Chapter 3 System Theory and Technologies 1 r... How to transport digital symbols...? 3.1.1 Introduction 3.1. Symbols, Bits and Baud 3.1.3 Wired Physical Layers 3.1.4 Radio based physical layer electromagnetic waves Modulation (basics) Spread spectrum 3.1.5 Optical physical layer 1
Electromagnic waves (1) Antenna: transormation voltage/current-> EM-ield Transmitter Radio-Channel Antenna: transormation EM-ield -> voltage/current Receiver 3 Emitting requency: wavelength: speed: polarization power [dbm] beam depends on - Transmitter - Antenna λ c Channel multipath -> intererence - constructive - destructive (ading) loss o power - absorption - relection depends on - requency - environment Receiving depends - antenna - sensitivity - power o EM-Field Electromagnetic waves () z Θ r io Θ d P y L Φ x i0 E = E r Θ i = L cos( Θ) 1 c + πε0 c d jωcd 0 L sin( Θ) jωc c c + + 4πε0 c d d jωcd 3 d exp jωc t c 3 E Φ d exp jωc t c = H r = H Θ = 0 4 H Φ i = 0 L sin( Θ) j ω c d c + exp j ω t c 4π c d d c
Ideal radio-channel TS P T G TA l G RA P R ER Transmission Ratio T PR λ = P 4π l G TA G G Antenna Gain (G dbi = 10 dbi. lg G) λ = c 0 / wavelenght (c 0 = 300.000 km/s) RA Loss: = Inverse Transmission Ratio 5 Source: Uwe Meier Free Space Propagation Free Space propagation P ( l) Pt Gt G (4π ) l r = L: System loss actor >1, L=1: no loss in HW System G: Antenna gain r λ L 6 Isotropic radiator: ideal antenna which radiate power uniormly in all directions. Eective isotropic radiated power(eirp): EIRP = P t G t Eective radiated power (ERP): Maximum radiated power as compared to λ/ dipol antenna Dipol: gain 1.64 (.15 db) above an isotropic antenna ERP.15 db smaller than EIRP 3
Ideal Radio Channel 100,00 TS P T G TA l G RA P R ER 90,00 80,00 nkdämpung in db Fun 70,00 60,00 50,00 5,8 GHz 40,00,44 GHz 869 MHz 30,00 434 MHz 0,00 0 10 0 30 40 50 60 70 80 90 100 S-E-Abstand in m 7 Antenna Gain: G TA = G RA = dbi = 1,58 Source: Uwe Meier Path loss PL [ db ] Pt 10 log P r Gt G = 10 log (4π ) λ l r = / T RA PR P db Far-ield: l >d_: l GTA G = 9,4 0 lg 0 lg + + km GHz dbi dbi D d ; d >> D; λ = d >> λ 8 D: largest physical linear dimension o antenna 4
Path loss close-in distance d0: known received power reerence point l >l0 > d Typical values or 1-GHz 1m (indoor) 100m or 1000m (outdoor) P l0 r ( l) = Pr ( l 0) l Pr ( l0) l0 Pr [ dbm] = 10 log + 0log 0.001W l 9 Real Radio-Channel T Direct Wave relected Wave R LOS diraction Obstacle shadow reraction R NLOS Shadow-boundary LOS: Line o sight 10 NLOS: Non line o sight Source: Uwe Meier 5
Multipath (Scattering) 11 Doppler-Shit π Δl ΔΦ = λ π v Δt = cos( Θ) λ d = 1 π dφ = dt 1 π ΔΦ Δt v = cos( Θ) λ x Δl v d y 1 6
Path loss 13 Relection Object with large dimensions compared to wavelength Ground relection Buildings... Diraction Bye surace with sharp irregularities (edges) Reraction Wave passes dierent materials Scattering Medium has elements small compared to wavelength Number o Obstacles/Volume is large Consequence: depends on the environment-> complex models or estimation Fading Rapid changes in signal strength over a small travel distance or time interval Random Frequency modulation due to varying Doppler shits on dierent multipath signals Time dispersion (echo's) cause by multipath propagation delays Inluenced by Multipath propagation o Speed o mobile Speed o surrounding Objects Transmission bandwidth o the signal 14 7
Real radio channel (received power) 5,8-GHz-Kanal (outdoor, Sinussignal) -50-55 LOS -60-65 Empangsleistung in dbm -70-75 -80-85 -90-95 -100-105 -110 0 10 0 30 40 50 60 70 80 90 100 110 10 130 140 150 160 170 180 Zeit in Sek. NLOS time-selective ading (movements) 15 Source: Uwe Meier Real radio channel,4-ghz-channel (indoor, transmission ratio in db) no relections relections (LOS) -55-60 -60-65 -65-70 -70-75 -75-80 -85-90 ISM 1.8..4.6.8 3 x 10 9 requency selective ading (multiple path) -80-85 -90-95 ISM 1.8..4.6.8 3 1,8... 3 GHz 1,8... 3 GHz x 10 9 16 Source: Uwe Meier 8
Real radio channel Received power in a city buildings sender 17 Source: Uwe Meier Real radio channel Received power in a city 434 MHz,44 GHz Depends on the requency 18 Source: Uwe Meier 9
Inormation 0 Bandwidth[Hz] Frequency [Hz] transmission o inormation needs bandwidth more bandwidth -> more inormation/time Higher requencies, bigger bandwidth easier available 19 ISM-Bands: Industrial-Scientiic-Medical No ee s Can be used all over the world, but there are some restrictions duty cycle maximum power Dierent requency-bands available Modulation, protocols or services as preerred 0 Cheap because o mass-market 10
