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41st Signal BattalionMaintenance Support Team
AN INTRODUCTION TO
Digital Microwave Principles
(DMR)
Mr. Thomas SamuelsU.S. Air Force
Space and Missile System Center Range Network Systems Upgrades (RNSU)
Peterson Air Force BaseColorado Springs, CO
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This course provides guidance for technicians and operators explaining Microwave BasicsPrinciples and Digital Microwave Communications, and how the Microwave BasicPrinciples apply to the Harris Megastar 155 Digital Microwave Radio commonly used bythe U.S. Army in the Republic of Korea.
Paving the way for learning how to maintain and providing trouble isolation techniques for the Harris Megastar 155 Digital Microwave Radio and associated Networking systems.
Microwave PrinciplesForeword 2
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Microwave PrinciplesLearning Guide
Microwave communication was developed with the basis of the electromagnetic field theory commonly called RadioFrequency propagation.
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After this course, you will be able to explain:Basic concepts and characteristics of a Digital Microwave Communication Systems
Functions and principles of each component of the Harris Megastar 155 Digital Microwave Radio andassociated Asynchronous Transfer Mode switching systems; commonly known as DigitalMultiplexers.
Common networking modes and application scenarios of Digital Microwave Communication asapplied to the Harris Megastar 155 Digital Microwave Radio
Propagation principles of Digital Microwave Communication and various types of fading
Anti-fading technologies
Microwave PrinciplesObjectives 4
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Microwave PrinciplesContents
1. Digital Microwave Communication Overview
2. Digital Microwave Communication Equipment
3. Digital Microwave Networking and Application
4. Microwave Propagation and Anti-fading Technologies
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Coaxial Cable Communication
MicrowaveCommunication
Optical Cable Communication
MuxDemux
MuxDemux
Microwave PrinciplesTransmission Methods in Current Communications Networks
SatelliteCommunication
M i c r o w a v e
T E
M i c r o w a v e
T E
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Microwave PrinciplesMicrowave Communication vs. Optical Fiber Communication
Microwave Communication
Powerful space cross ability, little landoccupied, not limited by land privatization
Small investment, short construction period,easy maintenance
Strong protection ability against natural disaster and easy to be recover
Limited frequency resources (frequency licenserequired)
Transmission quality greatly affected by climateand landform
Limited transmission capacity
Optical Fiber Communication
Optical fiber burying and land occupationrequired
Large investment ,long construction period
Outdoor optical fiber maintenance required andhard to recover from natural disaster
Not limited by frequency
license not required
Stable and reliable transmission quality and notaffected by external factors
Large transmission capacity
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Microwave PrinciplesDefinition of Microwave
Microwave is a type of electromagnetic wave. In a broad sense, the frequency range isfrom 300 MHz to 300 GHz. But In microwave communication, the frequency range isgenerally from 3 GHz to 30 GHz. The Microwave frequency used for transmission of digitaldata by the U.S. Army in the Republic of Korea is between 7 GHz and 8 GHz
According to the characteristics of microwave propagation, microwave frequencies can beconsidered as plane waves.
The plane wave has no electric field or magnetic field longitudinal components along thepropagation direction.
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Microwave PrinciplesDefinition of Digital Microwave
Digital microwave is a medium for transmitting digital information in the atmosphere through electronicmagnetic commonly called Radio Frequency (RF) waves.
Electromagnetic field theory is the basis on which microwave communication RF theory isdeveloped.
Microwave transmission refers to the communication that uses a microwave RF as carrier andadopts digital modulation techniques.
The baseband signal is modulated to an intermediate frequency (IF) first. Then heterodyned (mixed)with the microwave transmission frequency(RF).
NoteOnly phase shift key (PSK) modulation is applicable.
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Microwave PrinciplesDevelopment of Microwave Communication
480 voicechannels
2M 4M 6M
34M 140M
155MSDH digital microwavecommunication system
PDH digital microwavecommunication system
Small and medium capacitydigital microwavecommunication system
Analog microwavecommunication system
1950s
1970s
1980s
Late1990sto now
Transmission Capacity
NoteSmall Capacity < 10 Mbits/ChannelMedium Capacity 10 to 100 Mbits/ChannelLarge Capacity > 100 MBits/Channel
Mega Bits per Channel
Mega Bits per Channel
Mega Bits per Channel
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3.5
Regional Network
1.5 2.5
2 Mbits/sec8 Mbits/sec
34 Mbits/sec
Long Haul Trunk Network
Regional Network Local Network Boundary Network
2 Mbits/sec8 Mbits/sec
34 Mbits/sec140 Mbits/sec155 Mbits/sec
GHz
1 2 3 4 5 8 10 20 30 40 50
Microwave Radio Frequency used in by the U.S. Army in the Republic of Korea is 6 GHz to 8 GHz
10 10 10 11
6 7
Microwave PrinciplesDefinition of Digital Microwave
119
10 9 10 8 10 4 10 12 10 15 10 16 10 18 10 20
155 Mbits/sec
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1 x 1
0 9 1
G H z
6 x 1 0 9
6 G H z
2 x 1 0 9
2 G H z
3 x 1 0 9
3 G H z
4 x 1 0 9
4 G H z
5 x 1 0 9
5 G H z
7 x 1 0 9
7 G H z
8 x 1 0 9
8 G H z
9 x 1 0 9
9 G H z
1 0 x 1
0 9 1 0 G H z
Microwave PrinciplesMicrowave Radio Frequency Configuration
2 c m
3 c m
Microwave Radio Wave Length in Meters
1 c m
9 0 c m
8 0 c m
7 0 c m
6 0 c m
6 0 c m
4 c m
5 c m
(as defined by International Telecommunications Union radio spectrum (ITU-R) recommendations).
11 GHz,13 GHz,15 GHz,18 GHz
23 GHz26 GHz32 GHz38 GHz
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In each frequency band and frequency sub-band the transmit/receive (T/R spacing) and channel spacingare defined
Microwave PrinciplesMicrowave Radio Frequency Configuration - 2Frequency Band Selection and RF Channel Configuration
f 2 f 1 f n ChannelSpacing
Frequency Range
f c Center Frequency
Low Frequency Band High Frequency Band
T/R Spacing
T/R Spacing
ChannelSpacingf 1
f n f 2
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In each frequency band and frequency sub-band the transmit/receive (T/R spacing) and channel spacing aredefined
f 1 = 7442 MHz
T/R Spacing 154 Mbits
f 5 f 2
Microwave PrinciplesMicrowave Radio Frequency Configuration - 3Frequency Band Selection and RF Channel Configuration - 2
Frequency Range 7425 MHz 7725 MHzF c (7575 MHz)
28 Mbits
Frequency Range F c MHz T/R Spacing MHz Channel Spacing MHz Primary and Non-Primary Stations
7425 MHz 7725 MHz 7575 154 28 f n = f c 161 + 28n7575 161 7 f n = f c 7 + 28n (n:1-5)
7110 MHz 7775 MHz 7225 196 287597 196 28
7250 MHz 7550 MHz 7400 161 3.5
f 2 = 7470 MHz f 1 = 7596 MHz
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Transmission mediaCopper mediaMicrowave RadioOptical Fiber Infra Red Radio
Microwave radio terminal - three Basic Modules to interface with equipment and convert traffic to amodulated signal
Base Band (SPU)
Radio Frequency Unit (RFU) Antenna Coupling Unit ((ACU)IDUODU - (The IDU is connected to the ODU via the IF cable) not used.
