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Electrical Communications Systems 0909.331.01 Spring 2005

This lecture covers the fundamentals of digital baseband communications, including pulse amplitude modulation, TDM standards, and digital modulation techniques such as ASK, FSK, and PSK.

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Electrical Communications Systems 0909.331.01 Spring 2005

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  1. Electrical Communications Systems0909.331.01Spring 2005 Lecture 10bApril 13, 2005 Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/spring05/ecomms/

  2. Plan • Digital Baseband Communications • Pulse Amplitude Modulation • Sampling • Quantization • 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

  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. Pulse Code Modulation (PCM) • Standard for all digital communications Analog Signal Sample & Hold Digital Bitstream Quantize Encode PAM PCM

  6. 8 Analog PAM 6 4 2 0 -2 -4 -6 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 time Pulse Amplitude Modulation: Flat-top Sampling Matlab Demo: pam.m

  7. Quantization Uniform Non-Uniform m-Law A-Law Mid-rise Mid-tread Matlab Demos: quantization.m pcm.m • Mid-rise • Mid-tread • Mid-rise • Mid-tread Matlab Demos: companding.m pcm_mucompand.m pcm_mucompand2.m pcm_acompand.m pcm_acompand2.m

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

  10. 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

  11. 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

  12. 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

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

  14. ECOMMS: Topics

  15. 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

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

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

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

  19. 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!!!!!

  20. 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

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

  22. 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 ???

  23. 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

  24. 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

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

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

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