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TOBB ETU Bil557 – Kablosuz Ağlar. Bahar 2007 Çarşamba 0 8 : 30 – 12 :0 0 Sınıf : 1 75 Bülent Tavlı Oda: 169 btavli Ders Bilgileri - I. Bu derste neler öğreneceğiz ?

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TOBB ETU Bil557 – Kablosuz Ağlar

Bahar 2007

Çarşamba 08:30 – 12:00

Sınıf: 175

Bülent Tavlı

Oda: 169

[email protected]

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Ders Bilgileri - I

  • Bu derste neler öğreneceğiz?

    • Geleneksel cep telefonu (cellular networks) ve kablosuz ağları (wireless networks) olanaklı kılan kavramlar nelerdir?

    • Kablosuz iletişim sistemi tasarımlarındaki temel yapılar ve sistem performansını yükseltme yöntemleri nelerdir?

    • Kablosuz iletişimi konusunda en son aşama (state-of-the-art) araştırma nasıl yapılır?

  • Bu ders için nasıl bir altyapı gerekli?

    • Temel matematiksel analiz

    • İşaret işleme (signal processing)

    • Elektronik iletişim (Telecommunications)

    • Programlama (C/C++ ve Matlab)

  • Eğer bu konularda yetersizseniz 

    • Bu dersi yine de alabilirsiniz

    • Ama ek çaba ve zaman harcamanız gerekecek

  • Bilgi dağarcığınızı genişletmek için ve son derece popüler bir konuda verimli araştırma yapabilmek için mükemmel bir fırsat

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Ders Bilgileri - II

  • Ana kaynak

    • Wireless Communications and Networks, 2nd Edition, Prentice Hall by W. Stallings

    • Bu kitaptan kesinlikle bir tane edinmelisiniz!


  • Yardımcı 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. Tavlı and W. B. Heinzelman

    • Derste dağıtılacak makaleler ve diğer belgeler

  • Network Simulator (ns-2)


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Ders Bilgileri - III

  • Notlandırma

    • Ödevler (iki haftada bir): %20

    • Proje (rapor + sunum): %30

    • Arasınav: %25

    • Sonsınav: %25

  • Projeler kablosuz iletişim ve ağlar hakkında olmalı

    • Derinlemesine literatür taraması, Benzetim (simulation), Analiz, Uygulama

    • Tek başınıza veya en fazla üç kişilik gruplar halinde

    • Dönem sonunda konferans bildirisi formatında bir rapor verilecek ve konferans sunumu şeklinde bir sunum yapılacak

  • Proje takvimi

    • Şubat sonuna kadar projenizi belirleyip onay alın

    • Dönemin son haftası proje sunumu yapılacak

  • Akademik ahlak

    • Yardımlaşmanız teşvik edilmekle beraber kopye çekmeniz kesinlikle yasaktır

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Introduction to Wireless

Chapter 1

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What is wirelesscommunication?

  • Any form of communication that does not require the transmitter and receiver to be in physical contact through guided media

  • Electromagnetic wave propagated through free-space

    • 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

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Electromagnetic Specturm








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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 infrastructure

    • 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 signal

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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

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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 unreliable)

    • Require line-of-sight between transmitter and receiver

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Wireless Comes of Age

  • 1893: Nikola Tesla demonstrated the first ever wireless information transmission in New York City

  • 1897: Marconi demonstrated transmission of radio waves to a ship at sea 29 km away

  • 1915: Wireless telephony established-- VA and Paris

  • 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

  • 1960’s: Communications satellites launched

  • Late 1970's: IC technology advances enable affordable cellular telephony-- ushers in modern cellular era

  • Early 1990’s: Cellular telephony in Türkiye

  • 2007: İŞTCell cellular service is introduced by TürkCell 

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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 kbps)

    • 1990: GSM (Europe), TDMA, GMSK, 200 kHz channels, 890-960 MHz

    • 1991: USDC/IS-54 (US), TDMA, π/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 Mhz

  • 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

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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 (< 10 kbps, ZigBee), medium (up to 200 kbps), and high (> 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 devices

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Underlying concepts

  • Electromagnetics

    • Antennas, wave propagation, channel modeling

  • Signals and systems

    • Filtering, Fourier transforms, block-diagram design

  • Digital signal processing

    • Equalization, spread-spectrum, source coding

  • Communications

    • Modulation, noise analysis, channel capacity, channel coding

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Enabling Technologies

  • Digital integrated circuits

  • RF generation devices (efficient power amps, sleep modes, improved oscillators, smart antennas)

  • Source coding (data compression)

  • Modulation (improved efficiency)

  • Multiple-access techniques (increase number of users)

  • Channel coding/forward error correction (improve probability of successful reception)

  • Software programmable radios

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Protocol stack - I

Source coding


  • Provides abstraction when designing layers

  • We'll discuss each layer in turn...

Packet re-ordering (e.g., TCP)


Routing (e.g., IP)


Error correction, encryption

Data Link (MAC)

Modulation, power control, filtering



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Protocol Stack - II







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Part One: Background

  • Provides preview and context for rest of the course

  • Covers basic topics

    • Data Communications

    • TCP/IP

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Chapter 2: Transmission Fundamentals

  • Basic overview of transmission topics

  • Data communications concepts

    • Includes techniques of analog and digital data transmission

  • Channel capacity

  • Transmission media

  • Multiplexing

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Chapter 3: Communication Networks

  • Comparison of basic communication network technologies

    • Circuit switching

    • Packet switching

    • Frame relay

    • ATM

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Chapter 4: Protocols and the TCP/IP Protocol Suite

  • Protocol architecture

  • Overview of TCP/IP

  • Open systems interconnection (OSI) reference model

  • Internetworking

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Part Two: Wireless Communication Technology