Commonly used capacity configurations155 Mega Bits per Second
In the United States the basic Data Transfer Rate is a data stream 1.55 mbpsIn Europe the basic Data Transfer Rate is a data stream of 2.048 Mbps
Advantages Lower start up and operational cost
Synchronization Digital Hierarchy (SDH) is a technology used in telecommunication systems to transportlarge quantities of date over digital transport equipment such as microwave systems
In a SDH system every equipment is provide timing by an external timing source currently the industry is GPS timing.In a PDH system provides an internal clock generating its the synchronization.
Microwave PrinciplesDigital Microwave CommunicationModulation 1Characteristics and Advantages
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A device which varies a characteristic of a repetitious electrical or electromagnetic wave of less than infraredfrequency in accordance with a characteristic of an arbitrarily varying modulating signal.
Microwave PrinciplesMegastar 155 Microwave RadioModulation 2Modulation
Modulation defined - Addition of information (or signal) to an electronic or optical carrier.
Modulation can be applied to direct current (mainly by turning it on and off), to alternating current, or tooptical signals.
Example - think of a blanket waving as a form of modulation used in smoke signal transmission (the
carrier being a steady stream of smoke).
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NoteGeneric class for demodulators.
A demodulator is a device which extracts arbitrarily varying information from a signal formed by varyinga characteristic of a repetitious electrical or electromagnetic wave of less than infrared frequency.
Microwave PrinciplesMegastar 155 Microwave RadioModulation 3Demodulation
Demodulation definition - The conversion of a modulated carrier wave into a current equivalent to theoriginal signal. Also called detection .
The act or process by which an output wave or signal is obtained having the characteristics of the originalmodulating wave or signal; the reverse of modulation
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Microwave PrinciplesDigital Microwave CommunicationModulation 4
Amplitude Shift Keying (ASK)Uses the digital baseband signal to change the carrier amplitude (A), carrier frequency (f c) andcarrier phase ( ) remain unchanged.
Frequency Shift Keying (FSK)Uses the digital baseband signal to change the f c, A and remain unchanged.
Phase Shift Keying (PSK)Uses the digital baseband signal to change the , f c and A remain unchanged.
Quadrature Amplitude Modulation (QAM)Uses the digital baseband signal to change the and A, f c remains unchanged
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The baseband signal is the un-modulated digital signal. The baseband IF can not be directly transmittedover microwave radio channels and must be heterodyned (mixed) the RF (7GHz or 8GHz) for microwave medium for communication.
Digital Base band Intermediate Frequency SignalBaseband
ServiceSignal
Transmitted
Microwave PrinciplesDigital Microwave CommunicationModulation 5
PSK and QAM are mostfrequently used in digitalmicrowave transmission
Signal R
ate
Modulation
TransmittedServiceSignal
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Microwave PrinciplesDigital Microwave CommunicationModulation 6
Voltage
Digital
Voltage
Voltage
Digital
Digital
0
0
0
Time
Time
Time
Phase Shift
Phase Shift Amplitude Modulation
Phase Shift Modulation
Un-Modulated (reference)Modulated ( Phase Shifted)
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Microwave PrinciplesDigital Microwave CommunicationModulation 7Quadrature Amplitude Modulation - 1
QAM-16
QAM-64
QAM-128
The higher the modulation stagesmaller the channel/bandwidth getsmore sensitive to interferenceSynchronous Digital Hierarchy
DMRS 155/Mbits/secTransmission
Channel128 QAM
Bandwidth
< 26 MHz
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Quadrature Amplitude ModulationConstellation DiagramExamples-Quadrature AmplitudeModulation is actually indisplayed in Polar Coordinaterepresentation The I and Qcomponent is converted to atwo dimensional planerepresentation.
Where I is in the X PlaneQ is in the Y Plane
The Diagram is a working model
demonstrating I and Q
Microwave PrinciplesDigital Microwave CommunicationModulation 8Quadrature Amplitude Modulation - 2
QAM -12864 bits per Quaadrant
QAM 6416 bits per Quadrant
QAM-164 bit per quadrant
QPSK
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QAM is a family of encoding schemes that are widely used for encoding multiple bits of 1 and 0 per symbol that combine Amplitude and Phase Modulation, with frequency remaining constant.
16, 64, 128 QAM are a common forms using 8 bit, 32 bit , and 64 bit phase shifts and 2 changingamplitude levels, respectively.
For 16 bit QAM - Since there are 16 possible symbols, each symbol encodes 4 bits
For 64 bit QAM - Since there are 64 possible symbols each encoded symbol represents 8 bits
For 128 bit QAM - Since there are 128 possible symbols each encoded symbol represents 32 bits(The scheme most commonly used)
QAM and related techniques are commonly used for precise transmission and reception of digitaldata streams. (More commonly used for modems with a data rate of up to about 28 kilobits/second. )
Microwave PrinciplesDigital Microwave CommunicationModulation 9Quadrature Amplitude Modulation - 3
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Microwave PrinciplesDigital Microwave CommunicationModulation 10Quadrature Amplitude Modulation - 4
Voltage
Digital
VoltageDigital
0
0
Time
Time
Time
Phase Shift Modulation
Phase Shift
Amplitude Modulation Phase Shift
Un-Modulated (reference)Modulated ( Phase Shifted)
0
Voltage
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QAM is a combination of amplitude modulation, changing the amplitude or voltage of a sine wave toconvey information together with phase modulation.
Explaining QAM modulation
Two modulating carrier waves are derived by special pre-processing from the information bit stream. Replica carrier waves are generated; one carrier wave is a direct replica sin (I) and the other carrier wave is delayed by a quarter of acycle (90) cos (Q). Each of the two carrier waves are derived by modulating the signals to the amplitude of the twocarrier waves I and Q respectively.
The resultant two modulated signals are algebraically summed together, the result is an I and Q having a constantunchanging frequency while the amplitude and phase will vary to convey the information.
At the detector or decoder the original information bit stream can be reconstructed.
QAM conveys a higher information bit rate.
This method of modulation has the advantage of reducing or eliminating inter-modulation interferencecaused by a continuous carrier wave near the modulation sidebands.
This carrier wave for all intents and purposes is a 'Double Sideband Signal' (DSB) with or without acarrier (reduced). (Only one side band is used for processing information).
