Factors to consider when implementing a MW link

8/10/2019 Factors to consider when implementing a MW link

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Contents

Abstract

Acknowledgements

Declaration

What is a transmission medium? 1

What are the transmission mediums that we can see in the day to day world? 2-4o Guided media 2-4o Unguided media 4

Why we need a micro wave radio transmission? 5-6What is terrestrial microwave link planning? 7-42

o Initial planning and site selection 7-8

o Topographical analysis 8-11

o Preliminary path and frequency planning analysis 12-31

o Site Survey 31-42

The tools that we use in radio network planning 43-53

Problem fond and Solution suggestions for that 53-56

References 57


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Acknowledgement

I owe my great thank to everybody who helped me and supported me during this project,

from its beginning to the end.

My deepest thank goes to Mr. Sameera Bandaranayke and Mr.N.R.Bernadge who guided me

throughout the project with attention and care. And also for the Mobitel (Pvt) ltd collaterals

who gave me information to build up my project document.

I would also be thankful for all my friends who helped me to complete this project

successfully.

Last, but not least my sincere gratitude goes to all the authors of the books and the articles,

and the authors of the websites that I have used in my project.

Thank you.


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What is a transmission media?

In Telecommunications, information can be transmitted between two nodes or one to

multiple nodes or in broadcast method by using single either it is analogy or digital. The

way that we use to transmit the information signal or the data between nodes is calledas the transmission media.

In modern day world digital transmission is used exclusively. Even where the analogue

transmission used today we convert it to digital by using a method called Sampling in order

to facilitate long distance transmission.

These digitalise signals are combined by using a technique called Time Division

Multiplexing (TDM). The most popular TDM system is known as the Tier 1 (T1) system, in

which an analogue voice channel is sampled 8,000 times per second, and each sample is

encoded into a 7-bit byte. Twenty-four such channels are mixed in to two copper pairs andtransmitted at a bit rate of 1.544 megabits per second (Mbps).

T1 in North America (E1 in the rest of the world) remains an important method of

transmitting voice and data in the public switched telephone network (PSTN).

A talking path (i.e., a switched circuit) in the PSTN can be either analogue or digital or a

combination thereof. In fact, a digital signal can be transmitted over a packet-switched

network as easily as a circuit-switched network. Digitized voice is similar to data; therefore,

if data can be transmitted over a packet network, then so can digitized voice.

One of the most common applications is now known as voice over IP (VOIP). The challenge,

of course is to get the transmitted signal to a destination fast enough (delay-related issues), as

in instances in which the conversation may be time sensitive. A second challenge is to get

each packet, which is a small piece of a voice conversation, to its destination in the proper

way.


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What are the transmission mediums that we can see in the day

to day world?

There are three types of media (physical layers) can be used in transmitting information in the

telecommunications world:

Copper lines (twisted-pair and coaxial cables), for low- and medium-capacity

transmission over a short distance

Fibre-optic transmission, for medium- and high-capacity transmission over any

distance

Wireless transmission, including:

o Low (mobile radio) and medium-capacity (microwave point-to-point) over

short and medium distances

o

Satellite for low- and medium-capacity transmission over long distances

Basically these transmission media are categorised under tow main groups. They are

Guided Transmission media and Unguided Transmission media.

Guided Transmission media

There is a transmission media that transport electrical waves between two nodes

through physical medium such as metal, glass, plastic etc.

Unguided Transmission media

A transmission media which transports, electrical waves between two nodes

through non physical medium such as air.

Copper cables Air

Fibre cables Vacuum

Transmission mediums

Guided Unguided


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Guided media

Copper cables

In years ago, copper wire was the only means of transporting information. Technically

it was known as an unshielded twisted pair (UTP). It consists of a large number of

pairs of copper wire of varying size within a cable. The cable did not have a shield, so

the signal (primarily the high-frequency part of the signal) was able to leak out. In

addition, the twisting on the copper pair was very casual, designed as much to identify

which wires belonged to a pair as to handle transmission problems. Even with these

limitations, it was quite satisfactory for use in voice communications.

Coaxial cable technologies were primarily developed for the cable TV industry. In the

last few years, this technology has been extended to provide an Internet services to

residences. The high capacity of coaxial cable allows it to support multiple TV

channels, and this capacity can also be used for high-speed internet access. Like fibre

optics, the cost of cable installation limits the deployment of new services, and current

deployments are not typically in areas that allow this service which is to be offered to

business establishments.

Fiber optic systems

Fibre cables has becoming the third transmission medium apart from copper and

microwaves.

Fiber optic cables can be placed in ducts, buried in the ground or suspended in the air

between poles or can be installed as part of the ground wire on the high-voltage

transmission towers optical power ground wire (OPGW), and so forth.


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Now, with the use of fiber cable higher data rates are a common in the industry

installed as part of the ground wire on the high-voltage transmission towers optical

power ground wire (OPGW), and so forth.

Though fiber cable provides huge amount of data rates for some areas laying fiber maybe costly.

Wireless Systems or Unguided media

Wireless communications can take several forms: microwave (point-to-point or point-

to-multipoint), synchronous satellites, low Earth orbit satellites (LEOs), cellular,

personal communications service (PCS), and so on. For years, microwave radio

transmissions have been used in the telecommunications industry for the transport of

point-to-point data where information transmissions occur through carrier signals.

Microwave carrier signals are typically relatively short in wavelength and can transmit

information using various modulation methods.

The targeted wireless transmission type that we discuss here is microwave point to

point communication that we used in mobile communication.

Advantages and Disadvantages of Terrestrial Microwave Links

Advantages Disadvantages

Rapid installation Limited transmission capacity

Cost-effective Line-of-sight will be disrupted if any obstacle,

such as new buildings, are in the way

Low planning costs Disruptionscan be caused by the weather

Insensitive towards unplanned disruptions (e.g.

those caused by underground work) or natural

disasters

Relay stations necessary for long distances

High degree of flexibility as a result of being able tode-install and re-install at other locations


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Why we need terrestrial microwave wireless transmission?

Radio links poses some advantages over the fiber- optic cables. For an example

cost-effective transmission links in inaccessible terrain and difficult environments

the quick coverage of large areas by new operators

higher security due to the fact that equipment can be physically concentrated

Radio-relay transmission is therefore a very attractive alternative for applications ranging from the

coverage of the rural, sparsely populated areas, of developing countries having ineffective or

minimal infrastructures to the well-developed industrial countries that require expansion of their

telecommunications networks.

Considering the three transmission media mentioned above, radio-relay transmission is the most

suitable option for networks that are located in areas of difficult terrain topography or where other

limitations are imposed on the use of optical fiber and/or copper coaxial cables. Generally

speaking, radio-relay transmission is most suitable in the following applications:

Long-haul routes for national and international networks covering areas of difficult terrain

topography

National networks containing radio-relay in parallel with optical fiber

Backbone routes

Urban access routes connecting interurban optical-fiber cable routes and in-town terminalstations

Rapid geographical changes of station location as a consequence of catastrophic or

emergency situations

Short-term projects

Access links from cellular to public networks

Cellular transmission networks

Radio in the local loop

Point-to-multipoint operation

It is possible to combine the different applications presented above, thus making radio-relay

transmission a very competitive optionboth technically and economically.


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What is Terrestrial Microwave Link planning?

