Modulation for Analog Communication. Yao Wang Polytechnic University, Brooklyn, NY

Transcription

1 Modulaion or Analog Communiaion Yao Wang Polyehni Universiy, Brooklyn, NY11201 hp://eeweb.poly.edu/~yao

2 Ouline Baseband ommuniaion: bandwidh requiremen Modulaion o oninuous signals Ampliude modulaion Quadraure ampliude modulaion Oher modulaion ehniques: requeny/phase modulaion Frequeny division muliplexing Appliaion o modulaion Demo o AM and QAM Yao Wang, 2006 EE3414: Analog Communiaions 2

3 Baseband Communiaions Signal srengh aenuaes wih disane. Needs repeaers o ampliy he signals in sages Reeived signal is orruped by noise R=A S+ n Reeived signal qualiy depends on hannel noise and noise beween repeaers aumulae To ransmi a signal wih bandwidh B, we need >=B Hz in hannel bandwidh I he signal is low-pass 0-B, mus he hannel operae a 0-B range o requeny? How do we send muliple signals over he hannel? Yao Wang, 2006 EE3414: Analog Communiaions 3

4 A Typial Communiaion Sysem Signal o be ransmied analog or digial Reeived signal Modulaor Demodulaor Transmier Reeiver Yao Wang, 2006 EE3414: Analog Communiaions 4

5 Modulaion = Frequeny Shiing Baseband signal Modulaed signal 0 Frequeny Yao Wang, 2006 EE3414: Analog Communiaions 5

6 Why do we need modulaion? A ommuniaion hannel only operaes a a erain requeny range elephone ables, erresrial over he air broadas, eherne, opial iber, e. Modulaion ranslaes a signal rom is baseband o he operaing range o he hannel By modulaing dieren signals o dieren requeny bands, hey an be ransmied simulaneously over he same hannel requeny division muliplexing Yao Wang, 2006 EE3414: Analog Communiaions 6

7 Frequeny Division Muliplexing To ransmi he hree signals over he same hannel, eah signal is shied o a dieren arrier requeny and hen summed ogeher. From Figure 7.22 in Signals and Sysems Yao Wang, 2006 EE3414: Analog Communiaions 7

8 How do we shi he requeny o a signal? By muliplying wih a sinusoid signal! x y = x os ω os ω arrier signal ω : arrier requeny Yao Wang, 2006 EE3414: Analog Communiaions 8

9 Yao Wang, 2006 EE3414: Analog Communiaions 9 Basi Equaliies Basi equaliy Proo on he board 2 1 os2 2 2 j j X X x X e x X e x π π π

10 Frequeny Domain Inerpreaion o Modulaion From Figure 7.5 in Signals/Syse ms x os ω y = x os ω Yao Wang, 2006 EE3414: Analog Communiaions 10

11 How o ge bak o he baseband? Demodulaion By muliplying wih he same sinusoid + low pass ilering! y w H ω 2 x os ω ω m ω m LPF Yao Wang, 2006 EE3414: Analog Communiaions 11

12 Frequeny Domain Inerpreaion o Demodulaion Figure 7.7 in Signals and Sysems Yao Wang, 2006 EE3414: Analog Communiaions 12

13 Yao Wang, 2006 EE3414: Analog Communiaions 13 Temporal Domain Inerpreaion reain he irs erm and remove he seond erm. LPF will The os os os Using he equaliy os 2 os os2 Demodulaion : os2 Modulaion : 2 2 x x x w x y w x y π π θ θ π π π + = + = + = = = =

14 Example How o ransmi a signal wih requeny ranging in -5KHz,5KHz using a hannel operaing in 100KHz,110KHz? Wha should be he arrier requeny? Draw he blok diagrams or he modulaor and demodulaor, and skeh he sperum o he modulaed and demodulaed signals. Yao Wang, 2006 EE3414: Analog Communiaions 14

15 Frequeny Division Muliplexing: Frequeny domain inerpreaion Figure 7.22 in Signals and Sysems y = x os ω a a a y = x os ω a a a y = x os ω a a a w = y + y y a b + Yao Wang, 2006 EE3414: Analog Communiaions 15

16 FDM Transmier Figure 7.21 in Signals and Sysems Yao Wang, 2006 EE3414: Analog Communiaions 16

17 FDM Reeiver Demuliplexing os ω a Demodulaion Figure 7.23 in Signals and Sysems Yao Wang, 2006 EE3414: Analog Communiaions 17

