Planning for Dummies

7/31/2019 Planning for Dummies

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Ive been involved with radio for ages. My career

started when I was a teenager, growing up in Norway.

I set up an antenna to receive Radio Luxembourg

(1.440 kHz) on my fathers ancient Tandberg Slvsuper 5.

I stretched a 30-metre copper wire from our house to

the nearest hill, and spent rainy days lying on the sofa

listening to rock-n-roll. That winter we had a huge

thunderstorm. You can guess the rest. My father had toreplace his beloved old Tandberg and I learned my first

hard lesson about radio. Luckily, radio links have come

a long way (literally!) since then and so have I!

Ive now been invited to share some of my hard-earned

knowledge with you. I hope you enjoy this guide.

Preface

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Introduction

p l a n n i n g f o r d u m m i e s

3

This book is for you, even if

you have no experience

whatsoever of radio relay

planning and want to install

a link today. The intention

is to give you a brief

introduction to the mysteries of

radio relay planning, so that you will be able

to design and bring into service a radio link of your own.

The focus of this book is on high frequency equipment, 15 GHz and

upwards, systems such as Nera CityLink, which has become a potent

competitor to fibre optic and leased lines in enterprise networks. By reading

the following pages you will become a competent radio planner. This will

certainly pay you back since radio gives the least headaches per kilometre.

Just install it and forget it.

How to use the book

Youll find the information has been organised

into chapters with the most important topics

covered first.

The chapters may be read in any

order, so it is up to you where and

what you read first. I have also

taken the opportunity of adding in

some anecdotal stories to clarify a

point and lighten the read.


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Icons

This icon marks useful hints for the planning of radio links.

This icon appears alongside topics that cover possible dangers

to be avoided.

Topics marked with this icon are advanced subjects containing

valuable information worth knowing.

This icon marks topics included to answer some common

questions and add a little spice to the guide.

Further reading

There is much more to radio relay planning than can be covered in

this guide. If you wish to cover the subject in greater detail, NERA

Telecommunications offers a more comprehensive publication entitled

Planning Line-of-sight Radio Relay Systems, by Ingvar Henne and

myself. This is also aimed at readers who need basic engineering

information on the subject.

Further information is available from the reports

and recommendations given by the ITU-R(International Telecommunication Union

Radiocommunication), in particular the

Recommendation ITU-R P.530-7, Propagation

data and prediction methods required for the

design of terrestrial line-of-sight systems. The web

site at www.itu.ch will help you to find and order

the recommendations you need. There are also a

number of published works on radio wave

propagation and radio relay planning; see the

bibliography at the end of the guide.

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Radio Relay Systems

What are they?

The main purpose of a radio link is to transport data and voice traffic from

one place to another. The radio link uses the air as the transport medium to

send encoded electro-magnetic waves. A typical link consists of two radios

and two antennas separated by a distance from a couple of hundred metres

up to about 20 kilometres. Usually each radio is split into an indoor and an

outdoor unit with a cable in between. The reason for doing so is to ensure

maximum output power.


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How they work

The data and voice

traffic is fed into the radio

either using an electrical or

optical line. In the radio the

digital signals are coded into

analogue signals and converted

to microwaves with a typical length

of a few centimetres. Microwaves are used

because they are able to propagate high bit rates

safely through the air. The microwaves are sent using a

highly directive parabolic shaped antenna. At the other end the signals

are received and restored to the digital format. This works both ways,

simultaneously, of course.

Effectively, the link can be looked upon as just another fibre optic cable,but it is less expensive, easier to install and can be relocated fast.

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You cannot bend microwaves

Have you ever installed a TV antenna? If so, you may have noticed that

it is possible to receive a signal even though you cannot see the TV

transponder. The reason is that the electromagnetic waves have the ability

to bend around the terrain when the wavelength is long compared to the

height variations of the terrain. However, microwaves, which are only

centimetres in length, are small relative to the surroundings and hence do

not have this bending property. In order to establish a radio link you must

have line of sight between the two radio position sites.

I have seen the light

The simplest way to determine whether you have line of sight, is to useyour own eyes or binoculars. If the other site is not easily spotted, a

mirror with a diameter of 20cm or less can be used for verification.

Position yourself at your chosen site and a colleague at your target site.

