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Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Digital Microwave Communication Principles
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 2Page 2
Foreword
This course is developed to meet the requirement of Huawei
Optical Network RTN microwave products.
This course informs engineers of the basics on digital microwave
communications, which will pave the way for learning the RTN
series microwave products later.
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 3Page 3
Learning Guide
Microwave communication is developed on the basis of the
electromagnetic field theory.
Therefore, before learning this course, you are supposed to have
mastered the following knowledge:
Network communications technology basics
Electromagnetic field basic theory
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 4Page 4
ObjectivesObjectives
After this course, you will be able to explain:
Concept and characteristics of digital microwave communications
Functions and principles of each component of digital microwave
equipment
Common networking modes and application scenarios of digital
microwave equipment
Propagation principles of digital microwave communication and
various types of fading
Anti-fading technologies
Procedure and key points in designing microwave transmission link
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 5Page 5
Contents
1. Digital Microwave Communication Overview
2. Digital Microwave Communication Equipment
3. Digital Microwave Networking and Application
4. Microwave Propagation and Anti-fading Technologies
5. Designing Microwave Transmission Links
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 6Page 6
Transmission Methods in Current Communications Networks
Optical fiber communication
Microwave communication
Satellite communication
MUX/DEMUX MUX/DEMUX
Micro
wave T
E
Micro
wave T
E
Coaxial cable communication
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 7Page 7
Microwave Communication vs. Optical Fiber Communication
Powerful space cross ability, little land occupied, not limited by land privatization
Optical fiber burying and land occupation required
Small investment, short construction period, easy maintenance
Large investment ,long construction period
Strong protection ability against natural disaster and easy to be recover
Outdoor optical fiber maintenance required and hard to recover from natural disaster
Limited frequency resources (frequency license required)
Large transmission capacityLimited transmission capacity
Not limited by frequency, license not required
Stable and reliable transmission quality and not affected by external factors
Transmission quality greatly affected by climate and landform
Microwave Microwave Communication Communication
Optical Fiber Optical Fiber CommunicationCommunication
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 8Page 8
Definition of Microwave Microwave
Microwave is a kind of electromagnetic wave. In a broad
sense, the microwave frequency range is from 300 MHz to
300 GHz. But In microwave communication, the frequency
range is generally from 3 GHz to 30 GHz.
According to the characteristics of microwave propagation,
microwave can be considered as plane wave.
The plane wave has no electric field and magnetic field
longitudinal components along the propagation direction. The
electric field and magnetic field components are vertical to
the propagation direction. Therefore, it is called transverse
electromagnetic wave and TEM wave for short.
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 9Page 9
Development of Microwave Communication
Note:
Small capacity: < 10M
Medium capacity: 10M to 100M
Large capacity: > 100M
155M
34/140M
2/4/6/8M
480 voice channels
SDH digital microwave communication
system
PDH digital microwave communication
system Small and medium
capacity digital microwave communication system
Analog microwave communication
system
Transmission capacity bit/s/ch)
1950s
1970s
1980s
Late 1990s to now
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 10Page 10
Concept of Digital Microwave Communication
Digital microwave communication is a way of transmitting digital
information in atmosphere through microwave or radio frequency (RF).
Microwave communication refers to the communication that use microwave as
carrier .
Digital microwave communication refers to the microwave communication that
adopts the digital modulation.
The baseband signal is modulated to intermediate frequency (IF) first . Then
the intermediate frequency is converted into the microwave frequency.
The baseband signal can also be modulated directly to microwave frequency,
but only phase shift keying (PSK) modulation method is applicable.
The electromagnetic field theory is the basis on which the microwave
communication theory is developed.
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 11Page 11
Microwave Frequency Band Selection and RF Channel Configuration (1)
Generally-used frequency bands in digital microwave transmission:
7G/8G/11G/13G/15G/18G/23G/26G/32G/38G (defined by ITU-R Recommendations)
85432 10
20
1 30
40
50
1.5 GHz
2.5 GHz
Long haul trunk
network2/8/34 Mbit/s
11 GHz
GHz
34/140/155 Mbit/s
2/8/34/140/155 Mbit/s
3.3 GHz
Regional network
Regional network, local network, and boundary
network
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 12Page 12
In each frequency band, subband frequency ranges, transmitting/receiving spacing (T/R spacing), and channel spacing are defined.
f0 (center frequency)
Frequency range
Channel
spacingf1
f2 fn f1’ f2
’ fn’
Channel spacing
T/R spacingT/R spacing
Low frequency band
High frequency band
Protection
spacing
Adjacent channel T/R
spacing
Microwave Frequency Band Selection and RF Channel Configuration (2)
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 13Page 13
Microwave Frequency Band Selection and RF Channel Configuration (3)
f0 (7575M)
Frequency range (7425M–7725M)
28M
f1=7442 f5f1
’=7596 f2’ f5
’
T/R spacing: 154M
f2=7470
7G
Frequency
Range
F0 (MHz) T/R Spacing (MHz)
Channel
Spacing (MHz)
Primary and
Non-primary
Stations
7425–7725 7575 154 28
Fn=f0-161+28n, Fn’=f0- 7+28n, (n: 1–5)
7575 161 7
7110–7750 7275 196 28
7597 196 28
7250–7550 7400 161 3.5
… … … … …
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 14Page 14
Digital Microwave Communication Modulation (1)
Digital baseband signal is the unmodulated digital signal. The baseband signal cannot be directly transmitted over microwave radio channels and must be converted into carrier signal for microwave transmission.
Digital baseband signal IF signal
Base
band sig
nal
rate
Channel b
andw
idth
Modulation
Service signal
transmitted
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 15Page 15
Digital Microwave Communication Modulation (2)
ASK: Amplitude Shift Keying. Use the digital baseband signal to change the carrier amplitude (A). Wc and φ remain unchanged.
