Digital_Microwave_Communication_Principl (1).ppt

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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 2
Page 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.

Page 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

Page 4
Objectives
 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

Page 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

Page 6
Transmission Methods
in Current Communications Networks
Optical fiber communication
Microwave
communication
Satellite communication
MUX/DEMUX MUX/DEMUX
Microwave
TE
Microwave
TE
Coaxial cable communication

Page 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 capacity
Limited 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 Communication Optical Fiber Communication

Page 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.

Page 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

Page 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.

Page 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)
8
5
4
3
2 10 20
1 30 40 50
1.5 GHz 2.5 GHz
Long haul
trunk network
2/8/34
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

Page 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
spacing
f1
f2 fn f1
’ f2
’ fn
’
Channel
spacing
T/R spacing
T/R spacing
Low frequency band High frequency band
Protection
spacing
Adjacent channel
T/R spacing

Page 13
f0 (7575M)
Frequency range (7425M–7725M)
28M
f1=7442 f5 f1
’=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
… … … … …

Page 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
Baseband
signal
rate
Channel
bandwidth
Modulation
Service signal
transmitted

Page 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.

Page 16
Microwave Frame Structure (1)
 RFCOH
RFCOH
ATPC
64 kbit/s
DMY
64 kbit/s
MLCM
11.84 Mbit/s
RSC
864 kbit/s
WS
2.24 Mbit/s
XPIC
16 kbit/s
ID
32 kbit/s
INI
144 kbit/s
FA
288 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 Channel
MLCM: Multi-Level Coding Modulation
INI: N:1 switching command
DMY: Dummy
ID: Identifier
XPIC: Cross-polarization Interference Cancellation
FA: Frame Alignment
ATPC: Automatic Transmit Power Control
WS: Wayside Service

Page 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
C1
I
I
C1
I
I
C1
I
I
C1
I
I
C2
I
I
b
I
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12 bits (the 1st word) 12 bits (the 148th word)
I: STM-1 information bit
C1/C2: Two-level correction coding monitoring bits
FS: Frame synchronization
a/b: Other complementary overheads

Page 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?

Page 19
Contents

Page 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

Page 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
…

Page 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

Page 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)

Page 24
Split-Mount Microwave Equipment (2)
 Unit Functions
 Antenna: Focuses the RF signals transmitted by ODUs and increases the signal
gain.
 ODU: RF processing, conversion of IF/RF signals.
 IF cable: Transmitting of IF signal, management signal and power supply of ODU.
 IDU: Performs access, dispatch, multiplex/demultiplex, and
modulation/demodulation for services.

Page 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

Page 26
Microwave Antenna (1)
 Antennas are used to send and receive microwave signals.
Parabolic antennas and cassegrainian antennas are two common types 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 Cassegrainian antenna

Page 27
Main lobe
Side lobe
 2 Dimension  3 Dimension
 The side lobes can cause interference with adjacent point-to-point links and
consequently must be minimized through careful antenna design and
installation.

Page 28
“Standard” “Standard with radome”
 Radome is a radio-frequency transparent cover used to protect the antenna
from such things as wind load, snow and ice, or dust build-up that would
otherwise cause excessive mechanical stress on the tower structure and
undesirable radiation pattern distortion. Significantly reduces the wind load of
an antenna system by preventing the dish and shield from “catching” wind.

Page 29
“Standard”
Side lobe
Main lobe

Page 30
Absorbing
Material
“High performance”

Page 31
“Standard”
“High
Performance”

Page 32
 Different frequency channels in same frequency band can share one antenna.
T
x
R
x
T
x
R
x
Channe
l
Channe
l
1
1
n
n
1
1
n
n

Page 33
 SALIENT FEATURES OF MICROWAVE ANTENNA
 Narrow / Sharp Beam Formation
 Low Spill Over
 Low Back Lobe Radiation
 High Directive/Bore Sight Efficiency
 Low Side Lobes
 High Cross Polarization Discrimination
 High Front to Back Ratio
 Low VSWR

