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Digital Microwave
Communication
Principles
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.
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
Contents
1.
Digital Microwave Communication Overview
Transmission Methods
in Current Communications
Networks
Optical fiber communication
Microwave communication Satellite communication MUX/DEMUX MUX/DEMUX M ic ro w a v e T E M ic ro w a v e T E
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.
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
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 1 0 2 0 1 3 0 4 0 5 0 1.5 GHz 2.5 GHzLong 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 GHzRegional network
Regional network, local
network, and boundary
Digital Microwave
Communication Modulation (1)
英
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
B a se b a n d s ig n a l ra te C h a n n e l b a n d w id th Modulati on Service signal transmitted
Questions
What is microwave?
What is digital microwave communication?
What are the frequently used digital microwave frequency
bands?
What are the frequently used modulation schemes? Which are
Contents
1.
Digital Microwave Communication Overview
2.
Digital Microwave Communication Equipment
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/DEMU X Mode
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
…
…
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
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)
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
Split-Mount Microwave
Equipment
– Installation
antenna (separate mount) OD U IF cable 英英英Separate
Mount
Soft waveguide IDU IF port antenna (direct mount) ODU IDUDirect
Mount
IF cable IF portMicrowave 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.
Different frequency channels in same frequency band can share one
antenna.
Microwave Antenna (2)
T
x
R
x
T
x
R
x
Chann
el
Chann
el
1
1
n
n
1
1
n
n
Antenna Adjustment (1)
Side view Side lobe
Main lobe
Half-power angle Tail lobe
Top view Main lobe
Side lobe
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
Antenna Adjustment (2)
Side lobe position AGC Voltage detection
point VAGC
Main lobe position
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.
Correct
Wrong
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
Questio
ns
What types are microwave equipment classified into?
What units do the split-mount microwave equipment have?
And what are their functions??
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
Contents
1.
Digital Microwave Communication Overview
2.Digital Microwave Communication Equipment
Common Networking Modes of
Digital Microwave
Ring network
Chain network
Add/Drop
network
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
application
Questio
ns
What are the networking modes frequently used for digital
microwave?
What are the types of digital microwave stations?
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
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 RFSOH control unitSwitching
P P M M11 M M22 M M33 P P M M11 M M22 M M33 ch ch11 ch ch22 ch chPP ch ch33 ch ch11 ch ch22 ch chPP ch ch33
Protection Modes of
Digital Microwave Equipment (3)
Configurati
on Protection Mode
Remark
s 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 and channel protection Inter-frequency N+1 FD Equipment protection and channel protection Inter-frequency Large-capacity backbone network