ISM-Band s only EU div. Anwend. Hz 868 M WLAN Bluetooth ZigBee Nanonet Frequenz WLAN HiperLAN 5,1 GH Hz 43 34 MHz only EU div. Anwend. 5 MHz 91 only USA div. Anwend.,4 4 GHz,,7 GHz 5, WLAN HiperLAN 1 Frequency allocation Germany 6,957... 7,83 MHz ISM 40, 66... 40, 7 MHz ISM 433,05... 434,79 MHz ISM 868... 870 MHz ISM (ZigBee) 890... 960 MHz GSM-D (seit 199) 1,71... 1,88 GHz GSM-E = DCS 1800 (seit 1994) 1,88... 1,99 GHz DECT 1,885...,05 GHz;,1..., GHz UMTS,4...,4835 GHz ISM (WLAN, Bluetooth, ZigBee,...) 5,75... 5,875 GHz ISM (WLAN) 4... 4,5 GHz ISM ISM industrial, scientiic, medical GSM global system or mobiles DECT digital European cordless telecommunications UMTS universal mobile telecommunication system 11
Digital modulation Transormation o a digital (binary) base band-signal into another requency-range Modulation o an harmonic carrier change amplitude change phase change requency each kind o modulation needs bandwidth communication oten is characterized by the requency o the carrier Baseband binary Modulator Booster antenna modulated RF 3 Harmonic carrier Digital modulation 1 Bit 1 Symbol Modulator Demodulator unidirektional, simplex Transceiver Transceiver bidirektional, duplex 4 1
basics: base band-transmission Bit 1 TB Base band t [s] Bit 0 Bit rate: 1/TB [Bit/s] Nyquist bandwidth: N=1/TB [Hz] bandwidth N [Hz] 5 ASK: Amplitude Shit Keying Bit 1 Bit 0 TB t [s] modulated carrier Bit rate: 1/TB [Bit/s] bandwidth: N-H=1/TB [Hz] TP -> T=1/Tp Bandwidth T [Hz] 6 Matlab 13
PSK: Phase Shit Keying Sequence o bits modulated signal time t/t im 7 0 -cos (Phase= 180 ) 1 cos (Phase= 0 ) re Matlab FSK: Frequency Shit Keying Sequence o bits 0 = A + B modulated signal Δ = B A 8 Δ A 0 B 0 1 time t/t μ = Δ r Δ = 1 Matlab 14
4-PSK / QAM 00 a im 10 im -a a re re 01 -a 11 4-PSK bits -> 1 o 4 symbols 16 QAM 4 bits -> 1 o 16 symbols 9 more bits build one symbol! Matlab Deinition o Spread Spectrum (SS) A transmission technique in which a Pseudonoise code (independent o the inormation data) is employed a modulation waveorm to spread spread the signal energy over a bandwidth much greater than signal inormation Bandwidth. At a receiver the signal is despread using a synchronized replica o o the Pseudo-noise code 30 15
History/Background Introduced during second world war Dominated long time military communication applications 1980 irst commercial applications Used in 3G cellular systems Used in.4 GHz ISM-Band, because this was a condition 31 DSSS principle (1) T S T C tx Binary data X Modulator -PSK pn t PN-Code Baseband RF ~ bandpass 3 coherent demodulation 16
DSSS principle () Short code system: PN-Code duration equal to a data symbol duration symbol 1 0 0 1 d t N c T c pn t d t pn t 33 DSSS principle (3) Long code system PN code length much longer than a data symbol symbol 1 0 0 1 d t N c T c pn t d t pn t 34 17
DSSS: Properties o spectrum T c RF -R c RF W SS instantaneously: broadband RF + R c 35 FHSS principle (1) Binary data Modulator -FSK Mixer X Band pass tx carrier Base band ~ Frequency Synthesizer PN-Code pn t /n band pass 36 n: Deines hopping rate no coherent demodulation 18
FHSS principle () ast hopping PN-Code duration equal to a data symbol duration (or shorter) symbol - 0 3 + 0 1 T c 4 1 0 0 1 37 T Hop FHSS principle (3) Slow hopping PN-Code equal to a data symbol symbol 1 0 0 1 4 3 + 0 1 T Hop - 0 38 19
FHSS: Properties o spectrum hop T c channel 1 3 4 5 6 7 N D Ch RF W SS = N. D Ch instantaneously: smallband on average: broadband 39 DSSS principle d t rx b d tx b tx rx r X Modulator Demodulator X channel pn r pn t RF PN ~ ~ RF PN Code Code Base band -R s T S R S band pass d t T S T C Base band 40 T R c S -R C R C 0
Intererence d t X tx b + Intererence i rx b X d r pn t pn r PN Code channel PN Code 41 Intererence (Narrowband) d t X pn t PN Code tx b T S Data-signal + channel Intererence i whitened intererence R S narrowband -R s R S intererence DS-signal (spread) R T c S -R C R C rx b T S X PN Code d r pn r DS-signal (de-spread) R C 4 1
Intererence (Broadband) d t X pn t PN Code tx b T S Data-signal + channel Intererence i whitened intererence R S broadband -R s R S DS-signal intererence (spread) R T c S -R C R C rx b T S X PN Code d r pn r DS-signal (de-spread) R C 43 Intererence (Gaussian noise) d t X pn t PN Code tx b T S Data-signal + channel Intererence i whitened Gaussian noise -R R s S -R R s S DS-signal (spread) gaussian noise T c -R C R C rx b T S X PN Code d r pn r DS-signal (despread) R C 44