Telecommunication Systems 1

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Telecommunication Systems1

• Prof. Dr. Tayfun Akgül

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COMMUNICATION ENGINEERING

• Course Code ISE301
  
• Course title Telecommunication Systems
• Credit Hours 3
  
  
• Semester Fall 2009
  
• Instructor Prof. Dr. Tayfun AKGÜL
• Course Page http//atlas.cc.itu.edu.tr/akgult
  ay/
• Refernece Book A. B. Carlson, P.B. Crilly, J.C.
  Rutledge, Communication Systems, McGraw-Hill,
  4th Edition, 2002.

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Syllabus - I

• Introduction to Signals
• General Topics in Communications and Modulation
• Spectral Analysis
• Fourier Series
• Fourier Transform
• Frequency Domain Representation of Finite Energy
  Signals and Periodic Signals
• Signal Energy and Energy Spectral Density
• Signal Power and Power Spectral Density
• Signal Transmission through a Linear System
• Convolution Integral and Transfer Function
• Ideal and Practical Filters
• Signal Distortion over a Communication Channel

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Syllabus - II

• Amplitude (Linear) Modulation (AM)
• Amplitude Modulation (AM)
• Double Side Band Suppressed Carrier (DSBSC)
• Single Side Band (SSB)
• Vestigial Side Band (VSB)
• AM Modulator and Demodulator Circuits
• AM transmitter block diagram
• Angle (Exponential) Modulation
• Phase Modulation (PM)
• Frequency Modulation (FM)
• Modulation Index
• Spectrum of FM Signals
• Relationship between PM and FM
• FM Modulator and Demodulator Circuits
• FM Transmitter Block Diagram
• FM Receiver

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Outline

• What is a communications system?
• Block Diagram
• Why go to higher frequencies?
• Telecommunication
• Wireless Communication
• Another Classification of Signals (Waveforms)
• Power, Distortion, Noise
• Shannon Capacity
• How transmissions flow over media
• Coaxial Cable
• Unshielded Twisted Pair
• Glass Media
• Wireless
• Connectors
• The Bands

• Signals and Systems
• Signals and Systems
• What is a signal?
• Signal Basics
• Analog / Digital Signals
• Real vs Complex
• Periodic vs. Aperiodic
• Bounded vs. Unbounded
• Causal vs. Noncausal
• Even vs. Odd
• Power vs. Energy

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Signal and System

• Signals are variables that carry information
• System is an assemblage of entities/objects, real
  or abstract, comprising a whole with each every
  component/element interacting or related to
  another one.
• Systems process input signals to produce output
  signals
• Examples
• Motion, sound, picture, video, traffic light
• Natural system (ecosystem), human-made system
  (machines, computer storage system), abstract
  system (traffic, computer programs), descriptive
  system (plans)

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Signal Examples

• Electrical signals --- voltages and currents in a
  circuit
• Acoustic signals --- audio or speech signals
  (analog or digital)
• Video signals --- intensity variations in an
  image (e.g. a CAT scan)
• Biological signals --- sequence of bases in a
  gene
• Noise unwanted signal

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Measuring Signals
Amplitude
Period
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Definitions

• Voltage the force which moves an electrical
  current against resistance
• Waveform the shape of the signal (previous
  slide is a sine wave) derived from its amplitude
  and frequency over a fixed time (other waveform
  is the square wave)
• Amplitude the maximum value of a signal,
  measured from its average state
• Frequency (pitch) the number of cycles produced
  in a second Hertz (Hz). Relate this to the
  speed of a processor eg 1.4GigaHertz or 1.4
  billion cycles per second

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Signal Basics

• Continuous time (CT) and discrete time (DT)
  signals
• CT signals take on real or complex values as a
  function of an independent variable that ranges
  over the real numbers and are denoted as x(t).
• DT signals take on real or complex values as a
  function of an independent variable that ranges
  over the integers and are denoted as xn.
• Note the subtle use of parentheses and square
  brackets to distinguish between CT and DT
  signals.

