REPORTFINAL OKUMURA

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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REPORTFINAL OKUMURA

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