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Microwave Engineering with Pathloss IV
Imran Siddiqui
Email :[email protected]
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Microwave Communication
A communication system that utilizes the radio frequency band spanning 2 to 60 GHz. As per IEEE, electromagnetic waves between 30 and 300 GHz are called millimeter waves (MMW) instead of microwaves as their wavelengths are about 1 to 10mm.
Small capacity systems generally employ the frequencies less than 3 GHz while medium and large capacity systems utilize frequencies ranging from 3 to 15 GHz. Frequencies > 15 GHz are essentially used for short-haul transmission.
Microwave radio communication requires a clear line-of-sight (LOS) condition.
Radio LOS takes into account the concept of Fresnel ellipsoids and their clearance criteria.
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Available RF Spectrum
Band2-4 GHz
6-8 GHz
10 GHz
11 GHz
13-18 GHz
23-38 GHz
AdvantageBest propagation - no power fading (decoupling, ducting).Effective space diversity.
Lowest outage in non-ducting areas. Best high capacity, long-haul performance Very effective space diversity. Good discrimination to interference and long-delayed reflections.
Good longer path performance .Effective space diversity. Low rain outage in thunderstorm areas.
Wide spectrum (1000 MHz) available Many high capacity channels available
Narrow and wideband channels availableUncrowded bands (2000 MHz @ 18 GHz).
Few bandwidth constrictions .Uncrowded bands (e.g. 2400 MHz wide band at 23 GHz)
AdvantageBest propagation - no power fading (decoupling, ducting).Effective space diversity.
Lowest outage in non-ducting areas. Best high capacity, long-haul performance Very effective space diversity. Good discrimination to interference and long-delayed reflections.
Good longer path performance .Effective space diversity. Low rain outage in thunderstorm areas.
Wide spectrum (1000 MHz) available Many high capacity channels available
Narrow and wideband channels availableUncrowded bands (2000 MHz @ 18 GHz).
Few bandwidth constrictions .Uncrowded bands (e.g. 2400 MHz wide band at 23 GHz)
DisadvantageWideband links are vulnerable to dispersive fading. Reduced fade margins due to lower antenna gains. Higher interference levels. 2 GHz impacted by UMTS, FWA. High clearance paths are vulnerable to reflections. 4 GHz shared with satellites.
Longer paths are vulnerable to power fades due to ducting and decoupling in an adverse climate, requiring higher path clearances in some areas. Bands are crowded in some areas.
Limited bandwidth (4-16 T1/E1) RF channels.
Rain outage is a major factor in some areas. Shared with satellite services 10.9-12.75 GHz.
Outages are dominated by rain in thunderstorm areas, so path lengths are limited.
Very rain sensitive - e.g. needs 12-16 dB more fade margin (or 50% shorter paths) at 23 GHz than 18 GHz for equal outage in rain areas.
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TDM and PCM
The Bi-Polar PCM Digital Signal
(50% duty cycle)
11111111 12710100000 3210010000 1610001000 810000010 210000001 100000000 000000001 -100000010 -200001000 -800010000 -1600100000 -3201000000 -6401111111 -127
10011000* (Amplitude = 24)
Ch. 2 Analog Signal (VF)
µ-law (DS1)
1 1 1 0 0 0 1 1* 1 0 0 1 1 0 0 0* 1 0 1 0 0 1 1 1*
8-bit code of DS0 Ch. 1
8-bit code of DS0 Ch. 2
8-bit code of DS0 Ch. 3
DS1 Frame = 24 x 8-bit Bytes + 1 Framing Pulse = 193 bits193 bits x 8000 samples/sec = 1.544 Mbit/s
*DS0 VF Supervisory Signalson the
Least Significant Bit (LSB)
0 772 1544 3000 kHzNote the negligible energy
below 10 kHz and above 1.544 MHz
En
erg
y
Am
pli
tud
e
PC
M Q
uan
tizi
ng
Co
de
*Bi-Polar Violation (Alarm)
*
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Microwave Link Design Methodology
Microwave Link Design is a methodical, systematic and sometimes lengthy process that includes :
Loss/attenuation calculations.
Fading and fade margins calculations.
Frequency planning and interference calculations.
Quality and availability calculations.
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Micrwave Link Design
Microwave Link Design Process
The whole process is iterative and may go through many redesign phases before the required quality and availability are achieved.
Frequency Planning
Frequency Planning
Link BudgetLink Budget
Qualityand
AvailabilityCalculations
FadingPredictions
Interferenceanalysis
Propagation losses
Branching losses
Other Losses
Rainattenuation
Diffraction-refraction losses
Multipathpropagation
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Radio Path Link Budget
Transmitter 1
Receiver 1
Splitter Splitter
Transmitter 2
Receiver 2
OutputPower (Tx)
Branching Losses
waveguide
Pro
paga
tion
Los
ses
Ant
enna
G
ain
Ant
enna
G
ain
Branching Losses Received
Power (Rx)
Receiver threshold Value
Fade Margin
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Hierarchy in Multiple Access Networks
Analog FDM Hierarchy:FDM Subgroup: 3 Channels, 4-16 kHz, 4 kHz per channel Basic FDM Multiplex Group: 12 Channels, 12-60/60-108 kHz (2x48 kHz)2-nd order Multiplex Group: 60 Channels, 2x240 kHz3-rd order Multiplex Group: 300 Channels, 2x1.2 MHz4-th order Multiplex Group: 960 Channels, 2x4 MHzPlesiochronous Digital Hierarchy:Europe-ETSI: E1 (2048 kb/s, 30-31 channels 64 kb/s each), E2 (8448 kb/s, 4E1s, 120-124 channels) E3 (34.368 Mb/s, 16E1s, 480-496 channels E4 (139.264 Mb/s, 64E1s, 1920-1984 channels)USA-FCC: DS1 (1544 kb/s, 24 channels), DS2 (6312 kb/s, 4DS1, 96 channels) DS3 (44.736 Mb/s, 28DS1, 672 channels)Synchronous Digital Hierarchy: STM-1 (155.520 Mb/s, 63 E1s or 1 E4) STM-4 (622.08 Mb/s, 252 E1s) STM-16 (2488.32 Mb/s, 1088 E1s) STM-64 (9953.28 Mb/s, 4032 E1s)
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SDH Capacities
Line Rate(Mbit/s)
SDH Signal PDH Signal# E1 (2048 kbit/s)
Channel Transport
2.048 VC - 12 1 30
34.368 VC - 3 16 480
51.84 Sub-STM-1* 21 630
139.264 VC - 4 64 1,920
155.52 STM - 1 63 1,890
622.08 STM - 4 252 7,560
2488.32 STM - 16 1,008 30,240
9953.28 STM - 64 4,032 120,960
Reference: ITU-R Rec. F.750-3 (1997)
Radio or Fiber
Fiber
1:N Radio or Fiber
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SDH Frame Structure
Frame Length: 125RSOH : Regenerator Section OverheadMSOH: Multiplexer Section OverheadBit rate: 155.520 Mbps
sec
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SDH Frame Overhead
X … Bytes reserved fornational usage
M … Bytes reserved for media specific usage
(empty) … Bytes reserved for future standardization
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Typical Service Requirements
Bandwidth requirements for the applications listed are considered sufficient to provide adequate user experience on a single workstation.
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Transmission Media
Copper or Fiberoptics Cable - Leased Services Monthly fee…operator never owns the network Often long repair times ... customers are out of service Limited availability...e.g. ~99.8% (~17 hr/yr traffic loss)
Fiberoptics Cable - Purchase High installing cost ($30k-300k per km) favors very high capacity (2.5-10 Gb/s, per
“colour” with WDM) data transport Vulnerable to route damage with long service interruptions
Wireless Optical (Infrared, Laser, etc.) - Purchase Very short range - affected by optical visibility (300 m – 3 km) Low to high capacity, now to ~10 Gbit/s (OC-192/STM-64)
Microwave Radio - Purchase Low life cycle cost Rapid deployment, responsive service implementation, and under full user control (sites
and routes are secure)
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Terrestrial Radio-relay links
Terminal “A”
RadioMultiplex
Tx
Rx
RadioMultiplex
Tx
Rx
Terminal “B”
Antenna
Path
Feeder
Interference
Data Data
Antenna
Feeder
Radio meets superior reliability, higher security, and more demanding performance and quality standards.
Radio user has total control over site access and restore time.Radio grows with the network: Easily expandable and accommodates future relocation.Radio has an operational life long after the leased-line payback has passed (~2 yrs).Radio provides clear channel and protection capabilities.
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Advantages of MW wireless solution
Advantages of MW wireless solution
Disadvantages of MW wireless solution
Disadvantages of MW wireless solution
Low fixed costs Fast implementation (days) Focus deployment on best opportunities Winning cost profile in urban and rural markets Speed allows entry into new markets Unregulated at local levels 80% of cost is electronics (not labor and structures)
Line of sight (LOS) propagation Weather affects availability Aesthetics problems of customer antenna, community base stations and towers MMW technology is relatively new to commercial applications (55 GHz)
Advantages and Disadvantages
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Radio Wave Propagation
GEO, MEO, and LEO Satellites
Sky Wave(HF only)
REFRACTED WAVE
NON-REFRACTED (k=1) WAVE
REFLECTED WAVE
TransmittingAntenna
ReceivingAntenna
Troposphere
Ionosphere
Ground Wave(LF/MF only)
True Earth’s Curvature
MULTIPATH RAYS
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MW versus Optic Fibre
Favors Microwave
Microwave or fiber
FavorsFiber
Required Transport Capacity
Favors: Radio Fiber
Availability/security Payload (transport) Cost effectiveness Implementation time
Terrain considerations
Transport ChoicesShort
Tu
rn-U
p T
ime
Graph shows typical installation and commissioning time vs. transmission capacity.
Microwave is favored for short installation times and low-to-medium transport capacities.
Lightwave is obviously favored for its high to very high transport capacities.
Radio generally has a lower fixed cost/unit capacity and thus is less expensive for medium capacities.
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MW Radio in Cellular Networks
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2.5G GSM Network
Intranet
MSC
Server
Router
Intranet
Serving GPRSSupport Node(SGSN)
BSCBTS
Um
Gateway GPRSSupport Node(GGSN)
Server
Router
PSTNNetwork
GPRSbackbonenetwork
Internet LAN
Frame Relay Network (New)
Options: IP over FR: IP over ATM over SDH : IP over DWDM: IP over FWA
Leased lines
Fibre, Microwave
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MW radio-relay point-to-point wireless transmission is applicable to all communication networks.
MW applied for Mobile, Broadcast and Backhauling
2G
3G
WiMAX
3G LTE
WiFi
xDSL
FTTN
FTTU
GPON
WiMAX
BTS
Microwave for metro
Microwave for backboneBSC
Regional TV Studio
Microwave
Microwave
WiMAXWiMAX
Microwave
WAC
Mobile 2G and 3GMobile 2G and 3G
TV BroadcastingTV Broadcasting
MicrowavesBackhaulingMicrowavesBackhauling
MicrowavesBackbone
MicrowavesBackbone
OMSN
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Broadband Services in TDM Transmission Solution
The Broadband effect:
Traffic
Revenues
Data Era
Voice Era
Cost
TDM Backhaul ModelTDM Backhaul Model
TDM solution loose its effectiveness as data traffic becomes predominant, since it is bursty in nature,Improved versions of TDM platforms are available to mitigate this effect in its early phase (Nodal Solutions; Higher spectral efficiency using SW configured modulation schemes 16- QAM, 64-QAM, 128-QAM, 256-QAM; Super-PDH platforms).
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Exercise
Task: Convert to logarithmic dB units:Task: Convert to logarithmic dB units:
Power Amplification:• Twice• 20 times• 400 times• 500 000 times
Power Attenuation:• One half• 1/20•1/400•1/500 000
Use calculator and round the values to integer number of deci-bells.
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Logarithmic Units
1pW = -90 dBm1nW = -60 dBm1 W = -30 dBm1mW = 0 dBm1W = 1000 mW = 30 dBm2W = 2000 mW = 33 dBm4W = 4000 mW = 36 dBm10W = 40 dBm40W = 46 dBm
mW
PdBmP
1log10][
V
UVdBU
1log20][
Power expressed in dBm:Power expressed in dBm: Voltage expressed in dBuV:Voltage expressed in dBuV:
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Synchronization
Slip Rate: f x frames/s x 86400 s/daySlip Rate: f x frames/s x 86400 s/day
Type of Service EffectVoice Clicks
Video Frozen frames or missing lines
Modem Outage
Encryption Slow throughput
Fax Missing lines
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Antenna Center-line Determination
The antenna height should be chosen in such a way that obstruction losses during adverse propagation conditions are acceptable.