Terrestrial microwave link planning can be a quite complicated and time-consuming task. The

degree of difficulty is a function of that which is to be included in the task. For instance, the task

may include initial planning plus an overview of the entire network, frequency planning, sitesurvey, path analysis, installation and tests. Network operational requirements may also constitute

a crucial factor in the planning process.

Generally when speaking, the initial design of a radio network planning there are four steps;

Initial planning and site selection

Topographical analysis

Preliminary path and frequency planning analysis

Site survey

When planning a radio network, we have to consider three key points. Those are;

Availability, currently expressed as a fraction of time

Quality, currently expressed in bit-error ratio (BER) for digital links

Cost, expressed in the actual currency

If we cant design our radio network to full fill above mentioned key point our radio network will

be a total failure though we went through the main four steps.

Initial Site selection and PlanningWhen it comes to the initial site selection and planning step few questions (customer

questionnaire) need to be answered with regards to the topics such as economic, area topology, the

existing network and what the services hope to be established with the installation. The following

questions will be such exemplarily question should be asked. With these questions we can do the

planning process with more understandable manner. Who is the operator, what economic resources that he process, and what kind of services is

the operator going to offer?

Are we planning for many years ahead or just dealing with todays demand?

Are we expanding the existing network or designing a new one?

If there is an existing network, what spare capacity is available?

What are the requirements for reliability and performance of the network?


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After getting answers for above questioners some basic things can be done. Those are;

Identify all the main nodes in the network like switch location, hub sites, collocated sites,

and so on.

Meet with customers, contractors, vendors, and/or partners) and determine responsibilities

for the transmission (leased lines, fiber, MW) network design and deployment. Clearly define and describe in detail the scope of work (SOW). There is no such thing as

too detailed a scope of work.

Complete the scope and task delineation list (who is doing what). To avoid any future

confusion, this document should be as detailed as possible.

Sign the nondisclosure agreements (NDAs) with all parties (customer, vendors, partners,

and so forth) involved in the project.

Identify potential microwave sites, MW link capacity requirements, and MW frequency

bands/channels available and/or approved for the project and conforming to relevant ITU-

R (or other regional) recommendations.

Identify the available license-exempt microwave spectrum in case rapid deployment

microwave systems (spread-spectrum or some other type) are required.

Identify existing MW systems in the area and the source of information (microwave

frequency coordination).

Attain information (drawings, maps, and so forth) of the existing transmission facilities in

the area (e.g., MW, fiber optics, copper) as well as PSTN offices and POPs of the local

Telco companies.

Determine existing tower and other antenna mounting structures capabilities, establish

whether there is sufficient space for the MW radio equipment and antenna installation

(provide site layouts and tower profiles), and verify access to those sites.

Find out all the customer-specific requirements (preferred equipment and services

suppliers, power backup requirements, schedule, internal processes, and so forth).

Identify equipment and service resources (for international projects, try to find local

companies).

Develop a preliminary transmission network build-out schedule.

Topological analysisWhen considering the second step of network design process which is topological analysis we

have to have clear idea about the network topologies that we can see commonly in microwave

networks.

There are few main topologies we can commonly see in microwave networks. They are;

Star

Ring

Tree

Chain

Mesh

Figure 2: Common topology arrangements


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Star topology

A common pattern in which are all cell-sites directly connected to the switch & to form a star

network. The advantage of this configuration is that the cell-sites may be established to expand

capacity requirements in a particular area separately from capacity requirements in other parts of

the network. The network may be gradually taken into service in accordance with theestablishment of new sites.

This configuration also has the following disadvantages:

o It involves a large number of antennas in one place. This may cause space and strength

problems for antenna support structures. Large and robust structures are generally more

expensive.

o The high number of incoming routes may lead to problems in finding a sufficient number

of available channels.

This configuration is used mainly in leased lines networks and only under special circumstance in

microwave networks.

Figure 3: A Simple Star Topology

Ring Topology

By using radio links in a ring topology network, each node in the ring (i.e., each base station in

wireless network) is provided with two alternative routes. In the event of a failure in one link, the

traffic can be sent in the other direction of the ring. The main advantage of this configuration is

that it improves the availability of the network and can be built using PDH as well as SDH

technology.

If the ring has sufficient capacity to carry all the traffic from every site in both directions, then

complete redundancy has been achieved.

Unavailability time caused by hardware failure is reduced without the necessity of doubling the

radio equipment. That means that an unprotected (1 + 0) configuration can be used for all the linksforming the ring without sacrificing the availability of the network. Most links in the ring use a


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higher capacity than would be used in a simple tandem chain. This means that each link works

with lower system gain than in a corresponding tandem chain, which is compensated by less fade

margin needed due to the ring protection. As a result, the links in a ring-protected network should

be able to use smaller antennas.

It is important to notice that the physical layout does not necessarily have to form a ring; it is theactual flow of traffic (i.e. logical connection) that determines the ring topology.

It is important to notice that the physical layout does not necessarily have to form a ring; it is the

actual flow of traffic (i.e. logical connection) that determines the ring topology.

Figure 4: A Simple ring topology

Chain topology

The overall transmission performance of a tandem (also called daisy-chain) network is largely

influenced by the propagation characteristics of the individual hops. It is sometimes possible to

achieve the same overall physical connection by using different combinations of hop lengths.

Increasing the length of individual hops inevitably results in an increase in the probability of

outage for those hops. On the other hand, such an approach could mean that fewer hops might berequired, and the overall performance of the tandem network might not be impaired.

In the wireless network, this type of configuration consists of linking cell-sites in a chain such that

every cell-site in the chain acts as an active repeater for the previous one (see Figure 4.3). This

figure illustrates two chains converging to a common switch and, in this particular case; the

configuration can also be considered a tree. A common application of chain is the connection of

cell-sites along roads (called highway cell sites).

Closer to the switch, where the capacity is higher, it is recommended to have some degree of

hardware protection (1 + 1 configuration). If some of the microwave sites are in the remote areaswhere time-to-repair can be long, protected configuration is also recommended.


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Figure 5: A Simple Chain Topology

Mesh topology

The mesh topology is a mixture of the previously described configurations and is currently employed to

improve the availability to the network.

Figure 6: A Mesh Topology

With the information gathered from above questions we can decide what type of protection model

we need to apply. Do we need to implement new sites or can we use the existing sites. For this we

can use the existing topological map of the network.


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After the topological analysis we can decide path of the network. When we decide regarding the

path of a microwave network there are few factors which are to be considered.

o

We need to consider about the LOS availability

o Distance between the two nodes

o Protection topology arrangement

o Antenna diameters that we have to use

o Losses that could happen

o Solutions for the losses and LOS issues

LOS availability;

There is a main factor in microwave link designing. Microwave links that we use in

communication are point to point links. So we need line of sight (LOS) availability between twonodes that we hope to connect. For LOS conformation we can use electronic tools as well as site

surveys. By the use of electronic tools we can examine the site locations and the path clearance

with use of GPS co-ordinations.

For more confirmation we can use site survey, by visiting the sites personally and confirming the

path clearance.

The ultimate goal of LOS survey is to have MW connectivity between the two sites to ascertain

the Line of Site clearance. The LOS survey is carried out physically checking the terrain between

the hop and selecting the sites for acquisition. The survey is highly critical because any failure in

LOS can lead to a delay in project and a subsequent loss on account. Then all site networks are

depending on this LOS survey. If we do it wrong, network planning will be very difficult. This

LOS survey is very important.

