Communications Fundamentals FAQ

Chapter 8 FAQ

1. 8.15.1 What Is Multiple Access and How Does It Differ from Multiplexing
   1. What Is Multiple Access?
   2. Why Is Multiple Access Necessary?
   3. How Is Multiple Access Different from Multiplexing?
   4. Can a Communication System Use Both?
   5. What Communication Resources Can Be Shared?
   6. What Are the Main Multiple-Access Techniques?
   7. Where Is Multiple Access Used?
   8. Does Multiple Access Occur Only in Wireless Systems?
   9. What Makes Wireless Multiple Access Difficult?
   10. How Have Multiple-Access Techniques Evolved?
   11. Why Are Modern Systems Becoming More Complex?
   12. Why Is Efficient Multiple Access So Important?
   13. How Does This Chapter Build on the Previous One?
   14. Why Is Multiple Access Important?
2. 8.15.2 What Is Frequency-Division Multiple Access (FDMA)
   1. What Is Frequency-Division Multiple Access?
   2. Why Is It Called Frequency-Division Multiple Access?
   3. How Does FDMA Work?
   4. Why Doesn't Every User Share the Same Frequency?
   5. What Are Guard Bands?
   6. Why Must Frequencies Remain Accurate?
   7. What Happens When All Channels Are Busy?
   8. Does Every User Receive the Same Bandwidth?
   9. Where Is FDMA Used?
   10. Was FDMA Used in Early Cellular Networks?
   11. How Is FDMA Used in Satellite Communications?
   12. What Is Intermodulation?
   13. Why Are Satellite Power Amplifiers Operated Below Saturation?
   14. What Are the Advantages of FDMA?
   15. What Are the Disadvantages of FDMA?
   16. Is FDMA Still Important Today?
   17. Why Is FDMA Important?
3. 8.15.3 What Is Time-Division Multiple Access (TDMA)
   1. What Is Time-Division Multiple Access?
   2. Why Is It Called Time-Division Multiple Access?
   3. How Does TDMA Work?
   4. What Is a Time Slot?
   5. What Is a Frame?
   6. Why Does TDMA Use Burst Transmission?
   7. Why Is Synchronization So Important?
   8. What Are Guard Intervals?
   9. What Is Timing Advance?
   10. Why Is Timing Advance Necessary?
   11. Where Was TDMA Used?
   12. Why Did GSM Use TDMA?
   13. What Are the Advantages of TDMA?
   14. What Are the Disadvantages of TDMA?
   15. How Does TDMA Compare with FDMA?
   16. Is TDMA Still Used Today?
   17. Why Is TDMA Important?
4. 8.15.4 What Is Code-Division Multiple Access (CDMA)
   1. What Is Code-Division Multiple Access?
   2. Why Is It Called Code-Division Multiple Access?
   3. What Is Spread Spectrum?
   4. How Does CDMA Work?
   5. What Is a Chip?
   6. What Is a Spreading Code?
   7. What Types of Codes Are Used?
   8. What Is Processing Gain?
   9. Why Can Many Users Share the Same Frequency?
   10. Is There Any Interference?
   11. What Is the Near-Far Problem?
   12. How Is the Near-Far Problem Solved?
   13. Why Is Power Control So Important?
   14. What Is a RAKE Receiver?
   15. Why Is Multipath Helpful?
   16. Where Was CDMA Used?
   17. What Are the Advantages of CDMA?
   18. What Are the Disadvantages?
   19. Is CDMA Still Used Today?
   20. Why Was CDMA Such a Major Advance?
5. 8.15.5 What Is Spatial-Division Multiple Access (SDMA)
   1. What Is Spatial-Division Multiple Access?
   2. Why Is It Called Spatial-Division Multiple Access?
   3. How Does SDMA Work?
   4. What Is Beamforming?
   5. What Is a Smart Antenna?
   6. How Is SDMA Used in Cellular Networks?
   7. How Is SDMA Used in Satellites?
   8. What Is Frequency Reuse?
   9. What Is MIMO?
   10. How Can Several Users Share One Frequency?
   11. What Is Massive MIMO?
   12. Does Multipath Help or Hinder SDMA?
   13. What Are the Advantages of SDMA?
   14. What Are the Challenges?
   15. Where Is SDMA Used?
   16. Can SDMA Be Combined with Other Multiple-Access Techniques?
   17. Why Is SDMA Important?
6. 8.15.6 What Are ALOHA and Slotted ALOHA
   1. What Is ALOHA?
   2. Why Is It Called ALOHA?
   3. Why Was ALOHA Developed?
   4. How Does ALOHA Work?
   5. What Is a Collision?
   6. Why Are Random Delays Used?
   7. What Is the Vulnerable Period?
   8. How Efficient Is Pure ALOHA?
   9. What Is Slotted ALOHA?
   10. Why Does Slotted ALOHA Improve Performance?
   11. How Efficient Is Slotted ALOHA?
   12. Does Slotted ALOHA Require Synchronization?
   13. Where Has ALOHA Been Used?
   14. Why Is ALOHA Well Suited to Satellite Communications?
   15. What Are the Advantages of ALOHA?
   16. What Are the Disadvantages?
   17. How Did ALOHA Influence Later Communication Systems?
   18. Did ALOHA Lead to Ethernet?
   19. Why Is ALOHA Important?
7. 8.15.7 What Is Carrier Sense Multiple Access (CSMA)
