Intro to PracticalDigital CommunicationsDiscrete data transmissionModulation and de-modulationVector signal representationBPSK exampleManchester modulation example (Ethernet)More constellationsHow do we choose basis functions?Constellation energyCorrelative demodulatorPractical implementationSummarySources6.973 Communication System Design – Spring 2006Massachusetts Institute of TechnologyCite as: Vladimir Stojanovic, course materials for 6.973 Communication System Design, Spring 2006.MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].Intro to PracticalDigital CommunicationsLecture 2Vladimir StojanovićDiscrete data transmission Messages are encoded into signal pointssignal pointssignal waveform Signal points are mapped to signal waveforms ModulationCite as: Vladimir Stojanovic, course materials for 6.973 Communication System Design, Spring 2006.MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.973 Communication System Design18sModulation and de-modulation e.g. Binary Phase-Shift Keying (BPSK)x0(t)x1(t)Cite as: Vladimir Stojanovic, course materials for 6.973 Communication System Design, Spring 2006.MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].196.973 Communication System Design6.973 Communication System Design20 Maps continuous signals to discrete vectors Significantly simplifies system analysissignal pointssignal waveformsbasis functionsModulatorCite as: Vladimir Stojanovic, course materials for 6.973 Communication System Design, Spring 2006.MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].Vector signal representation21BPSK exampleSignal constellation What is the information rate (R) of this modulation?Cite as: Vladimir Stojanovic, course materials for 6.973 Communication System Design, Spring 2006.MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.973 Communication System Design6.973 Communication System Design22Manchester modulation example (Ethernet) Different waveforms can have same vector representationsCite as: Vladimir Stojanovic, course materials for 6.973 Communication System Design, Spring 2006.MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].More constellationsϕ1()t-3 -1 1 3ϕ-3 -1 1 31()tQuadrature Amplitude Modulation (QAM)Pulse Amplitude Modulation ϕ2()t(PAM)31-1e.g. PAM4-3e.g. 16-QAMPAM and QAM have pulses as basis functionsCite as: Vladimir Stojanovic, course materials for 6.973 Communication System Design, Spring 2006.MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.973 Communication System Design236.973 Communication System Design24 Need to be orthonormal – (b/c of demodulation) Inner products Continuous Discrete Invariant to choice of basis functions Average energy of the constellationInvariant to the choice of basis functionsCite as: Vladimir Stojanovic, course materials for 6.973 Communication System Design, Spring 2006.MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].How do we choose basis functions? Implications of the inner product invariance to basis functions If energy is a signal, it is the same regardless of the mod waveform used As long as basis functions are orthogonal Parseval’s identityCite as: Vladimir Stojanovic, course materials for 6.973 Communication System Design, Spring 2006.MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.973 Communication System Design25Constellation energy6.973 Communication System Design26 Straightforward demodulator implementation Use the fact that basis functions are orthogonal Collect the signal energy Hard to build in practiceDemodulatorModulatorCite as: Vladimir Stojanovic, course materials for 6.973 Communication System Design, Spring 2006.MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].Correlative demodulator6.973 Communication System Design27Cor Note equivalent to Can implement with an “integrate-and-dump”Cite as: Vladimir Stojanovic, course materials for 6.973 Communication System Design, Spring 2006.MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].Practical implementationrelative demodulator Matched-filter demodulatorSummary In this course you’ll be able to learn Practical digital communication techniques Hands-on, little math Hardware implementations Algorithmic transformations Micro-architectures ASIC flow and behavioral modeling In other words, everything you’ll need to start building cutting-edge digital communication systems Started intro to digital communications Modulation – signal constellation, basis functions Demodulation – basis function invariance, matched-filter Next – basics of detection, signalling on band-limited channelsCite as: Vladimir Stojanovic, course materials for 6.973 Communication System Design, Spring 2006.MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.973 Communication System Design2829Sources VppSim/CppSim is a tool developed by prof. Michael Perrott Digital communications material is adapted from prof. John Cioffi’s Stanford Course readers http://www.stanford.edu/class/ee379a,b,c/Cite as: Vladimir Stojanovic, course materials for 6.973 Communication System Design, Spring 2006.MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.973 Communication System