Communications Fundamentals FAQ

Chapter 4 FAQ

1. 4.18.1 What Is Channel Coding and Why Is It Needed
   1. What Is Channel Coding?
   2. Why Do Communication Channels Introduce Errors?
   3. What Types of Errors Occur in Communication Systems?
   4. Why Can't We Simply Increase Signal Power?
   5. What Is Redundancy?
   6. Why Is Redundancy Necessary?
   7. Isn't Redundancy Removed by Source Coding?
   8. How Does Channel Coding Work?
   9. What Is Error Detection?
   10. What Is Error Correction?
   11. What Is Forward Error Correction?
   12. How Much Redundancy Is Required?
   13. What Is Code Rate?
   14. Why Is Channel Coding So Important?
   15. What Is Coding Gain?
   16. Where Is Channel Coding Used?
   17. What Are the Limitations of Channel Coding?
   18. How Does Channel Coding Relate to Shannon's Work?
   19. Why Is Channel Coding Fundamental to Modern Communications?
2. 4.18.2 What Is Shannon's Information Capacity Theorem
   1. Who Was Claude Shannon?
   2. What Is Channel Capacity?
   3. Why is it called Shannon–Hartley equation?
   4. Why Not Just Call It Shannon's Equation?
   5. Why Does Noise Limit Communication?
   6. What Does the Equation Tell Us?
   7. Why Is the Logarithmic Relationship Important?
   8. What Is Signal-to-Noise Ratio?
   9. What Is the Shannon Limit?
   10. Does Shannon's Theorem Describe a Real System?
   11. What Is Spectral Efficiency?
   12. Why Is Spectral Efficiency Important?
   13. What Is the Relationship Between Capacity and Eb/N₀?
   14. What Is Special About −1.59 dB?
   15. What Are Power-Limited Systems?
   16. What Are Bandwidth-Limited Systems?
   17. Can Capacity Be Increased Indefinitely?
   18. How Close Do Modern Systems Come to Capacity?
   19. What Is the Importance of Shannon's Theorem?
   20. Where Is Shannon's Theorem Used?
   21. Why Is Shannon's Information Capacity Theorem Important?
3. 4.18.3 What is Shannon's Channel Coding Theorem
   1. What Is Shannon's Channel Coding Theorem?
   2. What Does Reliable Communication Mean?
   3. Why Was Shannon's Result So Important?
   4. What Is Channel Capacity?
   5. What Is Coding Rate?
   6. What Does the Theorem Actually Prove?
   7. Why Doesn't the Theorem Tell Us How to Build a Code?
   8. Why Are Long Codewords Important?
   9. What Happens Above Capacity?
   10. What Is the Shannon Limit?
   11. How Close Can Practical Systems Get to Capacity?
   12. What Are Capacity-Approaching Codes?
   13. What Is Coding Gain?
   14. Why Is Shannon's Theorem Important for Wireless Communications?
   15. Why Is the Theorem Important for Satellite Communications?
   16. Does Shannon's Theorem Apply Only to Communications?
   17. What Are the Practical Implications for Engineers?
   18. Why Is Shannon's Channel Coding Theorem Important?
4. 4.18.4 How Do Error Detection and Error Correction Work
   1. Why Do Communication Systems Need Error Control?
   2. What Is Error Detection?
   3. What Is Error Correction?
   4. How Does Redundancy Enable Error Detection?
   5. What Is a Codeword?
   6. What Is a Parity Bit?
   7. What Errors Can Parity Detect?
   8. What Is a Checksum?
   9. What Is a Cyclic Redundancy Check?
   10. Why Are CRCs So Effective?
   11. What Is Forward Error Correction?
   12. How Does Error Correction Work?
   13. What Is Hamming Distance?
   14. How Many Errors Can a Code Detect?
   15. How Many Errors Can a Code Correct?
   16. What Is a Syndrome?
   17. What Happens When Too Many Errors Occur?
   18. What Is Automatic Repeat Request?
   19. What Is Hybrid ARQ?
   20. When Is Error Correction Preferred?
   21. Where Are Error Detection and Correction Used?
   22. Why Are Error Detection and Error Correction Important?
5. 4.18.5 What Are Hamming Distance and Minimum Distance
   1. What Is Hamming Distance?
   2. Why Is It Called Hamming Distance?
   3. How Is Hamming Distance Calculated?
   4. What Does Hamming Distance Tell Us?
   5. What Is Minimum Distance?
   6. Why Is Minimum Distance More Important Than Ordinary Distance?
   7. How Can Codewords Be Visualized?
   8. How Does Distance Relate to Error Detection?
   9. Why Can't a Code Detect More Than (dmin - 1) Errors?
   10. How Does Distance Relate to Error Correction?
   11. How Many Errors Can a Code Correct?
   12. Why Is the Division by Two Necessary?
   13. What Is a Hamming Sphere?
   14. Why Must Hamming Spheres Not Overlap?
   15. What Is a Hamming Code?
   16. How Does Minimum Distance Affect Code Design?
   17. What Are Typical Minimum Distances?
   18. Why Is Distance Important in Modern Communications?
   19. How Do Hamming Distance and Minimum Distance Relate to Coding Gain?
   20. Why Are Hamming Distance and Minimum Distance Important?
6. 4.18.6 What Are Parity Bits, Checksums, and CRCs
   1. What Is Error Detection?
   2. Why Is Error Detection Necessary?
   3. What Is Redundancy?
   4. What Is a Parity Bit?
   5. How Does Even Parity Work?
   6. How Does Odd Parity Work?
