with different parameters and the results obtained may
be useful for improving the performance of the system and providing better coverage to the
subscribers. This model is the fundamental model used for determining the loss occurred in
propogation. There are different models that are given by pioneers in this field that can be
used to improve the system performance.
In future work, this model can be used for calculation of path loss in different environments
like Suburban, urban, open area and densely congested areas can be calculateted .
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REFERENCE
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