FSK: Frequency Shift Keying. Use the digital baseband signal to change the carrier frequency (Wc). A and φ remain unchanged.
PSK: Phase Shift Keying. Use the digital baseband signal to change the carrier phase (φ). Wc and A remain unchanged.
QAM: Quadrature Amplitude Modulation. ). Use the digital baseband signal to change the carrier phase (φ) and amplitude (A). Wc remains unchanged.
A*COS(Wc*t+φ)
Amplitude
Frequency
Phase
PSK and QAM are most
frequently used in digital
microwave.
The following formula indicates a digital baseband signal being converted into a digital frequency band signal.
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 16Page 16
Microwave Frame Structure (1) RFCOH
RFCOH
ATPC64
kbit/s
DMY64
kbit/s
MLCM11.84 Mbit/s
RSC864
kbit/s
WS2.24
Mbit/s
XPIC16
kbit/s
ID32 kbit/s
INI144
kbit/s
FA288
kbit/s
15.552 Mbit/s
SOH Payload
STM-1 155.52 Mbit/s
171.072 Mbit/s
RFCOH: Radio Frame Complementary Overhead RSC: Radio Service ChannelMLCM: Multi-Level Coding Modulation INI: N:1 switching commandDMY: DummyID: IdentifierXPIC: Cross-polarization Interference CancellationFA: Frame AlignmentATPC: Automatic Transmit Power Control WS: Wayside Service
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 17Page 17
Microwave Frame Structure (2) RFCOH is multiplexed into the STM-1 data and a block multiframe is formed.
Each multiframe has six rows and each row has 3564 bits. One multiframe is
composed of two basic frames. Each basic frame has 1776 bits. The
remaining 12 bits are used for frame alignment.Multiframe 3564 bits
Basic frame 2
1776 bits (148 words)
FS
6
bits
Basic frame 1
1776 bits ( 148 words )
FS
6
bits
6 bits
C1IIC1IIC1IIC1II
C2IIbIIIIIIII
IIIIIIIIIIII
IIIIIIIIIIII
IIIIIIIIIIII
IIIIIIIIIIII
C1IIC1IIC1IIC1II
C2IIbIIaIIIII
IIIIIIIIIIII
IIIIIIIIIIII
IIIIIIIIIIII
IIIIIIIIIIII
12 bits (the 1st word) 12 bits (the 148th word)
I: STM-1 information bitC1/C2: Two-level correction coding monitoring bitsFS: Frame synchronization a/b: Other complementary overheads
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 18Page 18
Questions
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 frequently used modulation schemes? Which are the most frequently used modulation schemes?
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 19Page 19
Contents
1. Digital Microwave Communication Overview
2. Digital Microwave Communication Equipment
3. Digital Microwave Networking and Application
4. Microwave Propagation and Anti-fading Technologies
5. Designing Microwave Transmission Links
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 20Page 20
Microwave Equipment Category
System Digital microwave
PDH SDH
Split-mount radio
Trunk radio
All outdoor radio
Small and medium capacity (2–16E1,
34M)
Large capacity (STM-0, STM-1, 2xSTM-
1)Capacity
Structure
(Discontinued)
Analog microwave
MUX/DEMUX Mode
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 21Page 21
Trunk Microwave Equipment
• High cost, large transmission capacity, more stable performance, applicable to long haul and trunk transmission
• RF, IF, signal processing, and MUX/DEMUX units are all indoor. Only the antenna system is outdoor.
SDH microwave equipment
BRU: Branch RF Unit
MSTU: Main Signal Transmission Unit (transceiver, modem, SDH electrical interface, hitless switching)
SCSU: Supervision, Control and Switching Unit
BBIU: Baseband Interface Unit (option) (STM-1 optical interface, C4 PDH interface)
P
M1
M2
……
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 22Page 22
All Outdoor Microwave Equipment
• All the units are outdoor.
• Installation is easy.
• The equipment room can be saved.
All outdoor microwave equipment
IF and baseband processing unit
IF cable
RF processing unit
Service and power cable
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 23Page 23
Split-Mount Microwave Equipment (1) The RF unit is an outdoor unit
(ODU). The IF, signal processing,
and MUX/DEMUX units are
integrated in the indoor unit
(IDU). The ODU and IDU are
connected through an IF cable.
The ODU can either be directly
mounted onto the antenna or
connected to the antenna
through a short soft waveguide.
Although the capacity is smaller
than the trunk, due to the easy
installation and maintenance, fast
network construction, it’s the
most widely used microwave
equipment.
Split-mount microwave equipment
Antenna
ODU (Outdoor
Unit)
IF cable
IDU (Indoor Unit)
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 24Page 24
Split-Mount Microwave Equipment (2)
Unit Functions
Antenna: Focuses the RF signals transmitted by ODUs and increases the signal g
ain.
ODU: RF processing, conversion of IF/RF signals.
IF cable: Transmitting of IF signal, management signal and power supply of OD
U.
IDU: Performs access, dispatch, multiplex/demultiplex, and modulation/demod
ulation for services.
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 25Page 25
Split-Mount Microwave Equipment – Installation
antenna (separate mount)
ODU
IF cable
中频口
Separate Mount
Soft waveguide
IDU IF port
antenna (direct mount)
ODU
IDU
Direct Mount
IF cable
IF port
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 26Page 26
Microwave Antenna (1)
Antennas are used to send and receive microwave signals.
Parabolic antennas is common type of microwave antennas.
Microwave antenna diameters includes: 0.3m, 0.6m, 1.2m, 1.8m,2.0m, 2.4m, 3.0m,
3.2metc.
