The role of vsat systems in broadband networks and intelligent networks

The scope of this paper is to present the status and the preliminary results of the research activities that Telespazio is carrying out with the aim at identifying the role of the VSAT systems in the advanced telecommunications services, which will be dominant in the second half of nineties and beyond. The first part of the paper is devoted to an overview of the evolution trend of the terrestrial networks. The main body of the paper presents the results of our investigations on the application of VSAT systems in two fields: broadband networks and intelligent networks. Background information has been intentionally added for the easier comprehension of the topics presented in the paper. A list of acronyms appears as an Appendix.     

Ku-Band satellite data networks using very small aperture terminals—part I: Multi-access protocols

This 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 II

1 To published in the next issue

of this paper on Ku-band VSAT networks, the issue of overall system design is considered.     

The development of VSAT performance standards in the United States of America

During the 1980s, when satellite communication systems and applications experienced significant growth, the Federal Communications Commission (FCC) in the U.S. recognized that special regulations were required for the licensing and operation of VSAT systems in order to maintain efficient use of the radio spectrum and geostationary orbit (GSO) and to expedite the authorization of VSAT networks featuring large numbers of earth-stations. The FSS allocated frequency bands, which are used extensively by domestic satellite communication systems in the U.S. and throughout Region 2, are in the 4–6 GHz and 12–14 GHz bands. In order to satisfy the heavy demand in the U.S. for fixed satellite services in these bands, the FCC devised an orbit plan of two degrees spacing between satellites in the relevant portion of the GSO. In a co-coverage environment, the two most important technical factors for controlling interference between neighbouring satellite systems are (1) earth-station antenna discrimination and (2) cross-polarization. Since VSAT systems, by definition, use very small aperture terminals with relatively low levels of antenna discrimination, it was necessary to establish limits for transmit power flux densities and the minimum size of antennas. These limits, based on compatible operation at two-degree satellite orbit separations, evolved into VSAT standards for the U.S. domestic satellite industry. To expedite the licensing of large numbers of VSAT terminals, conforming systems were given ‘blanket authorizations’ for all VSATs in a network. This paper traces the history of the development of VSAT standards in the U.S. and discusses the technical considerations which were used in these developments. A brief review of receive-only (RO) terminals is also provided.     

Measurements of 11 GHz attenuation using the intelsat V beacon in Indonesia

A campaign of measurements in Indonesia has been carried out according to a co-operation agreement concluded between the Indonesian and French Administrations with the aim of estimating rain attenuation on slant paths. The experiment was planned using two earth-stations, at Cibinong and Padang, both receiving a K_u-band beacon from an INTELSAT V satellite, coupled with rain-rate measurements at a number of sites. Rain-rate statistics are given for several locations in the Indonesian Archipelago. Cumulative distributions of attenuation and simultaneous rain rate, obtained at the earth-stations, are presented. The analysis of the results has led to the proposal of an adaptation of the CCIR attenuation prediction method for low latitudes.     

International standards in radio communication

A REVIEW is given of some of the international technical standards activities and Recommendations of the International Radio Consultative Committee (CCIR) for radio communications. A new Recommendation for the digital coding of television signals provides a basis for a single world standard for video signals in broadcasting studios, recording, and exchange of programs. Work is underway on high-definition television and a standard for satellite direct broadcasting downlink. Fixed satellite earth-station antenna standards (developed earlier), and performance criteria for satellite links in the integrated services digital network are being improved. Digital microwave radio relay standards include allowable bit error ratio, channel arrangements, and baseband interconnection. Mobile service Recommendations include system standards for VHF/UHF automated radiotelephony, a future global maritime distress and safety system, and radio paging codes and formats. Standards for the use of ARQ in HF and maritime communications, and the use of Universal Coordinated Time (UTC) in international telecommunications, are based on CCIR Recommendations.     

