TOBB ETU Bil457/Bil557 Wireless Networks Lecture 01 September 11, 2008 - PowerPoint PPT Presentation


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TOBB ETU Bil457/Bil557 Wireless Networks Lecture 01 September 11, 2008


Early forms of wireless communication Wireless Comes of Age Some Milestones in Wireless Communications Modern Cellular Standards Fast facts ... – PowerPoint PPT presentation

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Title: TOBB ETU Bil457/Bil557 Wireless Networks Lecture 01 September 11, 2008

TOBB ETU Bil457/Bil557 Wireless Networks Lecture
01 September 11, 2008
Ders Bilgileri - I
  • Bu derste neler ögrenecegiz?
  • Geleneksel cep telefonu (cellular networks) ve
    kablosuz aglari (wireless networks) olanakli
    kilan kavramlar nelerdir?
  • Kablosuz iletisim sistemi tasarimlarindaki temel
    yapilar ve sistem performansini yükseltme
    yöntemleri nelerdir?
  • Kablosuz iletisimi konusunda en son asama
    (state-of-the-art) arastirma nasil yapilir?
  • Bu ders için nasil bir altyapi gerekli?
  • Temel matematiksel analiz
  • Isaret isleme (signal processing)
  • Elektronik iletisim (Telecommunications)
  • Programlama (C/C ve Matlab)
  • Eger bu konularda yetersizseniz ?
  • Bu dersi yine de alabilirsiniz
  • Ama ek çaba ve zaman harcamaniz gerekecek
  • Bilgi dagarciginizi genisletmek için ve son
    derece popüler bir konuda verimli arastirma
    yapabilmek için güzel bir firsat

Ders Bilgileri - II
  • Ana kaynak
  • Wireless Communications and Networks, 2nd
    Edition, Prentice Hall by W. Stallings
  • Bu kitaptan kesinlikle bir tane edinmelisiniz!
  • http//
  • Yardimci kaynaklar
  • Wireless Communications Principles and Practice
    , 2nd Edition, Prentice Hall by T. Rappaport
  • Ad Hoc Wireless Networks Architectures and
    Protocols, Prentice Hall by C. S. R. Murthy and
    B. S. Manoj
  • Mobile Ad Hoc Networks Energy-Efficient
    Real-Time Data Communications, Springer by B.
    Tavli and W. B. Heinzelman
  • Derste dagitilacak makaleler ve diger belgeler
  • Network Simulator (ns-2)
  • http//

Ders Bilgileri - III
  • Notlandirma
  • AraSinav 25 katki
  • Proje 40 katki
  • SonSinav 35 katki
  • Projeler kablosuz iletisim ve aglar hakkinda
  • Derinlemesine literatür taramasi, Benzetim
    (simulation), Analiz, Uygulama
  • Tek basiniza veya en fazla üç kisilik gruplar
  • Dönem sonunda konferans bildirisi formatinda bir
    rapor verilecek ve konferans sunumu seklinde bir
    sunum yapilacak
  • Proje takvimi
  • Eylül sonuna kadar projenizi belirleyip onay alin
  • Dönemin son haftasi proje sunumu yapilacak
  • Akademik ahlak
  • Yardimlasmaniz tesvik edilmekle beraber kopye
    kesinlikle yasaktir

Introduction to Wireless
  • Chapter 1

What is wireless communication?
  • Any form of communication that does not require
    the transmitter and receiver to be in physical
    contact through guided media
  • Electromagnetic wave propagated through
  • Radar, RF, Microwave, IR, Optical
  • Simplex one-way communication (e.g., radio, TV)
  • Half-duplex two-way communication but not
    simultaneous (e.g., push-to-talk radios)
  • Full-duplex two-way communication (e.g.,
    cellular phones)
  • Frequency-division duplex (FDD)
  • Time-division duplex (TDD) simulated full-duplex