Also, designer must consider the increased risk for ground reflections if too large a clearance is used.
Antenna heights for a path can be obtained:
Graphically from path profiles By using mathematical formulae Using Link planning software tools (e.g. Pathloss v.4.0,
Enterprise Connect, TEMS Link Planner, Ellipse, Harris Magic)
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Path Calculations
270
330
390
440
500
Ele
vati
on
, m
A
MS
L
300
360
410
470
270
330
390
440
500
300
360
410
470
k = 4/3F = 0.6
Site: Yates CenterLat.: 37-51-02.NLong.: 095-43-53. W
Marmaton37-49-40. N
095-09-44. W
____
__ __ __ __ ____
__ __ __ __ ____
__ __ __ __ ____
__ __ __ __ ____
__ __ __ __ ____
__ __ __ __ ____
__
0 5 10 15 20 25 30
Distance, km
k=4/3
0.6F1
1.9 GHz
k=4/3
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Frequency Spectrum Allocation
Radio signals have to be frequency-separated if neither antenna discrimination nor topographical shielding provides the necessary suppression of interfering
signals.Distinct segments of MW frequency spectrum exhibits different propagation
characteristics (mutli-path effects, rain attenuation, absorption). Particular frequency bands differ by their spectral width hence can support
different link capacities (channel separations range between 1.75 to 56 MHz).All frequencies used in a radio-relay network should normally be selected from
an established frequency plan, generated either by international or nationalorganization.
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Receiver Sensitivity
Receiver sensitivity of a digital radio, is a minimum signal level on thereceiver’s input terminals, that secures specified maximum allowable BER behind receivers detector (typically 10-3 or 10-6 ), including FEC.
Receiver sensitivity is affected by:
Type of modulation method employed Type of carrier and clock recovery circuits Noise figure of the receiver path Phase noise level of the local oscillator Type of FEC and soft-detection employed
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Receiver Sensitivity and C/N
Sensitivity (minimum required Rx power) can be also expressed in terms of minimum required Carrier-to-Noise Ratio (C/N).Sensitivity (minimum required Rx power) can be also expressed in terms of minimum required Carrier-to-Noise Ratio (C/N).
NCNP Th /min [dBm; dBm, dB]
Where thermal noise:
dBTh NFkTBN 30)log(10
k… Boltzman’s constant = 1.38 x 10-23 J/KT… Absolute temperature of the receiver in K (0 oC = 273.15 K)B … Noise bandwidth in HzNF … Noise Figure of the receiver in dB
E.g. for BPSK minimum required C/N= 6 dB, for QPSK minimumRequired C/N=10 dB, for 16-QAM minimum required C/N= 17 dB@10-3
[dBm; dBW, dB]
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Receiver Thresholds
The 10-6 BER (or other BER<10-6) Static Threshold is for factory and in-service field verification of receiver noise and interference levels, measured manually with attenuators
The 10-3 BER Dynamic Threshold is for outage calculations and “hands-off” field measurements in a normal fading environment with BER network management, following ITU-T G.821 performance definitions.
The BER-SES Dynamic Threshold is the same as the above dynamic threshold, but is used for outage calculations following ITU-T G. 826 performance definitions. Usual range of BER-SES is 10-3 – 10-4.
Three Digital Radio Thresholds: One for factory and field in-service testing, and two for outage calculations, performance measurements, etc.
Three Digital Radio Thresholds: One for factory and field in-service testing, and two for outage calculations, performance measurements, etc.
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Comparison of Modulation Methods
Receiver sensitivities for BER = 10-6 (3.5, 10.5 GHz)Receiver sensitivities for BER = 10-6 (3.5, 10.5 GHz)
For the same input data rate, more crowded M-QAM constellations use channel frequency band more effectively, but require higher C/I
Higher level M-QAM are susceptible to selective fading and other types of linear distortion.
M-QAM schemes require linear RF power amplification. Spectrum is expensive => Spectrum efficiency wins the battle
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Free Space Loss and Absorption
2
4
DAFS
DAFSdB
4
log20
A free space equation simply assumes that radio waves are transmitted equally in all directions. Hence the power density is equal in every point of a sphere having transmitter in its center. Receiver captures only small part of the power, which is proportional to the effective area of receiving antenna – isotropic radiator.
In decibels:
Where D… distance between transmitter and receiver … wavelength
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Atmospheric Absorption Curves
Significant for frequency bands above 15 GHz.
Significant for frequency bands above 15 GHz.
Absorption on water vapor H2O Absorption on oxygen molecules O2
Absorption on other gasses: smog, exhaustions, etc.
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Terrain Related Effects
Specular Reflection: For MW hops routed across large or medium sized bodies of water (see, lakes, rivers), part of the energy radiated by the transmitter can be almost totally reflected from the water level, then reach the receiver and add destructively with a direct signal. This causes a power fade, the depth of which changes nocturnally (K-variation).
Diffraction effects: MW energy reaching an obstacle, the longitudinal dimension of which is comparable to the wavelength, is bent behind the obstacle. This bending is called diffraction. The rays behind the obstacle, that are bent under different angles, add up in a complex manner and cause cross-sectional variation in power density. Common manifestation of such varying power density is an attenuation on the direct path between Tx and Rx. This attenuation is subjected to K-variation and is closely coupled to Fresnel zones clearance.
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Long High Hop
K = 4/3
0.25° Discriminationto the
Reflection
1500
500
0
1000
0 20 40 60 80 100(161 km)
0.249°Grazing Angle
5 ns
Multi
path D
elay
K = 0.543°
DecouplingAngle
Distance,Mi
2000
2400(731m)
1150 ft(350 m)
Ele
vati
on
AM
SL
, Ft
Short delays (up to 5 nsec) must be tolerable if radio DFM is high enough (>50dB), since there is very little antenna discrimination on long paths. Coupling of the reflected ray can be sometimes controlled by up-tilting the antennae (0-0.5 deg.)
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Short High Hop
1150 ft (351m)
K = 4/31.25O Discriminationto the
Reflection
1200(365m)
750
500
250
0
1000
0 4 8 12 16 20(32 km)
1.248O
Grazing Angle
25 n
s
Multi
path D
elay
K =0.109O Decoupling
Angle
Distance,Mi
Ele
vati
on
AM
SL
, Ft
For high grazing angles (1-5 deg.), vertical polarization shall be preferred. Decoupling of the reflected ray is difficult to control and delays can be high (up to 25 ns).
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Basic of Fresnel Zone
Fresnel Zone - Areas of constructive and destructive interference created when electromagnetic wave propagation in free space is reflected (multipath) or diffracted as the wave intersects obstacles. Fresnel zones are specified employing ordinal numbers that correspond to the number of half wavelength multiples that represent the difference in radio wave propagation path from the direct path.
The Fresnel Zone must be clear of all obstructions.
Typically the first Fresnel zone (N=1) is used to determine obstruction loss.
The direct path between the transmitter and the receiver needs a clearance above ground of at least 60% of the radius of the first Fresnel zone to achieve free space propagation conditions.
Earth-radius factor k compensates the refraction in the atmosphere.
Clearance is described as any criterion to ensure sufficient antenna heights so that, in the worst case of refraction the receiver antenna is not placed in the diffraction region.
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Fresnel Zones Concept
Radius of the n-th Fresnel zone:
21
21
dd
ddnr
Where … wavelength
Electromagnetic energy directed by the transmitting antenna needs 3D unobstructed space to travel to the particular receiver. More then 90% of the energy radiated in particular direction is concentrated in so called 1-st Fresnel zone. 1-st Fresnel zone must remain unobstructed to avoid diffraction losses. Even Fresnel zone are important to judge upon reflection points.
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Fade Margin
–10-2 —----
–10-3 —----
–10-4 —----
–10-5 —----
–10-6 —----
–10-7 —----
–10-8 —----
–10-9 —----
–10-10 —----
–10-11 —----
–10-12 —5 10 15 20 25 30 35 40
C/N or C/I Ratio, dB
— - - - - — - - - - — - - - - — - - - - — - - - - — - - - - — - - - - —
BE
R
—----—----—----—----—----—----—----—
(OUTAGE)
BPSK
4PSK4QAMQPSK
9QPR
8PSK 16QAM 32QAM
49QPR 64QAM
225QPR 128QAM32PSK
256QAM
Excludes FEC Coding Gains
(STATIC)
512QAM25QPR
Fade Margin is a difference between median received signal level, calculated from Power Budget equation, and BER=10-3 threshold of the receiver system.This difference has to account for stochastic propagation phenomena, that can compromise system reliability.
These phenomena are: Attenuation due to rain. Intersystem interference. Multipath fading. K-factor variation. Ducting.
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Table of Contents – Pathloss v.4.0
Introduction to Pathloss v.4.0
Hop Definition
Terrain Profiling & Clearance Criteria
Microwave Worksheet
Applying Diversity and Protection
Diffraction Module Overview
Reflection Analysis
Multipath Operation
Network Description
Intra-system Interference
Design with Passive Repeater
Map Grid Module
Radio and Antenna Data Files
Case Studies
Introduction to Pathloss v.4.0
Hop Definition
Terrain Profiling & Clearance Criteria
Microwave Worksheet
Applying Diversity and Protection
Diffraction Module Overview
Reflection Analysis
Multipath Operation
Network Description
Intra-system Interference
Design with Passive Repeater
Map Grid Module
Radio and Antenna Data Files
Case Studies
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Pathloss v.4.0 is Developed by
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Pathloss Web Sites
Pathloss Forum (Questions and Answers about the planning with Pathloss v.4.0)
Regular Maintenance Updates
Radio and Antenna Description files for new products on the market
Documentation on new Pathloss v.4.0 features (e.g. on GIS formats) and appendix to the User Manual
Ordering Information and Part Number List
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Introduction of Pathloss
The Pathloss program is a comprehensive path design tool for radio links operating in the frequency range from 30 MHz to 100 GHz.
The program is organized into eight path design modules, an area signal coverage module and a network module which integrates the radio paths.Coverage module and a network module which integrates the radio paths and area coverage analysis. Switching between modules is accomplished by selecting the module from the menu bar.
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Cont… Introduction of Pathloss
Pathloss 4.0 (PL4B)Basic Pathloss program. Contains all of the necessary tools to carry out point to point radio system design.
Pathloss 4.0 (PL4C)As above, but with the additional power of a full featured radiocoverage prediction module.
Pathloss 4.0 (PL4I)Basic Pathloss program with complete Microwave network interference capabilities.
Pathloss 4.0 (PL4CI)Basic Pathloss program with both the coverage prediction and the Microwave interference modules.
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Prerequisites
Following prerequisites imply successful participation in the Pathloss course:
Knowledge of basic principles of MW Transmission Engineering and Link planning Laptop/desktop computer with installation of Pathloss v.4.0 planning software : For your country or region of interest:• NED (SRTM 3”) Data http://srtm.usgs.gov/geodata/• Void Killer SW allows to correct raw STRM 3” with GTOPO 30”• Or any other DTM compatible with Pathloss v.4.0.
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Cont…Introduction of Pathloss
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Planning Concept
Planning modules contained in Pathloss:
Summary Module Terrain Data Generation Antenna Height Calculation Worksheet Module (Reliability Calculation) Diffraction Module Reflection Module Multipath Module Network Module (Frequency Planning) Map Grid Coverage Module (only for PtMP systems)
Pathloss v.4.0 is an advanced planning software for design of microwave radio-relay links and networks. It allows a qualified user to perform step by step analysis of all important propagation related phenomena, needed to generate a planning report containing all the data necessary for correct and reliable implementation of MW radio-relay hop.
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Pathloss Basic Parameters
Adjusting the display options availableIn Configure Selection:
Antenna Configuration:
1. TR-Transmit/Receive Antenna2. Tx-Transmitting Antenna3. Rx-Receiving Antenna4. DR-Diversity Receiving Antenna5. TH- Transmitting/Hybrid Diversity
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Coordinate Systems
• The user can choose most suitable local geodetic datum (e.g. in Nigeria it is Minna Nigeria), Singapore use South Asia datum and Ellipsoid is Modified Fischer 1960.For East Malaysia use Timbalai 1948 datum and Everest (Sabah Sarawak) Ellipsoid and Pakistan use WGS84 datum and WGS84 Ellipsoid.
Typical choice for world-wide datum is WGS 84 (World Geographic System 1984)
If special maps have to be handled, ellipsoid can be defined independently from datum (e.g. GRS80)
Note: WGS 84datum uses WGS84 ellipsoid.
Grid coordinate system can be chosen to define planar projection from geodetic
systems defined on ellipsoid
Most common: UTM-Universal Transverse Mercator.
