ISSN:0737-2884    

DOI:10.1002/sat.4600020102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractWithin Western Europe several countries have indicated their intention to start DBS services in the 12 GHz band in 1985/6 or soon after. Against this background the European Broadcasting Union has recommended a common transmission standard known as C‐MAC/packet. An outline is given of the system, with a discussion of the requirements for a broadcasting satellite and receivers for individual receptio

ISSN:0737-2884    

DOI:10.1002/sat.4600020103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractThe paper traces the development of the market for communications and direct broadcasting satellites in Europe, since the original specification of the European Communications Satellite (ECS) in 1977. It reviews the experiments undertaken on the Orbital Test Satellite (OTS) and the way in which demonstrations with this satellite have influenced the way in which ECS is being developed.It continues by considering the impact of television on the market, first cable television and its distribution requirements, then direct broadcasting by satellite, where the introduction of homes into the customer configuration will bring with it programme content as a salient feature in market development.Finally it speculates on the possibilities for the future, both in terms of the effect of new and higher frequencies on satellite communications systems, and the possible effects that interaction from small earth‐stations could have on satellite desig

ISSN:0737-2884    

DOI:10.1002/sat.4600020104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractThe word ‘telematics’ was used for the first time in France in 1978 by Simon Nora and Alain Minc; it is a contraction of the French words ‘tétécommunications’ and ‘informatique’, and defines a marriage between computers and data transmission networks. This paper describes the five systems which will be implemented to provide telematic services via satellite in Europe during the next few years: EUTELSAT, TELECOM 1, UNISAT, DFS and ITALSAT. The main characteristics of the ‘special service’ transponders are presented, showing that, in Europe, (a) 2 to 5 transponders per satellite will be devoted to the special (telematic) services; (b) 4 satellites out of the 5 use the 12.5–12.75 GHz down‐link band for this purpose (only ITALSAT uses the 20 GHz down‐link for the same purpose), and (c) e.i.r.p.s at 12 GHz are in the range 40–49 dBW.The ground and space segments corresponding to this new service are presented. The main peculiarity of the ground segment is the exclusive use of ‘small’ earth‐stations equipped with fixed antennas and SCPC or 25–60 Mb/s TDMA multiple access equipment. Telematic services include videoconference at 2048 kb/s, voice services, computer‐to‐computer transfer of data, data distribution, remote printing, electronic mail, high‐speed facsimile, offshore voice and data services, digital network overflow, transatlantic digital business etc…Customer bit rates start from 2.4, 4.8, 9.6 and 32 kb/s (for TELECOM 1) up to 2048 kb/s by 64 kb/s steps. Bit error rates are maintained below 10−6(standard) or 10−10(higher grade) during 99 per cent of the year using FEC. The five networks for telematics via satellite in Europe are independent. A large efficiency improvement of the different services should be obtained through a future interconnection of

ISSN:0737-2884    

DOI:10.1002/sat.4600020105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractA condensed orbital history, from mid‐1965 to mid‐1983, of the satellites in the INTELSAT system is presented in the form of a chart; this shows both the operational duties which the satellites performed and the occurrence of incidents which affected their performance in or

ISSN:0737-2884    

DOI:10.1002/sat.4600020106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractThis is Part One of a two‐part article on the current status of INTELSAT's leased services, a relatively unfamiliar subject when compared with INTELSAT's standard communications services.In Part One, domestic service and international television service will be covered. For both services, statistics on existing and planned levels of use will be provided. Key aspects of the terms and conditions governing the lease will be outlined, and the annual charges summarized. The variety of services possible when using these leases, and the earth station networks chosen by users to meet their communications goals are also described.A brief look at the future of these two services will be given, and the topics of Part Two. INTELSAT Business Service (IBS), and the low‐density telephony service (VISTA) will be introdu

ISSN:0737-2884    

DOI:10.1002/sat.4600020107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractDemands for increased channel capacity in future communication satellite systems coupled with basic limitations in terms of satellite power and frequency spectrum will lead to requirements for advanced multiple‐beam antenna systems with frequency re‐use capability.This paper describes the results of a study of multiple‐beam antenna systems suitable for an advanced European business services satellite. Initially, background work is described which serves to define the overall system, analyse the link performance and specify the antenna requirements. A generalized parametric study of the capabilities of a model antenna is discussed to set the bounds of feasibility, as it was appreciated that some specification targets might prove impossible to attain. In parallel, a comparative survey of a wide range of antenna types is presented to determine the most promising configurations. Based on these two outputs, candidate antenna configurations are analysed in detail to predict accurately the capability of the more promising antenna types to meet the range of performance objectives. Finally, detailed electrical design studies are performed for specific example mis

ISSN:0737-2884    

DOI:10.1002/sat.4600020108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractRadomes have traditionally only been used in military satellite systems. However, higher availability civil applications are demanding their consideration in the higher frequency bands and for dualpolarization frequency re‐use systems. This paper investigates the depolarization performance of metal space frame radomes and presents results of XPD for radome covered antennas in the 4/6 and 11/14 GHz bands and for antennas of 30, 11, 5 and 3 m diameters. It is demonstrated that current polarization specifications adopted in the INTELSAT system should be able to be met by radome covered earth‐stations using conventional anten

ISSN:0737-2884    

DOI:10.1002/sat.4600020109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractThe results of six experiments to measure 6/4 GHz signal depolarization are presented. The measurement sites varied from the tropics to 57°N latitude and elevation angles between 12° and 38° were employed. In two of the experiments, simultaneous measurements at 6 GHz and 4 GHz were made along the same path to measure the correlation between the depolarizations occurring at the two frequencies.It was found that, in all cases, rain was the dominant depolarizing mechanism. Where the occurrence of ice depolarization was significant the magnitude of the ice depolarization occurring was not system limiting on a statistical basis. The correlation between up‐link and down‐link depolarization occurring along the same path was found to be very good both on an instantaneous basis and a statistical basis. The use of open‐loop up‐link depolarization compensation mechanisms should therefore be feasible. An examination of the depolarization fluctuation spectra obtained in some severe depolarizing events during one of the experiments would indicate that the settling time for such a mechanism should be on the order of 1 s. The use of simple, ‘non‐perfect’, depolarization compensation mechanisms allied to a low‐cost, spectrally efficient FEC system may prove to be the best compromise in some locations that experience sev

ISSN:0737-2884    

DOI:10.1002/sat.4600020110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractThe problem of pulse code modulation (PCM) bit errors causing voice frequency (VF) modem errors has been studied in detail. The error mechanism consists of the addition of an impulse response type error signal added to the reconstructed VF data signal waveform at the digital‐to‐analogue (D/A) output of the PCM decoder. This error signal may cause a burst of errors registering in the VF modem receiver, depending on which PCM bit is in error.Numerous data have been collected in a laboratory experiment and analysed in various ways. The average bit error rate (BER) enhancement factor of VF data over PCM is between 10 and 20. For each PCM bit in error, an average of two VF data bits are in error. The analysis leads to suggestions for possible solutions to the prob

ISSN:0737-2884    

DOI:10.1002/sat.4600020111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY