Bridging the digital divide: The delivery of digital radio, via satellite, promises to reduce the information gap between the developing and developed worlds - Value-added Services - Brief Article

For over seven decades, most developing countries - for their radio service powered medium wave AM broadcasting. And when you consider that one million to two million people per station is a typical ratio in the developing world (combined with the fact that there is negligible alternate media choice for information) it is clear that this part of the world lags considerably behind developed nations. In developed countries, there are typically 30-50,000 people per station, with other media providing alternate choice for information. This yawning digital divide can be reduced, however, by direct satellite digital radio reception.

At the ITU WARC '79, developing countries proposed spectrum allocation for experimental satellite radio broadcasting. Although an allocation was not agreed, the initiative led to what became a decade of technical studies in the ITUCCIR leading to informed technical and economic comparative information for consideration in the potential deployment of BSS (Sound) in L and S bands. Also, by the end of that decade digital technology was already being proven beneficial for some applications.

Thus, for WARC 92, the agenda provided for consideration of spectrum allocation for satellite ORB and complementary terrestrial broadcasting (seen at the time as primarily for gap filling). WARC 92 established a worldwide allocation of 40MHz in the 1452-1492MHz frequency band, with initial systems confined to use of 1467-1492MHz under approved coordination provisions, with the remaining 15MHz to be the subject of planning considerations at a subsequent conference.

WorldSpace: a hybrid solution

The original WorldSpace design concept was for delivery of digital sound broadcasting (DSB) services via satellite far reception by inexpensive indoor/outdoor fixed and portable, personal, low cost receivers. Services are operational throughout Africa and Middle East and parts of Europe (AfriStar), as well as Asia/part Pacific (AsiaStar) and the Caribbean and Latin America (AmenStar).

The specifications have received international recognition and have been approved by the ITU as a worldwide standard for DSB, known as Digital System DS - it is a recommended preferred transmission means to portable personal receivers.

WorldSpace has also recently developed and successfully tested in South Africa and Germany a new hybrid satellite/terrestrial DSB system that has also been approved by the ITU as a worldwide standard (known as Digital System DH). This system can deliver high quality services to inexpensive receivers in moving cars, vehicles and high-speed trains in bath urban and rural areas. This technology will be used by the USA XM Radio company for delivery of Digital Audio Radio services in the US (in S-band), with royalty payments to WorldSpace.

More recently, Alcatel and WorldSpace have announced a partnership venture for L-band Satellite Digital Radio for Europe.

System overview

The WorldSpace satellite DSB system (DS) is configured to optimise performance for satellite delivery using coherent QPSK modulation with block and convolutional coding, and non-linear amplification at TWTA saturation. The system provides for a flexible multiplex of digitised audio sources to be modulated onto a downlink TDM carrier, and uses a hierarchical multiplex structure of three layers (physical, service and transport) that conforms to an OSI model.

The main features of the WorldSpace satellite DSB system are:

* each satellite has three beams;

* each L band beam covers 14-28 million square km;

* each beam has two transponders (one transparent, one with on-board processing);

* each transponder provides 96 channels operating at 16 kbps;

* channels can be multiplexed to form broadcast channels operating at 16128kbps; and

* services can be individually encrypted for pay-per-use.

Thus we can envisage the availability of some combinations of, for example, 96x32Kbps quality channels or, with adaptations, for simple crystal clear talk (16Kbps) or up to 128Kbps (CD quality) and data broadcasting and streaming to desktop PCs.

The new hybrid system uses selective combining of digital signals radiated from a satellite with the same digital signal received and repeated by terrestrial stations of a single frequency network.

The terrestrial delivery system component is based on multi carrier modulation (MCM). MCM is a multipoth-resistant orthogonal frequency division multiplex technique that has gained wide acceptance as the technique of choice for similar terrestrial communications systems. The MOM extension utilises multiple frequencies to avoid frequency selective fades, and to narrow the RF receive signal bandwidth to minimise delay spread. This modulation scheme is most suitable for reliable reception in urban mobile environments, and leads to spectrum efficient solutions when single frequency networks are used. For the WorldSpace MCM extension, a new physical layer specification has been added to the current service, transport and physical layers of Digital System DS.

