Wireless Transmission Basics

Transcription

1 Areas o researh in mobile ommuniaion Wireless Transmission Basis Frequenies Signals Anenna Signal propagaion Mulipleing Spread sperum Modulaion Cellular sysems Wireless Communiaion ransmission qualiy (bandwidh, error rae, delay) modulaion, oding, inererene media aess, regulaions... Mobiliy loaion dependen servies loaion ranspareny qualiy o servie suppor (delay, jier, seuriy)... Porabiliy power onsumpion limied ompuing power, sies o display,... usabiliy... Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing Simple reerene model used here Inluene o mobile ommuniaion o he layer model Appliaion Transpor Nework Daa Link Physial Radio Nework Daa Link Physial Nework Daa Link Physial Medium Appliaion Transpor Nework Daa Link Physial Appliaion layer Transpor layer Nework layer Daa link layer Physial layer servie loaion new appliaions, mulimedia adapive appliaions ongesion and low onrol qualiy o servie addressing, rouing, devie loaion hand-over auheniaion media aess mulipleing media aess onrol enrypion modulaion inererene aenuaion requeny Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 3 Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 4

2 Overlay Neworks - he global goal Frequenies or ommuniaion inegraion o heerogeneous ied and mobile neworks wih varying ransmission haraerisis wised pair oa able opial ransmission regional Mm 300 H 0 km 30 kh 00 m 3 MH m 300 MH 0 mm 30 GH 00 µm 3 TH µm 300 TH verial handover in-house ampus-based meropolian area horional handover VLF LF MF HF VHF UHF SHF EHF inrared visible ligh UV VLF = Very Low Frequeny LF = Low Frequeny MF = Medium Frequeny HF = High Frequeny VHF = Very High Frequeny Frequeny and wave lengh: λ = / wave lengh λ, speed o ligh 30 8 m/s, requeny UHF = Ulra High Frequeny SHF = Super High Frequeny EHF = Era High Frequeny UV = Ulraviole Ligh Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 5 Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 6 Frequenies or mobile ommuniaion VHF-/UHF-ranges or mobile radio simple, small anenna or ars deerminisi propagaion haraerisis, reliable onneions SHF and higher or direed radio links, saellie ommuniaion small anenna, beam orming large bandwidh available Wireless LANs use requenies in UHF o SHF range some sysems planned up o EHF limiaions due o absorpion by waer and oygen moleules (resonane requenies) weaher dependen ading, loss aused by heavy rainall e. Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 7 Frequenies and regulaions ITU-R holds auions or new requenies, manages requeny bands worldwide (WRC, World Radio Conerenes) Europe USA Japan Cellular Phones Cordless Phones Wireless LANs Ohers GSM , / , , / , / UMTS (FDD) , 0-90 UMTS (TDD) , CT , CT DECT IEEE HIPERLAN , RF-Conrol 7, 8, 48, 433, 868 AMPS, TDMA, CDMA , TDMA, CDMA, GSM , PACS , PACS-UB IEEE , RF-Conrol 35, 95 PDC 80-86, , , PHS JCT IEEE RF-Conrol 46, 868 Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 8

3 Signals I Fourier represenaion o periodi s physial represenaion o daa union o ime and loaion parameers: parameers represening he value o daa lassiiaion oninuous ime/disree ime oninuous values/disree values analog = oninuous ime and oninuous values digial = disree ime and disree values parameers o periodi s: period T, requeny =/T, ampliude A, phase shi ϕ sine wave as speial periodi or a arrier: s() = A sin( π + ϕ ) 0 g( ) = + n= ideal periodi a sin(πn) + n n n= 0 b os(πn) real omposiion (based on harmonis) Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 9 Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 0 Signals II Anennas: isoropi radiaor Dieren represenaions o s ampliude (ampliude domain) A [V] requeny sperum (requeny domain) phase sae diagram (ampliude M and phase ϕ in polar oordinaes) [s] A [V] Q = M sin ϕ ϕ I= M os ϕ Radiaion and reepion o eleromagnei waves, oupling o wires o spae or radio ransmission Isoropi radiaor: equal radiaion in all direions (hree dimensional) - only a heoreial reerene anenna Real anennas always have direive ees (verially and/or horionally) Radiaion paern: measuremen o radiaion around an anenna ϕ [H] Composed s ranserred ino requeny domain using Fourier ransormaion Digial s need ininie requenies or pere ransmission modulaion wih a arrier requeny or ransmission (analog!) y y ideal isoropi radiaor Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing

