1-Microwave Technology Overview

Microwave Technology Overview

August 2011

1. Definition and Applications

2. Radio Frequency Spectrum Utilization

3. Generic Structure of a Radio link

4. Protections

Contents

Definition And Applications1

In this chapter you will learn…

… That this section is aimed at introducing the subject by defining the Microwave Radio Relay Link, its transmission capabilities and its application inside telecommunication networks

Characteristics

TerrestrialPoint to pointFixed Line of Sight

Definition: Characteristics

Definitions of Microwave Radio Relay Links

What are the differences between Microwave Radio relay and different radio systems used in telecommunications such as mobile radio, radio broadcasting, satellite or others? To understand this, it is necessary to define the specific features of our subject, namely:

Line of Sight: Radio Relays use microwaves, that are electromagnetic waves with less than 10 centimeters

wavelength. These waves can hardly propagate behind obstacles, therefore, in general circumstances, a good visibility is required between transmitting and receiving antennas.

Fixed: The Microwave Radio Relay systems are not meant to operate in mobile conditions.

Point to Point: Only two Radio terminals are connected together at a time. This allows using high directive antennas

with the possibility of reaching greater distances even when using low transmitted powers. The communication between the two terminals is meant to be both bidirectional or unidirectional.

Terrestrial: Unlike fixed point to point satellite links, Microwave Radio Relay systems connect two points on the

earth surface, where the electromagnetic wave propagation is in the lower part of the atmosphere,i.e., near ground.

As a consequence , the presence of atmosphere and ground affects the RF propagation thus introducing, with given probability, an attenuated or distorted received signal.

Propagation models allow to calculate the probability of outage due to attenuation or distortion caused by atmospheric effects.

The Radio Link is usually designed in such a way that the Power Received in normal propagation conditions, is much greater than the Receiver Threshold, that’s the received power with a minimum acceptable quality of the signal.

Microwave Link Architectures

Site A Site B

Multiple Hop (Linear)Site A Site B

Repeater 1 Repeater 2 Repeater 3

Site C

Site DSite A

Site B

Star connection (multipoint)

Single Hop

Taking into account the visibility between terminals and the possibility of connecting two

points at a time, it becomes necessary to define different Microwave Radio link architectures to match the real topology of the network. They are:

Single Hop:

When conditions of visibility, distance and environment are favorable, the link can be realized with a “single hop” Microwave Radio Relay. The maximum distances that can be achieved with a single hop is between 5-10 kilometers for Radio working in the frequency band above 18 Giga Hertz, and is up to 50-80 kilometers or even more for Radio working in the frequency ranges below 10 Giga Hertz.

Multiple Hop:

If visibility between the two terminal sites to be connected is poor or the distance is too great, the multiple hop architecture must be used. In this case the intermediate radio acts as regenerator, or in other words as active repeater of the signal. In some cases, passive repeaters can be used when the problem is due to visibility, and not to distance.

Star connection:

When several sites must be reached from a main site, a multipoint connection architecture is used. The only way to implement it is by using Microwave Radio Links, and three different hops with three radio terminals in the same location.

Microwave Link Architectures - Definitions

Carried Signals

MW Radio Systems in principle can carry any kind

of signal. Speaking of digital transmission and its

application, it may offer different signal interfaces

and must be able to support any kind of signal

architecture, in particular:

PDH interfaces (ITU-T

rec. G.703)

SDH interfaces (ITU-T

rec. G. 707)

Ethernet interfaces

Which signals can be transported via Microwave Radio? Radio Relay can be equipped with a variety of interfaces, suitable for any kind of network architecture, namely:

For a network based on PDH (Plesiochronous Digital Hierarchy), the E1 and E3 European interfaces as well as the North American T1, T2 and T3 interfaces should be included. In the PDH network, the Microwave Radio Relay transport the signals in a transparent manner.

