1. Digital Microwave Communication Principle ISSUE 1.01

1

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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


Learning Guide

� Before this course, you may refer to these references first:

� SDH Principle

� Network Communication Technology

� Electromagnetism Basics


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


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


Transmission Methods for Communication

Fiber

Microwave

Satellite

MUX MUXRadioTer.

RadioTer.

Coaxial Cable

4


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


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


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.


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


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


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


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


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


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


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


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


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?

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Contents




Equipment



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


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

……


All-outdoor MW Equipment

All-outdoor MW equipment

IF and baseband signal processing unit

IF cable

RF signal processing unit

Service and power cable

12


Split-mount MW Equipment

split-mount MW equipment

Antenna

RF unit or Outdoor unit(ODU)

IF Cable

Indoor Unit


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.

13


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


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

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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


Antenna Aligning

Side viewSide lobe

Rear lobe

Top viewRear lobe

Side lobe

Main lobe

Main lobe

15


Antenna Aligning

CorrectWrongWrong


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


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.


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


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.



� 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



� 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.


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

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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？


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


Contents




Equipment



Common Networking Application

RingPoint to point

link

Add / drop link

Tree

21


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


Types of Relay Stations

Relay station

Active

Passive • Parabolic reflectors

• Plane reflector

• Regenerative relay

• IF relay

• RF relay

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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.


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


Passive Relay (actual picture)

Plane reflectors Parabolic reflectors


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


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?


Contents




Equipment


25


Contents


4.1 Microwave Propagation and fading

4.2 Antifading Technologies


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


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.


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


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


Absorption Loss

� It is mainly caused by atmosphere.

28


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.


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


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


Duct Type Fading

� When electric waves pass the atmospheric waveguide, super reflection occurs.

sketch map of Duct Type fading

30


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


Flat Fading

1 h

Receive level in free space

Threshold (-30dB )

Signal interruption

Upward fading

Fast fading Slow

fading

31


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.


Contents


4.1 Microwave Propagation and fading

4.2 Antifading Technologies

32


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


Adaptive Frequency Equalization

Signal spectrum

Multi-path fading

Slope frequency domain

equalization

Spectrum after

equalization

33


Adaptive Time Equalization

BeforeEqualization

… …T T T

AfterEqualization

C-n C0 Cn

Ts-Ts-2Ts Ts-Ts-2Ts


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


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’


Diversity Reception

� Diversity reception is used to minimize the effects of

fading. It includes:

� Space diversity (SD)

� Frequency diversity (FD)

� Polarization diversity

� Angle diversity

35


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


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


Other Antifading Methods

� blocking the reflected wave by some terrain or obstacles.


Other Antifading Methods (cont.)

� Different height antennas in one hop.

37


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?


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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1. Digital Microwave Communication Principle ISSUE 1.01

Documents

optix rtn

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