At the full network plane, that all links are very important. If any link is blocked, whole network

plane will destroyed, all links are connecting each others. LOS survey is very important to our

network planning.

The distance between the two sites;

Which, are to be calculated because it will be an important factor, when it comes to choose the

antenna diameters and frequency selection? More the distance would get the antenna diameter

would get bigger, more the distance would get the frequencies that we have to use will get lower.

The protection topology arrangement;

Depending on the capacity or the criticalness of the sites we have to arrange a protection topology

arrangement to the microwave link that we design. There are protection types that we can apply to

the microwave link and to the topology as well.

For the microwave links there are protections types that we use with the configuration for example

here we include two common configuration types that we can see.


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1+0: one ODU (Out Door Unit) and one IDU (In Door Unit). No redundancy

1+1: one ODU and one IDU. Redundancy is available.

With topology arrangement we can select what type of what type of arrangement that we need that

is also depending with the criticalness of the microwave link.

Antenna diameters that we have to use;

We can select the antenna diameter depending on the distance. There are common diameters we

you use in microwave transmission networks. Those are

0.3m, 0.6m, 0.9m,1.2m, 1.8m, 2.4m, 3m, 4.6m.

Distance Km Frequency Antenna Size

0-2.5 23G 0.3m

2.5-6.5 18G 0.6m

6-9.5 15G 1.2m

9-15 13G 1.2m

10-20 11G 1.8m

15< 8G 2.4m/2.7m/3m/3.3m

Table: Relationship of distance and the antenna dia meters

Loss that can happen;

The loss/attenuation calculation is composed of three main contributions: propagation, branching,

and miscellaneous (or other) losses.

The propagation losses contribution comes from the losses due to the Earths atmosphere and

terraine.g., free-space as well as gas, precipitation (mainly rain), ground reflection, and

obstacles.

The branching losses contribution comes from the hardware required to deliver the

transmitter/receiver output to the antennae.g., waveguides as well as splitters and attenuators.

The miscellaneous losses contribution has a somewhatunpredictable and sporadic character,

e.g., sandstorms and dust storms as well as fog, clouds, smoke, and moving objects crossing the

path. In addition, poor equipment installation and less than perfect antenna alignment (field

margin) may give rise to unpredictable losses.

The miscellaneous contribution normally is not calculated, but it can be considered in the planning process

as an additional loss and then as part of the fade margin.


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o Propagation Losses

Free Space Path Loss

Electromagnetic waves are attenuated while propagating between two geometrically separated

points. The free-space path loss model is used to predict received signal strength when the

transmitter and receiver have a clear, unobstructed line-of-sight path between them.The attenuation is directly proportional to the square of distance and frequency and gives the free-

space loss that represents most of the total attenuation caused by wave propagation effects.

The frequency and distance dependence of the loss between two isotropic antennas is expressed in

absolute numbers by the following equation:

LFSPL=[4d2] = [4fd]2

[] (C)2

Where;

d = distance between transmit and receive antennas (m)

l = operating wavelength (m)

c = speed of light in vacuum (m/s)

f = frequency (Hz)

It is very important to notice that the free-space path loss model expressed here is valid only for

distances that are in the far field of the transmitter antenna.

Free-space loss is always present, and it is dependent on distance and frequency. After converting

to units of frequency and expressing it in the logarithmic (decibel) form, the equation becomes

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

Where

f = frequency (GHz)

d = line-of-sight (LOS) range between antennas (km)

Vegetation attenuation

LOS between stations is required for point-to-point microwave links. For an unexpected obstacle

intercepting the Fresnel zone (e.g., growing vegetation), the additional loss can be calculated.

High-resolution path profiles and careful site and path surveys are important to avoid unexpected

obstacle attenuation. Vegetation is continuously growing, and the rate of growth is very important.

It is important to include a provision for at least ten years of vegetation growth.

Foliage losses at millimetre-wave frequencies are significant. An early empirical relationship was

developed (CCIR Report 236-2) that can predict the loss. For the case in which the foliage depth

is less than 400 m, the loss is given by

L=0.2f0.3d0.6[dB]


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Where

f = frequency (MHz)

d = depth of foliage (m)

This relationship is applicable for frequencies in the range 200 MHz to 95 GHz. For example, the

foliage loss at 40 GHz for a penetration of 10 m (which is about equivalent to a large tree or two

in tandem) is about 19 dB. This is clearly a very serious attenuation and has to be considered or,

even better, completely avoided.

Weissbergers modified exponential decay model, or simply, Weissbergers model, is a radio

wave propagation model that estimates the path loss due to the presence of vegetation on a point-

to-point telecommunication link and gives slightly different results. If frequency is given in GHz,

we have

0.45f 0.284d for 0


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The two absorption peaks present in the frequency range of commercial radio links are located

around 23 GHz (water molecules) and 60 GHz (oxygen molecules). Specific attenuation (in

dB/km) for water vapour and oxygen are separately calculated and then summed to give the total

specific attenuation. The specific attenuation is strongly dependent on frequency, temperature, and

the absolute or relative humidity (RH) of the atmosphere

Figure 7: Gas attenuation versus frequency

Incidentally, the patterns for oxygen and water vapor absorption are quite different, and their

peaks and valleys do not coincide. Above 100 GHz, oxygen molecule absorption is quickly

reduced to an insignificant level, while the water vapor absorption trend is still upward and

manifests a series of high peaks and deeps with the increase in frequency.

From 1030 GHz, absorption of either sort is not a very serious problem, and only one absorption

peak of any significance is present, occurring at 23 GHz. Consequently, the entire spectrum

category is useful. Above 30 GHz, water vapor absorption rise is very sharp, exceeding 10 dB/km

at 60 GHz.

Many other atmospheric gases and pollutants have absorption lines in the millimeter bands (e.g.,

SO2, NO2, O2, H2O, CO2, and N2O); however, the absorption loss is primarily due to water

vapor and oxygen only.

Attenuation Due to Precipitation

Precipitation can take the form of rain, snow, hail, fog, and haze. Considering about the climate

conditions in Sri Lanka rain, fog and haze would be calculated. All of these consist of water

particles. Rain attenuation is, however, the main contributor in the frequency range used by

commercial radio links. Rain attenuation increases with frequency and becomes a major

contributor in the frequency bands above 10 GHz.

The main parameter used in the calculation of rain attenuation is rain intensity (rain rate), which is

obtained from cumulative distributions. These distributions are the percentage of time for which agiven rain intensity is attained or exceeded and are furnished for 15 different rain zones covering

the entire Earths surface.


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The specific attenuation of rain is dependent on many parameters, such as the form and size

distribution of the raindrops, polarization, rain intensity, and frequency. The contribution due to

rain attenuation is not included in the link budget and is used only in the calculation of rain fading.

It is important to notice that rain attenuation increases exponentially with rain intensity (mm/hr)

and that horizontal polarization gives more rain attenuation than vertical polarization.

Obstacle Losses

Diffraction is the mechanism responsible for obstacle loss/attenuation. In fact, obstacle loss is also

known in the literature as diffraction loss or diffraction attenuation.

Depending on the shape, size, and properties of the obstacle, diffraction calculations can be

cumbersome and time consuming. Since microwave paths normally require LOS, relatively

simple methods for calculating the obstacle loss are currently employed. One powerful but simple

method for calculation of obstacle loss is the single-peak method, which is based on the knife-edge approximation. This method can easily be extended to comprise the three most significant

peaks inside the Fresnel zones.

