1. Digital Microwave Communication Principle ISSUE 1.01
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Transcript of 1. Digital Microwave Communication Principle ISSUE 1.01
1
www.huawei.com
Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Digital Microwave Communication Principle
Page1Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Foreword
� This course is developed for the requirement from OptiX RTN
equipments.
� This course mainly introduce the basic knowledge of digital
microwave communication. Engineers can have a basic to
understand the further OptiX RTN equipments after finish the
course.
2
Page2Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Learning Guide
� Before this course, you may refer to these references first:
� SDH Principle
� Network Communication Technology
� Electromagnetism Basics
Page3Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Objectives
� Upon completion of this course, you will be able to:
� Describe the concept and characters of digital microwave
communication
� Describe the theory and function of every parts in the digital
microwave system
� List the networking application for digital microwave systems
� List the fadings in microwave propagation
� List the common technologies of antifading
3
Page4Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. Digital Microwave Communication Overview
2. Digital Microwave Equipment Introduction
3. Networking and Application of Digital Microwave
Equipment
4. Microwave Propagation and Antifading Technologies
Page5Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Transmission Methods for Communication
Fiber
Microwave
Satellite
MUX MUXRadioTer.
RadioTer.
Coaxial Cable
4
Page6Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Fiber and Microwave transmission
Easy to cross the space, few land needed, avoid the private land
Optical cable construction,large land used.
Microwave (MW) Optical Fiber
Low investment, short period,easy to maintain
High investment, long Construction period
Anti-natural disaster strongly ,easy to be restored fast
Outside cable maintenance,natural disaster influence
Need to apply the frequency license
No frequency license required
Performance affected by weatherand landform
Performance stable, less influence from outside
Low transmission capacity High transmission capacity
Page7Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Microwave (MW) Definition
� Microwave (MW)
� A kind of electromagnetic wave.
� Radio frequency range is from 300MHz to 300GHz.
� Be regard as plane wave.
� The electric field and magnetic field exist at vertical of
transmission direction of plane wave. So it is called as
Transverse Electric and Magnetic field wave (TEM).
5
Page8Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Digital MW communication concepts
� The communication that use microwave as carrier is
microwave communication.
� The microwave communication with digital baseband signal
is Digital microwave communication.
� There is an intermediate frequency between digital
baseband signal and radio frequency signal.
Page9Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Developing of MW communication
Note: capacity less than 10M is considered as low capacity, from10~100M is medium capacity, and more than 100M is large capacity.
155M
34/140M
2/4/6/8M
480 tone channels
SDH Digital
MW system
PDH Digital
MW System
Medium, low capacity Digital MW System
Analog MW
System
Capacity(/ch)
1950’s
1970’s
1980’s
1990’s to now
6
Page10Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Frequency Band and Radio Channel
� The common frequency bands :
� 7G/8G/11G/13G/15G/18G/23G/26G/32G/38G (by ITU-R rec. )
85432 10 201 30 40 50
1.5 2.5GHzregion
networks
long-distance backbone network
area and local network, boundary network
2834
Mbit/s
28
34140155Mbit/s
3.3 11 GHz
GHz
34140155Mbit/s
Page11Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Frequency Band and Radio Channel (cont.)� The central frequency, T/R spacing and channel spacing are
defined in every frequency band.
f0(central freq.)
Frequency scope
Channel spacingf1 f2 fn f1’ f2’ fn’
Channel spacing
T/R spacing T/R spacing
Low frequency band High frequency band
Protectionspacing
Adjacent T/R
spacing
Protectionspacing
7
Page12Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Frequency Band and Radio Channel (cont.)
f0(7575M)
Frequency scope(7425-7725MHz)
28M
f1=7442 f5 f1’=7596 f2’ f5’
T/R spacing: 154M
f2=7470
……
3.5
28
28
7
28
channel spacing(MHz)
……
Fn , Fn’
High site / low site
……………….