For network based on SDH (Synchronous Digital Hierarchy), European interfaces (STM-n) as well as the North American (OC-n) interfaces should be included. In the SDH network, the Microwave Radio Relay usually operates as an SDH Regenerator.

For packet data network, normally 10BaseT & 100BaseT Fast Ethernet interfaces are commonly used, However, moving to high speed network, 1000BaseT Gigabit Ethernet interface is also becoming common nowadays.

Carried Signals

Transmission Capacity

The transmission capacity depends on the

applications.

Usually we define:

High Capacity systems: from 155 Mbps

to 622 Mbps capacity (*)

Low Capacity systems: from 2 Mbps

to 34 Mbps capacity

(*) In principle if spectrum is available it can be even more, but in practice

a radio system is not convenient above this capacity.

The different kinds of signals can be carried within the transmission capacity limits of the Microwave Radio equipment. Transmission capacity depends on the purpose, frequency band and spectrum occupancy for which the specific equipment has been designed.

Low capacity Microwave Radio Relays usually include multiplexer devices which carry up to 16 or even 32 E1 or T1 signals. Other types of signal interfaces, such as E3, T2, T3, Fast Ethernet, are normally accepted.

Together with the transported signals, the radio relays are usually provided with additional capacity for service and supervisory channels.

High capacity Microwave Radio Relays usually carry one or two SDH traffic per radio channel. Higher capacities are obtained with multiple radio systems.

Together with the transported signals, high capacity Microwave Radio Links usually have additional capacity for service and supervisory channels, and may also carry some extra E1 signals as way-side traffic.

Transmission Capacity

Application in the transmission networks - 1

Other than commonly use as a communication link,

there are other several conditions where MW Radio

can also applied:

Cable backup or SDH ring enclosure

Temporary links

High security requirement

Application in the transmission networks - 2

In a Network, from a functional point of view, the MW Radio System can play the same role of the physical bearers (fibers or cables), except when very high capacity is required (>1Gbit/s)

In particular, when the cable is not yet available, it can be well used in the following situations due to:

Quick & easy installation and relocation

To avoid rental cost to the incumbent operator

To reach small population groups on difficult terrain where the cable is not convenient to be deployed

To quickly realize long distance connections without pre-existing transport infrastructures.

In which case the use of a microwave radio link is more advantageous than a physical bearer?

Quick and easy installation is very often a “must” for new operators, in order to offer service in a competitive environment and to obtain fast pay-back on investments. In this case, to lay-down new cables means high start-up investment and is time consuming. The alternative solution of renting lines from the pre-existing operator implies evident recurrent cost disadvantages.

But even an incumbent operator may find situations where cables are not convenient to be deployed, such as when having to reach small population groups on difficult terrain.

Application in the transmission networks - 3

Even when copper or optical cable is already available we can find situations where the application of the MW link is advantageous:

• A problem that operators may encounter both in remote areas and in crowded cities is that the cable might break . In conclusion, sometimes it is very convenient to provide MW link backup in order to avoid long periods of complete service unavailability.

• In particular this kind of link redundancy might improve SDH rings availability by realizing, via the radio, one of the branches of the ring (ring enclosure).

• Another situation to consider is that some events, like sport or concerts, may be organized in areas where their standard occupancy require only low bandwidth or capacities. In these cases only MW link are suitable to cover such temporary link requirements.

• Finally, when high security level is required for certain links, the Microwave radio is better than cable because it is much easier to protect the two terminals rather than all the path of a physical line. In addition, the high directivity of the antennas used makes interception difficult.

Application in the transmission networks - 3

Example of Applications: Optical Networks

ADM

ADM ADM

ADM

SDH/SONETRing

SDH/SONETBackboneNetwork

ADM

ADM ADM

ADM

STM1/OC3

Fiber

STM1/OC3

n x STM1STM1/OC3

Remote DistributionNode

Local

Example of Applications: MPLS networks

n*FE, GE

n*FE, GE

TDM

/ETH

LAN router

TDM/

ETH

MPLS

Router

LAN router

LAN router

n*FE, GE

Router

Router

Example of Applications: Mobile Backhauling

Point of Concentration

Access

Network

Point of Concentration

TDM/ETH

Aggregation

Transport

Network

BSC

RNC

TDM/ETH

BTS/Node B

Co-located

Example of Applications: Private Data networks

Exchange

Exchange

Radio Frequency Spectrum Utilization2

In this chapter you will learn…

… This section aims at explaining how the radio spectrum is utilized by the microwave radio links.