There are a number of different methods for estimating diffraction losses, some of them based on

the use of serious mathematical calculations. Here, we will show an estimate of the attenuation of

the signal (in dB), that results from diffraction over a single obstacle (building or tree), using the

knife-edge method.

Figure 8: Knife edge diffraction modelling

Fresnel zone

The concept of Fresnel zone clearance may be used to analyze interference by obstacles near the path of a

radio beam. The first zone must be kept largely free from obstructions to avoid interfering with the radio

reception. However, some obstruction of the Fresnel zones can often be tolerated, as a rule of thumb the

maximum obstruction allowable is 40%, but the recommended obstruction is 20% or less.


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Figure 9: Fresnel zone

These two blue lines are showing First and second Fresnel zone of the link. According to path loss tool, we

can get the idea about this Fresnel zone.

For establishing Fresnel zones, first determine the RF Line of Sight (RF LoS), which in simple terms is a

straight line between the transmitting and receiving antennas. Now the zone surrounding the RF LoS is

said to be the Fresnel zone.

The general equation for calculating the Fresnel zone radius at any point P in between the endpoints of the

link is the following:

Where,

Fn= The nth Fresnel Zone radius in meters

d1= the distance of P from one end in meters

d2= the distance of P from the other end in meters

= The wavelength of the transmitted signal in meters

According to this calculations, we need 100% clearance of first Fresnel zone, and also second

Fresnel zone 60%.if it if not there some attenuation of the microwave signal.


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Ground Reflection

Reflection on the Earths surface may give rise to multipath propagation. Depending on the path

geometry, the direct ray at the receiver may be interfered with by the ground-reflected ray, and the

reflection loss can be significant. Since the refraction properties of the atmosphere are constantly

changing (k-value changes), the reflection loss varies (fades). The loss due to reflection on the

ground is dependent on the total reflection coefficient of the ground and the phase shift.

Figure which is below this paragraph illustrates the signal strength as a function of the total

reflection coefficient. The highest value (AMax) of signal strength is obtained for a phase angle of

0, and the lowest value (AMin) is for a phase angle of 180.

The reflection coefficient is dependent on the frequency, grazing angle (angle between the ray

beam and the horizontal plane), polarization, and other ground properties. The grazing angle of

radio-relay paths is very smallusually less than 1.

It is strongly recommended to avoid ground reflection, which can be achieved by shielding the

path against the indirect ray. For large grazing angles, the difference between vertical and

horizontal polarization is substantial.

Changing the antenna heights can move the location of the reflection point. This approach is

usually known as the hi-lo technique, which forces the reflection point to move closer to the

lowest antenna by affecting the height of the higher antenna. The grazing angle increases, and the

path becomes less sensitive to k-value variations.

Figure 10: Signal strength versus reflection coefficient

Space diversity also provides good protection against reflection, and it is usually applied for paths

over open water surfaces.

Obviously, on many paths, particularly at higher frequencies, it is difficult to obtain an accurate

estimate of the effective surface reflection coefficient because of various uncertainties such as the

surface conductivity, surface roughness, and so on, and the degree of subjectivity currently needed

to obtain a calculation. The calculation procedure may only be a rough guide in such situations to


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help identify problem paths or to help choose one path from another, even if this possibility exists

in the first place.

The contribution resulting from reflection loss is not automatically included in the link budget.

However, when reflection cannot be avoided, the fade margin may be adjusted by including this

contribution as additional loss in the link budget.

Fading and Fade Margins

Fading is defined as the variation of the strength of a received radio carrier signal due to atmosphericchanges and/or ground and water reflections in the propagation path. Fading types normally considered

when planning microwave point-to-point paths are as follows:

Multipath fading, which is divided into

Flat fading

Frequency-selective fading Rain fading Refraction-diffraction fading (k-type fading)

All fading types are strongly dependent on the path length and are estimated as the probability of

exceeding a given (calculated) fade margin.

Multipath fading

Multipath fading is the dominant fading mechanism for frequencies lower than approximately 10

GHz. A reflected wave causes a phenomenon known as multipath, meaning that the radio signal

can travel multiple paths to reach the receiver. Typically, multipath occurs when a reflected wave

reaches the receiver at the same time as the direct wave that travels in a straight line from the

transmitter.

Multipath propagation gives rise to two kinds of signal degrading effects, i.e., flat fading and

frequency selective fading. The flat fading effect is due to thermal noise and interference.

Certainly, both flat and selective fading typically occur in combination.

Two scenarios of multipath are possible:

If the two signals reach the receiver in phase, then the signal is amplified. This is known as an up

fade. Up fades can also occur when the radio wave is trapped within an atmospheric duct. As can

be seen from the following formula, higher up fades are possible for longer paths:

Up fade max=10 log d0.03d (dB)

Path length d is in kilometres and, for the 50 km path; maximum up fade can be up to 16.6 dB.


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If the two waves reach the receiver out of phase, they weaken the overall received signal. If the

two waves are 180 apart when they reach the receiver, they can completely cancel each other out

so that a radio does not receive a signal at all. A location where a signal is canceled out by

multipath is called a null or down fade.

Under fading conditions, the direct signal may be attenuated and/or distortion increased to the

point where frequency selective notches result and dispersive fading occurs. Such distortion

results in ISI (inter-symbol interference) in the demodulator, an increase in data signal BER, and a

possible loss of data signal recovery.

Smooth surfaces, such as a body of water, a flat stretch of earth, or a metal roof, reflect radio

signals. In the following figure the body of water reflects a wave that cancels out the direct signal

and could bring down the radio link.

Figure 11: Multipath Fading

Some important facts about multipath fading are as follows:

Multipath fading is normally more active over bodies of water (lakes, sea, and so forth) than over

land. It is common practice on over-water paths to use a low-high antenna pair to move any

multipath reflections out of the antenna main beam.

It is important to avoid ground reflection. Multipath fading is more likely on paths across flat

ground than on paths over rough terrain. Horizontal paths give most flat fading.


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A rule of thumb is that multipath fading, for radio links having bandwidths less than 40 MHz and

path lengths less than approximately 30 km (20 mi), is described as being flat instead of frequency

selective.

Increasing path inclination reduces the effects of flat fading. Reducing path clearance (i.e.,

lowering antennas) will reduce the effect of flat fading, because the risk of multipath propagation

is decreased; however, this technique may increase the risk for refraction-diffraction fading.

On over-water paths, for example, the path inclination might be adjusted to place the surface

reflection on a land surface rather than on water, and even better, on a land surface covered by

trees or other vegetation. The reflection point moves towards an antenna that is being lowered and

away from an antenna that is being raised.

On over-water paths at frequencies above about 3 GHz, it is advantageous to choose vertical

polarization over horizontal polarization. At grazing angles greater than about 0.7, a reduction in

the surface reflection of 2 to 17 dB can be expected over that at horizontal polarization.

Antenna beam tilting effects have been effectively employed to overcome multipath fading

induced by surface multipath or super refractive/ducting layers in microwave point-to-point (LOS)

links. In both cases, upward tilting of the antenna cuts-off or reduces the radio frequency energy

refracted and reduces the multipath fading.

Flat Fading

A flat fading is a reduction in input signal level where all frequencies in the channel of interest are

equally affected. Flat fading implies barely noticeable variation of the amplitude of the signal

across the channel bandwidth.