Page 34
Antenna Adjustment (1)
Side view
Side lobe
Main lobe
Half-power angle Tail lobe
Top view
Main lobe
Side lobe
Half-power angle Tail lobe

Page 35
 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.
Side lobe position
AGC
Voltage
detection point
VAGC
Main lobe position
Angle

Page 36
 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.
Correct
Wrong
Wrong

Page 37
– 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
( 0
0
5
.
0 












2
D
P
P
G
i
io

Page 38
 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 with
that in the main lobe direction. An antenna protection ratio of 180° is called front-to-back
ratio.
– Antenna (2)

Page 39
– ODU (1)
ODU system architecture
Uplink IF/RF conversion
Frequency
mixing
Sideband
filtering
Power
amplification
RF
attenuation
ATPC
Power
detection
RF loop
Local
oscillation
(Tx)
Local
oscillation
(Rx)
Frequency
mixing
Filtering
Low-noise
amplification
Bandpass
filtering
Alarm and control
Downlink RF/IF conversion
Supervi
sion and
control
signal
IF
amplificat
ion
IF
amplification

Page 40
 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.
– ODU (2)

Page 41
 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.
– ODU (3)

Page 42
– 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.

Page 43
 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.
– ODU (5)

Page 44
– 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.

Page 45
– IDU
Cable
interface
From/to ODU
Tx IF
Rx IF
Modulat
ion
Demod
ulation
Microwave
frame
multiplexing
Microwave
frame
demultiplexing
Cross-
conne
ction
Tributary
unit
Line unit
IF unit
Service
channel
Service
channel
DC/DC conversion
Supervision and control
O&M
interface
Power
interface

Page 46
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?

Page 47
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

Page 48
Contents

Page 49
Common Networking Modes of
Digital Microwave
Ring network Chain network
Add/Drop
network
Hub network

Page 50
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.

Page 51
Types of Relay Stations
Relay station
• Back-to-back antenna
• Plane reflector
Active
Passive
• Regenerative repeater
• IF repeater
• RF repeater

Page 52
 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

Page 53
 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

Page 54
Plane Reflector Passive Relay Station (1)
 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 a
s   
1421 20 20
1 2
. log log
a A
 cos
2
d1
(km)
(km)
d2


Page 55
 Passives ( Billboard ), due to their large surface area they are prone to be shifted
out of alignment due to winds and requires realignment (causing outages or degraded
performance).
 Billboard systems have a very large footprint and typically causes major concerns
over the way it looks, with neighbors and planning commisions.
 Passives are prone to multipath if the area behind the billboard is not clear sky. MW
signals can reflect off the hillside behind the passive and cause multipath problems.
RF Repeaters have been shown to reduce this problem significantly (50 dB
improvement in C/I).
 Passives can suffer from decoupling fades, especially over 6GHz. When the
terminal antenna is large, as needed for a successful passive, the beam width is very
small, 0.5 ~ 0.9 degrees. Atmospherics may cause the beam to shift position and not
illuminate the passive fully or at all. This "decoupling" of the beam causes severe
fading because less beam energy is reflected.

Page 56
 Beamwidth of the signal exiting a passive reflector is extremely narrow, 0.1 ~ 0.2 degrees.
This narrow beam is difficult to aim and if the passive alignment shifts, the beam may miss
the terminal. Another form of decoupling fade.
 MW RF Repeaters avoid decoupling fades by using more standard sized antennas with
somewhat wider beamwidths.
 MW RF Repeaters have been used in a number of locations that were otherwise suitable
for passive reflectors because the RF Repeater took up less space, offered less of an
objectionable view in sensitive areas (National Parks, National Forests).
 Passive reflectors work best when one path is quite short and the other is longer. MW RF
Repeaters are not limited in this way and perform will especially at mid-path locations.
Microwave RF Repeaters can operate over much longer paths than passive reflectors.
Microwave RF Repeater paths are in many cases as long as terminal to terminal paths.

