Chapter 8 / 8.14

8.14 REVISION QUESTIONS

1. Explain the distinction between multiplexing and multiple access. Why does multiple access arise only when transmitters are geographically separated?

1. Identify the four deterministic dimensions along which channel resources may be partitioned. What physical properties of signals correspond to each dimension?

1. Contrast deterministic multiple-access techniques with contention-based techniques in terms of collision behavior and performance guarantees.

1. Why does throughput eventually decrease as offered load increases in contention-based systems?

1. Explain the fundamental principle of FDMA. How does frequency separation prevent interference?

1. Why are guard bands required in practical FDMA systems?

1. Describe the impact of nonlinear amplification on multi-carrier FDMA signals. What is intermodulation distortion?

1. How does the number of simultaneously transmitted carriers affect efficiency in FDMA systems?

1. Explain the operating principle of OFDMA. How does it differ from classical FDMA?

1. Compare the advantages and disadvantages of classical FDMA and OFDMA in broadband systems.

1. Explain how TDMA achieves separation among users. Why is synchronization essential?

1. Distinguish between synchronous and asynchronous TDMA.

1. Describe the purpose of reference bursts in a TDMA frame.

1. How does burst structure influence guard times and spectral efficiency?

1. Compare the performance tradeoffs between TDMA and FDMA in terms of latency, synchronization complexity, and amplifier constraints.

1. Explain the concept of processing gain in direct-sequence CDMA.

1. Why is CDMA considered interference-limited rather than bandwidth-limited?

1. What is the near–far problem in CDMA systems, and how is it mitigated?

1. Distinguish between synchronous and asynchronous CDMA.

1. Why does CDMA exhibit “soft capacity” rather than a fixed user limit?

1. Explain how spatial separation can serve as a multiple-access dimension.

1. Distinguish between spatial reuse and spatial multiplexing.

1. How does beamforming improve capacity and interference suppression?

1. Under what propagation conditions does spatial multiplexing (MIMO) provide capacity gains?

1. Compare pure ALOHA and slotted ALOHA in terms of vulnerable period and maximum throughput.

1. Explain how controlled ALOHA can increase throughput beyond that of slotted ALOHA.

1. Describe the principle of carrier-sense multiple access (CSMA). Why does its performance depend on propagation delay?

1. Contrast collision detection and collision avoidance.

1. Under what traffic conditions are contention-based techniques more efficient than deterministic scheduling?

1. Explain the fundamental purpose of spread-spectrum signaling. How does processing gain improve interference resilience?

1. Compare direct-sequence and frequency-hopping spread spectrum in terms of instantaneous bandwidth, synchronization requirements, and interference behavior.

1. Describe how time-hopping spread spectrum differs from TDMA and frequency hopping.

1. Explain why practical systems often combine FDMA and TDMA.

1. Describe how multicarrier techniques combine aspects of frequency partitioning and scheduling.

1. Explain the basic principle of non-orthogonal multiple access (NOMA). What role does successive interference cancellation play?

1. Discuss the primary practical challenges that limit widespread deployment of NOMA.

1. Distinguish between resource partitioning and access control. Why is this distinction important in the design of modern communication systems?

1. Compare FAMA and DAMA. Under what traffic conditions is each approach most efficient?

1. Explain how contention-based access differs fundamentally from both FAMA and DAMA in terms of performance guarantees and collision behavior.

1. Give one example for each of FDMA, TDMA, and CDMA showing how the same physical partitioning method can operate under different access-control policies.