Building Blocks of Wireless Communication Systems

Transcription

1 Building Blcks Wireless Cmmunicain Sysems Building Blcks Wireless Cmmunicain Sysems Ing. Karel Ulvec, Ph.D. CTU in Prague, Faculy Elecrical Engineering Only r sudy purpses r sudens he! 1/ Cnen Building Blcks Wireless Cmmunicain Sysems - Blcks radi inerace wireless cmmunicain sysems Cnen Radi inerace Filer Aenuar Ampliier Mixer - Desired and undesired mixing prducs - Applicains Vlage cnrl scillar Phase lck lp Quadraure mdular Wireless cmmunicain channel - Basic prperies -Fading /

2 Building Blcks Wireless Cmmunicain Sysems Blcks radi inerace Wireless Cmmunicain Sysems Sysem general mdel cmmunicain chain Radi inerace Wih respec hardware: radiinerace mdular and her blcks ransmier, demdular and her blcks receiver Generally: radi inerace anyhing cncerned wih wireless ransmissin (wireless cmmunicain channel as well) Example building blcks receiver s RF inpu blck RF ampliier s Mixer IF IF ampl. and iler Demdular LF ampliier Lcal scillar 3/ Building Blcks Wireless Cmmunicain Sysems Filer T remve unwaned requency cmpnens (nise, disurbances, signals her sysems) Filrain in he specral (requency) dmain Pars ampliude ranser uncin pass-band / sp-band Types Lw-pass iler ransers signals wih requencies up he maximal value (upper cu requency) High-pass iler ransers signals wih requencies abve he minimal value (lwer cu requency) Band-pass iler ransers signals wih requencies beween he minimal value and he maximal value Band-rejec iler absrbs signals wih requencies beween he minimal value and he maximal value Cu pass-band requencies are given by 3 db decrease ampliude ranser uncin Pass-band bandwidh Bis given by requencies wih 3 db r 6 db decrease ampliuderanser uncin Sp-band edge requencies crrespnd wih signal aenuain (r examples 5 db r 3 db) Furher ineresing parameers pass-band ripple, minimal aenuain in sp-band 4/

3 Building Blcks Wireless Cmmunicain Sysems Aenuar Wideband building blck r signal level aenuain ( avid signal disrin as example) The value he aenuain in given requency range is impran parameer Ampliier T ampliy signal level in given requency range (usually) T cnver impedance(impedance maching, gain can be clse uni r even lwer) Impran parameer is gain in given requency range bandwidh B Similarly as r iler, Bis given by requencies wih 3 db r 6 db decrease ampliuderanser uncin Lw and high cu requencies crrespnd usually wih 3 db decrease ampliude ranser uncin Wideband ampliiers are ampliiers wih negaive eedback, hey have la gain in wide requency range 5/ Building Blcks Wireless Cmmunicain Sysems Mixer Nn-linear blck which cnver signal a ne requency in signal a anher (higher r lwer) requency Impran characerisic is he upu prducs pwer level dependence n he inpu signal pwer level See muliplicaive mixer n ig. u1= U1cs(ω 1) u = u1 u u = U cs(ω ) u lcal scillar signal Fr ideal mixer we bain sum and dierence prducs U1U U1U u = u1u = U1 cs( ω 1) U cs( ω) = cs( ω ω1) + cs( ω + ω1) 6/