… Therefore, it is necessary to first recall the elementary concepts of electromagnetic waves (as wavelength, frequency and polarization) to introduce the concepts of modulation, then to explain how the frequency bands are assigned for different purposes and, finally, how the assigned frequency bands are exploited by the microwave radio channels.

Electromagnetic Waves: definitions

Electromagnetic Waves: Polarization

E

H

EARTH

Vertical Polarization

H

E

EARTH

Horizontal Polarization

Modulation concepts

Modulation is an operation that translates a signal

from the lower frequencies (the baseband) into the

radio frequencies, thus maintaining the same

information of the original signal

Modulation is used as follows:

It is almost physically impossible for the radio

transmission of the lower frequency signals

What is meant by modulation ? Why to use it ?

It allows to translate different signals on different frequencies and to transmit

them at the same time without spectral overlapping

Modulation concepts

V

fMODULATOR

RF

Oscillator

Fo

Bw = 2fmax

Fo+ fmax

f0

FoFo - fmax

B

2fmax

fmax

Channel Spacing

What is a Channel Spacing?

A transmitted modulated signal occupies a given band around the carrier frequency, depending on the kind of modulation and transmission capacity. It is then possible to transmit another modulated signal at a frequency distance (channel spacing) that prevent the two spectra from overlapping and can be separated by the receiver filters. Another possibility of separating two channels is of using different antenna polarizations (vertical or horizontal).

A channel spacing states how the radio relay must allocate its transmission spectrum (the radio channel) inside a given frequency range.

Most of the radio relay applications require bi-directional communication, hence two radio channels are necessary for each link (GO and RETURN channel).

Channel Plans

...

z

x

1

Pol.

H(V)

V(H)

2

3

4y

1’

2’

3’

4’ N’

...

z

F

GO CHANNELS RETURN CHANNELS

N-1 N-1’

x/2 x/2

N

Frequency Bands and Channel Plans

Band Frequency Typical Use

VLF up to 30 kHz Navigation systems

LF 30 – 300 kHz Long-range broadcast, navigation systems

MF 300 – 3000 kHz Medium wave broadcast and communications

HF 3 – 30 MHz Long-range commercial and military communications

VHF 30 – 300 MHz Mobile communications

UHF 300 – 3000 MHz Mobile communications

SHF 3 – 30 GHz Point-to-point microwave links, including satellite communications

EHF >30 GHz Point-to-point microwave links (and other applications)

Generic use of the full radio spectrum

Frequency Bands and Channel Plans

Radio frequency ranges and channel plans for radio-relay systems (Up to 17 GHz)

Band (GHz)

Frequency range (GHz)

Rec. ITU-R F-Series

Channel spacing(MHz)

1.4 1.35-1.53 Rec. [Doc. 9/12] 0.25; 0.5; 1; 2;3.5

2 1.427-2.69

1.7-2.1; 1.9-2.3

1.7-2.3

1.9-2.3

1.9-2.3

1.9-2.3

2.3-.25

2.29-2.26

2.5-2.7

701

382

283

1098

1098, Annexes 1 and 2

1098, Annex 3

746, Annex 1

Rec. [Doc. 9/13]

283

0.5 (pattern)

29

14

3.5; 2.5 (patterns)

14

10

1; 2; 4; 14; 28

0.25;0.5;1;1.75;2;3.5

7;14;2.5 (pattern)

14

4 3.8-4.2

3.6-4.2

3.6-4.2

382

635

635, Annex 1

29

10 (pattern)

