Answer Key
- The primary recommendation is that Digital Systems A, B, D<sub>S</sub>, D<sub>H</sub>, and E can be used for satellite digital sound broadcasting services to vehicular, portable, and fixed receivers in the 1 400-2 700 MHz frequency range. It also recommends that administrations wishing to implement Broadcasting-Satellite Service (BSS) (sound) should use the provided tables to evaluate the merits of each system against their specific requirements.
- The five systems are Digital System A, B, D<sub>S</sub>, D<sub>H</sub>, and E. All five systems are intended for vehicular, portable, and fixed receivers for digital sound broadcasting services, although Digital System C is noted as being for terrestrial use only.
- Digital System A is specifically designed for multipath operation. It works on the basis of a power summation of echoes falling within a given time interval and allows the use of multiple on-channel repeaters to cover shadowed areas, improving reception in urban and challenging environments.
- Digital System B uses several mitigation techniques for signal blockage. These include time diversity (retransmission), reception diversity (using two separated antennas), and transmission diversity (transmitting the same data stream on separate frequencies), which are implemented as add-on processing functions in the modular receiver.
- Digital System D<sub>S</sub>, also known as WorldSpace system, is primarily designed to provide satellite digital audio and data broadcasting for reception by inexpensive fixed and portable receivers. The system uses ISO/MPEG Layer III as its audio coding algorithm, supporting various bit rates and quality levels.
- Digital System D<sub>H</sub> is a hybrid satellite/terrestrial system that extends the structure of Digital System D<sub>S</sub>. It adds a terrestrial delivery component based on Multi-carrier modulation (MCM), allowing it to re-radiate the satellite signal terrestrially to improve reception in urban areas and other places where the satellite signal may be blocked.
- In Digital System E, gap-fillers are used to retransmit the satellite signal to cover areas blocked by obstacles like buildings and large constructions. There are two types: direct amplifying gap-fillers for smaller areas and frequency conversion gap-fillers for larger areas up to a 3 km radius.
- Mode I is for terrestrial single-frequency networks (SFN) and allows the greatest transmitter separations. Mode II is for local radio applications requiring one terrestrial transmitter or for hybrid satellite/terrestrial transmission up to 1.5 GHz. Mode III is most appropriate for satellite and complementary terrestrial transmission at all frequencies up to 3 GHz and is the preferred mode for cable transmission.
- Digital System A offers a data rate from 8 to 384 kbit/s per audio channel and uses the MPEG-2 Layer II audio codec. In contrast, Digital System B provides a data rate from 16 to 320 kbit/s per audio channel and uses the Perceptual audio codec (PAC).
- Multi-carrier modulation (MCM) is a multipath-resistant orthogonal frequency division multiplex technique that has gained wide acceptance for terrestrial emitters. Digital System D<sub>H</sub> extends the system structure of Digital System D<sub>S</sub> by adding a terrestrial delivery component based on MCM, which is a standard utilized for terrestrial digital audio broadcast services like Digital System A.