microwave principles - topepdf

7/29/2019 Microwave Principles - TopePDF

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MICROWAVE TRANSMISSIONPRINCIPLES

By

Tope Okunlola

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IntroductionRadio Frequencies

Wireless telecommunications involve theuse of radio frequencies for

telecommunication purposes

Radio Frequencies are electromagnetic

radiation spanning from roughly 300Khz to

300Ghz



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Microwave Frequencies

They are sub band of the Radio Frequency

spectrum

They roughly range from 2Ghz to 60Ghz

They are used for modern commercial

telecommunications purposes



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Microwave Link

A Microwave Link is a communications

system that uses radio waves in the

microwave frequency range to transmit

information between two fixed locations on

the earth. That is, it is a point to point

wireless communication technology for the

transmission of data, voice and video(Broadband). Microwave links move large

amounts of information at high speed.



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Microwave Users

Wireless ISPs use microwave links to

provide high speed internet access to their

clients

Telephone companies transmit calls

between switching centers on microwave

links

Cellular telephone calls are carried

between cells on microwave link

Broadcasters send programmes from

studio to transmission station on microwave

link



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Microwave Advantages

It has the following advantages:

Fast and Easy Deployment

Cheaper cost of deploymentCheaper cost of Radio Equipment

Flexibility in terms of upgrading,

redeploying, and capacity increase

Resilience to natural calamities/problems



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Microwave Network

This consists of the portions of the network

communicating by Radio (Microwave)

frequenciesCommercial telecommunications Networks

use Radios for both its Access and Transport

Networks



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Access Network

This comprises of the subscriber wireless

terminals and the Base Station Access

Radios

It is also known as the Point to Multipoint

Network

There must be a means of transporting

information from one BS to another as

subscribers may reside on different BSIn a wireless telecommunication system,

access network is always wireless



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Transport Network

This is the network that serves as a pipe to

carry voice, data and Video signals from one

BS to anotherIt is also known as Point to Point

It is also known as the Backbone

In a wireless telecommunication system,

transport network is not always wirelessTransport choices may be mixed in the

Transport network



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Transport Choices

Leased linesMicrowave

Fibre Optics

Satellite



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Microwave Protection Scheme

Space Diversity

Frequency Diversity

Monitored Hot StandbyRoute Diversity

Hybrid Diversity



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Microwave Topology

Linear/Chain

Star

Tree

Ring



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Components of Microwave

Radio Equipment

Transmission cable

Antenna



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Contents

Line of Sight: there are Visual LOS and RF

LOS; Visual LOS occurs when one is able

to see the transmitting antenna with thevisible eyes from the receiving end, and

vise versa. RF LOS occurs like visual LOS

with the exception that the LOS can be

affected by the blockage of the Fresnel

Zone.

Microwave Terms with meaningsMicrowave Terms with meanings



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Fresnel Zone: This is the portion of the

space (air) that the RF transmitted signals

travel through from the transmitter to thereceiver. It is ellipsoid. The first 60% of the

fresnel zone must be free of obstruction for

a good link.



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Microwave Terms with meaningsMicrowave Terms with meanings Obstructions: This may be Natural, or Man made.

Natural e.g. Mountains, hills. Man Made e.g.

Buildings. They may be referred to as clutter or

terrain when designing many hops.

Hop: A hop is a single link involving two Base

Stations communication each other.

Transmitting Power: This is the amount powerthat is released from the antenna source into the

atmosphere. It does not include Loss of cables and

Gain of antenna. It is measured in mW or dBm.



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Propagation Loss:

i. Reflection: This occurs when part of the

signals transmitted are reflected back bythe earth terrain and clutter. The

wavelength of the reflected signals is

smaller compared to the diameter of the

obstructing surface.




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ii. Refraction: This occurs when part of the signals

transmitted passes through another medium of

different density and then bends away from thenormal route.

iii. Scattering: This occurs when part of the

transmitted signals meet some obstacles that are

having diameters smaller compared to theirwavelength. These obstacles may be rough

surfaces, or even fine particles in the air.



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Microwave Terms with meaningsMicrowave Terms with meaningsiv. Diffraction: This occurs when the transmitted

signals meet obstacles on the way and could not

pass through, but passes either sides of the

obstacles. It is effect of the waves turning, or

bending around the obstacles.

v. Absorption: This occurs when part of the

transmitted signals strikes and are absorbed intothe obstacles in a way that it does not pass

through, reflect off, or bend around the object.



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iv. Path Length: This is the distance between the

Transmitter and the Receiver. In other words, the

distance of a hop.v. Free Space Loss: This is the loss that occurs in the

air/space when the wave is being transmitted from the

transmitting antenna to the receiving antenna. It is the

loss occurred in the path. It can be referred to as Path

Loss. Mathematically,FSL: 92.45 + 20LogF + 20LogD

D= distance in Km, F= Frequency in GHz



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Microwave Terms with meaningsMicrowave Terms with meaningsiv. Loss: This is a decrease in signal strength. Loss can be

cable loss, or FSL. Signal degradation can be caused as a

result of Impedance mismatches in the cables and the

connectors. This is also referred to as attenuation. The unit

is decibel, Db.

v. Gain: This is an increase in signal amplitude. It can be

when an external power source such as RF amplifier is

used to amplify the signal or a high gain antenna is used to

focus the beam width of a signal to increase the signal

amplitude. The unit is decibel, Db.

vi. Antenna: An antenna converts electrical energy from the

cable into waves in case of a transmitting antenna, and

waves into electrical signal in case of a receiving antenna.