90;80;60;40

5 4.4-5.0

4.4-5.0

4.4-5.0

4.54-4.9

746, Annex 2

1099

1099, Annex 1

1099, Annex 2

28

10 (pattern)

40;60;80

40;20

6L 5.925-6.425

5.85-6.425

383

383, Annex1

29.65

90;80:60

6L 6.425-7.11

6.425-7.11

384

384, Annex1

40;20

80

7 7.425-7.725

7.425-7.725

7.435-7.75

7.11-7.75

385

385, Annex 1

385, Annex 2

385, Annex 3

7

28

5

28

Band (GHz)

Frequency range (GHz)

Rec. ITU-R F-Series

Channel spacing(MHz)

8 8.2-8.5

7.725-8.275

7.725-8.275

8.275-8.5

386

386, Annex 1

386, Annex 2

386, Annex 3

11.662

28.65

40.74

14; 7

10 10.3-10.68

10.5-10.68

10.55-10.68

746, Annex 3

747, Annex 1

747, Annex 2

20; 5; 2

7;3;5 (patterns)

5;2.5;1.25 (patterns)

11 10.7-11.7

10.7-11.7

10.7-11.7

10.7-11.7

387, Annex 1 and 2

387, Annex 3

387, Annex 4

387, Annex 5

40

67

60

80

12 11.7-12.5

12.2-12.7

746, Annex 4, § 3

746, Annex 4, § 2

19.18

20 (pattern)

13 12.75-13.25

12.75-13.25

12.7-13.25

497

497, Annex 1

746, Annex 4, §1

28; 7; 3.5

35

25; 12.5

14 14.25-14.5

14.25-14.5

746, Annex 5

746, Annex 6

28; 14; 7; 3.5

20

15 14.4-15.35

14.4-15.35

14.4-15.35

636

636, Annex 1

636, Annex 2

28; 14; 7; 3.5

2.5 (pattern)

2.5

Frequency bands and Channel Plans

Radio frequency ranges and cannel plans for radio-relay systems (above 17 GHz)

Band (GHz)

Frequency range (GHz)

Rec. ITU-R F-Series

Channel spacing(MHz)

18 17.7-19.7

17.7-21.2

17.7-19.7

17.7-19.7

17.7-19.7

595

595, Annex 1

595, Annex 2

595, Annex 3

595, Annex 4

220; 110; 55; 27.5

160

220; 80; 40; 20; 10; 6

3.5

13.75; 27.5

23 21.2-23.6

21.2-23.6

21.2-23.6

21.2-23.6

21.2-23.6

21.2-23.6

22.0-23.6

637

637, Annex 1

637, Annex 2

637, Annex 3

637, Annex 4

637, Annex 5

637, Annex 1

3.5; 2.5 (patterns)

112 to 3.5

28; 3.5

28; 14; 7; 3.5

50

112 to 3.5

112 to 3.5

27 24.25-25.25

24.25-25.25

25.25-27.5

25.25-27.5

27.5-29.5

27.5-29.5

27.5-29.5

748

748, Annex 3

748

748, Annex 1

748

748, Annex 2

748, Annex 3

3.5; 2.5 (patterns)

56; 28

3.5; 2.5 (patterns)

112 to 3.5

3.5; 2.5 (patterns)

112 to 3.5

112; 56; 28

31 31.0-31.3 746, Annex 7 25; 50

38 36.0-40.5 749

749, Annex 3

3.5; 2.5 (patterns)

112 to 3.5

55 54.25-58.2

54.25-57.2

57.2-58.2

1100

1100, Annex 1

1100, Annex 2

3.5; 2.5 (patterns)

