Instructions: The following questions require a comprehensive synthesis of information from the source document. Do not provide answers.

1. Compare and contrast the architectural approaches of Digital System A (using COFDM) and Digital System E (using CDM) for achieving robust reception in mobile environments. Discuss their respective methods for modulation, error correction, and handling of multipath fading.
2. Analyze the role of diversity in the systems presented in Recommendation BO.1130-4. Elaborate on the different forms of diversity (time, space, reception, frequency) mentioned for Systems B and D_H and explain how they address the specific challenges of satellite and mobile broadcasting.
3. Discuss the trade-offs between system features and receiver complexity/cost as implied by the descriptions of the five systems. How do design choices, such as the use of state-of-the-art microwave and large-scale integrated circuit technology (as in Systems D_S and E), aim to balance high performance with the goal of low-cost consumer receivers?
4. Trace the signal processing path for a single audio service in Digital System A, starting from the application layer down to the physical layer, as described in Annex 2. Detail the function of key processes such as audio source encoding, multiplexing, channel coding (convolutional encoding), interleaving, and modulation (4-DPSK OFDM).
5. Evaluate the evolution of the WorldSpace systems from Digital System D_S to the hybrid Digital System D_H. What specific technical enhancements (such as the MCM component and fast QPSK phase ambiguity recovery) were introduced, and how did they improve performance for mobile reception in areas partially shadowed by terrain and trees?