Chapter 4: Practical Communication Systems

1
Chapter 4Practical Communication Systems
2
Outline

• Fibre Optic Communication System
• Telephone System
• Radio Communication System
• Satellite Communication System
• Telecommunication Networks

3
Outline

• Fibre Optic Communication System
• 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

4
Outline

• Telephone system
• Introduction
• Public telephone network
• Telephone connection signalling
• Mobile telephone system
• Cellular concept
• Frequency re-use in cellular communication

5
Outline

• Radio communication System
• Introduction
• Radio wave propagation
• Microwave radio system (analog and digital
  microwaves radio transmitters and receiver)
• Radio services

6
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

7
Outline

• Telecommunication Networks
• Introduction
• LAN, MAN and WAN
• Network Topology

8
Fibre Optic Communication System

• 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

9
Fibre Optic Communication System

• Elements in an optical fiber communication link

10
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

11
Fibre optic - Basic elements

• 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)

12
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
13
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

Multimode step-index fiber
14
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

Multimode graded-index
15
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

16
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)

17
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
18
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

19
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

20
Satellite communication system
The uplink and downlink use different carrier
frequencies to avoid interference, and the
frequency translation is done in the transponder.
21
Satellite transponder

• 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

22
Satellite transponder
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
23
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

24
Earth station
Tel
Data
To Satellite transponder
Video
Up-Converter
AN EARTH STATION TRANSMITTER
25
Earth station
Tel
Data
To Satellite transponder
Video
Up-Converter
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.

26
Earth station
From satellite transponder
AN EARTH STATION RECEIVER
Data
Baseband out (FDM or PCM/TDM)
Demodulator (FM, PSK or QAM
Video
Tel
Down-Converter
- 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)
27
Frequency Allocation
28
Satellite Orbit

• 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".

29
Satellite Orbit

• Three basic types of orbits are
• Polar orbit
• North-south orbit
• Used for navigation, weather
• satellite, meteorological etc
• Not used for telecommunication
• purposes
• 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
30
Satellite Orbit

• 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 earths surface.
• The satellite is visible from 1/3
• of the earths surface, so 3
• satellite are needed for full
• coverage of the earth

Basic orbits
31
Satellite Orbit
Polar orbit
Elliptically inclined
Equatorial orbit
32
System performance
LNA low noise amplifier Pt - total
radiated power, Pt Po - Lf EIRP - Effective
Isotropic Radiated Power EIRP Pt
Gt
HPA high power amplifier Po - HPA output
power Lf - feeder loss Gt - transmit
antenna gain Lp - path loss Gr - receive
antenna gain
33
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.

34
(No Transcript)
35
Uplink Chains

• 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.

36
Downlink Chains

• 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.

37
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

38
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

39
Telecommunication Networks

• 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.

40
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)

41
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

42
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)

43
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

44
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

45
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

46
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)

47
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
  

48
(No Transcript)
49
Local Area Network Topologies

• Local Area Networks (LANs) use one of the
  following designs. These designs are referred to
  as 'topologies'.

50
(No Transcript)
51
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.

52
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

53
Telephone

• Mobile telephone system
• Mobile set (handset)
• Radio base station (RBS)
• Mobile switching centre (MSC)
• Cellular concept
• Frequency re-use in cellular communication

54
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

55
Mobile Telephone System
56
Radio Communication 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

57
Radio Communication System

• Microwave radio system (analogue and digital
  microwaves radio transmitters and receiver)

The main difference is the modulation technique
used and the multiplexing technique
58
Radio Communication System

• Radio services