Communications Fundamentals FAQ

Chapter 3 FAQ

1. 3.8.1 What Is Source Coding
   1. Why Do Communications Systems Need Source Coding?
   2. What Types of Information Can Be Source Coded?
   3. How Does Source Coding Improve Efficiency?
   4. What Is Redundancy?
   5. Is All Redundancy Unnecessary?
   6. What Is the Difference Between Lossless and Lossy Coding?
   7. How Does Source Coding Relate to Analog-to-Digital Conversion?
   8. What Are Waveform Coders?
   9. What Are Model-Based Coders?
   10. What Are Hybrid Coders?
   11. How Much Compression Is Possible?
   12. Where Is Source Coding Used Today?
   13. How Does Source Coding Fit into a Communications System?
   14. Why Is Source Coding Important?
2. 3.8.2 What Is the Difference Between Source Coding and Channel Coding
   1. Why Are Both Source Coding and Channel Coding Needed?
   2. What Is Source Coding?
   3. What Is Channel Coding?
   4. How Does Source Coding Remove Redundancy?
   5. How Does Channel Coding Add Redundancy?
   6. Why Do the Two Processes Seem Contradictory?
   7. Which Process Occurs First?
   8. Why Doesn't Source Coding Remove All Redundancy?
   9. What Is Lossless Source Coding?
   10. What Is Lossy Source Coding?
   11. How Does Channel Coding Improve Reliability?
   12. How Much Redundancy Does Channel Coding Add?
   13. Can Source Coding and Channel Coding Be Considered Together?
   14. What Are Some Practical Examples?
   15. Which Contributes More to Modern Communications?
   16. Why Is the Distinction Important?
3. 3.8.3 What is the Nyquist Sampling Rate
   1. Why Must Analog Signals Be Sampled?
   2. What Is the Nyquist Sampling Theorem?
   3. What Is the Nyquist Rate?
   4. Why Is the Sampling Rate Twice the Highest Frequency?
   5. What Is a Band-Limited Signal?
   6. What Is Aliasing?
   7. How Does Aliasing Occur?
   8. What Is an Anti-Aliasing Filter?
   9. Why Is Telephone Speech Sampled at 8 kHz?
   10. Why Is Audio Often Sampled at 44.1 kHz?
   11. Does Sampling Faster Always Improve Quality?
   12. What Is Oversampling?
   13. How Is the Original Signal Reconstructed?
   14. Does the Nyquist Theorem Apply to Images and Video?
   15. Why Is the Nyquist Sampling Theorem Important?
4. 3.8.4 What Is Pulse-code Modulation (PCM)
