chapter 4: practical communication systemsee.ump.edu.my/hazlina/teaching_pcom/chapter4 practical...

18/09/2016 Nurul/DEE 3413/Practical Com System 1

Chapter 4:

Practical Communication Systems


Outline

Fibre Optic Communication System

Telephone System

Radio Communication System

Satellite Communication System

Telecommunication Networks


Outline:


Introduction

Elements in an optical fiber communication link

Propagation mode

Advantages fiber optic cables over conventional electrical cables

Attenuation in fiber optic link

Application of fiber optic system


Outline:

Telephone system

Introduction

Public telephone network

Telephone connection signalling

Mobile telephone system

Cellular concept

Frequency re-use in cellular

communication


Outline:

Radio communication System

Introduction

Radio wave propagation

Microwave radio system (analog and digital

microwaves radio transmitters and

receiver)

Radio services


Outline:

Satellite communication system Introduction

Satellite transponder

Satellite system links

Earth stations

Frequency allocations

Satellite orbit

System performance

Applications of satellite communications

Advantages of satellite system

Disadvantages of satellite system


Outline:


Introduction

LAN, MAN and WAN

Network Topology



Introduction

Fiber optic system is a communication system that

carries information through a guided fiber optic

cable

Light frequencies used in fiber optic systems are

between 1014 and 4x1014 Hz

Thus, the higher the carrier the carrier frequency,

the wider the bandwidth and consequently, the

greater the information carrying capacity



Elements in an optical fiber

communication link


Fibre optic - Basic elements

The main elements are:

Driving circuitry: Serves as an electrical interface between the input circuitry and

light source and to drive the light source

Light source LED / LASER

Convert electrical energy to optical energy, where the amount of light emitted is proportional to the amount of drive current

Light source-to-fiber coupler An interface to couple the light emitted by the source into the

optical fiber cable

Fiber optics Long thin strand of glass or plastic fiber used to signal in a form of

light from a point to another point


Fiber optics Long thin strand of glass or plastic fiber used to signal in a form of

light from a point to another point

Fiber-to-detector coupler Interface between fiber and light detector to couple as much light as

possible from the fiber cable into the light detector

Light detector PIN (p-type-intrinsic-n-type) diode / an APD (avalance photodiode)

Fibre optic - Basic elements


Propagation Mode

Monomode fiber (core 8 ~ 12

um)

Only one path for the light to

propagate

along fiber

All light rays follow the same

path down

the cable and take the same

time to

travel the length of the cable

Monomode step-index fiber


Propagation Mode

Multimode step index fiber (50

~200 um)

More than one path for light

propagate

along fiber

Light ways are propagated

down the cable

in a zig-zag pattern and all the

light rays

do not follow the same path

with

different propagation time

fastest modeslowest mode

input pulse output pulse

Multimode step-index fiber


Propagation Mode

Multimode graded index fiber

Light is propagated down the

fiber

by refraction which result a

continuous bending at the light

rays,

Then the rays traveling near

the center,

so that all the rays arrive at the

end

point at the same time input pulse output pulse

Multimode graded-index


Fiber optic - Advantages

Wider bandwidth: have higher information to carry

Lower loss/attenuation: there is less signal attenuation over long distance

Light weight: higher than copper cable and offer good benefit where weight is critical (plane)

Small size: smaller diameter than electrical cable

Strength: as it has cladding, they offer more strength

Security: cannot be ‘tapped’ easily as electrical cable


Attenuation

The attenuation in fiber optics are due

mainly to:

Scattering losses (kehilangan serakan)

Absorption losses (kehilangan penyerapan)

Bending losses (kehilangan pembengkokan /lenturan)

Splicing loss

Coupling losses (kehilangan gandingan)


Attenuation – standard fiber

1st window wavelength :0.85 um The lowest minimum loss: 5 to 10 db/km

2nd window 1.30 um 0.5 to 2 dB/km

3rd window 1.55 um 01. to 0.5 dB/km


Application of fiber optic cable

Some of the applications of fiber optic

Long haul, backbone public and private networks

Local loop networks

Fiber backbone networks (LAN connectivity)

High resolution image and digital video

Computer networks, wide area and local area

Shipboard communications

Aircraft communications and controls

Interconnection of measuring and monitoring instruments in plants and laboratories


Satellite communication system

Satellite communications utilizes radio frequencies in the

microwave range as the communications medium and uses

satellites to 'bounce' an earth-bound station's uplink signal

back down to a receiving earth station.