  • Underlying technology of wireless transmission

  • Encoding of analog and digital data for wireless transmission

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Chapter 5: Antennas and Propagation

  • Principles of radio and microwave

    • Antenna performance

    • Wireless transmission modes

    • Fading

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Chapter 6: Signal Encoding Techniques

  • Wireless transmission

    • Analog and digital data

    • Analog and digital signals

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Chapter 7: Spread Spectrum

  • Frequency hopping

  • Direct sequence spread spectrum

  • Code division multiple access (CDMA)

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Chapter 8: Coding and Error Control

  • Forward error correction (FEC)

  • Using redundancy for error detection

  • Automatic repeat request (ARQ) techniques

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Part Three: Wireless Networking

  • Examines major types of networks

    • Satellite-based networks

    • Cellular networks

    • Cordless systems

    • Fixed wireless access schemes

  • Use of mobile IP and Wireless Access Protocol (WAP) to provide Internet and Web access

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Chapter 9: Satellite Communications

  • Geostationary satellites (GEOS)

  • Low-earth orbiting satellites (LEOS)

  • Medium-earth orbiting satellites (MEOS)

  • Capacity allocation

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Chapter 10: Cellular Wireless Networks

  • Cellular wireless network design issues

  • First generation analog (traditional mobile telephony service)

  • Second generation digital cellular networks

    • Time-division multiple access (TDMA)

    • Code-division multiple access (CDMA)

  • Third generation networks

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Chapter 11: Cordless Systems and Wireless Local Loop

  • Cordless systems

  • Wireless local loop (WLL)

    • Sometimes called radio in the loop (RITL) or fixed wireless access (FWA)

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Chapter 12: Mobile IP and Wireless Access Protocol

  • Modifications to IP protocol to accommodate wireless access to Internet

  • Wireless Application Protocol (WAP)

    • Provides mobile users access to telephony and information services including Internet and Web

    • Includes wireless phones, pagers and personal digital assistants (PDAs)

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Part Four: Wireless Local Area Networks

  • Examines underlying wireless LAN technology

  • Examines standardized approaches to local wireless networking

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Chapter 13: Wireless LAN Technology

  • Overview of LANs and wireless LAN technology and applications

  • Transmission techniques of wireless LANs

    • Spread spectrum

    • Narrowband microwave

    • Infrared

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Chapter 14: IEEE 802.11 Wireless LAN Standard

  • Wireless LAN standards defined by IEEE 802.11 committee

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Chapter 15: Bluetooth

  • Bluetooth is an open specification for wireless communication and networking

    • Personal computers

    • Mobile phones

    • Other wireless devices

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Advanced Topics

  • Ad Hoc Networks

  • Sensor Networks

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Part One

Technical Background

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Electromagnetic Signal

  • Function of time

  • Can also be expressed as a function of frequency

    • Signal consists of components of different frequencies

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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 ) -¥< t < +¥

      • 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

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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

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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; A=0.5

    • (c) Increased frequency; f = 2, thus T = ½

    • (d) Phase shift;  = /4 radians (45 degrees)

  • note: 2 radians = 360° = 1 period

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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

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Frequency-Domain Concepts

  • Fundamental frequency - when all frequency components of a signal are integer multiples of one frequency, it’s referred to as the fundamental frequency

  • Spectrum - range of frequencies that a signal contains

  • Absolute bandwidth - width of the spectrum of a signal

  • Effective bandwidth (or just bandwidth) - narrow band of frequencies that most of the signal’s energy is contained in

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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 distortions

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Data Communication Terms

  • Data - entities that convey meaning, or information

  • Signals - electric or electromagnetic representations of data

  • Transmission - communication of data by the propagation and processing of signals

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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 cable)

    • Fiber optic cable

    • Atmosphere or space propagation

  • Analog signals can propagate analog and digital data

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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 data

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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

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Analog Transmission

  • Transmit analog signals without regard to content

  • Attenuation limits length of transmission link

  • Cascaded amplifiers boost signal’s energy for longer distances but cause distortion

    • Analog data can tolerate distortion

    • Introduces errors in digital data

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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

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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

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Nyquist Bandwidth

  • For binary signals (two voltage levels)

    • C = 2B

  • With multilevel signaling

    • C = 2B log2M

      • M = number of discrete signal or voltage levels

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Signal-to-Noise Ratio

  • Ratio of the power in a signal to the power contained in the noise that’s 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

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Shannon Capacity Formula

  • Equation:

  • Represents theoretical maximum that can be achieved

  • 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

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Example of Nyquist and Shannon Formulations

  • Spectrum of a channel between 3 MHz and 4 MHz ; SNRdB = 24 dB

  • Using Shannon’s formula

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Example of Nyquist and Shannon Formulations

  • How many signaling levels are required?

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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

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Unguided Media

  • Transmission and reception are achieved by means of an antenna

  • Configurations for wireless transmission

    • Directional

    • Omnidirectional

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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

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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 antenna

    • Located at substantial heights above ground level

  • Applications

    • Long haul telecommunications service

    • Short point-to-point links between buildings

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Satellite Microwave

  • Description of communication satellite

    • Microwave relay station

    • Used to link two or more ground-based microwave transmitter/receivers

    • 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

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Broadcast Radio

  • Description of broadcast radio antennas

    • Omnidirectional

    • Antennas not required to be dish-shaped

    • Antennas need not be rigidly mounted to a precise alignment

  • Applications

    • Broadcast radio

      • VHF and part of the UHF band; 30 MHZ to 1GHz

      • Covers FM radio and UHF and VHF television

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  • Capacity of transmission medium usually exceeds capacity required for transmission of a single signal

  • Multiplexing - carrying multiple signals on a single medium

    • More efficient use of transmission medium

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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

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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