Class Notes_Lect14

Class Notes_Lect14 - Constellations N - A constellation...

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Unformatted text preview: Constellations N - A constellation diagram is a graphical repres .ion of the complex envelope of I_n_ unique symbol states - The bandwidth efficiency is proportional to the number of constellation points (i.e. m states) - Densely packed implies BW efficient Spring, 09 10 alecfl‘oficiente L A B O R A T O RY ©O\ 6v! Baficm \ f,— . %‘~§YV\'V) o\;_—_~ OK (JO JV b Sl.h1-U’Pd . 5" LA 04:25) 6‘02“ M ‘1“ W‘S‘kefl Skmpfi' m Q by)»] :L W‘“@2 ,. A k fl _ {:3 w ‘ a Eflkffi T 2 ago, flog . :1 '3'? Polar Representation Spring, 09 11 MSK PSK —- :2. 7—“ CH - {xxx b N Team Mag & Phase Freq. Change Change, QAM FSK ‘3”? :. ’2—1T «9106* *‘E - The signal is expressed in polar form as a magnitude )j and phase relative to a reference signal - The carrier becomes a frequency and phase reference and the signal is interpreted relative to the carrier OWL VOW (Lil) _‘ \ .. {Mats JV — .u; 6/, Amplitude Shift Keying (ASK) NRZ Binafl Symbol \ V‘ cos(2nfct) sv’ -\\ {OM\.}A' - One binary state represented by presence of carrier and other binary state represented by absence of carrier - Similar to analog AM modulation - Term on/off “keying” borrowed from telegraph key - Similar to analog AM modulation, transmission is highly susceptible to noise - Used in voice-grade lines, up to 1200 bps - Used to transmit digital data over optical fiber - Non constant envelope "" ' "'""' Spring, 09 13 5bttr05cieuce E ts kc T8ch , ® “3 Du cm+. firm a ® _ WALJEH w Ow : mqhfl— m4 __. 56") __ 95 601F£Cz+ 00th 1+ m— qb‘VV‘F“ ’TFQWS K1) Cm’r. ‘FSC . C LVa’cHl Chews“ as «(h V o '27— C) W£mcmfiw>$m. 3' —9®’—E—a) 4: = kv’Il-Vm 1- ~96 MU) VCo {1V aha 9 mm) V‘V " “kl/V ink-0 1‘ wa MU‘) +£o 1:9 “go “A: 1973ka "W1 ® Binary Frequency Shift Keying (BFSK) 1:031; cos(2nfc1t) COS(27‘CfC2t) Continuous FSK \ i z , , : 008(21'Cfc1t) COS(27th2t) Discontinuous FSK .___—- - Discontinuous FSK - Two oscillators (fc1, 1‘02) are selected according to the baseband binary data - Discontinuous FSK - Single oscillator is frequency modulated by the baseband binary data - Continuous FSK is a constant envelope modulation scheme - Good performance under non-linear distortion - Less susceptible to error than ASK - Used for cordless phone (DECT) and paging systems % . Spring, 09 14 filectrotheuce L A B O R A T O HY on $U£c+ _—- m¢n¥c+ " Binary Phase Shift Keying (BPSK) Polar NRZ Binary Symbol ’\ COS(27rfCt) - Another form of generating PSK is using Differential PSK (DPSK) - Phase shift with reference to previous bit - Binary O — signal burst of same phase as previous signal burst - Binary 1 — signal burst of opposite phase to previous signal burst - BPSK can be expanded to a M-ary scheme by employing multiple phases - Very robust, used extensively in satellite communications - Non constant envelope Spring, 09 15 ifutroécientg £5) ASK ~> “3-2” H 142; (M V“) _ . \V' -fimfl 4. MC‘ “:1 m L Q (mix) . ...
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This note was uploaded on 11/21/2011 for the course ECE 620 taught by Professor Khalil during the Fall '11 term at Ohio State.

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Class Notes_Lect14 - Constellations N - A constellation...

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