Chapter 7 / 7.10

7.10 REVISION QUESTIONS

1. Draw and explain the block diagram of an FDM system including transmitter and receiver.

1. Explain why FDM is well suited to analog signals.

1. Why is SSB modulation commonly used in FDM systems?

1. What is the purpose of guard bands in FDM, and how do they influence system bandwidth? Derive the expression for the total transmission bandwidth of an FDM system comprising N channels.

1. Explain the roles of CTE, GTE, and STE in FDM.

1. Compare the ITU and AT&T FDM hierarchies in terms of channel grouping and scalability.

1. Draw and explain the block diagram of a TDM system, identifying the functions of the input and output commutators.

1. Why must input signals in a TDM system be band-limited prior to sampling?

1. State and explain the Nyquist sampling criterion and its significance in TDM systems.

1. Derive the relationship between channel bandwidth and the number of multiplexed channels in a TDM system.

1. Explain why synchronization is critical in TDM systems and describe the consequences of loss of synchronism.

1. Describe STDM and describe how it differs from synchronous TDM.

1. Explain why STDM is particularly well suited to data communications but less appropriate for delay-sensitive real-time voice without additional QoS mechanisms.

1. Describe bit-oriented and byte-oriented multiplexing and distinguish between them.

1. Explain why modern high-speed transport systems (e.g., SONET/SDH, Ethernet) favor byte-oriented multiplexing.

1. A synchronous TDM system has 16 channels but only 6 are active at a given time. Explain qualitatively how STDM could improve bandwidth utilization in this scenario.

1. Briefly compare and contrast FDM and TDM.

1. Compare the E-carrier and T-carrier systems in terms of frame structure, bit rate, and signaling.

1. What is meant by plesiochronous operation, and why does it present challenges at higher bit rates?

1. Explain why the limitations of plesiochronous TDM (PDH) systems motivated the development of SONET and SDH.

1. Distinguish between SONET and SDH and explain why they are considered interoperable.

1. List two operational advantages of SONET/SDH for large-scale optical networks.

1. What is WDM, and how does it relate conceptually to FDM?

1. Compare CWDM and DWDM in terms of channel spacing, typical applications, system cost, and channel count.

1. Briefly describe OFDM and explain how OFDM combines aspects of TDM and FDM.

1. Why does OFDM reduce sensitivity to inter-symbol interference compared with single-carrier systems?

1. Explain why channel equalization is simpler in OFDM than in high symbol-rate single-carrier systems.

1. Describe the purpose of pilot symbols in OFDM and how they are used for channel estimation.

1. Compare FDM, TDM, WDM, and OFDM in terms of bandwidth efficiency, implementation complexity, and typical applications.

1. Explain why TDM is generally preferred for centralized digital traffic aggregation, while FDM can be advantageous for geographically distributed terminals.

1. Discuss the economic advantages of upgrading network capacity using WDM rather than installing new fiber.

1. Define SDM. How does it differ conceptually from FDM, TDM, and WDM?

1. Explain why SDM does not require additional spectrum to increase capacity. Under what propagation conditions can capacity scale approximately linearly with the number of antennas?

1. Distinguish clearly between spatial multiplexing and spatial diversity. What performance objective does each technique primarily address?

1. Explain the role of multipath propagation in MIMO systems. Why are rich scattering environments advantageous for spatial multiplexing?

1. How do phased-array antennas and beamforming contribute to SDM? What is meant by achieving orthogonality through directional isolation?