Communications Fundamentals FAQ

Chapter 6 FAQ

1. 6.18.1 What Is Modulation and Why Is It Necessary
   1. What Is Modulation?
   2. What Is a Carrier Wave?
   3. What Is a Baseband Signal?
   4. Why Can't We Simply Transmit the Baseband Signal?
   5. Does Modulation Change the Information?
   6. What Carrier Characteristics Can Be Modified?
   7. Is Modulation Used Only in Radio?
   8. How Has Modulation Evolved?
   9. What Makes a Good Modulation Scheme?
   10. Why Is Modulation So Important?
2. 6.18.2 What Is the Difference Between Baseband and Passband Signals
   1. What Is a Baseband Signal?
   2. Why Is It Called Baseband?
   3. What Is a Passband Signal?
   4. Why Is It Called Passband?
   5. What Is the Relationship Between Baseband and Passband?
   6. Why Is Frequency Translation Necessary?
   7. How Does Modulation Produce a Passband Signal?
   8. What Happens to the Spectrum?
   9. Can Baseband Signals Be Transmitted Directly?
   10. What Is a Baseband Communication System?
   11. What Is a Passband Communication System?
   12. Why Are Wireless Systems Almost Always Passband?
   13. What Is Upconversion?
   14. What Is Downconversion?
   15. Why Is Intermediate Frequency Often Used?
   16. Is Digital Communication Still Baseband?
   17. What Is Complex Baseband?
   18. Why Is the Difference Important?
3. 6.18.3 What Is the Difference Between Analog and Digital Modulation
   1. What Is Analog Modulation?
   2. What Is Digital Modulation?
   3. What Is the Fundamental Difference?
   4. Does Digital Modulation Always Mean Digital Information?
   5. What Carrier Characteristics Are Varied?
   6. What Are Examples of Analog Modulation?
   7. What Are Examples of Digital Modulation?
   8. Why Has Digital Modulation Become So Popular?
   9. Does Digital Always Produce Better Quality?
   10. How Does Noise Affect Analog Systems?
   11. How Does Noise Affect Digital Systems?
   12. Why Is Error Correction Easier with Digital Systems?
   13. Which Uses Bandwidth More Efficiently?
   14. Which Uses Power More Efficiently?
   15. Are Analog Systems Simpler?
   16. Why Are Analog Systems Still Used?
   17. How Are Modern Communication Systems Designed?
   18. Will Analog Modulation Disappear?
   19. Why Is Understanding Both Important?
4. 6.18.4 What Is Amplitude Modulation (AM) and How Does It Work
   1. What Is Amplitude Modulation?
   2. Why Is It Called Amplitude Modulation?
   3. How Does AM Work?
   4. What Does an AM Waveform Look Like?
   5. What Is the Carrier?
   6. What Are Sidebands?
   7. Why Are Sidebands Important?
   8. How Much Bandwidth Does AM Require?
   9. What Is Modulation Depth?
   10. What Is Overmodulation?
   11. Why Is AM Considered Power Inefficient?
   12. Why Is AM Still Used?
   13. Why Is AM Used for Aviation?
   14. Why Is AM Used for Medium-Wave Broadcasting?
   15. What Is the Envelope Detector?
   16. What Are the Limitations of AM?
   17. How Has AM Influenced Modern Communications?
   18. Why Is Understanding AM Important?
5. 6.18.5 Why Is Single-Sideband (SSB) Used for HF Radio
   1. What Is Single-Sideband Modulation?
   2. Why Was SSB Developed?
   3. How Does SSB Differ from Conventional AM?
   4. Why Does One Sideband Contain All the Information?
   5. How Much Bandwidth Does SSB Save?
   6. Why Is Bandwidth So Important?
   7. How Much Power Does SSB Save?
   8. Why Is This Important for HF Communications?
   9. What Is Carrier Suppression?
   10. Why Do SSB Receivers Need Fine Tuning?
   11. What Is a Beat Frequency Oscillator?
   12. What Is the Difference Between USB and LSB?
   13. Why Are Both USB and LSB Used?
   14. Is SSB More Difficult to Generate?
   15. Does SSB Have Any Disadvantages?
   16. Is SSB Used for Broadcasting?
   17. Is SSB Still Important Today?
