MW Basics & Design

Microwave Transmission

Basics & Design

STCSYSTEL Training Center

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Contents

Transmission techniques Microwave Radio Basics Radio Network Planning Aspects Radio Network Planning Process Radio wave Propagation Link Engineering & Reliability Interference Analysis PtP MW Transmission Issues Useful Formulae

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What is Transport ?

Transport is an entity that carries information between Network Nodes

Information is sent over a carrier between Network Nodes.

Carrier is sent over a Transmission Media

Commonly used Transmission Media : Copper Cables• Microwave Radio• Optical Fiber• Infra Red Radio

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Transmission techniques

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• PDH• SDH• Ethernet

Transmission techniques

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MW LINK traffic

MW LINK

MW LINK MW LINK

MW LINK

x4

x4 x4

E1

E2 E3 E4

x63

x4 x4STM-1 STM-4 STM-16

PDH

SDH

x3 x12Mbit/s

8Mbit/s 34Mbit/s 140Mbit/s

155Mbit/s 622Mbit/s 2.5Gbit/s

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Synchronous Transmission Network

• 1980 Synchronous Optical Network, Sonet• ANSI Standard• Synchronous Transfer Signal

STS-1: 51,84Mbit/sSTS-3: 155,52 Mbit/s (OC-3)STS-12: 622,08 Mbit/sSTS-48: 2488,32 Mbit/s

• 1988 (1990) Synchronous Digital Hierarchy, SDH• ETSI Standard• Synchronous Transfer Mode

(STM-0 51.84Mbit/s) STM-1 155,52 Mbit/s STM-4 622,08 Mbit/s STM-16 2488,32 Mbit/s STM-64 10 Gbit/s

MW LINK

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SDH Multiplexing Hierarchy

• All Network Elements usethe same clock.+ Bit-rates are always an absolute multiple of the lower one.+ “Allows” for higher capacities

• Byte interleaved multiplexing.+ Tributaries can be mapped into and extracted from any Mux. order.

PDH

STM-16

STM-1 STM-4

ATM

Clock

STM-1155.52

STM-4622.08

STM-162488.32

STM-649953.28Mbit/s

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Overhead

Section Overhead

+ Path OverheadTraffic

Physical network supervision

Logical network supervision

+ Path OverheadTraffic

SDH/Sonet frames contains path and section supervision data.• Path Overhead: POH, End to end supervision• Section Overhead: SOH, physical network supervision

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• Different combinations of PDH tributaries are possible.

Schematic ETSI mapping model

ATM

x3

x21

x63 (x84 in Sonet)

T

x334 Mbit/s

x1140 Mbit/s

x632 Mbit/s

ESTM-1

Ethernet

45 Mbit/s

6 Mbit/s

1,5 Mbit/s

Packet

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STM-1 frame

Section Overhead

(SOH)

VC-4Traffic + Path Overhead

150,336 Mbit/s261 columns

125μs (155,52 Mbit/s)

1 9 270

Columns

1

3

5

9

Rows

10

Section Overhead

(SOH)

AU-pointer

n x 9 columns n x 261 columns

64kbit/s

STM-n

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Low order POH

63xE1 mapping into STM-1

E1 2.048Mbit/s

Justification bits

C-12 2.224Mbit/s

VC-12 2.240Mbit/s

Pointer

TU-12 2.304Mbit/s

E1

x 3+ High order POH

+ Stuffing

VC-4150.336Mbit/s+ Pointer

+ SOHSTM-1

155.52Mbit/s

5.184Mbit/s

x 7+ Pointer

TUG-349.536Mbit/s

TUG-26.912Mbit/s

x 3

(=3xE1)

(=21xE1)

(=63xE1)

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Microwave Radio BasicsBasic ModulesConfigurationApplicationsAdvantages

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Microwave Radio - Modules

Microwave Radio Terminal has 3 Basic Modules

Digital Modem : To interface with customer equipment and to convert customer traffic to a modulated signal

RF Unit : To Up and Down Convert signal in RF Range

Passive Parabolic Antenna : For Transmitting and Receiving RF Signal

Two Microwave Terminals Forms a Hop Microwave Communication requires LOS

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Basic Hardware Configurations

Non Protected or 1+ 0 Configuration

Protected or 1+1 Configuration, also known as MHSB [monitored hot standby]

In MHSB Modem and RF Unit are duplicated

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Microwave Radio – Capacity Configurations

