An Introduction To Wireless Technologies
An Introduction to WirelessTechnologiesPart 1F. Ricci2010/2011
Content Wireless communication standards Computer Networks Reference model for a network architecture Frequencies and regulations Wireless communication technologies Signals Bandwidth limited signals Signal modulation Data transfer rate Signal propagationMost of the slides of this lecture come from prof. JochenSchiller’s didactical material for the book “MobileCommunications”, Addison Wesley, 2003.
Analogue vs. Digital Analogue transmission of analogue data The air pressure variations (analogue data) areconverted (microphone) into an electricalanalog signal in which either the instantaneousvoltage or current is directly proportional tothe instantaneous air pressure and thentransmitted (e.g., traditional phone or radio)Analogue transmission of digital data The electric analog signal is digitized, orconverted to a digital signal, through anAnalog-to-Digital converter and thenmodulated into analogue signals andtrasmitted (e.g., digital phones as GSM).
Wireless systems: overviewcellular phones1981:NMT 450satellites1986:NMT T1 1988:Inmarsat-C1991:CDMA1991:D-AMPS1993:PDC1989:CT 0:GPRS199x:proprietary1997:HYPERLANIEEE 802.111999:802.11b, Bluetooth2000:IEEE 802.11a2001:IMT-2000 (UMTS)digital4G – fourth generation: when and how?wireless 00?:Fourth Generation(Internet based)
Cellular Generations First Second Digital, packet-switched, TDMA (GPRS, EDGE)40-400 KbpsThird Digital, circuit switched (HSCSD High-SpeedCircuit Switched Data), Internet-enabled (WAP)10 Kbps2.5 Digital, circuit-switched (GSM) 10 KbpsAdvanced second Analog, circuit-switched (AMPS, TACS)Digital, packet-switched, Wideband CDMA(UMTS)0.4 – 2 MbpsFourth Data rate 100 Mbps; achieves “telepresence”
Nokia N95 Operating Frequency: WCDMA2100 (HSDPA),EGSM900, GSM850/1800/1900 MHz (EGPRS)Memory: Up to 160 MB internal dynamicmemory; memory card slot - microSD memorycards (up to 2 GB)Display: 2.6" QVGA (240 x 320 pixels) TFT –ambient light detector - up to 16 million colorsData Transfer: WCDMA 2100 (HSDPA) with simultaneousvoice and packet data (Packet Switchingmax speed UL/DL 384/3.6MB, CircuitSwitching max speed 64kbps)Dual Transfer Mode (DTM) support forsimultaneous voice and packet data connection inGSM/EDGE networks - max speed DL/UL:177.6/118.4 kbits/sEGPRS class B, multi slot class 32, max speed DL/UL 296 / 177.6 kbits/s
Services2GPSTNISDN2G UMTS/3GE-mail file10 Kbyte8 sec3 sec1 sec0.7 sec0.04 secWeb Page9 Kbyte9 sec3 sec1 sec0.8 sec0.04secText File40 Kbyte33 sec11 sec5 sec3 sec0.2 secLarge Report2 Mbyte28 min9 min4 min2 min7 secVideo Clip4 Mbyte48 min18 min8 min4 min14 secFilm with TVQuality1100 hr350 hr104 hr52 hr 5hrSource: UMTS Forum
Computer Networks A computer network is two or more computersconnected together using a telecommunication systemfor the purpose of communicating and sharing resourcesWhy they are interesting? Overcome geographic limitsAccess remote dataSeparate clients and serverGoal: Universal Communication (any to any)Network
Type of Networks PAN: a personal area network is a computer network (CN)used for communication among computer devices (includingtelephones and personal digital assistants) close to one person LAN: a local area network is a CN covering a small geographicarea, like a home, office, or group of buildings Technologies: Ethernet (wired) or Wi-Fi (wireless)MAN: Metropolitan Area Networks are large CNs usuallyspanning a city Technologies: USB and Firewire (wired), IrDA andBluetooth (wireless)Technologies: Ethernet (wired) or WiMAX (wireless)WAN: Wide Area Network is a CN that covers a broad area,e.g., cross metropolitan, regional, or national boundaries Examples: InternetWireless Technologies: HSDPA, EDGE, GPRS, GSM.
