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EE521 Analog and Digital Communications. James K. Beard, Ph. D. jkbeard@temple.edu Tuesday, February 22, 2005 http://astro.temple.edu/~jkbeard/. Attendance. Essentials. Text: Bernard Sklar, Digital Communications , Second Edition SystemView Student version included with text

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Ee521 analog and digital communications

EE521 Analog and Digital Communications

James K. Beard, Ph. D.

jkbeard@temple.edu

Tuesday, February 22, 2005

http://astro.temple.edu/~jkbeard/

Week 6


Attendance
Attendance

Week 6


Essentials
Essentials

  • Text: Bernard Sklar, Digital Communications, Second Edition

  • SystemView

    • Student version included with text

    • Trial version has 90-day timeout

    • I have a mini-CD for you – and permission from Eagleware/Elanix

  • Office

    • E&A 348

    • Tuesday afternoons 3:30 PM to 4:30 PM & before class

    • MWF 10:30 AM to 11:30 AM

  • Final Exam Scheduled

    • Tuesday, May 10, 6:00 PM to 8:00 PM

    • Here in this classroom

Week 6


Today s topics
Today’s Topics

  • Quiz Review and the Take-Home Quiz

  • SystemView Trial Version

  • Term Projects

  • Individual Conferences

  • Discussion (as time permits)

Week 6


Quiz overview
Quiz Overview

  • Practice Quiz was from text homework

    • Problem 1.1 page 51

    • Problem 2.2 page 101

    • Problem 3.1 page 162

  • Quiz was similar

    • From homework problems

    • Modifications to problem statement and parameters

Week 6


Quiz timeline
Quiz timeline

  • Quiz last week

    • Open book

    • Calculator

    • No notes (will allow notes for next quiz & final)

  • Follow-up quiz announced at end of class

    • Take-home

    • Will require SystemView to complete

    • Will be deployed on Blackboard this week

Week 6


The curve
The Curve

Week 6



Problem 1
Problem 1

  • Energy vs. power signals

    • Section 1.2.4 pp 14-16

    • Energy signal – nonzero but finite energy

    • Power signal – nonzero but finite power

  • Definitions, equation s(1.7) and (1.8)

Week 6


Problem 1 equations
Problem 1 Equations

  • Part (a)

  • Part (b)

  • Part (c)

  • Part (d)

Week 6



Energy spectra
Energy Spectra

  • Section 1.4 pp 19, 20

  • Autocorrellation of energy signal

  • Power spectrum

Week 6


Problem 1 power spectra
Problem 1 Power Spectra

  • Section 1.4 pp. 19, 20

  • Autocorrelation of power signal

  • Power spectrum

Week 6



Problem 2 the block diagram

Naturally sampled low pass analog waveform

LPF

Local Oscillator

Problem 2, The Block Diagram

Week 6



Problem 2 part ii the figure
Problem 2 Part II – The Figure

BW

BW – signal bandwidth

W – maximum spectral spread

W

Week 6


Problem 2 part 2
Problem 2 Part 2

  • The signal x1(t) has a power spectrum Shifted left by k.fs

  • The signal x2(t)

    • Has a power spectrum that is one of the replicas shown in the previous slide

    • Spectral distortion results from the slope of the natural sampling overall shape

    • Error and distortion are determined by’

      • Alising into the passband from the other spectral replicas

      • Residual high frequency terms from the LPF stopband

  • Within these errors, x2(t) is a scaled replica of xs(t)

  • Within this and the PAM quantization, xs(t) is a replica of the input signal

Week 6


Problem 2 part iii 1 of 2
Problem 2 Part III (1 of 2)

  • The minimum sample rate is 2.W

    • Lower sample rates will allow splatter to alias into the signal band

    • Signal will still be reproduced, with larger errors

  • The LPF

    • Passband extends to BW/2

    • Stopband begins at fs-W/2

Week 6


Problem 2 part iii 2 of 2
Problem 2 Part III (2 of 2)

  • For a natural sampling duty cycle of d

    • The minimum system sample rate for two samples is 2.fs/d

    • Using a system sample rate that is a multiple of fs

      • Provides the same sampling for every gate

      • Allows accuracy of natural sampling with lower system sample rates

  • The sample rate

    • Determines the LPF transition band of fs-(W+BW)/2

    • Higher is better for filter cost/performance trade space

  • The spectrum aliasing number k

    • Should be significantly smaller than 1/d

    • Avoid selecting spectrum near the null in natural sampling spectra

Week 6


Question 3 the block diagram

LPF

Bandpass signal

Local Oscillator

2

2

2

Question 3 – The Block Diagram

Week 6


Problem 3 part i
Problem 3 Part I

  • The output signal xO(t) is the bandpass signal xB(t) shifted down in frequency by f0

  • For all-analog signals, the LPF

    • Will supplement the last I.F. filter

    • Can provide better performance than a bandpass filter

  • For sampled signals, the LPF

    • Provides anti-aliasing filtering – suppression of spectral images

    • May allow decimation to sample rate near BW

Week 6


Question 3 part ii
Question 3, Part II

  • Considerations are similar to those of Question 2

    • In Question 2, natural sampling generated an array of bandpass signals

    • The complex rest of the circuit was a quadrature demodulator that selected one of the bandpass signals

    • The duty cycle is not a part of Question 3

  • Minimum sample rate is 2.W

  • LPF

    • Bandpass to BW/2

    • Stopband begins at fs – W/2

Week 6


Problem 3 part iii
Problem 3 Part III

  • Sample rates fs that alias f0 to ±fs/4

  • Nyquist criteria, including spectral spread

  • Lowest sample rate is for a k of

Week 6


Problem iii part iv
Problem III Part IV

  • Look at numerical values of LPF specs

    • Bandpass to BW/2

    • Stopband begins at fs – W/2

    • Transition band is fs-(BW+W)/2

    • Shape factor is (2.fs-W)/BW

  • LPF trade space is better for higher fs

Week 6


Problem 3 part v
Problem 3 Part V

  • The sample rate at I.F. is 2.W

  • For complex signals, the Nyquist rate is W

  • Allowing for a shape factor for the LPF increases the sample rate above 2.W

  • Decimation

    • Minimum is a factor of 2 to produce a sample rate of W complex

    • Aliasing considerations can drive a complex data rate higher than W

    • Higher sample rates and simpler LPF will allow decimation of 3 or 4 to produce a complex sample rate near W

    • Dual-stage digital LPF can provide a very high performance – a shape factor only slightly larger than 1

Week 6


Systemview
SystemView

  • I have a mini-CD-ROM with the trial version

  • When you install

    • During business hours

    • When asked for “Regular” or “Professional” select “Professional”

    • Call Maureen Chisholm at 678-218-4603 to get your activation code

  • Other resources

    • The student version will probably carry you another week

    • The full version is available in E&A 604E – watch for two icons on the desktop and select the Professional version

Week 6


Term projects
Term Projects

  • Interpret, plan, model

  • Use SystemView

  • Assignments deployed by email last week

  • Your preferences and comments are encouraged

    • Office hours

    • Email

Week 6


Individual conferences
Individual Conferences

  • Look at your term projects while you’re waiting your turn

  • Stay when your turn is done

  • Class will resume after individual conferences for discussion of term projects and SystemView

Week 6


Assignment
Assignment

  • Take-home quiz

    • Do the quiz you have

    • Print out the PDF file, these slides and go for 100%

  • Do the input blocks to your Term Project in SystemView

    • Generate a signal

    • Add noise

    • Modulate

    • Set the clock

    • Run it and look at the time/frequency domains

Week 6