4 Building Blcks Wireless Cmmunicain Sysems Mixer desired and undesired mixing prducs Because nnlineariy, we bain als prducs: DC, wih requency inpu signal ω 1, wih requency scillar signal ω, heir secnd and higher harmnics and mixing prducs wih requencies ±nω 1 ± mω (n and m psiive inegers) assigned as inermdulain prducs wih rder m + n Usually prduc ω 1 ω r ω 1 + ω is desired ne and all hers mus be aenuaed by iler iler a mixer upu (in receivers his iler is called inermediae iler, i inluences seleciviy in clse range arund desired requency) Image (mirrr) signal (i is n mixing prduc!), see ig. desired received signal wih req. s is cnvered inermediae signal wih req. IF, accrding rmula IF = s ( > s ) ampl. IF IF IF Bu, upu signal wih req. IF is als prduced by inpu signal wih req. z, because IF = z, image signal mus be aenuaed a he inpu mixer (in case receivers, his inpu iler inluences image signal rejecin) s z 7/ Building Blcks Wireless Cmmunicain Sysems Mixer desired vs. undesired prducs Nn-ideal signal lcal scillar can cause undesired prducs as well, s called reciprcal mixing, see ig. IF IF phase nise s s1 bandwidh upu (IF) iler Srng signal wih requency s (near received signal wih requency s1 ) causes prducs by mixing wih phase nise lcal scillar, nise backgrund a he upu raises (in case very srng signal, i can disable recepin weak waned signal) 8/

5 Building Blcks Wireless Cmmunicain Sysems Mixer applicain Frequency cnversin increasing r decreasing Mixer urher applicains General, signals u 1 and u diers in phase by ϕ() u = u u cs( ω 1 ) U cs( ω + ϕ( )) 1 = U 1 Fr ω 1 = ω U1U u = u u = phase deecr U1U cs( ϕ ( )) + cs(ω + ϕ( )), aer requency ilrain 1 u = u u U1U = cs( ϕ( )) 1 In case ampliude mdulaed signal, inpu signal has ime-varying ampliude U 1 ();i lcal scillar has he same requency ω as carrier requency ω 1 = ω (synchrnus) and phase ϕ = (cheren), hen ( U U u = u1u = U1 ) cs() = U1( ) synchrnus cheren AM deecr 9/ Building Blcks Wireless Cmmunicain Sysems Vlage Cnrlled Oscillar (VCO) Blck generaing peridical upu signal wih requency ω crrespnding he inpu vlage I ω is requency in case zer vlage, we can cmpue requency ω= ω + K U, where K is VCO gain [rad/v/s] Phase Lck Lp (PLL) Nn-linear blck which wrks as a clsed-lp requency-cnrl sysem I generaes an upu signal whse phase is relaed he phase an inpu signal (r synchrnizain as example) In her applicains anher signal can be used as upu (FM deecr as example) 1/

6 Building Blcks Wireless Cmmunicain Sysems PLL See blck diagram n ig. x(,ϕ) u(, φ) v(, φ) phase lp A deecr iler x(, ϕ) VCO Signal u(,φ)is in relain phase dierence he inpu signal x(,ϕ)and VCO signal φ ( )= ϕ( )-ϕ( ), his dierence is called as phase errr signal Signal u(,φ)is ilered aenuae higher requency prduc he phase deecr and ampliied wih gain A Signal v(,φ)cnrls VCO, s ha phase dierence is cnsan due clsed-lp sysem i als means ha requencies a he upu is he same as a he inpu I inpu signal is requency mdulaed (FM), signal v(,φ)can be used as FM demdulaed signal FM demdular 11/ Building Blcks Wireless Cmmunicain Sysems PLL Parameers Free-running Frequency requency VCO, in case n inpu signal (PLL is n synchrnized) Lck Range (r Synchrnizain Range) in his range PLL can llw inpu signal requency (in case ha PLL is synchrnized), see ig. Capure Range (r Acquisiin Range) is he requency range, in which PLL is able acquire synchrnizain wih inpu signal (rm he nn-synchrnized sae), see he ig. Increasing inpu signal requncy v U UP max U UP min UP min... lck range L C L UP max in Decreasing inpu signal requncy v U DOWN max... capure range C DOWN min DOWN max in U DOWN min 1/