Commonly Used Capacity Configurations

4 x 2 Mbps or 4 x E1



155 Mbps or STM1

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Microwave Radio - Applications

As Transport Medium in Basic Service Networks

Mobile Cellular Network

Last Mile Access

Private Networks

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Microwave Radio Advantages

Advantages over Optical Fiber / Copper Cable System Rapid Deployment

Flexibility

Lower Startup and Operational Cost

No ROW Issues

Low MTTR

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Microwave Radio - Manufacturers

Few well known Radio Manufacturers Motorola Nokia Nera NEC Siemens Digital Microwave Corporation Fujitsu Ericsson Alcatel Hariss

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Microwave Network Planning Aspects

1. Network Architecture2. Route Configuration3. Choice of Frequency Band

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Network Architecture

Common Network Architectures Spur or Chain

Star

Ring

Mesh

Combination of Above

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Chain ArchitectureB

C

D

E

A

•For N Stations N-1 Links are required•Nth station depends on N-1 Links

Spur Architecture

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Star Architecture

•For N Stations N-1 Links are required•Each Station depends on Only 1 Link

BC

DE

A

Star Architecture

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Loop Architecture

•For N Stations N Links are required•Route Diversity is available for all stations

B

C

DE

A

Loop Architecture

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Loop protection is effective against faults, which are caused by e.g.

•power failure

•equipment failure

•unexpected cut of cable

•human mistake

•rain and multipath fading cutting microwave radio connections

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BTSDN2 or METROHUBMW RADIOSINGLE MODE MW LINKHSB MODE MW LINK

COPPER CONNECTION

Figure 2. Primary solution where loop masters (DN2) are co- located in the BSC.

To Next BSC

To Next BSC

BSC

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Figure 3. Solution of using remote loop master (DN2) co-located in a remote BTS

To Next BSC

To Next BSC

BSC

BTSDN2 or METROHUBMW RADIOSINGLE MODE MW LINKHSB MODE MW LINK

COPPER CONNECTION

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Mesh Architecture

•Each Station is Connected to Every Other•Full Proof Route Protection•For N sites (Nx2)-1

C

DE

A

Mesh Architecture

B

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Typical Network Architecture

B

GDE

I

Typical Architecture

J

FA

C

• Typical Network Consist of Rings and Spurs

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Network Routes & Route Capacities

Inter- City routes - Backbone Backbone routes are planned at Lower

Frequency Bands 2, 6 and 7 GHz Frequency Bands are used Backbone routes are normally high capacity

routes Nominal Hop Distances 25 – 40 Km

Intra – City routes - Access Access routes are planned at Higher Frequency

Bands 15,18 and 23 GHz Frequency Bands are used Nominal Hop Distance 1 – 10 Km

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Frequency Bands

Frequency Band 7, 15, 18 and 23 GHz are allowed to Private Operators for deployment in Transport Network

15,18 and 23 GHz bands are used for Access Network

7 GHz band is used for Backbone Network Different Channeling Plans are available in

these bands to accommodate different bandwidth requirements

Bandwidth requirement is decided by Radio Capacity offered by the Manufacturer

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MICROWAVE PROPAGATION

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Free Space Propagation

• Microwave Propagation in Free Space is Governed by Laws of Optics

• Like any Optical Wave , Microwave also undergoes

- Refraction- Reflection

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Free Space Propagation - Refraction

• Ray bending due to layers of different densities

Bent Rays In Atmosphere

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• In effect the Earth appears elevated • Earth elevation is denoted by K Factor• K Factor depends on Rate of Change of

Refractivity with height• K= 2/3 Earth appears more elevated • K= 4/3 Earth appears flatter w.r.t K=2/3• K= Ray Follows Earth Curvature

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Effect of Refractivity Change

K = 2/3

Actual Ground

K = 4/3

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Free Space Propagation – Reflections

Microwaves are reflected over Smooth Surfaces Water Bodies

Reflected Signals are 180 out of phase Reflection can be a major cause of outages Link needs to be planned carefully to avoid

reflections

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RF Propagation Reflections

• Reflections can come from ANYWHERE - behind, under, in-front

• 6 cm difference can change Path geometry

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Fresnel Zone

The Fresnel zone is the area of space between the two antennas in which the radio signal travels.