Use the mirror to catch the sun and reflect it towards the target site.

To steady your aim, point the suns rays at the ground, then move the

mirror carefully upwards until the rays hit the target site. A mobile

phone or walkie-talkie will help you and your colleague communicate

to determine whether the rays were clearly visible at the target site.

Line of sight


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It is usually best to use the mirror at the lowest situated site since it

is much easier to spot and direct the reflected ray to something that

is visible against a background. It is worth remembering that the sun

is simplest to catch and redirect at the most northerly site in the northern

hemisphere and the most southerly site in the southern hemisphere.

If, like me, you live in a place where the sun does not shine that

often, you can use a camera flash instead to ensure line of sight.

A normal camera flash is easily spotted up to about 10 kilometres.

When setting up a link you should try to avoid transmitting over flat

areas or water. If you do there is a possibility of having a reflected

signal in addition to the original signal which can disturb the

communication. If you have to transmit over such areas, you should try

to conceal the antenna from the reflection point or point the antennas

slightly upwards to minimise the effect of the reflection.

When planning radio relays, it is common to use terrain profiles.

These are drawings showing terrain obstacles, (taken for instance from

a 1:50.000 map) between the sites. On this drawing the Fresnel zone

is superimposed in order to determine antenna heights. If the signal

path is long, the actual terrain heights have to be increased slightly

(mostly towards the middle of the path), to compensate for a minute

degree of bending of microwaves in air and also for the curvature ofthe earth. This added height is called earth-bulge.

As mentioned earlier the radio links transport traffic using electro-

magnetic waves. Since the wavelength of microwaves is small we

can treat the waves as a ray, but we need a little extra space around

the line of sight in order to get as much energy as possible from one site to

another. This space is cigar shaped and is named the Fresnel zone.

The extent of the Fresnel zone varies with the frequency of the signal

and the distances from the sites.

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The size of the Fresnel zone is a function of the frequency, the path

length and the distance from the sites. The illustration below gives theFresnel zone size at the middle of the signal path.

400

375

350

325

Altitude[m]

0.0 5.0 15.010.0Distance [km]

2

12

9

8

7

6

5

4

3

10

11

1 2 3 4 5 9876 13121110 20191817161514

10 GHz

15GHz

20GHz

25GHz

30GHz

35GHz

40GHz

Path Length [km]

Fresne

lzone

[m]


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It is a sad fact that nearly everything in life is limited, and that goes for

the transmitting range of a radio link as well. When microwave power is

transmitted from one site it gets diluted in the air and is received as a

very weak signal at the other end. The signal strength drops with the

square of the distance and if the sites are too far apart it is not possible

to discriminate the signal from the background noise. In addition radiolinks are susceptible to rain and that must also be taken into account

when designing the radio link.

To establish losses and gains a link budget must be drawn.

For convenience engineers use dBm in calculating signal power.

dBm relates to Watt logarithmically providing a simple calculation

(0 dBm = 1 mW, and consequently 1 W = +30 dBm).

A Nera CityLink example budget

Output power: +20 dBm

Antenna gain: +39 dB

Free space loss (10 km, 18 GHz): -138 dB

Antenna gain: +39 dB

Received level: -40 dBm

The lowest power level the Nera CityLink can function with is -73 dBm

which provides about 33 dB margin. These excessive dBs are termed

fading margin and help to maintain high performance and availability

in rainy conditions.

10

Link budget


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FREE SPACE LOSS:

Imagine that you put up

an aerial that transmits

power in all directions.

The power transmitted will

be diluted in the air and the

power received at a distance

(r) will be proportional to the

transmitted power divided by the area of a sphere with radius r.

From electromagnetic theory it can be shown, (dont ask me how!), that

maximum radiated energy from a point source is inversely proportional to the

square of the frequency. Putting this together we get a formula for calculating free

space loss as a function of distance and frequency. The graph shows the results

for the actual Nera CityLink frequencies.

ANTENNA GAIN: You may wonder about the notion antenna gain.How is it possible to get gain from a passive device? Has the perpetum

mobile been accidentally invented? No of course not. The antenna gain is

to do with the way we define and calculate free space loss. In the free space loss

calculation, antennas radiating in all directions (omnidirectional) were

considered, but microwave

antennas with their

parabolic design are able

to focus the power in a

certain direction. The more

directive the antenna is, the

higher the antenna gain

will be. The antenna gain

is proportional to the

square of the diameter

and frequency.