Flat fading is dependent on path length, frequency, and path inclination. In addition, it is strongly

dependent on the geoclimatic factor (temperature/pressure variations), which is the factor that

accounts for the refraction properties in the atmosphere, antenna altitudes, and the type of terrain.

Deep flat fading is assumed to follow the Rayleigh distribution.

If necessary, the flat fade margin of a link can be improved, including using larger antennas, a

higher-power microwave transmitter, lower-loss feed line, and splitting a longer path into two

shorter hops in several ways.

Frequency selective fading

Frequency-selective fading implies amplitude and group delay distortions across the channel

bandwidth produced by the multipath nature of the transmission media. Actually it happens

because of some ionized particles in the transmission media. It particularly affects medium- and

high-capacity radio links (>32 Mbps).


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Rain fading

Rain attenuation basically happens because of the oxygen and vapour gaseous absorption. Oxygen

loss is negligible for frequencies up to about 50 GHz. The first and best known effect of rain is

that it attenuates the signal. The attenuation is caused by the scattering and absorption of

electromagnetic waves by drops of liquid water. The scattering diffuses the signal, while

absorption involves the resonance of the waves with individual molecules of water. Water vapor

absorption is highly dependent on the frequency as well as the density of the water vapor

(absolute humidity, gm/m3). Water vapor absorption can be significant for long paths (>10 km).

Loss has a local maximum at 23 GHz and a local minimum at about 31 GHz. Absorption

increases the molecular energy, corresponding to a slight increase in temperature, and these results

in an equivalent loss of signal energy.

The extent of the attenuation due to rain is primarily a function of the form and the size

distribution of the raindrops. Rain fading starts increasing noticeably at about 10 GHz and, for

frequencies above 15 GHz, rain fading is normally the dominant fading mechanism.

Rain events are statistically predictable with reasonable accuracy if short-integration or

instantaneous rain measurements are available. Models that are based on measured cumulative

distributions of rain events are currently employed in the prediction of the probability that a

certain fade margin will be exceeded. The model estimates the time (normally expressed in

percentage of a year) during which a given fade depth (fade margin) is exceeded. Next, the result

is converted to worst-month statistic. The concept of worst month for a certain specific value of

the worst month is defined as that month with the highest probability of exceeding that specific

value.

Apart from the rain the other forms of precipitation such as fog and haze do not affect radio-relay

links as much as rain events and are considered negligible.

The rain rate enters into this equation because it is a measure of the average size of the raindrops.

When the rain rate increases (i.e., it rains harder), the raindrops are larger, and thus there is more

attenuation. Rain models differ principally in the way the effective path length L is calculated.

Two authoritative rain models that are widely used are the Crane model and the ITU-R P.530-xx

model, but there are a number of other models developed specifically for a certain region and/or

application.

Heavy rainfall, usually in cells accompanying thunderstorm activity and weather fronts, has a

great impact on path availability above 10 GHz. Rain outage increases dramatically with

frequency and then with path length. Fading due to rain attenuation is described empirically from

link tests and point rainfall data. Location variation is based on selected point rainfall data and

radar reflectivity data accumulated around the world. Ten- to fifteen-minute duration fades to over

50 dB have been recorded on an 18-GHz, 5-km path, for example, and increased outage at 23

GHz can require a 2-to-1 reduction in path length compared to 18 GHz for a given availability.


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Much is known about the qualitative aspects, but the problems faced by the microwave

transmission engineer remain formidable. To estimate probability distribution, instantaneous

rainfall data is needed.

Unfortunately, the available rainfall data is usually in the form of a statistical description of the

amount of rain that falls at a given measurement point over various time periods.

Important fact is the total annual rainfall in an area has little relation to the rain attenuation for the

area. In some cases, the greatest annual rainfalls are produced by long periods of steady rain of

relatively low intensity at any given time. Other areas of the country, with lower annual rates,

experience thunderstorms and frontal squalls, which produce short-duration rain rates of extreme

intensity.

The incidence of rainstorms of this type determines the rain rates for an area, and thus the high-

frequency microwave links long-term path outage time and unavailability. Even the rain

statistics for a day or an hour have little relationship to rain attenuation.

A day with only a fraction of an inch/centimeter of total rainfall may have a path outage due to a

short period of concentrated, extremely high-intensity rain. Another day with several

inches/centimeters of total rainfall may experience little or no path attenuation, because the rain is

spread over a long time period or large area. The predicted annual outage may not occur for years

and then accumulate over a single rainy season for a long-term average.

The worst rain outages occur during the heaviest thunderstorms.

Refraction and Diffraction

In the real world, the k-factor varies with time and location in accordance with complex physical

interactions involving the refractivity gradient (dn/dh) in the lowest part of the atmosphere and

other mechanisms as detailed in the propagation P series of ITU Recommendations.

An important objective in planning terrestrial microwave link systems is to ensure that outages

resulting from these variations are extremely rare events; thus, system fade margins, linked to

error performance and availability objectives, of the appropriate order are implemented to ensure

that this is so. Accordingly, to take account of the statistical nature of radio wave propagation, the

application of appropriate propagation prediction models is necessary.

Refraction-diffraction fading, also known as k-type fading, is characterized by seasonal and daily

variations in the Earth-radius factor k. For low k values, the Earths surface becomes more curved,

and terrain irregularities, manmade structures, and other objects may intercept the Fresnel zones.

The probability of refraction-diffraction fading is therefore indirectly connected to obstruction

attenuation for a given value of Earth-radius factor. Since the Earth-radius factor is not constant,

the probability of refraction-diffraction fading is calculated based on cumulative distributions of

the Earth-radius factor.

For high k values, the Earths surface gets close to a plane surface, and better LOS (lower antennaheights) is obtained.


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Losses could happen in the hardware

o Cable loss

o Connector loss

o Coupler loss (Applied in 1+1 configuration)

Common Solutions for the losses and LOS Problems

Diversity techniques are used as a solution for multipath problem is available. There are few

diversity techniques that we use. Those are;

Space diversity

Frequency diversity

Polarization diversity

Hybrid diversity

Space diversity

Output of the transmitter is fed to more than one antenna and received by more than one antenna.

Figure 12 : Space diversity

Space diversity technique is the widely used diversity technique used to combat Multipath fading.

Frequency diversity

The signal is transmitted using several frequency channels or spread over a wide spectrum that is

affected by frequency-selective fading.


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Figure 13: Frequency diversity

Polarization diversity

Multiple versions of a signal are transmitted and received via antennas with different polarization.

A diversity combining technique is applied on the receiver side. This is a solution for multiple

climate conditions.

Hybrid diversity

Hybrid diversity (HD) is an enhancement (SD+FD) of space diversity that uses frequencydiversity (when permitted). Hybrid diversity is the most effective of all of the diversity

arrangements and is preferred in difficult propagation areas, such as those covering very long

distances or transmitting over water. Here, one side of the link has one antenna and the other one

has two antennas (SD).

In the LOS issues we mostly we like to change the path of the link. But some time we will not be

able to change the path as well. In those kinds of issues we used put repeaters.

In cases where a direct microwave path cannot be established (i.e., there is no line of sight)

between two points, it is possible to establish a path by using a repeater. The function of such a

repeater is to redirect the beam so as to pass the microwave beam around or over the obstacle

(e.g., a building or hill).

The main requirement is that there should be a clear line of sight between the repeater and both

sides of the microwave link. This could be an active repeater (two microwave radios connected

back to back) if distances are long, or a passive repeater if distances are relatively short.