A satellite system consist of:

A transponder (a radio repeater in the sky)

A ground-based station to control this operation

A user network of earth stations that provide the facilities for transmission and reception of communication traffics through the satellite station


The uplink and downlink use different carrier frequencies to avoid interference, and the frequency

translation is done in the transponder.

Satellite communication system



Satellite transponder acts like a repeater,

consists of a receiver and a transmitter. The

main functions of a satellite transponder are:

To pick up the transmitted signal from the

transmission on the earth

To amplify the signal

To translate the carrier frequency to another

frequency

To retransmit the amplified signal to the receiver on

the earth



Earth

station

Earth

station

Band pass

filter

Low noise

Amplifier

(LNA)

Mixer Band pass

filter

(BPF)

Low power

Amplifier

Local

oscillator

Frequency translator

A satellite transponder

BPF – limits the total noise

LNA amplifiers – receive signal and fed it to the frequency translator

Freq. translator – convert the high-band uplink frequency to the low-band downlink frequency


Satellite system link

Uplink Path of the satellite signal from the earth transmitter to the

receiver of the satellite.

The freq. signal being transmitted from the earth station to the satellite is called uplink frequency

eg: uplink freq. for C-band is 6 Ghz

Downlink Path of the satellite signal from the satellite transmitter to the

receiver on the earth

The retransmitted signal from the satellite to the receiving stations is called the down-link

eg: downlink freq. for C-band is 4 GHz


Earth station

Baseband in

FDM or

PCM/TDM

Modulator

(FM, PSK or

QAM)

Mixer Band pass

filter

(BPF)

High Power

Amplifier

(HPA)

Generator

Up-Converter

Tel

Data Video

To

Satellite

transponder

AN EARTH STATION TRANSMITTER

Low noise

Amplifier

(LNA)

Demodulator

(FM, PSK

or QAM

Mixer Band pass

filter

(BPF)

Generator

Down-Converter

Baseband out

(FDM or

PCM/TDM) Tel

Data Video

From satellite

transponder

AN EARTH STATION RECEIVER


Earth station

Baseband in

FDM or

PCM/TDM

Modulator

(FM, PSK or

QAM)

Mixer Band pass

filter

(BPF)

High Power

Amplifier

(HPA)

Generator

Up-Converter

Tel

Data Video

To

Satellite

transponder

AN EARTH STATION TRANSMITTER

- Intermediate freq (IF) modulator converts the input baseband signals

to either an FM, a PSK or a QAM modulated intermediate frequency.

- The up converter converts the IF to an appropriate RF carrier freq.

- The High Power Amplifier (HPA) provides the adequate input

sensitivity and output power to propagate the signal to the satellite

transponder.


Earth station

Low noise

Amplifier

(LNA)

Demodulator

(FM, PSK

or QAM

Mixer Band pass

filter

(BPF)

Generator

Down-Converter

Baseband out

(FDM or

PCM/TDM) Tel

Data

Video

From satellite

transponder AN EARTH STATION RECEIVER

- LNA which is highly sensitive and low-noise device amplifiers the

received signal.

- The RF to IF down-converter is a mixer and bans pass filter

combination, which converts the received RF signal to an

intermediate frequency (IF)


Frequency Allocation


Sattellite Orbits Satellites are launched into orbit, which is to say

that they are shot up into the sky on rockets to get

them up above the atmosphere where there is no

friction. The idea is to get them flying so fast, that

when they fall back to earth, they fall towards earth

at the same rate as the earth's surface falls away

from them. When an object's path around the earth

"trajectory" matches the earth's curvature, the

object is said to be "in orbit".

