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Wideband communication (WC) is considered with reference to the general architecture of the public communication network. Two aspects of WC are discussed: wideband transmission within the network (linked to the traffic intensity to be dealt with) and wideband communication in the user access area (linked to the introduction of wideband services). In regard to the first aspect, the evolution of cable transmission (copper and optical fibers), radio relays, and satellite systems is considered: the main limitations on the transmission capacity are discussed with particular emphasis on transmission capacity per carrier. In regard to the second aspect, the possible wideband services are reviewed as requested by (or offered to) the business user and domestic users. Again, the possibility of using cable, radio, or satellite to reach the user is examined. WC within local area networks is discussed. >

Adaptive shared resource methods may be the only available effective countermeasure to rain-induced attenuation in satellite communication systems above 20 GHz. Two of these methods, frequency diversity (FDV) and burst length control (BLC) are examined and compared by using a unified approach. The fundamental statistical relationships between unassisted and assisted conditions are derived, and optimum values are identified. It is found that BLC (which improves power margins) is easier to implement than FDV, but FDV (which improves outage probability and retains most of its advantages at higher frequencies) is more effective in reducing built-in power margins in ‘unassisted’ conditions. From a large database at 11.6 GHz collected in the Sirio experiment, some realistic FDV results are derived for systems using 20/30 GHz bands for unassisted conditions and 12/14 GHz bands for assisted conditions. As the ESA Olympus satellite will carry both 20/30 GHz and 12/14 GHz transponders, an FDV experiment with Olympus has been proposed by CSTS; the characteristics of the three earth-stations planned to be built in Italy for the experiment are described.

The results of a campaign of attenuation measurements carried out by means of the Italian satellite SIRIO at the two frequencies 11.6 and 17.8 GHz are presented. The campaign lasted five years (1978- 1982) and yielded almost continuous measurements at the lower frequency (acquired in three Italian stations) and measurements for a considerable fraction of time at the higher one (acquired in two of the three stations). The major aim of these measurements was to acquire long-term statistics to be employed in future earth-space radiolink design. This objective has been fully accomplished, owing to the very long life of the satellite, and the acquired data have been already utilized, properly extrapolated in frequency, for designing the domestic satellite system Italsat planned to start in 1987. Year-to-year and site-to-site variation have been found to be very high. Conversely the ratio between equiprobable values of attenuation at the two frequencies has proved to be very similar in the two stations and rather stable across the attenuation range.

Publisher Summary This chapter provides an overview of the features and the objectives of the Italian Sirio satellite program and the characteristics of its systems. The principal objective is to investigate the applicability of frequencies above 10 GHz to satellite communication systems through an SHF propagation and communication experiment. Sirio is a spin-stabilized geostationary satellite with a mechanically despun antenna for the propagation and communication experiment. The nominal spin rate is 90 rpm. The Sirio program is developed in the frame of the Italian space program by the Consiglio Nazionale delle Ricerche (CNR). Project management is at the Servizio Attivita Spaziali (SAS) of CNR, while the experimental activity is under the scientific direction of the Centro Telecomunicazioni Spaziali of CNR at the Politecnico di Milano. Prime contractorship for the Sirio satellite has been entrusted to Compagnia Industriale Aerospaziale while the contractorship for the Sirio Operation Control Center and for the Sirio SHF ground stations has been entrusted to Telespazio. Telespazio is also giving technical and administrative assistance to CNR for the development of the program. NASA will take care of the satellite launch.

A procedure for the design of nearly optimum unconditionally stable phase-lock (PL) demodulators is given. The various noise contributions at threshold are investigated and procedures to reduce the noise due to losses of lock are discussed. Experimental results of a nearly optimum 24-telephone-channel PL demodulator equipped with a particular type of threshold noise compensator are given.

Publisher Summary This chapter provides an overview of the features and the objectives of the Italian Sirio satellite program and the characteristics of its systems. The principal objective is to investigate the applicability of frequencies above 10 GHz to satellite communication systems through an SHF propagation and communication experiment. Sirio is a spin-stabilized geostationary satellite with a mechanically despun antenna for the propagation and communication experiment. The nominal spin rate is 90 rpm. The Sirio program is developed in the frame of the Italian space program by the Consiglio Nazionale delle Ricerche (CNR). Project management is at the Servizio Attivita Spaziali (SAS) of CNR, while the experimental activity is under the scientific direction of the Centro Telecomunicazioni Spaziali of CNR at the Politecnico di Milano. Prime contractorship for the Sirio satellite has been entrusted to Compagnia Industriale Aerospaziale while the contractorship for the Sirio Operation Control Center and for the Sirio SHF ground stations has been entrusted to Telespazio. Telespazio is also giving technical and administrative assistance to CNR for the development of the program. NASA will take care of the satellite launch.

Publisher Summary This chapter provides an overview of the features and the objectives of the Italian Sirio satellite program and the characteristics of its systems. The principal objective is to investigate the applicability of frequencies above 10 GHz to satellite communication systems through an SHF propagation and communication experiment. Sirio is a spin-stabilized geostationary satellite with a mechanically despun antenna for the propagation and communication experiment. The nominal spin rate is 90 rpm. The Sirio program is developed in the frame of the Italian space program by the Consiglio Nazionale delle Ricerche (CNR). Project management is at the Servizio Attivita Spaziali (SAS) of CNR, while the experimental activity is under the scientific direction of the Centro Telecomunicazioni Spaziali of CNR at the Politecnico di Milano. Prime contractorship for the Sirio satellite has been entrusted to Compagnia Industriale Aerospaziale while the contractorship for the Sirio Operation Control Center and for the Sirio SHF ground stations has been entrusted to Telespazio. Telespazio is also giving technical and administrative assistance to CNR for the development of the program. NASA will take care of the satellite launch.

The rapidly increasing demand for communication through satellites requires a more efficient use of the bands presently available and of course the use of new frequency bands, e.g. of the bands above 10 GHz. The increasing demand referred to above is due not only to traffic increase on intercontinental routes, but also to the foreseen use of satellites for regional communication systems. The latter are characterized by a still higher request of telephone channels and by a regular requirement for television transmission, in the form of distribution or broadcasting.

The importance of using frequencies above 10 GHz in satellite communication systems arises partly from the saturation of the bands presently in use. In addition, above 10 GHz, frequency bands have been specifically assigned to satellite communication systems, allowing earth stations to be located more freely, particularly near or within the cities. Directive multibeam antennas are also more easily realizable on board the satellites. These advantages are of particular relevance for domestic satellites. On the other hand, the propagation of such frequencies is mainly affected by rain attenuation.