   7. What Errors Can Parity Detect?
   8. What Errors Can Parity Miss?
   9. Where Is Parity Used?
   10. What Is a Checksum?
   11. How Does a Checksum Work?
   12. Why Are Checksums Better Than Parity?
   13. Where Are Checksums Used?
   14. What Is a Cyclic Redundancy Check?
   15. Why Is It Called a Cyclic Redundancy Check?
   16. How Does CRC Generation Work?
   17. What Is Modulo-2 Arithmetic?
   18. What Is a Generator Polynomial?
   19. Why Are CRCs So Effective?
   20. What Is a Burst Error?
   21. Why Are CRCs Preferred in Modern Systems?
   22. Where Are CRCs Used?
   23. Can Error Detection Correct Errors?
   24. What Happens When an Error Is Detected?
   25. How Do Parity, Checksums, and CRCs Compare?
   26. Why Are Parity Bits, Checksums, and CRCs Important?
7. 4.18.7 What Are Block Codes and Hamming Codes
   1. What Is a Block Code?
   2. Why Are They Called Block Codes?
   3. What Do the Terms (n,k) Mean?
   4. What Is Code Rate?
   5. Why Is Redundancy Needed?
   6. What Is a Codeword?
   7. What Makes One Block Code Better Than Another?
   8. What Is a Linear Block Code?
   9. What Is a Generator Matrix?
   10. What Is a Parity-Check Matrix?
   11. Who Was Richard Hamming?
   12. What Is a Hamming Code?
   13. Why Is the (7,4) Hamming Code So Important?
   14. How Are Hamming Codes Constructed?
   15. What Is Syndrome Decoding?
   16. How Does a Hamming Code Correct Errors?
   17. How Many Errors Can a Hamming Code Correct?
   18. What Is an Extended Hamming Code?
   19. Where Are Hamming Codes Used?
   20. What Are the Advantages of Block Codes?
   21. What Are the Limitations of Hamming Codes?
   22. How Do Block Codes Influence Modern Coding Systems?
   23. Why Are Block Codes and Hamming Codes Important?
8. 4.18.8 What Are Cyclic Codes
   1. What Is a Cyclic Code?
   2. Why Are Cyclic Codes Useful?
   3. How Are Cyclic Codes Represented?
   4. Why Use Polynomials?
   5. What Is a Generator Polynomial?
   6. What Is a Systematic Codeword?
   7. What Is a Non-Systematic Codeword?
   8. How Are Cyclic Codes Generated?
   9. How Are Errors Detected?
   10. What Is a BCH Code?
   11. Why Were BCH Codes Important?
   12. How Are BCH Codes Specified?
   13. How Do BCH Codes Correct Errors?
   14. What Is a Reed–Solomon Code?
   15. What Is the Difference Between Bits and Symbols?
   16. Why Are Reed–Solomon Codes Good for Burst Errors?
   17. How Are Reed–Solomon Codes Specified?
   18. Where Have Reed–Solomon Codes Been Used?
   19. What Is Concatenated Coding?
   20. How Do BCH and Reed–Solomon Codes Compare?
   21. Are BCH and Reed–Solomon Codes Still Used?
   22. Why Are Cyclic Codes Important?
9. 4.18.9 What Are Convolutional Codes, Turbo Codes, LDPC Codes, and Polar Codes
   1. What Is a Convolutional Code?
   2. Why Are They Called Convolutional Codes?
   3. How Does a Convolutional Encoder Work?
   4. What Is Constraint Length?
   5. What Is Code Rate?
   6. What Is a Trellis Diagram?
   7. What Is Viterbi Decoding?
   8. Why Was the Viterbi Algorithm Important?
   9. Where Were Convolutional Codes Used?
   10. What Are the Limitations of Convolutional Codes?
   11. What Are Turbo Codes?
   12. Why Are They Called Turbo Codes?
   13. How Does a Turbo Encoder Work?
   14. What Is an Interleaver?
   15. How Does Turbo Decoding Work?
   16. How Close Do Turbo Codes Come to Capacity?
   17. What Are LDPC Codes?
   18. Why Are They Called Low-Density Parity-Check Codes?
   19. How Are LDPC Codes Decoded?
   20. Why Are LDPC Codes Important?
   21. Where Are LDPC Codes Used?
   22. What Are Polar Codes?
   23. What Is Channel Polarization?
   24. Why Are Polar Codes Important?
   25. Where Are Polar Codes Used?
   26. How Do These Codes Compare?
   27. Which Performs Best?
   28. How Close Do Modern Codes Come to the Shannon Limit?
   29. Why Are Convolutional, Turbo, LDPC, and Polar Codes Important?
10. 4.18.10 What Is Forward Error Correction and Automatic Repeat Request
    1. What Is Forward Error Correction?
    2. Why Is It Called Forward Error Correction?
    3. How Does Forward Error Correction Work?
    4. What Types of Codes Are Used for FEC?
    5. What Are the Advantages of FEC?
    6. What Are the Disadvantages of FEC?
    7. What Is Automatic Repeat Request?
    8. Why Is It Called Automatic Repeat Request?
    9. Why Is Automatic Repeat Request Abbreviated as ARQ?
    10. How Does ARQ Work?
    11. What Is an Acknowledgment?
    12. Why Does ARQ Require Error Detection?
    13. What Is Stop-and-Wait ARQ?
    14. What Is Go-Back-N ARQ?
    15. What Is Selective Repeat ARQ?
    16. What Are the Advantages of ARQ?
    17. What Are the Disadvantages of ARQ?
    18. When Is FEC Preferred?
    19. When Is ARQ Preferred?
    20. What Is Hybrid ARQ?
    21. Why Is Hybrid ARQ So Effective?
    22. Where Is Hybrid ARQ Used?
    23. How Do FEC and ARQ Compare?
    24. Which Is More Efficient?
    25. Why Are FEC and ARQ Important?