16174007250--7550
19672757110--7750
7597
7575
7575
F0 (MHz)
196
1547425--7725
161
T/R spacing (MHz)Freq. scope
Page13Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Modulation modes for Digital MW
� The microwave carrier is digital modulated by the baseband
signal.
Digital base band signalIntermedia frequency
(IF) signal
Base bandSignalrate
Channelbandwidthmodulation
Servicesignal
8
Page14Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Modulation modes for Digital MW (cont.)� The frequency carrier signal can be described as:
� Amplitude Shift Keying (ASK): A is variable, Wc and φ are constant� Frequency Shift Keying (FSK): Wc is variable, A and φ are constant
Phase Shift Keying (PSK): φ is variable, A and Wc are constant� Quadrature Amplitude Modulation (QAM): A and φ are variable, Wc is
constant
A*COS((((Wc*t+φ))))
Amplitude Frequency
Phase
PSK and QAM are commonly
used in digital MW
Page15Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
MW Frame Structure
� Radio frame complementary overhead (RFCOH):
RFCOH
ATPC64Kb/s
DMY64Kb/s
MLCM11.84Mb/s
RSC864Kb/s
WS2.24Mb/s
XPIC16Kb/
s
ID32Kb/s
INI144Kb/s
FA288Kb/s
15.552Mb/s
SOH Payload
STM-1 155.52Mb/s
171.072Mb/s
RSC:MW service controlMLCM: Multi-level coded modulation IN: N:1 switch instructionDMY: Dummy ID: IdentificationXPIC: Cross polarization interference counteract FA: Frame synchronizationATPC: Automatic transmitter power control WS:Wayside services
9
Page16Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
MW Frame Structure (cont.)
� RFCOH and STM-1 data are blocked by multi-frame, there are six rows in a multi-frame, 3564 bits per rows. A multi-frame consists of two sub-frames, and 1776 bits for one row in a sub-frame. The other 12 bits are used as FS.
Multi-frame 3564bit
Sub-frame 2
1776bit(148 units)
FS
6bit
Sub-frame 1
1776bit(148 units)
FS
6bit
6rows
C1IIC1IIC1IIC1II
C2IIbIIIIIIII
IIIIIIIIIIII
IIIIIIIIIIII
IIIIIIIIIIII
IIIIIIIIIIII
C1IIC1IIC1IIC1II
C2IIbIIaIIIII
IIIIIIIIIIII
IIIIIIIIIIII
IIIIIIIIIIII
IIIIIIIIIIII
12bit first unit 12bit 148th unit
I:STM-1 date bit C1,C2: 2 Level error correction monitor bit FS: Frame sync. a,b: other RFCOH
Page17Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Questions
� What is microwave? What is digital microwave communication?
� What are the frequency bands commonly used in digital MW?
� What are the concepts in digital MW frequency band arrangement ?
� What modulation modes is commonly used? What modulation
modes are used in digital MW?
10
Page18Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. Digital Microwave Communication Overview
2. Digital Microwave Equipment Introduction
3. Networking and Application of Digital Microwave
Equipment
4. Microwave Propagation and Antifading Technologies
Page19Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Types of Digital MW Equipment
Digital MW
PDH SDH
split-mount MW
Trunk MW
All-outdoor MW
medium, low capacity
(2~16E1,34M)
Large capacity
(STM-0,STM-1,2 x STM-1) Discontinued
Analog MWModes
Capacity
Structure
Multiplexing
11
Page20Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Trunk MW Equipment
SDH MW Equipment
BRU: Branch of RF unit
MSTU: Main signal transceiver unit (transceiver, modem, SDH electric interface, hitless module)
SCSU: surveil, control, switch unit
BBIU: baseband interface unit (optional: STM-1 optical interface, C4 PDH interface)
P
M1
M2
……
Page21Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
All-outdoor MW Equipment
All-outdoor MW equipment
IF and baseband signal processing unit
IF cable
RF signal processing unit
Service and power cable
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Page22Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Split-mount MW Equipment
split-mount MW equipment
Antenna
RF unit or Outdoor unit(ODU)
IF Cable
Indoor Unit
Page23Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Split-mount MW Equipment (cont.)
