bluuebunny/crossref_metadata_2025 huggingface dataset:
Schmorl's nodes: clinical significance and implications for the bioarchaeological record
Authors: Faccia K. J. , Williams R. C.
Published: July 2007

Back pain is one of the major contributors to disability and loss of productivity in modern populations. However, osteological correlates of back pain are often absent or, as yet, unidentified. As bioarchaeologists depend on osteological evidence to interpret quality of life in the past, back pain, with its profound effects on modern populations, is largely overlooked in archaeological samples. This study addresses this shortcoming in bioarchaeological analysis by exploring the relationship between a defined vertebral osteological lesion, the Schmorl's node, and its effect on quality of life in a clinical population. Using patient insight, healthcare practitioner diagnoses and MR imaging analyses, this study investigates: (1) Schmorl's nodes and sociodemographic factors; (2) the number, location and quantitative aspects (e.g. length, depth, area) of Schmorl's nodes, and how these influence the reporting of pain; (3) the dynamic effects of Schmorl's nodes, in combination with other variables, in the reporting of pain; and (4) the perception and impact of pain that patients attribute to Schmorl's nodes with regard to quality‐of‐life issues. The results of this study indicate that Schmorl's nodes located in the central portion of the vertebral body are significantly associated with patient reporting of pain, and that the presence of osteophytes, in the affected vertebral region, may increase the likelihood that an individual will report pain. This finding provides bioarchaeologists with an osteological correlate to begin interpreting the presence and impact of pain in archaeological populations, with implications for scoring Schmorl's nodes. Copyright © 2007 John Wiley & Sons, Ltd.
In vitro amplification and detection of variant Creutzfeldt–Jakob disease PrPSc
Authors: Jones M , Peden AH , Prowse CV , Gröner A , Manson JC , Turner ML , Ironside JW , MacGregor IR , Head MW
Published: July 2007

Variant Creutzfeldt–Jakob disease (vCJD) poses a serious risk of secondary transmission and the need to detect infectivity in asymptomatic individuals is therefore of major importance. Following infection, it is assumed that minute amounts of disease‐associated prion protein (PrPSc) replicate by conversion of the host cellular prion protein (PrPC). Therefore, methods of rapidly reproducing this conversion process in vitro would be valuable tools in the development of such tests. We show that one such technique, protein misfolding cyclic amplification (PMCA), can amplify vCJD PrPSc from human brain tissue, and that the degree of amplification is dependent upon the substrate PRNP codon 129 polymorphism. Both human platelets and transgenic mouse brain are shown to be suitable alternative substrate sources, and amplified PrPSc can be detected using a conformation‐dependent immunoassay (CDI), allowing the detection of putative proteinase K sensitive forms of PrPSc. Copyright © 2007 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
A starlike amphiphilic graft copolymer with hydrophilic poly(acrylic acid) backbones and hydrophobic polystyrene side chains
Authors: Peng Dan , Feng Chun , Lu Guolin , Zhang Sen , Zhang Xiaohuan , Huang Xiaoyu
Published: July 2007

A well‐defined starlike amphiphilic graft copolymer bearing hydrophilic poly(acrylic acid) backbones and hydrophobic polystyrene side chains was synthesized by successive atom transfer radical polymerization followed by the hydrolysis of poly‐(methoxymethyl acrylate) backbone. A grafting‐from strategy was employed for the synthesis of a graft copolymer with narrow molecular weight distribution. Hydrophobic polystyrene side chains were connected to the backbones through stable CC bonds. The poly(methoxymethyl acrylate) backbones can be easily hydrolyzed with HCl without affecting the hydrophobic polystyrene side chains. This kind of amphiphilic graft copolymer can form stable sphere micelles in water. The sizes of the micelles were dependent on the ionic strength and pH value. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3687–3697, 2007
Screening for mental disorders in laryngeal cancer patients: a comparison of 6 methods
Authors: Singer Susanne , Danker Helge , Dietz Andreas , Hornemann Beate , Koscielny Sven , Oeken Jens , Matthäus Christoph , Vogel Hans‐Joachim , Krauß Oliver
Published: July 2007

Objectives: The aim of this study was to determine how accurate mental distress screening instruments are in identifying psychological sequelae in ambulatory laryngeal cancer patients who have undergone surgery.

Methods: Two‐hundred and fifty subjects were tested for mental disorders according to the guidelines defined in the Diagnostic Statistical Manual of Psychological Illnesses, Version 4. Screening instruments tested were: the ‘Hospital Anxiety and Depression Scale’ (HADS), the subscale ‘Emotional Functioning’ of the European Organization for Research and Treatment of Cancer Quality of Life Core Questionnaire (EORTC QLQ‐C30), the ‘Hornheider Fragebogen’ (HFB), and a single‐item visual analogues scale (VAS). Accuracy was assessed by calculating the sensitivity rates, specificity rates, and areas under the curve from the receiver operating characteristic curves.

