A COMPARATIVE STUDY OF FREE SPACE AND OKUMURA-HATA … · COST 231 has extended Hata’s model to the frequency band of 1500MHz ≤ f. c ≤ 2000MHz by analysing Okumura’s propagation

International Journal of Advancements in Research & Technology, Volume 5, Issue 5, May-2016 34 ISSN 2278-7763

Copyright © 2016 SciResPub. IJOART

A COMPARATIVE STUDY OF FREE SPACE AND OKUMURA-HATA MODELS IN

GSM SIGNAL PATH LOSS PREDICTION IN SOUTH-SOUTH NIGERIA.

OYUBU A.O

Department of Electrical/Electronic Engineering, Delta State University, Abraka, Oleh

Campus,

Nigeria.

Email:[email protected]

ABSTRACT

One of the most fundamental tasks in Radio network planning is Radio propagation prediction. This is

done to foresee the coverage of the proposed system whilst considering the practical limitations that

characterize the propagation environment. As a result, many prediction models have been developed and deployed over the years. In this paper, two of such models; Okumura-Hata, and Free Space, are

comparatively studied at three different locations in Ughelli, a suburban terrain of Delta state in South-

South, Nigeria with the sole aim of comparing their accuracy in Path loss prediction. A netmonitor software installed in a smart phone, and a Garmin Nuvi Global Positioning System (GPS) device were

used to measure the Received Signal Strength (RSS) and Distances between Base Transceiver Stations

(BTS), and Mobile Station (MS) respectively. The analysis of the result showed that Okumura-Hata

model is more accurate in pathloss prediction.

Key Words: Path Loss, Netmonitor software, Garmin Nuvi, GPS, MS, RSS, BTS.

1. INTRODUCTION

The performance of wireless communication

systems relies largely on the design of the

transmission strategy. Over the years,

various propagation models have been

developed for assessing wireless

communication system for high quality and

service delivery. These models differ in their

properties with locations due to

environmental and geographical conditions

[1][2].The power loss involved in

transmission between the Base Transceiver

Station (BTS) and the Mobile Station (MS)

is known as path loss and it depends

particularly on the antenna height, carrier

frequency, and distance. Since path loss is

essentially the reduction in power density of

an electromagnetic wave as it propagates

through space, it can also be influenced by

terrain contours, environment (urban or rural,

vegetation and foliage), propagation medium

(dry or moist air). At higher frequencies, the

range for a given path loss is reduced;

therefore, more cells are required to cover a

given area.

Ekpeyong et al [3] comparatively studied

three propagation models-COST 231,ECC

33 and the Lee path models for UMTS based

cellular systems with the aim of knowing the

most reliable one (through simulation)

suitable for efficient use of the available

resources. In his work, Shoewu (2011),

showed that the Okumura-Hata model is

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very effective for radio wave propagation

path loss prediction in suburban areas in the

western part of Nigeria [4].Similarly, Sharma

(2010) concluded that propagation path loss

model may give different results if they are

used in different environment other than the

environment in which they are designed.

Data collected from the test locations were

compared with free space, and Okumura-

Hata model’s calculations for path loss. The

result obtained clearly depicts that the

Okumura-Hata model predicts better even

with increasing distances from the Base

transceiver Stations

2. TYPE OF PATH-LOSS

PROPAGATION PREDICTION

MODELS

2.1. Theoretical models

It is derived by physical hypothetical

assumption, in addition to some moderate

conditions. For instance, when we consider

the over-rooftop, diffraction model is derived

using physical optics, assuming constant

heights and spacing of buildings [5]. The

propagation models are divided into two

basic types; namely: Free space propagation

and Plane earth propagation model.

2.1.1 Free Space Propagation 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 attenuation.

Equation (1) illustrates how the power flux

is calculated.

Pd = Pt / 4πd² (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 an 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) below. 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:

(a) The aperture of receiving antenna Ao,

(b) the wavelength of received signal λ, (c)

and the power flux density at receiving

antenna Pd.

