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Digital Modulation Techniques and TDM Standards in Electrical Communications

This lecture covers essential topics in digital communications, focusing on Digital Modulation Techniques and Time Division Multiplexing (TDM) standards. It explores Pulse Amplitude Modulation, Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), and M-ary PSK/QAM. The lecture also details North American TDMA hierarchy, line encoding, and the significance of digital modulation in communications. Key diagrams such as constellation and eye diagrams are presented, enhancing understanding of digital bandpass signals and their applications.

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Digital Modulation Techniques and TDM Standards in Electrical Communications

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  1. Electrical Communications SystemsECE.09.331Spring 2010 Lecture 12aApril 13, 2010 Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/spring10/ecomms/

  2. Plan • Pulse Amplitude Modulation • TDM Standards • T1 (DS-1) Line • North American TDMA Hierarchy • Line Encoding • 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

  3. ECOMMS: Topics

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

  5. Decode Time Division Multiplexing Message 1 Quantize & Encode Message 2 Channel Message N Message 1 LPF Message 2 LPF Message N LPF

  6. Channel 1 Channel 24 Channel 2 1 1 1 2 2 2 3 3 3 4 4 4 5 5 5 6 6 6 7 7 7 8 8 8 T1-Line TDM Format 1 Frame = (24 Channels + F) = 125 ms F 193 bits Frame Sync Bit Even Frames: 0 0 1 1 1 0 Odd Frames: 1 0 1 0 1 0 Every Sixth Frame LSB (8th bit) is a Signaling bit Bipolar R-Z Line Encoding

  7. 24 6 1 7 1 1 1 2 4 1 5th M U X 3rd M U X 2nd M U X 4th M U X DS-2 6.312 Mbs 96 VF DS-3 44.736 Mbs 672 VF DS-4 274.176 Mbs 4032 VF DS-1 1.44 Mbs 24 VF North American TDMA Hierarchy 64 kbs 1 VF DS-0 1st M U X DS-5 560.160 Mbs 8064 VF • Figure 3-40, p. 207 in Couch • Table 3-8, p. 208 in Couch • Table 3-9, p. 209 in Couch

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

  9. Line Encoding Couch, p. 162 Couch, p. 157

  10. ECOMMS: Topics

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

  12. Digital Bandpass Communications • Why digital modulation? Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf

  13. Industry Trends Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf

  14. Applications Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf

  15. Digital Modulation Carrier signal: Ac cos (2pfct + f) Modulation: m(t) Modulated signal: Ac (t) cos (2pfc(t) t + f(t))  m(t); discrete Vary Vary Vary amplitude frequency phase Variations are discrete!!!!!

  16. Recall: Dig Comm Principle Digital message 1 1 1 0 1 0……… 0 0 Digital code Analog message modulate 1 0 1 0 Sinusoidal carrier AM FM PM AM & PM

  17. Signal Vector Representation s(t) = Ac(t) cos (2pfct + f(t)) fixed!!! Q S Magnitude Phase 0 degrees I I-Q Plane

  18. Phase Change Magnitude Change S2 Q Q S1 S1 S2 I I Magnitude & Phase Change Q S1 S2 I Signal Changes:Representation in the IQ Plane I-Q Diagrams or Constellations Frequency Change ???

  19. Binary Phase Shift Keying (BPSK) s(t) = Ac cos(2pfct + f(t)) IQ Diagram Q p radians f(t) 1 0 0 radians t I

  20. Quadrature Phase Shift Keying(QPSK) IQ Diagram s(t) = Ac cos(2pfct + f(t)) Q 3p/4 01 11 10 f(t) p/4 00 p/4 t I 10 -p/4 11 01 00 -3p/4

  21. M-ary Phase Shift Keying(M-ary PSK) Q I Octophase I-Q Constellation

  22. M-ary Quadrature Amplitude Modulation(M-ary-QAM) Q I 16 QAM I-Q Constellation

  23. Different ways of looking at a digitally modulated signal

  24. Time & Frequency Domain View Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf

  25. Frequency & Power View Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf

  26. I-Q Constellation Diagram Matlab Demo: qpsk.m Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf

  27. Eye Diagram Matlab: >>eyediagram Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf

  28. Summary

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