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Summary Module
Data entered into Summary Module, Option in Module-Summary
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Radio Lookup Tables
Defining look-up table from Equipment option with Radio Code Index table andModule-Worksheet-Double click on Antenna-Lookup.
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Radio Specifications
Radio parameters: This table is not editable Radio specification has defined via converting a radio data file. only few of the entries in the table are mandatory. Pathloss can use rough calculation of certain missing parameters likeRx-selectivity curve or T/I curves. There are minimum 5 parameters to define a radio .Option is on Module-Summary-Double click on Code-View.
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Antenna Lookup Tables
Defining look-up table from Antenna Code Index table
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Antenna Radiation Pattern
Co-polar and Cross-polar patterns
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Active & Passive Antenna
Antenna types
Pasive Active
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Polarization
Polarization
The electric and magnetic fields of electromagnetic wave are perpendicular to each other. Their intensities rise and fall together, reaching their maximums 90 degrees apart (Fig. 5-1). The direction of wave’s polarization is determined by electric field i.e. in a vertically polarized wave, the electric lines of force lie in a vertical direction and in a horizontally polarized wave, the electric lines of force lie in a horizontal direction. When a single-wire antenna is used to extract energy from a passing radio wave, maximum pickup will result when the antenna is oriented in the same direction as the electric field. Hence, a vertical antenna is used for the efficient reception of vertically polarized waves, and a horizontal antenna is used for the reception of horizontally polarized waves.
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Antenna Beamwidth
Antenna beam width
In a radiation patter due to antenna directivity the points, in which power comparing to the maximum power is decreased by – 3 dB may be noticed. The angle between these points is called a beam width. In other words the beam width is an opening angle between the points where the radiated power is 3 dB lower than in the main direction
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Graphical Representation of Antenna Beam width Beam width definition
GSM Cell PlanningFigure 5-2Page X
Main directionBeam width
3 dBAntenna lobe
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Types of Antenna in MW
Antenna Gain Side lobe levels and front-to-back ratio Beam width Voltage Standing-wave Ratio (VSWR) Cross-polarization discrimination Mechanical stability
The most common type of antenna used on MW links is a parabolic dish. For higher frequency bands (15-38 GHz) parabolic dish can be substituted by microstrip patch-array antennae (flat antennae).
The antenna parameters are very important for the system performance.
The most important antenna parameters from propagation point of view are:
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VSWR, Cross-polarization Discrimination
Voltage Standing-wave Ration (VSWR) is important parameter for high Speed communication systems with stringent linearity objectives. To avoid inter-modulation distortion, VSWR should be minimized by proper antenna selection and cable length adjustment. Standard antennae in MW bands have VSWR within a range of 1.06 – 1.15 typically.
Another important parameter for MW frequency planning is a discrimination between co-polar and cross-polar signal by the antenna. A good cross-polarization discrimination enables full utilization of the frequency band in both the vertical and horizontal polarization planes. Typical values are within range of 20–30 dB for standard antennae. Cross-polarization discrimination reaches its largest value in direction of the main lobe.
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Beam-width & Radiation Pattern
… angle in horizontal or vertical plane
The half power beam width of antenna is defines as the angular width of the main beam at the –3 dB point, relative to the bore-sight. For parabolic antennae:
The half power beam width of antenna is defines as the angular width of the main beam at the –3 dB point, relative to the bore-sight. For parabolic antennae:
DdB
353
where D… diameter of antenna [m]
[degrees]
Side and back-lobe levels are importantparameters in frequency planning andinterference calculations. Low side lobesallow for more efficient use of the fre-quency spectrum. A front-to-back ratioindicates the levels for angles within aRange of 90-180 degrees.
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Antenna Alignment
0dB
0 dB
A. Poor Alignment (One Antenna Peaked on a Side Lobe)
-10 to -20dB(First Side Lobe) High
Antenna
-1dB
B. Optimum Antenna Alignment (Best compromise between path and propagation)
0dB
Desired Path
-10dB
Low Antenna
Reflected Path
Attain free-space or optimum Received Signal Levels
Discriminate against ground reflections which cause fading and may reduce link Dispersive Fade Margins,
Accommodate, by size and/or up-tilt, K-factor angle-of-arrival variations which may cause antenna decoupling and severe fading.
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Antenna Gain
Antenna gain evaluates antenna’s capability to focus electromagnetic energyto preferred direction (bore-sight). For parabolic antennae used on MW bands,gain can be expressed as :
2
4
SA [dBi]
Where S… aperture area … wavelength … aperture efficiency (0.55-0.70)
f
c c = 3x10 8
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Exercise
Task: Calculate the theoretical gain and beam-width for the following types of parabolic antenna:
1. Antenna 1.2 m in diameter (0.75) for 15 GHz band 2. Antenna 0.3 m in diameter (0.7) for 38 GHz band 3. Antenna 0.6 m in diameter (0.7) for 38 GHz band 4. Antenna 3.0 m in diameter (0.8) for 7 GHz band
Hint: Figures in parenthesis indicate the aperture efficiency.
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Typical antenna characteristics (standard, X-polar)
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Antenna Mounting – Full Indoor & Split Systems
Split SystemFull Indoor System
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Frequency Planning Rules
Radio signals have to be frequency-separated if neither antenna discrimination nor topographical shielding provides the necessary suppression of interfering signals.
The degree of separation depends on the transmitted bandwidth - the spectrum bandwidth in MHz. Raster: 1.75;3.5;7;14;28;56 MHz.
This separation – called adjacent-channel separation - should be as small as possible to give a frequency economic solution. This requires some kind of standardization, a frequency plan.
Certain basic rules should be followed setting up the frequency plan. All frequencies used in a radio-relay network should normally be selected from an established frequency plan, approved either by an international or national standardization body.
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Frequency Planning
The objective of frequency planning is to assign frequencies to a network using as few frequencies as possible and in a manner such that the quality and availability of the radio link path is minimally affected by interference. The following aspects are the basic considerations involved in the assignment of radio frequencies.
Determining a frequency band that is suitable for the specific link (path length, site location, terrain topography and atmospheric effects)
Prevention of mutual interference such as interference among radio frequency channels in the actual path, interference to and from other radio paths, interference to and from satellite communication systems
Correct selection of a frequency band allows the required transmission capacity while efficiently utilizing the available radio frequency spectrum
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Frequency Planning
Assignment of a radio frequency or radio frequency channel is the authorization given by an administration for a radio station to use a radio frequency or radio frequency channel under specified conditions. It is created in accordance with the Series-F recommendations given by the ITU-R.
Frequency Channel Arrangements
The available frequency band is subdivided into two halves, a lower (go) and an upper (return) duplex half. The duplex spacing is always sufficiently large so that the radio equipment can operate interference free under duplex operation. The width of each channel depends on the capacity of the radio link and the type of modulation used
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Frequency Planning
The most important goal of frequency planning is to allocate available channels to the different links in the network without exceeding the quality and availability objectives of the individual links because of radio interference.
Frequency planning of a few paths can be carried out manually but, for larger networks, it is highly recommended to employ a software transmission design tool. One such vendor independent tool is Pathloss 4.0. This tool is probably one of the best tools for complex microwave design. It includes North American and ITU standards, different diversity schemes, diffraction and reflection (multipath) analysis, rain effects, interference analysis etc.
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Frequency Planning for Different Network Topologies
Chain/cascade configuration is used for horizontal and vertical Polarization
LU Uf1 HP f1 VP f1 HP
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Ring Configuration
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 reliable alternative.
UU
L
UU
L
L
UUf1 HP
f1 VP
f1 VP f1 VP
f1 HP
f1 VP
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Star Configuration
The link carrying the traffic out of the hub should use a frequency band other than the one employed inside the cluster.
L
UU UU
UU UU
UUf1 HP
f2 VP
f1 HP
f1 HP
f2 VP
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Frequency Channel Tables
Frequency channels are chosen from predefined raster which follows ITU-R Recs. or local regulations,Polarization is defined independently.Option available in Summary- Equipment-TX - Channel-Lookup.
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Map Study and Path Profile Preparation
Preliminary map studies help in determining the actual topography of the terrain, the height, and obstacles along the desired path.
Soon after, tentative antenna sites have been selected, and the relative elevations of the terrain between these sites has been determined, preparation of path profiles can begin.
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Field Survey and Site Determination
Confirmation of LOS
Check-up of suspected reflection points, vegetation, water, buildings and other man-made obstacles
Determination of height of, and distance to critical obstacles
Determination and confirmation of the path profile
Determination of site co-ordinates and altitudes
Site survey
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Purpose of Terrain Profiling
Location of the reflection zone (dish heights).Calculating dish discriminations to the reflection (dish sizes)Determining Fresnel clearance at the reflection (diversity, spacing).Calculating Path inclination angle. Calculating Reflection grazing angle (V- or H-pol assignment)Finding Ray height at the reflection or obstruction areaCalculating Reflected ray time delay (nsec). Choosing Optimum diversity dish separations to specular reflections.Calculating Arrival angle with K-factor variations.Calculating diffraction Obstruction loss vs. terrain type.
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Generated Profile in Terrain Data Module
Representation of Terrain Data
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Types of Digital Terrain Models (DTM)
Window for choosing source directory with GTOPO 30 DTM data Window for choosing type of DTM
(Digital Terrain Model) to be used for planning and LOS analysis.Option is in Configure-Terrain
Database.
Window with adjustable parameters for UTM DTM data. UTM zone used by the data file Index file describing the UTM data
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UTM Database
Index File for UTM Data
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SRTM Database
Importing BIL, HDR, BLW files from USGS DVD
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Clutter Insertion
Clutter inserted in Terrain Data module, Double click on Structure option.
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Propagation Losses
Obstacle Loss –also called Diffraction Loss or Diffraction Attenuation. One method of calculation is based on Knife edge approximation.
Having an obstacle free 60% of the Fresnel zone gives 0 dB loss.
0 dB20dB16dB6dB0 dB
First Fresnel Zone
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Earth Radius Factor K - Values Variations
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Radio Refractivity
K = Effective Earth’s Radius
6378 km
Ray day-to-night arrival angle change could approach 1o on long paths traversing humid areas
Sea LevelTrue Earth Radius (6378 km)
k = 0.33
k = 0.5
k = 1 (Dry, Elevated)
k = (follows Earth’s curvature)
k = -1
Subrefractive - Earth Bulge
Superrefractive - Ducting
“Earth’s Bulge”Obstruction
Duct Entrapment
8
Obstruction
k = 4/3rds Average Refractivity in Temperate Areas
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Earth Curvature
h =2x6.378 K
d1 d2
The K factor in the above equation is a constant whose value depends upon the actual propagation conditions of the microwave energy along the path (gradient of refractive index).
Various values of the K are used to describe radio ray trajectories that differ from a straight line.
Where:
h represents Earth bulge height relative to he terminal stations [m]
d1 and d2 are distances from terminal stations [km]
Where:
h represents Earth bulge height relative to he terminal stations [m]
d1 and d2 are distances from terminal stations [km]
Parabolic transformation of Earth’s bulge:
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Bending in the Atmosphere
Snell's law indicates that the rays bend towards the denser of the two media. In the atmosphere the index of refraction is varying continuously with gradient of dN/dh= – 40 ppm/km. Normal n=1.000320 Consequently no distinctive boundary will be found as in figure below.
Ray bending in the atmosphere may be considered as a large number of boundaries with a small variation n.
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Bending cont.
During normal conditions, temperature, humidity and pressure in the lower atmosphere decrease almost linearly with increased altitude.
The above corresponds to a linear decrease in the refractive index of the atmosphere and the velocity of microwaves traveling through the atmosphere increases as the refractive index decreases
As the wave front passes through a normal atmosphere, the increased phase velocities at the top of the wave front cause microwave to bend slightly downward in relatively uniform curve.
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Gradient of Refraction
1
1571
h
N
K
ii n
cv
251073.36.77
T
eH
T
pN
610).1( inN
h
N
is gradient of refractive index ni
expressed in N units (std. –40 N/km)
ni is atmospheric refractive index (standard value 1.000320 near sea level)
p is atmospheric pressure (std. value 1013 hPa)
T is atmospheric temperature (std. value 288 K)
e is saturation pressure due to the water vapor (10 hPa)
H is relative atmospheric humidity (std. value 50%)
c is velocity of light (299 798 km/s)
h represents height in kilometers
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Refractive Ray Bending
G = 0, K = 1 (No refraction)
G = > 0, K = 2/3
G = - 157 K approaches infinity
Moderate Negative Gradient: Flat Earth
G < - 157, K < 0
DUCTING
G = - 79 , K =2
G = - 40 , K =4/3 ( Mean)STANDARD
EARTH
SUPERREFRACTIVE
SUBREFRACTIVE
G = - 314 K = -1
Steep Gradient: Possible Blackout
G = - 470 K = -0.5
Extreme Gradient: Blackout
G = 80 K = 2/3 Slightly Sub refractive
G = 157 K = ½ Moderately Sub refractive
G = 220 K = 5/12
Humidity Inversion: Extreme Earths Bulge: Diffraction Fade
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Gradient of Refractive Index
Also the negative values are more extreme than the positive values,
NOTE: Positive gradient cause diffraction loss (substandard bending) or sub-refraction,
NOTE: When the gradient becomes more negative than dN/dh = -100 N Units/km (super-refractive) and leads to multipath fading,
When the gradient becomes more negative than dN/dh = - 157, ducting conditions occur resulting in severe mutipath fading, beam spreading and even blackout conditions,
ITU in recommendation P.453 provides a series of curves that give the percentage of time, dN/dh is less than – 100 N-unit/km. This gives the probability of multipath being a problem. It is the PL chart.
