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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Electrical Communications Systems ECE.09.331 Spring 2009 Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/spring09/ecomms/ Lecture 12b April 15, 2009

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Plan Digital Bandpass Communications Why digital modulation? Digital Modulation: Introduction (ASK, FSK, PSK) Binary Phase Shift Keying (BPSK) Quadrature Phase Shift Keying (QPSK) M-ary PSK and M-ary QAM Observing Digital Bandpass Signals Constellation diagrams Eye Diagrams

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University ECOMMS: Topics

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Digital Communications Transceiver Anti- aliasing Filter Data Encryption Encoder Source Encoder Error Control Encoder Channel/ Line Encoder Modulator MUX Audio Amp Source Decoder Data Encryption Decoder Error Control Decoder Equalization / Decision Circuits Demod- ulator DEMUX Reconstruction/ DAC ADC CODEC MODEM Analog o/p Multiple access channel Analog i/p Sampling Quantization

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Digital Bandpass Communications Why digital modulation? Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Industry Trends Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Applications Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Digital Modulation Carrier signal: A c cos (2 f c t + ) Modulation: m(t) Modulated signal:A c (t) cos (2 f c (t) t + (t)) Vary Vary Vary amplitude frequency phase Variations are discrete!!!!! m(t); discrete

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Recall: Dig Comm Principle 1 0 1 0……… 1 0 Analog message Digital code Digital message Sinusoidal carrier modulate AM FM PM AM & PM 1 0

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Signal Vector Representation Phase Magnitude S 0 degrees I Q I-Q Plane s(t) = A c (t) cos (2 f c t + (t)) fixed!!!

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Signal Changes: Representation in the IQ Plane S1S1 S2S2 I Q Magnitude Change S1S1 S2S2 I Q Phase Change S1S1 S2S2 I Q Magnitude & Phase Change Frequency Change ??? I-Q Diagrams or Constellations

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Binary Phase Shift Keying (BPSK) I Q 10 IQ Diagram t (t) 0 radians radians s(t) = A c cos(2 f c t + (t))

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Quadrature Phase Shift Keying (QPSK) I Q 11 IQ Diagram s(t) = A c cos(2 f c t + (t)) t (t) 01 10 00 00 10 01 11

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University M-ary Phase Shift Keying (M-ary PSK) I Q Octophase I-Q Constellation

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University M-ary Quadrature Amplitude Modulation (M-ary-QAM) I Q 16 QAM I-Q Constellation

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Different ways of looking at a digitally modulated signal

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Time & Frequency Domain View Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Frequency & Power View Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University I-Q Constellation Diagram Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf Matlab Demo: qpsk.m

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Eye Diagram Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf Matlab: >>eyediagram

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S. Mandayam/ ECOMMS/ECE Dept./Rowan UniversitySummary

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