Page 57
Active Relay Stations
Active or regenerating repeaters are used when the distance between terminal
stations is too great to allow a received signal of acceptable level and also when it is
necessary to insert and drop channels at points between terminal stations.
Passive Relay Stations
Sometimes if there is an obstacle such as a high mountain in the line-of-sight
microwave path, where the cost, maintenance and power requirements for an active
repeater would be prohibitive. The passive repeater is located in such a position as to
act as a microwave mirror, reflecting the microwave signal as a mirror reflects a light
beam, to bypass the obstruction.
Comparison between Active and Passive repeater
Active repeater Passive repeater
More expensive Cheaper
More capacity Lower capacity
More hardware equipment More reliable
CAN ANYBODY TELL THE ADVANTAGES & DISADVANTAGES
BETWEEN ACTIVE AND PASSIVE REPEATERS?
Relay Stations Comparisons

Page 58
Passive Relay Station (Photos)
Passive relay station
(plane reflector)
Passive relay station
(parabolic reflectors)

Page 59
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
application

Page 60
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?

Page 61
Contents

Page 62
Contents
 4.1 Factors Affecting Electric Wave Propagation
 4.2 Various Fading in Microwave Propagation
 4.3 Anti-fading Technologies for Digital Microwave

Page 63
 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)
R
O
T
P
F1
d2
d1
 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).

Page 64
Key Parameters in
 Bounded by elliptical loci of constant delay
 Alternate zones differ in phase by 180
 Line of sight (LOS) corresponds to 1st zone
 If LOS is partially blocked, 2nd zone can destructively interfere (diffraction
loss)
Fresnel zones are ellipses with the T&R at the foci; L1 = L2+λ
Path 1
Path 2

Page 65
Total received signal
Direct signal
1st zone
Reflected signal
180
180
/2
Key Parameters in

Page 66
Total received signal
Direct signal
2nd zone
1st zone
Reflected signal
180
180

Key Parameters in

Page 67
 Formula of the first Fresnel zone radius:
Key Parameters in
 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 2
1
1
km
d
GHz
f
km
d
km
d
F




Page 68
Key Parameters in
 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
B
h1
h2
d
d1 d2
hp
hc
hs
M F
h3
h4
h5
h6

Page 69
 Typically the first Fresnel zone (N=1) is used to determine obstruction loss
 The direct path between the transmitter and the receiver needs a
clearance above ground of at least 60% of the radius of the first Fresnel
zone to achieve free space propagation conditions
 Earth-radius factor k compensates the refraction in the atmosphere
 Clearance is described as any criterion to ensure sufficient antenna
heights so that, in the worst case of refraction (for which k is minimum)
the receiver antenna is not placed in the diffraction region
Key Parameters in

Page 70
 Clearance criteria to be satisfied under normal propagation
conditions
 Clearance of 60% or greater at the minimum k suggested for the
certain path
 Clearance of 100% or greater at k=4/3
 In case of space diversity, the antenna can have a 60% clearance at
k=4/3 plus allowance for tree growth, buildings (usually 3 meter)
Key Parameters in

Page 71
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

Page 72
 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

Page 73
 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 (1)

Page 74
 The specific attenuation of rain is dependent on many parameters such
as the form and size of distribution of the raindrops, polarization, rain
intensity and frequency
 Horizontal polarization gives more rain attenuation than vertical
polarization
 Rain attenuation increases with frequency and becomes a major
contributor in the frequency bands above 10 GHz
 The contribution due to rain attenuation is not included in the link budget
and is used only in the calculation of rain fading
 Radios with Automatic Transmitter Power Control (ATPC) have been
used in some highly vulnerable links
 Vertical polarization is far less susceptible to rainfall attenuation (40 to
60%) than are horizontal polarization frequencies.
Factors Affecting Electric Wave
Propagation – Atmosphere (2)

Page 75
Contents

Page 76
Fading in Microwave Propagation
Fading
mechanism
Absorption
fading
Rain
fading
Scintillation
fading
K-type
fading
Duct
type
fading
Fading time Received
level
Influence of
fading on signal
Fast
fading
Slow
fading
Up
fading
Down
fading
Flat
fading
Frequency
selective
fading
Free
space
propagation
fading
 Fading: Random variation of the received level. The variation is irregular and the
reasons for this are various.