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K-factor Fading
Density profiles in Subrefractive, Standard, and Superrefractive Atmospheric Boundary Layers (ABL)
Refractivity Terms
S
Top of LayerDenver: NS = 301 - (1.6km x 40 ppm/km) = 239
Standard Atmosphere
Density Lapse Rate
dN/dh = +157 N-units/km (k=1/2)+7
5 (k
=2/
3)h, km
dN/dh = -314 N-units/km (k=-1)-157 (k = )-100 (k = 3)
-58 (k = 1.6)
-40 (k = 4/3)
0 (
k =
1)
NS = 239N0 = 301 370 469 548
Inland CoastalMedian
N = Atmospheric density (refractive index)N0 = N at sea levelNs = N at ground surface level
Normal Propagation90-95%
(Wave refracted downwards)
N-units(Radio Refractive Index
at Sea Level)
Subrefractive1-5% of the time(Wave refracted
upwards)
SuperRefractiveTrapping0-1% (severeducting orblackout)
Super Refractive 1-5 % Ducting(Horizon extended)
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Ducting and Blackout Fade
Ducting: The atmosphere has a very dense layer at the ground (or at certain height above) with a thin layer on the top of it. For such layer configuration, there will be almost total reflection present on this layer boundary.
Effect of ducting results in considerable higher signal levels then those calculated from standard propagation models.
Danger: Interference from remote sources!Difficult to predict quantitatively.
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Super-refraction (black out)
Anomalous propagation occurs outside the normal range of K from 1 to infinity. This catastrophic phenomenon is known as Blackout fading.
K becomes negative
K = - 1/2
When an extreme drop in atmospheric density with height (a negative refractive index) occurs, or when the gradient is positive, climatic conditions are conducive to anomalous
propagation.
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Concept of Clearance
Fresnel Zone Boundaries
+10 0 -10 -20 -30 -40
A
A
OBSTRUCTION ZONE(Obstructed path)
CLEARANCE OR
INTERFERENCE ZONE(Reflective path)
GRAZING
0.6 1 2 3 4 5
Site A 64km path, k=1 (on true earth’s radius profile) Site B
FRESNEL ZONE NUMBERS RSL, dB FROM FREE SPACE
Ray F1 = 56m DIAMETER
GRAZING PATH(6-20 dB LOSS)
0.6F1@k=1 PATH
Knife E
dge
Smooth Earth
AverageTerrain
0.6F1 PATHCLEARANCE
= FREE SPACE(NO LOSS)
CROSS-SECTION A-A
5 4 3 2 1 0.6
0
0.6 1 2 3 45
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Choosing Clearance Criteria
Clearance criteria are chosen separately for Main and Diversity Antenna, Two values of K-factor are involved (K for normal conditions [median value
K=4/3] and minimum K [0.60-0.80]), Fixed provision for vegetation growth can be entered as well.Option available in Configure - Antenna height - Operation — Set Clearance Criteria.
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Typical antenna characteristics (standard, X-polar)
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Towers and Masts
Poles for rooftop installations Self-supported Lattice towers (20 – 150 m) Tube towers (10 – 40 m) Guyed Masts (10 – 100 m) up to 300 m for TV transmitters
Accessories: Leaders, Platforms, Mounting Brackets,Obstruction Lights, Aircraft Warning Lights
Soil bearing shall be measured during comprehensive site survey and test drilling shall be performed to determine optimum size of the tower base.
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Microwave Installation – Ground Based Tower
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Microwave Installation – Rooftop Structures
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Shelters and Containers
Bricked technology houses – expensive but provides most suitable environment for technology
Shelters – cost-effective, less esthetic, requires air-conditioning Containers - for sites with limited technology requirements (e.g. remote BTS)
Chosen technology housing shall reflect the radio type, requirements for expansion and power back-up times.
Accessories: Heating and Air-conditioning Cable trays and inlets Burglary Alarm Mains Power Board Grounding system
Accessories: Heating and Air-conditioning Cable trays and inlets Burglary Alarm Mains Power Board Grounding system
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Shelter for Full Indoor Equipment
Branching Connection
Pressure Windows
Waveguide Connector
Wall/Roof Feed-Thru or Plate/Boot
Grounding Kit
Dehydrator
Clamps
Waveguide
Cable / Waveguide Bridge
Grounding Bar
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Outdoor Container for Split System
Standard Shelter BS Integration
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Auxiliary Equipment
Dehydrator
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Antenna Center-line Calculation
Option in Module – Antenna Height
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Path Calculations
270
330
390
440
500
Ele
vati
on
, m
A
MS
L
300
360
410
470
270
330
390
440
500
300
360
410
470
k = 4/3F = 0.6
Site: Yates CenterLat.: 37-51-02.NLong.: 095-43-53. W
Marmaton37-49-40. N
095-09-44. W
____
__ __ __ __ ____
__ __ __ __ ____
__ __ __ __ ____
__ __ __ __ ____
__ __ __ __ ____
__ __ __ __ ____
__
0 5 10 15 20 25 30
Distance, km
k=4/3
0.6F1
1.9 GHz
k=4/3
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Path Clearance Criteria
“HEAVY” ROUTEAbout 6 GHz and above in
moderate to heavy fade areas
“LIGHT” ROUTEAbout 2 GHz and below in all areas, and all paths in good to average fade areas
0.6 F1 @ K = 4/30.6 F1 @ K = 2/3 (Kmin)
andF1 @ K = 4/3
MAIN PATH(Top Dishes)
0.6 F1 @ K = 4/3+3m Close-In
For tree growth, etc.typically 10-12mbelow main dish
DIVERSITY PATH(Top-To-Bottom Dishes)
No Special AllowanceOver a 50m
Surface Ducting Layer,grazing @ K = 1/2
DUCTINGMain path clearance with known surface duct entrapment (paths 30 kilometers)
See the next page for minimum K (Kmin) concept.
0.3 F1 @ K = 4/3or grazing @ K = 4/3,
typically 10-20mbelow main dish
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Survey Equipment
The Survey Report contains System Description Site Description and Layout Antenna and Tower Heights Path Profile Fresnel Zone Drawing and Diffraction Calculation Photographs of the site Panorama photographs
List of Survey Equipment: Maps in scale 1:50 000 or better Digital camera Binocular Compass Barometric altimeters (pair) Signaling mirrors, He-filled balloon Flash light Tape measure Hand-held radio or Cell phone Hand-held GPS receiver DGPS set (2 receivers) Theodolite with tripod Laptop with DTM and planning SW Spectrum analyzer with accessories Test antennae Test transmitter
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Site Selection Considerations
System Related: Distance to the customer (BTS search ring) LOS to the existing and possible future neighbors Local climatic conditionsVegetation, clutter (buildings, chimneys) in the vicinity Currently installed technology in the vicinity
Construction Related: Site accessibility (distance to the roads) Available electric power source (PUC, Sunny Days) Soil bearing Underground water level
Other: Type of land ownership Security (guard needed) Military area considerations
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Map Study
The purpose of the preliminary map study is to familiarize with the overall system layout and to assemble information including, but not limited to, the best available topographic mapping for the area under consideration, site addresses, site names or designations, site coordinates and elevations.
Establishing of site coordinates
Generation of Path profile
Identification of Reflective surfaces
Identification of Critical points
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Digitized Maps
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Generating Profile Report
Print Profile Report in Module option for LOS Verification
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Microwave Worksheet
Net Pathloss Components
Free Space Loss and Absorption
Multipath Propagation Reliability Prediction Models
Vigants-Barnet Model
K.Q Factor
ITU-R P.530-6
ITU-R P.530-7
ITU-R P.530-9/10
Rain Attenuation Models
Crane Model
ITU-R P.530-7
Rain and Co-channel Operation
Section Performance Calculation
Loss / Attenuation Calculation.
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Net Path Loss Components
Calculated net path loss components in Module option – Microwave worksheet
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Loss / Attenuation Calculations
The loss/attenuation calculations are composed of three main contributions :
Propagation losses
(Due to Earth’s atmosphere and terrain).
Branching losses
(Comes from the hardware used to deliver the transmitter/receiver output to/from the antenna).
Miscellaneous (other) losses
(unpredictable and sporadic in character like fog, moving objects crossing the path, poor equipment installation and less than perfect antenna alignment etc).
This contribution is not calculated but is considered in the planning process as an additional loss.
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Link Budget Calculation
Path-loss equation used for MW (3 - 38 GHz)Path-loss equation used for MW (3 - 38 GHz)
aDDfdBA log20log2045.92
Where f … RF frequency in GHz D… Propagation distance in km a … Attenuation due to the air and water vapor in dB/km (Typically 0.1 – 0.4)
MiscRxTxTLTxTLRxTot AGGAAAA
Where ATL… Transmission line losses and branching circuit losses on Rx and Tx side G … Antenna gain on Rx and Tx side AMisc … Miscellaneous losses (e.g. antenna misalignment, Tx power variations)
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Fade Margin
–10-2 —----
–10-3 —----
–10-4 —----
–10-5 —----
–10-6 —----
–10-7 —----
–10-8 —----
–10-9 —----
–10-10 —----
–10-11 —----
–10-12 —5 10 15 20 25 30 35 40
C/N or C/I Ratio, dB
— - - - - — - - - - — - - - - — - - - - — - - - - — - - - - — - - - - —
BE
R
—----—----—----—----—----—----—----—
(OUTAGE)
BPSK
4PSK4QAMQPSK
9QPR
8PSK 16QAM 32QAM
49QPR 64QAM
225QPR 128QAM32PSK
256QAM
Excludes FEC Coding Gains
(STATIC)
512QAM25QPR
Fade Margin is a difference between median received signal level, calculated from Power Budget equation, and BER=10-3 threshold of the receiver system.This difference has to account for stochastic propagation phenomena, that can compromise system reliability.
These phenomena are: Attenuation due to rain. Intersystem interference. Multipath fading. K-factor variation. Ducting.
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Fading and Fade Margins
Rain Fading
Rain attenuates the signal caused by the scattering and absorption of electromagnetic waves by rain drops.
It is significant for long paths (>10Km)
It starts increasing at about 10GHz and for frequencies above 15 GHz, rain fading is the dominant fading mechanism.
Rain outage increases dramatically with frequency and then with path length.
The specific attenuation of rain is dependent on many parameters such as the form and size of distribution of the raindrops, polarization, rain intensity and frequency.
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Recommendation for Rain Fading
Microwave path lengths must be reduced in areas where rain outages are severe.
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 a period of time. The total annual rainfall in an area has little relation to the rain attenuation for the area.
Hence a margin is included to compensate for the effects of rain at a given level of availability. Increased fade margin (margins as high as 45 to 60dB) is of some help in rainfall attenuation fading.
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How Reducing the Effects of Rain
Multipath fading is at its minimum during periods of heavy rainfall with well aligned dishes, so entire path fade margin is available to combat the rain attenuation (wet-radome loss effects are minimum with shrouded antennas)
Route diversity with paths separated by more than about 8 Km can be used successfully.Radios with Automatic Transmitter Power Control have been used in some highly vulnerable links.Vertical polarization is far less susceptible to rainfall attenuation (40 to 60%) than are horizontal polarization frequencies.
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Refraction – Diffraction Fading
Also known as K-type fading
For low k values, the Earth’s surface becomes curved and terrain irregularities, man-made structures and other objects may intercept the Fresnel Zone.
For high k values, the Earth’s surface gets close to a plane surface and better LOS (lower antenna height) is obtained.
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.
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Ground Reflection
Reflection on the Earth’s surface may give rise to multipath propagation.
The direct ray at the receiver may interfered with by the ground-reflected ray and the reflection loss can be significant.
Since the refraction properties of the atmosphere are constantly changing the reflection loss varies.
The loss due to reflection on the ground is dependent on the total reflection coefficient of the ground and the phase shift.
