ISSN:0737-2884    

DOI:10.1002/sat.4600050302

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

年代:1987

数据来源: WILEY

摘要:

AbstractThis two‐part paper presents a comprehensive overview on the technology of very small aperture terminal (VSAT)‐based satellite data networks, which have received increasing attention in recent years because of a combination of technical and economic factors. Ku‐band networks with customer‐premise earth‐stations can overcome the inherent local access bottleneck in wide‐area terrestrial data networks by suitably exploiting the unique multi‐access and broadcast features of satellite communication. In this part of the paper, the issue of multiple access, which is an important critical path technology in the ongoing evolution of VSAT data networks, is considered in detail. Satellite multi‐access protocols are classified in terms of channel synchronization (slotted and unslotted) and the qualitative nature of message access (fixed assigned, contention and reservation). In addition to well known techniques such as ALOHA, slotted ALOHA, tree CRA, packet CDMA and demand assigned (DAMA) TDMA, a number of new approaches to efficient unslotted access, including selective reject (SREJ) ALOHA, time‐of‐arrival CRA and locally synchronous reservation, are discussed. The general review is followed by a detailed performance comparison of a number of candidate first‐generation VSAT protocols, namely ALOHA, slotted ALOHA, SREJ‐ALOHA, DAMA with TDMA reservation access and DAMA with slotted ALOHA reservation access. The performance evaluation, based on detailed simulations with VSAT equipment and transaction traffic parameters, is summarized by curves of average delay and throughput vs. number of VSATs per channel for each of the protocols considered. Higher‐order differences in delay performance are illustrated with appropriate delay distribution results and the sensitivity of performance with respect to key equipment and traffic parameters is investigated. For the transaction traffic model under consideration, the results suggest the use of SREJ‐ALOHA among contention techniques or DAMA with slotted ALOHA reservation among controlled access alternatives. The trade‐off between contention and reservation access is shown to be more complex, depending on the combination of average delay, peak delay, transmission cost and equipment complexity suited to the particular application.In Part IITo published in the next issueof this paper on Ku‐band VSAT networks, the issue of over

ISSN:0737-2884    

DOI:10.1002/sat.4600050303

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

年代:1987

数据来源: WILEY

摘要:

AbstractPresently, there are several countries in the process of converting their national communication system to an integrated digital communication system and eventually, to an integrated services digital network (ISDN). In some developing nations, where a satellite is used for long‐haul transmission to remote and isolated areas, and where there is no terrestrial connection to those areas, the question has been raised whether the satellite can remain a part of such a network, and if so, can it be used to synchronize the remote digital clusters.The matter of concern is the satellite's residual motion. The residual relative motion between the satellite and a ground station produces doppler and therefore, frequency shifts which may cause loss of information, the amount of doppler or carrier frequency shift is location dependent, in general it increases with station latitude and satellite inclination. However, for a given geographic area and a given accuracy in satellite station keeping, it can be shown that satellite links can provide network synchronization to remote digital clusters within the slip rate requirements of a domestic integrated services digital network. In order to permit a less stringent orbit maintenance, or to include earth‐stations of higher geographical latitudes, it is practical to include doppler buffers as part of the satellite earth‐station equi

ISSN:0737-2884    

DOI:10.1002/sat.4600050304

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

年代:1987

数据来源: WILEY

摘要:

AbstractThis paper examines the technology and constraints of very small aperture terminals (VSAT) networks, a special type of wide‐area thin‐route satellite network that represents a recent innovation in the field of satellite communications. VSAT network architectures suitable for both data and voice communications are studied in this paper. Several issues concerning the frequency of operations, that is, C‐band versus Ku‐band are examined, and trade‐offs between non‐spread spectrum and spread spectrum techniques, as well as modulation and multiple access schemes, are considered in detail. Link design examples are given to illustrate the performance of various types of VS

ISSN:0737-2884    

DOI:10.1002/sat.4600050305

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

年代:1987

数据来源: WILEY

摘要:

AbstractThe cross‐polarization, signal attenuation and boresight shift for a number of dielectric space frame (DSF) radomes have been investigated using the induced field ratio method. It is shown that DSF radomes produce substantially less cross‐polarization than their metal counterparts. It is concluded that in view of INTELSAT's specification of 30.7 dB cross‐polar discrimination within an antenna's tracking beamwidth for frequency re‐use communication system antennas, DSF radomes, in particular those considered, would not yield appreciable system degradation. The general method presented is extendable to other radomes structures provided that connectivity information is av

ISSN:0737-2884    

DOI:10.1002/sat.4600050306

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

年代:1987

数据来源: WILEY

摘要:

AbstractSeveral domestic satellite systems have been more than 10 years in operation. During this time, the world has experienced a dramatic growth in communication. While the demand for more telephony and data circuits and television channels is still on the rise, new methods of signal transmission and circuit compression have been developed which may balance or reduce the need for more satellite trunk capacity. And while whole national networks are converting to digital transmission, new transmission media like optical fibre, are finding application, and may take over some of the heavy traffic routes previously carried by satellite. On the other side, business data communication between roof‐top terminals, thin route traffic to remote users, television distribution by direct satellite broadcasting are becoming more popular and satellite land mobile communication may soon be a reality.Thus the domestic satellite's role appears to be slowly changing towards thin route and mobile traffic and DBS‐type distribution and perhaps even radio position determination. System planners are adapting to the new trends in satellite communication and are trying to accommodate the various service payloads on a single satellite.This article discusses some aspects of the emerging multi‐purpose domestic satellite, which carries fixed and mobile services, TV direct broadcasting and radio position determination, in view of network digitalization, network expansion, circuit compression, synchronization. The discussion centres on transponder supply and demand, satellite replenishment,Ku‐band vs.C‐band for TV direct satellite broadcasting, choice of modulation/multiple access for mobile communication, and expected accuracy in radio position dete

ISSN:0737-2884    

DOI:10.1002/sat.4600050307

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

年代:1987

数据来源: WILEY

摘要:

AbstractOver one hundred hours of British Telecom's half‐second event data from the OTS and ATS‐6 satellites has been analysed with respect to short‐term frequency scaling of attenuation. The ratio of attenuation at two frequencies is particularly vulnerable to system effects and noise. Data analysis techniques are discussed and it is shown that a least‐squares analysis is not suitable when the time period is short. Appreciable variation occurred in the mean value of the short‐term ratio from one event to another. Only on a few occasions did significant changes occur during an event. Simultaneous data from other equipment gives confidence that these changes are due to propagatio

ISSN:0737-2884    

DOI:10.1002/sat.4600050308

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

年代:1987

数据来源: WILEY

ISSN:0737-2884    

DOI:10.1002/sat.4600050309

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

年代:1987

数据来源: WILEY

ISSN:0737-2884    

DOI:10.1002/sat.4600050301

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

年代:1987

数据来源: WILEY