Flight 2 version of in-orbit test transponder (IOTT2) for on-board regenerative satellites

This paper presents the design and realization of regenerative satellite on-board bypass test equipment. Furthermore, two particular examples of an in-orbit test transponder (IOTT) are discussed in detail. The IOTT1, developed for the first 30/20 GHz ITALSAT satellite (F1), was launched in January of 1991. IOTT1 has been a useful tool during satellite assembly, integration and pre-launch tests. IOTT1 was successfully used to fully characterize the multibeam ITALSAT satellite in orbit. In general, the IOTT functions to bypass the demodulator, the baseband switchboard and the modulator of the multibeam package of the ITALSAT spacecraft payload, providing the ability to fully characterize the satellite's transponders using well-established IOT test techniques. This paper describes and compares the design, fabrication and test of both ITALSAT in-orbit test RF bypass transponders (IOTT1 and IOTT2) mounted on board the ITALSAT multibeam spacecraft, (F1) and (F2), respectively. The IOTT1 contains the first MMIC circuitry ever launched into space on a communications satellite. The improved IOTT2, fabricated for the second 30/20 GHz ITALSAT satellite (F2), is schedule for launch in early 1996. These fully space-qualified designs incorporate COMSAT Laboratories' designed and fabricated MMIC K_u-band amplifiers, lightweight waveguide K_u-band channel filters and electronic power conditioner (EPC) and combined IOTT telemetry/command (T&C) circuitry.     

Digital satellite networks in Europe

Developments of digital satellite networks are progressing in Europe at international as well as national levels. EUTELSAT and its signatories are actively setting up two regional networks based on the ECS satellites built by ESA. One will carry large bundles of telephone circuits between national gateways; the other will provide special services to corporate organizations and businesses. On the other hand, several countries are implementing or planning their own national networks, all for small-station services. These are France with Telecom 1, Sweden with TELE-X, Norway with NORSAT II, Italy with ITALSAT, the Federal Republic of Germany with DFS/Copernicus, and the United Kingdom with UNISAT. These projects are described here and their characteristics compared. The paper brings out the great diversity in the approaches, as illustrated by Telecom 1 where the accent is on the development of an ISDN, TELE-X where it is on the low cost of user stations, and ITALSAT on the flexibility of the network.     

Frequency diversity and its applications

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.     

Personal communications via iNTELSAT Ku-band transponders

The concept of a fully meshed network of very small terminals is presented for personal communications over K_u-band satellite transponders. In this concept, undesirable double-hop delays are avoided for voice communications between these terminals. The bandwidth and power resources of the transponder are efficiently shared by users in a simple demand-assigned manner via code-division multiple access (CDMA).^1,2 Voice, data and facsimile are statistically multiplexed at each terminal. In order to minamize terminal costs, frequency-precorrected and level-preadjusted continuous wave (CW) tones are sent from the central network control station in each beam. The terminals in each down-link beam can use these pilots as references for antenna acquisition and tracking, as reliable frequency sources, and as indicators of signal fade for up-link power control (ULPC). The potential CDMA ‘near-far’ problem due to up-link fades is mitigated by using ULPC. Quasi-burst-mode transmission is employed to minimize the potential loss of clock and pseudorandom number code synchronization. When these terminals are used only to interconnect into the public switched telephony networks (PSTNs) through large, hub-like gateway stations, they can employ flat-plate antenna technology. The complete terminal can thereby be packaged into a briefcase so that it is easily transportable for personal use.     

European research on Ka-band slant path propagation

Europe saw two major initiatives in the mid-1980's to verify the viability of 20-50 GHz frequency bands for high capacity radio transmission. The first was the experimental telecommunication satellite OLYMPUS commissioned by the European Space Agency; the second was the ITALSAT program planned by the Italian Space Agency. Both spacecraft were equipped with highly stable propagation beacon payloads for accurate measurement of propagation conditions. Two international groups of experimenters (OPEX for OLYMPUS and CEPIT for ITALSAT), who had agreed on a set of common procedures for the earth stations' design, experiment management, and comparison of results, carried out the propagation measurements in a collaborative manner. This paper gives a summary of these activities and their results     