Parabolic antenna
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 27Page 27
Different frequency channels in same frequency band can share one antenna.
Microwave Antenna (2)
TxRx
TxRx
Channel
Channel
1
1
n
n
1
1
n
n
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 28Page 28
Antenna Adjustment (1)
Side view Side lobe
Main lobeHalf-power angle Tail lobe
Top view
Main lobe
Side lobe
Half-power angle Tail lobe
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 29Page 29
During antenna adjustment, change the direction vertically or horizontally. Meanwhile, use a multimeter to test the RSSI at the receiving end. Usually, the voltage wave will be displayed as shown in the lower right corner. The peak point of the voltage wave indicates the main lobe position in the vertical or horizontal direction. Large-scope adjustment is unnecessary. Perform fine adjustment on the antenna to the peak voltage point.
When antennas are poorly aligned, a small voltage may be detected in one direction. In this case, perform coarse adjustment on the antennas at both ends, so that the antennas are roughly aligned.
The antennas at both ends that are well aligned face a little bit upward. Though 1–2 dB is lost, reflection interference will be avoided.
Antenna Adjustment (2)Antenna Adjustment (2)
Side lobe position
AGCVoltage
detection point
VAGC
Main lobe position
Angle
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 30Page 30
Antenna Adjustment (3)Antenna Adjustment (3)
During antenna adjustment, the
two wrong adjustment cases are
show here. One antenna is aligned
to another antenna through the side
lobe. As a result, the RSSI cannot
meet the requirements.
CorrectWrongWrong
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 31Page 31
Split-Mount Microwave Equipment
– Antenna (1) Antenna gain
Definition: Ratio of the input power of an isotropic antenna Pio to the input power
of a parabolic antenna Pi when the electric field at a point is the same for the
isotropic antenna and the parabolic antenna.
Calculating formula of antenna gain:
Half-power angle
Usually, the given antenna specifications contain the gain in the largest radiation
(main lobe) direction, denoted by dBi. The half-power point, or the –3 dB point is
the point which is deviated from the central line of the main lobe and where the
power is decreased by half. The angle between the two half-power points is called
the half-power angle.
Calculating formula of half-power angle:
Half-power angle
D
)70~65( 005.0
2D
P
PG
i
io
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 32Page 32
Cross polarization discrimination
Suppression ratio of the antenna receiving heteropolarizing waves, usually, larger than 30 dB.
XdB = 10lgPo/Px
Po: Receiving power of normal polarized wave
Px: Receiving power of abnormal polarized wave
Antenna protection ratio Attenuation degree of the receiving capability in a direction of an antenna compared wi
th that in the main lobe direction. An antenna protection ratio of 180° is called front-to-back ratio.
Split-Mount Microwave Equipment – Antenna (2)
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 33Page 33
Split-Mount Microwave Equipment – ODU (1) ODU system architectureUplink IF/RF conversion
Frequencymixing
Sidebandfiltering
Poweramplification
RFattenuation
ATPCPower
detection
RF loop
Localoscillation
(Tx)
Localoscillation
(Rx)
Frequencymixing
FilteringLow-noise
amplificationBandpass
filtering
Alarm and control
Downlink RF/IF conversion
Supervision andcontrolsignal
IFamplificat
ion
IFamplification
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 34Page 34
Specifications of Transmitter
Working frequency band
Generally, trunk radios use 6, 7, and 8 GHz frequency bands. 11, 13 GHz and
higher frequency bands are used in the access layer (e.g. BTS access).
Output power
The power at the output port of a transmitter. Generally, the output power is
15 to
30 dBm.
Split-Mount Microwave Equipment – ODU (2)
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 35Page 35
Local frequency stability
If the working frequency of the transmitter is unstable, the demodulated effectived
signal ratio will be decreased and the bit error ratio will be increased. The value
range of the local frequency stability is 3 to 10 ppm.
Transmit Frequency Spectrum Frame
The frequency spectrum of the transmitted signal must meet specified
requirements, to avoid occupying too much bandwidth and thus causing too much
interference to adjacent channels. The limitations to frequency spectrum is
called transmit frequency spectrum frame.
Split-Mount Microwave Equipment – ODU (3)
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 36Page 36
Split-Mount Microwave Equipment – ODU (4) Specifications of Receiver
Working frequency band
Receivers work together with transmitters. The receiving frequency on
the local
station is the transmitting frequency of the same channel on the
opposite station.
Local frequency stability
The same as that of transmitters: 3 to 10 ppm
Noise figure
The noise figure of digital microwave receivers is 2.5 dB to 5 dB.
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 37Page 37
Passband
To effectively suppress interference and achieve the best transmission quality, the
passband and amplitude frequency characteristics should be properly chosen. The
receiver passband characteristics depend on the IF filter.
Selectivity
Ability of receivers of suppressing the various interferences outside the passband,
especially the interference from adjacent channels, image interference and the
interference between transmitted and received signals.
Automatic gain control (AGC) range
Automatic control of receiver gain. With this function, input RF signals change within a
certain range and the IF signal level remains unchanges.
Split-Mount Microwave Equipment – ODU (5)
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 38Page 38
Split-Mount Microwave Equipment – ODU (6)
ODU specifications are related to radio frequencies. As one ODU cannot cover an entire frequency band, usually, a frequency band will be divided into several subbands and each subband corresponds to one ODU. Different T/R spacing corresponds to different ODUs. Primary and non-primary stations have different ODUs.
Types of ODUs = Number of frequency
bands x Number of T/R spacing x Number of
subbands x 2(ODUs of some
manufacturers are also classified by capacity.
f0(7575M)
Frequency range (7425M–7725M)
Subband A
7442
T/R spacing: 154M
7498
Subband B
Subband C
Subband A
Subband B
Subband C
Non-primary station Primary station
ODUs are of rich types and small volume. Usually, ODUs are produced by small manufacturers and integrated by big manufacturers.
