CE000382 Communications

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CE00038-2Communications
Introduction to Communication Systems
Mostafa Abdel-Aleem Room K318, Phone 01785
35 3255 Email M.E.Abdel-Aleem_at_staffs.ac.uk

• Acknowledgment
• Dr Mohammad N Patwary
• Room C336 (Beacon)
• Email m.n.patwary_at_staffs.ac.uk
• Phone 353 557

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Introduction

• Every day, in our work and in our leisure time,
  we come in contact with and use a variety of
  communication systems.
• The most common communication media being the
  telephone, radio, television and Internet.
• Through these media we are able to
• communicate (almost) instantaneously with people
  all over the world, even on different continents,
• perform our daily business and receive
  information about various developments and events
  that occur all around the world.
• Electronic mail and Facsimile transmission have
  made it possible to rapidly communicate written
  massages across larger distances.

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Developments in Communication

• The growth in communication services over the
  past fifty years has been phenomenal.
• The invention of the Transistor in 1947 by
  Walter Brattain, John Bardee and William
  Shockley
• the Integrated Circuit (IC) in 1958, by Jack
  Kilby and Robert Noyce and
• the Laser by Townes and Schawlow in 1958,
• have made possible the development of
  small-size, low-power, low-weight and high-speed
  electronic Circuits, which are used in the
  construction of Satellite Communication systems,
  wide-band microwave radio systems, and light-wave
  communication systems using fibre optics cables.
• A satellite named Telster I was launched in
  1962 and used to transmit TV signals between
  Europe and the United States.
• Commercial Satellite communication services began
  in 1965 with the launching of the Early Bird
  Satellite.

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Developments in Communication

• Currently, most of the wire-line communication
  systems are being replaced by Fibre optic cables,
  which provide extremely high bandwidth and make
  possible the transmission of a wide variety of
  information sources, including voice, data and
  video.
• Cellular Radio has been developed to provide
  telephone service to people in automobiles,
  buses, and trains. High speed communication
  networks link computers and a variety of
  peripheral devices literally around the world.
• Today we are witnessing a significant growth in
  the introduction and use of personal
  communication services, including voice, data,
  and video transmission.
• Satellite and fibre optic network provide
  high-speed communication services around the
  world. Indeed, this is the birth of the Modern
  telecommunication Era.

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A Communication system

• The heart of any communication system consists of
  three basic parts, namely
• The transmitter
• The channel
• The receiver.

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A Communication system

• Electrical Communication systems are designed to
  send messages or information from a source that
  generates the messages to one or more
  destinations. In general, a communication system
  can be represented by the functional block
  diagram

Information source and input transducer
Transmitter
Channel
Receiver
Output Signal and output transducer
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A Communication system

• The information generated by the source (may be
  of the form of voice (speech source), a picture
  (image source), or plain text in some particular
  language, such as English, Japanese, German,
  French, etc.
• An essential feature of any source that generates
  information is that its output is described in
  probabilistic term i.e. the output of the source
  is not deterministic. Otherwise, there would be
  no need to transmit the message.
• A transducer is usually required to convert the
  output of the source into an electrical signal
  that is suitable for transmission.
• For example, a microphone serves as the
  transducer, that converts an acoustic speech
  signal into an electrical signal, and a video
  camera converts an image into an electrical
  signal. At the destination, a similar transducer
  is required to convert the electrical signal that
  are received into a form that is suitable for the
  user i.e. acoustic signal, image etc.

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The transmitter

• The transmitter converts the signal into a form
  that is suitable for transmission through the
  physical channel or Transmission medium.
• For example, in radio and TV broadcast, the
  Federal Communication Commission (FCC) specifies
  the frequency range for each transmitting
  station.
• The transmitter must translate the information
  signal to be transmitted into the appropriate
  frequency range that matches the frequency
  allocation assigned to the transmitter.
• Thus, signals transmitted by multiple radio
  stations do not interface with one another.
• Similar functions are performed in telephone
  communication systems where the electrical speech
  signals from many users are transmitted over the
  same wire.