Microwave PrinciplesDigital Microwave CommunicationModulation 12Quadrature Amplitude Modulation - 6
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Microwave PrinciplesDigital Microwave CommunicationModulation 13Quadrature Amplitude Modulation - 7
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171.072 MB/s
1.552 MB/s STM-1 155.2 MB/s
RFCOH SOH PAYLOAD
MCLM11.84Mb/s
DMY64Kb/s
XPIC16Kb/s
ATPC64Kb/s
WS2.24Kb/s
RSC864Kb/s
INI144Kb/s
ID32Kb/s
FA288Kb/s
RFCOH: Radio Frame Complementary Over HeadMLCM: Multi-Level Coded ModulationDMY: DummyXPIC: cross polarization interference counteract
ATPC: Automatic Transmitter Power ControlWS: Wayside ServicesRSC: Radio Service ChannelINI: Switch Instruction
ID: Identifier FA: Frame Alignment
Microwave PrinciplesMicrowave CommunicationDigital Frame Structure 1
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Multiframe 3564 bits
6 bits FS6 bits
Basic Frame 11776 bits (148 words)
FS6 bits
Basic Frame 21776 bits (148 words)
I STM1 information bit (OCR information bit)C1 correction coding supervision bit of first level,C2 correction coding supervision bit of second levelFS frame synchronization bita other complementary overhead bits
b other complementary overhead bits
Microwave PrinciplesMicrowave CommunicationDigital Frame Structure 2
I I I I I I I I I I I I I I I I I I I I I I I I
I I I I I I I I I I I I I I I I I I I I I I I I
I I I I I I I I I I I I I I I I I I I I I I I I
I I I I I I I I I I I I I I I I I I I I I I I I
I I I I I I I I I I I I I I I I I I I I I I I I
I I I I I I I I b I I C2 I I I I I a I I b I I C2
I I C1 I I C1 I I C1 I I C1 I I C1 I I C1 I I C1 I C1 I
12 bits (1 st Word) 12 bits (148 th Word)
RFCOH is multiplexed into the STM-1 data and a block multi-frame is formed. Each multi-frame has six rows and each row has 3564 bits. Onemulti-frame is composed of two basic frames. Each basic frame has 1776 bits. The remaining 12 bits are used for frame alignment
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What is microwave?
What is digital microwave communication?
What are the frequently used digital microwave frequency bands?
What concepts are involved in microwave frequency setting?
What are the most frequently used modulation schemes?
Microwave PrinciplesQuestions
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Microwave PrinciplesContentsModule 2
Digital Microwave Communication Equipment
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Microwave PrinciplesMicrowave Equipment Category
System Digital Microwave
PDH SDH
Analog Microwave
MUX/DEMUXMode
Capacity
Structure
Small and Medium Capacity
2 16 E1 34 Mbits/sec
Large CapacitySTM-0, STM-1, 2xSTM-1
Discontinued
Trunk
Split Mount Radio
All Outdoor Radio
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Microwave PrinciplesMicrowave Antenna 1
0.3m - 1 foot0.6m - 2 feet1.2m - 4 feet1.8m - 6 feet2.0m2.4m - 8 feet3.0m - 10 fee3.7m - 12 feet
Antennas are used to send and receive microwave signals, a Parabolic antenna is the common type of the
microwave antenna.
Microwave antenna diameters includes
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Microwave Principles Antenna Adjustment 3
Main lobe
Side View
Top View
Main lobe
Main lobeHalf-power angle
Half-power angle
Tail lobe
Tail lobe
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During antenna adjustment, the two wrongadjustment cases are shown here. One antenna isaligned to another antenna through the sidelobe.
As a result, the RSSI can not meet therequirements.
Wrong Wrong Correct
Microwave Principles Antenna Adjustment 4 37
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During antenna adjustment,Use a spectrum analyzer to observe the RSSI at the
receiving end, perform fine adjustments on theantenna and observe the RF is signal is a maximumas observed on the spectrum analyzer, asdemonstrated in the illustration to the right.
Change the antenna direction vertically or horizontally,use a multimeter to observe voltage, the peak point of the voltage, perform fine adjustments on the antennato peak the voltage point, (usually the voltage peakwill be displayed as shown in the lower right corner) .
When antennas are poorly aligned a small or no RFsignal will be displayed, or a small voltage may bedetected in one direction. In this case, perform coarseadjustment on the antennas at both ends, so that theantennas are roughly aligned.
The antennas at both ends that are well aligned face alittle bit upward. Though 1 2 dB is lost, reflectioninterference will be avoided
AGC Voltagedetection point
Side LobePosition
Main lobeposition
Angle
RF Display
Microwave Principles Antenna Adjustment 5
AGC
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Microwave PrinciplesTrunk Microwave Equipment
Low costLarge transmission capacityMore stable performanceapplicable to long-haul and trunktransmission
antenna system is outdoors
IF
The RF processing isperformed in the RadioFrequency Unit(RFU)
signal processing unit (SPU) - known as baseband module
The Exciter is where and RFcreated and, where the RFand IF signals areheterodyned (mixed)
Antenna Coupling Unit (ACU)
SDH MICROWAVE RADIOHarris Megastar 155Digital Microwave Transmission
Parabolic antenna
RF
Modulator MUX
Demodulator DEMUX
R a d i oF r e
q u en
c y Uni t
( RF
U )
Option(OC3)optical interface
Multi-Mode
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The MegaStar 155 Microwave Radio is a high capacity point-to-point digital microwave radio available at 7/8 GHz.
Is a compact, single platform.
Can be upgraded from 1 to 7 high capacity channels (155 MBit/s each).
Features include 10BASE-T transport for OEM equipment connection to SNMP management, support for OpenNetwork Management through an SNMP proxy, convenient provisioning with remote software download,
Remote and Localinventorying
Plug and play module replacement
Easy maintenance with local IF loopback with built in test signal for BER measurement.
consists of primary and redundant circuit cards and modules
Microwave PrinciplesMegastar 155 Microwave Radio
Standard FeaturesProvides a high level of readiness
Receiver fully digital adaptive time domain equalization (ATDE)Receiver fully digital adaptive slope equalizationForward Error Correction (FEC)Anticipatory errorless receiver switchingReverse Path ProtectionTransmitter Automatic Transmit Power Control (ATPC)
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Microwave PrinciplesMegastar 155 Microwave Radio
Standard FeaturesProvides a high level of readiness
Receiver fully digital adaptive time domain equalization (ATDE)Receiver fully digital adaptive s lope equalizationForward Error Correction (FEC)
Anticipatory errorless receiver switchingReverse Path ProtectionTransmitter Automatic Transmit Power Control (ATPC)
Offers self-aligning operation
Inventory Reporting(SCAN) System Control and Alarm Network - Remote MonitoringFarscan Local Diagnostics using portable computer (Laptop)
Replace Me/Loss of Signal LEDAutomatic calibration of replacement circuit packsLocal/Remote firmware replacement
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Microwave PrinciplesMegastar 155 Microwave Radio
3A. Signal Processor (SPU) 1
1A. Antenna Coupling Unit (ACU) 1
Can consist of 2 Microwave Radio Systems in one shelf andeach Systems consist of 3 subsystems each
2B. Radio Frequency Unit (rfu) 22A. Radio Frequency Unit RFU) 1
1B. Antenna Coupling Unit (ACU) 2
3B. Signal Processor (SPU) 2
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Processes Digital Data
Sends Digital Data to RF combiner for mixing digital data with the 70 MHz Intermediate Frequency (IF)commonly called the carrier frequency.