120

155

145

140

135

130

125

150

0 5 10 15 20

40GHz

35GHz

30GHz

25GHz

20GHz

15GHz

Distance [km]

Freespace

loss

[db]

50

35

30

40

45

18 23 25

0.45m0.60m

1.20m

Frequency [GHz]

An

tennaga

in[dBi]

Antennadiameter


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Rain, showers later. For more than thirty

years I have had the resulting pleasure of

this weather forecast. Rain doesnt just

bother me, it also has an attenuating

effect on microwaves. If there is a rain

shower in the radio link path, some of

the energy will be lost due to scattering

and absorption by the rain drops and

the signal strength will diminish.

The attenuating effect of rain depends on

the rain intensity (number of drops and

their size) and the frequency of the

signal. The rain intensity is measured in

millimetres pr. hour [mm/h] and for

radio link purposes the intensity

measured for 0.01% of the timeat a given place is used. When you know

the frequency and rainrate for a given link

it is possible to

calculate the specific

attenuation. This figure

tells you how much

the signal strength will

be attenuated in onekilometre with rain.

0.01

100

1.0

0.1

10

0 5 10 2015 3025 4035

150 mm/h

100 mm/h

50 mm/h

25 mm/h

5 mm/h

1.25 mm/h

0,25 mm/h

Frequency [GHz]

Spec

ifica

ttenua

tion

[dB/km

]

Rain attenuation for vertical polarisation as a function of frequency and rain rate

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Availability


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The volume and intensity of rainfall varies

geographically; both are generally greateralong the equator than in the

temperate regions. As the rain

intensity increases the rain cell size

gets smaller and normally only parts

of the radio link path are affected.


3

>140

>120

>100

>90

>80

>70

>60

>50

>40

>30

>20

>10 Rain intensity (mm/h)


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By multiplying the

specific rain

attenuation with the

effective path length

you get the needed

fading margin for a

link performing with

an unavailability

0.01%. Usually you

need a much better

performance, so the fading margin must be scaled to obtain

the desired unavailability figures.

0

14

12

10

8

6

4

2

16

18

1 5 10 15 302520 4035 5045

20mm/h

40mm/h

60mm/h

80mm/h100mm/h

Path Length [km]

Effec

tivepa

thleng

th[km

]

The ingredients needed for the unavailability calculation

1. Estimate the rainrate by using the world precipitation map

2. Find the specific attenuation for the given rainrate and desired

frequency

3. Use the rainrate and path length to get the effective path length

4. Multiply effective path length and the specific attenuation to get A,the fade margin for 0.01% unavailability

5. Scale the fade margin to achieve desired unavailability

50

35

30

25

20

40

45

0.000001 0.00001 0.0001 0.10.010.001Outage probability [%]

Fa

demarg

in[dB]

A=5

A=10

A=15

A=20

A=25

A=25

A=35

A=40

0

15

10

5

A = rain attenuation [dB]

for 0.01% of the time

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If you are planning a long radio link path you should stick to vertical

polarisation. When the rain intensity increases the raindrops get bigger

and change from their original spherical shape, becoming flatter due to

air resistance. With vertical polarisation most of the energy is in the

vertical plane and hence the wave sees less rain than if it were

horizontally polarised. The use of vertical polarisation may decrease

the outage time by as much as 30% compared to horizontal

polarisation.

World record of precipitation

I thought that Bergen, Norway, with its two metres of annual rainfall

was about the wettest place on earth, but take a look at this graph.

In Cherrapunji, India it rains 30 metres a year and in Cilaos,

La Reunion 2 metres fall in just a couple of days.

1 2 34 6 986 12604020

Duration

Ra

infa

ll[inc

hes]

Minutes Hours Days Months

10518 24 20 30 32 98 12 24

2000

1000800600

400

200

10080

60

40

20

10

86

4

2

1

Ra

infall[mm

]

50,800

25,40020,38015,240

10,150

5080

25402032

1524

1016

508

254

204153

102

51

2.5

R=16

.6D

0.475

FUSSEN, BAVARIAPLUMB POINT, JAMAICA

CURTEA DE ARGES, RUMANIAHOLT, MO

ROCKPORT, W VAD MANIS, TEXAS

SMETHPORT, PA

BELOUVE LA REUNIONCILAOS LA REUNION

CHERRAPUNJI, INDIA

UNIONVILLE, MD


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Objectives

Frequencies

In order to establish a link you need to

select a radio frequency for transmission.