走向宽带化的VSAT卫星通信

受数据音频视频广播、计算机卫星宽带交互接入和音视频会议等业务的推动,VSAT卫星通信网向宽带业务发展巳成为必然趋势。分别对应以上业务的VSAT卫星通信网也日益趋于融合成一个统一的宽带VSAT通信网。发展宽带VSAT通信网的关键技术涉及到宽带数据广播、宽带多址接入、卫星通信规程、网络综合管理和宽带虚拟子网等。     

VSAT networks in the intelsat system

This paper describes how VSAT networks currently operate in the INTELSAT system. Four classes of VSAT networks (data transaction; circuit-switched; data distribution; microterminals) are identified, and it is verified that all of them can operate with INTELSAT satellites. Most VSAT networks in operation on INTELSAT today operate in fractional transponder leases. Fractional transponder capacity estimates are presented for a wide range of scenarios and different INTELSAT satellite series. These estimates clearly show increasing bandwidth utilization efficiencies for newer generations of INTELSAT satellites. Provided that VSAT and hub sizes are appropriately selected, efficiencies are already significant with existing satellites. Two possible ways of increasing the utilization of satellite resources are examined in the paper: demand assignment multiple access (DAMA) and multiple channel-per-carrier (MCPC) techniques. The impact of using DAMA in circuit-switched VSAT networks is quantified.     

VSAT standards,status and applications in europe

This paper is an attempt to present the current status of VSAT systems in Europe, based on two aspects. 1. The first part describes the actions conducted by the European Telecommunications Standards Institute (ETSI) for issuing proper technical standards. It is also explained how these standards are included in the general framework of the European legislation, the purpose of which is to create the conditions for a really open telecommunications market all over Europe, and more particularly to favour the implementation of independent (private) satellite communications networks, mainly for corporate services on a free competition basis, both as concerns operators and manufacturers. 2. The second part gives an overview of the actual implementation of VSAT networks in Europe and of the expected market trends.     

Effects of solar transit in Ku-band VSAT systems

Behavior of networks of very small aperture satellite terminals (VSATs) operating at Ku band during the solar transit period, is compared to more traditional C or Ku-band satellite networks. Based on analyses and experiments, it is explained why solar transit outages are rarer in Ku-band VSAT systems than conventional satellite communications systems. In many cases, Ku-band VSAT systems will operate through periods of Sun transits without any significant increase in transmission error rates or incidences of link outages     

VSAT网络实时拓扑结构与通联分析模型

以通信体制为TDM/MF-TDMA/DAMA的星形VSAT网络为研究对象,探讨了实时拓扑结构与通联分析在此类VSAT网络中的应用与实现原理,提出了基于分组的双线程分层分类参数提取方法,并采用UML面向对象的建模方法,建立了此类VSAT网络实时拓扑结构与通联分析的通用模型。     

Design and operational issues of VSAT application in ISDN-typenetworks

Advances in satellite technology in the area of very small aperture terminals (VSATs) offer economical data and voice services for corporate networks and rural applications. The authors describe VSAT application and technology with emphasis on analyzing the issues of quality after the sale. The quality and maintenance requirements of the VSAT networks in operation are defined. The reliability, maintainability, and availability calculations for VSAT networks with different topologies are evaluated. Results show that both star and point-to-point VSAT networks are capable of meeting higher availability standards     

Feedback-assisted MAC protocol for real time traffic in high rate wireless personal area networks

During the past decade, there has been much standardization effort for indoor or shot-range networks, as communication devices and applications for such networks populate. As a prominent example of these activities, the IEEE 802.15.3 Task Group (TG) published a standard for high-rate wireless personal area network (HR-WPAN). To support strictly timed multimedia services, the TG adopts a time-slotted channel access protocol controlled by a central device (DEV). Although the channel time allocation algorithm plays a key role in deciding the network performance, it remains unspecified in the standard. Therefore, in this paper, we propose a novel feedback-assisted channel time allocation method for HR-WPAN. After initial channel times are allocated based on packet inter-arrival time statistics, the allocation is dynamically adjusted by utilizing feedback information from each DEV. The feedback information includes the buffer status, the packet transmission delay, and the physical transmission rate. By utilizing this feedback information, the central DEV can allocate sufficient channel time for transmissions of pending packets from a DEV. Moreover, the allocated channel times can be synchronized to the packet arrival times so that the overall transmission delay is reduced. To cope with time-varying wireless channels, a dynamic rate selection algorithm assisted by physical layer information is proposed in this paper. Performance evaluation is carried out through extensive simulations, from which significant performance enhancements are observed.     