Frequency domain representation of output
Microwave PrinciplesMegastar 155 Microwave RadioIntermediate Frequency
70 MHz70 MHz
Single Side Band Carrier (IF) frequency
70 MHz 70 MHz
Double Side Band Carrier (IF) frequency
Frequency domain representation of input
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The IF mixer extracts 70 MHz carrier frequency from the receiver RF
Processes the 70 MHz carrier frequency to the demodulator input a part of the base band(Megastar 155 SPU)
Microwave PrinciplesMegastar 155 Microwave RadioIntermediate Frequency
Undesired Signals Undesired Signals
70 MHz
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Receiver ALow Noise Converter
PLS
IF Amplifier
ACU
Couples RF signal from Power Amplifier assembly to antenna
Receiver BLow Noise Converter
PLS
IF Amplifier
Transmitter APower Amplifier A
RF Switch & Filter Assembly A
PLS A
Transmitter BPower Amplifier B
RF Switch & Filter Assembly B
PLS B
RFU
B A
Single Power Amplifier ConfigurationMicrowave Principles
Megastar 155 Microwave Radio
ACU
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ACU
Receiver ALow Noise Converter
PLS
IF Amplifier
RF Switch & Filter Assembly A
ACU
Couples RF signal from Power Amplifier assembly to antenna
Receiver BLow Noise Converter
PLS
IF Amplifier
RF Switch & Filter Assembly B
Transmitter A
Power Amplifier A
RF Switch & Filter Assembly A
PLS A
Transmitter BPower Amplifier B
RF Switch & Filter Assembly B
PLS B
RFU
B A
Parallel Power Amplifier Configuration
Microwave PrinciplesMegastar 155 Microwave Radio
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ACU
Receiver ALow Noise Converter
PLS
IF Amplifier
ACU
Couples RF signal from Power Amplifier assembly to antenna
Receiver BLow Noise Converter
PLS
IF Amplifier
Transmitter APower Amplifier A
RF Switch & Filter Assembly A
PLS A
Transmitter BPower Amplifier B
RF Switch & Filter Assembly B
PLS B
RFU
B AMicrowave PrinciplesMegastar 155 Microwave Radio
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Slot 9Slot 12Slot 6
Slot 15Slot 5Slot 4
Slot 17Slot 16 Slot 18
Slot 13Slot 8 Slot 10
Microwave PrinciplesMegastar 155 Microwave RadioSignal Processor Unit (SPU)
Slot 1Slot 2
Slot 3
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Slot 9 Slot 12
Microwave PrinciplesMegastar 155 Microwave RadioTransmitter Signal FlowTributary Interface Card
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Microwave PrinciplesMegastar 155 Microwave RadioTransmitter Signal FlowModulator Card
Slot 8 Slot 16
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Selects the active Tributary Interface Transmitter
Modulates 70 MHz Intermediate Frequency (IF) carrier
128 Quadrature Amplitude Modulation (QAM)
processes IF signal to transmitter (a part of the RFU assembly).
Houses digital to analog converter.
Two Fault Indicators and one connector
Fault LED indicates a fault or signal loss in the Modulator Unit
Active LED indicates Modulator is Active
IF carrier out SMA connector Tx 70 MHz IF carrier out to the RFU
Controlled and monitored through SPU controller.
Microwave PrinciplesMegastar 155 Microwave RadioTransmitter Signal FlowModulator Card
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RF Switch Assembly
Heterodynes the 70 MHz IF carrier frommodulator and signal from LO together toproduce double sideband signal.
Passes upper or lower side band signaland RF carrier signal to RF switchassembly. Upper or lower sideband signal
feeds through sideband select f ilter. (Thisfilter passes only desired RF signal topower amplifier.)
RF Out
IF in
Microwave PrinciplesMegastar 155 Microwave RadioTransmitter Signal FlowRadio Frequency (RF) Switch
RF In
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Part of the Power Amplifier assembly located in the power amplifier
Controls the status and communications task for the RFU through the controller located in the SPU.
Provides monitoring of the RFU assembly through the controller assembly in theSPU
Supplies DC power for all associated RFU modules.
Transmitter Assembly
Receiver Assembly
Microwave PrinciplesMegastar 155 Microwave RadioTransmitter Signal FlowRadio Frequency Unit Controller
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Filters and routes RF signals from transmitter power amplifier to antenna port.
Single Power Amplifier Antenna Coupler Unit
Antenna Coupler Unit
Microwave PrinciplesMegastar 155 Microwave RadioTransmitter Signal Flow
Antenna Coupler Unit
Dual Power Amplifier
Two Types of Transmitter
Power output configurations
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Provides DC Power to transmitter, receiver, and RFUcontroller
Consists of power amplifier subassembly, RF controller and bias card.
Provides RF amplification of the IF signal.
ATPC - Automatic Transmitter Power Control.
RF Out
RF In
Power Switch
Fault LED
Active LED
Microwave PrinciplesMegastar 155 Microwave RadioTransmitter Signal FlowSingle Power Amplifier Configuration
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Provides DC Power to transmitter, receiver, and RFUcontroller
Consists of power amplifier subassembly, RFcontroller and bias card.
Provides RF amplification of the IF signal.
ATPC - Automatic
RF Out
RFIn
Power Switch
Fault LED
Active LED
Transmitter
Power ControlMicrowave PrinciplesMegastar 155 Microwave RadioTransmitter Signal FlowDual Power Amplifier Configuration
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Single Power Amplifier Antenna Coupling Unit
Filters and routes RF signals from transmitter power amplifier to antenna port.
Dual Power Amplifier Antenna Coupling Unit (ACU)
Filters and routes RF signals from transmitter power amplifier to antenna port.
If needed power is boosted from the second power amplifier in the configuration
Microwave PrinciplesMegastar 155 Microwave RadioTransmitter Signal Flow
Antenna Coupler Unit
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Antenna SystemSpace Diversity (only for receiver)
Waveguide
The antenna transfers the Radio Frequencyfrom the transmitter module and receiver module.