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Analog Signals

• Human Voice best example
• Ear recognises sounds 20KHz or less
• AM Radio 535KHz to 1605KHz
• FM Radio 88MHz to 108MHz

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Digital signals

• Represented by Square Wave
• All data represented by binary values
• Single Binary Digit Bit
• Transmission of contiguous group of bits is a bit
  stream
• Not all decimal values can be represented by
  binary

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Analogue vs. Digital

• Analogue Advantages
• Best suited for audio and video
• Consume less bandwidth
• Available world wide
• Less susceptible to noise
• Digital Advantages
• Best for computer data
• Can be easily compressed
• Can be encrypted
• Equipment is more common and less expensive
• Can provide better clarity

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Analog or Digital

• Analog Message continuous in amplitude and over
  time
• AM, FM for voice sound
• Traditional TV for analog video
• First generation cellular phone (analog mode)
• Record player
• Digital message 0 or 1, or discrete value
• VCD, DVD
• 2G/3G cellular phone
• Data on your disk
• Your grade
• Digital age why digital communication will
  prevail

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A/D and D/A

• Analog to Digital conversion Digital to Analog
  conversion
• Gateway from the communication device to the
  channel
• Nyquist Sampling theorem
• From time domain If the highest frequency in the
  signal is B Hz, the signal can be reconstructed
  from its samples, taken at a rate not less than
  2B samples per second

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A/D and D/A

• Quantization
• From amplitude domain
• N bit quantization, L intervals L2N
• Usually 8 to 16 bits
• Error Performance Signal to noise ratio

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Real vs. Complex

• Q. Why do we deal with complex signals?
• A. They are often analytically simpler to deal
  with than real signals, especially in digital
  communications.

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Periodic vs. Aperiodic Signals

• Periodic signals have the property that x(t T)
  x(t) for all t.
• The smallest value of T that satisfies the
  definition is called the period.
• Shown below are an aperiodic signal (left) and a
  periodic signal (right).

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Causal vs. Non-causal

• A causal signal is zero for t lt 0 and an
  non-causal signal is zero for t gt 0
• Right- and left-sided signals
• A right-sided signal is zero for t lt T and a
  left-sided signal is zero for t gt T where T can
  be positive or negative.

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Bounded vs. Unbounded

• Every system is bounded, but meaningful signal is
  always bounded

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Even vs. Odd

• Even signals xe(t) and odd signals xo(t) are
  defined as
• xe(t) xe(-t) and xo(t) -xo(-t).
• Any signal is a sum of unique odd and even
  signals. Using
• x(t) xe(t)xo(t) and x(-t) xe(t) - xo(t),
  yields
• xe(t) 0.5(x(t)x(-t)) and xo(t) 0.5(x(t) -
  x(-t)).

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Signal Properties Terminology

• Waveform
• Time-average operator
• Periodicity
• DC value
• Power
• RMS Value
• Normalized Power
• Normalized Energy

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Power and Energy Signals

• Energy Signal
• Finite duration
• Normalized energy is finite and non-zero
• Normalized power averaged over infinite time is
  zero
• Physically realizable

• Power Signal
• Infinite duration
• Normalized power is finite and non-zero
• Normalized energy averaged over infinite time is
  infinite
• Mathematically tractable

• Although real signals are energy signals, we
  analyze them pretending they are power signals!

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The Decibel (dB)

• Measure of power transfer
• 1 dB 10 log10 (Pout / Pin)
• 1 dBm 10 log10 (P / 10-3) where P is in Watts
• 1 dBmV 20 log10 (V / 10-3) where V is in Volts

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Communication System
History and fact of communication
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What is a communications system?

• Communications Systems Systems designed to
  transmit and receive information

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Block Diagram
Info Sink
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Telecommunication

• Telegraph
• Fixed line telephone
• Cable
• Wired networks
• Internet
• Fiber communications
• Communication bus inside computers to communicate
  between CPU and memory

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Wireless Comm Evolution UMTS (3G)
http//www.3g-generation.com/ http//www.nttdocomo
.com/reports/010902_ir_presentation_january.pdf
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Wireless Communications

• Satellite
• TV
• Cordless phone
• Cellular phone
• Wireless LAN, WIFI
• Wireless MAN, WIMAX
• Bluetooth
• Ultra Wide Band
• Wireless Laser
• Microwave
• GPS
• Ad hoc/Sensor Networks

