Microwave Planning Procedure

7/28/2019 Microwave Planning Procedure

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MICROWAVE LINK DESIGN

10th November 2008

10.00 am

BPL MOBILE


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Overview

Site Survey

Link Budget

Frequency Planning


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Field Survey

Field Survey comprises of :

a) Site Survey

b) Path Survey


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Binoculars

GPS navigation device

Compass

Camera

Altimeter

Laptop If required Material request form

100 tape measure

Mobile Phone

Thermometer Mirror

Flag or Torch

Balloons If Required

SOI,City/area map withdesire scale

Site survey form

The following equipment/materials is required toconduct a site survey and must be provided by the sitesurvey team:

Field Survey


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Site Survey

Basic site data

Path information

Antenna/ODUinstallation

Equipment/IDUinstallation

Customer termination

IDU/ODU IF Cable run

Special Condition

Special Requirement

Site Diagram

Site Photograph Special Consideration

while gathering criticalsite information


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Map study and Preparation of Site

Terrain Aspect :

*Avoid selecting :

a) Flat terrain

b) Hilly or mountainous terrain specially

with steep slopes.

c) Seasonally flooded


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Map study

Type Of Map :

a) Topographical maps (scale: 1:100k or 1:50k )

b) Stereoscopic photographs

c) If either of above is not available use road and tourist

maps and navigational charts.

Note: Map can be procured from Survey of India


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Field Survey

Aim of Field Survey:

* Gather the critical site specific data necessary to completethe detailed engineering design and work plans.

* Characterize the microwave path to ensure designcredibility beyond a purely theoretical approach.


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Site Survey

Easy way to determine optical line of site is to visit oneproposed antenna location and look to see if the oppositelocation is free from obstacles.


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Site SurveyDetermining LOS should be done very early in the surveyactivity to avoid wasting valuable time.

For short distances determining line-of-sight may be easily

done with the naked eye, while sighting over longerdistances may require the use of binoculars.

If locating the opposite site is difficult, you may want to tryusing a mirror, strobe light, flag, weather balloon or

compass (with prior knowledge of site coordinates).


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Site SurveyThe amount of clearance required for obstacles is expressedin terms of Fresnel zones.

Fresnel zones consist of series of concentric ellipsoid

surfaces, which surround the straight-line path between twoantennas. The Fresnel Zone must be clear of allobstructions.


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Radius of the first Fresnel zone

R=17.32(d1*d2/fd)1/2

where d = distance between antennas (in Km)

R= first Fresnel zone radius in meters

f= frequency in GHz

d1

d2

d=d1+d2

R

Site Survey


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Typically the first Fresnel zone (N=1) is used todetermine obstruction loss

The direct path between the transmitter and thereceiver needs a clearance above ground of at least

60% of the radius of the first Fresnel zone to achievefree space propagation conditions

Site Survey


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Antenna Height

Graphical Method:

First draw path profile

Determine 1st Fresnel zone radius at various critical points.

This radius are added to height of obstacles and then markedon profile.

Consider height of antenna at one location and join the pointwith the marked point . On extending the line we get the heightof antenna at other end.

In Similar way try different combination.


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Path Survey

400

100

200

300

0.5 4.54.03.53.02.52.01.51.0 5.0

Typical Path Profile

Distance (miles)


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Microwave Link Design

Microwave Link Design is a methodical,

systematic and sometimes lengthy process that

includes

Loss/attenuation CalculationsFading and fade margins calculations

Frequency planning and interference calculations

Quality and availability calculations


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Microwave Link Design ProcessThe whole process is iterative and may go through many redesign phases before

the required quality and availability are achieved

Frequency

Planning

Link Budget

Quality

and

Availability

Calculations

Fading

Predictions

Interference

analysis

Propagation losses

Branching

losses

Other Losses

Rain

attenuation

Diffraction-

refraction

losses

Multipath

propagation


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Loss / Attenuation Calculations

The loss/attenuation calculations are composed of three main

contributions

Propagation losses

(Due to Earths atmosphere and terrain)

Branching losses

(comes from the hardware used to deliver the

transmitter/receiver output to/from the antenna)


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Loss / Attenuation Calculations

Miscellaneous (other) losses

(unpredictable and sporadic in character like fog, moving

objects crossing the path, poor equipment installation and

less than perfect antenna alignment etc)

This contribution is not calculated but is considered in the

planning process as an additional loss


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Propagation LossesFree-space loss - when the transmitter and receiver have aclear, unobstructed line-of-sight

Lfsl=92.45+20log(f)+20log(d) [dB]

where f = frequency (GHz)

d = LOS range between antennas (km)

Vegetation attenuation (provision should be taken for 5 years

of vegetation growth)

L=0.2f0.3R0.6(dB)

f=frequency (MHz)R=depth of vegetation in meters


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Propagation LossesObstacle Loss

also called Diffraction Loss or Diffraction

Attenuation. One method of calculation is based on knife edge

approximation.

Having an obstacle free 60% of the Fresnel zone gives 0 dB loss

0 dB

20dB16dB6dB0 dB

First Fresnel Zone


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Propagation Losses

Gas absorption

Primarily due to the water vapor and oxygen in the

atmosphere in the radio relay region.The absorption

peaks are located around 23GHz for water molecules

and 50 to 70 GHz for oxygen molecules.The specific

attenuation (dB/Km)is strongly dependent on frequency,

temperature and the absolute or relative humidity of the

atmosphere.


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Gas attenuation versus frequency

T=30

o

RH=50%

Frequency (GHz)

0 25 50

0.4

T=40oC

RH=80%

1.0

23GHzTotal specific

gas attenuation

(dB/Km)


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Propagation Losses

The specific attenuation of rain is dependent on many

parameters such as the form and size of distribution of

the raindrops, polarization, rain intensity and frequency

Horizontal polarization gives more rain attenuation than

vertical polarization

Rain attenuation increases with frequency and becomes

a major contributor in the frequency bands above 10 GHz

The contribution due to rain attenuation is not included in

the link budget and is used only in the calculation

of rain fading

Microwave Planning Procedure

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