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 39Page 39
Split-Mount Microwave Equipment – IDU
Cable
inte
rface
From/to ODU
Tx IF
Rx IF
Modulation
Demodulation
Microwave frame
multiplexing
Microwave frame
demultiplexing
Cross-connection
Tributary unit
Line unit
IF unit
Service channel
Service channel
DC/DC conversion
Supervision and control
O&M interface
Power interface
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 40Page 40
Questions
What types are microwave equipment classified into?
What units do the split-mount microwave equipment have? And what are their functions??
How to adjust antennas?
What are the key specifications of antennas?
What are the key specifications of ODU transmitters and receivers?
Can you describe the entire signal flow of microwave transmission?
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 41Page 41
Summary
Classification of digital microwave equipment
Components of split-mount microwave equipment and
their functions
Antenna installation and key specifications of antennas
Functional modules and key performance indexes of ODU
Functional modules of IDU
Signal flow of microwave transmission
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 42Page 42
Contents
1. Digital Microwave Communication Overview
2. Digital Microwave Communication Equipment
3. Digital Microwave Networking and Application
4. Microwave Propagation and Anti-fading Technologies
5. Designing Microwave Transmission Links
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 43Page 43
Common Networking Modes of Digital Microwave
Ring network Chain network
Add/Drop network
Hub network
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 44Page 44
Types of Digital Microwave Stations
Terminal station
Terminal station
Terminal station
Pivotal station
Add/Drop relay
station
Relay station
• Digital microwave stations are classified into Pivotal stations, add/drop relay stations, relay stations and terminal stations.
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 45Page 45
Types of Relay Stations
Relay station
• Back-to-back antenna• Plane reflector
Active
Passive
• Regenerative repeater• IF repeater• RF repeater
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 46Page 46
Radio Frequency relay station An active, bi-directional radio repeater system without frequency shift. The RF relay station directly amplifies the signal over radio frequency.
Regenerator relay station A high-frequency repeater of high performance. The regenerator relay station is used to extend the transmission distance of microwave communication systems, or to deflect the transmission direction of the signal to avoid obstructions and ensure the signal quality is not degraded. After complete regeneration and amplification, the received signal is forwarded.
Active Relay Station
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 47Page 47
Parabolic reflector passive relay station The parabolic reflector passive relay station is composed of two parabolic antennas connected by a soft waveguide back to back. The two-parabolic passive relay station often uses large-diameter antennas. Meters are necessary to adjust antennas, which is time consuming. The near end is less than 5 km away.
Passive Relay Station
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 48Page 48
Plane Reflector Passive Relay Station
Plane reflector passive relay station: A metal board which has smooth surface, proper effective area, proper angle and distance with the two communication points. It is also a passive relay microwave station.
Full-distance free space loss:
“a” is the effective area (m2) of the flat reflector.
L d d as 1421 20 201 2. log log
a A cos 2
d1(km)
(km)d2
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 49Page 49
Passive Relay Station (Photos)
Passive relay station (plane reflector)
Passive relay station(parabolic reflectors)
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 50Page 50
Application of Digital Microwave
Complementary networks to optical networks (access the services from
the last 1 km)
BTS backhaul transmission
Redundancy backup of
important links
VIP customer access
Emergency communications
(conventions, activities, danger
elimination, disaster relief, etc.)
Special transmission conditions (rivers,
lakes, islands, etc.)
Microwave Microwave applicationapplication
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 51Page 51
Questions
What are the networking modes 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?
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 52Page 52
Contents
1. Digital Microwave Communication Overview
2. Digital Microwave Communication Equipment
3. Digital Microwave Networking and Application
4. Microwave Propagation and Anti-fading
Technologies
5. Designing Microwave Transmission Links
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 53Page 53
Contents
4. 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
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 54Page 54
Fresnel Zone and Fresnel Zone Radius Fresnel zone: The sum of the distance from P to T and the distance from P to R complies with the formula, TP+PR-TR= n/2 (n=1,2,3, …). The elliptical region encircled by the trail of P is called the Fresnel zone.
Key Parameters in Microwave Propagation (1)
ROT
P
F1
d2d1
Fresnel zone radius: The vertical distance from P to the TR line in the Fresnel zone. The first Fresnel zone radius is represented by F1 (n=1).
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 55Page 55
Formula of the first Fresnel zone radius:
Key Parameters in Microwave Propagation (2)
The first Fresnel zone is the region where the microwave transmission energy is the most concentrated. The obstruction in the Fresnel zone should be as little as possible. With the increase of the Fresnel zone serial numbers, the field strength of the receiving point reduces as per arithmetic series.
)()(
)()(32.17 21
1 kmdGHzf
kmdkmdF
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 56Page 56
Key Parameters in Microwave Propagation (3)
Clearance
Along the microwave propagation trail, the obstruction from buildings, trees, and mountain peaks is sometimes inevitable. If the height of the obstacle enters the first Fresnel zone, additional loss might be caused. As a result, the received level is decreased and the transmission quality is affected. Clearance is used to avoid the case described previously.
The vertical distance from the obstacle to AB line segment is called the clearance of the obstacle on the trail. For convenience, the vertical distance hc from the obstacle to the ground surface is used to represent the clearance. In practice, the error is not big because the line segment AB is approximately parallel to the ground surface. If the first Fresnel zone radius of the obstacle is F1, then hc/ F1 is the relative clearance.
A
Bh1
h2
dd1 d2
hphc
hs
M F
h3
h4
h5
h6
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 57Page 57
Factors Affecting Electric Wave Propagation – Terrain
The reflected wave from the ground surface is the major factor that affects the received level.