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Comm. Sys. Bock Diagram
Noise
Channel
Rx
m(t)
Tx
r(t)
s(t)

• Low Frequencies
• lt20 kHz
• Original data rate

• High Frequencies
• gt300 kHz
• Transmission data rate

Formal definitions will be provided later
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Aside Why go to higher frequencies?
Half-wave dipole antenna
c f l c 3E08 ms-1 Calculate l for f 5
kHz f 300 kHz
Tx
l/2
There are also other reasons for going from
baseband to bandpass
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Another Classification of Signals (Waveforms)

• Deterministic Signals Can be modeled as a
  completely specified function of time
• Random or Stochastic Signals Cannot be
  completely specified as a function of time must
  be modeled probabilistically

• What type of signals are information bearing?

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Power, Distortion, Noise

• Transmit power
• Constrained by device, battery, health issue,
  etc.
• Channel responses to different frequency and
  different time
• Satellite almost flat over frequency, change
  slightly over time
• Cable or line response very different over
  frequency, change slightly over time.
• Fiber perfect
• Wireless worst. Multipath reflection causes
  fluctuation in frequency response. Doppler shift
  causes fluctuation over time
• Noise and interference
• AWGN Additive White Gaussian noise
• Interferences power line, microwave, other users
  (CDMA phone)

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Shannon Capacity

• Shannon Theory
• It establishes that given a noisy channel with
  information capacity C and information
  transmitted at a rate R, then if RltC, there
  exists a coding technique which allows the
  probability of error at the receiver to be made
  arbitrarily small. This means that theoretically,
  it is possible to transmit information without
  error up to a limit, C.
• The converse is also important. If RgtC, the
  probability of error at the receiver increases
  without bound as the rate is increased. So no
  useful information can be transmitted beyond the
  channel capacity. The theorem does not address
  the rare situation in which rate and capacity are
  equal.
• Shannon Capacity

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How transmissions flow over media

• Simplex only in one direction
• Half-Duplex Travels in either direction, but
  not both directions at the same time
• Full-Duplex can travel in either direction
  simultaneously

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Coaxial Cable

• First type of networking media used
• Available in different types (RG-6 Cable TV,
  RG58/U Thin Ethernet, RG8 Thick Ethernet
• Largely replaced by twisted pair for networks

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Unshielded Twisted Pair

• Advantages
• Inexpensive
• Easy to terminate
• Widely used, tested
• Supports many network types

• Disadvantages
• Susceptible to interference
• Prone to damage during installation
• Distance limitations not understood or followed

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Glass Media

• Core of silica, extruded glass or plastic
• Single-mode is 0.06 of a micron in diameter
• Multimode 0.5 microns
• Cladding can be Kevlar, fibreglass or even steel
• Outer coating made from fire-proof plastic

• Advantages
• Can be installed over long distances
• Provides large amounts of bandwidth
• Not susceptible to EMI RFI
• Can not be easily tapped (secure)

• Disadvantages
• Most expensive media to purchase and install
• Rigorous guidelines for installation

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Wireless
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Wireless (2)

• Radio transmits at 10KHz to 1KHz
• Microwaves transmit at 1GHz to 500GHz
• Infrared transmits at 500GHz to 1THz
• Radio transmission may include
• Narrow band
• High-powered
• Frequency hopping spread spectrum (the hop is
  controlled by accurate timing)
• Direct-sequence-modulation spread spectrum (uses
  multiple frequencies at the same time,
  transmitting data in chips at high speed)

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Connectors
Fibre Optic
RJ45
Token Ring
Thicknet
T-Piece
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The Bands
3MHz
30MHz
300MHz
3GHz
30GHz
300GHz
300KHz
30KHz
3THz
3KHz
VLF
LF
MF
HF
VHF
UHF
SHF
EHF
ELF
Far Infra- Red
Submillimeter Range
Radio
Optical
300mm
1500nm
1PetaHz
1ExaHz
Near Infra- Red
R e d
O r a n g e
Y e l l o w
G r e e n
B l u e
I n d i g o
V i o l e t
Ultraviolet
X-Ray
700nm
600nm
400nm
500nm
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