Reference ModelBase transceiver stationBase station NetworkNetworkNetworkNetworkData LinkData LinkData LinkData LinkPhysicalPhysicalPhysicalPhysicalRadioMedium
Reference model Physical layer: conversion of stream of bits intosignals – carrier generation - frequency selection– signal detection – encryption Data link layer: accessing the medium –multiplexing - error correction – synchronization Network layer: routing packets – addressing handover between networks Transport layer: establish an end-to-endconnection – quality of service – flow andcongestion control Application layer: service location – supportmultimedia – wireless access to www
Wireless Network The difference between wired and wireless is thephysical layer and the data link layer Wired network technology is based on wires orfibers Data transmission in wireless networks take placeusing electromagnetic waves which propagatesthrough space (scattered, reflected, attenuated) Data are modulated onto carrier frequencies(amplitude, frequency) The data link layer (accessing the medium,multiplexing, error correction, synchronization)requires more complex mechanisms.
Waves' interference
IEEE standard 802.11fixedterminalmobile terminalinfrastructurenetworkaccess pointapplicationapplicationTransport layerTCPTCPNetwork layerIPLLC802.11 MAC802.11 PHYData link layerPhysical link l.IPLLCLLC802.11 MAC802.3 MAC802.3 MAC802.11 PHY802.3 PHY802.3 PHYCSMA/CA Carrier Sense Multiple Access / Collision AvoidanceCSMA/CA Carrier Sense Multiple Access / Collision Detection
CSMA/CDhttp://en.wikipedia.org/wiki/CSMA/CD
CSMA/CARequest to Send(RTS) packet sentby the sender S,and a Clear toSend (CTS) packetsent by theintended receiver R.Alerting all nodeswithin range of thesender, receiver orboth, to nottransmit for theduration of themain transmission.http://en.wikipedia.org/wiki/
Mobile Communication TechnologiesLocal wireless networksWLAN 802.11WiFi802.11a802.11b802.11h802.11i/e/ /w802.11gZigBee802.15.4Personal wireless nwWPAN 02.15.3a/bBluetoothWireless distribution networksWMAN 802.16 (Broadband Wireless Access)WiMAX Mobility802.20 (Mobile Broadband Wireless Access)
Bluetooth A standard permitting wireless connection of:Personal computersPrintersMobile phonesHandsfree headsetsLCD projectorsModemsWireless LAN devicesNotebooksDesktop PCsPDAs
Bluetooth Characteristics Operates in the 2.4 GHz band - Packet switched1 milliwatt - as opposed to 500 mW cellphoneLow cost10m to 100m rangeUses Frequency Hop (FH) spread spectrum, which dividesthe frequency band into a number of hop channels. Duringconnection, devices hop from one channel to another 1600times per secondData transfer rate 1-2 megabits/second (GPRS is 50kbits/s)Supports up to 8 devices in a piconet ( two or moreBluetooth units sharing a channel).Built-in securityNon line-of-sight transmission through walls and briefcasesEasy integration of TCP/IP for logy/Pages/Basics.aspx
Wi-Fi Wi-Fi is a technology for WLAN based on the IEEE802.11 (a, b, g) specifications Originally developed for PC in WLAN Increasingly used for more services: Internet and VoIP phone access, gaming, and basic connectivity of consumer electronics suchas televisions and DVD players, or digital cameras, In the future Wi-Fi will be used by cars in highways insupport of an Intelligent Transportation System toincrease safety, gather statistics, and enable mobilecommerce (IEEE 802.11p) Wi-Fi supports structured (access point) and ad-hocnetworks (a PC and a digital camera).
Wi-Fi An access point (AP) broadcasts its SSID (Service SetIdentifier, "Network name") via packets (beacons)broadcasted every 100 ms at 1 Mbit/sBased on the settings (e.g. the SSID), the client maydecide whether to connect to an APWi-Fi transmission, as a non-circuit-switched wiredEthernet network, can generate collisionsWi-Fi uses CSMA/CA (Carrier Sense Multiple Access withCollision Avoidance) to avoid collisionsCSMA the sender before transmitting it senses thecarrier – if there is another device communicating then itwaits a random time an retryCA the sender before transmitting contacts the receiverand ask for an acknowledgement – if not received therequest is repeated after a random time interval.