4 Anennas: simple dipoles Anennas: direed and seoried Real anennas are no isoropi radiaors bu, e.g., dipoles wih lenghs λ/4 on ar roos or λ/ as Herian dipole shape o anenna proporional o wavelengh Oen used or mirowave onneions or base saions or mobile phones (e.g., radio overage o a valley) λ/4 λ/ Eample: Radiaion paern o a simple Herian dipole y y y side view (y-plane) y side view (y-plane) op view (-plane) direed anenna simple dipole side view (y-plane) side view (y-plane) op view (-plane) Gain: maimum power in he direion o he main lobe ompared o he power o an isoropi radiaor (wih he same average power) seoried anenna op view, 3 seor op view, 6 seor Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 3 Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 4 Anennas: diversiy Signal propagaion ranges Grouping o or more anennas muli-elemen anenna arrays Anenna diversiy swihed diversiy, seleion diversiy reeiver hooses anenna wih larges oupu diversiy ombining ombine oupu power o produe gain ophasing needed o avoid anellaion λ/4 λ/ + λ/4 λ/ λ/ + λ/ Transmission range ommuniaion possible low error rae Deeion range deeion o he possible no ommuniaion possible Inererene range may no be deeed adds o he bakground noise sender ransmission deeion inererene disane ground plane Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 5 Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 6

5 Signal propagaion Real world eample Propagaion in ree spae always like ligh (sraigh line) Reeiving power proporional o /d² in vauum muh more in real environmens (d = disane beween sender and reeiver) Reeiving power addiionally inluened by ading (requeny dependen) shadowing releion a large obsales reraion depending on he densiy o a medium saering a small obsales diraion a edges shadowing releion reraion saering diraion Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 7 Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 8 Mulipah propagaion Signal an ake many dieren pahs beween sender and reeiver due o releion, saering, diraion LOS pulses mulipah pulses Ees o mobiliy Channel haraerisis hange over ime and loaion pahs hange dieren delay variaions o dieren pars dieren phases o pars quik hanges in he power reeived (shor erm ading) a sender Time dispersion: is dispersed over ime a reeiver inererene wih neighbor symbols, Iner Symbol Inererene (ISI) The reahes a reeiver direly and phase shied disored depending on he phases o he dieren pars Addiional hanges in disane o sender obsales urher away slow hanges in he average power reeived (long erm ading) power shor erm ading long erm ading Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 9 Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 0

6 Mulipleing Frequeny muliple Mulipleing in 4 dimensions spae (s i ) ime () requeny () ode () Goal: muliple use o a shared medium Imporan: guard spaes needed! hannels k i s k k k 3 k 4 k 5 k 6 s Separaion o he whole sperum ino smaller requeny bands A hannel ges a erain band o he sperum or he whole ime Advanages: no dynami oordinaion neessary works also or analog s k k k 3 k 4 k 5 k 6 Disadvanages: wase o bandwidh i he rai is disribued unevenly s 3 inleible guard spaes Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing Time muliple Time and requeny muliple A hannel ges he whole sperum or a erain amoun o ime Advanages: Combinaion o boh mehods A hannel ges a erain requeny band or a erain amoun o ime Eample: GSM only one arrier in he medium a any ime hroughpu high even or many users Disadvanages: preise synhroniaion neessary k k k 3 k 4 k 5 k 6 Advanages: beer proeion agains apping proeion agains requeny seleive inererene higher daa raes ompared o ode muliple bu: preise oordinaion required k k k 3 k 4 k 5 k 6 Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 3 Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 4

7 Code muliple Modulaion Eah hannel has a unique ode All hannels use he same sperum a he same ime Advanages: bandwidh eiien no oordinaion and synhroniaion neessary good proeion agains inererene and apping Disadvanages: lower user daa raes more omple regeneraion Implemened using spread sperum ehnology k k k 3 k 4 k 5 k 6 Digial modulaion digial daa is ranslaed ino an analog (baseband) ASK, FSK, PSK - main ous in his haper dierenes in speral eiieny, power eiieny, robusness Analog modulaion shis ener requeny o baseband up o he radio arrier Moivaion smaller anennas (e.g., λ/4) Frequeny Division Mulipleing medium haraerisis Basi shemes Ampliude Modulaion (AM) Frequeny Modulaion (FM) Phase Modulaion (PM) Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 5 Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 6 Modulaion and demodulaion Digial modulaion analog baseband digial daa digial analog 0000 modulaion modulaion radio ransmier radio arrier Modulaion o digial s known as Shi Keying Ampliude Shi Keying (ASK): very simple low bandwidh requiremens 0 very susepible o inererene Frequeny Shi Keying (FSK): needs larger bandwidh 0 analog demodulaion radio arrier analog baseband synhroniaion deision digial daa 0000 radio reeiver Phase Shi Keying (PSK): more omple robus agains inererene 0 Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 7 Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 8

8 Advaned Frequeny Shi Keying Eample o MSK bandwidh needed or FSK depends on he disane beween he arrier requenies speial pre-ompuaion avoids sudden phase shis MSK (Minimum Shi Keying) bi separaed ino even and odd bis, he duraion o eah bi is doubled depending on he bi values (even, odd) he higher or lower requeny, original or invered is hosen he requeny o one arrier is wie he requeny o he oher Equivalen o ose QPSK daa even bis odd bis low requeny high requeny bi even 0 0 odd 0 0 h n n h value h: high requeny n: low requeny +: original -: invered even higher bandwidh eiieny using a Gaussian low-pass iler GMSK (Gaussian MSK), used in GSM MSK No phase shis! Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 9 Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 30 Advaned Phase Shi Keying Quadraure Ampliude Modulaion BPSK (Binary Phase Shi Keying): bi value 0: sine wave bi value : invered sine wave very simple PSK low speral eiieny robus, used e.g. in saellie sysems QPSK (Quadraure Phase Shi Keying): bis oded as one symbol symbol deermines shi o sine wave needs less bandwidh ompared o BPSK more omple Oen also ransmission o relaive, no absolue phase shi: DQPSK - Dierenial QPSK (IS-36, PHS) A Q I 0 0 Q I Quadraure Ampliude Modulaion (QAM): ombines ampliude and phase modulaion i is possible o ode n bis using one symbol n disree levels, n= idenial o QPSK bi error rae inreases wih n, bu less errors ompared o omparable PSK shemes Q φ a I 000 Eample: 6-QAM (4 bis = symbol) Symbols 00 and 000 have he same phase φ, bu dieren ampliude a and 000 have dieren phase, bu same ampliude. used in sandard 9600 bi/s modems Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 3 Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 3