For Clear Line of Sight Fresnel Zone Should be clear of obstacles

It is depands on Distance and Frequency

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FRESNEL ZONES

1st Fresnel Zone

Mid Path

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FRESNEL ZONE CLEARANCES

1ST Fresnal Zone = 17.3 (d1*d2)/f(d1+d2)

d1 = Distance in Kilometers from Antenna ‘A’ to mid pointd2 = Distance in Kilometers from Antenna ‘B’ to mid pointf = Frequency in GHz

Ad1 d2

B

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RF propagationFirst Fresnel Zone

Food M art

Direct Path = L

First Fresnel Zone

Reflected path = L + l/2

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RF propagationFree space versus non free space

Non-free space• Line of sight required• Objects protrude in the fresnel

zone, but do not block the path

Free Space • Line of sight• No objects in the fresnel zone• Antenna height is significant• Distance relative short (due to

effects of curvature of the earth)

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FRESNEL ZONE & EARTH BULGE

D2/8

Earth Bulge

Height = D2/8 + 43.3D/4F

43.3D/4F 60% first Fresnel Zone

D = Distance Between Antennas

H

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Earth Curvature

Obstacle Clearance

Fresnel Zone Clearance Antenna

HeightAntenna Height

Midpoint clearance = 0.6F + Earth curvature + 10' when K=1

First Fresnel Distance (meters) F1= 17.3 [(d1*d2)/(f*D)]1/2 where D=path length Km, f=frequency (GHz) , d1= distance from Antenna1(Km) , d2 = distance from Antenna 2 (Km)

Earth Curvature h = (d1*d2) /2 where h = change in vertical distance from Horizontal line (meters), d1&d2 distance from antennas 1&2 respectively

Clearance for Earth’s Curvature

•13 feet for 10 Km path


Fresnel Zone Clearance = 0.6 first Fresnel distance (Clear Path for Signal at mid point)• 30 feet for 10 Km path


RF PropagationAntenna Height requirements

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Microwave Network Planning Process

1. Design Basis2. Line of Sight Survey3. Link Engineering 4. Interference Analysis

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N

N

Y

Y

RF Nominal Planning (NP)/ Application for Frequency

License

Define BSC Borders

Estimate BSC Locations

Preliminary Transmission Planning and LOS

Checking for possible BSCs

Finalize BSC Locations

Microwave Link Planning and LOS Checking for

BTSs

Update LOS Reports, Frequency Plan, Planning

Database, Equipment Summary

Customer to apply SACFA based on Nokia Technical

Inputs

Change BTS Prime Candidate

?

Change BTS Prime Candidate

?

Figure 1. Microwave Link Planning Process

Planning Process EX.

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Design Basis

Choice of Radio Equipment

Fresnel Zone Clearance Objectives

Availability / Reliability Objectives

Interference Degradation Objectives

Tower Height & Loading Restrictions

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Microwave Network Planning Process

Map Study for feasibility of Line of Sight and Estimating Tower Heights

Actual Field Survey for refining map data and finalizing Antenna Heights

Link Power Budgeting & Engineering Frequency and Polarization Assignments Interference Analysis (Network Level) Final Link Engineering (Network Level)

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Map Study

Maps are available in different Scales Sites are Plotted on Map Intersection with Water Bodies is also noted AMSL [above mean sea level] of Sight is

determined by Interpolation

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Map Study

Vegetation height (15-20m) is added to Map Data Path Profile is drawn on Graph for Earth Bulge

Factor (K) =4/3 and 2/3 Fresnel Zone Depths are Calculated & Plotted for

Design Frequency Band Antennae Heights are Estimated for Design

Clearance Criteria

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Field Survey

Equipment Required Data Required GPS Receiver - Map Study Data Camera Magnetic Compass Altimeter Binocular / Telescope Flashing Mirror Flags Inclinometer Balloon Set Measuring Tapes

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Field Survey

Field Survey Map Data Validation Gathering Field inputs (Terrain Type, Average

Tree/Obstacle Height, Critical Obstruction etc.) Line of Sight Check, if feasible ,using flags, mirror Data related to other stations in the vicinity , their

coordinates, frequency of operation, antenna size, heights, power etc.