� Antenna: focus RF signal sent by ODU, enlarge
signal gain
� ODU: RF signal processing,conversion between IF
signal and RF signal.
� IF cable: Transmission for IF service signal , ODU
management signal and supply power for ODU.
� IDU: service access and distribute, multiple, modem
and so on.
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Page24Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Split-mount MW Equipment -Installation
Antenna
(ODU) IF cable
频口
Separate installation
Soft waveguide
IDU IF interface
Antenna
ODU
IDU
Direct installation
IF cable
IF interface
Page25Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Antenna
� The antenna propagates the electric wave from transmitter into one direction, and receive the electric wave. Paraboloid antenna and Kasai Green antenna are usually used.
� The common diameter of antenna are: 0.3, 0.6, 1.2, 1.8, 2.4, and 3.0m, etc.
Paraboloid antenna Kasai Green antenna
14
Page26Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Antenna (cont.)
� Several channels in one frequency band can share one antenna.
Tx
Rx
Tx
Rx
Channel Channel
1
1
n
n
1
1
n
n
Page27Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Antenna Aligning
Side viewSide lobe
Rear lobe
Top viewRear lobe
Side lobe
Main lobe
Main lobe
15
Page28Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Antenna Aligning
CorrectWrongWrong
Page29Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Antenna Specifications
� Antenna gain
� The input power ratio of isotropic antenna (Pio) to surface antenna (Pi) when getting the same electric field intensity at the same point.
� It can be calculated by formula( unit: dB) :
� Half power angle (3 dB beam width)
� From the main lobe deviates to both sides, the points where the power decrease half are half power point. The angle between the two half power points is half power angle.
� Approximate calculation formula
is:
ηλ
π ∗
==2
D
P
PG
i
io
D
λθ )70~65( 005.0 = Half power angle
16
Page30Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Antenna Specifications (cont.)
� Cross polarization discrimination (XPD)
� The suppressive intensity of power received from expected
polarization (Po) to the other polarization (Px). It should more than
30db. Formula is:
XdB=10lgPo/Px
� Antenna protection ratio
� It is the ratio of the receiving attenuation in antenna other lobes to
the receiving attenuation in antenna main lobe. The 180 degree
antenna protection ratio also be called as the front / rear protection
ratio.
Page31Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Outdoor Unit
� The main specifications of transmitter
� Working frequency band:
� One ODU can cover one frequency band or some part of a
frequency band.
� Output power:
� The power at the output port of transmitter.
� The typical range of power is from 15 to 30 dBm.
17
Page32Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Outdoor Unit (cont.)
� The main specifications of transmitter (cont.)
� Frequency stability
� The oscillation frequency stability of microwave device is from 3
to 10 ppm.
� Transmitting frequency spectrum frame
� A restricted frequency scope is frequency spectrum frame.
Page33Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Outdoor Unit (cont.)
� The main specifications of receiver
� Work frequency band:
� The receiving frequency of local station is the same with the
remote station.
� Frequency stability
� The requirement is from 3 to 10ppm.
� Noise Figure
� The noise figure of digital microwave receiver is from 2.5 to
5dB.
18
Page34Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Outdoor Unit (cont.)
� The main specifications of receiver (cont.)
� Passband
� The typical value is 1 to 2 times of transmission code element
rate.
� Selectivity
� The suppressing ability against interference beyond transmission
bands
� Automatic gain control (AGC) range
� Automatic control the gain to keep the same IF output power level when receiving RF power level shift in a range because of
fading.