Electromagnetic Specturm
http// science/know_l1
Why use wireless communication?
  • Provides mobility
  • A user can send and receive messages no matter
    where he/she is located
  • Added convenience / reduced cost
  • Enables communications without adding expensive
  • Can easily setup temporary wireless LANs
    (disaster situations)
  • Developing nations use cellular telephony rather
    than laying wires to each home
  • Use resources only when sending or receiving

Why is wireless different than wired?
  • Noisy, time-varying channel
  • BER varies by orders of magnitude
  • Enviromental conditions affect transmission
  • Shared medium
  • Other users create interference
  • Must develop ways to share the channel
  • Bandwidth is limited
  • TÜK, FCC determines the frequency allocation
  • ISM band for unlicensed spectrum (902-928 MHz,
    2.4-2.5 GHz, 5.725-5.875 GHz)
  • Requires intelligent signal processing and
    communications to make efficient use of limited
    bandwidth in error-prone environment

Early forms of wireless communication
  • Primitive
  • Sound (e.g., beating of drums)
  • Sight (e.g., smoke signals)
  • PA (public address) system
  • Disadvantages of these forms of communication
  • Limited alphabets
  • Noisy
  • Broadcast (no privacy or security)
  • Limited distance (or requires relaying which is
  • Require line-of-sight between transmitter and

Wireless Comes of Age
  • 1893 Nikola Tesla demonstrated the first ever
    wireless information transmission in New York
  • 1897 Marconi demonstrated transmission of radio
    waves to a ship at sea 29 km away
  • 1915 Wireless telephony established-- VA and
  • 1920's Radio broadcasting became popular
  • 1930's TV broadcasting began
  • 1946 First public mobile telephone service in US
  • 1960's Bell Labs developed cellular concept--
    brought mobile telephony to masses
  • 1960s Communications satellites launched
  • Late 1970's IC technology advances enable
    affordable cellular telephony-- ushers in modern
    cellular era
  • Early 1990s Cellular telephony in Türkiye
  • 2008 carry the phone number myriad all cellular
    companies ?

Some Milestones in Wireless Communications
Modern Cellular Standards
  • First generation (1G) systems (analog)
  • 1979 NTT (Japan), FDMA, FM, 25 kHz channels,
    870-940 MHz)
  • 1981 NMT (Sweden and Norway), FDMA, FM, 25 kHz,
    450-470 MHz
  • 1983 AMPS (US), FDMA, FM, 30 kHz channels,
    824-894 MHz
  • 1985 TACS (Europe), FDMA, FM, 25 kHz channels,
    900 MHz
  • Second generation (2G) systems (digital)
  • Supported voice and low-rate data (up to 9.6
  • 1990 GSM (Europe), TDMA, GMSK, 200 kHz channels,
    890-960 MHz
  • 1991 USDC/IS-54 (US), TDMA, p/4 DQPSK, 30 kHz
    channels, 824-894 MHz
  • 1993 IS-95 (US), CDMA, BPSK/QPSK, 1.25 MHz
    channels, 824-894 MHz and 1.8-2.0 GHz
  • 1993 CDPD (US) FHSS GMSK 30 kHz channels 824-894
  • Enhanced 2G (2.5G) systems
  • Increased data rates
  • General Packet Radio System (GPRS) packet-based
    overlay to GSM, up to 171.2 kbps
  • Enhanced Data rates for GSM Evolution (EDGE)
    modulation enhancements to GSM to support up to
    180 kbps
  • 3rd generation (3G) systems
  • Up to 2 Mbps
  • Internet, VoIP
  • 2004-2005 IMT-2000, 2000 MHz range - W-CDMA
    (UMTS), cdma2000, TD-SCMA