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The transmitter

• In general, the transmitter performs the matching
  of the message signal to the channel by a process
  called modulation.
• Usually, modulation involves the use of a strong
  carrier signal (usually sinusoidal) to carry the
  information signal on its amplitude, frequency or
  phase.
• For example,
• In Amplitude Modulation (AM) radio broadcast, the
  information signal that is transmitted is
  contained in the amplitude variations of the
  sinusoidal carrier having a centre frequency in
  the frequency band allocated to the radio
  transmitting station.
• In Frequency Modulation (FM) radio broadcast, the
  information signal that is transmitted is
  contained in the frequency variations of the
  sinusoidal carrier.
• In Phase Modulation (PM) the information signal
  is contained in the phase variations of the
  sinusoidal carrier.

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The transmitter

• In general, carrier modulation techniques such as
  AM, FM and PM is performed at the transmitter to
  convert the information signal to a form that
  matches the characteristics of the channel and is
  suitable to be transmitted through it.
• Thus, through the process of modulation, the
  information signal is translated into frequency
  to match the allocation of the channel.
• The choice of the type of modulation is based on
  several factors, such as the amount of bandwidth
  allocated, the types of noise and interference
  that the signal encounters in transmission over
  the channel, and the electronic devices that are
  available for signal amplification prior to
  transmission.
• In any case, the modulation process makes it
  possible to accommodate the transmission of
  multiple messages from many users over the same
  physical channel.
• In addition to modulation, other functions that
  are usually performed at the transmitter are
  filtering of the information-bearing signal,
  amplification of the modulated signal, and in the
  case of wireless transmission, radiation of the
  signal by means of a transmitting antenna.

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The channel

• The communication channel is the physical medium
  that is used to send the signal from the
  transmitter to the receiver.
• In wireless transmission, the channel is usually
  the atmosphere (free space).
• On the other hand, telephone channels usually
  employ a variety of physical media, including
  wire-lines, optical fibre cables, wireless
  (microwave radio).
• Whatever the physical medium of the signal
  transmission, the essential feature is that the
  transmitted signal is corrupted in a random
  manner by a variety of possible mechanism.

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The noise

• The most common form of signal degradation comes
  in the form of additive noise, which is generated
  at the front end of the receiver, where signal
  amplification is performed, and is often called
  thermal noise.
• In wireless transmission, additional additive
  disturbance are manmade noise and atmospheric
  noise picked up by a receiving antenna.
• Automobile ignition noise is an example of
  manmade noise, and electrical lightning
  discharges from thunderstorms in an example of
  atmospheric noise.
• Interference from the other users of the channel
  is another form of additive noise that often
  arises in both wireless and wire-line
  communication systems.

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The channel

• Another form of signal degradation is multi-path
  propagation.
• Such signal distortion is characterised as
  non-additive signal disturbance which manifests
  itself as time variation in the signal amplitude,
  usually called fading.
• Both additive and non-additive signal distortions
  are usually characterised as random phenomena and
  described in statistical terms.
• The effect of these signal distortions must be
  taken into account on the design of the
  communication systems.
• In the design of the communication systems, the
  system designer works with mathematical models
  that statistically characterize the signal
  distortion encountered on physical channels.

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The channel

• Often, the statistical description that is used
  in a mathematical model is a result of actual
  empirical measurements obtained from the
  experiments involving signal transmission over
  such channels.
• In such cases, there is a physical justification
  for the mathematical model used in the design of
  communication systems.
• On the other hand, in some communication system
  designs, the statistical characteristics of the
  channel may vary significantly with time.
• In such cases, the system designer may design a
  communication system that is robust to the
  variety of signal distortions. This can be
  accomplished by having the system adapt some of
  its parameters to the channel distortion
  encountered.

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The Receiver

• The function of the receiver is to recover the
  original message signal contained in the received
  signal.
• If the message signal is transmitted by carrier
  modulation, the receiver performs the carrier
  demodulation in order to extract the message from
  the sinusoidal carrier.
• Since the demodulation is performed in the
  presence of additive noise and possibly other
  signal distortion, the demodulated message signal
  is generally degraded to some extent by the
  presence of these distortions in the received
  signal.

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The Receiver

• The fidelity of the received message signal is a
  function of
• the type of modulation,
• the strength of the additive noise,
• the type and strength of any other additive
  interference and
• the type of any non-additive interference.
• Besides performing the primary function of signal
  demodulation, the receiver also performs a number
  of peripheral functions, including signal
  filtering and noise/interference suppression

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Ways of communications

• Telephone
• Wired Phone
• Wireless
• Cordless
• Paging
• Mobile
• Voice
• Text
• MMS
• Facsimile
• Navigation System
• Satellite
• GPS
• Radar
• Sonar

• Letter by post
• Telegraph
• Television
• Radio
• Internet
• Internet Telephony (VoIP)
• Email Etc.