Microwave PrinciplesMegastar 155 Microwave Radio
Antenna Signal Flow
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Couples RF signal from antenna to low noise converter
Microwave PrinciplesMegastar 155 Microwave RadioReceive Signal Flow
Antenna Coupling Unit
Low Noise Converter
Phase Lock Source
IF filter/amplifier
Receiver Assembly
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Low Noise Converter (LNC)
Amplifies received signal from ACU
Mixes received signal with local oscillator frequency
The LNC processes the data to the IF amplifier wherethe 70 MHz IF carrier is separated from the RF
Microwave PrinciplesMegastar 155 Microwave RadioReceive Signal FlowRadio Frequency Unit
RF in
Fault Indicator
Low Noise Converter
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provides constant output /selectivity level approximately 7db lower than receiver power
Improves delay and equalization with AGC current.
IF Amplifier Fault
Microwave PrinciplesMegastar 155 Microwave RadioReceive Signal FlowIntermediate Frequency (IF) Amplifier
IF out
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Slope equalizes received 70 MHz IF carrier from RFU.Demodulates IF carrier information into digitized symbols (analog to digital converter).
Recovers clock from received signal.
Controlled and monitored by SPU.
Notegeneric class for demodulators .
A demodulator is a device which extracts arbitrarily varying information from a signal formed by varying a characteristic of
a repetitious electrical or electromagnetic wave of less than infrared frequency. Classification herein is broadly by thetype of modulation exhibited by the input signal.
Microwave PrinciplesMegastar 155 Microwave RadioReceive Signal FlowDemodulator
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Slot 6 Slot 15
Microwave PrinciplesMegastar 155 Microwave RadioReceive Signal FlowDecoder
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Decodes the demodulated digital data QAM In-Phase and Quadrature signals
Controls the demodulator card Voltage Controlled Oscillator (VCO)
Provides error correction based on Forward Error Correction (FEC) technology
Controlled and monitored by SPU controller
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Provides physical connection multi-mode fiber OC-3 connectivity.
Recovers clock pulse of the incoming signal.
Switches receivers errorless using DADE Differential Absolute Delay Equalization circuitry
The SPU one unit in a non-protected and two units in a protected configuration
Three fault indicatorsFault LED indicates a fault
Transmitter (Tx) LED indicates active transmitter
Receive (Rx) LED indicates active receiver
The tributary Interface Unit is controlled and monitored via the SPU Controller
NOTE
The Transmit and Receive indicators do not have to be on the same Tributary Indicator Card
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Slot 4 Slot 17
Microwave PrinciplesMegastar 155 Microwave RadioDC to DC converter
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Requires + 24 volts DC to + 48 volts DC from proper power source.Unit provides +12 VDC, -12 VDC and +5.2 VDC (regulated voltage) for SPU circuit card operation.
Standard power source
- 56 VDC to - 21 VDC or + 56 VDC to +21 VDC (with respect to ground).
USFK Digital Microwave Radio uses -48 Volts DC
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Slot 10
Microwave PrinciplesMegastar 155 Microwave RadioController Card
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Monitors alarms and status of SPU shelf Provides control for transmitter/receiver switching
Stores and runs Megastar processor information
With loss of SPU Controller card
Process 90% of incoming traffic
Loses automatic switching capabilities
One Controller card per system (no redundancy)
Microwave PrinciplesMegastar 155 Microwave RadioController Card
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Farscan /NETBOSS (formerly Star Scan) diagnostic utility programTNOSC (Camp Walker) uses NETBOSS at monitor console for monitoring and diagnostic testing
MST uses Farscan loaded on laptop for local diagnostic testing
64 KBPS allocated for overhead as F1 channel used for monitoring Megastar 155 Microwave Radiosystem through out South Korea
Security levels 0 through 7 determine type and number of manual commands available at each site -level determined by Master Farscan Administrator
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Module fault indicator guideBlinking red - loss of signal prior to output signalSteady red - probable fault at observed indicator signalGreen - Signal is good at module
Microwave PrinciplesMegastar 155 Microwave RadioSystem Maintenance
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Monitored and supervised via Farscan (Local Diagnostics) and NETBOSS (Remote Diagnostic) software.Remote monitoring by TNOSC at Camp Walker.Trouble isolation
When necessary performed by MST through laptop computer connection.
Megastar Microwave radio automatically switches after fault detection the following sub systems:Transmitter Receiver
No calibration or testing required after replacement of defective parts or defective units (modules).
Microwave PrinciplesMegastar 155 Microwave RadioSystem Maintenance
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Microwave PrinciplesMegastar 155 Microwave RadioSimplified Overall Block Diagram (final)
Antenna
ATM36170
ATM36170
Signal Processor Unit
TributaryInterface
Demodulator/Decoder
Antenna
Modulator
O&MInterface
O&M Conversion
SupervisionControl
DC to DCConversion
Power Interface
Power Interface
DC to DCConversion
O&M Conversion
SupervisionControlO&MInterface
ANTENNA COUPLINGUNIT (ACU)
RF InRF Out
RECEIVER A/B
Transmitter A/B
RADIO FREQUENCY UNIT(RFU)
70 MHz IF
RF Out
RF InRF Out
RECEIVER A/B
Transmitter A/B
RADIO FREQUENCY UNIT(RFU)
Signal Processor Unit Demodulator/
Decoder
TributaryInterface
ANTENNA COUPLINGUNIT (ACU)
Transmit frequency+
70 Mhz
70 MHz IF
Receive Frequency+
70 Mhz
RF OutRF In
Transmit Frequency+
70 Mhz
Receive frequency+
70 Mhz
W a v e
G u i
d e
70 MHz IF70 MHz IF
Modulator
W a v e
G u i
d e
RF In
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Microwave PrinciplesMegastar 155 Microwave RadioOverall Block Diagram
TributaryInterface Unit
Supervision Channel
LineUnit
DC to DC conversion
O&M Interface
Power Interface
MicrowaveFrameMultiplexing
Service Channel
Microwave
FrameDe-Multiplexing
Modulation
Rx IF
Tx IF
From/To Antenna
Cable In
ter f ace
Service Channel
De-Modulation
Cr oss Connects
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Microwave PrinciplesQuestions
What types are microwave equipment classified into?
What are the key specifications of the microwave radio signal processing unit (sometimes called the baseband module)?
What are the key specifications of the microwave radio transmitter and receiver ?
What are the key specifications of the antenna coupling unit?
Can you describe the entire signal flow of a microwave transmission?
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Microwave PrinciplesSummary
Classification of digital modules in microwave equipment
Components of microwave equipment and their functions
Antenna installation and key specifications of antennas
Functional modules of basic microwave radio
Signal flow of microwave transmission
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Microwave PrinciplesContentsModule 3
Digital Microwave Networking and Application
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Relay Station
Terminal Station
Terminal Station
Terminal Station
Pivotal Station
ADD-DROPRelay Station
Microwave PrinciplesRelay Stations 1Types of Digital Microwave
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Microwave PrinciplesRelay Station 2Types
Terminal Station
Terminal Station
Terminal Station
Relay Station
Pivotal Station
ADD/DROPRelay Station
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Microwave PrinciplesRelay Stations 3Types
Relay Station
Passive
Active
RF Repeater
RegenerativeRepeater
IF Repeater
Back to back AntennaPlane
Reflector
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Active - bi-directional - without frequency shift.