Page35Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Indoor Unit
� Accessing service like E1 or STM-1
� Processing RFCOH
� Conversion signals between baseband and IF
Cable interface
From/to ODU
Tx IF
Rx IF
modulation
demodulation
Multiplex of microwave
frame
Demultiplex of microwave
frame
Service accessing
IF unitService channel
Service channel
DC/DC convert
Monitor and control unit
Interface of OM
19
Page36Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Questions
� What are the classification of digital MW equipment?
� What components are there in the split-mount digital MW equipment?What are the functions of them?
� What are the main parameters of antenna?
� What are the parameters of ODU transmitter and receiver?
Page37Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Summary
� Classification of digital microwave equipment
� Functions of the components in split-mount digital MW
equipment
� Parameters of antenna
� Parameters of ODU
� Function of IDU
20
Page38Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. Digital Microwave Communication Overview
2. Digital Microwave Equipment Introduction
3. Networking and Application of Digital Microwave
Equipment
4. Microwave Propagation and Antifading Technologies
Page39Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Common Networking Application
RingPoint to point
link
Add / drop link
Tree
21
Page40Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Types of Digital MW Stations
� The digital MW station includes terminal station, relay station and pivotal station
Terminal station
Terminal station
Terminal station
Pivotal station
Pivotal station
Relay station
Page41Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Types of Relay Stations
Relay station
Active
Passive • Parabolic reflectors
• Plane reflector
• Regenerative relay
• IF relay
• RF relay
22
Page42Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Active Relay Stations
� RF direct station:
� Amplifying MW signal at RF band bidirectionally without frequency shift.
� Regenerative relay station:
� It extends the MW propagation distance and change direction to round the obstacles.
Page43Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Passive Relay Stations
� Parabolic reflectors:
� It consists of two parabolic antennas which are connected back to back with a section of waveguide.
� Plane reflectors:
� A metal panel with a smooth surface and effective acreage.
23
Page44Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Passive Relay (actual picture)
Plane reflectors Parabolic reflectors
Page45Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Application of Digital MW
Supplement for optical
network (the last mile access)
Backhaul transmission
for mobile BTS
Critical link backup
VIP customer access
Emergency communication(large activity,
crisis)
Special transmission
situation (river, lake, island)
MicrowaveMicrowaveapplicationapplication
24
Page46Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Questions
� Which network application are commonly used by digital MW?
� What types of stations are there in the digital MW system?
� What types of the relay stations are there?
� What are the applications for digital MW system?
Page47Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. Digital Microwave Communication Overview
2. Digital Microwave Equipment Introduction
3. Networking and Application of Digital Microwave
Equipment
4. Microwave Propagation and Antifading Technologies
25
Page48Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Contents
4. Microwave Propagation and Antifading Technologies
4.1 Microwave Propagation and fading
4.2 Antifading Technologies
Page49Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Factors Affect MW Propagation
� Landform:� The reflection from land affect receiving signal from main direction
� 4 types of the landform:� A: mountainous region (or the region of dense buildings)� B: foothill (the fluctuation of ground is gently)
� C: flatland� D: large acreage of water
Direct
Reflection
Direct
Reflection
26
Page50Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Factors Affect MW Propagation (cont.)
� Atmosphere and weather:
� Atmosphere absorption mainly affect the microwave whose
frequency is over 12 GHz.
� Refraction, reflection, dispersion in the troposphere.
� Scattering and absorption loss caused by rain, fog and snow.
It mainly affect the microwave whose frequency is over 10
GHz.
Page51Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Classification of the Fading
mechanism
Absorption loss
Fading of rain and fog
Scintillation fading
K facter fading
Duct Type fading
Sustained duration
Received level Effect
Fast Fading
Slow Fading
Upward Fading
Downward fading
Flat fading
Frequency selective fading
Fading in free space
Fading
27
Page52Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Free Space Fading
� Formula: A = 92.4 + 20 log d + 20 log f� d = distance in km f = frequency in GHz
Power Level
PTX = Output power
G = Antenna gain
A = Free space loss
M = Fading Margin
PTX
distance
GTX GRX
PRX
A
MReceiving threshold
G
d
G
f
PRX = Receiving power
Page53Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Absorption Loss
� It is mainly caused by atmosphere.