Effective area Ae of an isotropic antenna is:

Ae = λ² / 4π (2)

While power received is:

Pr = Pd × Ae = Pt ×λ² /(4πd)²

(3)

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While equation (4) illustrates the path loss

(Lp):

Lp = Power transmitted (Pt ) - Power

received (Pr ) (4)

When substituting equation (3) in equation

(4), it yields equation (5):

Lp (dB) = 20 log10 (4π) + 20 log10 (d)

- 20 log10 (λ) (5)

Then substituting (λ) (in km) = 0.3 / f

(in MHz) and rationalizing the equation

produces the generic free space pathloss

formula, which is stated in equation (6):

Lp(dB) =

32.5 + 20 log10 (d) + 20 log10 ( f ) (6)

2.1.2 Plane Earth Propagation 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). Path Loss Equation for the plane (1)

Earth Model is illustrated in equation (7).

Lpe =

40log10 (d)-20log10 (h1)-20log10 (h2) (7)

Where d represents the path length in meters

and h1 and h2 are the antenna heights at the

base station and the mobile, respectively.

The plane earth model in not appropriate for

mobile GSM systems as it does not consider

the reflections from buildings, multiple

propagation or diffraction effects.

Furthermore, if the mobile height changes

(as it will in practice) then the predicted path

loss will also be changed.

2.2. Empirical Propagation

Model

It is derived from in-depth field

measurements. It is efficient and simple to

use. The input data for the empirical models

are generally qualitative, also not very

correct, for instance like dense urban area,

rural area and so on [6-8]. The two basic

propagation models (free space loss and

plane earth loss) would require detailed

knowledge of the location, dimension and

constitutive parameters of every tree,

building, and terrain feature in the area to be

covered. This is far too complex to be

practical and [10] would yield an

unnecessary amount of detail. One

appropriate way of accounting for these

complex effects is via an empirical model.

There are various empirical prediction

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models which include, Okumura – Hata

model, Cost 231 – Hata model, [11] Cost 231

Walfisch – Ikegami model, Sakagami- Kuboi

model,the Lee model. These models depend

on location, frequency range and clutter type

such as urban, sub-urban and countryside.

2.2.1 Okumura’s Measurements

Okumura carried out extensive drive test

measurements with range of clutter type,

frequency, transmitter height, and

transmitter power. It states that, the signal

strength decreases at much greater rate with

distance than that predicted by free space

loss [11].

2.2.2 Okumura-Hata’s Propagation

Model

Hata model was based on Okumura’s field

test results and predicted various equations

for path loss with different types of clutter.

The limitations on Hata Model due to range

of test results from carrier frequency(fc)

150MHz to 1500MHz, the distance from the

base station ranges from 1Km to 20Km, the

height of base station antenna (hb) ranges

from 30m to 200m and the height of mobile

antenna (hm) ranges from 1m to 10m. Hata

created a number of representative path loss

mathematical models for each of the urban,

suburban and open country environments, as

illustrated in equations (6-8), respectively.

Path Loss for urban clutter:

Lp (urban) = 69.55+ 26.16log10 ( fc )-

13.82log10(hb) -a(hm) + (44.9-6.55log10(hb )

log10 (d) (8)

a(hm) = (1.1log10( fc )-0.7)hm -

(1.56log10 ( fc )-0.8) (9)

Lp (suburban) = Lp (urban)-

2{log10 ( fc /28)}²-5.4 (10)

Path loss for the open country is :

Lp (open rural area) = Lp (urban)-4.78{log10

( fc )}² +18.33log10 ( fc )-40.94 (11)

Hata model is not suitable for micro-cell

planning where antenna is below roof

height and its maximum carrier frequency

is 1500MHz. It is not valid for 1800 MHz

and 1900 MHz systems. [12]

2.2.3 COST 231-Hata model

Committee 231 of the European

Cooperation in the field of Scientific and

Technical Research (EURO- COST)

extends the Hata model for scientific

frequencies of interest (900MHz &

1800MHz). The model, which was

renamed COST – Hata model, is applicable

for only cases in which the antenna heights

are above the rooftops of the surrounding

buildings. COST 231 has extended Hata’s

model to the frequency band of 1500MHz

≤ fc ≤ 2000MHz by analysing Okumura’s

propagation curves frequency band

[12].The proposed model for path loss is

given as:

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PL (dB) = 46.3+33.9log (fc) -13.82log (hr)

+[44.9-6.55log(ht)]log(d)+Cm

(12)