140; 56; 28; 14

100

Generic Structure of a Radio link3

Radio link system

Generic Structure

Power

room Power

room

Site A Site B

Parabolic antennas

Tower Tower

FeederFeeder

Equipment

roomEquipment

room

Generic Structure

TRANSMISSION SIDE

RF Tx FILTER

BB INPUT SIGNALIF SIGNAL RF RF OUTPUT

IF/RF TRANMITTERMODULATOR

IF

BB INTERNAL

RF Rx FILTER

BB OUTPUT SIGNALIF SIGNALRFRF INPUT BB INTERNAL

RECEIVING SIDE

BASEBAND

INTERFACE

BASEBAND

INTERFACEDEMODULATOR

IF

R/IFF RECEIVER

Structures of Radio Equipment

Full-Indoor

Split-Mount

BB/MOD/TRANSMITTER

RECEIVER/DEM/BBMW Waveguide

RF

CIRCULATOR

Indoor Outdoor

BB /MOD Units

BB /DEM Units IF CABLE

TRANSMITTER

RECEIVER

Radio Equipment: Full Indoor Structure

Tower

Feeder

Radio

Equipment

(8 transceivers)

Antenna

Radio Equipment: Split-Mount Structure

Tower

Coax

Cable

Microwave Radio - Antenna System

Standard Antenna with Horizontal Polarization

Standard Antenna with Vertical Polarization

High Performance Antenna with radome

Different Equipment Configurations –Protection & Multichannel4

In this chapter you will learn…

… This module aims at introducing the concept of multiple microwave radio-relay equipment in order to increase the capacity or the availability (protection) of the link, and to describe the different possible configurations.

Different Equipment Configurations

Transmission Capacity

Grade of Availability

The configuration of a microwave equipment is depending on the requirement of the specific radio link

application, that may be different as:

This requirement defines if the system can be realized by using a single radio channel or multiple radio channels

This requirement defines if a protection radio channel (the stand-by channel) must be added to the main channel (or channels)

Protection – Definitions

Why protection?

Protection circuits enhance both availability and quality of digital radio systems.

In fact the general reason for the use of switching is the protection against equipment failures in order to increase availability.

But in case the quality of radio channels is limited by multipath propagation conditions, protection switching may also be used to increase error performance (quality) of the link.

Protection – Definitions

Based on the transmission capacity requirement of

the Radio Relay two types of protection are

generally implemented :

N+11+1

The typical notation to indicate the number of radio channels of a system is: N + M , where N stands for the number of main

channels and M stands for the number of stand-by channels (usually 1, but 0 in case of non protected system)

Protection: 1+1 Generic configuration

Mod. Tx

Dem.Tx

BB section

BB

1+1 PROTECTION

Standby channel

Rx Dem.

RxMod.

BB section

Working channel

BB

Hitless Switch

Interface Interface

It is possible to implement three different types of 1+1 protection

1+1 hot standby 1+1 with frequency diversity 1+1 with space diversity

1+1 Protection: 1+1 Hot-Stand-By (HSB) configuration

Mod. Tx

Dem.Tx

BB Section

BB

1+1 PROTECTION

Standby channel

Rx Dem.

RxMod.

BB Section

Working channel

BB

f1 f1

f1 f1

Interface Interface

1+1 Protection: 1+1 Frequency Diversity (FD) configuration

Mod. Tx

Dem.Tx

BB Section

BB

1+1 PROTECTION

Standby channel

Rx Dem.

RxMod.

BB Section

Working channel

BB

f1 f1

f2 f2

Interface Interface

1+1 Protection: 1+1 Hot-Stand-By with Space Diversity (HSB-DA)

1+1 PROTECTION

Mod. Tx

Dem.Tx

BB Section

BB

Standby channel

Rx Dem.

RxMod.

BB Section

Working channel

BBInterfaceInterface

Equipment Configurations - Split-Mount Architecture

Signal from/to

Network

IF Cable

RRA/TFE+MODEM TRANSCEIVER

IDU

(Indoor Unit)

ODU

(Outdoor Unit)

2xRRA/TFE+

2MODEM

2x

TRANSCEIVERS

Compact

Configuration

(1+0)

1+1/2+0

Configuration

A)

B) Signal from/to

Network

- End-of-Document -