Proximity to Airport / Airstrip with their co-ordinates Field inputs are used to refine existing path

profile data , reflection point determination, reflection analysis

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RF propagationEnvironmental conditions

• Line of Sight– No objects in path

between antenna– a. Neighboring

Buildings– b. Trees or other

obstructions• Interference

– c. Power lines

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Fading

• Phenomenon of Attenuation of Signal Due to Atmospheric and Propagation Conditions is called Fading

• Fading can occur due to • Refractions• Reflections• Atmospheric Anomalies

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Fading

• Types of Fading• Multipath Fading• Frequency Selective Fading• Rain Fading

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Multipath Fading

• Multipath fading is caused due to reflected / refracted signals arriving at receiver• Reflected Signals arrive with

• Delay• Phase Shift

• Result in degradation of intended Signal

• Space Diversity Radio Configuration is used to Counter Multipath Fading

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Frequency Selective Fading

• Frequency Selective Fading • Due to Atmospheric anomalies different

frequencies undergo different attenuation levels

• Frequency Diversity Radio Configuration is used to Counter Frequency Selective Fading

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Rain Fading

• Frequency Band > 10 GHz are affected due to Rain as Droplet size is comparable to Wavelengths

• Rain Fading Occur over and above Multipath and Frequency Selective Fading

• Horizontal Polarization is more prone to Rain Fades

• Path Diversity / Route Diversity is the only counter measure for Rain Fade

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Drop Shape and Polarization

2.0mm

1mm 1.5mm

2.5mm

As raindrops increasein size, they get moreextended in the Horizontaldirection, and thereforewill attenuate horizontalpolarization more thanvertical polarization

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Fade Margin

• Margin required to account for Fading – Fade Margin

• Higher Fade Margin provide better Link Reliability

• Fade Margin of 35 – 40 dB is normally provided

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Link Engineering & Reliability

1. Link Budgeting2. Reliability Predictions3. Interference Analysis

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Hop Model

Station BStation A

Outdoor Unit

Indoor Unit

Traffic

Outdoor Unit

Indoor Unit

Traffic

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Link Power Budget

Received Signal Level = Rxl

RxlB = TxA – LA + GA – Fl + GB – LB Where

TXA = Trans Power Station ALA = Losses at Station A (Misc.)GA = Antenna Gain at Station AFl = Free Space LossesGB = Antenna Gain at Station BLB = Losses at Station BRxlB = Rx. Level at Station B

RXL must be > Receiver Sensitivity always

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Link Power Budget – Receiver Sensitivity

Lowest Possible Signal which can be detected by Receiver is called Receiver Sensitivity or Threshold•Threshold Value is Manufacturer Specific

•Depends on Radio Design

•Higher (-ve) Value Indicates better Radio Design

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Link Engineering

Software Tools are used Inputs to the tool

Sight Co-ordinates Path Profile Data Terrain Data & Rain Data Equipment Data Antenna Data Frequency and Polarization Data

Tool Output Availability Prediction

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RF propagation Simple Path Analysis Concept (alternative)

WP II

PC Card

pigtail cable

Lightning Protector

RF Cable Antenna

WP II

PC Card

pigtail cable

Lightning Protector

RF CableAntenna

+ Transmit Power

- LOSS Cable/connectors

+ Antenna Gain + Antenna Gain

- LOSS Cable/connectors

RSL (receive signal level) + Fade Margin = sensitivity

- Path Loss over link distance

Calculate signal in one direction if Antennas and active components are equal

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Link Engineering – Interference

Interference is caused due to undesirable RF Signal Coupling

Threshold is degraded due to interference

Degraded Threshold results in reduced reliability

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Examples of Undesirable RF Couplings

Finite Value of XPD in Antenna is the Prime Cause

Solution : Use of High Performance Antenna

F1H

V

Cross Poler Coupling

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Examples of Undesirable RF Coupling

Receiver Filter Cut-off is tappered Solution : Use Radio with better

Specifications

F2

Adjacent Channel

F1

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Finite value of FTB Ratio of Antenna is Prime Cause

Solution : Antenna with High FTB Ratio

Front to Back

T : HiR : Low

T : HiR : Low

T : LowR : Hi

T : LowR : Hi

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Solution : Choose Antenna Heights such a way there is no LOS for over reach

Over Reach

T : LowR : Hi

T : HiR : Low

T : HiR : Low

T : LowR : Hi

T : LowR : Hi

T : HiR : Low

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Interference is calculated at Network Level Interference due to links

Within Network Outside Network (Links of other Operators)