Spread SCPC/FDMA,spread TDMA/FDMA and SSMA/FDMA transmission through A non-linear satellite channel with an earth-station off-axis emission constraint

This paper analyses and compares possible access schemes to be used in satellite networks with a large number of small earth-stations. Basically, frequency division (FDMA), time division (TDMA), and spread spectrum multiple access (SSMA) are considered. For TDMA, one single carrier originated in one particular earth-station is transmitted in each sub-band and therefore a single-channel-per-carrier system results (SCPC/FDMA). For TDMA and SSMA, it is assumed that groups of earth-stations using either of these access schemes share the full available band in FDMA. The corresponding systems are thus TDMA/FDMA and SSMA/FDMA. Moreover, for SCPC/FDMA and TDMA/FDMA individual carriers may be spread to the extent that the available bandwidth is always fully occupied. Spectral efficiencies for these three access modes (Spread SCPC/FDMA, Spread TDMA/FDMA and SSMA/FDMA) are computed and compared for transmission through a non-linear satellite channel and optimum operating points for the non-linear amplifier are also determined. Comparisons are also performed for the situation in which transmitting earth-stations are bounded to obey an off-axis emission constraint.     

The working of the CCIR

The introduction of new technologies, the extension of radio utilisation to higher and higher frequencies and the increased use of satellite systems has necessitated the restructuring and reorganisation of the CCIR. In an endeavour to streamline the working methods and to reduce the costs of the Geneva secretariat, Study Groups will establish working parties and task groups which will have a continuing existence between Study Group meetings. Changes are also being made to CCIR publications. The author discusses these changes     

ITU-T standardization of audiovisual communication systems in ATMand LAN environments

This paper presents the ITU-T Study Group 15 development of H-series Recommendations that allow interworking between different audiovisual communication terminals manufactured by different equipment providers. The paper focuses on H.310 and H.321 systems for broad-band ATM environments and H.322 and H.323 systems for LAN environments where the quality of service may or may not be guaranteed. The paper first lists the Recommendations developed by the ITU-T for audiovisual communication systems and the network environments in which they may be used. It then describes the design philosophy, the network specific characteristics, and hardware trials for each system. Then it describes the communication control protocol defined in H.245 which is used commonly by different audiovisual communication systems. Finally, the paper discusses interworking scenarios for communication between the different types of terminal on different networks     

基于卫星数据通信网络ISBN的视频／音频多路广播

介绍ＩＰ多路广播技术在广域网中的应用，通过描述ＴＣＰ／ＩＰ协议中ＩＰ多路广播的特点和基于卫星数据网的多路广播网络结构，结合多路广播应用软件在休斯综合卫星业务图ＩＳＢＮ上的实现，提供了一种充分利用卫星通信独有的覆盖面广的广播优势和经济有效的传播多媒体信息的技术手段。     

Depolarization properties of metal space frame radomes for use in satellite communication systems

Radomes 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 antennas.     

My memory of efforts in developing CCIR Recommendation 534-3:method for calculating sporadic-E field strength

Study Group 6 of the ITU Radio Communication Sector (ITU-R, formerly CCIR) deals with ionospheric propagation. The Study Group has twelve Recommendations, among which those recommending methods for calculating and predicting radio-signal strengths are the ones that telecommunications service providers need most. Rec. 534-3, concerning the method for calculating sporadic-E field strength, is one such Recommendation. Radio-wave propagation via the sporadic-E layer (Es) was expected, during the “short-wave age”, to be a possible communications medium. But today, it is treated as a potential source of interference with television signals, because of its irregular behavior. The progress in studies of Es propagation characteristics, and the existence of data banks of f₀Es data (f₀Es is the critical frequency of the ordinary wave in vertical-incidence radio sounding), obtained through worldwide observations, made it possible to construct a prediction method with worldwide applicability. The author describes the birth of the Recommendation, and the efforts made towards its realization