Page 77
Free Space Transmission Loss
 Free space loss: A = 92.4 + 20 log d + 20 log f
(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
M
Receiving threshold
G
d
G
f
PRX = Receive power

Page 78
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)
1GHz
7.5GHz
12GHz
23GHz
60GHz
0.01dB
10dB
1dB
0.1dB

Page 79
Attenuation
Coefficient
dB
/
km
Radio Frequency GHz
10 50 100 1000
500
1000
100
10
1
0,1
0,01
H2O
O2
O2
H2O H2O
15 °C
H2O 7,5 g/m3
1013 hPa
25 g/m3
Attenuation due to Gases

Page 80
 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

Page 81
 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.
Re
Re
Re
R
K-Type Fading (1)

Page 82
 Microwave propagation
k > 1: Positive refraction
k = 1: No refraction
k < 1: Negative refraction
K-Type Fading (2)

Page 83
 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
4/3
1
k = ∞
Equivalent earth radius (r·k)
Ground surface
k = ∞

Page 84
 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

Page 85
 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)

Page 86
Frequency (MHz)
Received
power
(dBm)
Normal
Flat Selective fading
Multipath Fading
– Frequency Selective Fading

Page 87
1h
Received level
in free space
Threshold level
(-30 dB)
Signal
interruption
Up fading
Multipath Fading – Flat Fading

Page 88
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

Page 89
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.
闪烁衰落示意图
Scintillation fading

Page 90
 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

Page 91
Contents

Page 92
Category Effect
Equipment level
countermeasure
Adaptive equalization Waveform distortion
Automatic transmit power
control (ATPC)
Power reduction
Forward error correction
(FEC)
Power reduction
System level
countermeasure
Diversity receiving technology
Power reduction and
waveform distortion
Anti-fading Technologies
for Digital Microwave System (1)

Page 93
Signal frequency
spectrum
Multipath fading
Slope 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

Page 94
 Time domain equalization
 Time domain equalization directly counteracts the intersymbol
interference.
Before
… …
T T T
After
C-n C0 Cn
Ts
-Ts
-2Ts Ts
-Ts
-2Ts

Page 95
 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 ATPC
Modulator Transmitter
Receiver
Demodulator
ATPC
Receiver
ATPC
Transmitter Modulator
Demodulator

Page 96
 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

Page 97
 ATPC adjustment process (gradual change)
ATPC dynamic range
-72
-55
-45
-35
-25
102
85
75
45
31
21
Received
level
(dBm)
Link loss (dB)
High level
Low level
Transmitter
output
level
(dBm)

Page 98
 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
340MHz
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
Electric
field
direction
Horizontal polarization
Vertical polarization

Page 99
 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)
H
f1
f2

Page 100
 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

Page 101
 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

Page 102
 Space Diversity:
 Cheaper then frequency diversity.
 No protections from rain
 Frequency Diversity:
 Requires 2 times the bandwidth, more equipment and
complexity.
 Much less effective than space diversity.
 Can work on one radio while the other works ( with no
diversity)

Page 103
Dh =
(nl＋l/2)d
2h1
l: wavelength
d: path distance
h1: height of the antenna at the transmit end
h1
Tx
Rx
Dh
d
 Dh calculation in space diversity
 Approximately, Dh can be calculated according to this formula:

Page 104
 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.

Page 105
 Method II: high and low antennas

Page 106
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

Page 107
 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
Switching
control unit
Switching
control unit
RFSOH
P
M1
M2
M3
P
M1
M2
M3
ch1
ch2
chP
ch3
ch1
ch2
chP
ch3

Page 108
Protection Modes of
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 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
Inter-
frequency
N+1 FD Equipment protection
Inter-
frequency
Large-capacity
backbone network

Page 109
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?