28
Page54Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Rain & Fog Fading
� Generally, different frequency band has different loss.
� less than 10 GHz, its fading caused by rain and fog is not
serious.
� over 10 GHz, relay distance is limited by fading caused by
rains.
� over 20GHz, the relay distance is only about several
kilometers for the rain & fog fading.
Page55Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
K Factor Fading
� A equivalent radius: Re=KR (R is the real radius of earth).
� the value of K is depend on the local meteorological phenomena
Re R
29
Page56Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Scintillation Fading
� The particle cluster formed in local atmosphere for pressure, temperature or humidity is different as other area, and the electric wave is scattered by it.
sketch map of Scintillation fading
Page57Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Duct Type Fading
� When electric waves pass the atmospheric waveguide, super reflection occurs.
sketch map of Duct Type fading
30
Page58Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Multi-Path Propagation and Fading
� The receiving paths
includes direct path and
other reflection paths.
� Multi-path fading is caused
by the signals interference
from different propagation
paths
Ground
Page59Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Flat Fading
1 h
Receive level in free space
Threshold (-30dB )
Signal interruption
Upward fading
Fast fading Slow
fading
31
Page60Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Frequency Selective Fading
Freq. (MHz)
Rec
eivi
ng p
ower
(dB
m)
Normal
Flat Selective fading
� Frequency selective fading will cause the in-band distortion and decrease system original fading margin.
Page61Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Contents
4. Microwave Propagation and Antifading Technologies
4.1 Microwave Propagation and fading
4.2 Antifading Technologies
32
Page62Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Antifading Technologies
Wave shape distortion and Power reduction
Diversity receive technologies
Antifading technologies related with
system
Power reductionForward Error Correct
Power reductionAutomatic Transmit Power
Control
Wave shape distortionCross Polarization Interference Counteract
Wave shape distortionAdaptive EqualizationAntifading
technologies related with
device
Improving effectsTypes
Page63Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Adaptive Frequency Equalization
Signal spectrum
Multi-path fading
Slope frequency domain
equalization
Spectrum after
equalization
33
Page64Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Adaptive Time Equalization
BeforeEqualization
… …T T T
AfterEqualization
C-n C0 Cn
Ts-Ts-2Ts Ts-Ts-2Ts
Page65Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Automatic Transmit Power Control
� ATPC is used to reduce interference to adjacent system, upward-fading, DC power consumption and refine characteristic of residual error rate.
modulator transmitter
receiverdemodulator
ATPC
receiver
ATPC
transmitter modulator
demodulator
34
Page66Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
XPIC
� XPIC is cross-polarization interference counteracter.
Direction of electric field
Horizontalpolarization
Verticalpolarization
Frequency configuration in U6GHz 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’
Page67Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Diversity Reception
� Diversity reception is used to minimize the effects of
fading. It includes:
� Space diversity (SD)
� Frequency diversity (FD)
� Polarization diversity
� Angle diversity
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Page68Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Frequency Diversity
� The merit is only need one set of feeder and antenna, but its demerit is that utilization of frequency band is low.
f1
f2
Page69Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Space Diversity
� The merit is saving frequency resource, but demerit is system is complex and need two or more sets of feeder and antenna.
f1
f1
36
Page70Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Other Antifading Methods
� blocking the reflected wave by some terrain or obstacles.
Page71Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Other Antifading Methods (cont.)
� Different height antennas in one hop.
37
Page72Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Questions
� What are the factors which affect microwave propagation?
� What types of the fading are there in microwave
propagation?
� What types of antifading technologies can be used?
Page73Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Summary
� Digital microwave communication definitions.
� Frequency bands and radio channel arrangement
� Structure and function of digital microwave equipment
� Application of digital microwave communication
� Microwave propagation and fading
� Antifading technologies
38
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