Smooth ground or water surface can reflect the part of the signal energy transmitted
by the antenna to the receiving 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, when doing microwave link design, avoid reflected waves as much as
possible. If reflection is inevitable, make use of the terrain ups and downs to block the
reflected waves.
Straight line
Reflection
Straight line
Reflection
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 58Page 58
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: plain 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 plane such as water surface.
Factors Affecting Electric Wave Propagation – Terrain
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 59Page 59
Troposphere indicates the low altitude atmosphere within 10 km from the ground. Microwave antennas will not be higher than troposphere, so the electric wave propagation in aerosphere can be narrowed down to that in troposphere. Main effects of troposphere on electric wave propagation are listed below:
Absorption caused by gas resonance. This type of absorption can affect the microwave at 12 GHz or higher.
Absorption and scattering caused by rain, fog, and snow. This type of absorption can affect the microwave at 10 GHz or higher.
Refraction, absorption, reflection and scattering caused by inhomogeneity of atmosphere. Refraction is the most significant impact to the microwave propagation.
Factors Affecting Electric Wave Propagation – Atmosphere
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 60Page 60
Contents
4. 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
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 61Page 61
Fading in Microwave Propagation
Fading mechanis
m
Abso
rptio
n fa
din
g
Rain
fadin
g
Scin
tillatio
n
fadin
g
K-ty
pe
fadin
g
Duct ty
pe fa
din
g
Fading time
Received level
Influence of fading on
signal
Fast fa
din
g
Slo
w fa
din
g
Up fa
din
g
Dow
n
fadin
g
Fla
t fadin
g
Fre
quency
sele
ctive
fadin
g
Fre
e sp
ace
pro
pagatio
n fa
din
g
Fading: Random variation of the received level. The variation is irregular and the reasons for this are various.
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 62Page 62
Free Space Transmission Loss
Free space loss: A = 92.4 + 20 log dd + 20 log ff
(d: d: km, f: GHz). If d or f is doubled, the loss will increase by 6 dB.
Power level
PTX = Transmit power
G = Antenna gain
A0 = Free space loss
M = Fading margin
PTX
Distance
GTX GRX
PRX
A0
MReceiving threshold
G
d
G
f
PRX = Receive power
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Absorption Fading
Molecules of all substances are composed of charged particles. These particles have their own electromagnetic resonant frequencies. When the microwave frequencies of these substances are close to their resonance frequencies, resonance absorption occurs to the microwave. Statistic shows that absorption to the microwave frequency lower than 12 GHz is smaller than 0.1 dB/km. Compared with free space loss, the absorption loss can be ignored.
Atmosphere absorption curve (dB/km)1GHz7.5GHz12GHz23GHz60GHz
0.01dB
10dB
1dB
0.1dB
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For frequencies lower than 10 GHz, rain loss can be ignored. Only a few db may be added to a relay section.
For frequencies higher than 10 GHz, repeater spacing is mainly affected by rain loss. For example, for the 13 GHz frequency or higher, 100 mm/h rainfall
causes a loss of 5 dB/km. Hence, for the 13 GHz and 15 GHz frequencies,
the maximum relay distance is about 10 km. For the 20 GHz frequency and
higher, the relay distance is limited in few kilometres due to rain loss.
High frequency bands can be used for user-level transmission. The higher the frequency band is, the more severe the rain fading.
Rain Fading
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Atmosphere refraction As a result of atmosphere refraction, the microwave propagation trail
is bent. It is considered that the electromagnetic wave is propagated
along a straight line above the earth with an equivalent earth radius of
, = 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 the meteorological phenomena of the
section. The K value may change within a comparatively large range. This
can affect line-of-sight propagation.
ReRe
Re R
K-Type Fading (1)
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Microwave propagation
k > 1: Positive refraction
k = 1: No refraction
k < 1: Negative refraction
K-Type Fading (2)
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Equivalent earth radius In temperate zones, the refraction when the K value is 4/3 is regarded as the standard refraction, where the atmosphere is the
standard atmosphere and Re which is 4R/3 is the standard
equivalent earth radius.
K-Type Fading (3)
4/3 1
2/3
Actual earth radius (r)
Ground surface
2/3
4/31
k = ∞
Equivalent earth radius (r·k)
Ground surface
k = ∞
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Multipath fading: Due to multipath propagation of refracted waves, reflected waves, and scattered waves, multiple electric waves are received at the receiving end. The composition of these electric waves will result in severe interference fading.
Reasons for multipath fading: reflections due to non-uniform atmosphere, water surface and smooth ground surface.
Down fading: fading where the composite wave level is lower than the free space received level. Up fading: fading where the composite wave level is higher than the free space received level.
Non-uniform atmosphere Water surface Smooth ground surface.
Multipath Fading (1)
Ground surface
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Multipath fading is a type of interference fading caused by multipath
transmission. Multipath fading is caused by mutual interference between the
direct wave and reflected wave (or diffracted wave on some conditions) with
different phases.
Multipath fading grows more severe when the wave passes water surface
or smooth ground surface. Therefore, when designing the route, try to avoid
smooth water and ground surface. When these terrains are inevitable, use the
high and low antenna technologies to bring the reflection point closer to one
end so as to reduce the impact of the reflected wave, or use the high and low
antennas and space diversity technologies or the antennas that are against
reflected waves to overcome multipath fading.
Multipath Fading (2)
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Frequency (MHz)
Rece
ived p
ow
er
(dB
m)
Normal
Flat Selective fading
Multipath Fading – Frequency Selective Fading
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1h
Received level in free space
Threshold level(-30 dB)
Signal interruption
Up fading
Multipath Fading – Flat Fading
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Duct Type Fading
Due to the effects of the meteorological conditions such as ground cooling in the night, burnt warm by the sun in the morning, smooth sea surface, and anticyclone, a non-uniform structure is formed in atmosphere. This phenomenon is called atmospheric duct.