Directly amplifies the signal over radio frequency.
Microwave PrinciplesRelay Station 4
Active Relay Station
The regenerator relay station is used to extend the transmission distance of microwave communicationsystems, or to deflect the transmission direction of the signal to avoid obstructions and ensure the signalquality is not degraded. After complete generation and amplification, the received signal is forwarded
Regenerator Relay Station
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Microwave PrinciplesRelay Station 5
Active Relay Station
PassiveStation
Special Meters are necessary to adjust antennas, (is time consuming)
Near end is less than 5 km away
Parabolic reflector passive relay stationComposed of two parabolic antennas connected by a soft waveguide back to back
Often uses large-diameter antennas
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Passive Relay Station
Microwave PrinciplesRelay Station 6Plane Reflector Passive Relay Station
Metal board having smooth surface, proper effective area, proper angle and distancewith two communication points
Two Communication PortsTwo Communication Points
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Passive Relay Station - Plane Reflector Passive Relay Station - Parabolic Antenna
Microwave PrinciplesRelay Station 7Passive Relay (Photos)
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Microwave Principles Application of Digital Microwave
BTS BackhaulTransmission
Complementarynetworks to opticalnetworks, (accessnetworks from the
last 1km)Special
transmissionConditions
Rivers, lakes,
islands, etcMicrowave
Applications
Redundancy backup of important links
VIP Customer Access
EmergencyCommunications
conventions,activities, danger
elimination, disaster relief, etc.
BTS BackhaulTransmission
Complementarynetworks to opticalnetworks, (accessnetworks from the
last 1km)
Special transmissionConditions Rivers,lakes, islands, etc
Microwave Applications
VIP Customer Access
Redundancy backup of important links
EmergencyCommunications
conventions,activities, danger
elimination, disaster
relief, etc
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What networking modes are frequently used for digital microwave?
What are the types of digital microwave stations?
What are the types of relay stations?
What is the major application of digital microwave?
Microwave PrinciplesQuestions
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Microwave PrinciplesModule 4
Microwave Propagation and Anti-fading Technologies
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Microwave PrinciplesContents
Microwave Propagation and Anti-fading Technologies
4.1 Factors Affecting Electric Wave Propagation
4.2 Various Fading in Microwave Propagation
4.3 Anti-fading Technologies for Digital Microwave
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Microwave PrinciplesContents
Microwave Propagation and Anti-fading Technologies
4.1 Factors Affecting Electric Wave Propagation
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RT
P
Microwave PrinciplesParameters in Microwave PropagationParameters 1
Fresnel Zone - Fresnel Zone Radius
The elliptical region encircled by the trail of P is called Fresnel zone
Fresnel zone radius: Vertical distance from P to the TR line is the first Fresnel zone radius represented by F n (n=1).
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Microwave PrinciplesParameters in Microwave PropagationParameters 2Fresnel Zone - 2
F r e s n e l
Z o n e
Total Distance
A n t e n n a
H e i g h
t
E a r
t h C u r v a
t u r e
O b s t r u c
t i o n s
98
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Microwave PrinciplesMicrowave PropagationParameters 2Fresnel Zone - 3
Along the microwave propagation trail, obstruction from buildings, trees, and mountain peaks issometimes inevitable.
If the height of the obstacle enters the first Fresnel zone, additional loss might be caused.
The received level is decreased and the transmission quality is affected. Clearance is used to avoid thecase described previously
The vertical distance from the obstacle to AB line segment is called the clearance of the obstacle on thetrail. For convenience, the vertical distance h c from the obstacle to the ground surface is used to representthe clearance.
In practice, the error is not big because the line segment AB is approximately parallel to the groundsurface. If the first Fresnel zone radius of the obstacle is F 1, then h c / F1 is the relative clearance
h1
h0
A B
hc h s
d1 d2d
h0
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Smooth ground or water surface can reflect part of the signal energy transmitted by the antenna to thereceiving antenna and cause interference to the main wave(direct wave).
The vector sum of the reflected wave and main wave increases or decreases the composite wave.
As a result, the transmission becomes unstable, therefore in microwave link design, avoid reflected wavesas much as possible
If reflection is inevitable, make use of the terrain ups and downs to block the reflected waves
Microwave PrinciplesWave PropagationFactors Affecting - ElectricTerrain
0
Micro a e Principles
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Passive Relay Station
Microwave PrinciplesRadio Frequency Relay StationPlane Reflector Passive Relay Station
Metal board having smooth surface, proper effective area, proper angle and distancewith two communication points
Two Communication PortsTwo Communication Points
1
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Different reflection conditions of different terrains have different effects on electric wave propagation.Terrains are classified into the following four types:
Type A mountains (or cities with dense buildings)Type B hills (gently wavy ground surface)Type C plains (flat Land)Type D large-area water surface
The reflection coefficient of mountains is the smallest, and thus the mountain terrain is most suitable for microwave transmission. The hill terrain is less suitable. When designing circuits, try to avoid smooth planesuch as water surface
Microwave PrinciplesWave PropagationFactors Affecting ElectricTerrain 2
2
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The troposphere indicates the low altitude atmosphere within 10 km from the ground, microwave antennaswill not be higher than the troposphere, so the electric wave propagation in aerosphere can be narrowedthat in the troposphere. Main effects of the troposphere on electric wave propagation are listed below:
Absorption caused by gas resonance. This type of absorption can affect microwave radiation at 12 GHz or higher.
Absorption and scattering caused by rain, fog, and snow. This type of absorption can affect the microwave radiation at 10GHz or higher.
Refraction, absorption, reflection and scattering caused by homogeneity of atmosphere. Refraction is the most significant
impact to microwave radiation and propagation
Microwave PrinciplesWave PropagationFactors Affecting Electric
Atmosphere
3
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4.2 Various FadingTypes in Microwave Propagation
Microwave PrinciplesMicrowave PropagationFading
4
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Microwave PrinciplesMicrowave Propagation
Anti-Fading Technologies 8Frequency Diversity
Signals at different frequencies have different fading characteristics Accordingly, two or more microwavefrequencies with certain frequency spacing to transmit and receive the same information is then selected or
composed to reduce the influence of fading. This work mode is called frequency diversity.
Advantage The effect is obvious. Only one antenna is required.Disadvantage The utilization ratio of frequency bands is low
Apart from the anti-fading technologies introduced previously, a frequently used tips:Make use of some terrain and ground objects to block reflected waves
f1
f2
5
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Microwave PrinciplesMicrowave Propagation
Anti-Fading Technologies - 9Space Diversity
Signals have different multipath effect over different paths and thus have different fading characteristics. Accordingly, two or more suites of antennas a to different altitude levels to receive the signals at the samefrequency which are composed or selected. This work mode is called space diversity. If there are in pairs
of antennas, it is called n-fold diversity. Advantage The frequency resources are saved.Disadvantage The equipment is complicated, as two or more suites of antennas are required.