Interfering Signal degrades Fade Margin Engineering Calculation re-done with

degraded Fade Margin

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Counter Measures Avoid Hi-Lo violation in loop Frequency Discrimination Polarization Discrimination Angular Discrimination High Performance Antennae Lower Transmit Power , if possible

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PtP Microwave Transmission - Issues

Link Performance is Seriously Affected due to Atmospheric Anomalies like Ducting Ground Reflections Selective Fading Excessive Rains Interferences Thunderstorms / High Winds causing Antenna

Misalignment Earthing Equipment Failure

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Some Useful Formulae

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Link Budget

+Tx A Rx B

A B

+GA +GB

-Lfs-Arain

BRainfsAAB GALGTxRx +--+=

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)log(2045.92 fdL fs

d=1km ---> L = 124 dBmd=2km ---> L = 130 dBm

d=1km ---> L = 121 dBmd=2km ---> L = 127 dBm

39 GHz 26 GHzExamples

Free Space Loss

d = distance in kilometers f = frequency in GHz

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RF PropagationBasic loss formula

Propagation Loss

d = distance between Tx and Rx antenna [meter]PT = transmit power [mW]PR = receive power [mW]G = antennae gain

R TP P Gd

( )l4

2

Pr ~ 1/f2 * D2 which means 2X Frequency = 1/4 Power

2 X Distance = 1/4 Power

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Useful Formulae – Earth Bulge

Earth Bulge at a distance d1 Km

= d1 * d2 / (12.75 * K) Meter

Where d2 = (d – d1) Km (d Km Hop Distance)

K = K Factor

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Useful Formulae – Fresnel Zone

Nth Fresnel Zone Depth at a distance d1 Km

= N * 17.3 * ( (d1*d2) / (f * d) ) –1/2 Meter

Where d2 = (d – d1) Km d = Hop Distance in Km

f = Frequency in GHz N = No. of Fresnel zone (eg. 1st or 2nd )

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Tower Height Calculation :

Th = Ep + C + OH + Slope – Ea

C = B1 + F

Slope = (( Ea – Eb) d1)/ D

F = 17.3 ((d1xd2)/f X D) -1/2

B = (d1 x d2) / (12.75 x K )

Where, Th = Tower HeightEp = Peak / Critical ObstructionC = Other lossesB1 = Earth BuldgeF = Fresnel ZoneOH = Overhead ObstructionEa= Height of Site AEb= Height of Site Bd1= Dist. From site A to Obstructiond2= Dist. From site B to ObstructionD = Path Distancef= FrequencyK= 4/3

d1 d2

Ea Ep Eb

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Useful Formulae – Antenna Gain

Antenna Gain

= 17.6 + 20 * log10 (f *d) dBi See Note

Where d= Antennae Diameter in Meter f= Frequency in GHz

Note # Assuming 60% Efficiency

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Useful Formulae – Free Space Loss

Free Space Loss

Fl= 92.4 + 20 * log10 (f *d) dB

Where

d = Hop Distance in Km

f = Frequency in GHz

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Useful Formulae – Geo Climatic Factor

Geo Climatic Factor

G = 10 –T * (Pl)1.5

Where T= Terrain Factor= 6.5 for Overland Path Not in Mountain= 7.1 for Overland Path in Mountain= 6.0 for Over Large Bodies of Water

Pl = Pl factor

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Useful Formulae – System Gain

System Gain = (Transmit Power + ABS(Threshold) ) dB

Fade Margin = FM = (Nominal Received Signal – Threshold) dB

Path Inclination = ABS ((h1 + A1) – (h2 + A2) ) / d

Where h1 = Ant. Ht. At Stn A AGL Meter

h2 = Ant. Ht. At Stn B AGL Meter A1 = AMSL of Stn A Meter

A2 = AMSL of Stn B Meterd = Hop Distance in KM

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Useful Formulae – Fade Occurrence Factor

Fade Occurrence Factor = = G * d 3.6 *f 0.89 * (1+ ) -1.4

Where G = Geo Climatic Factord = Hop Distance in Kmf = Frequency in GHz = Path Inclination in mRad

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Useful Formulae – Outage Probability

Worst Month Outage Probability (One Way) % = OWM

OWM % = * 10 –(FM/10)

Annual Unavailability (One Way) % = OWM * 0.3

Assuming 4 Worst Months in a Year

Annual Availability (Two Way) % = 100-(OWM*0.3*2)

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