Page 110
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

Page 111
Contents

Page 112
Contents
 5.1 Basis of Designing a Microwave Transmission Line
 5.2 Procedures for Designing a Microwave Transmission Line
 5.3 Link Budget

Page 113
 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

Page 114
Requirement on a Microwave
Transmission Line
 Because the microwave is a short wave and has weak ability of diffraction, the
normal communication can be realized in the line-of-sight transmission without obstacles.
Line propagation Irradiated wave
Antenna
D

Page 115
 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

Page 116
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.

Page 117
 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)

Page 118
 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.
-24
-26
-22
-20
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
4
2
-28
6
8
-2.5-2.0-1.5-1.0-0.5 0 0.51.0 1.5 2.0 2.5
Loss caused by block of knife-edged obstacle
HC/F1
Additional
loss
(dB)

Page 119
 Clearance calculation
h2
d1
d2
d
hb
hs
hc
h1
K
d
d
hb
2
1
0785
.
0

 Calculation formula for path clearance
s
b
c h
h
d
d
h
d
h
h 


 1
2
2
1
The value of clearance is
required greater than that
of the first Fresnel Zone’s
radius.
 stands for the projecting
height of the earth.
b
h
 K stands for the atmosphere refraction factor.

Page 120
 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 arrives at the
receive point in the free space transmission.




















2
1
2
0
cos
2
1
F
h
E
E
V ce



E
0
E

: 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

Page 121
 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
equal 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 is
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
clearance is called the free space clearance,
represented by H0 and expressed in the
following formula:
H0 = 0.577F 1 = (λd1d2/d)1/2
-40
-35
-30
-25
-20
-15
-10
-5
0
5
10
0
.
6
4
1
.
0
4
1
.
3
1
1
.
4
3
1
.
5
6
1
.
7
6
1
.
9
3
2
.
0
1
2
.
1
0
2
.
2
6
2
.
3
9
2
.
4
6
2
.
5
4
2
.
6
6
2
.
7
8
2
.
8
5
3
.
0
2
φ＝0.2
φ＝0.5
φ＝0.8
φ＝1
V（dB）
Relation curve of V and Hc/F1
HC/F1=N


Page 122
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.

Page 123
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.

Page 124
 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

Page 125
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.

Page 126
 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.
Over-reach
interference
f1 f1 f1
f2 f2 f2
The signal from the first
microwave station
interferes with the
signal of the same
frequency from the third
microwave station.

Page 127
 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.

Page 128
 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.
Input
Input
There is special network
planning software, and the
commonly used is CTE
Pathloss.

Page 129
 The link budget is a calculation involving the gain and loss factors associated with
the antennas, transmitters, transmission lines and propagation environment, to
determine the maximum distance at which a transmitter and receiver can
successfully operate.
 Receiver sensitivity threshold is the signal level at which the radio runs continuous
errors at a specified bit rate.
 System gain depends on the modulation used (2PSK, 4PSK, 8PSK, 16QAM,
32QAM, 64QAM,128QAM,256QAM) and on the design of the radio.
Link Budget (1)

Page 130
 The gains from the antenna at each end are added to the system gain (larger
antennas provide a higher gain).
 The free space loss of the radio signal is subtracted. The longer the link the higher
the loss.
 These calculations give the fade margin.
 In most cases since the same duplex radio setup is applied to both stations the
calculation of the received signal level is independent of direction.
 The fade margin is calculated with respect to the receiver threshold level for a
given bit-error rate (BER).The radio can handle anything that affects the radio
signal within the fade margin but if it is exceeded, then the link could go down and
therefore become unavailable.
Link Budget (2)

Page 131
 The threshold level for BER=10-6 for microwave equipment used to be about 3dB
higher than for BER=10-3. Consequently the fade margin was 3 dB larger for
BER=10-6 than BER=10-3. In new generation microwave radios with power forward
error correction schemes this difference is 0.5 to 1.5 dB
Link Budget (2)

Page 132
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?

Digital_Microwave_Communication_Principl (1).ppt

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