Satellite Orbit


Satellite Orbit

Three basic types of orbits are:

1. Polar orbit

North-south orbit

Used for navigation, weather

satellite, meteorological etc

Not used for telecommunication

purposes

2. Elliptically inclined orbit

Used for Russian domestic systems,

with inclination of 63 degrees and a

12 hour orbit period, but visible for

8 hours only

So 3 satellites are needed for

continuous coverage

Basic Orbits


Satellite Orbit

3) Circular equatorial orbit

It is called geosynchronous orbit

At a height of about 35800 km, has 24 hour orbit period, and its

angular speed is equal to the rotational speed of the earth.

So it appears stationary or motionless over a fixed point on the earth’s surface.

The satellite is visible from 1/3

of the earth’s surface, so 3

satellite are needed for full

coverage of the earth

Basic orbits


Equatorial

orbit

Polar orbit

Elliptically

inclined

Satellite Orbit


System performance

Transponder

Gain, Gsat

HPA LNA

Uplink Downlink

Gr Gt

Lp Lp

Pr

Gr Gt

Lf

Pt

Po Pin

Earth station transmitter Earth station receiver

HPA – high power amplifier

Po - HPA output power

Lf - feeder loss

Gt - transmit antenna gain

Lp - path loss

Gr - receive antenna gain

LNA – low noise amplifier

Pt - total radiated power, Pt = Po - Lf

EIRP - Effective Isotropic Radiated Power

EIRP = Pt * Gt


Uplink And Downlink Chains

The term uplink chain is used to refer to the series of pieces

of equipment that are used to produce a radio frequency

signal for sending out data. The description provided here is

imprecise as the exact configuration can vary widely.

The downlink chain is built using nearly the same equipment

in reverse order.


Digital data - modulator ( Intermediate Frequency range (70-140 Mhz)). The modulators use standards such as Digital Video Broadcast to organize communication over the microwave link.

The Intermediate Frequency - "up converter" - a higher frequency

Noise removed - a band pass filter - then amplified.

Signal - transmitted - wave guide to the dish.

The feed horn at the focal point of the dish emits the high frequency radio transmission, which the dish focuses into a directional transmission at the satellite.

Uplink Chains

http://www.inetdaemon.com/tutorials/satellite/frequency.html


The signal is received at the sattellite dish

The signal is amplified and fed to the Down Converter

The Down Converter down mixers the signal to create an intermediate frequency

The intermediate frequency is fed to the demodulator and converted into a data signal

The datastream is forwarded into the network via a router.

Downlink Chains

http://www.inetdaemon.com/tutorials/satellite/frequency.html


Application of satellite communication

Some of the application s of satellite communications are:

Digital audio broadcasting

Television distribution

Serving remote areas

Point-to-multipoint communications

Remote monitoring and control

Vehicle tracking

Mobile communications

Maritime and air navigation

Video teleconferencing


Advantages/disadvantages of

satellite system

Advantages of a satellite system include:

It can access to wide geographical area

Wide bandwidth

High reliability

Distance sensitive cost

Independent of terrestrial infrastructure

Disadvantages of satellite system

High initial cost

It has propagation delay



“A network is a communication system that interconnects many users and is designed to let any user send messages to any and/or all other users on a common set of communication links”

The word network is used generally to mean a set of computers that are connected together in such a way as to permit them to communicate and share information.