WiMAX IEEE 802.16: Broadband Wireless Access / WirelessMAN /WiMax (Worldwide Interoperability for Microwave Access) Connecting Wi-Fi hotspots with each other and to otherparts of the Internet Providing a wireless alternative to cable and DSL forlast mile broadband access Providing high-speed mobile data and telecommunicationsservices Providing Nomadic connectivity 75 Mbit/s up to 50 km LOS, up to 10 km NLOS; 2-5 GHzband Initial standards without roaming or mobility support 802.16e adds mobility support, allows for roaming at .wimax-italia.it/
Wireless TelephonyAIR LINKWIREDPUBLIC SWITCHEDTELEPHONE NETWORKSOURCE: IEC.ORG
Advantages of wireless LANs Very flexible within the reception area Ad-hoc networks without previous planningpossible (almost) no wiring difficulties (e.g. historicbuildings, firewalls) More robust against disasters like, e.g.,earthquakes, fire - or users pulling a plug.
Wireless networks disadvantages Higher loss-rates due to interference emissions of, e.g., engines, lightningRestrictive regulations of frequencies frequencies have to be coordinated, useful frequencies arealmost all occupiedLow data transmission rates local some Mbit/s, regional currently, e.g., 53kbit/s with GSM/GPRSHigher delays, higher jitter connection setup time with GSM in the second range, severalhundred milliseconds for other wireless systemsLower security, simpler active attacking radio interface accessible for everyone, base station can besimulated, thus attracting calls from mobile phonesAlways shared medium secure access mechanisms important
Electromagnetic Waves Electromagnetic radiation (EMR) takes the form of selfpropagating waves in a vacuum or in matterIt consists of electric and magnetic field componentswhich oscillate in phase perpendicular to each other andperpendicular to the direction of energy propagationA wave is a disturbance that propagates through spaceand time, usually with transference of energyThe wavelength (denoted as λ) is the distance betweentwo sequential crestsThe period T is the time for one complete cycle for anoscillation of a waveThe frequency f is how many periods per unit time (forexample one second) and is measured in hertz: f 1/Tthe velocity of a wave is the velocity at which variationsin the shape of the wave's amplitude propagate throughspace: v λ*f
Wave al/Tutorial/StartCD.htm
Waves with different frequencies and lengthperiod1GHzλ 30cm3 GHzλ 10cm
Electromagnetic SpectrumRADIOVHF VERY HIGH FREQUENCYUHF ULTRA HIGH FREQUENCYSHF SUPER HIGH FREQUENCYEHF EXTRA HIGH FREQUENCYHARMFUL RADIATIONLIGHT3G CELLULAR1.5-5.2 GHz1G, 2G CELLULAR0.4-1.5GHzc λ*fc 299 792 458 m/s 3*108 m/s4G CELLULAR56-100 GHzUWB3.1-10.6 GHzSOURCE: JSC.MIL
Frequencies and regulations ITU-R (International Telecommunication Union –Radiocommunication) holds auctions for new frequencies,manages frequency bands worldwideValues in MHz
Signals I Signals are a function of time and locationPhysical representation of dataUsers can exchange data through the transmissionof signalsThe Layer 1 is responsible for conversion of data,i.e., bits, into signals and viceversaSignal parameters of periodic signals: period T,frequency f 1/T, amplitude A, phase shift ϕ sine wave as special periodic signal for a carrier:s(t) At sin(2 π ft t ϕt)Sine waves are of special interest as it is possible toconstruct every periodic signal using only sine andcosine functions (Fourier equation).http://en.wikipedia.org/wiki/Fourier serieshttp://en.wikipedia.org/wiki/Fourier transform
Fourier analysis of periodic signals 1g(t) c an sin(2πnft) bn cos(2πnft)2n 1n 11100 tideal periodic signaltreal composition(based on harmonics)f 1/T is the fundamental frequency first harmonicIt is the lowest frequency present in the spectrum ofthe signal.
