Understanding the fundamental design philosophy and intended application of each system is a crucial prerequisite to a granular technical comparison. Each system has been architected with specific goals, whether it be maximizing robustness in mobile environments, enabling low-cost receivers, or optimizing for hybrid satellite-terrestrial networks. This section provides a concise summary of each of the five systems.

2.1 Digital System A

Digital System A, also known as Eureka 147 DAB (Digital Audio Broadcasting), is designed to provide high-quality digital audio for both satellite and terrestrial broadcasting applications. A key objective of this system is to enable the use of a common, low-cost receiver for vehicular, portable, and fixed reception. It is specifically engineered for high performance in urban environments with significant multipath and shadowing, leveraging terrestrial on-channel repeaters as “gap-fillers” to ensure consistent coverage. The system architecture supports a flexible multiplex of various services, including multiple audio programmes and associated data services.

2.2 Digital System B

Digital System B is a flexible and power-efficient system developed for digital audio and data broadcasting to fixed, portable, and mobile receivers. Originally proposed by Voice of America/Jet Propulsion Laboratory (VOA/JPL), its design prioritizes efficient use of satellite transponder power. The system uses Quadrature Phase Shift Keying (QPSK) modulation with robust error correction. To address multipath interference in terrestrial deployments, especially those using on-channel boosters, it incorporates an adaptive equaliser in the receiver. The receiver design is modular, with the expectation that low-cost consumer models can be developed.

2.3 Digital System Ds

Digital System Ds, also known as the WorldSpace system, is primarily designed to provide satellite digital audio and data broadcasting for fixed and portable reception via inexpensive receivers. It operates in the 1452-1492 MHz band and is engineered to optimize performance for satellite service delivery. This is achieved through coherent QPSK modulation, concatenated block and convolutional error correction, and linear amplification. The system allows for a flexible multiplex of digitized audio sources to be modulated onto a downlink Time Division Multiplex (TDM) carrier, with a focus on achieving low-cost production and high-quality performance.

2.4 Digital System Dh

Digital System Dh is a hybrid satellite/terrestrial system that extends the architecture of Digital System Ds to provide robust mobile reception. While the satellite delivery component is based on the same broadcast channel transport used in System Ds, it incorporates several enhancements to improve line-of-sight (LoS) reception in areas partially shadowed by obstacles like trees. The key innovation in System Dh is the addition of a terrestrial delivery component based on Multi-carrier Modulation (MCM), a technique that has gained wide acceptance for its resilience to multipath, making it ideal for pervasive mobile reception from terrestrial emitters.

2.5 Digital System E

Digital System E, also known as the ARIB (Association of Radio Industries and Businesses) system, is designed to provide satellite and complementary terrestrial on-channel repeater services for high-quality audio and multimedia data. It targets vehicular, portable, and fixed reception in the 2630-2655 MHz band. The system’s architecture is based on Code Division Multiplexing (CDM) with QPSK modulation and concatenated error correction. A primary objective in the design of System E is the achievement of low-cost production and high-quality performance through the use of state-of-the-art microwave and digital large-scale integrated circuit technology.

These foundational summaries highlight the distinct architectural choices made for each system, which will be explored in greater detail in the feature-by-feature analysis that follows.