If you, for instance, have a radio in the

18 GHz band there are more than fifteen

different frequencies to choose from.

But you can not just pick a frequency at

will, because there may be others alreadyusing the same frequency band. Should you

accidentally choose a frequency already

16

How good should the transmission quality of the link be? As good as it

gets, but there will always be a trade off between quality and affordability.

Unless you are planning a large trunk network (which I dont recommend

with only this guide as reference!), the availability objectives for high

performance links in access networks are in the range of 99.99% to

99.999% of the time. Please refer to ITU recommendations for details on

availability if your link is part of a larger telecommunications network.

The bit-error-ratio (BER) should typically not exceed 10-6 for links carrying

data traffic (e.g., ATM- or IP-traffic), or 10-3 for telephony.

The unavailability objectives usually cover both propagation effects and

equipment effects. Yes, even Nera equipment may fail, even though it is

highly unlikely. The mutual size of the two portions is more or less up to

you, but it is common among administrations and route designers to use

30%-50% of the outage for rain.

Availability [%] Unavailability [%] Unavailability [min. annually]

99.99 0.01 5299.995 0.005 2699.999 0.001 5.2


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used by somebody in the vicinity, it may cause interference and as a result

deteriorate the transmission quality. Use of frequencies is co-ordinated and

planned. Such co-ordination is usually

handled by the regulatory

authorities or administrations in

the various countries and can

be a complicated procedure.

You must apply for the

frequencies you need using

application forms which are

typically a couple of pages

of information about the

position, frequencies,

transmitted power and

other relevant technical

details of your planned link.

But, do not despair. When

you buy a Nera radio, we

will fill in the form for you

and plan your net as part of

the service. The only thing you

have to do is to buy the radio.

Frequency bands are divided into two half-bands, one half-band for

transmission, the other half-band for reception. If you have more than

one link using the same site, all transmitters and receivers must be in

the same half-band. If not, transmitted signals may leak into nearby receiversand cause severe interference.


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Installation, bringing into service or commissioning. Whatever you

call it, the name of the game is to get up and running fast. If like me,

you only read manuals when you have to, Nera have made it simple.

The manual is thin with lots of illustrations, easy to read and right to

the point.

After you have opened the packages and checked that all items accord

to the list, the installation can start. You can begin with either the

indoor unit or the outdoor unit. As a nuts and bolts man who prefersthe outdoor life, I usually start with the antenna and the outdoor unit.

When the units have been installed and cables have been connected it

is time for commissioning, i.e. turning on the power. The Indoor unit

will respond with the message *PWR On Boot *Please wait... and after

a short while the message Starting Application, will tell you that

everything is all right.

On the cover of the Nera CityLink manual, you will find the NEWConfigurator. It is PC software for easy commissioning and

configuration of the Nera CityLink. In order to speed up the initial

configuration, the NEW Configurator contains a wizard that guides

you through the necessary steps.

The last thing you have to do is to align

the antennas. You do one antenna at

a time. A coarse alignment can bedone by using line of sight or a

compass. The fine alignment

is done by adjusting for

maximum input power using

the outdoor units audible

signal or AGC voltage.

On the air

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The ultimate test of manhood

Some years

ago I had the

pleasure of

setting up a test link

at 15 GHz to

investigate the

amount of outage dueto rain and sleet.

After the installation,

it was time for

antenna alignment

which is thought to be

tricky especially on

higher frequencies. My colleagues, who know how impractical I am, decided

to let me do the antenna alignment. They stood watching and smiling to

themselves. This made me a little uncomfortable at first, but not for long.

First of all most links are close to the horizontal due to the relative longer

length of the path compared to the height difference between sites. If the

antennas are rotated in the same direction, clockwise for instance, the

ultimate peek in received power should be easily detected. Armed with this

knowledge, a leveller and a power meter, I faced the task (and my audience).