Results: The relative frequency of mental disorders was 19.8%. All of the screening instruments tested were found to be highly accurate. The best levels of sensitivity and specificity were associated with the total score of the HADS.

Conclusions: These results confirm that a significant minority of laryngeal cancer patients suffer from severe mental distress, and that accurate screening for clinically significant mental disorders is possible using any of the instruments evaluated here. Copyright © 2007 John Wiley & Sons, Ltd.
Cancer families with children: factors associated with family functioning—a comparative study in Finland
Authors: Schmitt F. , Santalahti P. , Saarelainen S. , Savonlahti E. , Romer G. , Piha J.
Published: July 2007

Objective: The objective is to examine the factors associated with family functioning in families with children where a parent has cancer in comparison to families without cancer.

Sample and methods: Eighty‐five families including 85 cancer patients, 61 healthy spouses and 68 children between 11 and 17 years of age, and a control group of 59 families including 105 adults and 65 children were given a set of questionnaires including a background variable questionnaire, the Family Assessment Device, the Beck Depression Inventory and the Sense of Coherence (SOC). A statistical multilevel model allowing the use of data from several informants belonging to the same family was constructed for the analysis of associations between variables.

Results: Maternal depression and SOC of family members were associated with family functioning; maternal depression impaired family functioning and family members' SOC improved it. No difference was found between the clinical group and the control group.

Conclusion: In clinical work with cancer families with children, maternal depression and SOC should be focused on. Copyright © 2007 John Wiley & Sons, Ltd.
Quantitative EDX microanalysis of Bi2Te3 in the TEM
Authors: Peranio N. , Eibl O.
Published: July 2007

Quantitative chemical analysis by energy dispersive X‐ray spectrometry (EDX) in a transmission electron microscope (TEM) Zeiss912Ω was applied to p‐type (Bi,Sb)2Te3 and n‐type Bi2(Te,Se)3 thermoelectric materials. Preliminary results yielded artifacts due to Bi spurious X‐rays and hole‐counts significantly beyond zero. A stray aperture was inserted in the TEM to absorb the stray radiation. With this aperture inserted a high‐accuracy quantitative chemical analysis was established. The hole‐counts decreased by a factor of 5 and the scatter of data decreased by a factor of 4 with respect to no aperture inserted. The mole fractions of Te and Se were 54.4 at% and 5.5 at% and varied by 0.5 at% for n‐type material. A similar behaviour was found for Sb and Bi in p‐type material. The variation in stoichiometry is smaller on the sub‐micrometer scale and increases with increasing length scale for both, n‐type and p‐type Bi2Te3. Measurements in the TEM confirmed the inhomogeneous chemical composition found by wavelength dispersive X‐ray spectrometry. The improved accuracy of the quantitative EDX analysis is also important for other compounds with unique physical properties. This was demonstrated on thin foils containing heavy elements and on powders of light elements dispersed on Cu‐grids, i.e., the high‐TC superconductor Bi2Sr2CaCu2O8 and the mineral salt hydroxyapatite Ca10(PO4)6OH2. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of ZnO nanorods for evanescent field optical sensors
Authors: Börner Sandra , Rüter Christian E. , Voss Tobias , Kip Detlef , Schade Wolfgang
Published: July 2007

The optical wave guiding properties of ZnO nanorods are simulated and studied in detail using a block‐iterative frequency‐domain method and the results of a finite difference method as reference data. The simulations are performed for different wavelengths in the infrared spectral region that are related to specific gas absorption lines. Here both single ZnO nanorods and nanorod arrays with varying period lengths are investigated. The evanescent field distributions and penetration depths into the surrounding media are analyzed and compared as a function of wavelength and rod diameter. Our results give a general overview on the size range where ZnO nanorods may be used for evanescent field interaction based sensors for the detection of gas molecules like CO, CO2 or O2. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Innovation and operation with robotized underwater systems
Authors: Rigaud Vincent
Published: July 2007

