PLANNING TOOL FOR LMDS COVERAGE USING 3D

GEOGRAPHIC INFORMATION SYSTEM DATA

Landaabalo Agba , Laure Freytag , Bernard Jecko

IRCOM (Institut de Recherche en Communications Optiques et Micro-ondes) CNRS UMR n°6615 - équipe "CREAPE"

Faculté des Sciences - 123, Avenue Albert Thomas - 87060 LIMOGES Cedex, FRANCE

Keywords: LMDS, GIS, coverage prediction, Ray Tracing, planning tool

Abstract: Local Multipoint Distribution Services (LMDS) Network operating in 40.5 – 43.5 GHz band in Europe

requires relevant planning tool for its deployment. An accurate knowledge of the propagation environment

(buildings, trees…) is necessary especially in urban areas. This paper presents software based on Ray

Tracing method using 3D Geographic Information System (GIS) database. Several series of simulations

were done and the effects on propagation issues of some parameters were interpreted. Measurements were

also achieved and were compared with simulation curves. Finally, cosecant-squared and switch beam

antennas are briefly presented as solutions to avoid shadowed zones and to improve coverage area.

1 INTRODUCTION

Some years ago, Local Multipoint Distribution

Services (LMDS) is revealed as a real asset to

provide broadband and high capacity access services

to end users. Its deployment needs to develop a

relevant planning tool as it exists for others wireless

systems such as GSM. Furthermore, the assigned

frequency band can be different from a country to

another. To facilitate the design of LMDS network,

we elaborate a computer program based on Ray

Tracing method. This program uses 3D Geographic

Information System (GIS) data.

This paper presents the principles and the

algorithm of the software. The simulation results and

the comparison with measurements are also showed.

Finally, some solutions to enhance and to improve

the coverage area are presented. Cosecant-squared

antenna and switch beam antenna are some of them.

2 A SIMULATION SOFTWARE

PACKAGE

Nowadays the fixed wireless systems such as LMDS

are not to be any more presented. Nevertheless some

advantages are useful to be reminded. These

advantages include the ability to connect with users

in remote areas without laying new cables and the

capacity for broad bandwidth that is not impeded by

fibber or cable capacities. Furthermore, the fixed

wireless networks are easy and fast to be deployed

with incremental infrastructure investment.

Even though, LMDS network is one of the

simplest networks in installation and operation, we

still need to simulate its design to reduce the

installation time and to increase the coverage area by

using the minimum base stations that will reduce the

installation costs and will increase the network

efficiency.

2.1 3D-GIS data with Ray Tracing

method

Geographic information system databases enable

telecommunication professionals to integrate maps

and information to make better decisions. They are

composed by different layers which give geographic

information (where things are) with descriptive

information (what things are) (What is GIS). LMDS

operates at high frequencies (40.5 – 43.5 GHz in

many European countries) for which any physical

obstructions effectively block the signal. GIS data

requirements are therefore based on line-of-sight

parameters.

Agba L., Freytag L. and Jecko B. (2004).

PLANNING TOOL FOR LMDS COVERAGE USING 3D GEOGRAPHIC INFORMATION SYSTEM DATA.

In Proceedings of the First International Conference on E-Business and Telecommunication Networks, pages 81-86

DOI: 10.5220/0001381600810086

 SciTePress

P −=

Figure 1: Example of 3D GIS data visualization with

some main layers

To meet these requirements, a virtual metropolis

must be constructed for each city depicting all

buildings and vegetation with a resolution and an

accuracy less than 1 meter. In our case, we use only

some GIS layers that can affect the LMDS link;

these layers are depicted in the figure 1-b.

The building layer is the most important with

two main effects. The direct effect appears when

there are obstacles between the transmitter and the

receiver. The indirect effect is the reflected signal

caused by the construction materials of buildings

(such as: glass, wood, stone, metals...). The building

models must have an incredible level of detail –

elevator shafts, air conditioning ducts, and peaked

roofs are possible obstacles in the design of LMDS

network.

The second important layer is the vegetation

layer that represents the trees areas and forests. This

layer can reduce the quality of service or even

disconnect the LMDS service. Also, we have to

notice that the effect of this layer is seasonal and it

can be changed according to the four seasons of the

year unlike the buildings layer which remains

unchanged all over the year.

Using 3D GIS data can dramatically improve the

reliability and efficiency of a network design. Our

software package makes able to know all effects of

the buildings materials, weather conditions and

terrain textures on the LMDS network, and how

many users will be able to use this network and what

quality of service they will expect.

The computer program is based on Ray Tracing

method (Jensen et al., 1990) stems from Geometrical

Optics (GO) and Uniform Theory of Diffraction

(UTD). It provides several advantages over other

prediction methods

(Rappaport, 1997)

• Precise Signal power level prediction

• Incorporation of 3D pattern of antennas

• Angle of arrival information

• Multipath time delay information

The program traces rays in a digital cityscape.

