1 / 43

Chapter 3

Chapter 3. Digital Communication Fundamentals for Cognitive Radio. “ Cognitive Radio Communications and Networks: Principles and Practice ” By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009). 1. Outline. Fundamental of Data Transmission Digital Modulation Techniques

Download Presentation

Chapter 3

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.


Presentation Transcript

  1. Chapter 3 Digital Communication Fundamentals for Cognitive Radio “Cognitive Radio Communications and Networks: Principles and Practice” By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009) 1

  2. Outline • Fundamental of Data Transmission • Digital Modulation Techniques • Probability of Bit Error • Multicarrier Modulation • Multicarrier Equlization • Intersymbol Interference • Pulse Shaping 2

  3. Data Transmission Anatomy of a wireless Digital Comm Sys 3

  4. Data Transmission • Fundamental Limits • Shannon–Hartley theorem S is the total received signal power over the bandwidth (in case of a modulated signal, often denoted C, i.e. modulated carrier), measured in watt or volt; N is the total noise or interference power over the bandwidth, measured in watt or volt; and S/N is the signal-to-noise ratio (SNR) or the carrier-to-noise ratio (CNR) of the communication signal to the Gaussian noise interference expressed as a linear power ratio (not as logarithmic decibels). 4

  5. Data Transmission • Source of Transmission Error The linear filter channel with additive noise 5

  6. Data Transmission • Additive White Gaussian Noise (AWGN)‏ • White noise assumption in most situations • Gaussian pdf 6

  7. Data Transmission • Additive White Gaussian Noise (AWGN)‏ Histogram of AWGN superimposed on the probability density function for a Gaussian random variable of N(0,0.25)‏ Power spectral density of AWGN with N(0,0.25)‏ 7

  8. Data Transmission • Nearest neighbor detection AWGN N(0,0.01)‏ AWGN N(0,0.25)‏ 8

  9. Digital Modulation Techniques • Representation of Signals • Euclidean Distance between Signals • Decision Rule • Power Efficiency • M-ary Phase Shift Keying • M-ary Quadrature Amplitude Modulation 9

  10. Representation of Signals 10

  11. Euclidean Distance between Signals • For any two signals and , the Euclidean Distance between them is defined as • Vector form 11

  12. Decision Rule • Nearest neighbor rule: Determine is if is the closest to rewritten as waveform representation 12

  13. Power Efficiency • Measures the largest minimum signal distance achieved given lowest transmit power • Energy per symbol • Energy per bit 13

  14. Power Efficiency • Power efficiency 14

  15. M-ary Phase Shift Keying 15

  16. M-ary Quadrature Amplitude Modulation 16

  17. M-ary Quadrature Amplitude Modulation 17

  18. M-ary Quadrature Amplitude Modulation Receiver Simple receiver structure makes M-QAM popular in digital communication systems. 18

  19. Probability of Bit Error • Also known as bit error rate • Starting from the modulation scheme with two signal waveforms, and • Assuming the noise term has a Gaussian distribution 19

  20. Derivation of BER • Assuming was transmitted, then an error event occurs if • where 20

  21. Derivation of BER • P(error)= • is the noise density • is the correlation between and • Q-function defines the area under the tail of a Gaussian pdf 21

  22. Derivation of BER • When , • and • therefore 22

  23. Upper Bound on BER • At least one error occurs • Therefore 23

  24. Lower Bound on BER • The smaller , the more likely an error happens. • Therefore 24

  25. Multicarrier modulation • Advantages: • Transmission agility • High datarate • Immunity to non-flat fading response. • “divide-and-conquer” channel distortion • Adaptive bit loading 25

  26. Multicarrier modulation • Disadvantages: • Sensitive to narrowband noise • Sensitive to amplitude clipping • Sensitive to timing jitter, delay 26

  27. Multicarrier Modulation Transmitter Receiver 27

  28. Comparison between single carrier and multicarrier • tt 28

  29. OFDM • Orthogonal Frequency Division Multiplexing 29

  30. FB-OFDM • Orthogonal Frequency Division Multiplexing with Filterbank FB-MC subcarrier spectrum employing a seuqre-root raised cosine prototype lowpass filter with a rolloff of 0.25 30

  31. OFDM Transmitter Receiver 31

  32. Multicarrier Equalization • Interference in multicarrier systems 32

  33. Distortion Reduction • Channel coding • Add redundancy to improve recovering 33

  34. Distortion Reduction • Channel equalization Before equalization After equalization 34

  35. Distortion Reduction • Channel equalization • Pre-equalization requires a feedback path from the receiver 35

  36. Intersymbol Interference • Signal being distorted by the temporal spreading and resulting overlap of individual symbol pulses Simplified block diagram for a wireless channel 36

  37. Intersymbol Interference RC-LPF filter response of combined modulation pulses when T=1, A=1 37

  38. Intersymbol Interference • Peak Interference/Distortion • When all symbols before and after have destruct effect on the symbol on cursor 38

  39. Pulse Shaping • Nyquist Pulse Shaping Theory • Time domain condition for zero ISI No ISI if sampling at t=kT 39

  40. Nyquist Pulse Shaping Theory • Nyquist-I Pulse (W=1/(2T))‏ 40

  41. Nyquist Pulse Shaping Theory • Nyquist-II Pulse (W>1/(2T))‏ 41

  42. Nyquist Pulse Shaping Theory • Frequency domain No ISI criterion 42

  43. Chapter 3 Summary • Digital communication theory at the core of cognitive radio operations • Mathematical tools necessary for enabling advanced features • Various modulation schemes can be used for transmission under different constraints and expectations • Bit Error Rate is primarily used to define performance 43

More Related