If microwave beams pass through the atmospheric duct while the receiving point is outside the duct layer, the field strength at the receiving point is from not only the direct wave and ground reflected wave, but also the reflected wave from the edge of the duct layer. As a result, severe interference fading occurs and causes interruption to the communications.
Duct type fading
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Scintillation Fading
When the dielectric constant of local atmosphere is different from the ambient due to the particle clusters formed under different pressure, temperature, and humidity conditions, scattering 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 the receiving point changes randomly.
Scintillation fading is a type of fast fading which lasts a short time. The level changes little and the main wave is barely affected. Scintillation fading will not cause communications interruption.
Scintillation fading
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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 daylight, in summer than in
winter. In the daylight, sunshine is good for air convection. In summer,
weather changes frequently. In sunny days without wind, atmosphere is non-uniform and atmosphere
subdivision easily forms and hardly clears. Multipath transmission often
occurs in such conditions. Fading is more severe along water route than land route, because both the
reflection coefficient of water surface and the atmosphere refraction
coefficient above water surface are bigger. Fading is more severe along plain route than mountain route, because
atmosphere subdivision often occurs over plain and the ground reflection
factor of the plain is bigger. Rain and fog weather causes much influence on high-frequency microwave.
Summary
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 75Page 75
Contents
4. 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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Category Effect
Equipment level
countermeasure
Adaptive equalization Waveform distortion
Automatic transmit power control (ATPC)
Power reduction
Forward error correction (FEC)
Power reduction
System level countermeasu
re
Diversity receiving technology
Power reduction and waveform distortion
Anti-fading Technologies for Digital Microwave System (1)
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Signal frequency spectrum
Multipath fadingSlope equalization
Frequency spectrum after equalization
The frequency domain equalization only equalizes the amplitude frequency response characteristics of the signal instead of the phase frequency spectrum characteristics. The circuit is simple.
Frequency domain equalization
Anti-fading Technologies for Digital Microwave System (2)
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Time domain equalization Time domain equalization directly counteracts the intersymbol interference.
Anti-fading Technologies for Digital Microwave System (3)
Before
… …T T T
After
C-n C0 Cn
Ts-Ts-2Ts Ts-Ts-2Ts
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Anti-fading Technologies for Digital Microwave System (4) Automatic transmit power control (ATPC)
Under normal propagation conditions, the output power of the transmitter
is always at a lower level, for example, 10 to 15 dB lower than the normal
level. When propagation fading occurs and the receiver detects that the
propagation fading is lower than the minimum received level specified by
ATPC, the RFCOH is used to let the transmitter to raise the transmit
power.
Working principle of ATPCModulatoModulato
rrTransmitteTransmitte
rr
ReceiverReceiverDemodulatDemodulatoror
ATPCATPC
ReceiverReceiver
ATPCATPC
TransmitteTransmitterr
ModulatoModulatorr
DemodulatDemodulatoror
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Anti-fading Technologies for Digital Microwave System (5)
ATPC: The output power of the transmitter automatically traces and changes
with the received level of the receiver within the control range of ATPC.
The time rate of severe propagation fading is usually small (<1%). After
ATPC is configured, the transmitter works at a power 10 to 15 dB lower than
the nominal power for over 99% of the time. In this way, adjacent channel
interference and power consumption can be reduced.
Effects of ATPC: Reduces the interference to adjacent systems and over-reach interference
Reduces DC power consumption
Reduces up fading
Improves residual BER
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Anti-fading Technologies for Digital Microwave System (6) ATPC adjustment process (gradual change)
ATPC dynamic range-72
-55
-45
-35
-25
102857545
31
21
Rece
ived le
vel (d
Bm
)
Link loss (dB)
High level
Low level
Tra
nsm
itter o
utp
ut le
vel (d
Bm
)
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 82Page 82
Anti-fading Technologies for Digital Microwave System (7)
Cross-polarization interference cancellation (XPIC)
In microwave transmission,
XPIC is used to transmit two
different signals over one
frequency. The utilization ratio of
the frequency spectrum is
doubled. To avoid severe
interference between two
different polarized signals, the
interference compensation
technology must be used.
Frequency configuration of U6 GHz frequency band (ITU-R F.384-5)
30MHz 80MHz
60MHz
340 MHz
1 2 3 4 5 6 7 8
680MHz
V (H)
H (V)
1’ 2’ 3’ 4’ 5’ 6’ 7’ 8’
30MHz
80MHz 60MHz
340MHz
680 MHz
1 2 3 4 5 6 7 8
V (H)
H (V)
1X 2X 3X 4X 5X 6X 7X 8X
1’ 2’ 3’ 4’ 5’ 6’ 7’ 8’
1X’ 2X’ 3X' 4X’ 5X’ 6X’ 7X’ 8X’
Shape of waveguide interface
Ele
ctric field
dire
ction Horizontal
polarization
Vertical polarization
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Anti-fading Technologies for Digital Microwave System (8)
Diversity technologies
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 angle diversity.
Space diversity and frequency diversity are more frequently used. Space diversity is economical and has a good 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.
Frequency diversity (FD)Space diversity (SD)
Hf1f1
f2f2
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Anti-fading Technologies for Digital Microwave System (9)
Frequency diversity Signals at different frequencies have different fading characteristics. Accordingly, two or more microwave frequencies with certain frequency spacing to transmit and receive the same information which is then selected or composed, to reduce the influence of fading. This work mode is called frequency diversity. Advantages: The effect is obvious. Only one antenna is required. Disadvantages: The utilization ratio of frequency bands is low.
f1
f2
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Anti-fading Technologies for Digital Microwave System (10) Space diversity
Signals have different multipath effect over different paths and thus have different fading characteristics. Accordingly, two or more suites of antennas at different altitude levels to receive the signals at the same frequency which are composed or selected. This work mode is called space diversity. If there are n pairs of antennas, it is called n-fold diversity.