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vii. Antenna Gain: This is proportional to the antenna

physical shape and size. Antenna creates the effect of

amplification by virtue of its physical shape. Antenna

gain is as a result of focusing the signal into a tighter

beam. The focusing of the radiation is measured by wayofbeamwidths, which are either measured in horizontal

or vertical degrees. Antenna are of different types viz:-

Omni directional, Semi directional, Highly directional.

viii. Voltage Wave Standing Ratio: This occurs when there is

mismatched impedance that is, resistance to current flow

measured in Ohms between the devices in the

Microwave system. The effect can be a decrease in the

amplitude of the transmitted signal.



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Microwave Terms with meaningsMicrowave Terms with meaningsx. Radiated Power: This is the amount of power as measured

in the main lobe of the transmitting antenna. This puts into

consideration the losses and the gains encountered during

propagation. It can be referred to as Effective IsotropicRadiated Power. Mathematically, EIRP = Transmit Power

+ Transmit Antenna Gain + Cable Loss of the transmitter.

It is measured in mW or dBm.

xi. Receiver Sensitivity: This is also known as Receiver

Threshold. It is the minimum Power level at the Input of aradio receiver for it to decode a packet of data without an

error, to transfer information without error. A good

example is the Elastic Limit.



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Microwave Terms with meaningsMicrowave Terms with meaningsxii. Fade Margin: This is also known as Link Margin. This is the

allowance given to the link when designing, for it to function

properly putting multipath effects into consideration and any

unforeseen contingencies that may occur even afterimplementation. It can be viewed as link insurance. The

bigger the FM the better the link reliability. Mathematically,

FM = Received Signal Level Receiver Sensitivity.

xiii. Link Reliability: This is the percentage of the time the link is

expected to be up. The higher the FM, the more reliable thelink is. At least 99.995% is required for a short-haul. And

99.9999% for a long-haul. Reliability is also referred to as

Availability.



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Microwave Terms with meaningsMicrowave Terms with meaningsxiv. Signal to Noise Ratio: This is the minimum

power difference to achieve between the wanted

received signal and the noise level/floor. The

noise can be thermal noise, interfering noisefrom other network or within the same network.

For the microwave system to be able to work at

a certain data rate, the system needs a minimum

S/N ratio. If the signal is more powerful than thenoise, signal/noise ratio will be positive; if the

signal is buried in the noise, the signal/noise

ratio will be negative.



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Microwave Terms with meaningsMicrowave Terms with meaningsxv. Multipath Fading: This occurs as a result of the signalstraveling in many/multiple paths or directions between the

transmitter and the receiver. It occurs as a result of the

signals being reflected, refracted, scattered, absorbed, and

diffracted. Some of these signals are lost in the air beforereaching the receiver, thus reducing the RSL of the link.

The effect can be reduced by space diversity.

xvi. Radio Relay: This is the Transmitting Station that is used

to boost signals from one Base Station to the other. It is

eitherActive Station orPassive Station. An ActiveStation consists of the transmission equipments, while the

Passive Station consists of a good reflective surface placed

at certain angles to boost the signals.



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Microwave Terms with meaningsMicrowave Terms with meaningsxvii. Received Signal Level: This is the signal level received

that is measured at the antenna port of the receiving

antenna. It is measured in dBm. The higher the RSL, the

better the link. Mathematically, RSL = transmit power +transmit antenna gain transmit cable losses free space

loss + receive antenna gain receive cable loss.



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Link BudgetLink BudgetThis is the Power Budget of a microwave link. It

takes into account all the gains and losses in the link.

It is computation of the whole transmission chain.The link working condition is: total transmit + total

Propagation + total receive; must be greater than

Zero (0). The remain gives the Margin of the

system.



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Link Budget ContdLink Budget Contd

Mathematically, Link Budget:

Total Transmit (dBm): Transmit Output Power (dBm) cable

loss (dB) + antenna gain (dB).

Propagation (dB): Free Space Loss (dB)

Total Received (dBm): antenna gain (dBi) cable loss (dB)

receiver sensitivity (dBm)



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InterferenceInterferenceIn microwave links, interference occurs whenever a receiver

receives a signal from an unintended transmitter. It can either

be Intrasystem orIntersystem.

Intrasystem Interference occurs when the interference sourceis from within the system itself, like through antennas,

waveguides. Severe forms of intrasystem interference occurs

as a result of bad transmission network design; things like bad

frequency or polarization assignment.Intersystem Interference occurs when the interference source

is from another network.



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ModulationModulationThis is process of putting information on the radio waves by

altering the characteristics on the radio waves being

Transmitted. It can be done by either digital or by analog. In

other words, you modulate to carry your information throughaltering the characteristics since information signals cannot

travel far but microwave can. Waves characteristics to be

altered are:

1. Amplitude2. Frequency

3. Phase



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Modulation contdModulation contd

Few examples of analog modulation scheme are:

AM, FM while few of digital are: QAMS, QPSK.



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Important ConsiderationsImportant Considerations

Perform link analysis and budget for each hop to

determine antenna sizes to use.

Per hop reliability objectives are expected to bemet.

Frequency and Polarization to be well assigned

to reduce interference to the minimum level.



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Planning ToolsPlanning Tools

Software tools are used in the planning and the

design simulation and analysis. Examples of such are:

ATDI ICS telecoms and Pathloss 4.0



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THANKS!THANKS!

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