MULTIPLEXING. Multiplexing. Space, Frequency, Time, Code 9/1/15. Multiplexing: Multiplexing in 4 dimensions: Task: Jasleen Kaur

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1 MULTIPLEXING Spae, Frequeny, Time, Code 22 Muliplexing Muliplexing: Ø Goal: muliple use o a shared medium Muliplexing in 4 dimensions: Ø Spae (s), Frequeny (), Time (), Code () Task: Ø Assign spae, ime, requeny, ode o eah ommuniaion hannel Ø Minimize inererene Using guard spaes Ø Maximize medium uilizaion 23 Jasleen Kaur

2 Spae Division Muliplex A separae sender or eah ommuniaion hannel hannels k i Ø Wih wide enough disane beween senders Guard spaes Used by FM radio saions Ø Many saions around he world use same requeny wihou inererene Wha i several radio saions wan o broadas in same iy? s 1 s 3 s 2 24 Frequeny Division Muliplex Subdivide he requeny dimension ino several nonoverlapping requeny bands Ø Senders an use heir assigned band oninuously Used or radio saions wihin same region Pros: Ø No dynami oordinaion Cons: Ø Wase o bandwidh i usage is non-uniorm Ø Limis # o senders Ø Inlexible assignmen 25 Jasleen Kaur

3 Time Division Muliplex A sender ges he whole bandwidh or a erain amoun o ime Advanages Ø Only one arrier in he medium a any ime Ø Throughpu high even or many users Disadvanages Ø Preise synhronizaion neessary 26 Frequeny and Time Muliplex Combinaion: Ø A sender an use a requeny band or a erain amoun o ime Ø Used by GSM Pros: Ø (weak) proeion agains apping Ø proeion agains requenyseleive inererene Cons: Ø Preise oordinaion required 27 Jasleen Kaur

4 Code Division Muliplex Eah hannel has a unique ode Ø All hannels use same sperum a same ime Ø guard spaes realized by using orhogonal ode Pros: Ø Good proeion agains inererene and apping Ø Bandwidh eiien Cons: Ø Relaively omplex reeiver Ø Preise synhronizaion required Ø Preise power onrol required All signals should reah reeiver wih nearly equal srengh 28 DIGITAL MODULATION Ampliude, Frequeny, Phase 29 Jasleen Kaur

5 Modulaion digial daa digial modulaion baseband signal modulaion Radio Transmier radio arrier demodulaion radio arrier baseband signal synhronizaion deision Radio Reeiver digial daa Digial modulaion: Ø Digial daa is ranslaed ino an (baseband) signal Analog modulaion: Ø Shis ener requeny up o ha o radio arrier 30 digial daa Analog Modulaion digial modulaion Radio Transmier baseband signal modulaion radio arrier Why modulaion? Ø Smaller arrier wavelengh or smaller anennas Ø To enable FDM Ø To exploi/avoid requeny-dependen medium haraerisis 3 basi shemes: AM (ampliude), FM (requeny), PM (phase) 31 Jasleen Kaur

6 Digial Modulaion Modulaion o digial signals known as Shi Keying Issues: Ø Speral eiieny: How eiienly is he requeny sperum uilized Ø Power eiieny: How muh power is needed o ranser bis Very imporan or porable devies Ø Robusness o muli-pah propagaion, noise, inererene 32 Digial Modulaion Mehods Ampliude Shi Keying Ø Binary values are represened by dieren ampliudes Ø Low bandwidh requiremens Ø Very susepible o inererene Used only in direed inra-red beams Frequeny Shi Keying Ø Needs larger bandwidh Ø Less susepible o errors Phase Shi Keying Ø Uses shis in he signal phase 180 o, i hange in daa Ø Synhronizaion required (req, phase) Ø Mos resisan o inererene Ø Complex reeiver/ransmier Jasleen Kaur

7 Advaned Frequeny Shi Keying Minimum Shi Keying (MSK): avoids abrup phase hanges Ø Bis duraions doubled and divided ino even, odd bis Depending on he bi values (even, odd) he higher or lower requeny, original or invered is hosen Ø Higher requeny is wie he lower requeny daa even bis odd bis bi even odd signal h n n h value low requeny high requeny h: high requeny n: low requeny +: original signal -: invered signal MSK signal 34 Advaned Phase Shi Keying Binary PSK: phase shi o 180 o Q Ø Very simple, bu low eiieny 1 0 I Quadraure PSK: phase shi o 45 o Ø Codes wo bis ino one phase shi Relaive o phase o a reerene signal Requires requen synhronizaion Relaive o phase o previous wo bis More eiien and less omplex Q 11 I 01 Ø Ahieves high bi-raes or same bandwidh Can be exended o: Ø More angles A Ø Combine wih ASK Ø Leads o more reeiver omplexiy Jasleen Kaur

8 Muli-arrier modulaion Splis high bi-rae sream ino many wih lower bi-raes Ø Eah is sen using an independen arrier requeny Pros: Ø Independen requenies do no inerere wih eah oher Ø Frequeny-seleive ading doesn inluene whole signal Ø Guard spaes used beween symbol (groups) Helps handle muli-pah propagaion, ISI miigaion Ø Compuaionally eiien based on FFT DAB uses sub-arriers 36 Jasleen Kaur