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Class Note for COSC 6397 at UH


Class Note for COSC 6397 at UH

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This 19 page Class Notes was uploaded by an elite notetaker on Friday February 6, 2015. The Class Notes belongs to a course at University of Houston taught by a professor in Fall. Since its upload, it has received 15 views.

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Date Created: 02/06/15
Lecture 2 Wireless Channel Propagation amp Modulation Techniques 13 Q Police Radar quot Transmittad RADAR W a f 1 I Understanding mum Tn h39 r39 I RADAR amp mm 5 539 Rallsma quot Wave g mum 5 f Trang39n mat 39 quot quot M wng J j 39 39 39 car I I 7 7L 7 I V 739 r a 14 39 I quot Basics ml I Random variable X ii If a probability distribution has density fx then intuitively the infinitesimal interval X X dx has probability fx dx Ll Cumulative distribution function Fm J fxdx i i Mean EGO jix xwx iii Variance co oz x Exzfxdx l i Ex Gaussigii distribution Probability Density Function exp 5 gt 2 039 fx 270 15 39 I quot Basics Fl F s T f x eXp i27rxsdx Fourier Transformation f x T F s expi27z xsds I Time domain I Frequencydomain m391 ii A Period T gt I Sme39Wave Signal Stuugh T H 11 16 ID IMHI I 1 I I I I I I 39l I i I n 39I I l I t 39I I I I II I I 1 1 I t I I DI I 1 I I I I 1 39l I I I q I I I I 1 f I I I J A C f R reflection Ex 3e824e9 1250m Di diffraction S Scattering 39 Propagation Model 30 35 1 540 39 345 V A 550 I 34 65 7o 4 A e 14 15 16 17 18 19 20 21 22 23 24 25 2639 27 28 T R Separation motor I Largescale propagation model the average received signal strength at a given distance from the transmitter Useful for estimating the radio coverage area I Smallscale propagation model the variability of the signal strength in close spatial proximity to a particular location or short time durations 18 39 I Freespace Model I Friis free space equation 3 GHGV are the antenna gains at the transmitter and receiver D k is the wavelength PGG 12 I I r Ci d is the distance Prd 472d2L i l L is a loss factor not related to propagation 19 Free Space Model 7 I Path loss PLdB 1010g 1010g r 67612 47l2d2 I Only valid beyond farfield distance d ZDZ D is the transmitter antenna aperture f 2 dfgtgtDdfgtgtr d E Bltdgt11ltddlt gtid2dozdf 20 39 I L39 Ground Reflection TwoRay Model 39I39Hrunsmiuer Elm 103 2 R 1 receiver Figure 47 Tworay ground reflection model A dquot d39Jh th 012 Jh hr2 012 z 2 d 3 when d is large compared to h h 2 2 PVPGGV d439 fordgt 20 21 39 I L Lognormal Shadowing PLddB Em X Ego 10n10gdi X 0 X0 is a zeromean Gaussian distributed random variable in dB with standard deviation 6 also in dB Table 42 Path Loss Exponents for Different Environments Environment Path Loss Exponent n IJ FI t C space Urban arca cellular radio 27 to 35 Sltadtm c d urban cellular radio 3 to 5 ln buildingy lineaol39wight 111 to 8 Obstructed in building 4 to 6 Obstructed in factories 2 to 3 22 Smallscale Fading I Factors that contribute to smallscale fading II Multipath propagation El Speed of the mobile I Speed of surrounding objects El The transmission ht 1113 TN 1 Figure 54 An example of the time varying discrete time impulse response model for a multipath radio channel Discrete models are useful in simulation where modulation data must be convolved with the channel impulse response Tra02 23 39 39 Parameters of Mobile Multipath Channels I Time Dispersion relative to direct lineof sight I Mean excess delay RMS delay spread Excess delay spread X dB Coherence bandwidth Measures the range of frequencies where the channel can be considered flat 0C 1RMS delay spread I Frequency dispersion TD 0C fm O I l RMS Delay Spread 46 40 ns Maximum Excess Delay lt 10 dB 84 ns 0 Threshold Laval 20 dB A AA A A UV39HW39WWW Mean Excess Delay 4505 ns Normalized Received Power dB Scale 1 o 30 J I I I l I I I 50 0 50 100 150 200 250 300 350 l00 450 Excess Delay ns Figure 510 Example of an indoor power delay profile rrns delay spread mean excess delay maximum excess delay 10 dB and threshold level are shown 39 1 L39 Doppler Shift Geometry l l K I 9 e 9 X I Y m Figure 51 Illustration of Doppler effect 1A 137 V cos x1 25 39 Q Police Radar 2ulargel f fre eeted 39 flransm illed f c 26 39 1 U Two independent fading issues SmallScale Fading Based on multipath time delay spread Flat Fading Frequency Selective Fading 1 BW of signal lt BW of channel 1 BW of signal gt BW of channel 2 Delay spread lt Symbol period 2 Delay spread gt Symbol period SmallScale Fading Based on Doppler spread Fast Fading Slow Fading 1 High Doppler spread 1 Low Doppler spread 2 Coherence time lt Symbol period 2 Coherence time gt Symbol period 3 Channel variations faster than base 3 Channel variations slower than band signal variations baseband signal variations Figure 511 Types of smallscale fading I Fiatfading nonfreq Se39eCtive I Amplitude varying Channelnarrowband Channels 39I I39m gt MI I gt m hii T rm 0 0 T 0 T H Tltlt 1quot x I 51 H39 RU J Elf J i Lf aJ 311 JV 1 if Figure 512 Flat fading channel characteristics 28 39 1 iii Raylelg h fading Models a flat fading channel or an individual multipath component r2 20392 Typical simulated Rayleigh fading at the carrier Receiver speed 120 kmhr W igexpe CT 25 xz Signal Level dB about rms L U1 4O L L o 50 1 oo 1 50 200 250 Elapsed Time ms Figure 515 A typical Rayleigh fading envelope at 900 MHz from Fun93 lEEE 29 39 1 L39 Frequency selective fading I Introduce intersymbol interference m rm gt 1m 1 m Mr I rm 0 T 0 1 0 TS TT 5m H0 Rm r u f JJ f U f JJ f Figure 513 Frequency selective fading channel characteristics 30 39 I quot Digital Communication Systems Digital Base band Analog bandpass Analog l AID Source Channel Source E Converter Encoder Encoder j Modulator l l a a Analog i ii l l a E Synchomization 4 R a a e l l l l l quotquotquotquotquotquotquotquotquotquotquotquotquot 39T quotquotquotquotquotquot quoti quotquotquotquotquot i v t i v39 l DEA Source Channel l Sink 39 Convener 39 Decoder Decoder 4 DEtecmr I Modulation to translate a baseband message signal to a bandpass signal which is suitable for transmission 1 Amplitude i7 Frequency rquot Phase l Spread spectrum modulation 31


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