Network applications: Offices

Linking various personal computers

Interconnecting larger computers located in different buildings or cities etc.

http://www.inetdaemon.com/tutorials/computers/index.html


LAN, MAN and WAN

Three categories of networking depends on the

application: LAN, MAN and WAN

LAN (Local Area Networks)

MAN (Metropolitan Area Networks)

WAN (Wide Area Networks)


LAN

Is a data communication network across a limited

area, at most 5 km

Permit the users (normally 10 – 100 users) to share

information and computers sources include data

storage, software, printer, etc

Is used to connect several offices within the same

building, or in a working group or as a campus

backbone


MAN

Medium- sized network

Cover an area between 5 – 50 km

Typically MAN may use coaxial cables or optical fiber as the medium

Provide services such as audio, data and video

High capacity backbone (1.544 Mbps or 45 Mbps)


WAN

Cover a large area, more than 50 km

Typically, WAN is a packet switching network

Used in internet, electronic mail, airline reservation system

In some cases, WAN is built of smaller LANs that are closely linked, or made of mixed combinations of LANs and special longer distance links

Connect computers located over large geographical areas through some combination of telephone lines, satellite, radio transmission and optical fiber over public switched telephone network (PSTN) or private network facilities


Network Topology

Network topology is a physical schematic for the different configuration or arrangements, to show the interconnection of the users

The logical topology concerns signal flow in the network or how data actually travels

There are 3 basic topologies: Star network topology

Ring network topology

Bus network topology


Ring network topology

users - connected in closed path

token-passing ring protocol - predictable access time to the network

Ring scheme node accepts the message- processes - extracts data -modifies

message - passes it on to the next node

A drawback of the ring The failure of any node - cause breakdown over come by :

Dual or redundant path as a standby path

Watchdog circuitry: When it detect a problem with the node, it sets a switch which electrically by-passes that node


Bus network topology

all user nodes - connected

by a bus - a coaxial cable

or parallel-wire line

The signals can move in

both directions along the

bus

Advantage - use a single path - saves cost

Drawback – rewiring difficulty - complicated protocols – CSMA/CD (carrier sense multiple access/collision detect)


Star network topology

all user nodes - connected

to a central hub

The signals are sent to

central point

Advantage – expanding flexibility

Drawback – slow – need to go through central hub


Local Area Network Topologies

Local Area Networks (LANs) use one of the following

designs. These designs are referred to as 'topologies'.


Example:

1. A satellite transponder has a gain of 50 dB. Its

receiving and transmitting antenna have equal gain of

20 dB. If the receiving antenna receives a signal

power of 10 uW from the earth transmitter, determine

the signal power at the output of the satellite

transmitting antenna.


Telephone

Telephone system

Public telephone network

- Local loop or local network

- Junction network

- Trunk network or toll network

- # international gateway

Telephone connection signalling

- Speech signal/information signal (in analogue form)

- Control signal (in analogue or digital form)

- Dialling tone

- Ringing tone

- Busy tone


Mobile telephone system

Mobile set (handset)

Radio base station (RBS)

Mobile switching centre (MSC)

Cellular concept

Frequency re-use in cellular communication

Telephone


Mobile Telephone System

Basic elements of a mobile telephone system are:

Mobile set (handset) Act as a small radio station equipment with transmitter and

receiver which has an antenna and push button set to enable users to make or receive call through public network

Radio base station (RBS) Handle the exchange between user and respected area

(serves as a centre node for all users)

Receive signal and rebroadcast it at higher power

Mobile switching centre (MSC) Handles the exchange from RBS to PSTN


Mobile Telephone System



Radio communication System Introduction

- Is a wireless communication system by using the propagation of electromagnetic signals through free-space

- Two categories of radio systems:

- Conventional AM or FM radio

- Digital radio system

- In digital radio system, the modulating and demodulated signals are digital pulses.

- Three digital modulation techniques that are commonly used in digital radio systems:

- FSK, PSK and QAM

Radio wave propagation - Ground wave : low freq (LF) and medium freq (MF) bands

- Space wave: VHF, UHF and higher freq bands

- Sky wave: MF and HF bands


Microwave radio system (analogue and digital microwaves

radio transmitters and receiver)

The main difference is the modulation technique used and the multiplexing technique



Radio services


chapter 4: practical communication systemsee.ump.edu.my/hazlina/teaching_pcom/chapter4 practical...

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