This paper reports on the status and design of the operational remotely operated vehicle “Victor 6000”, rated for 6000 m depth and of the 3000 m depth autonomous underwater vehicle “Asterxx” operated by Ifremer the French Institute for Sea Exploitation. Victor 6000 is part of a global system built of subsystems, “scientific modules,” winch and cable, dead weight and umbilical, positioning subsystem using acoustic ultra short base line (USBL) techniques, and software for data and dive management. In 2005 the system was equipped with a second toolsled dedicated to high resolution mapping of the sea bed, with both acoustical and optical devices. Asterxx, the first autonomous underwater vehicle (AUV) developed by IFREMER, is 4.5 m in length with a diameter of 0.69 m. Depending on the payload, its weight is between 600 and 800 kg in air,with a diving depth of 3000 m. Its cruising speed is between 0.5 and 2.5 ms. The AUV is capable of carrying various payloads for a wide spectrum of applications. The vehicle can cruise up to 100 km. For coastal applications this vehicle is operable by a limited crew potentially from a nonspecialized vessel. Both vehicles are used for oceanography as well as to continually evolve underwater systems to address new scientific challenges. © 2007 Wiley Periodicals, Inc.
An introduction to testing techniques in the intelsat TDMA/DSI system
Authors: Colby R. J. , Parthasarathy R. , Prouse D. W.
Published: July 2007

The INTELSAT TDMA/DSI System is a complex, centrally‐controlled communications system, the performance of which will depend to some extent on the effectiveness of the alignment, maintenance and testing procedures. However, the wide range of disciplines encountered in the system mean staff currently familiar with the existing FDMA network may have difficulty with these new and unfamiliar fields. The purpose of this series of four papers is to provide an understanding of the necessity for, and operation of, the SSOG test procedures for the INTELSAT TDMA/DSI system. In this first part, the overall system and its testing requirements will be discussed as a foundation for a discussion of the SSOG tests in Part 2.
Demand assignment for light‐route TDMA
Authors: Kamal S. S. , Matyas R. , Lyons R. G.
Published: July 2007

With the fluctuating inter‐nodal traffic levels that characterize light‐route networks, demand assignment (DA) provides the means of increasing the system's effective capacity. This paper focuses on the application of DA in light‐route TDMA, and proposes a control architecture that is well‐suited to service of heterogeneous traffic. The major advantage of the proposed architecture is its benefit from both the efficient resource management typical of centralized schemes, and the shorter response times of distributed schemes. The impact of the assignment algorithm on the grade of service to heterogeneous populations, and the difficulty in quantifying this impact are also addressed. Results from analytical and simulation models illustrating resource utilization are presented.
The smoothed step‐track antenna controller
Authors: Edwards D. J. , Terrell P. M.
Published: July 2007

The paper describes a new adaptive tracking system which, unlike simple step‐track sytems, does not use the stepping cycles to directly position the antenna. The system can cope with severe noise; about 15 dB worse than step track. The system is cheap and practical. Results are given for both large and small dish antennas.
Proposed novel technique for the measurement of antenna gain in satellite earth‐stations
Authors: Daly P. , Tits D.
Published: July 2007

In the design of communication satellite systems, knowledge of earth‐station receive antenna gain and gain stability is essential. Gain measurement relies on the establishment of a constant receive signal flux.

This paper attempts to show how a standard gain horn and a reference source can be used together with a closed‐loop satellite ALC circuit to provide a stable, known received flux at the input of the earth‐station antenna with unknown gain. Theoretical limitations of the technique are discussed as a forerunner to future practical measurements.

Elements of the reference receive chain are transportable and can therefore be used to cross‐calibrate antennas, even in the case of receive‐only terminals.
A condensed orbital history of intelsat satellites
Authors: Walker J. G.
Published: July 2007

A 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 orbit.
Inmarsat expands its horizons
Authors: Lundberg Olof
Published: July 2007

The International Maritime Satellite Organization (INMARSAT) is the world's only commercial satellite system providing mobile communications. This article describes the system and the services which are provided through it to the worldwide shipping and offshore industries. It provides some background on the establishment of the system and why maritime nations looked to satellites as the way to effect a dramatic improvement in maritime communications. The article discusses some of the research and development now being carried out which is expected to lead to the provision of new services, including aeronautical communications via satellite. Also mentioned is the role to be played by INMARSAT in the Future Global Maritime Distress and Safety System, now being developed by the International Maritime Organization for introduction in 1990. New services, such as these, and greatly expanded capacity are to be provided by INMARSAT in its second generation system, consisting of a new series of satellites for launch from 1988.
Viterbi decoding for impulsive interference satellite channels
Authors: Tsai Chee , Kurz Ludwik
Published: July 2007

