1. April 26, 2005Week 14 1 EE521 Analog and Digital Communications James K. Beard, Ph. D. jkbeard@temple.edu Tuesday, March 29, 2005 http://astro.temple.edu/~jkbeard/

2. Week 142 April 26, 2005 Attendance

3. Week 143 April 26, 2005 Essentials Text: Bernard Sklar, Digital Communications, Second Edition SystemView Office  E&A 349  MWF 10:30 AM to 11:30 AM  Hours during Finals Week TBA Term Projects Due TODAY, April 26 Final Exam  Tuesday, May 10, 6:00 PM to 8:00 PM  Here in this classroom  Posted within 3 days; you get your grade from Blackboard

4. Week 144 April 26, 2005 Today’s Topics Term Project Review EE551 in the Fall Evaluation  Starts promptly at 9:00 PM  Takes 15-20 minutes  I will leave the room  Need a student volunteer Hand out and collect forms Deliver to office here at Ft. Washington Main Office

5. Week 145 April 26, 2005 Term Project Generate a frequency sweep  Start frequency:  End frequency: Add noise to obtain a noise floor Digitize to 16 bits (later relaxed to 8 bits) Modulate using FSK, BPSK or QPSK Convert from baseband to a carrier frequency Model a fading channel with up to 12 paths. Demodulate and detect Analyze BER

6. Week 146 April 26, 2005 Modulation Problems with FSK 16 bits requires 16 X 7+ kHz or 120+ kBPS  It’s a lot of bandwidth  I.F. forced higher than the 450 kHz first mentioned  SystemView sample rate forced to high rates The MFSK token in the Communications library performs quantization  The bit stream isn’t available directly  The BER token requires that the bit stream be generated separately The MFSK input must be at the SystemView sample rate  Output will be at the inpuput sample rate  Sampled data must be re-sampled or held

7. Week 147 April 26, 2005 Getting the Bit Stream with MFSK Go from input to characters Go from characters to bit stream Scale and shift characters for MFSK modulator

8. Week 148 April 26, 2005 Modulation Problems with MPSK No high-level token for MPSK  Use two or four bit symbols  Use Quad Mod, sine function or PM to get PSK  Use PSK Demod to get back characters Gray code required to achieve theoretical BER Character rate 8 to 16 times sample rate  Same bandwidth problems as MFSK

9. Week 149 April 26, 2005 Other Operations Convert from baseband to a carrier frequency  Not required for channel models  Channel models take complex input  Carrier frequency is a parameter Modulation to carrier best demodulated to baseband for the channel model token  Simplifies the SystemView sample rate issue  Prepares the data for demodulation at the output  Can be done by modulating to a complex I.F. at baseband

10. Week 1410 April 26, 2005 The Channel Models Data formats are complex in, complex out The channel models include phase  Multiple paths are summed coherently  Result is a log normal, Rayleigh, or other fading channel  Model is meaningful for complex data Generate I.F. centered at zero or use quadrature demodulator for input to channel modles

11. Week 1411 April 26, 2005 BER Measurement Inject noise before the channel model  Sample the noise output before summing  You generate an accurate E b /N 0 easily there  Use a variance in the noise generator that gives a base (minimum) E b /N 0  Use an amplifier in dB with linked gain to control the E b /N 0 Use of Global Parameter Links, the BER token, and multiple iterations for BER curves explained in Appendix A of the Comms library documentation

12. Week 1412 April 26, 2005 Coding/Decoding Not specified in the term project scope Omitting coding  Avoided timing and synchronization issues on the decoder  Left us with basically a modulation and channel modeling project Coding  Offers an insight on the effect of FEC on the BER curve  Isn’t the whole picture without interleaving  Context will be part of next Fall’s EE551

13. April 26, 2005Week 14 13 EE521 Analog and Digital Communications Review Topics jkbeard@temple.edu

14. Week 1414 April 26, 2005 Complex Signals Base property is distinction of signal at negative frequencies from signal at positive frequencies Use in communications systems  Signal generation steps Digital character generation Character generation Complex FSK, MPSK, GMSK, etc. generation Real signal synthesis at I.F. for upconvert  Demodulation steps Complex demodulation used for coherent pilot PLL Complex demodulation of PSK, MSK, etc.

15. Week 1415 April 26, 2005 Principles of Complex Signals Multiplication Multiplication between a complex number and the complex conjugate of another

16. Week 1416 April 26, 2005 Power and Energy of Complex Signals Power Energy

17. Week 1417 April 26, 2005 Sampling and Aliasing Sampling a tone at f t at a rate of f s results in aliasing to frequencies f k The aliasing order k is any integer – zero, positive or negative The base ambiguity region of a sampled signal on the next slide

18. Week 1418 April 26, 2005 Ambiguity Range for Complex Signals

19. Week 1419 April 26, 2005 Sampling a Real Signal This is what we must do with a real R.F. signal The negative frequency image is always there even with a quadrature demodulator (why?) Study of the figure reveals  Nyquist’s sampling limit  Why we want to alias to ± f s /4

20. Week 1420 April 26, 2005 Three Types of Error Correcting Codes Convolutional codes  Most often used  Provide spectrum usage within 2 dB of the Shannon limit with Viterbi decoding Block codes  Good for simple codes such as Hamming codes  Simple to understand and use  Provide a basis for understanding other codes Recursive codes  Used in Turbo Codes; achieve almost the Shannon limit  May be the codes of the future  Usage is complicated because output does not terminated

21. Week 1421 April 26, 2005 Decoding Simple Block Codes Works with correct-one, detect-two codes Find the syndrome for single-bit errors Match with the syndrome of the received message Invert that bit in the received message to form the corrected message Check the syndrome for zero Invert the coding to find the decoded message

22. April 26, 2005Week 14 22 EE551Signal Processing and Communication Theory Fall, 2005 CRN 088905 Thursday evenings in Ft. Washington James K Beard

23. Week 1423 April 26, 2005 EE551 Format and Topics Base topics from Sklar  Review of EE521 topics  Ch. 7 and Ch. 8, Channel Coding: Part 2, Part 3  Ch. 9, Modulation and Coding Trade-Offs  Ch. 5, Communications Link Analysis  Ch. 10, Synchronization  Ch. 11, Multiplexing and Multiple Access  Ch. 12, Spread-Spectrum Techniques  Ch. 14, Encryption and Decryption  Ch. 15, Fading Channels Others TBD Term Project in SystemView Seminar format  Round-table on specified topics every week  You will present your term project

24. Week 1424 April 26, 2005 FINAL IS MAY 10

25. Week 1425 April 26, 2005 Your Grade for EE521 Based on  Quizzes  Term project  Final exam Do well on the Final Examination  First exam was fair  Second exam was good  Nobody helped themselves with the Quiz 2 Backup  A good Final Exam grade is paramount

26. Week 1426 April 26, 2005 Final Exam Procedure Show up here at 6:00 PM SHARP on May 10 Your exam will be waiting Rules  No talking  Questions Submitted to me on paper Responses on whiteboard for all  I will pick up exams promptly at 8:00 PM Check off your problems – don’t miss any If you get done early, check and re-check your work