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EE 6331, Spring, 2009 Advanced Telecommunication

EE 6331, Spring, 2009 Advanced Telecommunication. Zhu Han Department of Electrical and Computer Engineering Class 14 Mar. 5 th , 2009. Outline. Project Step 1-5 Step 6 Step 7 and 8 Review Linear modulation BPSK, DPSK; QPSK, offset QPSK, /4 QPSK Exam and Homework review Equations

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EE 6331, Spring, 2009 Advanced Telecommunication

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  1. EE 6331, Spring, 2009Advanced Telecommunication Zhu Han Department of Electrical and Computer Engineering Class 14 Mar. 5th, 2009

  2. Outline • Project • Step 1-5 • Step 6 • Step 7 and 8 • Review • Linear modulation • BPSK, DPSK; QPSK, offset QPSK, /4 QPSK • Exam and Homework review • Equations • Sample questions • Homework • Reviews ECE6331 Spring 2009

  3. Geometric Representation of Modulation Signal Vector space We can represented the elements of S as linear combination of basis signals. The number of basis signals are the dimension of the vector space. Basis signals are orthogonal to each-other. Each basis is normalized to have unit energy: ECE6331 Spring 2009

  4. Binary Phase Shift Keying Use alternative sine wave phase to encode bits Phases are separated by 180 degrees. Simple to implement, inefficient use of bandwidth. Very robust, used extensively in satellite communication. Q 0 State 1 State ECE6331 Spring 2009

  5. BPSK Example 1 1 0 1 0 1 Data Carrier Carrier+ p BPSK waveform ECE6331 Spring 2009

  6. BPSK Virtue of pulse shaping equations 6.68-6.71 ECE6331 Spring 2009

  7. Quadrature Phase Shift Keying Multilevel Modulation Technique: 2 bits per symbol More spectrally efficient, more complex receiver. Two times more bandwidth efficient than BPSK Q 11 State 01 State 00 State 10 State Phase of Carrier: p/4, 2p/4, 5p/4, 7p/4 ECE6331 Spring 2009

  8. Concept of a constellation diagram ECE6331 Spring 2009

  9. Example of samples of matched filter output for some bandpass modulation schemes ECE6331 Spring 2009

  10. Differential Coherent • DBPSK • 3dB loss • QPSK BER 6.79, the same as BPSK ECE6331 Spring 2009

  11. Offset QPSK waveforms ECE6331 Spring 2009

  12. Pi/4 QPSK signaling 135 degree Non-coherent detection ECE6331 Spring 2009

  13. Constant Envelope Modulation Amplitude of the carrier is constant, regardless of the variation in the modulating signal Better immunity to fluctuations due to fading. Better random noise immunity Power efficient They occupy larger bandwidth ECE6331 Spring 2009

  14. Frequency Shift Keying (FSK) The frequency of the carrier is changed according to the message state (high (1) or low (0)). One frequency encodes a 0 while another frequency encodes a 1 (a form of frequency modulation) Integral of m(x) is continues. Continues FSK ECE6331 Spring 2009

  15. FSK Bandwidth • Limiting factor: Physical capabilities of the carrier • Not susceptible to noise as much as ASK • Applications • On voice-grade lines, used up to 1200bps • Used for high-frequency (3 to 30 MHz) radio transmission • used at higher frequencies on LANs that use coaxial cable ECE6331 Spring 2009

  16. Multiple Frequency-Shift Keying (MFSK) • More than two frequencies are used • More bandwidth efficient but more susceptible to error • f i= f c+ (2i – 1 – M)f d • f c= the carrier frequency • f d= the difference frequency • M = number of different signal elements = 2 L • L = number of bits per signal element ECE6331 Spring 2009

  17. FSK Coherent Detection ECE6331 Spring 2009

  18. Noncoherent FSK ECE6331 Spring 2009

  19. MSK modulation Equation 6.104, 6.105 ECE6331 Spring 2009

  20. MSK reception ECE6331 Spring 2009

  21. Minimum Shift Keying spectra 6.107 6.108 ECE6331 Spring 2009

  22. GMSK spectral shaping ECE6331 Spring 2009

  23. GMSK spectra shaping ECE6331 Spring 2009

  24. Simple GMSK modulation and demodulation ECE6331 Spring 2009 EE 552/452 Spring 2007

  25. Digital GMSK demodulator ECE6331 Spring 2009

  26. 8-PSK Signal Constellation Equation 6.113-6.120 ECE6331 Spring 2009

  27. Pulse Shaped M-PSK ECE6331 Spring 2009

  28. QAM – Quadrature Amplitude Modulation • Modulation technique used in the cable/video networking world • Instead of a single signal change representing only 1 bps – multiple bits can be represented buy a single signal change • Combination of phase shifting and amplitude shifting (8 phases, 2 amplitudes) ECE6331 Spring 2009

  29. QAM • QAM • As an example of QAM, 12 different phases are combined with two different amplitudes • Since only 4 phase angles have 2 different amplitudes, there are a total of 16 combinations • With 16 signal combinations, each baud equals 4 bits of information (2 ^ 4 = 16) • Combine ASK and PSK such that each signal corresponds to multiple bits • More phases than amplitudes • Minimum bandwidth requirement same as ASK or PSK ECE6331 Spring 2009

  30. 16-QAM Signal Constellation ECE6331 Spring 2009

  31. QAM vs. MFSK ECE6331 Spring 2009

  32. Orthogonal frequency-division multiplexing • Special form of Multi-Carrier Transmission. • Multi-Carrier Modulation. • Divide a high bit-rate digital stream into several low bit-rate schemes and transmit in parallel (using Sub-Carriers) ECE6331 Spring 2009

  33. Comparison of Digital Modulation ECE6331 Spring 2009

  34. Comparison of Digital Modulation ECE6331 Spring 2009

  35. Spectral Efficiencies in practical radios • GSM- Digital Cellular • Data Rate = 270kb/s, bandwidth = 200kHz • Bandwidth Efficiency = 270/200 =1.35bits/sec/Hz • Modulation: Gaussian Minimum Shift Keying (FSK with orthogonal frequencies). • “Gaussian” refers to filter response. • IS-54 North American Digital Cellular • Data Rate = 48kb/s, bandwidth = 30kHz • Bandwidth Efficiency = 48/30 =1.6bits/sec/Hz • Modulation: pi/4 DQPSK ECE6331 Spring 2009

  36. Modulation Summary • Phase Shift Keying is often used, as it provides a highly bandwidth efficient modulation scheme. • QPSK, modulation is very robust, but requires some form of linear amplification. OQPSK and p/4-QPSK can be implemented, and reduce the envelope variations of the signal. • High level M-ary schemes (such as 64-QAM) are very bandwidth efficient, but more susceptible to noise and require linear amplification. • Constant envelope schemes (such as GMSK) can be employed since an efficient, non-linear amplifier can be used. • Coherent reception provides better performance than differential, but requires a more complex receiver. ECE6331 Spring 2009

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