Data taken from real satellite channels point to the fact that such non‐Gaussian behaviour as burst noise exists. Since the probability density function (p.d.f.) which minimizes the Fisher information (If) subject to the given variance of noise is Gaussian, performance can be improved by taking into account the non‐Gaussian nature of the actual noise p.d.f. To achieve the higher efficiency, a modem, which consists of a maximum likelihood sequence detector (MLSD) implemented by an adaptive Viterbi algorithm (VA), is introduced in this paper. The new form of the algorithm, based on the m‐interval polynomial approximation (MIPA) method, which adjusts the operation of the VA decoder to ensure its robustness to changing and/or non‐Gaussian noise conditions, leads to an improvement of the error probability in operation of the receiver. In contrast to coding techniques, this improvement through digital signal processing is not obtained at the expense of bandwidth expansion. Monte Carlo simulation results involving bit error rate (BER) support theoretical conclusions.
An introduction to testing techniques in the intelsat TDMA/DSI system. Part 3: Specialized test equipment for ssog tests
Authors: Colby R. J. , Parthasarathy R. , Prouse D. W.
Published: July 2007

This is the third paper in a four‐part series addressing the testing and alignment techniques to be used in the INTELSAT TDMA/DSI system. In the first part,1 the salient characteristics of the overall TDMA/DSI system were presented together with a discussion of the fundamental requirements for testing and alignment. In the second part,2 INTELSAT's satellite system operations guide (SSOG) for TDMA was introduced, the principles of SSOG testing were discussed and the need for several types of specialized test equipment identified. This third part reviews the features of TDMA which affect test equipment design and gives a detailed description of the three items of specialized test equipment which are essential requirements for the conduct of system tests and line‐up of individual links. The fourth part will complete the series with a report on operational experience gained in the initial stages of TDMA implementation within the INTELSAT system.
CPM—an efficient constant amplitude modulation scheme
Authors: Aulin Tor , Sundberg Carl‐Erik
Published: July 2007

There is an increasing demand for digitial radio transmission. The cost of a channel is proportional to the bandwidth. For many applications power is limited. For satellite applications constant amplitude modulation is advantageous because of non‐linear amplification. In this paper a class of power and bandwidth efficient constant amplitude continuous phase modulation (CPM) schemes is presented. The signals are analysed in great detail and the tools for both error probability analysis and power spectral calculations are presented. Numerical data for raised cosine (RC) pulse shaping is presented. This paper is basically an overview with new results on the trellis description of CPM. The transmission is assumed to be ideally coherent over the Gaussian channel. In a following paper we will deal with transmission imperfections such as bandlimitation and hard limiting and their effect on CPM1.
A rain attenuation model for satellite link attenuation predictions incorporating the spatial inhomogeneity of rainrate
Authors: Manning Robert M.
Published: July 2007

A model describing the spatial inhomogeneity of rainrate within a rain cell is derived and incorporated into a specific attenuation model to yield a more exact relationship than has been used heretofore relating rainrate and the attendant attenuation at frequencies above 10 GHz. The resulting unified attenuation model relates terrestrial and slant path attenuation, effective propagation distance and path diversity gain to parameters characterizing the earth‐station or stations (e.g. location, height, latitude, elevation angle and baseline distance from another station), the frequency of operation, and the two possible raintypes admitted into the model (i.e. convective rain and residual or debris rain). The model is particularly suited for the theoretical investigation of path diversity gain since this concept owes its existence to spatial inhomogeneity of rainrate.

This inhomogeneous rain attenuation model can be interfaced with an appropriate statistical rainrate prediction model, such as the Crane two‐component model, to yield more precise attenuation predictions.
Loopus opens a new dimension in satellite communications
Authors: Dondl Peter
Published: July 2007

Without any doubt the geostationary orbit is for many applications the most suitable orbit because of the apparent standstill of its satellites. Unfortunately geostationary satellites cannot illuminate the polar regions and furthermore the number of orbit positions is limited. With satellites on certain, dependent on the system, circular or elliptical orbits inclined against the equatorial plane, it is possible to form, off the geostationary orbit, loop‐shaped quasi‐positions—referred to as Loopus positions—which are served by satellites of alternate identity. The basic idea is to employ in shift several satellites along the same apparent track which, in the alternate play with the earth's rotation, form small loops at the celestial sphere. Change‐over takes place at the loop intersection point where a collision of the two satellites is just avoided. Thus a system with for example three satellites, which serve two Loopus positions, allows uninterrupted (quasi‐)stationary communication via earth‐stations in two coverage zones.
Intelsat tdma/dsi burst time plan development
Authors: King C. , Trusty P. , Jankowski J. , Duesing R. , Roach P.
Published: July 2007

The INTELSAT time‐division multiple‐access (TDMA) system, scheduled to begin operation in 1984, will be used with INTELSAT V and post‐INTELSAT V satellites. This system will operate on a 2ms time frame, employ digital speech interpolation (DSI) techniques for baseband processing, and will permit hopping between transponders. Four reference stations will provide timing and control information for each network.