For a small to medium sized city,

a(hr) = [1.1log(fc) -0.7] hr –

[1.56log (fc) – 0.8] (13)

For a large city,

a(hr) =8.29 [log(1.54 hr )]2 hr –1.1

for fc ≤ 300MHz (14)

a(hr) =3.2 [log(11.75 hr )]2 hr- 4.9

for fc ≥300MHz (15)

0 dB for a medium-sized city and suburban areas

3 dB for metropolitan areas Cm =

Range of parameters

f : 1500-2000MHz

ht : 30 – 200m

hr : 1 – 10m

3. METHODOLOGY

A GSM signal Analyser, NETMONITOR

application, installed in a Tecno phantom A3

android phone with functions which include

on-air survey, signal strength evaluation, and

interrogation of cells of a base transceiver

station to find and identify the network

operator type was used to measure the

received signal strength at five different test

points of 200m apart from the Base Station

for three different locations within Ughelli

for MTN network. This software provided

various parameters such as the operator code

of the network, the operator type, location

area code (LAC), cell identification (CID),

signal strength in dBm, GPS parameters and

the location of the base transceiver station

from which the phone was obtaining service

at that instance. A Garmin Nuvi GPS device

was used to obtain the distance between MS

and BTS at each test point for each of the

three locations where this investigation was

conducted.

4. RESULT PRESENTATION/

ANALYSIS

A. Measurement Details for All Locations

Investigated.

Table 3: Details of the investigation at

Otovwodo Road.

Quantity(Measured/Calculated) Value

Antenna Height (m) 33

Transmitting Frequency(MHz) 900

Antenna Gain(dBi) 17.5

Mobile used Tecno Phantom A3

Network MTN (621 30)

LAC/CID 60329/24981

VWSR 1.5

RL (dB) 14

EIRP(dBm) 49.5

Distance

(m)

Mean RSS level

(dBm)

Tx power

(dBm)

Attenuation

(dBm)

200 -63.20 40 23.20

400 -69.82 40 29.82

600 -67.13 40 27.13

800 -70.63 40 30.63

1000 -72.76 40 32.76


Market Road.







LAC/CID 60329/5251

VWSR 1.5

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RL (dB) 14

EIRP(dBm) 49.5

Distance

(m)

Mean RSS level

(dBm)

Tx power

(dBm)

Attenuation

(dBm)

200 -71.88 40 31.88

400 -71.94 40 31.94

600 -79.25 40 39.25

800 -81.25 40 41.25

1000 -82.75 40 42.75


Warri-Patani Road.







LAC/CID 60329/7553

VWSR 1.5

RL (dB) 14

EIRP(dBm) 49.5

Distanc(m) Mean RSS level

(dBm)

Tx power

(dBm)

Attenuation

(dBm)

200 -53.00 40 13.00

400 -65.25 40 25.25

600 -71.32 40 31.32

800 -69.19 40 29.19

1000 -80.94 40 40.94

B. Obtained pathloss at various

distances for all investigated

locations.

Table 6: Pathloss obtained, based

on field data/calculation

Distance

(m)

Pathloss for

Otovwodo Road (dBm)

Pathloss for

Market Road (dBm)

Pathloss for

Warri-Patani Road (dBm)

200 112.69 121.38 102.50

400 119.88 121.44 114.75

600 114.63 128.75 120.82

800 120.13 130.75 118.69

1000 122.56 132.25 130.44

Table 7: Pathloss obtained from

calculation, based on the

Okumura-Hata model

Distance

(m)

Pathloss for

Otovwodo Road (dBm)

Pathloss for

Market Road (dBm)

Pathloss for

Warri-Patani Road (dBm)

200 102.67 104.73 100.85

400 113.20 115.68 110.98

600 119.35 122.09 116.91

800 123.72 126.62 121.11

1000 127.11 130.16 124.38

Table 8: Pathloss obtained from

calculation, based on the free

space model

Distance

(m)

Pathloss for

Otovwodo

Road (dBm)

Pathloss for

Market Road

(dBm)

Pathloss for

Warri-Patani

Road (dBm)

200 77.56 77.56 77.56

400 83.56 83.56 83.56

600 87.10 87.10 87.10

800 89.60 89.60 89.60

1000 91.53 91.53 91.53

D. Screen Shots of Received

Signal Strength Measurement

For all locations investigated.