Fast facts Cellular subscribers
Fast facts cellular growth
Wireless data standards
  • IEEE 802.11 wireless LAN/ad-hoc networking, 1, 2
    or 11 Mbps, DSSS or FHSS with CSMA/CA
    RTS-CTS-ACK, 2.4 - 2.4835 GHz
  • Bluetooth replacement for cables, short low
    power (1 or 100 mW), low cost, 1 piconets with
    master-slave operation
  • HomeRF wireless home networking, 150 feet range,
    up to 10 devices, SWAP protocol
  • IEEE 802.15 wireless PAN, modes for low (lt 10
    kbps, ZigBee), medium (up to 200 kbps), and high
    (gt 20 Mbps) data rates
  • CDPD TCP/IP compatible packet transmission via
    digital overlay to existing analog cellular
    network, 19.2 kbps
  • PCS modified cellular protocols, goals--low
    power, voice and moderate-rate data, small,
    inexpensive terminals, large coverage area
  • MobileIP "routing support to permit IP nodes
    (hosts and routers) using either IPv4 or IPv6 to
    seamlessly roam among IP subnetworks and media
    types...maintenance of active TCP connections and
    UDP port bindings."
  • WAP communications protocol and application
    environment, enables viewing of Internet content
    in special text format on special WAP-enabled

Underlying concepts
  • Electromagnetics
  • Antennas, wave propagation, channel modeling
  • Signals and systems
  • Filtering, Fourier transforms, block-diagram
  • Digital signal processing
  • Equalization, spread-spectrum, source coding
  • Communications
  • Modulation, noise analysis, channel capacity,
    channel coding

Enabling Technologies
  • Digital integrated circuits
  • RF generation devices (efficient power amps,
    sleep modes, improved oscillators, smart
  • Source coding (data compression)
  • Modulation (improved efficiency)
  • Multiple-access techniques (increase number of
  • Channel coding/forward error correction (improve
    probability of successful reception)
  • Software programmable radios

Protocol stack - I
Source coding
Packet re-ordering (e.g., TCP)
Routing (e.g., IP)
Error correction, encryption
Data Link (MAC)
Modulation, power control, filtering
  • Provides abstraction when designing layers
  • We'll discuss each layer in turn...

Protocol Stack - II
Part One
  • Technical Background

Transmission Fundamentals
  • Chapter 2

Electromagnetic Signal
  • Function of time
  • Can also be expressed as a function of frequency
  • Signal consists of components of different

Time-Domain Concepts
  • Analog signal - signal intensity varies in a
    smooth fashion over time
  • No breaks or discontinuities in the signal
  • Digital signal - signal intensity maintains a
    constant level for some period of time and then
    changes to another constant level
  • Periodic signal - analog or digital signal
    pattern that repeats over time
  • s(t T ) s(t ) -8lt t lt 8
  • where T is the period of the signal

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Time-Domain Concepts
  • Aperiodic signal - analog or digital signal
    pattern that doesn't repeat over time
  • Peak amplitude (A) - maximum value or strength of
    the signal over time typically measured in volts
  • Frequency (f )
  • Rate, in cycles per second, or Hertz (Hz) at
    which the signal repeats

Time-Domain Concepts
  • Period (T ) - amount of time it takes for one
    repetition of the signal
  • T 1/f
  • Phase (?) - measure of the relative position in
    time within a single period of a signal
  • Wavelength (?) - distance occupied by a single
    cycle of the signal
  • Or, the distance between two points of
    corresponding phase of two consecutive cycles

Sine Wave Parameters
  • General sine wave
  • s(t ) A sin(2?ft ?)
  • Figure 2.3 shows the effect of varying each of
    the three parameters
  • (a) A 1, f 1 Hz, ? 0 thus T 1s
  • (b) Reduced peak amplitude A0.5
  • (c) Increased frequency f 2, thus T ½
  • (d) Phase shift ? ?/4 radians (45 degrees)
  • note 2? radians 360 1 period