This paper describes the approach taken by INTELSAT in the development of burst time plans (BTPs) for the TDMA/DSI system. Network control procedures, burst scheduling and BTP information dissemination are also discussed. The software that has been developed to generate the BTPs and the associated master time plans and condensed time plans is also described.
Testing and maintenance of intelsat tdma traffic terminals—a manufacturer's perspective
Authors: Keelty J. M.
Published: July 2007

In this paper the related matters of testing and maintenance of TDMA traffic terminals are discussed. Generally three types of testing are required: first of all testing to ensure that the equipment complies with the stipulations of INTELSAT (called application tests herein), secondly tests to ensure that a product has been manufactured in accordance with the design (manufacturing tests) and finally maintenance tests for the purpose of resolving equipment malfunctions. It is shown that application testing can be split between tests performed on an entire terminal and tests performed on individual subsystems, and that manufacturing testing best employs automatic software‐driven facilities. Finally it is shown that the best maintenance philosophy is to adopt a circuit card replacement strategy.
The intelsat tdma burst mode link analyser
Authors: Mahoney P.
Published: July 2007

In any wide bandwidth transmission system, the equalization of amplitude and group delay plays an important part in obtaining acceptable transmission quality. In the forthcoming INTELSAT TDMA/DSI system the need to measure the amplitude and group delay response in a time‐shared 80 MHz transponder has led to the design and construction of a new measuring instrument: the burst mode link analyser (BMLA). In this paper, the design principles and method of operation of the BMLA are discussed, together with an overview of its internal architecture.
The TDMA tutor® computer‐based training concept
Authors: Gough R. A.
Published: July 2007

Small personal computers are ideally suited to the task of teaching a complex subject such as the INTELSAT TDMA/DSI system when provided with correctly designed software and supported by conventional, written material. In this paper, the design of a successful low cost computer based training system is discussed including the basic architecture, system operation, scenario technique, utilities and displays. It will be shown that the TDMA TUTOR can reproduce the most useful of the displays to be met in practice which together with an unrestricted scenario creation method produces a powerful practice‐orientated training system allowing students to experiment with ‘live’ (simulated) TDMA terminals and gain a detailed understanding of TDMA operation without risk to a real system.
Satellites versus fibre optic cables
Authors: Crispin J. , Cummins J. M. , Lemus R. , Reyna J.
Published: July 2007

This paper compares the capacities and costs of the new fibre optic submarine cables and the forthcoming INTELSAT VI satellites. The results indicate that, contrary to generally accepted beliefs, satellites are cheaper than fibre optic cables on a per circuit point‐to‐point basis. Moreover, satellites are shown to possess the advantage of superior overall connectivity capability, in addition to simple point‐to‐point capacity. This is expected to be very important in the choice of future cost effective facilities.
Ku‐band satellite digital transmission systems
Authors: McGann W. E.
Published: July 2007

A nation‐wide data communications service is being placed in service by a major telecommunications carrier. This service will rely on a satellite network being provided and installed by Harris Satellite Communications Corporation.

The network supports information data rates from 56 kb/s to 2·048 Mb/s. This data communications network has been architectured to include a number of innovative monitor and control functions, up‐link power control, modular equipment shelter design and a modular antenna/feed subsystem.

This paper will detail this application.
Development of a prototype, experimental single‐channel sequencing navstar gps receiver: Part I—Hardware implementation
Authors: Allison M. T. , Daly P.
Published: July 2007

Late in 1988 the Navstar GPS satellite navigation operational phase is planned to commence, offering world‐wide, continuous and precise position‐fixing and timing information to observers on land, sea, air and in space. This paper describes the development of a particular type of Navstar receiver—a single‐channel, single‐frequency, sequencing C/A code unit—and results of various tests carried out on the present phase‐II satellite constellation. Part I of the paper deals essentially with the NAVSTAR satellite system and receiver hardware implementation, whereas Part II concentrates on receiver software and system performance.
A Classification of system structures involving frequency re‐use and cross‐polar cancellation
Authors: Mc Ewan N. J. , Ghorbani A.
Published: July 2007

The concept of frequency re‐use based on orthogonal polarization is clarified by classifying the system structures which might be involved. Distinctions are drawn on the basis of connectivity, of whether the system is broadcast or multiplexed, and of whether the frequency re‐use is ‘full’, ‘partial’ or ‘permuted partial’. Full re‐use is defined to mean that every distinct spatial path carries two spectrally overlapping polarizations and that both of these are wanted at the receiving point. It is concluded that the partial and permuted partial forms are usually as spectrally efficient as the full, and that the partial is generally simplest.