The highest value of signal strength is obtained for a phase angle of 0o and the lowest value is for a phase angle of 180o.
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Ground Reflection
The reflection coefficient is dependent on the frequency, grazing angle (angle between the ray beam and the horizontal plane), polarization and ground properties.
The grazing angle of radio-relay paths is very small – usually less than 1o
It is recommended to avoid ground reflection by shielding the path against the indirect ray.
The contribution resulting from reflection loss is not automatically included in the link budget. When reflection cannot be avoided, the fade margin may be adjusted by including this contribution as “additional loss” in the link budget.
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Fade Margin vs Unavailability
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Causes of Unavailability
Predictable rain outage in local-grade links above about 10-12 GHz, especially in tropical equatorial areas and costal regions,
Dual equipment failure within the MTTR period,
Maintenance error or manual intervention (e.g. failure of a locked-on module or path and error in switching the module),
Infrastructure failure (e.g. antenna, batteries),
Low fade margin in non-diversity links,
Power fade (long-term loss of fade margin) in lower clearance paths above about 6 GHz in some difficult areas, or with antenna misalignment,
Ducting (subrefractive, superrefractive) and black-out fading.
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Multipath Propagation Reliability Prediction Models
Multipath fading algorithm embedded in Pathloss: Vigants-Barnet ITU-R P.530-6 Recs. ITU-R P.530-7 Rec. (Normally used) . ITU-R P.530-9 Recs. K.Q Factor. K.Q Factor with Terrain Roughness.
Results presentation: Total annual time bellow level SESR, Availability as per G.821 definition
(Bit Error Rate) SESR, Availability as per G.826 definition
(Block Error Rate)
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Multipath Fading Mechanism
Unfortunately, normal atmospheric conditions do not always prevail.
Irregularities in the atmosphere cause energy components of a microwave beam to be reflected or refracted upwards or downwards instead of following normal slightly curved path to the receiving antenna.
As a result, two or more separate wave components may travel to the receiver over slightly different paths.
These components will be somewhat out of phase with each other because of the difference in the length of path each has traveled.
Also at each point of reflection approximately 180 degree phase shift normally occurs.
If two signal components travel paths are different by a wavelength, one signal component has been reflected, they will arrive 180 deg out of phase at the receiver and their vector sum will be zero.
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Vector Sums
Signal envelope variations:
Constructive sum:Destructive sum:
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Availability and Performance Recs
Performance Recommendations derived from ITU-T G.821: ITU-R F. 594 (Parameters and definitions) ITU-R F. 634 (Application to High Grade portion –below PRI rate) ITU-R F. 696 (Application to Medium Grade portion –below PRI rate) ITU-R F. 697 (Application to Local Grade portion –below PRI rate)Performance Recommendations derived from ITU-T G.826/828: ITU–R F.1092 Quality Rec. for the “International” Reference circuit - obsolete ITU–R F.1189 Quality Rec. for the “National” Reference circuit - obsolete ITU–R F.1397 Quality Rec. for the “International” Reference circuit – real hop. ITU–R F.1491 Quality Rec. for the “National” Reference circuit – real hop. ITU-R F. 1668 Quality Objectives for real digital fixed wireless linksAvailability Recommendations: ITU-R F.557 Availability Objective for Radio Relay Systems ITU-R F.695 Availability Objective for Real Radio Relay SystemsAvailability Recommendations derived from ITU-T G.827: ITU–R F. 1492 Application of G 827 to the “international” portion ITU–R F. 1493 Application of G 827 to the“national” portion ITU-R F.1703 Availability Objectives for real digital fixed wireless links
Performance Recommendations derived from ITU-T G.821: ITU-R F. 594 (Parameters and definitions) ITU-R F. 634 (Application to High Grade portion –below PRI rate) ITU-R F. 696 (Application to Medium Grade portion –below PRI rate) ITU-R F. 697 (Application to Local Grade portion –below PRI rate)Performance Recommendations derived from ITU-T G.826/828: ITU–R F.1092 Quality Rec. for the “International” Reference circuit - obsolete ITU–R F.1189 Quality Rec. for the “National” Reference circuit - obsolete ITU–R F.1397 Quality Rec. for the “International” Reference circuit – real hop. ITU–R F.1491 Quality Rec. for the “National” Reference circuit – real hop. ITU-R F. 1668 Quality Objectives for real digital fixed wireless linksAvailability Recommendations: ITU-R F.557 Availability Objective for Radio Relay Systems ITU-R F.695 Availability Objective for Real Radio Relay SystemsAvailability Recommendations derived from ITU-T G.827: ITU–R F. 1492 Application of G 827 to the “international” portion ITU–R F. 1493 Application of G 827 to the“national” portion ITU-R F.1703 Availability Objectives for real digital fixed wireless links
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Vigants-Barnet Model
Where: x =a - climatic factor.f – frequency [GHz]d – path length [km]b – Roughness factorCFM- Composite Fade Margin
In Vigants-Barnet model the fading occurrence factor P0 is a function of the Path length and location, the terrain roughness and frequency band used.
S is the standard deviation (RMS) of the terrain elevations, measured with 1 km step along the path, excluding the radio sites. The value is limited within 6 m < S < 42 m.
3.12.15
Sb
1010.CFM
oPP
Annual outage probability:Annual outage probability:
3
0 5043.0
dfbxP
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V-B Climatic Regions
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Example Vigants – Barnett
PND = SESR = 6x10-7 c f D3 10-CFM/10
= 0.0001042
Where:PND - Non-diversity probability of outage (SESR)c - NA climate-terrain factor
c = 1 (from c map bellow), or x(S/15.2)-1.3
x - NA climate factor, 1 (from x map bellow)S - Terrain roughness, 15.2 m (from profile)f - frequency 6.7 GHzD - Path length, 40 kmCFM - Composite Fade Margin, 34 dB
For Terrain Roughness Module-Worksheet-Operation-Reliability – Select Vigants – Barnett or KQ Factor.
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NA Climate Terrain Factor c
Caribbean, c = 4
Hawaii, c = 4
Alaska coast, c = 0.25Alaska interior, c = 1
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NA Climate Factor x
*Flat terrain (w = 20', c =6) in this climate area.
Hawaii, x = 2
Alaska, x = 1 (inland)x=0.5 (coastal)
Caribbean, x = 2
southern Yukon, British Columbia,x = 0.5 Other Canadian Provinces, x = 1
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K.Q Factor
PND = KŸQ f D3 10-CFM/10
= 0.0001042
Where (similar to NA path):
PND - Non-diversity probability of outage (SESR)KŸQ - ITU-R climate-terrain factorKŸQ = x(S)-1.3
x - Climate factor, 2.1x10-5 (see table in Pathloss manual-Worksheet)
S - Terrain roughness, 15.2 m (from profile)f - 6.7 GHzD - Path length, 40 kmCFM - Composite Fade Margin, 34 dB
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ITU-R P.530-6
Where: K – a geo-climatic factor (Worksheet-Path profile-Geoclim)f – frequency [GHz]d – path length [km]Ep – path inclination [m rad]theta - average grazing angle corresponding to K=4/3 [mrad]h1, h2 – antenna heights above mean sea level [m]
d
hharctgE p 1000
1000 21
The ITU-R P.530-6 model is applicable from fmin = 15/d [GHz]. The fading occurrence factor P0 is a function of Geo-climatic factor K (i.e. path location), path length and inclination, grazing angle as well as frequency band used.
Worst month outage probability:Worst month outage probability:1010.
CFM
oPP
1.12.193.03.30 1
pEfdKP
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ITU-R P.530-7
The ITU-R P.530-7 model is applicable from fmin = 15/d [GHz].The fading occurrence factor P0 is a function of Geo-climatic factor K (i.e. path location), path length and inclination, as well as frequency band used.
1010.CFM
oPP
Worst month outage probability:
Where: K – a geo-climatic factor from tables belowf – frequency [GHz]d – path length [km]Ep – path inclination [mrad]h1, h2 – antenna heights above mean sea level [m]
4.189.06.30 1
pEfdKP
d
hharctgE p 1000
1000 21
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Geo-climatic Factor ITU-R P.530-7
PL is the percentage of time for which the average refractivity gradient in the lowest100 m of the atmosphere is lower than –100 N-units/km.
5.11.07 01010.5 LCCC PK LonLat 5.11.07 01010.5 L
CCC PK LonLat
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Cont…Geo-climatic Factor
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ITU-R P.530-9/10
For detailed link design using ITU-R P.530-9, fading occurrence factor P0:
Lhfpd
KP 00085.0032.097.02.3 10)|ε|1(
1000
Then the outage probability:Then the outage probability:
0log2.125 PAt Calculate a transition (deep to shallow fading distribution) depth:
[dB]
1010.tA
oPP
ITU-R P.530-9 terrain factor K:
1003.09.342.0 10 dNasK
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ITU-R P.530-9 New Parameters
Where dN1 - the point refractivity gradient in the lowest 65 m of the atmosphere not exceeded for 1% of an average year,Sa - the area terrain roughness.
d1N is provided on a 1.5° grid in latitude and longitude in Recommendation ITU-R P.453. The correct value for the latitude and longitude at path centre should be obtained from the values for the four closest grid points by bilinear interpolation.
Sa is defined as the standard deviation of terrain heights (m) within a 110 km x 110 km area with a 30” resolution (e.g. the Globe GTOPO 30 data). The area should be aligned with the longitude, such that the two equal halves of the area are on each side of the longitude that goes through the path center.
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Rain Attenuation Models
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Crane Model
A B C D1 D2 D3 E F
0.1 6.5 6.8 7.2 11.0 15.0 22.0 35.0 5.5
0.05 8.0 9.5 11.0 16.0 22.0 31.0 52.0 8.0
0.01 15.0 19.0 28.0 37.0 49.0 63.0 98.0 23.0
0.005 19.0 26.0 41.0 50.0 64.0 81.0 117.0 34.0
0.001 28.0 54.0 80.0 90.0 102.0 127.0 164.0 66.0
CRANE NORTH AMERICAN RAIN REGIONCRANE NORTH AMERICAN RAIN REGION% of Time
Rain Rate
Exceeded
bc
eg
bc
eg
b
eaRA
cbDbcbdbbdbpp ..
.
.
1
b
eaRA
bDbpp .
1
d
eg cd.ln
17.03.2 pRg pRc ln03.0026.0 pRd ln6.08.3
for d <= D <= 22.5 km
for d > D
Where:Rp is rain rate (mm/hr) calculate by Crane table
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Rain Rate Values
Drizzle = 0.25 mm/hour
Light rain = 1.0 mm/hour
Moderate rain = 4.0 mm/hour
Heavy rain = 16.0 mm/hour
Thunderstorm = 35.0 mm/hour
Intense thunderstorm = 100.0 mm/hour
Region B = Polar taiga (moderate)
Region C = Moderate maritime
Region D1 = Moderate continental (dry)
Region D2 = Moderate continental (mid)
Region D3 = Moderate continental (wet)
Region E = Sub-tropical (wet)
Region F = Sub-tropical (arid)
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Cont…Crane Model
C (Alaska, Pacific Coast)
E (Hawaii)E (Caribbean)
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Rain Attenuation ITU-R P.530-7
A0.01%=aR0.01%b D [1/(1 + D/d)] [dB]
Where: A0.01% - Rain attenuation exceeded <0.01% of the time, dB
R0.01% - Rain rate <0.01% of the time, mm/hr, from table
a - Multiplier, f (frequency/polarization), from table bellow
b - Exponent, f (frequency/polarization), from table bellow
D - Path length, km
d - Effective path length, km
d = 35 exp (-0.015R0.01%) Rain Outage:
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Coefficients for Estimating Attenuation due to the Rain
h subscript stands for horizontal polarizationv subscript stands for vertical polarization
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Rain Availability Example
A0.01% = aR0.01%b D [1/(1 + D/d)], dB
- Rain attenuation exceeded <0.01% of the time, dB
- Required path fade margin, dB
R0.01% - Rain rate exceeded <0.01% of the time (145 mm/hr, P region)
Pakistan in K-Region (42 mm/hr).