   18. Has SSB Influenced Modern Digital Communications?
   19. Why Is Understanding SSB Important?
6. 6.18.7 What Determines the Bandwidth of a Modulated Signal
   1. What Is Bandwidth?
   2. Why Does Every Signal Occupy Bandwidth?
   3. What Determines the Bandwidth of an AM Signal?
   4. Why Does Single-Sideband Require Less Bandwidth?
   5. What Determines FM Bandwidth?
   6. Why Do Digital Signals Also Occupy Bandwidth?
   7. What Is Symbol Rate?
   8. What Is the Difference Between Bit Rate and Symbol Rate?
   9. What Is Pulse Shaping?
   10. What Is Inter-Symbol Interference?
   11. What Is the Roll-Off Factor?
   12. Does Higher Data Rate Always Require More Bandwidth?
   13. What Is Spectral Efficiency?
   14. Why Can't Bandwidth Be Reduced Indefinitely?
   15. How Does Filtering Affect Bandwidth?
   16. Why Do Regulatory Authorities Specify Channel Bandwidth?
   17. How Do Engineers Minimise Bandwidth?
   18. Why Is Understanding Bandwidth Important?
7. 6.18.8 What Is Spectral Efficiency and Why Is It Important
   1. What Is Spectral Efficiency?
   2. How Is Spectral Efficiency Calculated?
   3. Why Is Spectral Efficiency Important?
   4. Why Can't We Simply Use More Bandwidth?
   5. How Can Spectral Efficiency Be Improved?
   6. How Does Higher-Order Modulation Improve Spectral Efficiency?
   7. Why Isn't Higher-Order Modulation Always Used?
   8. What Is a Signal Constellation?
   9. What Is the Relationship Between Spectral Efficiency and Signal-to-Noise Ratio?
   10. What Is Adaptive Modulation?
   11. How Does Channel Coding Affect Spectral Efficiency?
   12. What Role Does OFDM Play?
   13. What Is MIMO?
   14. What Limits Spectral Efficiency?
   15. What Spectral Efficiencies Are Typical?
   16. Why Is Spectral Efficiency Especially Important for Satellites?
   17. Why Is Spectral Efficiency Important for Mobile Networks?
   18. Is Maximum Spectral Efficiency Always the Best Objective?
   19. Why Is Understanding Spectral Efficiency Important?
8. 6.18.9 What Is Quadrature Modulation and Why Is It So Widely Used
   1. What Does "Quadrature" Mean?
   2. What Does Orthogonal Mean?
   3. What Are the I and Q Channels?
   4. Why Can Two Signals Occupy the Same Frequency?
   5. Why Is This So Useful?
   6. How Does Quadrature Modulation Work?
   7. What Is a Constellation Diagram?
   8. How Does QPSK Use Quadrature Modulation?
   9. How Does QAM Use Quadrature Modulation?
   10. Why Doesn't Everyone Use Very Large Constellations?
   11. What Is Coherent Detection?
   12. What Happens If the Carrier Phase Is Wrong?
   13. Why Is Quadrature Modulation Used with OFDM?
   14. Where Is Quadrature Modulation Used?
   15. Is Quadrature Modulation Used in Satellite Communications?
   16. How Is Quadrature Modulation Implemented Today?
   17. Does Quadrature Modulation Have Any Disadvantages?
   18. Why Is Quadrature Modulation So Important?
9. 6.18.10 How Do Engineers Choose the Best Modulation Scheme
   1. What Factors Influence the Choice of Modulation?
   2. Why Is Bandwidth Important?
   3. Why Does Signal-to-Noise Ratio Matter?
   4. Why Is Transmitter Power Important?
   5. How Do Propagation Conditions Affect the Decision?
   6. Why Is Mobility Important?
   7. Why Is Receiver Complexity Important?
   8. Why Is Reliability Sometimes More Important Than Speed?
   9. Why Doesn't Everyone Use 256-QAM?
   10. What Is Adaptive Modulation?
   11. How Does Channel Coding Influence the Choice?
   12. Why Is OFDM Used in Modern Wireless Systems?
   13. Why Do Satellite Systems Use APSK Instead of QAM?
   14. Why Does HF Radio Still Use SSB?
   15. Why Do Mobile Phones Use Several Modulation Schemes?
   16. What About Future Communication Systems?
   17. Is There Ever a Perfect Choice?
   18. Why Is Understanding These Trade-Offs Important?