Means of cancelling cross‐polarization are also classified and related to the system structure. Discussion includes the types of cross‐coupling structure as well as the methods of deriving control signals for them.

It is concluded that the classical problem of restoring mutual isolation between two incoming wanted polarizations is not the most important in practice; more common problems will arise in partial re‐use where a receiver only has to maintain its single wanted polarization orthogonal to the interfering one, or a transmitter only has to adjust a single radiated polarization. In these cases a simpler ‘unitary’ canceller can be used.
Intelnet Services—A global data distribution and collection scheme
Authors: Jamshidi Simin , Nguyen Lan N.
Published: July 2007

Responding to the recent availability of very small earth‐stations (commonly called micro terminals) for data/voice communications, INTELSAT has introduced a new service called INTELNET.

INTELNET services are designed to operate with two different modulation and coding techniques, i.e. spread spectrum and binary phase‐shift keying (BPSK) with rate 1/2 forward error correction (FEC). The INTELNET I service is a data distribution service, whereas the INTELNET II service is a data collection service. These services are facilitated by the use of micro terminals at remote locations (i.e. outposts) which will be linked through the INTELSAT space segment to relatively large INTELSAT earth‐stations (e.g. Standard A, B, C and E‐3).

INTELNET services are leased transponder services offered on a range of INTELSAT satellites in C‐ or Ku‐bands on a pre‐emptible or non‐pre‐emptible basis. These services are offered on a full‐time or occasional‐use basis, by assigning predetermined satellite resources of bandwidth and power with a smallest allotment of 1 MHz.

In this paper, the system design and network architecture for the INTELNET I and II services are addressed. Representative transmission parameters have also been developed for the INTELNET I and II services. System cost considerations as a result of the use of micro terminals are analysed.
Technical and economic impact of the use of standard‐B earth stations in the intelsat system
Authors: Rancy F. , Zermizoglou P. , Meunier J.
Published: July 2007

More than 20 years after the INTELSAT system started up, satellite technology developments have led to considerable changes in the world‐wide international satellite transmission system. This evolution and the present capabilities offered by digital technologies make it possible to reassess the potential cost advantages of standard‐B earth stations over a wider portion of international telephone transmission routes. This paper addresses the technical and economic issues raised by the characteristics of the present and planned INTELSAT satellites, together with the current capabilities of digital techniques (forward error correction, low rate encoding, time and frequency division multiple access). The foreseeable impact of the use of such techniques on overall satellite telephone transmission costs is also presented, and compared with that forecasted for fibre optic cable circuits.
Models and algorithms for optimal traffic assignment in SS/TDMA switching systems
Authors: Minoux M. , Brouder C.
Published: July 2007

We address here optimal design and management issues related to traffic assignment problems in SS/TDMA systems of the INTELSAT‐VI type. A general model is described in which the problem is decomposed into three sub‐problems: (1) optimal or sub‐optimal assignment of earth stations to transponders; (2) optimal decomposition of the traffic flows into blocks and sub‐blocks; and (3) optimal assignment of the traffic sub‐blocks into the TDMA frame. Methods of solution are described for solving successively each of these sub‐problems in turn. Computational experiments carried out on a series of realistic problems confirm the interest of this approach both in terms of quality of the solutions obtained and in terms of computational efficiency. Directions for future research are suggested in the conclusion.
Advanced on‐board processing for user oriented communication systems
Authors: Colombo G. , Pennoni G.
Published: July 2007

The continuing improvement of RF components, particularly in the field of spot‐beam antennas, combined with the steady progress in digital technology, leads us to consider the advantages of a satellite system able to provide full connectivity to ground stations operating at different data rates. For low data rates, two different access methods: continuous TDM and Multi‐carrier TDMA, are compared for earth‐stations operating at 2Mb/s. The two methods are compared from the point of view of efficiency and adaptability in a non‐uniform load environment.

Some control criteria are proposed for the Multi‐carrier system.