   1. Why Was PCM Developed?
   2. What Are the Stages of PCM?
   3. How Does Sampling Work?
   4. Why Is Sampling Necessary?
   5. What Is Quantization?
   6. Why Is Quantization Necessary?
   7. What Is Quantization Noise?
   8. How Are Samples Converted into Binary Numbers?
   9. How Is the Original Signal Reconstructed?
   10. Why Does PCM Voice Use an 8 kHz Sampling Rate?
   11. Why Are 8 Bits Used for Each PCM Sample?
   12. How Is the 64 kbps PCM Data Rate Calculated?
   13. What Are the Advantages of PCM?
   14. What Are the Disadvantages of PCM?
   15. Where Is PCM Used Today?
   16. How Does PCM Relate to Other Source Coding Methods?
   17. Why Is PCM Important?
5. 3.8.5 Why Does PCM Voice Use 64 kbps
   1. What Is a PCM Voice Channel?
   2. Why Is Speech Sampled at 8 kHz?
   3. Why Are 8 Bits Used for Each Sample?
   4. How Is the 64 kbps Figure Calculated?
   5. Why Was 64 kbps Considered a Good Compromise?
   6. What Is a DS0 Channel?
   7. Why Does PCM Use Companding?
   8. How Good Is 64 kbps PCM Speech Quality?
   9. Why Do Modern Systems Often Use Lower Bit Rates?
   10. If Lower Bit Rates Are Possible, Why Is 64 kbps Still Important?
   11. Is 64 kbps Used Outside Telephony?
   12. What Happened to the 64 kbps Channel in Modern Networks?
   13. Why Is the 64 kbps Standard Important in Communications Engineering?
6. 3.8.6 What Is Quantization Noise
   1. What Causes Quantization Noise?
   2. Why Is Quantization Necessary?
   3. Why Does Quantization Noise Resemble Random Noise?
   4. How Large Can Quantization Error Become?
   5. What Is Signal-to-Quantization-Noise Ratio (SQNR)?
   6. Why Does Increasing the Number of Bits Improve Quality?
   7. Why Does Each Additional Bit Improve SQNR by About 6 dB?
   8. How Good Is 8-Bit Quantization?
   9. Why Does Audio Equipment Use 16 Bits or More?
   10. Is Quantization Noise Always Audible?
   11. Why Are Small Signals More Affected by Quantization Noise?
   12. What Is Companding?
   13. Can Quantization Noise Be Eliminated Completely?
   14. What Is Dithering?
   15. How Does Quantization Noise Affect Communications Systems?
   16. Why Is Quantization Noise Important?
7. 3.8.7 What Is Companding
   1. What Does Companding Mean?
   2. Why Is Companding Needed?
   3. Why Are Low-Level Signals More Affected by Quantization Noise?
   4. What Is Dynamic Range?
   5. How Does Compression Improve Quantization?
   6. What Happens After Transmission?
   7. How Does Companding Affect Quantization Levels?
   8. Why Is Human Hearing Relevant?
   9. What Is μ-law Companding?
   10. What Is A-law Companding?
   11. Why Are There Two Standards?
   12. How Much Improvement Does Companding Provide?
   13. Does Companding Increase Bit Rate?
   14. Is Companding Lossless?
   15. Where Is Companding Used?
   16. Is Companding Still Relevant Today?
   17. How Does Companding Compare with Increasing the Number of Bits?
   18. Why Is Companding Important?
8. 3.8.8 What Is Delta Modulation
   1. What Is Delta Modulation?
   2. Why Was Delta Modulation Developed?
   3. Why Is It Called Delta Modulation?
   4. How Does Delta Modulation Work?
   5. What Does the Receiver Do?
   6. Why Does Delta Modulation Use Only One Bit?
   7. How Does Delta Modulation Reduce Complexity?
   8. Is Delta Modulation More Efficient Than PCM?
   9. What Is the Step Size?
   10. What Happens If the Step Size Is Too Small?
   11. What Is Slope Overload Distortion?
   12. How Can Slope Overload Be Reduced?
   13. What Happens If the Step Size Is Too Large?
   14. What Is Granular Noise?
   15. Why Is There a Trade-Off Between Slope Overload and Granular Noise?
   16. What Is Adaptive Delta Modulation?
   17. How Does Adaptive Delta Modulation Work?
   18. How Does Delta Modulation Compare with PCM?
   19. Where Has Delta Modulation Been Used?
   20. Does Delta Modulation Influence Modern Systems?
   21. Why Is Delta Modulation Important?
9. 3.8.9 What Is Entropy Coding
   1. What Is Entropy Coding?
   2. Why Is Entropy Coding Important?
   3. What Is Information Content?
   4. What Is Entropy?
   5. Why Do Common Symbols Require Fewer Bits?
   6. What Is a Variable-Length Code?
   7. What Is a Prefix Code?
   8. What Is Huffman Coding?
   9. How Does Huffman Coding Work?
   10. What Is Arithmetic Coding?
   11. Why Is Arithmetic Coding More Efficient?
   12. What Is Adaptive Entropy Coding?
   13. Is Entropy Coding Lossless?
   14. Where Is Entropy Coding Used?
   15. How Does Entropy Coding Relate to Source Coding?
   16. Can Entropy Coding Reach the Entropy Limit?
10. 3.8.10 What Is the Difference Between Waveform, Model-Based, and Hybrid Speech Coding
    1. Why Is Speech Coding Important?
    2. What Is a Speech Coder?
    3. What Is Waveform Coding?
    4. How Do Waveform Coders Work?
    5. What Are Examples of Waveform Coders?
    6. What Are the Advantages of Waveform Coding?
    7. What Are the Disadvantages of Waveform Coding?
    8. What Is Model-Based Coding?
    9. How Is Human Speech Produced?
    10. What Is a Vocoder?
    11. What Is Linear Predictive Coding (LPC)?
    12. What Are the Advantages of Model-Based Coding?
    13. What Are the Disadvantages of Model-Based Coding?
    14. What Is Hybrid Coding?
    15. How Do Hybrid Coders Work?
    16. What Is CELP?
    17. Why Is CELP So Successful?
    18. Where Are Hybrid Coders Used?
    19. How Do the Three Approaches Compare?
    20. Which Approach Is Used Today?
    21. Why Is Understanding These Approaches Important?
11. 3.8.11 What Is Data Compression and How Does It Work
    1. What Is Data Compression?
    2. Why Is Data Compression Important?
    3. What Is Redundancy?
    4. How Does Compression Work?
    5. What Is a Compression Ratio?
    6. What Is Lossless Compression?
    7. How Does Lossless Compression Work?
    8. What Is Dictionary Coding?
    9. What Is Lempel-Ziv Coding?
    10. What Is Lossy Compression?
    11. Why Is Lossy Compression Acceptable?
    12. What Is Perceptual Coding?
    13. How Does Audio Compression Work?
    14. How Does Image Compression Work?
    15. What Is Transform Coding?
    16. How Does Video Compression Work?
    17. What Is Entropy Coding's Role in Compression?
    18. How Much Compression Is Possible?
    19. Can Data Always Be Compressed?
    20. How Does Compression Relate to Entropy?
    21. What Are the Trade-Offs in Compression?
    22. Where Is Data Compression Used?