   1. What Is Carrier Sense Multiple Access?
   2. Why Is It Called Carrier Sense Multiple Access?
   3. How Does CSMA Work?
   4. Why Does Listening Help?
   5. Can Collisions Still Occur?
   6. What Happens After a Collision?
   7. What Is Persistence?
   8. What Is 1-Persistent CSMA?
   9. What Is Non-Persistent CSMA?
   10. What Is p-Persistent CSMA?
   11. What Is CSMA/CD?
   12. How Does Collision Detection Work?
   13. What Happens After Collision Detection?
   14. What Is Binary Exponential Backoff?
   15. Why Doesn't Wi-Fi Use Collision Detection?
   16. What Is CSMA/CA?
   17. What Are RTS and CTS?
   18. What Is the Hidden Terminal Problem?
   19. Where Is CSMA Used?
   20. What Are the Advantages of CSMA?
   21. What Are the Disadvantages?
   22. Why Is CSMA Important?
8. 8.15.8 What Is Spread Spectrum and Why Was It Developed
   1. What Is Spread Spectrum?
   2. Why Is It Called Spread Spectrum?
   3. Why Would Engineers Intentionally Use More Bandwidth?
   4. How Does Spread Spectrum Work?
   5. What Is a Spreading Code?
   6. What Is a Pseudo-Random Sequence?
   7. What Is Processing Gain?
   8. Why Does Spread Spectrum Resist Interference?
   9. Why Is Spread Spectrum Resistant to Jamming?
   10. Why Is Spread Spectrum Difficult to Intercept?
   11. Does Spread Spectrum Improve Multipath Performance?
   12. Does Spread Spectrum Increase Capacity?
   13. Where Is Spread Spectrum Used?
   14. Are There Different Types of Spread Spectrum?
   15. What Are the Advantages of Spread Spectrum?
   16. What Are the Disadvantages?
   17. Why Was Spread Spectrum Such an Important Development?
9. 8.15.9 What Are Direct-Sequence Spread Spectrum (DSSS) and Frequency-Hopping Spread Spectrum (FHSS)
   1. What Is Direct-Sequence Spread Spectrum?
   2. How Does DSSS Work?
   3. What Is a Chip?
   4. What Is Frequency-Hopping Spread Spectrum?
   5. How Does FHSS Work?
   6. Why Are the Hopping Patterns Pseudo-Random?
   7. How Does DSSS Resist Interference?
   8. How Does FHSS Resist Interference?
   9. Which Technique Is Better Against Jamming?
   10. Which Technique Is More Resistant to Interception?
   11. Does DSSS Support Multiple Users?
   12. Does FHSS Support Multiple Users?
   13. Which Is More Complex?
   14. Where Is DSSS Used?
   15. Where Is FHSS Used?
   16. Can DSSS and FHSS Be Combined?
   17. What Are the Advantages of DSSS?
   18. What Are the Advantages of FHSS?
   19. Why Are Both Techniques Important?
10. 8.15.10 Why Do Modern Wireless Systems Combine Several Multiple-Access Techniques
    1. Why Isn't One Multiple-Access Technique Enough?
    2. What Does "Combining Techniques" Mean?
    3. What Multiple-Access Technique Does 4G LTE Use?
    4. What About the Uplink?
    5. How Does OFDMA Improve Capacity?
    6. What Role Does SDMA Play?
    7. How Does Massive MIMO Help?
    8. What Is Beamforming?
    9. Why Is Scheduling Important?
    10. What Is Adaptive Modulation?
    11. Why Is Channel Coding Also Important?
    12. How Does a Typical 5G System Combine Techniques?
    13. Why Is Frequency Reuse Still Important?
    14. How Does Artificial Intelligence Help?
    15. Will 6G Combine Even More Techniques?
    16. What Are the Advantages of Combining Multiple-Access Techniques?
    17. Are There Any Disadvantages?
    18. Why Is This Combination So Important?
11. 8.15.11 How Do Cellular Networks Allow Millions of Users to Share the Same Spectrum
    1. What Is a Cellular Network?
    2. Why Are Cells Used?
    3. What Is Frequency Reuse?
    4. Why Doesn't Frequency Reuse Cause Interference?
    5. What Is a Cell Cluster?
    6. What Is Sectorization?
    7. How Does Beamforming Improve Capacity?
    8. What Is Massive MIMO?
    9. Why Is Power Control Important?
    10. What Is Handover?
    11. Why Is Handover Necessary?
    12. How Does Scheduling Help?
    13. Why Doesn't Every User Receive the Same Resources?
    14. What Is Adaptive Modulation?
    15. How Many Users Can One Cell Support?
    16. Why Are Small Cells Becoming More Common?
    17. What Role Do Satellites Play?
    18. Why Is Artificial Intelligence Becoming Important?
    19. Why Are Cellular Networks So Efficient?
12. 8.15.12 Which Multiple-Access Technique Is Best
    1. Why Isn't There One Best Technique?
    2. When Is FDMA the Best Choice?
    3. When Is TDMA Most Appropriate?
    4. When Is CDMA Most Useful?
    5. Why Has OFDMA Become So Popular?
    6. When Is SDMA Most Effective?
    7. When Are Random-Access Techniques Preferred?
    8. Which Technique Uses Spectrum Most Efficiently?
    9. Which Technique Is Simplest?
    10. Which Technique Is Most Complex?
    11. Which Technique Is Most Resistant to Interference?
    12. Why Do Modern Systems Combine Techniques?
    13. How Does the Internet Illustrate This?
    14. Will New Multiple-Access Techniques Continue to Appear?
    15. What Should an Engineer Consider When Selecting a Technique?