18 Example How o ransmi wo signals eah wih requeny ranging in -10KHz,10KHz over a hannel operaing in he requeny range 300KHz,340KHz? Draw he blok diagrams or he modulaor and demodulaor, and skeh he sperum o he modulaed and demodulaed signals. Yao Wang, 2006 EE3414: Analog Communiaions 18

19 Demo: modulaing a sound signal ampliude_modulaion.m 0.2 X1 Waveorm 10 0 X1 Sperum s=22k x 10 4 Modulaed X1: Waveorm x Modulaed X1: Sperum 0.2 =50k Yao Wang, 2006 EE3414: Analog x 10Communiaions 4 x

20 0.5 DeModulaed X1: Waveorm 10 0 DeModulaed X1: Sperum x 10 4 Reonsrued X1: Waveorm x Reonsrued X1: Sperum Yao Wang, 2006 EE3414: Analog Communiaions

21 Lowpass Filer Magniude db Phase degrees Frequeny Hz x Frequeny Hz x 10 4 Lengh=20, Cu-o req=11k Yao Wang, 2006 EE3414: Analog Communiaions 21

22 Original and Reonsrued Waveorm 0.3 original reonsrued original reonsrued Yao Wang, 2006 EE3414: Analog Communiaions 22

23 Quadraure Ampliude Modulaion Wih ampliude modulaion: a signal wih bandwidh B needs 2B hannel bandwidh This is alled double sideband DSB AM Oher ehniques an redue he bandwidh requiremen Single sideband SSB Vesigial sideband VSB By using QAM, we an send 2 signals eah wih bandwidh B over a hannel bandwidh o 2B Equivalen o eah signal wih bandwidh B Yao Wang, 2006 EE3414: Analog Communiaions 23

24 Quadraure Ampliude Modulaion QAM A mehod o modulae wo signals ono he same arrier requeny, bu wih 90 o phase shi os 2π1 os 2π1 s 1 m m LPF s 1 s 2 sin 2 π 1 sin 2 π 1 LPF s 2 QAM modulaor QAM demodulaor Yao Wang, 2006 EE3414: Analog Communiaions 24

25 QAM in more deail Proo in ime domain he demodulaor an separae he signal on board! Disuss he sensiiviy o he sysem o synhronizaion o he arrier signal. Yao Wang, 2006 EE3414: Analog Communiaions 25

26 Oher Modulaion Mehods Ampliude modulaion y 0 = x os2π +θ The ampliude o he arrier signal is onrolled by he modulaing signal Piall o AM: hannel noise an orrup he ampliude easily. Frequeny modulaion dθ y = os θ, = 2π + k x d The requeny o he arrier signal is proporional o he modulaing signal Phase modulaion y = os2π + θ0 k x + p The phase o he arrier signal is proporional o he modulaing signal Yao Wang, 2006 EE3414: Analog Communiaions 26

27 Appliaion o Modulaion and FDM AM Radio 535KHz--1715KHz: Eah radio saion is assigned 10 KHz, o ransmi a mono-hannel audio bandlimied o 5KHz Using Ampliude modulaion o shi he baseband signal FM Radio 88MHz--108 MHz: Eah radio saion is assigned 200 KHz, o ransmi a sereo audio. The le and righ hannels eah limied o 15KHz are muliplexed ino a single baseband signal using ampliude modulaion Using requeny modulaion o shi he baseband signals TV broadas VHF: 54-88, MHz, UHF: MHz Eah saion is assigned 6 MHz The hree olor omponens and he audio signal are muliplexed ino a single baseband signal Using vesigial sideband AM o shi he baseband signals. Yao Wang, 2006 EE3414: Analog Communiaions 27

28 Wha Should You Know Undersand he bandwidh requiremen Channel bandwidh > signal bandwidh Undersand he priniple o ampliude modulaion Know how o modulae a signal o a erain requeny Know how o demodulae a signal bak o he baseband Can wrie he equaion and draw blok diagram or boh modulaion and demodulaion Can plo he signal sperum aer modulaion and demodulaion Undersand he priniple o requeny division muliplexing Can wrie he equaion and draw blok diagram or boh modulaion and demodulaion, or muliplexing o wo o hree signals. Undersand how do AM and FM radio and analog TV work in erms o modulaion and muliplexing. Yao Wang, 2006 EE3414: Analog Communiaions 28

29 Reerenes A. M. Noll, Chaper 10. A. V. Oppenheim and A. S. Willsky, Signals and Sysems, 2 nd ediion, Chaper 8, Se opies provided Yao Wang, 2006 EE3414: Analog Communiaions 29