Antenna distance, the distance between the diversity antennas is 100 to 200 times the wavelength infrequently used frequency bands
Apart from the anti-fading technologies introduced previously, a frequently used tips:high and low antennas
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Importance parameters affecting microwave propagation.
Various factors affecting microwave propagation.
Various fading types in the microwave propagation (free space propagation fading, atmosphericabsorption fading, rain or fog scattering fading, K type fading, multipath fading, duct type fading, andscintillation type fading).
Anti-fading technologies.
Anti-fading measures adopted on the equipment: adaptive equalization, and ATPC.
Anti-fading measures adopted in the system.
Microwave PrinciplesMicrowave PropagationPropagation and Anti-Fading TechnologiesSummary
8
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What networking modes are frequently used for digital microwave?
What are the types of digital microwave stations?
What are the types of relay stations?
What is the major application of digital microwave?
Questions9
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Microwave Principles
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Microwave PrinciplesContents
Microwave Propagation and Anti-fading Technologies
4.1 Factors Affecting Electric Wave Propagation
4.2 Various Fading in Microwave Propagation
4.3 Anti-fading Technologies for Digital Microwave
1
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Microwave PrinciplesContents
Microwave Propagation and Anti-fading Technologies
4.1 Factors Affecting Electric Wave Propagation
2
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RT
P
pParameters in Microwave PropagationFresnel Zone - 1Fresnel Zone - Fresnel Zone Radius
The elliptical region encircled by the trail of P is called Fresnel zone
Fresnel zone radius: Vertical distance from P to the TR line is the first Fresnel zone radius represented by F n (n=1).
3
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p gFresnel Zone - 2
F r e s n e l
Z o n e
Total Distance
A n t e n n a
H e i g h
t
E a r
t h C u r v a
t u r e
O b s t r u c
t i o n s
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pParameters in Microwave Propagation Fresnel Zone - 3
Along the microwave propagation trail, obstruction from buildings, trees, and mountain peaks issometimes inevitable.
If the height of the obstacle enters the first Fresnel zone, additional loss might be caused.
The received level is decreased and the transmission quality is affected. Clearance is used to avoid thecase described previously
The vertical distance from the obstacle to AB line segment is called the clearance of the obstacle on thetrail. For convenience, the vertical distance h c from the obstacle to the ground surface is used to representthe clearance.
In practice, the error is not big because the line segment AB is approximately parallel to the groundsurface. If the first Fresnel zone radius of the obstacle is F 1, then h c / F1 is the relative clearance
h1
h0
AA
B
hc h s
d1 d2d
h0
Microwave PrinciplesF Aff i El i W P i
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Smooth ground or water surface can reflect part of the signal energy transmitted by the antenna to thereceiving antenna and cause interference to the main wave(direct wave).
The vector sum of the reflected wave and main wave increases or decreases the composite wave.
As a result, the transmission becomes unstable, therefore in microwave link design, avoid reflected wavesas much as possible
If reflection is inevitable, make use of the terrain ups and downs to block the reflected waves
Factors Affecting Electric Wave PropagationTerrain
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Microwave PropagationFading
Fading: Random variation of the received level. Thevariation is irregular and the reasons for this arevarious.
Fading Mechanics Fading Time Received LevelInfluence of
Fading on Signal
Pr opoga
tion Fading
Fr ee Space
Absor pt
ioN
Fading
Rain
Fading
F
ading
Scintillation
K Typ
e Fading
Duct T
ype Fading
Fast Fading
Slow
Fading
Up
Fading
Down Fading
Flat
Fading
Fading
Selective Fr equency
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Microwave PropagationFading
Free space loss: A = 92.4 + 20 log d + 20 log f d - diameter f - frequency If d or f is doubled, the loss will increase by 6 dB
P T x = Transmit power P R x = Receive power G = Antenna Gain
AO = Free Space LossM = Pading Margin
M
G
G
G Tx G Rx d
f
Power
Level
P Rx
Receiver Threshold
Antenna Antenna
Distance
P Tx
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Microwave Propagation Absorption Fading
Molecules of all substances are composed of charged particles. Particles have their own electromagnetic resonant frequencies. When microwave frequencies of substances are close to resonance frequencies - resonance absorption occurs to themicrowave.
Statistics shows absorption to microwave frequencies lower than 12GHz is smaller than 0.1 dB/km.
Compared with free space loss, the absorption loss can be ignored.10 db
1 db
0.01 db
60 GHz 23 GHz 12 GHz 7.5 GHz 1.0 GHz
.1 db
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For frequencies lower than 10 GHz, rain loss can be ignored minimal db may be added to a relay section.
For frequencies higher than 10 GHz, repeater spacing is mainly affected by rain loss. For example 13 GHzfrequency or higher 100mm/h rainfall will causes a loss of 5 dB/km. Hence for the 13 GHz and 15 GHzfrequencies the maximum relay distance is about 10 km. For the 20 GHz frequency and higher the relaydistance is limited to one or two kilometers due to rain loss.
High microwave radio frequency bands can be used for user-level transmission. The higher the frequency bandis, the more severe the rain fading is.
Microwave PropagationRain Fading
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Atmosphere refraction
As a result of atmosphere refraction, the microwave propagation trail is bent. It is considered that theelectromagnetic wave is propagated along a straight line above the earth with an equivalent earth radiusof , = KR (R: actual earth radius.)
The average measured K value is about 4/3. However, the K value of a specific section is related to themeteorological phenomena of the section. The K value may change within a comparatively large range. This canaffect line-of-sight propagation.
R e
R e Rx
R e
Microwave PropagationK Type Fading - 1
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Atmosphere refraction
As a result of atmosphere refraction, the microwave propagation trail is bent. It is considered that theelectromagnetic wave is propagated along a straight line above the earth with an equivalent earth radiusof , = KR (R: actual earth radius.)
The average measured K value is about 4/3. However, the K value of a specific section is related to themeteorological phenomena of the section. The K value may change within a comparatively large range. This canaffect line-of-sight propagation.
Microwave PropagationK Type Fading - 1
R e
R e
Rx
R e
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k =
43
1
Ground surface Actual Earth Radius (r)
1
43
k =
Equivalent Earth Radius (r) 23
23
In temperate zones the refraction when the K value is 4/3 is referred as a standard atmosphere, and R e whichis 4/3 is the standard.
Microwave PropagationK Type Fading - 2Equivalent Earth Radius
43
1
23
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k > 1: Positive refraction
k = 1: No refraction
k < 1: Negative refraction
K Type Fading - 2
Microwave PrinciplesMicrowave PropagationMultipath Fading 1
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Multipath fading is caused by multipath propagation of refracted waves, reflected waves, scattered waves,
and multiple electric waves which are received at the receiving end. The composition of these electricwaves will result in severe interference fading.
Down fading - the composite wave level is lower than the free space received level.Up fading - the composite wave level is higher than the free space received level.