Sine Wave Parameters
Time vs. Distance
  • When the horizontal axis is time, as in Figure
    2.3, graphs display the value of a signal at a
    given point in space as a function of time
  • With the horizontal axis in space, graphs display
    the value of a signal at a given point in time as
    a function of distance
  • At a particular instant of time, the intensity of
    the signal varies as a function of distance from
    the source

Frequency-Domain Concepts
  • Fundamental frequency - when all frequency
    components of a signal are integer multiples of
    one frequency, its referred to as the
    fundamental frequency
  • Spectrum - range of frequencies that a signal
  • Absolute bandwidth - width of the spectrum of a
  • Effective bandwidth (or just bandwidth) - narrow
    band of frequencies that most of the signals
    energy is contained in

Frequency-Domain Concepts
  • Any electromagnetic signal can be shown to
    consist of a collection of periodic analog
    signals (sine waves) at different amplitudes,
    frequencies, and phases
  • The period of the total signal is equal to the
    period of the fundamental frequency

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Relationship between Data Rate and Bandwidth
  • The greater the bandwidth, the higher the
    information-carrying capacity
  • Conclusions
  • Any digital waveform will have infinite bandwidth
  • BUT the transmission system will limit the
    bandwidth that can be transmitted
  • AND, for any given medium, the greater the
    bandwidth transmitted, the greater the cost
  • HOWEVER, limiting the bandwidth creates

Data Communication Terms
  • Data - entities that convey meaning, or
  • Signals - electric or electromagnetic
    representations of data
  • Transmission - communication of data by the
    propagation and processing of signals

Examples of Analog and Digital Data
  • Analog
  • Video
  • Audio
  • Digital
  • Text
  • Integers

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Analog Signals
  • A continuously varying electromagnetic wave that
    may be propagated over a variety of media,
    depending on frequency
  • Examples of media
  • Copper wire media (twisted pair and coaxial
  • Fiber optic cable
  • Atmosphere or space propagation
  • Analog signals can propagate analog and digital

Digital Signals
  • A sequence of voltage pulses that may be
    transmitted over a copper wire medium
  • Generally cheaper than analog signaling
  • Less susceptible to noise interference
  • Suffer more from attenuation
  • Digital signals can propagate analog and digital

Analog Signaling
Digital Signaling
Reasons for Choosing Data and Signal Combinations
  • Digital data, digital signal
  • Equipment for encoding is less expensive than
    digital-to-analog equipment
  • Analog data, digital signal
  • Conversion permits use of modern digital
    transmission and switching equipment
  • Digital data, analog signal
  • Some transmission media will only propagate
    analog signals
  • Examples include optical fiber and satellite
  • Analog data, analog signal
  • Analog data easily converted to analog signal

Analog Transmission
  • Transmit analog signals without regard to content
  • Attenuation limits length of transmission link
  • Cascaded amplifiers boost signals energy for
    longer distances but cause distortion
  • Analog data can tolerate distortion
  • Introduces errors in digital data

Digital Transmission
  • Concerned with the content of the signal
  • Attenuation endangers integrity of data
  • Digital Signal
  • Repeaters achieve greater distance
  • Repeaters recover the signal and retransmit
  • Analog signal carrying digital data
  • Retransmission device recovers the digital data
    from analog signal
  • Generates new, clean analog signal

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About Channel Capacity
  • Impairments, such as noise, limit data rate that
    can be achieved
  • For digital data, to what extent do impairments
    limit data rate?
  • Channel Capacity the maximum rate at which data
    can be transmitted over a given communication
    path, or channel, under given conditions

Concepts Related to Channel Capacity
  • Data rate - rate at which data can be
    communicated (bps)
  • Bandwidth - the bandwidth of the transmitted
    signal as constrained by the transmitter and the
    nature of the transmission medium (Hertz)
  • Noise - average level of noise over the
    communications path
  • Error rate - rate at which errors occur
  • Error transmit 1 and receive 0 transmit 0 and
    receive 1