7 Building Blcks Wireless Cmmunicain Sysems Mdular digial mdulain wih ne carrier Signal can change beween inie number saes (mdulain saes) M D M D = b, where bis he number bis represening ne daa symbl, see ig. n he righ Signal can change requency (FSK Frequency Shi Keying), ampliude (ASK Ampliude Shi Keying), phase (PSK Phase Shi Keying), r ampliude and phase geher (QAM Quadraure Ampliude Mdulain) s ( ) = n A ( ) e n [ ω +Φ ( )] j n n 1 1 QPSK (M D = 4, b = ) 16QAM (M D = 16, b = 4) ASK FSK PSK Daa symbl (ne sae) has ime durain T s i is called symbl durain, hen symbl rae is R s = 1 / T s Symbl represens bbis, hen bi-rae is R b = b R s b= lg M D 64QAM (M D = 64, b = 6) 13/ Building Blcks Wireless Cmmunicain Sysems Mdular QAM Quadraure Ampliude Mdulain Signal is cmpsed w quadraure cmpnens In-phase (I) par uses ampliude mdulain and carrier wave has shape csine uncin Quadraure (Q) par uses ampliude mdulain and carrier wave has shape sine uncin Csine and sine uncins are quadraure See blck diagram quadraure (IQ) mdular n ig. inpu bi sream serial-parallel cnverer I Q mapper h M [ ] h M [ ] x Σ x s() sin( ω c) cs( ω c ) QPSK (Quadraure Phase Shi Keying) {-1,1} 16-QAM (a = 1) {-3,-1,1,3} Nn-unirm 16-QAM (a = ) {-4,-,,4} Nn-unirm 16-QAM (a = 4) {-6,-4,4,6} 64-QAM (a = 1) {-7,-5,-3,-1,1,3,5,7} Nn-unirm 64-QAM (a = ) {-8,-6,-4,-,,4,6,8} 14/

8 Building Blcks Wireless Cmmunicain Sysems Quadraure mdular ilrain h M [ ] Higher rae r sequence: , see he specrum he recangular signal n ig. belw u (V) Time dmain T s Specral dmain (pwer densiy) db /T s = R s Filer mus pass requencies rm DC R s /, see ig. belw Time dmain Specral dmain (pwer densiy) u (V) T s db - -4 perid sine signal R s / (max.) requency sine signal 15/ Building Blcks Wireless Cmmunicain Sysems Quadraure mdular ilrain h M [ ] Ideal lw pass iler (bu n easible) a (db) R/ R Real LPF wih bandwidh B = (1 + α), where αis s called rll- acr a (db) α= α=.3 α=1 a (db) α= α=.3 α=1 R/ R B (R/; R) R/ R B (R/; R) r α=.3 B=(1+.3)R/ r α=.3 B=(1+.3)R/ 16/

9 Building Blcks Wireless Cmmunicain Sysems Basic prperies wireless cmmunicain channel Aenuain (pah-lss, shadwing) Nise Impran is sysem bandwidh B sys Nise pwer P N = N B sys Signal Nise Rai SNR= P sig / P N, SNR (db) = 1 lg 1 (P sig / P N ) Relecins wih respec ime durain Dppler ransmier and/r receiver mves Mdels wireless cmmunicain channel AWGN Addiive Whie Gaussian Nise Addiive signal nise is added he desired signal Gaussian signal nise is mdeled as randm signal wih Gaussian disribuin Whie pwer specral densiy is cnsan N / 17/ Building Blcks Wireless Cmmunicain Sysems Basic ading ypes Accrding requency ranser uncin Frequency la Frequency selecive S() Y() Frequency la Y() Frequency selecive s() signal a he channel inpu S() specrum he signal s() y() signal a he channel upu Y () specrum he signal y() y() y() relecins Accrding ime variain in ampliude Time la Time selecive big variain during symbl durain s() y() Time la y() Time selecive 18/

10 Cnen Building Blcks Wireless Cmmunicain Sysems - Blcks radi inerace wireless cmmunicain sysems Examinain areas: Filer, iler ypes, cu pass-band requency, sp-band edge requencies, pass-band bandwidh Mixer (muliplicaive), desired and undesired mixing prducs, reciprcal mixing, he imprance ilers ahe inpu and a heupu mixer Phase lck lp; blck diagram, ree-running requency, lck range, capure range Quadraure mdular, saes mdulain, relainship beweenbi-rae and symbl-rae, cnsellain diagram examples r QAM mdulain 19/ Building Blcks Wireless Cmmunicain Sysems Thank yu r yur aenin. Quesins please /