The total power level is obtained by combining

incident power with reflected power from the sides

of buildings and rooftops across the simulation zone.

2.2 The Simulation Algorithm

The first step is to choose the coverage area and on

this area the optimal location of the base station

(BTS). Then, the Point-to-Region visibility is tested

between the BTS and the subscribers’ out door unit

(ODU) located on households. Two cases are

possible:

• Line-Of-Sight (LOS) areas are

corresponding to 60 % of the potential

single cell coverage area. The reflection

paths are found using method of images

which consists to place iteratively virtual

transmitters behind each surface in

computer 3D database. Each path contains

the same signal with a different time delay.

The total received power is calculated as

follows:

(1)

(2)

Where:

P Total received power

Total received field

A Total rain attenuation

E Incident received field

Reflected received field

N = number of reflected rays

Wave impedance

a. Modelling of a 3D environment

S = Stree

V = Ve

etation

B = Buildin

G = Ground

b. Main GIS layers used in LMDS design

∑

EEE

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Figure 2: Scheme of LMDS planning tool

The rain attenuation (dB) over a path is given by

relation (3). (ITU-RP 530-7)

(3)

Where:

T is the rain intensity (mm/h), d

eff

is the distance

(km), p is the percentage of connection availability.

The values of k and α are frequency and polarization

dependent factors given in ITU-R

Recommendations. (ITU-RP 838)

•

No Line-Of-Sight (NLOS) or shadowed

areas. The use of reflectors or repeaters will

dramatically reduce these areas and

increase the single cell coverage percentage

to more than 90%. The following formula

(Ruck, 1970) is used to calculate the

received power level which depends on the

passive reflector cross section.

(4)

Where:

Σ = Reflector cross section, its calculation depends

on the geometrical shape of the reflector and the

working frequency.

Pe, Pr = Transmitted and the received powers

Ge, Gr = Transmitted and the received Gains

= Distance transmitter - reflector

= Distance reflector - receiver

λ = wavelength

The chart (Figure 2) describes the main steps of

our coverage prediction model. It’s important to

notice that this planning tool can be used for any

other system operating at frequencies above 20 GHz.

The total power level can be depicted as power

curves or power maps. Somme simulation results

with measurements comparison are presented in the

following paragraph.

3 SIMULATION RESULTS AND

MEASUREMENTS

The results obtained using our planning tool allow to

interpret the effects of some parameters on LMDS

network design especially on the coverage

prediction. The figures (3-a, 3-b) show that the

power level is deeply connected in one hand to the

difference of height between the BTS and an ODU

and in the other hand to the weather conditions.

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• Transmitter &

receiver parameters

• Weather conditions

• Availability rate

timization o

antennas

arameters

timization o

BTS location

BTS site location

Reflector or

Repeater parameters

YES

3D GIS data base &

building materials

characteristics library

LOS coverage using

Ray Tracing Method

Received power level &

estimation of covera

e %

Point-to-Region

Visibilit

Shadowed areas covered

by reflectors or repeaters

Optimization of reflector or

repeater parameters

PLANNING TOOL FOR LMDS COVERAGE USING 3D GEOGRAPHIC INFORMATION SYSTEM DATA

Figure 3: Effects of some parameters on LMDS link

budget

The shadowed zone indicated on the

figure 3-a is

only due to the gap between the main lobe and the

side lobes when a directional transmitting antenna in

elevation plane is used. The maximum coverage

range decreases when the intensity of rain increases,

as it is showed on the

figure3-b with 99.99 % of the

availability rate. Some time, the improvement of the

coverage range is possible by a little reduction of

this rate.

On different sites located in Limoges-France,

several series of measurements were achieved using

a Panoramic Field Measuring Device (MCP3000).

The description of measurement conditions and the

comparison of curves are depicted on the following

figures 4-5. The comparison of power levels shows a

good agreement between simulations and

measurements. It is confirmed by the standard

deviation (SD) and the average error percentage of

the two cases presented below.

(5)

With SD = STDEVPA (MS-Excel function)

Error % of measurements: Case n°1 = 8.8%

Error % of measurements: Case n°2 = 3.1%

Figure 4: Measurements achievement: Case n°1

Figure 5: Measurements achievement: Case n°2

We successfully carried out studies of coverage

prediction around ESTER site located in Limoges.

