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EE521 Analog and Digital Communications

Today some topics will be presented on the whiteboard. The slides will be updated on the web site in a few days. EE521 Analog and Digital Communications. James K. Beard, Ph. D. jkbeard@temple.edu Tuesday, February 8, 2005 http://astro.temple.edu/~jkbeard/. Essentials.

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EE521 Analog and Digital Communications

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  1. Today some topics will be presented on the whiteboard. The slides will be updated on the web site in a few days. EE521 Analog and Digital Communications James K. Beard, Ph. D. jkbeard@temple.edu Tuesday, February 8, 2005 http://astro.temple.edu/~jkbeard/ Week 2

  2. Essentials • Text: Bernard Sklar, Digital Communications, Second Edition • SystemView • Student version included with text • Trial version has 90-day timeout • Office • E&A 709 • Tuesday afternoons 3:30 PM to 4:30 PM • Tuesdays before class at Ft. Washington • MWF 10:30 AM to 11:30 AM added Week 2

  3. Today’s Topics • SystemView • The Example File • Bandpass Modulation and Demodulation • Why Modulate? • Digital Bandpass Modulation Techniques • Detection of signals in Gaussian noise • Discussion (as time permits) Week 2

  4. Bandpass Modulation and Demodulation • Topics from Text Chapter 4 • 4.1, Why Modulate? • 4.2, Digital Bandpass Modulation Techniques • 4.3, Detection of Signals in Gaussian NOise Week 2

  5. Digital input Channel impulse response Digital output Sklar Chapter 4 From other sources Essential Legend: Information source Message symbols Optional Channel symbols X M I T Format Source encode Encrypt Channel encode Multi-plex Pulse modulate Bandpass modulate Fre-quency spread Multiple access Bit stream Synch-ronization Digital baseband waveform Digital bandpass waveform Channel R C V Format Source decode Decrypt Channel decode Demul-tiplex Detect Demod-ulate & Sample Freq-uency despread Multiple access To other destinations Channel symbols Message symbols Information sink Week 2

  6. Modulation • Input for this stage is baseband encoded • Pulse modulation • Bandpass or pulse shaping filtering • Output is IF • Ready to upconvert to RF and transmit • Optional frequency spread may be added • Optional multiple access may be added Week 2

  7. Functions of Modulation • Prepare for wireless transmission • Modulate on carrier at RF in band allocated for wireless communication • Formulate digital bandpass waveform • Optional successive steps • Spread-spectrum (Chapter 12, next semester) • Multiple access (Chapter 11, next semester) Week 2

  8. Digital Bandpass Modulation • Transition • From Baseband signaling • To bandpass signaling • Operations • Coherent • Special attention to tracking phase • Phase used in demodulation • Non-coherent Week 2

  9. Baseband Signaling • See Figure 4.1 page 170 • PCM waveforms • Non-return-to-zero • Return to zero • Phase encoded • Multilevel binary • M-ary pulse modulation • PAM • PPM • PDM Week 2

  10. Bandpass Signaling • See Figure 4.1 page 170 • Carrier strategies • Coherent • Non-coherent • Modulation types • Phase sift keying (PSK) • Frequency shift keying (FSK) • Amplitude shift keying (ASK) • Continuous phase modulation (CPM) • Hybrids Week 2

  11. Phasor Representation of Tones Modulated on a Carrier • Everything referenced to • Carrier frequency • Particular phase of carrier • Physical meaning can be inferred • Quadrature demodulation of tone • L.O. is the reference carrier and phase • Complex result is the phasor Week 2

  12. Features of Phasor Concept • Modulation is simple to represent • Phase modulation changes direction of phasor • Amplitude modulation changes length of phasor • Modulation can be posed in terms of phases of the modulation sidebands • Characterization of noise as 2-D Gaussian distribution Week 2

  13. Detection in Gaussian Noise • Characterization of Gaussian noise • 2-D distribution in phasor plot • Zero mean, sigma proportional to noise amplitude • Phasor concept allows vector addition to represent signal plus noise • Coherent detection • Selection of portions of phasor space • Design is reduced to definition of boundaries in phasor space Week 2

  14. Detection Operation • One-dimensional case from Figure 3.1 page 108 • Two steps • Downconvert and sample • Quadrature demodulator, or • Digital product dectector • Equalize channel and filtering effects • Decision thresholds • The decision threshold input is the predection point • Location of received Eb/N0 Week 2

  15. Design of Detection • Design of matched filter • This is the channel and filter equalization of Step 1 • Maximizes received Eb/N0 • Design of detection regions • Examples given in book are conceptual • Likelihood ratio defines decision region boundaries Week 2

  16. Quiz timeline • Practice quiz today • Open book • Look at problems and take a 15-minute cut at each • Class discussion for 15 minutes • Quiz next week • Open book • May cover some Chapter 4 topics • Follow-up quiz • Take-home • Will require SystemView to complete • Grade on first quiz • Depends on grades to first quiz • Take-home can be up to 25% of quiz grade Week 2

  17. Text and Assignment • Text • Benard Sklar, Digital Communicatinons ISBN 0-13-084788-7 • SystemView User's Manual, Elanix, Inc • http://www.elanix.com/ • http://www.elanix.com/pdf/SVUGuide.pdf • Assignment: Read Text • Chapter 4, 4.4 through 4.9 • Homework problem 4.1 • Browse appendices of text for review and supplementary material • Look at TUARC • K3TU, websites • http://www.temple.edu/ece/tuarc.htm • http://www.temple.edu/k3tu Week 2

  18. Practice Quiz • Problems from book homework • Problem 1.1 page 51 • Problem 2.2 page 101 • Problem 3.1 page 162 • Quiz will be similar • From homework problems • Modifications to problem statement and parameters Week 2

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