Figure 2: Otovwodo Road

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Figure 3: Market Road

Figure 4: Warri-Patani Road

E. RESULT ANALYSIS

Figure 5: Graph comparing pathloss for all the locations investigated based on

field data.

Figure 6: Graph comparing Pathloss based on field data with Pathloss based on both

models for Otovwodo Road.

0

20

40

60

80

100

120

140

0 200 400 600 800 1000 1200

Pat

hlo

ss (

dB

m)

Distance(m)

Pathloss for Otovwodo Road (dBm)

Pathloss for Market Road (dBm)

Pathloss for Warri-Patani Road (dBm)

0

20

40

60

80

100

120

140

0 200 400 600 800 1000 1200

Pat

hlo

ss (

dB

m)

Distance(m)

Field data Pathloss for Otovwodo Road (dBm)

Okumura-Hata model Pathloss for Otovwodo Road (dBm)

Free Space Pathloss for Otovwodo Road (dBm)

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models for Market Road.


models for Warri-Patani Road.

0

20

40

60

80

100

120

140

0 200 400 600 800 1000 1200

Pat

hlo

ss (

dB

m)

Distance (m)

Field data Pathloss for Warri-Patani Road (dBm)

Okumura-Hata model Pathloss for Warri-Patani Road (dBm)

Free Space Pathloss for Warri-Patani Road (dBm)

0

20

40

60

80

100

120

140

0 200 400 600 800 1000 1200

Pat

hlo

ss(d

Bm

)

Distance (m)

Field data Pathloss for Market Road (dBm)

Okumura-Hata model Pathloss for Market Road (dBm)

Free Space Pathloss for Market Road (dBm)

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Figure 9: Chart comparing transmitting power attenuation for the investigated

locations at various distances.

From the graph (Figure 5) comparing pathloss

for all the locations investigated based on field

data, Market road has the highest pathloss

with respect to Otovwodo and Warri-Patani

roads. This can be adduced to the presence of

many high rise structures in this location

which obviously affected the line of sight

clearance between the Base Transceiver

Station (BTS) and the Mobile Station

(MS).The chart (Figure 9) comparing the

transmitting power attenuation for the

investigated locations also supports this.

The other two locations, Otovwodo, and

Warri-Patani roads, can be seen to have fairly

close pathloss because the line of sight

between the Base Transceiver Station (BTS)

and the Mobile Station (MS) in these locations

is not seriously obstructed as it was in Market

road. The chart, figure 9, also supports this.

The graphs (figures 6, 7 and 8) comparing

pathloss obtained from the field data and both

models’ pathloss (Okumura-Hata, and Free

space) for all the locations where

investigations were carried out reveal that the

Okumura-Hata model for pathloss prediction’

pathloss for all distances are very close in

value to the field data pathloss. This is not the

case with the Freespace model which

completely differed from the field data

pathloss values which are the reference

pathloss in this study

5. CONCLUSION

The result of this investigation shows that the

Okumura-Hata model for pathloss prediction

is more accurate in predicting pathloss than

the free space model. The free space model

cannot be used as its values completely differ

from the field data pathloss values, thus will

predict erroneously. For all the locations

0

5

10

15

20

25

30

35

40

45

200 400 600 800 1000

Att

enu

atio

n(d

Bm

)

Distance(m)

Attenuation (dBm) at Otovwodo

Attenuation (dBm) Market Road

Attenuation (dBm) Warri-Patani Road

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where this study was conducted, the difference

in pathloss between field data pathloss and

both models’ are: 0.77dBm for Okumura-

Hata, and 32.11dBm for Free Space at

Otovwodo road, 7.05dBm for Okumura-Hata,

and 41.04dBm for Free Space at Market road,

and 2.59dBm for Okumura-Hata,and

31.57dBm for Free Space at Warri-Patani

road. This clearly shows that pathloss

prediction using the Free Space model will be

inaccurate.

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Documents

A COMPARATIVE STUDY OF FREE SPACE AND OKUMURA-HATA … · COST 231 has extended Hata’s model to the frequency band of 1500MHz ≤ f. c ≤ 2000MHz by analysing Okumura’s propagation