D - Path length, 5 km [mi x 1.6093]
a - Multiplier, f (18 GHz & V-polarization, from table: av= 0.058)
b - Exponent, f (18 GHz & V-polarization, from table: bv = 1.090)
d = 35 exp (-0.015R0.01%) = 3.98 km
A0.01% = 0.058 (145)1.09 5 [1/(1 + 5/3.98)]
= 29 dB (36 dB if horizontally-polarized, ah = 0.060 , bh = 1.127)
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Ap = A0.01% 0.12 p-(0.546 + 0.043 log p)
where: Ap = Rain attenuation exceeded p% of the time, dB
A0.01% = Rain attenuation exceeded 0.01% of the time,dB
p = probability of outage, % = 100 - availability, %
For 99.995% availability, p = 0.005% (26 min/yr outage), same path
A0.005% = A0.01% 0.12 (0.005-(0.546 + 0.043 log 0.005) )
= A0.01% 0.12 (0.005-0.45) = A0.01% x 1.28
= 32 x 1.28 = 41 dB (51 dB if H-pol) required fade margin
Multiplier Table (replaces the above multiplier computation)
p = 1% 0.1% 0.05% 0.01% 0.005% 0.001%
Availability = 99% 99.9% 99.95% 99.99% 99.995% 99.999%
Multiplier = 0.12 0.39 0.52 1.00 1.28 2.14
For Required Availabilities other than 99.99%:
Probability Scaling Examples
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Rain Rate in ITU-R Rain Regions
A B C D E F G H J K L M N P
0.1 2 3 5 8 6 8 12 10 20 12 15 22 35 65
0.03 5 6 9 13 12 15 20 18 28 23 33 40 65
0.01 8 12 15 19 22 28 30 32 35 42 60 63 95 145
0.003 14 21 26 29 41 54 45 55 45 70 105 95 140 200
0.001 22 32 42 42 70 78 65 83 55 100 150 120 180 250
ITU-R RAIN REGIONITU-R RAIN REGION% of Time
Rain Rate
Exceeded
If reliable local rain rate data are available, they shall be preferred to the world averaged data from ITU-R.
Pakistan in K - Region.By Worst Month Availability Pakistan in Region 3 and Class B
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Classification of Countries by Worst Month
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Excess Path Attenuation for Rainfall intensity exceeded
ITU-T rain regions (Table 1)
bdB aR
Where: ß dB is the unit excess path attenuation with respectto free-space loss exceeded for the percentage of time [dB/km]a, b are regression coefficients for given polarization ( Table 2)R is rain rate exceeded for specified percentage of time (Table 1)
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Coefficients for estimating attenuation due to the rain
h subscript stands for horizontal polarizationv subscript stands for vertical polarization
(Table 2)
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Rain Attenuation Curves
20
Frequency, GHz
H POL
V POL
Rain Rate (mm/hr)
Rain Rate (mm/hr)
200
150
100
5075
25
5
10
15
00 10 20 30 40
10
Att
enu
atio
n, d
B/k
m
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ITU-R Rain Regions Maps
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Map of Average Temperature
0F 0C-50 -46-40 -40-30 -34-20 -29-10 -23 0 -18 10 -12 20 -7
30 -1 40 4 50 10 60 16 70 21 80 27
50
6070
80
70
70
6050
4030
20100
-10
-20 -40 -50
-30
80 70
0F
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7.5 GHz Case
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Rain and Co-channel Operation
For co-channel operation, rain can also affect Cross-polar discrimination (XPD) and degrade XPD threshold. Severity of such degradation depends on system parameters like:
Antenna XPD and XPIF (Cross-polar Improvement Factor) of XPIC (Cross-polar Interference Canceller).
This option is available in Worksheet-Operation-Co-channel XPD
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Table with Results – Full Report
Text Report with Reliability Calculation, Option in Module- Worksheet - report
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Diversity Options
Frequency diversity: a single model available in Pathloss v.4.0,
Space Diversity: Baseband Switching,
- Method Nortel,
- Method Alcatel-Richardson,
- Method Harris Farinon
Space Diversity: IF Combining,
Methods are used to combine the improvement factors for flat and selective fading, respectively,
Angle diversity: Derived from SD under assumption of fixed antenna separation s= 9.1m. Improvement factor limited to I=20.
Option is available in Worksheet – Operation - Diversity Calculation
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Frequency Diversity
10/10.
80 CMFfd f
f
dfI
Where:f : frequency separation [GHz]f : carrier frequency [GHz], CMF: composite fade margin [dB]. This equation applies only for the following ranges of parameters: 2 f 11 GH 30 d 70 km f / f 5% Boundary value shall be used if boundary limit is exceeded. Ifd is limited to 5.
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Space Diversity
Baseband Switching:
IF Combining:
10223 10...102.1A
sd vsd
fI
20
][
10dBv
v
10
4
223 10.
1
.16..102.1
cA
sdv
vs
d
fI
2
1log.206.2
vAA tc
Where: s – Rx antenna separation [m] f – frequency [GHz] d – path length [km] vdB – difference between main and diversity antenna gains [dB] Ac – combined thermal fade margin [dB] At – greater of the main and diversity thermal fade margins [dB]
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SD Calculation Example
Outage Time: TSD=TND/ISD
NA Calculation: ISD=7x10-5 f s2 10CFM/10/D= 42 (SD dish separation s = 30 ft / 9.1 meter)
Tnd = U(0.0001042) x SESR (8 x 10e6) x Avg. Temp= 834 SES /yr
TSD = 834/42 = 20 SES/yr ITU-R Calculation: ISD=1.2x10-3 f s2 10CFM/10/D
= 42 (s = 9.1 m), same as NA aboveTnd = U(0.000142) x SESR(2.59 x 10e6) = 270
TSD = 270/42 = 7 SES/any month
Space Diversity Improvement Factor:
Where: Frequency f= 6.7 GHz, Composite fade margin CFM=34 dB and distance D= 40 km.
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Frequency Selective Fading
Selective fading or frequency selective fading is a radio propagation anomaly caused by partial cancellation of a radio signal by itself — the signal arrives at the receiver by two different paths and at least one of the paths is changing (lengthening or shortening). The two paths can both be from skyway or one be ground wave.
The Effect can be counteracted by applying some diversity scheme, for example OFDMA or by using two receivers with separate antennas spaced a quarter-wavelength apart, or a specially-designed diversity receivers with two antennas. Such a receiver continuously compares the signals arriving at the two antennas and presents the better signal.
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Multipath , Upfade and Downfade
Multipath Fading is the dominant fading mechanism for frequencies lower than 10GHz. A reflected wave causes a multipath, i.e. when a reflected wave reaches the receiver as the direct wave that travels in a straight line from the transmitter
If the two signals reach in phase then the signal amplifies. this is called upfade.
Upfade max=10 log d – 0.03d (dB) : d is path length in Km
If the two waves reach the receiver out of phase they weaken the overall signal. A location where a signal is canceled out by multipath is called null or downfade.
As a thumb rule, multipath fading, for radio links having bandwidths less than 40MHz and path lengths less than 30Km is described as flat instead of frequency selective.
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Flat Fading
A fade where all frequencies in the channel are equally affected. There is barely noticeable variation of the amplitude of the signal across the channel bandwidth .
Recommendation for Flat Fading are flat fade margin of a link can be improved by using larger antennas, a higher-power microwave transmitter, lower –loss feed line and splitting a longer path into two shorter hops.
On water paths at frequencies above 3 GHz, it is advantageous to choose vertical polarization.
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Calculating Frequency Selective Fading
o
mB
NMo
mB
Msel
NMM
WWP
220
220 101015.2
0
2
43.0
msfPsel
4/3
1002.0exp1 oP
2/3
507.0
dm
BM, BNM – minimum and non-minimum phase signature depth [dB]WM, WNM - minimum and non-minimum phase signature width [GHz]d – path length [km]
In case the signature area sf is not available (more conservative result):
Probability of outage due to the selective fading (ITU-R Rep. 784-3):Probability of outage due to the selective fading (ITU-R Rep. 784-3):
Where fading activity factor: And typical echo delay:
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Interference Fade Margin
For each interfering transmitter, the receive power level in dBm is compared to the maximum power level to determine whether the interference is acceptable.
Composite Fade Margin (CFM) is the fade margin applied to multipath fade outage equations for a digital microwave radio.
CFM = TFM + DFM + IFM + AIFM
CFM = -10 log (10-TFM/10 + 10 – DFM/10 + 10-IFM/10 + 10-AIFM/10 ).
Dispersive fade margin is provided by radio's manufacturer, and is determined by the type of modulation, effectiveness of any equalization in the receive path, and the multipath signal's time delay. Dispersive fade margin characterizes the radio's robustness to dispersive (spectrum-distortion) fades.
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Cont…Interference Fade Margin
Where
TFM = Flat fade margin (the difference between the normal (unfaded) RSL and the BER=1 x10-3 digital signal loss-of frame point)
DFM = Dispersive fade margin (contribution to outage that accounts for in-band distortion that can at times cause a digital system to fail when the flat fade is less than that required to reach the thermal noise threshold ).
IFM = Interference fade margin .
AIFM =Adjacent-channel interference fade margin (contribution to system outage resulting from the broad transmit spectra of digital systems that have sufficient energy that spills over into adjacent channel digital receivers).
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Dispersive Fade Margin
6(2) 12(4) 18(6) 24(8) 30(10) 36(12)
10
30
50
70 72 dB2n
sec
55 dB
50 dB = Minimum link DFM for no ES degradation due to dispersion
30 dB
25n
sec
6.3n
sec
(“R
um
mle
r’s
Mo
del
”)Required antenna
discrimination(A1+A2)
= Multipath Delay, nsec/feet (m)
Link DFM = Radio DFM + Antenna Discriminations to the Multipath Ray = 50 dB min. for Good Error Performance
Dis
pe
rsiv
e F
ad
e M
arg
in @
10
-3 B
ER
, d
B
Radio-only DFM
0 1010.DFS
osel PP
4.158log.106.17
sfDFS
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Microwave Link Multipath Outage Models
A major concern for microwave system users is how often and for how long a system might be out of service. An outage in a digital microwave link occurs with a loss of Digital Signal frame sync for more than 10 sec. Digital signal frame loss typically occurs when the BER increases beyond 1 x 10-3.
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Outage Availability and Unavailability
Outage (Unavailability) (%) = (SES / t) x 100
Where :
t = time period (expressed in seconds)
SES = severely errored second (Error not exceed 10-3 more then 0.2% of second in any month)
Availability is expressed as a percentage as : -
A = 100 - Outage (Unavailability).
A digital link is unavailable for service or performance prediction/verification after a ten consecutive BER> 1 x 10-3 SES outage period.
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SD Effect on Selective Fading
The SD improvement factor, for the dispersive (frequency selective) component of the fade margin, is independent of the vertical antenna separation for values greater then 3m. As the antenna separation is reduced bellow 3m, the improvement factor decreases rapidly:
Combining Method Nortel:
Combining Method Alcatel-Richardson:
sD=8.5m
Where: ISD – SD improvement factor for flat fading (all previous formulae) P – probability of flat fading (also PND) FM – thermal + interference fade margin DFM – dispersive fade margin RD – correlation coefficient
2
1010 1010~
D
DFM
D
FM
SDtotal sR
sP
selSD
sel
SDSDtotal I
P
I
PP
_
10_ 1009.0
DFM
selSD d
fI
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Variable Parameters
Parameters controlling space diversity: Diversity antenna diameter and gain Diversity antenna height (AGL) Loss of the transmission line and branching circuitry for diversity antennaOption available in Microwave Worksheet then double click on antenna.
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Diffraction Algorithms Overview
Diffraction loss represents the deficiency, with respect to free space loss, in electromagnetic energy of the radio beam that was diffracted (bent) behind the obstacle entering the area around the line of interconnection (line of sight) between receiver and transmitter.
There are two limiting cases that can be easily handled mathematically: Knife-edge like obstacle Earth bulge (ellipsoid like) obstacle Practical case are somewhat “in between” the above two cases and have to be solved numerically:
Pathloss contains following numerical diffraction algorithms:Knife Edge, Isolated Obstacle, Longley and Rice, Pathloss (automatic selection of the calculation algorithm), NSMA, Average, Height Gain, Two ray optics, TIREM.
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Diffraction
More complex diffraction algorithms use multiple knife-edges to better fit the shape of terrain and clutter: Bullington model Epstein Peterson model Deygout model Giovanelli model
More complex diffraction algorithms use multiple knife-edges to better fit the shape of terrain and clutter: Bullington model Epstein Peterson model Deygout model Giovanelli model
A wave-front reaching an obstacle, which is comparable in size to the wave-length, is bended around the obstacle in a phenomenon called diffraction. According to Huygen’s theory, each point of original wave-front is a source of elementary spherical wave, which all together form
a new wave-front behind the obstacle. This theory was later formulated mathematically by Fresnel, resulting in integral theory of diffraction. However analytical solution are available for simple cases only (knife-edge, ellipsoid, sphere).
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Diffraction Losses Knife-edge Obstacle
Signal level can be obtained by solvingFresnel integral. Approximate solution:
Where:21
21 )(2
dd
ddhv
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Bullington Model
Bullington’s model replaces two knife edges with a single equivalent edge to reduce the number of calculations.