The new version of the WorldSpace receiver is designed to facilitate the demodulation of both the satellite TDM and terrestrial MOM signal components. The new generation of receiver should be available from commercial production during 2003. The new system has other enhancements that improve the service quality including time (or time and space) diversity, frame interleaving, and improved coherent QPSK demodulation. It is backward compatible with the satellite only system.

WorldSpace completed final field testing of Digital System DH, including validation of the terrestrial signal for mobile reception, in Pretoria (South Africa) in October 2000, using a three transmitter single frequency network and live signals from the WorldSpace AfriStar satellite, which have validated the operating principles. The terrestrial augmentation component, Digital System DH, can now adequately meet the service requirements stipulated not just in Recommendation ITU-R BO.789, but also Recommendation ITU-R BS.774 for Satellit and Complementary Terrestrial Delivery of Digital Sound Broadcasting.

Thus greater service reliability can now be assured by overcoming problems of fading against the background for example of trees, under brides and in the built-up areas with low powered re- transmission.

To uplink to the transparent transponders of the WorldSpace satellites, a transparent feeder link station TFLS) is established within each beam area. For AsiaStar, for example, an initial TFLS has been established in Singapore. TFLS for uplinking programmes is estblished in Beijing in a joint venture or arrangement between WorldSpace and the Chinese Government entity, ChinaSat - an additional TFLS will be established in the future for the South Asia beam).

To uplink to the processe transponders of AsiaStar, small VSAT-like processed feeder link stations (PFLS) will be deployed throughout the Asian region to allow users to uplink directly from their studios to AsiaStar. A PFLS h s been established at the regional oper ting centre in Melbourne, and a larger RFLS has been cutover in Singapore.

Australia and South Pacific

The Australian government notified the DBSTAR satellite to the ITU in 1993, to reserve an orbit position (1 5 1.5[degree] 5[degree]E) for a possible satellite to provide DSB services to Australia. This notification was revised in 1999 to extend to provide coverage to three sub-regions: Australia, East Timor and Papua New Guinea; South-West Pacific; and a new ASEAN beam,

WorldSpace Asia conducted a feasibility study of using DBSTAR to provide satellite DSB services to Australia and part South Pacific in 1998, and is waiting for the Australian government to finalise its policy for the introduction of DSB in Australia. The revised DBSTAR beam arrangement is considered to enhance the economic viability of DBSTAR.

In a submission to the Parliamentary Committee into the adequacy of radio services in non-metropolitan Australia, WorldSpace-Asia (AsiaSpace Ltd) made a number of recommendations, including:

* it is important to preserve the DBSTAR satellite filing to take advantage of the benefits of satellite DSB, particularly for non-metropolitan Australia;

* satellite delivery has the advantages of coverage to all of Australia and its Territories, quicker implementation, and lower cost;

* the WorldSpace hybrid satellite/terrestrial DSB technology can provide enhanced services, including multimedia services, which can provide entertainment, education, and a range of information services, including information dissemination for emergency services; and

* it is imperative that spectrum be reserved for satellite DSB in Australia to ensure the benefits of DSB can be extended to all Australians, regardless of where they live.

The WorldSpace hybrid satellite/terrestrial DSB system could be used to provide, for example, universal coverage to Australia and its islands, which has long been a goal of national radio broadcasting policy. The system would require approximately 5MHz of L-band spectrum for the satellite and 5MHz for terrestrial augmentation (in L-band or another band) to provide coverage over the Australian Continent and its associated islands, ie a maximum of 10MHz of the 40MHz L-band allocation.

Following the three-beam concept of the existing WorldSpace fleet (providing three independent beams to the sub regions), the way is opened to bringing quality services to the zones covered by the revised DBSTAR notification. Such cooperation in common use of one satellite with independent beam coverage could provide a viable opportunity of service development -- and would prevent the disqualification of many communities from shoring in this quality service since, clearly, individual standalone satellites for each zone would not be an economic option.

WorldSpace Asia would be interested to participate in a study with others interesting in exploring the commercial feasibility of applications from the DBStar orbit position 151.5[degrees]E.

Richard Butler, former ITU secretary general

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