Nyquist Bandwidth
  • For binary signals (two voltage levels)
  • C 2B
  • With multilevel signaling
  • C 2B log2 M
  • M number of discrete signal or voltage levels

Signal-to-Noise Ratio
  • Ratio of the power in a signal to the power
    contained in the noise thats present at a
    particular point in the transmission
  • Typically measured at a receiver
  • Signal-to-noise ratio (SNR, or S/N)
  • A high SNR means a high-quality signal, low
    number of required intermediate repeaters
  • SNR sets upper bound on achievable data rate

Shannon Capacity Formula
  • Equation
  • Represents theoretical maximum that can be
  • In practice, only much lower rates achieved
  • Formula assumes white noise (thermal noise)
  • Impulse noise is not accounted for
  • Attenuation distortion or delay distortion not
    accounted for

Example of Nyquist and Shannon Formulations
  • Spectrum of a channel between 3 MHz and 4 MHz
    SNRdB 24 dB
  • Using Shannons formula

Example of Nyquist and Shannon Formulations
  • How many signaling levels are required?

Classifications of Transmission Media
  • Transmission Medium
  • Physical path between transmitter and receiver
  • Guided Media
  • Waves are guided along a solid medium
  • E.g., copper twisted pair, copper coaxial cable,
    optical fiber
  • Unguided Media
  • Provides means of transmission but does not guide
    electromagnetic signals
  • Usually referred to as wireless transmission
  • E.g., atmosphere, outer space

Unguided Media
  • Transmission and reception are achieved by means
    of an antenna
  • Configurations for wireless transmission
  • Directional
  • Omnidirectional

General Frequency Ranges
  • Microwave frequency range
  • 1 GHz to 40 GHz
  • Directional beams possible
  • Suitable for point-to-point transmission
  • Used for satellite communications
  • Radio frequency range
  • 30 MHz to 1 GHz
  • Suitable for omnidirectional applications
  • Infrared frequency range
  • Roughly, 3x1011 to 2x1014 Hz
  • Useful in local point-to-point multipoint
    applications within confined areas

Terrestrial Microwave
  • Description of common microwave antenna
  • Parabolic "dish", 3 m in diameter
  • Fixed rigidly and focuses a narrow beam
  • Achieves line-of-sight transmission to receiving
  • Located at substantial heights above ground level
  • Applications
  • Long haul telecommunications service
  • Short point-to-point links between buildings

Satellite Microwave
  • Description of communication satellite
  • Microwave relay station
  • Used to link two or more ground-based microwave
  • Receives transmissions on one frequency band
    (uplink), amplifies or repeats the signal, and
    transmits it on another frequency (downlink)
  • Applications
  • Television distribution
  • Long-distance telephone transmission
  • Private business networks

Broadcast Radio
  • Description of broadcast radio antennas
  • Omnidirectional
  • Antennas not required to be dish-shaped
  • Antennas need not be rigidly mounted to a precise
  • Applications
  • Broadcast radio
  • VHF and part of the UHF band 30 MHZ to 1GHz
  • Covers FM radio and UHF and VHF television

  • Capacity of transmission medium usually exceeds
    capacity required for transmission of a single
  • Multiplexing - carrying multiple signals on a
    single medium
  • More efficient use of transmission medium

Reasons for Widespread Use of Multiplexing
  • Cost per kbps of transmission facility declines
    with an increase in the data rate
  • Cost of transmission and receiving equipment
    declines with increased data rate
  • Most individual data communicating devices
    require relatively modest data rate support

Multiplexing Techniques
  • Frequency-division multiplexing (FDM)
  • Takes advantage of the fact that the useful
    bandwidth of the medium exceeds the required
    bandwidth of a given signal
  • Time-division multiplexing (TDM)
  • Takes advantage of the fact that the achievable
    bit rate of the medium exceeds the required data
    rate of a digital signal

Frequency-division Multiplexing
Time-division Multiplexing
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