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Multiple Knife-Edges Methods
Model Epstein-Peterson, Deygout
This model is used in most planning tools, including Pathloss algorithms. It resembles reality closely enough, but has a limited accuracy. E.g. oval shaped hills are not well modeled by multiple knife edges. Deygout method is limited to two knife-edges.
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Diffraction Loss Concept
Diffraction loss over “knife-edge like” obstacle, option available on Module - Diffraction - Average
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Diffraction Parameters
Diffraction loss can also be calculated as a function of frequency, K-factor and
antenna height.
All parameters used in these variable calculations are local, except polarization. Option is available in Module-Reflection-
Variables.
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Refractive Ray Bending
K = 1 (No refraction)
K = 2/3
K approaches infinity
Moderate Negative Gradient: Flat Earth
K < 0
DUCTING
K =2
K =4/3 ( Mean)STANDARD
EARTH
SUPERREFRACTIVE
SUBREFRACTIVE
K = -1
Steep Gradient: Possible Blackout
K = -0.5
Extreme Gradient: Blackout
K = 2/3 Slightly Sub refractive
K = ½ Moderately Sub refractive
K = 5/12
Humidity Inversion: Extreme Earths Bulge: Diffraction Fade
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Antenna Height Variation
Choosing antenna heights – 4 degrees of freedom. Option is available in Module-Reflection
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K –variation in Pathloss
Option available in Module-Reflection-Variable-Earth Radius Factor
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Two Ray Optics
Reflection analysis is based on two-ray optics and is limited to a single specular reflection. The received signal is a vector addition of the direct signal and the reflected signal. The amplitude of the reflected signal depends on:
Theoretical reflection coefficient Terrain roughness ray divergence ground cover over reflection surface antenna discrimination additional loss due to the lack of clearanceReceived signal amplitude:
Where: R – reflection coefficient amplitude (R=0 to R= -0.1)l - wavelength [m]Δr – difference in path-length between the direct and reflected signal path [m]
φv,h – phase shift which occurs on reflection (close to 180 deg.), polarization dependant
hv
rRRA ,
2 2cos21log10
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Dispersion Analysis
During dispersion analysis, Pathloss user can calculate: Location of the reflection point on the path, Delay of the reflected ray relative to direct ray, Reflection loss relative to the FSL of a direct ray.Option available Module-Reflection-Dispersion
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Modifying Reflection Parameters
Terrain roughness with reduce theoretical reflection coefficient. The higher the roughness, the lower the magnitude of reflection coefficient,Any ground cover will contribute by additional loss to the specular reflection
(water, desert: 0-1 dB; fields with grass: 1-3 dB; sage brush and high grass: 3-6 dB; trees and forests: 8-15 dB), Antenna discrimination (which depends on the main-lobe beamwidth) helps to discriminate the reflected signal. Ray divergence takes into account the scattering effects cause by Earth curvature.Option available Module-Reflection-Modify-Parameters.
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Constant Gradient Trace
Rays are straight.
Constant gradient ray trace used to determine reflective characteristics. Angle between rays determined by program. Option is available in Module-Multipath
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Variable Gradient Trace
Rays are curved.Atmospheric Duct
Variable gradient ray trace used to determine ducting & atmospheric anomalies. Angle between rays determined by program. Option is available in Module-Multipath
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Network Overview
Option available in Module-Network
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Network Background
Background is generated from the DTM installed, option available Module-Network-Site Data-Show background
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Site List
Can be printed out as a special report, option available Module-Network-Site Data-Site List
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Link List
Review of the incorporated xxx.pl4, option available Module-Network-Site Data-Site List
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Importing Sites into Pathloss
Sites can be imported into site list: by importing xxx.pl4 files by importing xxx.txt file by importing xxx.csv file transformed into text file by importing Mapinfo xxx.mif files
Links can be imported into site list: by importing xxx.txt file by importing xxx.csv file transformed into text file by importing Mapinfo xxx.mif files
Pathloss v.4.0 exports into xxx.csv filewhich can be converted into MS Excel xxx.xls file.
Option available in Module-Map grid-Site data- Site List-Import-Site Text File & Link file
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Interference Calculation Procedure
Interference analysis calculates threshold degradations of all the receivers in a specified network, using
frequency plan defined by the Pathloss user,
Digital Interference Objective is maximum allowable Rx threshold degradation, Coordination Distance specifies the
maximum length of interfering path, Maximum Frequency Separation excludes all the interferers that fall outside of it, Default Minimum Interference Level is
used if T/I data are not available for the Radio in its radio data file,
Calculation Margin sets the limit for reported interference cases.
Option in Module-Network-Interference-Calc Intra
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Interference Reports
Shows threshold degradation for each interferer-victim pair. Option is on Module-Network-Interference-Reports.
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Repeated Analysis Method
Error log indicating missing data in hop description file xxxx.pl4, which prevented a successful calculation of Rx threshold degradation during interference analysis. Option is on Module-Network-Interference-View Error Log.
A Transmission Planner repeatedly uses interference analysis to calculate threshold degradations, and manually modifies the frequency plan to ensure, the threshold degradations fall bellow tolerable level (1 dB intrasystem, 3 dB intersystem).
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Cross-reference Report
Highlighted case show the threshold degradation exceeding preset tolerable value. Option is on Module-Network-Interference-Reports.
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Passive Repeaters
WHY TO USE THEM:• When a microwave hop is required in a place which has some
unavoidable physical obstacles.
• Where a mountain peak has to be surmounted which may be so inaccessible that power cannot be provided for a usual active repeater.
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Configuration of Passive Link
View from reflector site
View from terminal site
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Double Plane Repeater
Bird-view
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Plane Reflector Passive Repeater
Option is available in Module-Worksheet-Operations-Create Passive Repeater
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Passive Repeater Data Plane Reflector
Option is available in Module-Worksheet-Report- Passive
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Back-to-back Antenna Passive Repeater
Option is available in Module-Worksheet-Operations-Create Passive Repeater
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Passive Repeater Data Back-to-back
Option is available in Module-Worksheet-Report- Passive
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Network Snapshot
Possibility of backdrop file insertion, option in module-network
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Backdrop Image in Pathloss v.4.0
Option is available in Module-Map grid-Site Data- Backdrop
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Elevation View
Option is available in Module-Map grid-Site Data- Elevation View
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Backdrop Configuration
Directory and Index File has to be configured for:
1. Backdrop Image2. Terrain Elevation Data3. Clutter Height Data
Backdrop Image must be in .TIF format
Datum or Ellipsoid as wellAs UTM Zone must correspondto that of the GIS source
Option is available in Module-Map grid-Site Data- Backdrop
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Microwave Wave Radio File Definition
Files for well known radio manufacturers are available on Pathloss CD-ROM, in Equipment/mrs directory.
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Microwave Wave Antenna File Definition
Files for well known antenna manufacturers are available on Pathloss CD-ROM, in Equipment /mas directory.
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Step by Step Procedure on MW RR Hop Design
1. Perform sites selection (map study, finding of coordinates)2. Choose transmission capacity and HW protection (as per customer, # of
BTS, etc.)3. Choose frequency band (based on distance and TRM capacity)4. Generate profile (DTM, map, determine HASL)5. Suggest preliminary antenna heights (use clearance criteria)6. Perform site survey, path survey (verify HASL, find CP, clutter)7. LOS OK/not OK! (for realistic minimum antenna height)8. Perform diffraction analysis (if needed in exceptional cases)9. Perform reflection analysis (if needed for specular reflections)10. SD for reflection mitigation needed/not needed??11. Determine precise minimum main (and SD) antenna heights12. Determine radio and feeder type
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Step by Step Procedure on MW RR Hop Design (cont.)
• Determine preliminary Tx power and Antenna Size/Type (based on frequency band, TRM capacity and distance of the hop)
• Apply SD if needed of FD/HD if applicable (2nd run)• Check clearance criteria for SD antenna (2nd run)• Calculate the link budget and fade margin• Calculate the percentages of outage due to the rain and multipath fading
(SES, ES, BBER, UAT)• Compare with performance allocations from the ITU standard (Rule of
thumb, scalable G.821 – green table)• Complies with standard? (If not, change antenna and/or Tx power, add SD
and repeat 13-19)• Perform End-to-end performance calculation for the complete link (standard
G. 826)• Complies with standard? (If not, change antenna and/or Tx power, add SD
and repeat 13-21)
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Step by Step Procedure on MW RR Hop Design (cont.2)
1. Allocate a frequency channel and choose polarization2. Decide upon co-channel operation (if needed)3. Decide upon ATPC range4. Perform intra-system interference analysis5. Threshold degradations less then 3 dB? (If not, repeat 22-26 with different
frequency channel and/or polarization)6. Print the performance calculation report and profile7. Allocate [IP] address for network management (if applicable)8. END
Note: The above is a generic procedure. Some steps can be cancelled in particular cases. For example, designing 30 hops in 23, 26 GHz band in the city, that
are just 1-2 km long, doesn’t require comprehensive performance analysis, since there will be no fading. Designing just one MW hop in the middle of a desert, obviously doesn’t require intra-system interference analysis.
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Process Flowchart: MW Link Design
Receive Customer Input• RPF• Budgetary Quote
Review Input• Understand• Clarify• Recommend
Obtain Min. Information•Protection Scheme•Coordinates or Path Length•Capacity
Min.InformationObtained?
Perform Preliminary Analysis and Design• Path Calculations• Routing• Equipment Determination• System Layout
ProfilesAvailable
?
Perform Field Survey• Verify Sites• Path Clearance• Antenna Centerlines• Mounting Conditions • Storage Capability
NO YESNO
AYES
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Cont…Process Flowchart
B
MeetClearance
Criteria?
MeetSES/any month
Objective?
Modify Design• Wave guide Type• Dish Size• Tx Output Power• Diversity Scheme
Modify Design• Change Centerline
Begin Frequency Interference Study• Intra-System• Inter-System
YES
YES
YES
NO
NOA
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Cont…Process Flowchart
Begin Frequency Interface Study• Intra-System• Inter-System
Frequency PairsAssigned?
Determine Pairs• ITU-T Channel Plans• Minimum T/R Spacing
Perform FrequencyInterference Study• T/I Curves• Antenna Type/Size and patterns• Tx Output Power• Polarization• Radio Capacities• Coordinates (or Azmuth’s and Distance)
NO
YES
B HL-LowViolations
?
NO
YES Modify Design• Move Frequency pairs
Intra-System Interference
Modify Design• Move Frequency pairs• Obtain Additional Pairs• Change Polarization• Upgrade Antennas
DONE
NO
YES
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Difficult Areas for Microwave Links
In areas with lots of rain, use the lowest frequency band allowed for the project.
Microwave hops over or in the vicinity of the large water surfaces and flat land areas can cause severe multipath fading. Reflections may be avoided by selecting sites that are shielded from the reflected rays.
Hot and humid coastal areas.
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Troubleshooting Procedure
Isolate the problem to the specific link with BER test, internal network management system reports, etc.
Isolate modules by switching off-line (substitution) by local or remote command.
Is the ES impairment two-way?
Does it correlate with nighttime power fade activity?
If the ES events are daytime occurrences with no fade activity, do open door alarms or other reports suggest “manual intervention”?
Are the ES events seen in both diversity receivers? Simultaneously?
If so, does a far-end transmit chain switch correct the problem?
If not, does it follow an antenna feeder system (Receiver, Demodulator, Decoder, Multiplexer)?
Are the ES Continuous or Random, Recurring or Periodic?
Are there events like Unavailability (>10 CSES), Outage (SES), Burst ES, Dribbling ES (excessive RBER)? What is their statistical distribution?
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Important Recommendations
Use higher frequency bands for shorter hops and lower frequency bands for longer hops.
Avoid lower frequency bands in urban areas.
Use star and hub configurations for smaller networks and ring configuration for larger networks.
In areas with heavy precipitation , if possible, use frequency bands below 10 GHz.
Use protected systems (1+1) for all important and/or high-capacity links.
Leave enough spare capacity for future expansion of the system.
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Important Recommendations
Space diversity is a very expensive way of improving the performance of the microwave link and it should be used carefully and as a last resort.
The activities of microwave path planning and frequency planning preferably should be performed in parallel with line of sight activities and other network design activities for best efficiency.
Use updated maps that are not more than a year old. The terrain itself can change drastically in a very short time period. Make sure everyone on the project is using the same maps, datums and coordinate systems.
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Important Recommendations
Perform detailed path surveys on ALL microwave hops. Maps are used only for initial planning, as a first approximation.
Below 10 GHz , multipath outage increases rapidly with path length. It also increases with frequency , climatic factors and average annual temperature. Multipath effect can be reduced with higher fade margin. If the path has excessive path outage the performance can be improved by using one of the diversity methods.