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Telephone Network
SC
Switching Center
Local Terminal (phone)
LT
?1km
LT
?1000km
SC
?1000km
SC
LT
?1000km
SC
?1000km
London
SC
Birmingham
Glasgow
SC
Manchester
SC
WAN
Wide Area Network
?1km
?1km
LT
To Other Countries
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Telephone History
1876 Bell phone
1895
1897
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Telephone History
1904
1927
1937
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Telephone History
2001 Office Phone
1963
1990
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Cordless System

• Cordless telephone (CT) is a communication system
  using radio to connect portable handset to a
  dedicated fixed port (base station) which is
  connected to PSTN as a normal telephone line
  (using ordinary telephone numbers)
• CT provide limited range and mobility in the
  vicinity of the base station (100 m)

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Cordless Telephone
Public Switched Telephone Network (PSTN)
Wireless link
100 m
Fixed Port
Cordless Handset
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Satellite Communication System

• In a geostationary satellite system, a message
  signal is transmitted from an earth station via
  an uplink to a satellite, amplified in a
  transponder on board the satellite, and then
  retransmitted via downlink to another earth
  station.

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Cellular Communication System

• Cellular telephones are personally portable
  devices that may be used in motor vehicles or by
  pedestrians.
• Communicating by radio-wave in the
  800-900-megahertz band, they permit a significant
  degree of mobility within a defined serving
  region that may be hundreds of square kilometers
  in area.

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Cellular System
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Cellular Telephone System
Base Transceiver Station
Forward Control channel Transmit control
information from BS to mobile unit
Forward voice channel Transmit voice
information from BS to mobile unit
Reverse Control channel Transmit control
information from mobile unit to BS

• Reverse Voice
• channel
• Transmit voice information
• from mobile unit to BS

Control Channel call setting call request
call initiation other control purpose
Mobile Switching Center (MSC) coordinates the
routing of calls in a large service area.
PSTN
PSTN Public Switching Telephone Network
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Cellular Coverage

• The geographic area to be served by a cellular
  radio system is broken up into smaller geographic
  areas, or cells.
• Uniform hexagons most frequently are employed to
  represent these cells on maps and diagrams
• In practice, though, radio-waves do not confine
  themselves to hexagonal areas, so that the actual
  cells have irregular shapes.
• All communication with a mobile or portable
  instrument within a given cell is made to the
  base station that serves the cell.

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Important Dates

• 1840 Morse code and improved telegraph
• 1876 Telephone patent
• 1894 Wireless transmission of signals
• 1906 Triode (electronic amplifier)
• 1917 Amplitude modulation (AM)
• 1928 Frequency modulation (FM)
• 1948 Discovery of Transistor and Information
  Theory
• 1954 Transistor radio

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Development of Mobile Telephone Systems.

• In the United States, interconnection of mobile
  radio transmitters and receivers (transceivers)
  with the PSTN began in 1946, with the
  introduction of mobile telephone service (MTS) by
  ATT.
• The MTS system employed frequencies in either the
  35-megahertz band or the 150-megahertz band.
• A mobile user who wished to place a call from a
  radio telephone had to search manually for an
  unused channel before placing the call.

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Mobile Telephone Service (MTS) by ATT

• In MTS the user spoke with a mobile operator, who
  actually dialed the call over the PSTN.
• The radio connection was simplex--i.e., only one
  party could speak at a time
• The call direction was controlled by a
  push-to-talk switch in the mobile handset.

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Path to 3G Mobile Communication Systems

• First Major Migration Path
• I Gen, 80s, ETACS (C-450,NMT-450..), (FDMA),
  Analog
• II Gen, 90s, GSM, GPRS, EDGE, (TDMA) Digital
• III Gen, 00s, W-CDMA , (CDMA), All Digital
• Second Major Migration Path
• I Gen, 80s, AMPS, (FDMA), Analog
• II Gen, 90s, IS-54 (TDMA), IS-95 (CDMA),
  Digital
• III Gen, 00s, Cdma2000 (CDMA), All Digital