Satellite spacing and frequency sharing for communication and broadcast services

Satellite relays complicate the problem of sharing a limited frequency spectrum that is in great demand. This paper reviews the problem and outlines a general approach for efficient use of orbits and spectrum. The protection of received signals, the equipment capabilities, and systems considerations pertinent to the problem are reviewed before systematically examining the principal direct and scatter modes of interference. Conclusions derived include the following. The full potential use of orbits and spectrum for satellite systems can provide enormous capacities greatly exceeding any current proposals, but it requires careful coordination of many system parameters. The use of spectrum for microwave or satellite relays to fixed terminals could evolve to intense full sharing by both types of service without seriously limiting either one or requiring unreasonable accommodation. The satellite down links for area coverage to small terminals (e.g., mobile and broadcast services) can share fully and intensively the spectrum above VHF that is used for terrestrial mobile and broadcast services without seriously limiting the potential of any of the services. Although the greatest potential capacity of the spectrum lies above 16 GHz, for most down-link applications propagation factors make it more attractive to share the spectrum below about 16 GHz much more intensively before making extensive use of the higher frequencies. Providing the satellite down-link spectrum for area coverage to small terminals deserves priority consideration. For this purpose the UHF band is most attractive; the merit of the spectrum rapidly diminishes for higher frequencies.     

A Wide-Band Satellite Microwave Switch Matrix for SS/TDMA Communications

A lightweight, broad-band, 8 × 8 crossbar microwave switch matrix (MSM) has been developed for satellite-switched timedivision multiple-access (SS/TDMA) operation anywhere in the 6 GHz up-link and/or 4 GHz down-link bands. The nearly transparent performance characteristics in the 3.5-6.5 GHz band, for any of the highly flexible interconnect possibilities, have been facilitated by the design of a low-power-consuming resistively matched PIN diode switch. Broad-band push-pull connectors are used to simplify assembly and disassembly of this modular three-dimensional matrix. The switch control electronics (SCE) circuits have been implemented as custom-designed LSI chips for integration within the MSM input distribution networks. Design considerations and performance characteristics of the satellite switch matrix are presented.     

Up-link power control of satellite earth-stations as a fade countermeasure of 20/30 GHz communications systems

All 20/30 GHz satellite communications systems suffer from atmospheric attenuation in cloudy or rainy weather, particularly if high link availabilities are required. In FDMA systems the power transfer characteristic of each carrier is linear, so any up-link fade degrades the overall performance on a dB-by-dB basis. This, together with the fact that the 30 GHz up-link attenuation is much greater than the 20 GHz down-link attenuation, makes adaptive countermeasures of up-link fades most important. This paper shows how the overall link performance can be improved by applying up-link power control. It is explained how this improvement depends on the up-link/down-link balance, the dynamic range of the up-link power control, and the up-link and down-link atmospheric attenuation. If a small number of carriers can be allocated in an intermodulation-free frequency plan, the satellite transponder can be operated near saturation in order to optimize the down-link performance. Computer simulations of up-link power control for such an FDMA scheme have been performed based on measured three-carrier characteristics of a transponder TWT. It is shown that the overall link performance in faded conditions can be significantly improved with up-link power control. This may be utilized to increase the availability of a satellite link or to relax the earth-station performance in terms of G/T or EIRP if the link margin provided by an earth-station with fixed EIRP is satisfactory.     

快速发展的蜂窝网通信和卫星通信

主要说明无线通信将应用于移动通信、个人通信和全球通信。数字蜂窝网将增设微蜂窝区 ,频率从 90 0MHz升至 1 .8～ 2GHz ,向宽带和多媒体方向发展 ,数据速率从 1 44kb /s升至 2Mb /s。手机将是TDMA /CDMA双模。蜂窝网不仅用于移动通信 ,而且用于固定用户的市内接入网。卫星通信将加快发展低轨道 /中轨道卫星通信网 ,而同步卫星仍需利用。移动卫星网可通电话 ,可进行多媒体通信 ,速率为 2Mb /s,并通过地面信关站 ,与陆地固定通信网结合一起 ,实现全球个人通信。     

Transmission of group 3 facsimile over inmarsat maritime digital satellite mobile channels

The importance of facsimile communication over public telephone networks is evidenced by the rapid growth in the number of Group 3 facsimile end-user terminals. In this paper the main characteristics of a real-time bit-rate reducing approach are described whereby facsimile signals are demodulated and their associated protocols converted by a facsimile interface unit (FIU) to a format suitable for transmission over Inmarsat-B maritime digital satellite channels. The FIU concept was developed to allow ‘off-the-shelf’ facsimile terminals to be interconnected via the PSTN through Inmarsat's satellite networks and to permit the provision of enhanced user services by converting Group 3 facsimile protocols to broadcast operation. In addition, the FIU concept is designed to compensate for the longer access and transport link delays encountered in mobile satellite systems, and to permit facsimile call recovery procedures to be successfully concatenated with satellite channel error detection mechanisms.     