-120

-110

-100

-90

-80

-70

-60

0 100 200 300 400 500

Distance (m)

Power (dB)

Sensitivity threshold = -110 dB

Received power: h = 30 m

Received power: h = 10 m

Shadowed area

a. Difference of height between antennas

-120

-110

-100

-90

-80

-70

-60

0 500 1000 1500 2000 2500 3000 3500 4000

Distance (m)

Power (dB)

Sensitivity threshold

Rain intensity = 8 mm/h

Rain intensity = 19 mm/h

Rain intensity = 32 mm/h

b. E

ect o

rain intensit

tsmeasuremenofAverage

Error

100

b. Com

arison Simulation-

easurements: Case n°1

-90

-85

-80

-75

-70

-65

-60

-55

-50

30 50 70 90 110 130 150 170 190

Distance (m)

Power (dB)

Simulation

Measurements

a. Measurements conditions: Case n°1

b. Com

arison Simulation-

easurements: Case n°1

-90

-85

-80

-75

-70

-65

-60

-55

-50

30 50 70 90 110 130 150 170 190

Distance (m)

Power (dB)

Simulation

Measurements

a. Measurements conditions: Case n°1a. Measurements conditions: Case n°1

-80

-76

-72

-68

-64

-60

30 50 70 90 110 130

Distance (m)

Power (dB)

Simulation

Measurements

b. Com

arison Simulation-

easurements: Case n°2

a. Measurements conditions: Case n° 2

-80

-76

-72

-68

-64

-60

30 50 70 90 110 130

Distance (m)

Power (dB)

Simulation

Measurements

b. Com

arison Simulation-

easurements: Case n°2

a. Measurements conditions: Case n° 2a. Measurements conditions: Case n° 2

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The figure 6 is an example of the power level map with its corresponding coverage area.

Figure 6: Example of coverage with power level map around ESTER site

4 TWO WAYS TO IMPROVE THE

COVERAGE AREA

A solution to overcome the shadowed areas (see

figure 3-a)

is to design a new antenna with cosecant-

squared pattern in elevation plane. (Freytag and

Jecko, 2002) The cosecant-squared diagram is given

by:

(6)

The principle

(figure 7-a) is to compensate the

propagation effect especially in the shadowed areas

near the transmitting antenna of the BTS. At 40

GHz, the coverage area is up to 2 till 3.5 Km from

the base station depending on weather conditions

(see figure 3-b). To increase this range, a switch

beam antenna is designed using Butler matrix 4*4

and its working principle is illustrated on the

figure

7-b

(Dall’omo, 2003). The pointing direction of each

beam is given by:

(7)

Where:

= phase gradient between 2 consecutive patches

= Angle between the beam m and the normal

direction of the array

d = Distance between 2 patches

λ = Wavelength

The effects on propagation issues of cosecant-

squared and switch beam antenna are respectively

depicted on

figure 7-c and figure 7-d. The shadowed

zones disappear with cosecant-squared antenna and

the coverage area is gone from 50% to 90% by using

switch beam antenna.

5 CONCLUSION

A computer program using Ray Tracing method for

coverage prediction has been implemented based on

3D GIS databases. This planning tool is applied to

LMDS by making several series of simulation in

order to have better understanding of propagation

phenomena in frequencies ranges around 40 GHz.

The comparison between simulations and

measurements was also presented. Finally, the

design of new antennas was carried out to improve

the LMDS coverage area.

Planned on-going research will be focused on

repeaters and will be investigated precisely in the

near future.

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PLANNING TOOL FOR LMDS COVERAGE USING 3D GEOGRAPHIC INFORMATION SYSTEM DATA

Figure 7: Principle and effect of cosecant-squared & switch beam antennas

REFERENCES

“What is GIS” http://www.GIS.com

Jensen, F., C. Garres & M. Sabbadini, 1990 “CAD

applications with GTD” Journées Internationales de

Nice sur les Antennes, Nice, pp.150-163

Rappaport, T., 1997 “Site-specific propagation” Virginia

Tech

RECOMMENDATION ITU-RP. 530-7, 1992

“Propagation data and prediction methods required

for the design of terrestrial line-of-sight systems” ITU

Radiocommunication Sector, pp.13-17

RECOMMENDATION ITU 838, 1992 “Specific

attenuation model for rain for use in prediction

methods” ITU Radiocommunication Sector, pp.205-

206

Ruck, G.T., 1970 “Radar cross section handbook”

PLENUM PRESS, NEW YORK – LONDON

Freytag, L., Jecko, B., 2002 “Cosecant-squared antenna

for the optimisation of LMDS system coverage”

Journées Internationales de Nice sur les Antennes,

Nice

Dall’omo, C., 2003 “Contribution à l’étude d’antennes à

pointage électronique en millimétrique. Conception et

réalisation de différentes topologies de matrices de

Butler » Thesis of Limoges University

Distance (m)

Sector based antenna

Distance (m)

Switch beam antenna

dBdB

Distance (m)

Sector based antenna

Distance (m)

Sector based antenna

Distance (m)

Switch beam antenna

Distance (m)

Switch beam antenna

d. Coverage improvement

by switch beam antenna

max

Coverage area

max

Coverage area

a. Principle of cosecant-squared antenna

b. Princi

le o

witch beam antenna

c. Shadowed areas coverage

by cosecant-squared antenna

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-90

-80

-70

-60

0 50 100 150 200 250 300 350 400 450 500

Distance (m)

Power (dB)

Sensitivity threshold

Directionnal antenna

Cosecant-squared antenna

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