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When it comes to the frequency planning there are few areas that we need to get know.

o

Less Than 3 GHzMany UHF analog microwave links still are deployed in the 400-MHz band with the 1.4-

GHz band now being used for low-capacity, digital links. The 2.4GHz is used for

unlicensed links. In these lower frequency bands, long hops, even greater than 100 km, can

be accommodated. This is due to the more robust modulation scheme sand the less

stringent line of sight (LOS) requirements. Due to the larger wavelength, the antenna

surface accuracy on solid parabolic dishes is not critical and simple horn feeds can be

used.

o 311 GHz

This group of frequencies is typically where the main medium-to-high capacity long haul

band links are deployed; 4 GHz, 6 GHz, 7/8 GHz, and 11 GHz are typical. The 5.8 GHz is

used for unlicensed links. These links require full LOS and are affected mainly by

multipath fading. Thirty miles (50 km) is considered the ideal hop length that balances the

requirement to maximize hop length with costs, ease of design, and deployment

complications. Short hops should not be put in these bands, as they are a waste of valuable

spectrum.

o 1338 GHz

This group of frequencies is used for short hops, and there is an abundance of spectrum.

The main fading effect is from rain attenuation. Links below 30 km can typically be

deployed in the 13-GHz or 15-GHz band, whereas for very short hops (less than 5 km), the

38-GHz band should be used. Other link frequencies in this category are 18 GHz, 23 GHz,

26 GHz (ETSI), 32 GHz (new band) and 38 GHz. The 24 GHz is used for unlicensed

links.

When it comes to frequency selection there are few factors need to be considered.

o Distance of the microwave link

o Atmospheric nature of the area

o Radio models that is available with vendor

o Interference

o Topological arrangement


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Distance of the microwave link

As we know frequencies get degraded with the distance it travels in the medium. Lower

frequencies travel higher distances than the higher frequencies that would travel. So the distance

of the planed microwave link is needed to select the frequency range.

Atmospheric nature of the area

Geographical factors play a role in selecting the frequencies such as;

If the area is full of greenery the vegetation attenuation can be happen

If area is an aquatic area losses can be happen such as absorption losses

If the area is open for EMI it can be another problem

If the frequency that we going to use is not matching with the frequencies that is already used in

the sites it cause an interference issue.

Such like problems can be happening if not consider about the geographical area.

Radio models that is available with vendor

When selecting the radio frequencies we have to look up with the vender specifications for the

radio models and the frequency bands that they operate at. It will allow us choose the suitable

frequencies for the sites.

These are the popular venders of the microwave equipments

1. Ericson

Famous equipment is vender in industry. These equipments are using in world wide. These

equipments are made in Europe

Generally in Sri Lanka, Dialog, Mobitel and Etisalat companies are using these equipments

2.

Alcatel

Alcatel also made in Europe. Little bit expensive than Huawei and ZTE. But these equipments are

having some good qualities. This is also very famous vender name in world. Mainly in Sri Lanka

Etisalat uses this brand for their microwave needs.


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3. Huawei

This is one of the most popular telecommunication equipment venders in Sri Lanka. These

equipments are cheaper than others. Airtel, Dialog, Mobitel and Hutch companies are

using these equipments most of times. These equipments are made in China.

4.

ZTE

This is also popular telecommunication equipment vender in Sri Lanka. Especially Mobitel

Company is using these equipments.

5. Siemens

This is Europe Company; they are providing quality equipments to telecommunication industry.

Little bit expensive than other venders. But it has some good stranded and quality.

6.

NEC

This NEC Company produces mostly Microwave equipments. (ODU and IDU). These

equipments are also use in Sri Lanka

7. Ceragon

Interference

. Interference is the general term for any kind of radiation disturbance on radio-link systems.Theeffect of interference can be happen if do not use the appropriate frequencies for the sites. There

are several ways that interference can happen;

1. From equipment housing one unit to that of another unit, between components housed in the

same cabinet, or among units in the same telecommunications room

2. From the transmitter antenna to the receivers equipment housing

3. From the transmitters antenna to the receivers antenna

4. From the transmitters equipment housing to the receivers antenna

5. As spurious signals in the power supply system

These factors can be eliminated by a proper documentation work. This means we need a properplan of frequencies that we have already used.

Topology arrangement

Interference aspects may severely limit the number of links in a network if appropriate caution is

not exercised in the earlier stages of frequency planning. In what follows, some general aspects,

based on former sections, are illustrated.

1. Since paths of a chain have very sharp angles, using the same channels by changing

polarization (HP/VP) may be a good alternative to using two alternate channels in the chain.


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2. Figure shows the same channel used alternately with horizontal (HP) and vertical (VP)

polarization. Upper (U) and lower (L) duplex halves for the transmitters are illustrated in each

site.

3. In the tree configuration, and for sharp angles, polarization discrimination ensures the

possibility of using the same channel with different polarization (HP and VP). Both transmitters

on the common node have the same duplex half (U).

4. In the ring configuration, the same channel, with the same polarization, is employed in the

perpendicular paths but with different polarization in the parallel paths. The transmitters are

alternately labeled upper (U) and lower (L) duplex halves. Although the picture does not represent

a physical ring configuration, the logical configuration and traffic flows is indeed ring in nature. If

the ring consisted of an odd number of sites, there would be a conflict of duplex halves, and

changing the frequency band would be a good alternative.

5. In the star configuration, as noted earlier, all transmitters on the common node should have the

same duplex half (L). Keep in mind that this configuration displays a difficult frequency planningscenario and is very sensitive to the geometry (mutual angles). If the node is a concentration point

for high-capacity links, wide bandwidth is required, thus making the allocation of smaller

channels in other portions of the network quite complicated. It is recommended that the link

carrying the traffic out of the hub should use a frequency band other than the one employed inside

the cluster.

6. Mesh configuration presents a complicated frequency planning scenario as a result of several

conflicts of duplex halves. In addition, it normally requires more channels than do other

configurations.


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Figure 14: Polarization arrangement for different topological arrangements

Site survey

The ultimate goal of LOS survey is to have MW connectivity between the two sites to ascertain

the Line of Site clearance. The LOS survey is carried out physically checking the terrain between

the hop and selecting the sites for acquisition. The survey is highly critical because any failure in

LOS can lead to a delay in project and a subsequent loss on account. Then all site networks aredepending on this LOS survey. If we do it wrong, network planning will be very difficult. This

LOS survey is very important.

At the full network plane, that all links are very important. If any link is blocked, whole network

plane will destroyed. Then these all LOS survey is very important to our network planning .If we

do a wrong survey, that one link can be very effective to network planning. Then we should be

make sure all things about the survey should be done up to the task.

What are the tools we need to do LOS survey?

o

Compass

o GPS


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o 100m tape

o 5m stele tape

o Binocular

o

Mirrors

o Touches

o Camera

o How can we do LOS survey properly?

Requirements for LOS survey

Get correct GPS coordinates at the site

First we should go to site and want to get exacts Latitude and longitude at the site. This coordinates should

be right under the tower. After it we must get the Elevation of the site. This is so important to do the survey

.because elevation is very useable to get Wright idea about terrain vive of earth.