Advantages: The frequency resources are saved.
Disadvantages: The equipment is complicated, as two or more suites of antennas are required.
Antenna distance: As per experience, the distance between the diversity antennas is 100 to 200 times the wavelength in frequently used frequency bands. f1
f1
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Dh =(nl + l/2)d
2h1l: wavelengthd: path distanceh1: height of the antenna at the transmit end
h1
Tx
Rx
nl + l/
2Dh
d
Dh calculation in space diversity
Anti-fading Technologies for Digital Microwave System (11)
Approximately, Dh can be calculated according to this formula:
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Apart from the anti-fading technologies introduced previously, here are two frequently used tips: Method I: Make use of some terrain and ground objects to block reflected waves.
Anti-fading Technologies for Digital Microwave System (12)
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Method II: high and low antennas
Anti-fading Technologies for Digital Microwave System (13)
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 89Page 89
Protection Modes of Digital Microwave Equipment (1)
With one hybrid coupler added between two ODUs and the antenna, the 1+1 HSB can be realized in the configuration of one antenna. Moreover, the FD technology can also be adopted.
The 1+1 HSB can also be realized in the configuration of two antennas. In this case, the FD and SD technologies can both be adopted, which improves the system availability.
Hybrid coupler
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N+1 (N≤3, 7, 11) Protection
In the following figure, Mn stands for the active channel and P stands for the standby channel. The active channel and the standby 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 backup is an inter-frequency backup. This protection mode (FD) is mainly used in the all indoor microwave equipment.
Products of different vendors support different specifications.
Protection Modes of Digital Microwave Equipment (2)
Switching control unit
Switching control unitRFSOH
PP
MM11
MM22
MM33
PP
MM11
MM22
MM33
chch11
chch22
chchPP
chch33
chch11
chch22
chchPP
chch33
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 91Page 91
Protection Modes of Digital Microwave Equipment (3)
Configuration
Protection ModeRemark
sApplication
1+0 NP Non-protection Terminal of the network
1+1 FD Channel protection Inter-frequency Select the proper
mode depending on the geographical
condition and requirements of the
customer
1+1 SD Equipment protection and channel protection
Intra-frequency
1+1 FD+SD Equipment protection and channel protection
Inter-frequency
N+1 FD Equipment protection and channel protection
Inter-frequency
Large-capacity backbone network
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 92Page 92
Questions
What factors can affect the microwave propagation?
What types of fading exists in the microwave propagation?
What are the two categories is the anti-fading technology?
What protection modes are available for the microwave?
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 93Page 93
Summary Importance parameters affecting microwave propagation
Various factors affecting microwave propagation
Various fading types in the microwave propagation (free space
propagation fading, atmospheric absorption fading, rain or fog
scattering fading, K type fading, multipath fading, duct type fading, and
scintillation type fading)
Anti-fading technologies
Anti-fading measures adopted on the equipment: adaptive equalization,
ATPC, and XPIC
Anti-fading measures adopted in the system: FD and SD
Protection modes of the microwave equipment
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 94Page 94
Contents
1. Digital Microwave Communication Overview
2. Digital Microwave Communication Equipment
3. Digital Microwave Networking and Application
4. Microwave Propagation and Anti-fading Technologies
5. Designing Microwave Transmission Links
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 95Page 95
Contents
5. Designing Microwave Transmission Links 5.1 Basis of Designing a Microwave
Transmission Line
5.2 Procedures for Designing a Microwave
Transmission Line
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Requirement on the point-to-point line-of-sight communication
Objective of designing a microwave transmission line
Transmission clearance
Meanings of K value in the microwave transmission planning
Basis of Designing a Microwave Transmission Line
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Requirement on a Microwave Transmission Line Because the microwave is a short wave and has weak ability of diffraction, the n
ormal communication can be realized in the line-of-sight transmission without obstacles.
Line propagation Irradiated waveAntenna
D
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In the microwave transmission, the transmit power is very small, only the antenna
in the accurate direction can realize the communication. For the communication of
long distance, use the antenna of greater diameter or increase the transmit power.
Requirement on a Microwave Transmission Line
3 dB
Direction demonstration of the microwave antenna
Microwave antenna
Half power angle of the microwave antenna
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k = 4/3
The first Fresnel zone
Objective of Designing a Microwave Transmission Line
In common geographical conditions, it is recommended that there be no obstacles within the first Fresnel zone if K is equal to 4/3.
When the microwave transmission line passes the water surface or the desert area, it is recommended that there are no obstacles within the first Fresnel zone if K is equal to 1.
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 100Page 100
Diffraction
The knife-edged obstacle blocks partial of the Fresnel zone. This also causes the diffraction of the microwave. Influenced by the two reasons, the level at the actual receive point must be lower than the free space level. The loss caused by the knife-edged obstacle is called additional loss.
Transmission Clearance (1)
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When the peak of the obstacle is in the line
connecting the transmit end and the receive
end, that is, the HC is equal to 0, the
additional loss is equal to 6 dB.
When the peak of the obstacle is above the
line connecting the transmit end and the
receive end, the additional loss is increased
greatly.
When the peak of the obstacle is below the
line connecting the transmit end the receive
end, the additional loss fluctuates around 0
dB. The transmission loss in the path and the
signal receiving level approach the values in
the free space transmission.