Both methods are particularly suited for small users.
System concept for a digital repeater intended for a future generation of german telecommunication satellites
Authors: Heine H. W.
Published: July 2007

The derivation of a system concept for the digital multi‐service repeater starts from evaluating the mission profile and the antenna concept elaborated so far. Furthermore, the repeater concept is shaped by Ka‐band propagation conditions, the kind of integration of a down‐link TV‐distribution service into the prevailing multi‐beam communications mode and readily available digital technologies. It is intended to embark on a completely regenerative approach using a unified switching concept for all services accompanied by a large amount of rearrangement functions in the foreground. An attempt is made to define those network control functions and procedures to be located on‐board exploiting the fact that the repeater already acts as a central switching node. The discussion of on‐board digital technologies concentrates upon a multicarrier demodulator concept and a candidate solution for the baseband switch. One general boundary condition is pronounced due to uncertainties about the actual traffic scenario in the future: all repeater resources must be accessible for the most important of the services considered, i.e. the provision of satellite business services.
Real‐time configurable SS/TDMA equipment for second generation french telecommunications satellite project
Authors: Oppetit A. , Thebault D. , Rousson J. L.
Published: July 2007

This paper describes new on‐board equipment built around a microprocessor and controlled by earth through a specialized link. It drives in real‐time a 4 × 4 microwave switch matrix (MSM) for operation in satellite‐switched time division multiple access (SS/TDMA). The system is designed to evaluate SS/TDMA performances when (i) frame and multiframe durations are changed, (ii) the switch states sequence which controls the MSM is updated in real‐time. Another specific feature of this versatile equipment is the possibility to modify upon earth request the program run by the microprocessor to be able to carry out further experiments.
On‐board processing for communication satellites: Technologies and implementations
Authors: Betaharon K. , Kinuhata K. , Nuspl P. P. , Peters R.
Published: July 2007

This paper presents technologies which are key candidates for advanced on‐board processing for future communication satellites. Satellite switching centres for microwave and baseband signals, on‐board coherent modems for 120Mb/s burst‐mode TDMA systems and their technologies are discussed. A brief description of on‐board demultiplexing and demodulation of low bit rate carriers is offered and study results on investigation of on‐board unique word detectors and large buffers are presented.
Advanced satellite switching centre with on‐board diagnostics
Authors: Betaharon K. , Kitazume S. , Takimoto Y. , Komiyama N.
Published: July 2007

Design and operation of a satellite switching centre (SSC) with its own built‐in diagnostics network are described. This SSC, designed for on‐board applications, utilizes state‐of‐the‐art technologies and techniques which have enhanced its performance significantly when compared to similar existing satellite switching centres. Additionally, unique features of this SSC are presented, specifically with respect to the built‐in diagnostic circuit which fully describes the SSCs health without disturbance of traffic signals. Finally, system aspects of utilizing such satellite switching centres are addressed.
Ku‐Band satellite data networks using very small aperture terminals—part I: Multi‐access protocols
Authors: Raychaudhuri D. , Joseph K.
Published: July 2007

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

To published in the next issue

of this paper on Ku‐band VSAT networks, the issue of overall system design is considered.
Planning considerations for domestic replacement satellites
Authors: Johannsen Klaus G.
Published: July 2007

Several 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 determination.
Equalization for PSK signals over non‐linear channels with non‐symmetrical frequency response
Authors: Said A. , Elrefaie A. , Kurz L.
Published: July 2007

In this paper, a minimum mean square error equalizer (MMSE) for receiving quadrature phase shift keyed (QPSK) signals over band‐limited non‐linear satellite channels is designed. The effect of intersymbol interference due to non‐symmetrical frequency response followed by AM/AM and AM/PM conversions are taken into account while optimizing the performance in the presence of down‐link additive white Gaussian noise.

The taps gain coefficients of the equalizer are obtained using numerical methods. The average probability of error is computed for two systems: the one sample detector and the (MMSE) equalizer. It is shown that significant improvement in performance is possible by replacing the one sample detector by an MMSE equalizer.
Space radio services and WARC‐MOB‐87
Authors: Withers D. J.
Published: July 2007

A recent conference of the ITU has agreed upon worldwide frequency allocations near 1600 MHz for communication by satellite with mobile stations on land, and has permitted the use of some aeronautical mobile‐satellite frequency bands for passengers' in‐flight telephone calls to the ground. Frequencies for systems for locating mobile stations by radio, using satellites, were allocated.
Identification of requirements for intersatellite links
Authors: Puccio A. , Saggese E. , Soprano C.
Published: July 2007

The intersatellite link (ISL) concept has been under evaluation for many years. It has been the subject of various European Space Agency studies, one of which is summarized here.1 The study was aimed at:

outlining a reference scenario for satellite communications in the period 1996–2005, when a new satellite generation (Eutelsat III) is expected to be operational in Europe;

analysing, within the above scenario, the opportunities for an ISL implementation;

performing a deep system analysis of the selected study cases in order to give the requirements for the first ISL generation;

evaluating a micro/millimetre wave implementation of the ISL;

evaluating an optical implementation of the ISL;

evaluating the technical and economic viability of an ISL and suggesting the best technique to be used in the first ISL generation.