After we are getting these detail. We can manually put this data to path loss. Then we can find the correct

azimuth of two sites and terrain view of the land

Figure 15: GPS co-ordinations


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Get correct tower leg azimuth of the tower

Then we must find the leg azimuths of the tower. Generally there are three types of towers and

we use different methods to get leg azimuths of these towers

1. Ground base 4 lag tower

Figure 16: Four Leg Towers

At the 4 leg tower, first we go behind the one leg and watch the opposite leg of the tower. Then get the

compass and direct it to those two legs, then turn the Wright north of compass. Then there is the valve.

That azimuth is the far end leg azimuth

40 (Example)


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As an example, if we think that valve is 40 degree. We can easily find the other leg azimuth.

Because this is 4 leg tows, 360/4 is 90.then difference (azimuth) between neighbor lags is 90

Then we can find other legs azimuths as a (40+90), (40+180), (40+270)

2.

Ground base 3 leg tower

Figure: Three Leg Towers

At the 3 leg tower, first we go between two legs. Actually center of the two legs and direct the compass to

other (3rd) leg. Then we can turn compass to north. Then there is the valve. That azimuth is the 3rdleg

azimuth

20 (example)


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As an example, if we think that valve is 20 degree. We can easily find the other leg azimuth.

Because this is 3 leg towers, its looks like eggers of equilateral triangle. Then 360/3 is 120.then

difference (azimuth) between neighbor legs is 120

Then we can find other legs azimuths as a (20+120), (20+240),

3. Roof top pole

Figure: Roof Top Pole

This is only one pole. We can directly propose the antenna for any azimuth using Pole.

To the documentation posses, we need to put correct north of the tower

Then, first we go behind the one leg and watch the neighbor leg of the tower. Then get the compass and

direct it to those two legs, then turn the Wright north of compass. Then there is the valve. According to

That azimuth we can find the north according to tower


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After these things we can find the correct leg we want to propose the antenna according to far end

azimuth.

Propose antenna location

This is the most important thing of this survey. First a fall we can get the rough idea

using Pathloss, about the height. Then we can climb a tower until that height. After if get the

compass and can look the far end direction. If the hop length is under 12 or 14 km, if the link is

clear, we can easily see the far end on the sunny day.

Figure 17: Far end Location

Afterwards we might find the far end. According it we can change our height. Because some areas

tree height and budding height is different than general tree height. Sometimes customers asking

some fix clearance margin like 5m, 10m.at that sort of time we need to propose the height

according to clearance margin. Using Pathloss we can find that height. Then we want to check

that height, according to antenna dimension we need some free space at the related leg on the

tower. We must make sure about that height. At that height link should be clear and free leg space

should be there.

If there is no space at that height, we have to propose the antenna more than that minimum height.


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Figure 17: Proposed Antenna Position

Other thing is; if we cantsee a clear view of the far end, we can use binocular to see the far end. It is an

extra advantage for identifying the far end tower.

Cable ladders

Figure18: Vertical cable ladder Figure 19: Horizontal cable ladder


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We must check the cable ladder to lay the IF cable. If there a no space. We need to propose new cable

ladder. This IF cable is very sensitive cable. It can be easily damage. Then we must lay the cable properly.

For that we must find space to lay the IF cable from BTS cabin to Microwave antenna. And also we want

to get the length of it. According to it we can find IF cable length.

Outside grounding bus bar

Figure 20: Outside Grounding Bus Bar

These tower heights are bigger than the objects that we can see in the normal ground level. So

lighting issues is the one of main issue for towers. Then we need to make good ground for all the

equipment related to tower. Then we want to check the grounding bus bar of the tower. If there

not any free space to connect our new microwave cable and other thing, we need to add new

outside grounding bus bar to tower.

Cable window

Figure 21: Cable entry point

At the shelter (BTS cabin), there is the window to lay the cable from inside to outside. It calls

cable window. This shelter is fully air condition. Then this window should be fully seal. Then we

need check that cable window to lay our new microwave IF cable. If there a no free cable hall atthe cable window. Then we need to propose new cable window.


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Inside grounding bus bar

Figure 22: Inside Grounding Bus Bar

At the shelter, we also need to ground the equipment properly. If it is not, that lighting issues

should effective to that equipments. Because of it we need to ground the new microwave

equipment at in the shelter. If there a no space at the Inside grounding bus bar, we need to propose

new bus bar.

Microwave In Door Unit(IDU) Rack

We know every microwave link have IDU. At the cabin,there is a rack for fixing IDU properly. According to the new fiber

system, BTS size is very small, then mini BTS also installing on that

rack. Also E1 patch panels are in this rack. If we going to install a

new microwave antenna, we want to check the free space of the IDU

rack. If there are no spaces, we need to propose new rack at the cabin.

Figure 23: Microwave Rack

Power Breakers


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Figure 24: Power boxes

Generally every microwave IDU racks having power breakers of protecting the IDUs from

lightings. Then there is a power breaker panel on the rack. We need to check that power breaker panel, if

there are no free (not using) breakers .we has to propose a new power breaker panel

These are the main requirements to install the new microwave antenna. At this survey,

we must properly check about these all the things. If anything not at the survey report .there should

be so difficult to do the installation process. These all the requirements are very important. But main

thing is LINE OF SITE clearance should be there

When checking the LOS availability there are few types of tests that we can do manually. Those are

balloon test, mirror test or light test.

Balloon test

We can hydrogen, coloured balloon for this test as we can find the far end site easily if there is an error in

locating the far end.

Figure 25: Balloon test


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Light test and mirror test

At the town area, hare are lots of building and other physical things disturbing to

telecommunication networks. And other thing is that areas population density also high. Then lots of roof

top towers are there. At that type of area, we can see more towers within 200,300m of land. Then

sometimes we can identify the correct tower form far end. Then we have to do light test or mirror test.

o Mirror test

Figure 26: Mirror Test

We need one or two mirrors to do this test. Two persons want to go that two ends of the link and we have

to go to propose position of the tower and reflect the light to other tower direction. If link is clear, we can

easily see the light reflection of the mirror. According to it, we can decide the clearance of the link

If we in the cloudy day. There are no sun shine to do the mirror test. Then we has to light test at night

o

Light test

We need one or two torch to do this test. Two persons want to go that two ends of the link at night time.

We have to go to propose position of the tower and on the light to other tower direction. If link is clear, we

can easily see the torch light ray. According to it, we can decide the clearance of the link.


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Issues of LOS surveys and how we overcome these issues

Looking at wrong tower

This is one of main issues for doing the survey. Selecting wrong tower and take the photos. At the

town area, there are there are lots of towers. Most of times that all towers are look like same. Then

when we look the direction of the far end, we must be sharp. If degree is wrong, we can see other

tower. Then we cant identify the correct tower.

For over come to this issue, we can put a red flag or something like it on the tower, or make

remember antennas of the far end tower .then we can find the other tower easily.

Compass issues

Where using magnetic compass to do the surveys. Because magnetic compasses are light weight

and easy handle on the tower. But there are lots of metal at on the tower. Then it can be disturbed

to compass and it helps showing us to wrong directions. If the compass is wrong, total survey can

be wrong.

Then over come to this issue, we can get the direction far from the tower. At on the tower, we can

pun compass out of the tower and get the direction.

o Another antenna installed at that our proposed antenna location

Sometimes several mobile networks are sharing the same tower. Then after we completing survey

we must put the remark about it on the propose antenna location. If it is not, another user can

install an antenna at that free space.

For over come to this issue, we can put a label at propose antenna location, and also antenna size

should be on there

o Sometimes Cant reach the critical point

Sometimes we cant reach to critical points, because most of time that points is in mountains.