Signals II Different representations of signals amplitude (amplitude domain) frequency spectrum (frequency domain) phase state diagram (amplitude M and phasepolar coordinates)Q M sin ϕA [V]A [V]ϕ int[s]ϕI M cos ϕϕ f [Hz]Composed signals transferred into frequency domainusing Fourier transformationDigital signals need: infinite frequencies for perfect transmission modulation with a carrier frequency for transmission(analog signal!)
Sound spectrum of two flutes
Bandwidth-Limited Signals A binary signal and its root-mean-square Fourier amplitudes.(b) – (c) Successive approximations to the original signalf 1/T is the fundamental frequency first harmonic
Bandwidth-Limited Signals (2)(d) – (e) Successive approximations to the originalsignal.
Bandwidth-Limited Signals (3)Relation between data rate and harmonics 8 bits sent through a channel with bandwidth equal to 3000Hz For instance, if we want to send at 2400bps we need T 8/2400 3.33 msec – this is the period of the first harmonic(the longest) – hence the frequency of the first harmonic is1000/3.3 300 The number of harmonic passing through the channel (3000Hz) is3000/300 10.
Digital modulation Modulation of digital signals known as Shift Keying Amplitude Shift Keying (ASK): very simple low bandwidth requirements very susceptible to interference101t101Frequency Shift Keying (FSK): needs larger bandwidth WHY?Phase Shift Keying (PSK): more complex robust against interferencet101t
Modulation and demodulationsee previous sebandsignalanalogmodulationradio transmitterradiocarrierin GSM a wave at one ofthe available channels,e.g., 960 adio receiver
Modulation Digital modulation digital data is translated into an analog signal(baseband) with: ASK, FSK, PSK differences in spectral efficiency, power efficiency,robustnessAnalog modulation: shifts center frequency of basebandsignal up to the radio carrier Motivation smaller antennas (e.g., λ/4) Frequency Division Multiplexing -it would not bepossible if we use always the same band medium characteristics Basic schemes Amplitude Modulation (AM) Frequency Modulation (FM) Phase Modulation (PM)
Frequency of Signals: Summary Frequency is measured in cycles per second, calledHertz.Electromagnetic radiation can be used in ranges ofincreasingly higher frequency: Radio ( GHz)100GHz - 3mm Microwave (1 GHz – 100 GHz)wavelength - 1Gb/sthroughput - Why? Infrared (100 GHz - 300 THz) Light (380-770 THz)Higher frequencies are more directional and (generally)more affected by weatherHigher frequencies can carry more bits/second (see next)A signal that changes over time can be represented by itsenergy at different frequencies (Fourier)The bandwidth of a signal is the difference between themaximum and the minimum significant frequencies of thesignal
Nyquist Sampling Theorem Nyquist Sampling Theorem: if all significant frequencies of a signal are lessthan B (observe the Fourier spectrum) and if we sample the signal with a frequency2B or higher, then we can exactly reconstruct the signal anything sampling rate less than 2B will loseinformationProven by Shannon in 1949This also says that the maximum amount ofinformation transferred through a channel withbandwidth B Hz is 2B bps (using 2 symbols –binary signal). WHY?
Example We must sample in two points to understand the amplitudeand phase of the sine function
Example With a signal for which the maximum frequency is higher than twice thesampling rate, the reconstructed signal may not resemble the originalsignal.
Example
Idea The larger the bandwidth the more complexsignals can be transmitted More complex signals can encode more data What is the relationship between bandwidth andmaximum data rate? See next slide
Data Transmission Rate Assume data are encoded digitally using K symbols (e.g.,just two 0/1), the bandwidth is B, then the maximum datarate is: D 2B log2K bits/s (Nyquist Theorem) For example, with 32 symbols and a bandwidth B 1MHz,the maximum data rate is 2*1M*log232 bits/s or 10Mb/s A symbol can be encoded as a unique signal level (AM), ora unique phase (PM), or a unique frequency (FM) In theory, we could have a very large number of symbols,allowing very high transmission rate without highbandwidth BUT In practice, we cannot use a high number of symbolsbecause we cannot tell them apart: all real circuits sufferfrom noise.
