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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 13 Mar. 3 rd , 2009. Outline. Exam Review ADC/DAC PCM Geometric representation of modulation signals Linear modulation BPSK, DPSK; QPSK, offset QPSK, /4 QPSK

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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 13 Mar. 3rd, 2009

  2. Outline • Exam • Review • ADC/DAC • PCM • Geometric representation of modulation signals • Linear modulation • BPSK, DPSK; QPSK, offset QPSK, /4 QPSK • Constant envelope modulation • BFSK, MSK, GMSK • Combined linear and constant envelope modulation • MPSK • QAM • MFSK and OFDM ECE6331 Spring 2009

  3. PAM, PWM, PPM, PCM ECE6331 Spring 2009

  4. Quantization • Scalar Quantizer Block Diagram • Mid-tread • Mid-rise ECE6331 Spring 2009

  5. Equations ECE6331 Spring 2009

  6. Quantization Noise ECE6331 Spring 2009

  7. Example • SNR for varying number of representation levels for sinusoidal modulation 1.8+6 X dB, example 3.1 ECE6331 Spring 2009

  8. Conditions for Optimality of Scalar Quantizers Let m(t) be a message signal drawn from a stationary process M(t) -A m  A m1= -A mL+1=A mk mk+1 for k=1,2,…., L The kth partition cell is defined as Jk: mk< m  mk+1 for k=1,2,…., L d(m,vk): distortion measure for using vk to represent values inside Jk. ECE6331 Spring 2009

  9. Condition for Optimal Quantizer ECE6331 Spring 2009

  10. Condition One ECE6331 Spring 2009

  11. Condition Two ECE6331 Spring 2009

  12. Vector Quantization image and voice compression, voice recognition statistical pattern recognition volume rendering ECE6331 Spring 2009

  13. 0111 0110 0100 0101 Resolution= 1 part in 2n 0011 0010 0001 0000 1111 1110 1100 1010 1101 1011 1001 PCM 0000 0110 0111 0011 1100 1001 1011 Numbers passed from ADC to computer to represent analogue voltage ECE6331 Spring 2009

  14. ^ ^ x y Non-uniform Quantizer F: nonlinear compressing function F-1: nonlinear expanding function F and F-1: nonlinear compander y Q F F-1 x Example F: y=log(x) F-1: x=exp(x) We will study nonuniform quantization by PCM example next A law and  law ECE6331 Spring 2009

  15.  Law/A Law ECE6331 Spring 2009

  16. Geometric Representation of Modulation Signal Digital Modulation involves Choosing a particular signal waveform for transmission for a particular symbol or signal For M possible signals, the set of all signal waveforms are: For binary modulation, each bit is mapped to a signal from a set of signal set S that has two signals We can view the elements of S as points in vector space ECE6331 Spring 2009

  17. 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

  18. Example Two signal waveforms to be used for transmission The basis signal Q I Constellation Diagram Dimension = 1 ECE6331 Spring 2009

  19. Constellation Diagram Properties of Modulation Scheme can be inferred from Constellation Diagram Bandwidth occupied by the modulation increases as the dimension of the modulated signal increases Bandwidth occupied by the modulation decreases as the signal points per dimension increases (getting more dense) Probability of bit error is proportional to the distance between the closest points in the constellation. Bit error decreases as the distance increases (sparse). Equation 6.62-6.64 ECE6331 Spring 2009

  20. Concept of a constellation diagram ECE6331 Spring 2009

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

  22. Linear Modulation Techniques Classify digital modulation techniques as: Linear The amplitude of the transmitted signal varies linearly with the modulating digital signal, m(t). They usually do not have constant envelope. More spectral efficient. Poor power efficiency Example: BPSK, QPSK. Non-linear ECE6331 Spring 2009

  23. 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

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

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

  26. BPSK Coherent demodulator 6.72 6.73 6.74 ECE6331 Spring 2009

  27. Differential PSK encoding Differential BPSK 0 = same phase as last signal element 1 = 180º shift from last signal element ECE6331 Spring 2009

  28. DPSK modulation and demodulation 6.75, 3dB loss EE 542/452 Spring 2008 EE 552/452 Spring 2007

  29. 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

  30. 4 different waveforms -cos+sin cos+sin 11 01 00 10 cos-sin -cos-sin ECE6331 Spring 2009

  31. QPSK Example ECE6331 Spring 2009

  32. QPSK Virtue of pulse shaping 6.80 ECE6331 Spring 2009

  33. QPSK modulation ECE6331 Spring 2009

  34. QPSK receiver ECE6331 Spring 2009

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

  36. Offset QPSK waveforms ECE6331 Spring 2009

  37. Offset OQPSK • QPSK can have 180 degree jump, amplitude fluctuation • By offsetting the timing of the odd and even bits by one bit-period, or half a symbol-period, the in-phase and quadrature components will never change at the same time. • 90 degree jump ECE6331 Spring 2009

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

  39. Pi/4 QPSK transmitter 6.81-6.86 Example 6.9 ECE6331 Spring 2009

  40. I. Differential detection of pi/4 QPSK Example 6.10 ECE6331 Spring 2009

  41. II. IF Differential Detection ECE6331 Spring 2009

  42. III. FM Discriminator detector ECE6331 Spring 2009

  43. 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

  44. 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

  45. 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

  46. 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

  47. FSK Coherent Detection ECE6331 Spring 2009

  48. Noncoherent FSK ECE6331 Spring 2009

  49. MSK modulation Equation 6.104, 6.105 ECE6331 Spring 2009

  50. MSK reception ECE6331 Spring 2009

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