The main results achieved in this analysis are that: (i) the usefulness of an early implementation of ISL has been demonstrated; (ii) verification of the system aspects in the communications networks using an ISL appears as one of the most important items; (iii) the availability of optical technologies will increase the opportunities offered to ISL implementation. From these results it is shown that a first‐generation (1995–2005) millimetre‐wave ISL would be preferable for future business systems, while a second‐generation (after 2005) optical ISL could extend the ISL field of application. It is also deemed important to have during 1995–2005 an in‐orbit experiment for optical ISL as a necessary step for a subsequent operational system.
In‐orbit demonstration of optical IOL/ISL—the silex project
Authors: Vanhove J. L. , Noeldeke C.
Published: July 2007

The use of optical communications for the high‐data‐rate links of the future European Data Relay System (EDRS) is receiving much attention. To confirm the feasibility of such communications links, an experimental system (SILEX) consisting of three satellites (two in geostationary orbit and one in low earth orbit) is planned for 1992 or 1993 to demonstrate both inter‐orbit link (IOL) and intersatellite link (ISL) capabilities. A detailed feasibility study was performed from January to July 1987 under a European Space Agency (ESA) contract with Matra (France) as prime contractor, ANT (West Germany), Telespazio and Selenia Spazio (Italy) as subcontractors, and contributions from Berlin (France) and Dornier (West Germany). The system is based on GaAlAs semiconductor technology (0.8 μm) with silicon avalanche photodiodes (APDs) as detectors and arrays of charge‐coupled devices (CCDs) for both acquisition and tracking sensors. The design will allow wavelength division multiplexing (WDM) and high‐data‐rate transmission to be demonstrated. The expected data rates are 120 Mb/s duplex for ISL, 1 Mb/s on the IOL forward link (GEO→LEO) and two to four simultaneous 60 or 120 Mb/s channels on the IOL return link (LEO→GEO).
Performance of optical intersatellite links
Authors: Wittig M. , Oppenhäuser G.
Published: July 2007

The performance of optical intersatellite links is described by a model. A significant difference between optical and microwave intersatellite links is the occurrence of so‐called burst errors. The statistics of bit error rate for an optical link are derived from simulations taking into account beam mispointing resulting from satellite motions and tracking channel noise. The effect of coding on the bit error rate is also shown. The mutual tracking system between two optical terminals located on different satellites can become unstable if the noise of the tracking loop exceeds a critical value. The results of tracking simulations are presented.
Laser diode intersatellite links: Communications subsystem
Authors: Arcidiacono A. , de Vita S.
Published: July 2007

This paper analyzes the critical areas in optical communications systems, placing particular emphasis on the modulation/demodulation techniques used in the ISL communications subsystem design for the ESA/PSDE programme. A 4‐PPM/QPM demodulator has been designed, and problems of implementing the system at high data rates have been addressed. Maximum likelihood demodulation techniques and slot and frame synchronization were used. An attempt was made to devise a way to achieve synchronization tracking without using unique words along data patterns. Finally, for the optical ISL the use of coding is suggested as a way to relax link budget requirements. Coding could reduce problems caused by pointing subsystem instabilities. The use of on‐board soft decoding without system bandwidth expansion is also foreseen.
On‐ground testing of a full‐scale homodyne CO2 laser transceiver for free‐space communications applications
Authors: Reiland W. , Popescu A.
Published: July 2007

The continuing interest in optical carriers for free‐space communications has led to the design and development of a variety of powerful communications systems. This paper describes a high‐data‐rate (140–1000 Mb/s), bidirectional CO2 laser homodyne system and the philosophy for on‐ground testing of a single transceiver package by means of a simulated counter‐terminal. The problems of laboratory testing and link down‐scaling are addressed. The simulation of the counter‐terminal and its impact on the transceiver package are discussed, along with the integration and test plan of the full‐scale laboratory breadboard model.
Fade countermeasures at Ka band for olympus
Authors: Willis M. J. , Evans B. G.
Published: July 2007

Fade countermeasure techniques that can be applied to Ka band satellite communication systems are reviewed. Considered in detail are diversity, adaptive forward error correction, fade spreading, up‐link power control and adaptive TDMA. The techniques are compared for their effectiveness at Ka band, and recommendations are made for operating systems. The two important control techniques of fade detection and fade control are discussed in terms of their ease of implementation for each countermeasure technique. Details of a planned experiment to evaluate the application of fade countermeasures to VSAT networks via the Olympus satellite are presented.