Then we have to go soon as when we can go .if we can see that critical point, we can get the idea

about tree height. Then we can get the elevation of several points around it and match the

elevation of the critical point. This is not the 100% over come for this issue. But this is only what

we can do for this issue


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The tools that we use in radio network planning

Most microwave network design software tools are developed by radio manufacturers and

therefore are biased toward the manufacturers own equipment. In other cases, the tool may be

proprietary and not sold on the open market.These tools are sometimes provided to engineeringpersonnel who are working on the customers site and performing network design. While some

microwave equipment manufacturers insist on using their own software tools, some operators and

consultants prefer to use commercially available tools.

One such vendor-independent tool is Pathloss 5.0 (and the older 4.0 version). This tool is probably

one of the best (and most moderately priced) tools for the complex microwave design, including

North American and ITU standards, different diversity schemes, diffraction and reflection

(multipath) analysis, rain effects, interference analysis, and others. Radio equipment parameters

for equipment from any vendor, channel tables, antenna diagrams, and so on are defined and

stored in the default parameters database for easy retrieval.

This tool is widely accepted by microwave system design engineers around the world.

Steps in pathloss tool to do a simple calculation;

Step 1- Enter site information

Open the Pathloss 5 program; you should see a window with a toolbar and menu. If there is a

menu item called "Initialize Program", you must initialize the program before continuing.

Click View - Site L istto bring up the Site index. You can also click the Site list button on thetoolbar.

We are going to manually add two sites to the project. Click on the first cell in the Site Name

Column. Enter a name for the site and press the Tab key to move on to the next cell. Enter

Latitude for the site and press Tab. Enter a Longitude. This is the minimum required information

for a site. Add a second site using the same method.
http://www.pathloss.com/pwiki/index.php?title=File:Site_list_01.JPG


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Close the Site list and the sites will be shown in the GIS window.

Sites can also me imported from a CSV file or any delimited text file. See Pathloss 5 - Import sites

from text file.

To determine what terrain data file(s) you will need, it is helpful to see a geographic grid.

Click Configure - Options - Network display options. Click Axi s - map grid. In the bottom right

area, check Show Geographi c Gri dand Show Labels.

Click the green check button to accept the settings changes. Make a note of the bounding

coordinates so you will know what terrain data you need.
http://www.pathloss.com/pwiki/index.php?title=File:Green-check.jpghttp://www.pathloss.com/pwiki/index.php?title=File:Geogrid_opts.JPGhttp://www.pathloss.com/pwiki/index.php?title=File:Site_list_02.JPGhttp://www.pathloss.com/pwiki/index.php?title=File:Green-check.jpghttp://www.pathloss.com/pwiki/index.php?title=File:Geogrid_opts.JPGhttp://www.pathloss.com/pwiki/index.php?title=File:Site_list_02.JPGhttp://www.pathloss.com/pwiki/index.php?title=File:Green-check.jpghttp://www.pathloss.com/pwiki/index.php?title=File:Geogrid_opts.JPGhttp://www.pathloss.com/pwiki/index.php?title=File:Site_list_02.JPG


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Step 2- Configure terrain data

Terrain data is available from many sources in a wide variety of formats. For this example we will

use SRTM terrain data. Full instructions on downloading and using this data is at SRTM.

Step 3- Create the links

For this example we will manually link the sites.

You should see the 2 sites marked on the screen. The mouse wheel can be used for zoom the

display in and out.

Select the Point to Point Link cursor from the toolbar. This cursor is used to create and

interact with links.

Left click
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on one of the sites and drag to the other site to create the link. You can now left click on the link

to access the modules of the link design tool.

Right clicking on links or sites will allow you to adjust attributes (appearance) and access other

options.

Step 4- Design the links

Generate Profile

The first step in designing the link is to generate a path profile. Select the Point to Point Link

tool and left click on the link. Select terr ain datafrom the pop-up menu.

This opens the terrain data module in the link design tool. Click on Operations - Generate

Profile. Make sure Primary Terrain DEM is selected and that the terrain database set up in the

first step is shown. Click the green check mark to generate the profile.

Once the operation is finished, a status window will be displayed. Review this data carefully.It

should display, "primary usage - 100.0%." If this is not shown or the usage is less than 100%,

check the file listed and the directory, make sure the file exists and is in the correct directory.

Click the green check to close the status window.
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Antenna Heights

Once the profile has been generated, antenna heights can be calculated. Click on Design -

Antenna heightsto enter the antenna heights module.

Click the calculate button to calculate antenna heights that satisfy the clearance criteria

(100%F1 at 4/3k is the default).

Transmission analysis

Click on Design - Tr ansmission analysisto open the link budget section of the program.
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The minimum required data for a complete reliability calculation is:

Frequency

Antenna gain

TX Power

RX Threshold level

Path information (roughness, climatic factor, temp)

Click on theRain cloudin the center of the path window, a dialog box will appear.

Enter the frequency in MHz. Click the green check button .

Click on the antenna graphic located on the left or right hand side of the screen. A dialog will

appear.
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Enter the antenna gain in the fields provided. You will need to specify the gain of the antenna for

both site 1 and site 2. Click the green check button

Click on the Radio graphic located on the left or right hand side of the screen. A dialog will

appear.

Enter the TX Power in watts or dBm and the RX Threshold level in dBm for both sides of the link

(both site 1 and site 2). Click the green check button

Click on the Terrain profile graphic located in the center of the screen. A dialog will appear.
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The required fields will all have blue arrow buttons beside them. The blue arrow button will

either calculate and populate the field or, in the case of Diffraction and Roughness, prompt for

additional information.

Start by clicking the blue arrow button for Diffraction loss. A dialog box will appear.

Accept the defaults by clicking the green check button. . Next, click the blue arrow button for

Climatic factor and then Terrain roughness after which a dialog will appear.
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Accept the default selections by clicking the calculator button followed by the green check

button.

Finally, click the Average annual temperature blue arrow button. Click the green check button

to accept and close the Path profile data dialog box.

You should now have the reliability calculations visible in the main window.

Step 5- Generate reports

From the Link Design Tool, select Design - Transmission Analysis

Select Report - Transmission Summary Report. This opens the report window which is actually a

robust editor similar to MS Word.
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Here you can make any final changes to the appearance of the report. When you are ready,

click F ile - Printto print the report.

Each module has its own report format. As well, you can select Design - Reportsto create batch

reports including data from any module and across multiple link files.
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Problem fond and Solution suggestions for that

Problem Found

House of Fashion is a major clothing store which is going to be open recently around the Borella

area. It is a major clothing store in Sri Lanka which accepts higher number of customers all the

time. Which means simultaneous it will increase the traffic that they will produce with in a small

area. According to the adjacent site analysis and the drive test analysis, these adjacent sites cant

handle a huge traffic that would generate targeting this area.

Solution That I Propose

Implement a new site linking to exciting site. The microwave must be calculated as critical one

because of the huge traffic that we accept and because of availability we would accepts from the

site to give maximum availability to the customers. At last it is capacity upgrade.

Design

When looking at the topological arrangement the perfect site to build up is COL 397 which

already has got a connection with COL 200 which is a main node of the Mobitel network. The

new site build up was COL 403.

After getting the GPS co ordinations of the new site we can get an idea from which direction we

can see the other site from a certain site.

With the survey part we did we are certa

Documents

Factors to consider when implementing a MW link