Reasons for multipath fading are reflections due to non-uniform atmosphere, water surface and smoothground surface.
Non-uniform atmosphere
Water surface
Smooth ground surface .
Ground Surface
Multipath Fading - 1
Antenna Antenna
Ground Wave
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Normal
FlatSelectivity Fading
Frequency (MHz)
Microwave PropagationMulti Path - Frequency Selective Fading
Multipath fading frequency selective fadingType of interference fading caused by multipath transmission. Multipath fading is caused by mutual interference between the directwave and reflected wave (or diffracted wave on some conditions) with different phases
Grows more severe when waves pass over water surfaces or smooth ground surfaces. When designing the route, try to avoidsmooth water and ground surface. When these terrains are inevitable use the high and low antenna technologies to bring thereflection point closer to one to reduce the impact of the reflected wave.
Use the high and low antennas and space diversity technologies, or the antennas that pointed away from reflectedwaves to overcome multipath fading.
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UpFading
SignalInterruption
ReceivedLevel in Free
Space
Threshold Level(-30 db)
1h
Microwave PropagationMulti Path - Flat Fading
Multi Path - Flat Fading
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Duct FadingDue to the effects of meteorological conditions such as
ground cooling in the night,burnt warm by the sun in the morning,smooth sea surface,anticyclone a non-uniform structure is formed in atmosphere.
This phenomenon is called atmospheric ducting.If microwave beams pass through the atmospheric duct while the receiving point is outside the ductlayer, the field strength at the receiving point is from not only the direct wave and the reflected
ground wave, but also the reflected wave from the edge of the duct layer. As a result, severeinterference fading occurs and causes interruption to the communications
Scintillation FadingScintillation fading is a type of fast fading which lasts a short time. The level changes little and themain wave is barely affected. Scintillation fading will not cause communications interruption.
When the dielectric constant of local atmosphere is different from the ambient atmosphere due to theparticle clusters formed under different
pressure,temperaturehumidity
NOTEScattering occurs to the electric wave. This is called scintillation fading. The amplitude and phase of different scattered waves vary with the atmosphere. As a result, the composite field strength at thereceiving point changes randomly.
Microwave PropagationDuct and Scintillation Fading
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Microwave PropagationScintillation and Duct Fading
Duct Fading
Scintillation Fading
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Microwave PropagationSummary
The higher the frequency is and the longer the hop distance is, the more severe the fading is.
Fading is more severe at night than in the day, in summer than in winter. In the day, sunshine is goodfor air convection. In summer weather changes frequently.
In sunny days without wind, atmosphere is non-uniform and atmosphere subdivision easily formsand hardly clears. Multipath transmission often occurs in such conditions.
Fading is more severe along water routes than land routes, caused by the reflection coefficient of water surface and the atmospheric refraction coefficient above water surface.
Fading is more severe along a plain (flat land) route than a mountain route, the atmospheresubdivision often occurs over the plain and the ground reflection factor of the plain is bigger.
Weather - rain and fog influences microwave frequencies.
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4.3 Anti-fading Technologies for Digital Microwave
Microwave Propagation Anti-Fading Technologies
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The frequency domain equalization only equalizes the amplitude frequency response characteristics of thesignal not the phase frequency spectrum characteristics .
Frequency domain equalization
Microwave Propagation Anti-Fading Technologies 2
SignalFrequencySpectrum
FrequencySpectrum After
EqualizationMultipath
Fading
SlopeEqualization
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T T
Before
After
-2Ts -Ts -2Ts
Ts Ts -Ts
Cn Co
Microwave Propagation Anti-Fading Technologies 3
T
Frequency domain equalizationTime domain equalization directly counteracts the inter-symbol interference
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Automatic transmit power control (ATPC) under normal propagation conditions, the output power of the transmitter is always at a lower level, (for example 10 dB to 15 dB lower than the normal level.
When propagation fading occurs and the receiver detects the propagation fading is lower than theminimum received level specified by ATPC, the RFCOH is used allow the transmitter to raise thetransmit power Working principle of ATPC
ATPC
Receiver Demodulator
ATPC
Microwave Propagation Anti-Fading Technologies - 4
Transmitter
Receiver
ATPC
Demodulator
Receiver Demodulator
ATPC
Modulator
Modulator
Transmitter Modulator
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ATPCThe output power of the transmitter automatically traces and changes with the received level of thereceiver within the control range of ATPC
The time rate of severe propagation fading is usually small (
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For diversity, two or multiple transmission paths are used to transmit the same information and the receiver output signals are selected or composed, to reduce the effect of fading.
Diversity has the following types, space diversity, frequency diversity, polarization diversity, and anglediversity.
Space diversity and frequency diversity are more frequently used. Space diversity is economical and has agood effect. Frequency diversity is often applied to multi-channel systems as it requires a wide bandwidth.Usually, the system that has one standby channel is configured with frequency diversity
H f 2
f 1
Anti-Fading Technologies 7Diversity
Space Diversity (SD)
f 1
f 2
Frequency Diversity (FD)
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4.3 Anti-fading Technologies for Digital Microwave
Microwave Propagation and Anti-Fading Technologies
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Digital Microwave Radio1+1 Hot Stand By configuration
Space Diversity technologies - the configuration of two antennas,
Adopted which improving system availability.
gEquipment Protection 1
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N+1 (N3, 7, 11) ProtectionIn the following figure, M n stands for the active channel and P stands for the standby channel. The active channel and thestandby channel have their independent modulation/demodulation unit and signal transmitting/receiving unit.
When the fault or fading occurs in the active channel, the signal is switched to the standby channel. The channel backupis an inter-frequency backup. This protection mode (FD) is mainly used in the all indoor microwave equipment.
RFSOH
Ch1 Ch2 Ch3
Cp Cp
Ch3 Ch2 Ch1
Products of different vendors support different specifications
gEquipment Protection Modes 2
Switching ControlUnit
Switching ControlUnit
Switching ControlUnit
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Configuration Protection Mode Remarks Application
1 + 0 NP Non-Protection Terminal of the Network
1 + 1 FD Channel Protection Inter-Frequency
Select the proper Mode depending onthe Geographical Conditions andRequirements of the Customer
1 + 1 SD Equipment andChannel Protection
Inter-Frequency
1 + 1 FD + SD Equipment andChannel Protection
Inter-Frequency
M + n FD Equipment andChannel Protection
Inter-Frequency
Large Capacity Backbone
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Importance parameters affecting microwave propagation.
Various factors affecting microwave propagation.
Various fading types in the microwave propagation (free space propagation fading, atmosphericabsorption fading, rain or fog scattering fading, K type fading, multipath fading, duct type fading, andscintillation type fading).
Anti-fading technologies.
Anti-fading measures adopted on the equipment: adaptive equalization, and ATPC.
Anti-fading measures adopted in the system.
Propagation and Anti-Fading TechnologiesSummary