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Channel Table 1 (1.4 – 6 GHz)
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Channel Table 2 (7-13 GHz)
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Channel Table 3 (14-23 GHz)
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Channel Table 4 (27-55 GHz)
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Case Studies
Design of MW 16E1 PDH Hop in 15 GHz
Diffraction Loss on PDH hop in 8 GHz
Reflection Analysis for Over-water 6 GHz hop
Rain Attenuation for PDH 8E1 hop in 18 GHz
MW PDH Link from BTS to BSC
Design of a MW SDH Transmission Link 4+0
Interference Analysis in Multan City, Pakistan
Backdrop Image of Sana’a, Yemen
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Where to find the Case Studies?
Go to the files copied from the CD-ROM you have received from the trainer:
Beside the individual Case Studies, there are some other radio and antenna definition files in this directory.
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Acronyms 1
1+1 -Single line protection switching (FD, HS, etc.)1:N, 2:N -Multiline protection switching (N = no. of bearer channels)
ABL -Atmospheric Boundary LayerACO -Alarm CutoffACU -Antenna Coupling UnitA/D -Analog-to-Digital (conversion)ADM -Add/Drop MultiplexerADPCM -Adaptive Differential PCMADSL -Asymmetric Digital Subscriber LineAGC -Automatic Gain ControlAIS -Alarm Indication Signal (“All Ones” at DS1, “Blue” at DS3) AMI -Alternate Mark Inversion (DS1)AMPS -Advanced Mobile Phone System (FDMA -Analog Cellular) ANSI -American National Standards InstituteAPS -Automatic Protection SwitchingASAE/AFDE -Adaptive [Frequency Domain] Slope Amplitude EqualizerASCII -American Standard Code for Information Interchange ATDE -Adaptive Time Domain (transversal) EqualizerATM -Asynchronous Transfer ModeATPC -Automatic Transmitter Power Control (also APC)AU -Administration Unit (SDH)AZD -Ambiguity Zone (error) Detection (QPR Radios)
B3ZS -Bipolar with 3-Zero Substitution (DS3) B6ZS -Bipolar with 6-Zero Substitution (DS2) B8ZS -Bipolar with 8-Zero Substitution (DS1) BBER -Background Block Error Rate (EB/time period) BER -Bit Error Ratio or Rate (Errors/time period) BERTS -BER Test Set (being replaced with internal NMS) BISDN -Broadband ISDNBITS -Building Integrated Timing SupplyBLSR -Bi-directional Line-Switched RingBPV -Bipolar ViolationBWA -Broadband Wireless Access
CAD/CAM -Computer Aided Design/ManufacturingCB - Channel Bank (1st order mux)CBR - Constant Bit Rate (ATM)CCC -Clear Channel CapabilityCCDP -Co-Channel Dual Polarized linkCCIR -International Radio Consultative Committee (now ITU-R)CCITT -International Telephone and Telegraph
Consultative Committee (now ITU-T)CDMA -Code Division Multiple Access (spread spectrum)CDPD -Cellular Digital Packet DataCDV -Cell Delay Variation (ATM)CEPT -Conference of European Postal and
Telecommunications administrationsCFM -Composite Fade MarginCGA -Carrier Group AlarmCIR -Carrier-to-Interference Ratio (also C/I Ratio) CIT -Craft Interface TerminalCLR -Cell Loss Ratio (ATM)CMI -Coded Mark Inversion (E4)CMISE -Common Management Information Service ElementCNR -Carrier-to-Noise Ratio (also C/N Ratio)CO -Central OfficeCODEC -Coder/DecoderCPE -Customer Premises EquipmentCRC -Cyclic Redundancy Check (on ESF T1 trunks)CSMA/CD -Carrier Sense Multiple Access with Collision DetectionCSU/DSU -Channel Service Unit/Data Service UnitCV -Coding Violation
DACS -Digital Access Crossconnect System (© LucentTechnologies ). See DCS.
DADE -Diversity Antenna Differential Equalization orDifferential Absolute Delay Equalization
DCC -Digital Communications Channel (e.g., SONET OAM&P)
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Acronyms 2
FM -Frequency ModulationFM-FDM -FM radio with FDM multiplex (also FDMA)FSK -Frequency Shift KeyingFTTC -Fiber To The CurbFTTH -Fiber To The HomeFWL -Fixed Wireless Local Loop (also WLL)FXO, FXS -Foreign eXchange unit at CO, subscriber (VF)
Gbit/s -Gigabits per second (also Gb/s, Gbps)GHz -Gigahertz(109 Hz)GPS -Global Positioning Satellite systemGUI -Graphical User Interface
HD -Hybrid DiversityHDB3 -High Density Bipolar order 3 (E1-E3)HFC -Hybrid Fiber/Coax cable (see FTTH and FTTC)HDSL -High bit-rate Digital Subscriber LineHNM -Harris Network Management SystemHP - High Performance (e.g., shrouded antenna)HS - Monitored Hot Standby (also MHSB)HSSI - High Speed Serial Interface
IEC - International Electrotechnology CommissionIF - Intermediate FrequencyIFM -Interference Fade MarginIP - Internet ProtocolISDN - Integrated Services Digital NetworkISI - Intersymbol InterferenceISO - International Standards OrganizationITU-R - International Telecommunication Union-
Radiocommunications SectorITU-T - International Telecommunication Union-
Telecommunication Standardization Sector
kbit/s -kilobits per second (also kb/s, kbps)kHz -kilohertz (103 Hz)
DCE -Data Circuit-Termination EquipmentDCS -Digital Access Crossconnect System (also DXC, TCS,
DACCS, DACS - Lucent)DLC -Digital Local Loop Carrier (fiber) DFM -Dispersive Fade MarginDRRS -Digital Radio-Relay SystemDS0, 1,2,3 -North American Digital Signals levels 0, 1, 2, 3DSP -Digital Signal ProcessingDS -Direct Sequence (spread spectrum - CDMA) DSX -Digital Cross-Connect panel (-1, -3 for DS1, DS3) DTE -Data Terminating Equipment
E1, E2, E3, E4 -CEPT Digital Trunks or SignalsEB -Errored Block (Sonet and SDH) %EFS -%Error-free seconds (over a measurement period) ESR -Errored Second Ratio (ES/time period)EIRP -ERP ref. to an Isotropic Antenna (= ERP+2.2 dB)EIA -Electronic Industries Association (ass’n w/TIA) EMC -Electromagnetic CompatibilityEMI -Electromagnetic InterferenceEPROM -Erasable Programmable Read-Only MemoryEPO -Error Performance ObjectiveERP -Effective Radiated Power ref. to a Dipole AntennaES -Errored SecondESF -Extended Super FrameESR -Errored Second Ratio (ES/Time Period) ETSI -European Telecommunication Standards
Institute (ANSI equivalent)
FD -Frequency DiversityFDDI -Fiber Distributed Data InterfaceFDM -Frequency Division MultiplexFDMA -Frequency Division Multiple Access (also FM-FDM)FEC -Forward Error CorrectionFH -Frequency Hopping (spread spectrum)FITS -Failures In Time (109 hours)
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Acronyms 3
LAN -Local Area NetworkLED -Light Emitting DiodeLNC -Low Noise ConverterLOS -Loss Of Signal, Line Of SightLOF -Loss Of Frame synchronizationLOP -Loss Of Pointer (SONET)LSB -Least Significant Bit
MAN -Metropolitan Area NetworkMbit/s -Megabits per second (also Mb/s, Mbps)MHz -Megahertz (106 Hz)micron -10-6 meter (= 1000 nm - lightwave)MIS -Management Information SystemMODEM -MODulator/DEModulatorMPEG -Motion Picture Experts Groupmrad -milliradian (also mr)msec -millisecond (also ms)MTBF -Mean Time Between FailureMTBMA -Mean Time Between Maintenance ActivitiesMTBO -Mean Time Between OutageMTR -Mean Time to Restore (after failure)MTSO -Mobile Telephone Switching Office (also MSO,
MTX, MSC)MTTR -Mean Time To Repair (at the site)MUX -Multiplexer
ND -Non-DiversityNE -Near-End or transport Network ElementNode -SONET/SDH line terminating devicenm -nanometer (10-9 meter), lightwaveNMS -Network Management SystemNNI -Network Node InterfaceNP -Non-ProtectedNPL -Net Path LossNRZ -Non-Return to Zeronsec -nanosecond (10-9 sec) - also ns
OAM&P -Operations, Administration, Maintenance, and Provisioning functions (usually SONET/SDH)
OC-1,-3 -Optical Carrier Level 1, 3 Signal (51, 155 Mbit/s)OC-3c -OC-3 Concatenated Signal for Broadband/ATMOCUDP -Office Channel Unit Data PortOOF -Out Of FrameOPX -Off-Premises eXtensions (VF)OQPSK -Offset QPSKOSI -Open Systems Interconnection
PA -Power AmplifierPAD -Packet Assembler/DisassemblerPBX -Private Branch eXchange (also PABX)PCM -Pulse Code ModulationPCR -Peak Cell Rate (ATM), Paperless Chart RecorderPCS -Personal Communications Services (also PCN)PDH -Plesiochronous Digital HierarchyPLL -Phased-Locked LoopP-MP -Point-to-Multipoint access radioPN -Psuedo-Noise sequence code (spread spectrum/CDMA)P-P -Point-to-Point radio-relay linkPOH -Path Overhead (SONET/SDH)POTS -Plain Old Telephone ServicePSTN -Public Switched Telephone NetworkPTE -Path Terminating Equipment (SONET)PVC -Permanent Virtual Circuit/Connection (ATM)
QAM -Quadrature Amplitude ModulationQD -Quadruple DiversityQoS -Quality of Service (ATM)QPRS -Quadrature Partial Response Signaling (also QPR)QPSK -Quadrature Phase Shift Keying
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Acronyms 4
RBER -Residual (dribbling) BERRing -Circular configuration of nodes RF -Radio FrequencyRR-STM -STM-0 (51 Mbit/s) for Radio Relay. Also sub-STM-1RRRP -Radio-Relay Reference Point (SDH)RSL -Receive Signal LevelRSVP -Resource reSerVation Protocol (ATM)RTU -Remote Terminal UnitRZ -Return to Zero
SCADA -Supervisory Control and Data AcquisitionSCU -Service Channel UnitSDH -Synchronous Digital Hierarchy (ETSI standard))SD -Space DiversitySEP -Severely Errored Period (G.828). See CSESSEPI -SEP IntensitySES -Severely-Errored SecondSESR -Severely-Errored Second Ratio (SES/time period)SF -Super Frame (format for DS1 signal)SMDS -Switched Multi-megabit Data ServiceSNA -Systems Network ArchitectureSNMP -Simple Network Management ProtocolSOH -Section Overhead (SONET/SDH)SONET -Synchronous Optical NETwork (ANSI standard)SPE -Synchronous Payload Envelope (SONET)SPU -Signal Processing UnitST -Split Transmitters (to separate antennas)STE -Section Terminating Equipment (SONET)STM-n -Synchronous Transport Module (SDH transport)STS-n -Synchronous Transport Signal (SONET transport)STS-3c -STS-3 Concatenated Signal (for Broadband/ATM)SVC -Switched Virtual Circuit (ATM)
T1,T3 -North American digital trunks or facilitiesT1M1 & T1X1 -ANSI telecommunications standards committees
TABS -Telemetry Asynchronous Byte Serial (Protocol) TBOS-Telemetry Byte-Oriented Serial (Protocol)
TCM -Trellis Code ModulationTDMA -Time Division Multiple AccessTFM -Thermal (flat) Fade Margin (also FFM)TIA -Telecommunications Industries Association
(ass’n w/EIA)TL1 -Transaction Language 1TMN -Telecommunication Management NetworkTSA -Time Slot AssignmentTSI -Time Slot InterchangeTU -Tributary Unit (SDH)TUG -Tributary Unit Group (SDH)
UAS -UnAvailable (failed) Seconds (also NAS)UBR -Unspecified Bit Rate (ATM)UNI -User-to-Network InterfaceUPSR -Unidirectional Path-Switched Ring
VBR -Variable Bit Rate (ATM)VC -Virtual Container (SDH)VCI -Virtual Channel Indicator (ATM)VDSL -Very high speed Digital Subscriber LineVF -Voice FrequencyVP -Virtual Path (ATM)VSAT -Very Small Aperture Terminal (satellite)VT -Virtual Tributary (SONET)VTG -Virtual Tributary Group (SONET)
WAN -Wide Area NetworkWLL -Wireless Local Loop (also FWL)www -World Wide Web
XPD -Cross-Pol antenna DiscriminationXPIC -Cross-Pol Interference Canceller for CCDP linksXPU -Expansion Unit