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/ 12/3/2018 Week 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 12/3/2018 Week 2

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) 12/3/2018 Week 2

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 12/3/2018 Week 2

Sklar Chapter 4 Legend: From other sources Essential Information 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 Digital input Channel impulse response Bit stream Synch-ronization Digital baseband waveform Digital bandpass waveform Channel Digital output 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 Information sink Message symbols 12/3/2018 Week 2

Modulation Input for this stage is baseband encoded Output is IF 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 12/3/2018 Week 2

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) 12/3/2018 Week 2

Digital Bandpass Modulation Transition From Baseband signaling To bandpass signaling Operations Coherent Special attention to tracking phase Phase used in demodulation Non-coherent 12/3/2018 Week 2

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 12/3/2018 Week 2

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 12/3/2018 Week 2

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 12/3/2018 Week 2

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 12/3/2018 Week 2

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 12/3/2018 Week 2

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 12/3/2018 Week 2

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 12/3/2018 Week 2

Quiz timeline Practice quiz today Quiz next week Follow-up quiz Open book Look at problems and take a 15-minute cut at each Class discussion for 15 minutes Quiz next week 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 12/3/2018 Week 2

Text and Assignment Text Assignment: Read 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 12/3/2018 Week 2

Practice Quiz Problems from book homework Quiz will be similar 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 12/3/2018 Week 2