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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/. Attendance. Essentials. Text: Bernard Sklar, Digital Communications , Second Edition SystemView Student version included with text

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EE521 Analog and Digital Communications

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  1. EE521 Analog and Digital Communications James K. Beard, Ph. D. jkbeard@temple.edu Tuesday, February 22, 2005 http://astro.temple.edu/~jkbeard/ Week 6

  2. Attendance Week 6

  3. 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

  4. Today’s Topics • Quiz Review and the Take-Home Quiz • SystemView Trial Version • Term Projects • Individual Conferences • Discussion (as time permits) Week 6

  5. 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

  6. 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

  7. The Curve Week 6

  8. Scoring Template Week 6

  9. 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

  10. Problem 1 Equations • Part (a) • Part (b) • Part (c) • Part (d) Week 6

  11. Problem 1 Powers & Energies Week 6

  12. Energy Spectra • Section 1.4 pp 19, 20 • Autocorrellation of energy signal • Power spectrum Week 6

  13. Problem 1 Power Spectra • Section 1.4 pp. 19, 20 • Autocorrelation of power signal • Power spectrum Week 6

  14. Problem 1 Spectra Week 6

  15. Naturally sampled low pass analog waveform LPF Local Oscillator Problem 2, The Block Diagram Week 6

  16. Spectrum of Naturally Sampled Signal Shows Part I Week 6

  17. Problem 2 Part II – The Figure BW BW – signal bandwidth W – maximum spectral spread W Week 6

  18. 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

  19. 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

  20. 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

  21. LPF Bandpass signal Local Oscillator 2 2 2 Question 3 – The Block Diagram Week 6

  22. 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

  23. 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

  24. 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

  25. 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

  26. 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

  27. 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

  28. Term Projects • Interpret, plan, model • Use SystemView • Assignments deployed by email last week • Your preferences and comments are encouraged • Office hours • Email Week 6

  29. 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

  30. 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

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