To be honest, it was easy. In a matter of minutes the antennas were aligned

and I could talk to Hilmar on the service phone. So the joke was on them!

And what about the measurements? Well, they were run for a year and

showed that the outage was far less than expected and theory had suggested.

After doing the installation and commissioning, you will be eager to get

on air, but just a little more patience please. First of all you should

check that the radio performs as expected. You can use the built-in test

facilities in the NEW Configurator to measure the quality. The radio shouldperform with less than 10 errors in 24 hours.

-85.00

-45.00

-55.00

-60.00

-65.00

-70.00

-75.00

-80.00

-50.00Input level

Rain intensity

Non-linear time scale

Inpu

tleve

l[dBm

]

14

.44

12

.00

12

.30

12

.45

13

.25

14

.04

14

.28

14

.36

12

.25

15

.19

15

.59

0.00

40.00

30.00

25.00

20.00

15.00

10.00

5.00

35.00

Ra

inintensi

ty[mm

/h](5m

in.)


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Security has never been my strong point. But since there are so manyallegations about the lack of security when using radio, lets consider

the issue. Imagine that you want to eavesdrop a link. The first

thing you need is an antenna, preferably

a big one, and an expensive, $99.999,

spectrum analyser. In order to get a

signal you must be close to the

transmitter or in its antenna beam which

is usually very unlikely.

The next thing to do is to guess the

data rate, possible overhead, modulation

method, filtering and modulation code

based on the received spectrum and get a

device that is able to do the decoding.

Then, when you have managed to get the digital

data, you must unscramble and synchronise it before you have access to

the SDH frames. The easiest way to do all this, which can be very

complicated, is to get a receiver from the same manufacturer who provided

the transmitter you want to eavesdrop. Just looking at the antenna and the

outdoor unit can give you a clue. Also a phone call to some engineers in

the organisation owning the transmitter can be very useful.

In order to extract the information from the SDH frames you need an SDH

processor and demultiplexer. With such a device you can get access to data

traffic at various rates. Finished? Oh no, now you have to guess what kindof traffic it is. Is it voice, video or pure data? It is hard to tell by just looking

at the data stream. Usually it is both encrypted and scrambled. If you

should be lucky enough to break the code, you will still face the problems

with protocols and language.

The conclusion must be that radio for all practical purposes is secure.

In fact, due to its complex nature it is even more secure than other

competing data transporting media. If you still have an interest in

eavesdropping, I think it is better to do that while you are commuting.

The diversity in subject, content and presentation will both amuse and

amaze you.

Breaking in a rough guide

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Bibliography

There are of course a lot of books on radio wave propagation and radio

relay planning and the following titles may be of interest to you

Giger Adolf, Low-Angle Microwave Propagation: Physics and

Modeling, Artech House, ISBN 0-89006-584-5

Hall Martin P.M., Effects of the troposphere on radio

communication, IEE, ISBN 0-86341-086-3

ITU-R, Handbook Digital Radio-Relay Systems,

ITU, ISBN 92-61-06281-4

Ivanek Ferdo, Terrestrial Digital Microwave Communications,

Artech House, ISBN 0-89006-302-8

Townsend A.A.R., Digital Line-Of-Sight Radio Links,

Prentice Hall, ISBN 0-13212-622-2


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Im singing in the rain

Just singing in the rain

What a glorious feeling

Im happy again

Im laughing at clouds

So dark up above

Cause the suns in my heart

And Im ready for love

Let the stormy clouds chase

Everyone from the placeCome on with the rain

Ive a smile on my face

Ill walk down the lane

With a happy refrain

Cause Im singing

Just singing in the rain


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Ever since I saw the first for dummies book in the bookstore,

I have considered it a good idea. These books give readers who do

not know anything about a subject a fast introduction to the basic

facts. I have long been waiting for a for dummies book on

planning of radio links. With titles like sex for dummies and

narcissism for dummies emerging, I do not have high hopes fora planning book arriving. Well, instead of waiting in vain, I have

written one myself and I hope that you will find it interesting as a

door opener to the fascinating world of radio link planning.

The book covers the basics for planning radio link in the

enterprise network and covers the following topics:

Radio relay systems Objectives

Line of sight Frequencies Link budget Commissioning

Availability Security

Documents

Planning for Dummies