Transmission Clearance (2)
-24-26
-22-20-18-16
-14-12-10-8-6
-4
-20
42
-28
6
8
-2.5-2.0-1.5-1.0-0.5 0 0.51.0 1.52.02.5
Loss caused by block of knife-edged obstacle
HC/F1
Addit
ional lo
ss (
dB
)
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Clearance calculation
h2
d1d2
dhb
hs
hc
h1
K
ddhb
210785.0
Calculation formula for path clearance
sbc hhd
dhdhh
1221
The value of clearance is required greater than that of the first Fresnel Zone’s radius.
Transmission Clearance (3)
stands for the projecting height of the earth.
bh
K stands for the atmosphere refraction factor.
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To present the influence of various factors on microwave transmission, the field
strength fading factor V is introduced. The field strength fading factor V is defined as
the ratio of the combined field strength when the irradiated wave and the reflected
wave arrive at the receive point to the field strength when the irradiated wave arrive
s at the receive point in the free space transmission.
Transmission Clearance (4)
2
1
2
0
cos21F
h
E
EV ce
E
0E
: Combined field strength when the irradiated wave and reflected wave arrive at the receive point: Field strength when the irradiated wave arrives at the received point in the free space transmission
: Equivalent ground reflection factor
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The relation of the V and can be represented by the curve in the figure on the right. In the case that Φ is equal to 1, with the influence of the earth considered, HC/F1 is equ
al to 0.577 when the signal receiving level is equal to the free space level the first time. In the case that Φ is smaller than 1, HC/F1 i
s approximately equal to 0.6 when the signal receiving level is equal to the free space level the first time. When the HC/F1 is equal to 0.577, the clear
ance is called the free space clearance, represented by H0 and expressed in the followin
g formula: H0 = 0.577F 1 = (λd1d2/d)1/2
Transmission Clearance (5)
-40
-35
-30
-25
-20
-15
-10
-5
0
5
10
φ=0.2
φ=0.5
φ=0.8
φ=1
V ( dB )
Relation curve of V and Hc/F1
HC/F1=N
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 105Page 105
Meaning of K Value in Microwave Transmission Planning (1)
To make the clearance cost-effective and reasonable in the engineering,
the height of the antenna should be adjusted according to the following
requirements.
In the case that Φ is not greater than 0.5, that is, for the circuit that
passes the area of small ground reflection factor like the mountainous
area, city, and hilly area, to avoid over great diffraction, the height of
the antenna should be adjusted according to the following
requirements:
When K = 2/3, HC ≥ 0.3F1 (for common obstacles)
HC ≥ 0 (for knife-shaped obstacles)
The diffraction fading should not be greater than 8 dB in this case.
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 106Page 106
Meaning of K Value in Microwave Transmission Planning (2)
In the case that Φ is greater than 0.7, that is, for the circuit that passes the area of great ground reflection factor like the plain area and water reticulation area, to avoid over great reflection fading, the height of the antenna should be adjusted according to the following requirements
When K = 2/3, HC ≥ 0.3F1 (for common obstacles)
HC ≥ 0 (for knife-edged obstacles)
When K = 4/3, HC ≈ F1
When K = ∞, HC ≤ 1.35F1 (The deep fading occurs when HC = 21/2 F1.) If these requirements cannot be met, change the height of the antenna or the route.
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 107Page 107
Step 1 Determine the route according to the engineering
map.
Step 2 Select the site of the microwave station.
Step 3 Draw the cross-sectional chart of the terrain.
Step 4 Calculate the parameters for site construction.
Procedure for Designing a Microwave Transmission Line
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 108Page 108
Procedure for Designing a Microwave Transmission Line (1)
We should select the area that rolls as much as possible, such as the hilly area. We should avoid passing the water surface and the flat and wide area that is not suitable for the transmission of the electric wave. In this way, the strong reflection signal and the accordingly caused deep fading can be avoided.
The line should avoid crossing through or penetrating into the mountainous area.
The line should go along with the railway, road and other areas with the convenient transportation.
Step 1 Determine the route according to engineering map.
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The distance between two sites should not be too long. The distance
between two relay stations should be equal, and each relay section
should have the proper clearance.
Select the Z route to avoid the over-reach interference. Avoid the interference from other radio services, such as the satellite
communication system, radar site, TV station, and broadcast station.
Step 2 Select the site of the microwave station.
Procedure for Designing a Microwave Transmission Line (2)
Over-reach interference
f1 f1 f1
f2 f2 f2The signal from the
first microwave station interferes
with the signal of the same frequency from the third
microwave station.
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Draw the cross-sectional chart of the terrain based on the data of each site.
Calculate the antenna height and transmission situation of each site. For the line that has strong reflection, adjust the mounting height of the antenna to block the reflected wave, or have the reflection point fall on the earth surface with small reflection factor.
Consider the path clearance. The clearance in the plain area should not be
over great, and that in the mountainous area should not be over small.
Step 3 Draw the cross-sectional chart of the terrain.
Procedure for Designing a Microwave Transmission Line (3)
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Calculate the terrain parameters when the route and the site are already determined.
Calculate the azimuth and the elevation angles of the antenna, distance between sites, free space transmission loss and receive level, rain fading index, line interruption probability, and allocated values and margin of the line index.
When the margin of the line index is eligible, plan the equipment and frequencies, make the approximate budget, and deliver the construction chart.
Step 4 Calculate the parameters for site construction.
Procedure for Designing a Microwave Transmission Line (4)
Input
Input
There is special network planning software, and the commonly used is CTE Pathloss.
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 112Page 112
Questions
What are the requirements for microwave communication?
What is the goal of microwave design?
What extra factors should be taken into consideration for
microwave planning?
Can you tell the procedure for designing a microwave
transmission line?
Thank You
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