Shannon's Theorem It is impossible to reach very high data rates on bandlimited circuits in the presence of noiseSignal power S, noise power NSNR signal-to-noise ratio in Decibel: SNR 10 log10 (S/N) dBFor example SNR 20dB means the signal is 100 timesmore powerful than the noiseShannon's theorem: the capacity C of a channel withbandwidth B (Hz) is: C B log2(1 S/N) b/sFor example if SNR 20dB and the channel has bandwidthB 1MHz: C 1M*log2(1 100) b/s 6.66 Mb/s Theoretical capacity is 2*1M*log2(K) - Nyquist – buteven if we use 16 symbols we cannot reach the capacity 2*1M*log2(16) 2*1M*4 8Mb/s.
Signal in wired networks There is a sender and a receiver The wire determine the propagation of the signal(the signal can only propagate through the wire twisted pair of copper wires (telephone) or a coaxial cable (TV antenna) As long as the wire is not interrupted everythingis ok and the signal has the same characteristicsat each point For wireless transmission this predictablebehavior is true only in a vacuum – withoutmatter between the sender and the receiver.
Signal propagation ranges Transmission range communication possible low error rateDetection range detection of the signalpossible no communicationpossibleInterference range signal may not bedetected signal adds to thebackground cereceiver
Path loss of radio signals In free space radio signal propagates as lightdoes – straight lineEven without matter between the sender and thereceiver, there is a free space loss Receiving power proportional to 1/d² (d distance between sender and receiver)If there is matter between sender and receiver The atmosphere heavily influencestransmission over long distance Rain can absorb radiation energy Radio waves can penetrate objects (thelower the frequency the better the penetration– higher frequencies behave like light!)
Inverse-square law The lines represent theflux emanating from thesource The total number of fluxlines depends on thestrength of the sourceand is constant withincreasing distance99/22 A greater density of fluxlines (lines per unit area)means a stronger field The density of flux lines is inversely proportional to thesquare of the distance from the source because the surfacearea of a sphere increases with the square of the radius. Thus the strength of the field is inversely proportional tothe square of the distance from the source.9/32
Signal propagation In real life we rarely have a line-of-sight (LOS) betweensender and receiverReceiving power additionally influenced by fading (frequency dependent) shadowing reflection at large obstacles refraction depending on the density of a medium scattering at small obstacles (size in the order of thewavelength) diffraction at ction
Diffraction Diffraction: the bending of waves when they passnear the edge of an obstacle or through smallopenings iffraction.htm
Real world example
Multipath propagation Signal can take many different paths between sender andreceiver due to reflection, scattering, diffractionmultipathLOS pulses pulsessignal at sendersignal at receiver Time dispersion: signal is dispersed over time interference with “neighbor” symbols, Inter SymbolInterference (ISI) The signal reaches a receiver directly and phase shifted distorted signal depending on the phases of thedifferent parts
Mobile Communication Technologies Local wireless networks WLAN 802.11 802.11a 802.11b 802.11i/e/ /w 802.11g WiFi 802.11h Personal wireless nw WPAN 802.15 802.15.4 802.15.1 802.15.2 Bluetooth 802.15.4a/b ZigBee 802.15.3 Wireless distribution networks WMAN 802.16 (Broadband Wireless Access) 802.20 (Mobile Bro
Wireless# Guide to Wireless Communications Chapter 1 Introduction to Wireless Communications . Wireless Local Area Network (WLAN) - Extension of a wired LAN Connecting to it through a device called a wireless . network Each computer on the WLAN has a wireless network interface card (NIC) - With an antenna built into it .
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W2E2 Wireless Women for Entrepreneurship & Empowerment W3C World Wide Web Consortium W4C Wireless for Communities WAS Wireless Access System W-CDMA Wideband Code Division Multiple Access WCN Wireless community networks Wi-Fi Wireless Fidelity WiMAX Worldwide Interoperability for Microwave Access WLAN Wireless local area network WLL Wireless in .
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