Load balancing multipath routing protocol for mass remote sensing data downlink in LEO satellite network

LEO satellite networks can provide seamless real-time data communication for all kinds of users,which developed rapidly in recent years.At the mean time,the massive payload data down-link system of space data sources,such as remote sensing satellites,still make use of traditional storage and forward mode.The real-time performance of space mission data will be improved effectively,if such satellites are connected to LEO satellite networks equipped with inter satellite links.However,it is necessary to design a specialized satellite network load balancing routing algorithm.Satellite parallel edge-disjoint multipath routing protocol (SPEMR) was designed for remote sensing satellite real-time down-link applications.OPNET simulation results indicate that the performance degradation index(DI) of the multipath scheme implemented by SPEMR is 0.32,which is only 32% of the TLR and 21% of the traditional DSP scheme.It is demonstrated that SPEMR has the better capability of transmitting massive data in real time.     

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.     

A wireless multimedia framework for the management of emergency situations in automotive applications: The AIDER system

Automotive applications would greatly benefit of multimedia telematic services for many purposes, from tourism and entertainment, to most important issues such as security and traffic management. Within this context, the AIDER system (AIDER is the acronym of Accident Information and Driver Emergency Rescue) is one of the most advanced multimedia mobile services targeted at emergency situations such as road accidents. The AIDER allows the interactive exchange of multimedia data (and in particular, audio, video and biomedical information) between the vehicle and a remote rescue centre, by using several different narrowband radio channels including cellular networks and satellite. In this paper an overview of the AIDER architecture is provided, focusing on the advanced video communication system.     

Predicting Antenna Noise Temperature Due to Rain Clouds at Microwave and Millimeter-Wave Frequencies

Model-oriented methods to predict antenna noise temperature due to rainfall along slant paths are developed and illustrated for communication systems at Ka-band and above. The adopted Sky Noise Eddington Model (SNEM) relies on an accurate analytical solution of the radiative transfer equation and on stratiform and convective rainfall stratified structures, synthetically generated from cloud-resolving model statistics. The approach to predict antenna noise temperature is based on the multiple regression analysis, trained by SNEM-derived cloud radiative data sets, and can handle either slant-path attenuation or columnar liquid water or rain rate as input predictors. Statistical scaling with respect to frequency and zenith angle is also analyzed and modeled in the microwave and millimeter-wave range. In order to test the proposed prediction technique, measurements of the ITALSAT satellite ground-station at Pomezia (Rome, Italy) are taken into consideration for two case studies. Combined data from the ITALSAT three-beacon receiver at 18.7, 39.6, and 49.5 GHz and from a three-channel microwave radiometer at 13.0, 23.8, and 31.6 GHz are processed. Results are shown and discussed in terms of antenna noise temperature estimation by using the satellite-beacon path attenuation as predicting variable.     

Trunking of TDM and narrowband services over IP Networks

The recent interest in IP as the vehicle for transporting TDM and narrowband services stems from the possibility of using a common transport network for voice, video, and data, and the flexibility with which new services can be introduced. A key step in the evolution of networks towards a ‘broadband’ IP‐based environment is the ‘graceful’ interworking of the IP networks with the existing networks and services, particularly with the circuit switched telephone network. A ‘graceful’ interworking approach is one whose complexity is minimal and preserves the user's perceived quality of service (QoS). To interwork with a circuit switched network whose services are pre‐dominantly time‐sensitive, the IP network must essentially behave as a transparent ‘link’ in the end‐to‐end connection. This paper presents an overview of the main technical problems to be addressed when trunking TDM and narrowband services over IP networks. Copyright © 2002 John Wiley & Sons, Ltd.     

Telecommunications services in China

An overview of telecommunications services in the public switched telephone network (PSTN) and public switched packet data network (PSDN) in China is presented. Public telephone, data, telegraph, telematic, and future directory services provided by these networks are discussed     

Performance analysis and measurement of a saw-based group demodulator for on-board processing in communications satellites

Future satellites for ‘thin route’, mobile and portable services will require group demodulators on board the satellite to take advantage of the cost benefits offered with regenerative architectures. The demodulators will translate FDMA up-links into TDM down-links. This paper describes the measured performance of a 24-channel multi-carrier (64 kb/s QPSK for each carrier) group demodulator which uses SAW chirp Fourier transform (CFT) processing. The recovered data are combined into a single TDM bit stream at the standard T1 rate of 1.544 Mb/s. The 40 dB side-lobe suppression obtained in the CFT has resulted in less than 0.35 dB combined interference degradation achieved with all channels active. The added degradation over Olympus with a saturated up-link amplifier is less than 1 dB.