c 2002-2007 Dr. Jay Weitzen 1

16.543 Lecture 7b: Digital Modulation II

BPSK, FSK, and QPSK

c 2002-2007 Dr. Jay Weitzen 2

Contents

• Binary Frequency Shift Modulation (B-FSK)– CPFSK– Coherent and Non-Coherent Detection– FSK Detection Performance

• M’ary FSK• M’ary and Generalized PSK

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Things To remember

• Error Performance is driven by distance between nearest neighbors

•Controlling transitions can sometimes be used to artificially expand distance (convolution coding).

•ML decoding is used

•Keep in mind bandwidth vs. capacity, vs. SNR from Shannon

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BFSK (orthogonal)

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Constellation Diagram

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CPFSK?

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CPFSK is desirable

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FSK Generation (1)

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FSK Generation (2)

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Coherent Demod of FSK

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Receiver Architecture (FSK)

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NC Detection of FSK

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PLL Detection of FSK

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FSK Performance

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FSK Summary

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M-ary FSK

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M-ary FSK Trades BW for SNR

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FSK approaches Shannon

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Generalized PSK

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Analytical Forms

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PRK and BPSK

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BPSK Modulators

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BPSK Demodulators

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BPSK Receiver Structures

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Effect of Filtering

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BW of BPSK

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Differential Encoding and DPSK

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Differential Encoding

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Differential Decoding

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DPSK

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NC Detection of DPSK

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BER for DPSK

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BER, NC vs. Coherent

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Remember Shannon!

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BW/BER Efficiency

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Generalized Multi-Level Modulation

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M-ary PSK

•All Constellation Points Lie on a Circle

• For QPSK cost in terms of Eb/No is same beyond that becomes very expensive to add more points

•Requires fully coherent detection

•Channel coding becomes important (gray code)

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Definition of MPSK

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PSK Constellations

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QPSK

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QPSK as 2 BPSK

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BW of QPSK

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QPSK Modulator

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Effect of Pulse Shaping

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QPSK Demodulator

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QPSK Detection Regions

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Carrier Recovery

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Error Performance of QPSK

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Problems with QPSK

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OQPSK

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Eye Diagrams for OQPSK

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FAQ’s about OQPSK

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Pi/4 QPSK

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π/4 qpsk vs. qpsk

Π/4 qpsk prevents transitions through 0, reducing linearity requirements on the power amplifier

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M-ary DPSK

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M-ary DPSK (2)

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DQPSK (1)

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DQPSK (2)

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Error Probabilities NC vs. C

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Error Probabilities for M-aryDQPSK