9 Hierarhial Modulaion DVB-T modulaes wo separae daa sreams ono a single DVB-T sream High Prioriy (HP) embedded wihin a Low Prioriy (LP) sream Muli arrier sysem, abou 000 or 8000 arriers QPSK, 6 QAM, 64QAM Eample: 64QAM good reepion: resolve he enire Q 64QAM onsellaion poor reepion, mobile reepion: resolve only QPSK porion 0 6 bi per QAM symbol, mos I signiian deermine QPSK HP servie oded in QPSK ( bi), LP uses remaining 4 bi Spread sperum ehnology Problem o radio ransmission: requeny dependen ading an wipe ou narrow band s or duraion o he inererene Soluion: spread he narrow band ino a broad band using a speial ode proeion agains narrow band inererene power inererene spread power deeion a reeiver proeion agains narrowband inererene Side ees: oeisene o several s wihou dynami oordinaion ap-proo Alernaives: Dire Sequene, Frequeny Hopping spread inererene Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 33 Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 34 Ees o spreading and inererene Spreading and requeny seleive ading dp/d dp/d hannel qualiy i) iii) dp/d ii) sender iv) reeiver dp/d v) user broadband inererene narrowband inererene dp/d hannel qualiy narrow band 3 4 guard spae 5 6 requeny narrowband hannels spread sperum hannels spread sperum requeny Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 35 Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 36

10 DSSS (Dire Sequene Spread Sperum) I DSSS (Dire Sequene Spread Sperum) II XOR o he wih pseudo-random number (hipping sequene) many hips per bi (e.g., 8) resul in higher bandwidh o he Advanages redues requeny seleive ading in ellular neworks base saions an use he same requeny range several base saions an dee and reover he so handover Disadvanages preise power onrol neessary b b : bi period : hip period user daa XOR hipping sequene = resuling reeived user daa hipping sequene radio arrier X demodulaor spread sperum ransmier reeiver lowpass ilered radio arrier hipping sequene modulaor X orrelaor produs ransmi inegraor sampled sums deision daa Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 37 Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 38 FHSS (Frequeny Hopping Spread Sperum) I FHSS (Frequeny Hopping Spread Sperum) II Disree hanges o arrier requeny sequene o requeny hanges deermined via pseudo random number sequene Two versions Fas Hopping: several requenies per user bi Slow Hopping: several user bis per requeny Advanages requeny seleive ading and inererene limied o shor period b 0 d d 0 user daa slow hopping (3 bis/hop) simple implemenaion uses only small porion o sperum a any ime Disadvanages as hopping (3 hops/bi) no as robus as DSSS simpler o dee b : bi period d : dwell ime Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 39 Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 40

11 FHSS (Frequeny Hopping Spread Sperum) III Cell sruure user daa narrowband modulaor modulaor spread ransmi Implemens spae division muliple: base saion overs a erain ransmission area (ell) Mobile saions ommuniae only via he base saion hopping sequene reeived ransmier demodulaor requeny synhesier narrowband requeny synhesier demodulaor hopping sequene daa reeiver Advanages o ell sruures: higher apaiy, higher number o users less ransmission power needed more robus, deenralied base saion deals wih inererene, ransmission area e. loally Problems: ied nework needed or he base saions handover (hanging rom one ell o anoher) neessary inererene wih oher ells Cell sies rom some 00 m in iies o, e.g., 35 km on he ounry side (GSM) - even less or higher requenies Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 4 Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 4 Frequeny planning I Frequeny planning II Frequeny reuse only wih a erain disane beween he base saions Sandard model using 7 requenies: ell luser Fied requeny assignmen: erain requenies are assigned o a erain ell problem: dieren rai load in dieren ells Dynami requeny assignmen: base saion hooses requenies depending on he requenies already used in neighbor ells more apaiy in ells wih more rai assignmen an also be based on inererene measuremens 3 h 3 h h h g g h 3 h 3 g g g g g 3 g 3 g 3 3 ell luser wih 3 seor anennas ell luser Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 43 Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 44

12 Cell breahing CDM sysems: ell sie depends on urren load Addiional rai appears as noise o oher users I he noise level is oo high users drop ou o ells Dr. Ka-Cheong Leung CSIS 7304 The Wireless Inerne and Mobile Compuing 45